Binder1

12 Lead ECG Recorders 

Steven Lewis 

Clinical Engineering 

United Lincolnshire Hospital Trust

Electrocardiography (ECG) 

The heart is responsible for pumping blood around the body by repeated, rhythmic 

contractions. The functional unit of the heart is the cardiac muscle cell or cardiomyocyte. Each 

cardiomyocyte maintains an electrical charge or potential across its cell membrane and 

contracts when this potential is discharged. In order for all of the cardiomyocytes to contract at 

the same time and produce an effective muscular contraction, the heart also maintains its own 

electrical conducting system which coordinates the electrical activity of the heart. 

Fig 1 – The Human Heart 

The electrical impulses take a specialised conduction pathway. 

This pathway is made up of 5 elements: 

1. The Sino-Atrial (SA) node 

2. The Atrio-Ventricular (AV) node 

3. The bundle of His 

4. The left and right bundle branches 

5. The Purkinje fibres 

Fig 2 – The Human Heart

The SA node is the natural pacemaker of the heart. Pacemakers and Temporary Pacing Wires 

(TPWs) are used when the SA node has ceased to function properly. 

The SA node releases electrical stimuli at a regular rate; this rate is dictated by the needs of the 

body. Each stimulus passes through the myocardial cells of the atria creating a wave of 

contraction which spreads rapidly through both atria. 

The heart is made up of around half a billion cells; the majority of the cells make up the 

ventricular walls. The rapidity of atrial contraction is such that around 100 million myocardial 

cells contract in less than one third of a second. The electrical stimulus from the SA node 

eventually reaches the AV node and is delayed briefly so that the contracting atria have enough 

time to pump all the blood into the ventricles. Once the atria are empty of blood the valves 

between the atria and ventricles close. At this point the atria begin to refill and the electrical 

stimulus passes through the AV node and Bundle of His into the Bundle branches and Purkinje 

fibres. 

The Purkinje fibres spread widely across the ventricles. In this way all the cells in the ventricles 

receive an electrical stimulus causing them to contract. 

As the ventricles contract, the right ventricle pumps blood to the lungs where carbon dioxide is 

released and oxygen is absorbed, whilst the left ventricle pumps blood into the aorta from 

where it passes into the coronary and arterial circulation. 

At this point the ventricles are empty, the atria are full and the valves between them are closed. 

The SA node is about to release another electrical stimulus and the process is about to repeat 

itself. The SA node recharges whilst the atria are refilling, and the AV node recharges when the 

ventricles are refilling. In this way there is no need for a pause in heart function. Again, this 

process takes less than one third of a second. 

The times given for the 3 different stages are based on a heart rate of 60 bpm, or 1 beat per 

second. 

The term used for the release (discharge) of an electrical stimulus is "depolarisation", and the 

term for recharging is "repolarisation". 

The sum total of the simultaneous electrical discharging and re-charging of all the 

cardiomyocytes in the heart is sufficient to be detected by sensing probes placed on the exterior 

of the body at various positions around the heart. The ECG records the vector sum and produces 

a combined trace. This is the principle behind the electrocardiograph or ECG which can be used 

to monitor the rhythm of the heart. 

Injured cardiomyocytes such as those suffering from lack of oxygen during a heart attack leak 

electrical current rather than discharge it in a coordinated manner, the altered electrical signal 

of the injured heart results in a characteristic ECG pattern which can lead to the diagnosis of 

acute myocardial infarction (Heart Attack). 

In contrast, dead cardiomyocytes or scarred cardiac muscle does not carry or maintain an 

electrical charge, and this absence of electrical activity is also detectable by ECG. Therefore, a 

previously unrecognised or "silent" heart attack can be diagnosed by electrocardiogram, and 

even localised to a particular area of the heart by using multiple sensing probes or ECG leads. 

(EBME, 2011) 

An ECG trace may be obtained with the electrodes attached in a variety of positions, however, 

the system of positioning leads for performing a 12-lead ECG is universal. This helps to ensure 

that, when a person's ECGs are compared, any changes on the ECG are due to cardiac injury, not 

a difference in placement of leads, this is extremely important with the increasing use of foreign 

travel. There are universal standards in place throughout the world.

These positions may differ slightly when a patient is on continuous cardiac monitoring. The 

leads routinely attached to wrists and ankles will be placed on shoulders and lower abdomen so 

that movement of limbs has minimal effect on the rhythm trace. These positions may also differ 

if a patient is shaking (maybe due to Parkinson's disease or hypothermia) or has muscle 

tremors. In this situation the leads may be moved onto the thighs and forearms. 

There are 10 wires on an ECG machine that are connected to specific parts of the body. These 

wires break down into 2 groups: 

1. 6 chest leads 

2. 4 limb or peripheral leads (one of these is "neutral") 

Fig 3 – 12 Lead ECG Placement 

The 6 leads are labelled as "V" leads and numbered V1 to V6. They are positioned in specific 

positions on the rib cage. 

Limb leads are made up of 4 leads placed on the extremities: left and right wrist; left and right 

ankle. 

Fig 4 – ECG Placement on a patient lying down.

Each of the 12 leads represents a particular orientation in space, as indicated below (RA = right 

arm; LA = left arm, LL = left foot): 

Bipolar limb leads (frontal plane): 

Lead I: RA (-) to LA (+) (Right Left, or lateral) 

Lead II: RA (-) to LL (+) (Superior Inferior) 

Lead III: LA (-) to LL (+) (Superior Inferior) 

Augmented unipolar limb leads (frontal plane): 

Lead aVR: RA (+) to [LA & LL] (-) (Rightward) 

Lead aVL: LA (+) to [RA & LL] (-) (Leftward) 

Lead aVF: LL (+) to [RA & LA] (-) (Inferior) 

Unipolar (+) chest leads (horizontal plane): 

Leads V1, V2, V3: (Posterior Anterior) 

Leads V4, V5, V6:(Right Left, or lateral) 

The "aV" stands for Augmented Vector, the last letter refers to a position, which are as 

follows: 

aV R Augmented Vector Right Right wrist/shoulder 

aV L Augmented Vector Left Left wrist/shoulder 

aV F Augmented Vector Foot Left foot/lower abdomen 

These 3 leads create a triangle with the heart in the middle, as below. The lines into the centre 

indicate the line of sight of these leads. 

Fig 5 – Einthoven’s Triangle. 

The 2 leads situated on the right and left wrist (or shoulders), aV R and aV L respectively, and the 

lead situated on the left ankle (or left lower abdomen) aV F, make up a triangle, known as 

"Einthoven’s Triangle.

ECG Leads have colour coded bands so that they can be easily identified. 

The ECG below shows where these leads are when printed. 

Fig 6 – ECG Printout 

The ECG is usually recorded on a time scale of 0.04 seconds/mm on the horizontal axis and a 

voltage sensitivity of 0.1mV/mm on the vertical axis. 

On standard ECG recording paper, 1 small square represents 0.04 seconds and one large square 

0.2 seconds. 

In the normal ECG waveform the P wave represents atrial depolarisation, the QRS complex 

ventricular depolarisation and the T wave ventricular repolarisation. 

The P - R Interval is taken from the start of the P wave to the start of the QRS complex. The Q - T 

interval is taken from the start of the QRS complex to the end of the T wave. This represents the 

time taken to depolarise and repolarise the ventricles. The S - T segment is the period between 

the end of the QRS complex and the start of the T wave. All cells are normally depolarised 

during this phase.

Fig 7 – ECG Waveforms 

ECG Normal Values 

P - R interval - 0.12 - 0.2 seconds (3-5 small squares of standard ECG paper) 

QRS complex - duration less than or equal to 0.1 seconds (2.5 small squares) 

Q - T interval- corrected for heart rate (QTc) QTc = QT/ RR interval less than or equal to 0.44 

seconds. 

Interference 

(EBME, 2012) 

There are a number of reasons for ECG rhythm disturbance, which could either be down to the 

patient, the leads or down to the environment the patient is being nursed in. 

Muscle tremor is something that can occur for a number of reasons, such as: 

 

 

 

Shivering due to cold 

Rigors 

Parkinson’s disease 

This can cause the ECG trace to look like the below image. 

Fig 8 – ECG Trace showing Muscle Tremor

Another disturbance, emanating directly from the surrounding environment, is electrical 

interference. The ECG machine is designed to pick up electrical activity within the heart but 

it could pick up electrical activity from other sources, causing a trace as below. 

Fig 9 – ECG Trace showing Electrical Interference 

Artefact is the name given to disturbances in rhythm monitoring caused by movement of the 

electrodes 

The movement can be caused in a number of ways. 

Fig 10 -ECG Trace showing Artefact 

 

 

 

 

 

If the electrodes have been in place for a prolonged period of time, the moist inner pad 

can dry up and the connection becomes poor. 

The weight of the leads can pull the electrode away from the skin and contact is lost 

intermittently, such as when the patient leans or roles over. 

The electrode has come away from the skin and is stuck to an item of clothing 

The patient is fiddling with the electrodes. 

When the skin is sweaty/dirty/hairy the electrodes may not stick well, resulting in an 

unstable trace 

However, the machine can also mistake artefact for fatal arrhythmias. In this case the machine 

will release a "fatal arrhythmia" alarm. 

The cables from the electrodes terminate in a single cable, which is plugged into the port on the 

ECG Monitor and are electrically isolated for patient safety. Circuitry also protects the monitor 

from any high voltages produced by a defibrillator or electro-cautery signals. The signal is 

filtered, amplified, conditioned and processed for display. Pulse rate is also calculated and 

displayed, with high and low alarms set with the standard being 150bpm high, 50bpm low. 

(The University of Nottingham, 2015)

Maintenance and Service Procedures 

Firstly check the ECG leads for noise, this is done by connecting the leads to a patient/ECG 

simulator and gently flexing the leads while watching the screen carefully for any noise. If any 

noise occurs the leads should be replaced. 

The lead select function must then be checked to ensure the monitor switches between all 

available leads. 

Lead fault detection must then be checked this is done by removing a lead from the simulator, 

the ECG machine must recognise this as a lead becoming detached and alarming this to ensure 

users don’t mistake a lead becoming detached for a clinical problem. 

Check heart rate calibration, set simulator to various rates and ensure monitor reads within 

specification, Clinical engineering general specification is for rates under 160bpm ±2bpm and 

for rates over 160bpm ±3bpm. 

Visually inspect screen gain and scroll rates, also perform a print out and check this. 

The 50Hz Filter is checked. 

The audible alarms are then checked by lowering and raising the rate on the simulator below 

and above the heart rate limits to ensure all alarms are working as expected. 

If applicable pacer detection is checked, to do this heart activity and pacer signals are simulated 

the monitor should display the heart rate that has been applied and also the pacer signal should 

be visible in the waveform. Then set the simulator to only give the pacer signal, the monitor 

should recognise this as the pacer signal and heart rate should read as zero. 

An Electrical Safety Test is then carried out.

Bibliography 

EBME, 2011. EBME - Cardiology. [Online] 

Available at: http://www.ebme.co.uk/articles/clinical-engineering/10-cardiology 

[Accessed Febuary 2014]. 

EBME, 2012. EBME - Cardiac Monitoring. [Online] 

Available at: http://www.ebme.co.uk/articles/clinical-engineering/20-cardiac-monitoring 

[Accessed March 2014]. 

Jones, A., 2009. PHYSICAL PRINCIPLES OF INTRA-ARTERIAL BLOOD PRESURE MEASUREMENTS, 

s.l.: s.n. 

The University of Nottingham, 2015. Cardiology Teaching Resource. [Online] 

Available at: 

http://www.nottingham.ac.uk/nursing/practice/resources/cardiology/function/index.php 

[Accessed June 2015].

Defibrillators 

Steven Lewis 



Defibrillation 

Electrical cardioversion and defibrillation have become routine procedures in the management 

of patients with cardiac arrhythmias. Cardioversion is the delivery of energy that is 

synchronised to the QRS complex, while defibrillation is the non-synchronised delivery of a 

shock randomly during the cardiac cycle. 

Most defibrillators are energy-based, meaning that the device charges a capacitor to a selected 

voltage and then rapidly delivers a pre-specified amount of energy in joules (J) to the 

myocardium to treat cardiac arrhythmias. The capacitance of a capacitor is the amount of 

electric charge it can store for every volt applied to it. With regard to defibrillators the amount 

of energy stored in a capacitor is very important. It can be calculated using the formula 

E = ½CV 2 , where E is the energy in joules, C the capacitance in farads and V the voltage 

measured in volts. This energy is dissipated in the patient’s body over a small time interval, 

about 10 milliseconds or one hundredth of a second. 

If the capacitance is 1000 μF and the voltage is 500 V then the stored energy is 125J. 

[E = ½ CV 2 ] 

E= ½ (1000 × 10 -6 ) x (500 2 ) = 125 J. 

Current European Society of Cardiology and AHA guidelines suggest the following initial energy 

selection for specific arrhythmias: 

 

 

 

 

For atrial fibrillation, 120 to 200 joules for biphasic devices and 200 joules for 

monophasic devices. 

For atrial flutter, 50 to 100 joules for biphasic devices and 100 joules for monophasic 

devices. 

For ventricular tachycardia with a pulse, 100 joules for biphasic devices and 200 joules 

for monophasic devices. 

For ventricular fibrillation or pulseless ventricular tachycardia, at least 150 joules for 

biphasic devices and 360 joules for monophasic devices. 

They also incorporate an inductor to prolong the duration of the delivered current, and a 

rectifier to convert alternating current (AC) to direct current (DC). (Knight, 2014) 

A defibrillator can deliver a controlled electrical shock to a heart that has a life-threatening 

rhythm, such as ventricular fibrillation (VF). In VF, the heart's chaotic activity prevents blood 

from pumping adequately or at all. Voltage stored by the defibrillator conducts electrical 

current (a shock) through the chest by way of electrodes or paddles placed on the chest. This 

brief pulse of current halts the chaotic activity of heart, by depolarising a large part of the heart 

muscle terminating the dysrhythmia allowing normal sinus rhythm to be re-established by the 

body’s internal pace maker located in the sinoatrial node of the heart, giving the heart a chance 

to re-start with a normal rhythm. 

Many factors affect the chance of defibrillation success including; placement of the electrode 

pads, time elapsed before the first shock is given, and certain health conditions. Successful 

defibrillation requires that enough current be delivered to the heart muscle during the shock. If 

the transthoracic impedance level is high the heart may not receive enough current for 

defibrillation to be successful. Impedance is the body's resistance to the flow of current; some 

people naturally have higher impedance than others. Therefore, it may take more current, a 

longer shock duration, and/or increased voltage to ensure success. (EBME, 2003)

The shock is delivered via two electrode pads/paddles placed as shown below. 

Fig 1 – Placement of Electrode Pads/Paddles 

Modern defibrillators may be manual or automated; they generally produce biphasic waveforms 

as opposed to monophasic waveforms, which increase safety and efficacy. Miniature 

implantable cardioverter-defibrillators (ICD) may be used in patients with recurrent lifethreatening 

arrhythmias. (Chaudhari, 2005) 

Monophasic Waveforms 

This is a type of defibrillation waveform where current flows in one direction. In this waveform, 

there is no ability to adjust for patient impedance, and it is generally recommended that all 

monophasic defibrillators deliver 200 - 300 J of energy to a maximum of 360J, applied to adult 

patients with the assumed average impedance of 50 ohms, to ensure maximum current is 

delivered which in the graph below is ≈ 45 amps. 

Biphasic Waveforms 

Fig 2 – Graphical representation of a Monophasic Waveform 

With biphasic shocks, the direction of current flow is reversed near the halfway point of the 

electrical defibrillation cycle. Biphasic waveforms were initially developed for use in 

implantable defibrillators and have since become the standard in external defibrillators. With 

biphasic waveforms there is a lower defibrillation threshold (DFT) that allows reductions of the 

energy levels administrated and may cause less myocardial damage. 

While all biphasic waveforms have been shown to allow termination of VF at lower current than 

monophasic defibrillators, there are two types of waveforms used in external defibrillators.

The waveforms are shown below and will have the desired effect at current values ranging from 

approx. 15 – 35 amps. 

Fig 3 – Graphical representation of two Biphasic Waveforms 

Types of Defibrillator 

Automated External Defibrillator (AED) 

AEDs are highly sophisticated, microprocessor-based devices that analyse multiple features of 

the surface ECG signal including frequency, amplitude, slope and wave morphology. They 

contain various filters for QRS signals, radio transmission and other interferences, as well as for 

poor electrode contact. Some devices are programmed to detect patient movement. 

The typical controls on an AED include a power button, a display screen on which trained 

rescuers can check the heart rhythm and a discharge button. Certain defibrillators have special 

controls for internal paddles or disposable electrodes. 

In AED Mode, the Defibrillator analyses the patient’s ECG and advises you whether or not to 

deliver a shock. Voice prompts guide you through the defibrillation process by providing 

instructions and patient information. Voice prompts are reinforced by messages/pictures that 

appear on the display. (Lozano, 2013) 

Manual Defibrillator 

Manual defibrillators are designed to give full control to the clinical users. The defibrillator 

records the patients ECG, the user then assess the ECG and selects the appropriate level of 

energy for defibrillation. 

Capnography 

End tidal Carbon Dioxide (EtCO 2 ) is the partial pressure or maximal concentration of carbon 

dioxide (CO 2) at the end of an exhaled breath, which is expressed as a percentage of CO 2 or 

mmHg. The normal values are 5% to 6% CO 2, which is equivalent to 35-45 mmHg. CO 2 reflects 

cardiac output and pulmonary blood flow as the gas is transported by the venous system to the 

right side of the heart and then pumped to the lungs by the right ventricles. When CO 2 diffuses 

out of the lungs into the exhaled air, a device called capnometer measures the partial pressure 

or maximal concentration of CO 2 at the end of exhalation.

Capnography uses an EtCO 2 sensor to continuously monitor the carbon dioxide that is inspired 

and exhaled by the patient. It is usually presented as a graph of expiratory CO 2 against time, or 

less commonly against expired volume. The sensor employs infrared (IR) spectroscopy to 

measure the concentration of CO 2 molecules that absorb infrared light. This consists of a source 

of infrared radiation, a chamber containing the gas sample, and a photo-detector. When the 

expired CO 2 passes between the beam of infrared light and photo-detector, the absorbance is 

proportional to the concentration of CO 2 in the gas sample. The gas samples can be analysed by 

the mainstream (in-line) or side-stream (diverting) techniques. (Physio-Control, 2013) 

During CPR, the amount of CO 2 excreted by the lungs is proportional to the amount of 

pulmonary blood flow; therefore capnography can be used to monitor the effectiveness of CPR 

and as an early indication of the Return of Spontaneous Circulation (ROSC). 

It has been shown that when a patient experiences ROSC the first indication is often a sudden 

rise in EtCO 2 as the rush of circulation washes un-transported CO 2 from tissues, likewise a 

sudden drop in EtCO 2 may indicate that the patient has lost pulse and CPR may need to be 

restarted. (Paramedicine, 2000) 

Maintenance & Service Procedures 

Defibrillators are serviced annually, during the service functional checks of all controls, displays 

and sound outputs are performed. ECG functions are checked including heart rate calibration 

and lead off detection, most defibrillators can detect whether the paddles/pads are connected 

or disconnected and this should also be checked. 

An analyser is used to ensure output energy levels are within specification and a check of all 

functions/analysis is performed when in AED mode. 

Pacer function and pacer detection are both tested, a functional check of the capnography (if 

applicable) and finally an electrical safety test is performed. 

There is also scheduled battery and patient lead replacement, the expiry dates on the pads 

should be checked to ensure they are still ok to use. If they are past there expiry date the ward 

staff should be informed and the pads removed from use and replaced. 

During maintenance & service procedures it is vital to ensure a defibrillator is never left alone 

charged. When repairing or opening the case for any reason it is important to follow the 

manufacturer’s guidelines for discharging the capacitor to ensure no harm comes to yourself or 

others.

Bibliography 

Chaudhari, M., 2005. Anaesthesia Journal. [Online] 

Available at: http://www.anaesthesiajournal.co.uk/article/S1472-0299(06)00175-5/abstract 

[Accessed September 2015]. 

EBME, 2003. EBME - Biphasic Defibrillator. [Online] 

Available at: http://www.ebme.co.uk/articles/clinical-engineering/12-biphasicdefibrillation?showall=&start=3 


Knight, B. P., 2014. UpToDate. [Online] 

Available at: http://www.uptodate.com/contents/basic-principles-and-technique-ofcardioversion-and-defibrillation 


Lozano, I. F., 2013. Principles of External defibrillators. [Online] 

Available at: http://www.heartrhythmcharity.org.uk/www/media/files/InTech- 

Principles_of_external_defibrillators.pdf 


Paramedicine, 2000. End Tidal CO2. [Online] 

Available at: http://www.paramedicine.com/pmc/End_Tidal_CO2.html 

[Accessed October 2015]. 

Phillps Medical Systems, 2005. M4735A (ELD) Heartstream XL Defibrillator Service/User Manual, 

Physio-Control, 2013. Lifepak® 20e Defibrillator Service/User manual.

Diagnostic Ultrasound 

Steven Lewis 



Diagnostic Ultrasound 

Ultrasound is the term used to describe sound of frequencies above 20 kilohertz (kHz), at this 

frequency it is beyond the range of human hearing. 

Diagnostic ultrasound is an imaging technique used for visualising all body regions that are not 

situated behind expanses of bone or air-containing tissue, such as the lungs. Examinations 

through thin, flat bones are possible at lower frequencies. It is also possible to bypass obstacles 

with endoscopes (endoscopic sonography). Frequencies of 2–20 Megahertz (MHz) are typical 

for diagnostic ultrasound. 

Transcutaneous ultrasound is used mainly for evaluating: 

 

 

 

 

 

Neck: thyroid gland, lymph nodes, abscesses, vessels (angiology). 

Chest: wall, pleura, peripherally situated disorders of the lung, mediastinal tumours 

(The mediastinum is the cavity that separates the lungs from the rest of the chest. It 

contains the heart, esophagus, trachea, thymus, and aorta), and the heart as a whole 

(echocardiography). 

Abdomen: The abdominal cavity is the space bounded by the vertebrae, abdominal 

muscles, diaphragm, and pelvic floor. The intraperitoneal space located within the 

abdominal cavity, but wrapped in peritoneum (membrane that forms the lining of the 

abdominal cavity). The structures within the intraperitoneal space e.g. the stomach. 

The structures in the abdominal cavity that are located behind the intraperitoneal space 

"retroperitoneal" e.g. the kidneys, and those structures below the intraperitoneal space 

called "subperitoneal" or "infraperitoneal" e.g. the bladder and small pelvis: organs, fluid 

containing structures, gastrointestinal tract, great vessels and lymph nodes, tumours 

and abnormal fluid collections. 

Extremities (joints, muscles and connective tissue, vessels). 

Obstetric sonography is commonly used during pregnancy. 

Diagnostic ultrasound imaging depends on the computerised analysis of reflected ultrasound 

waves, which non-invasively build up fine images of internal body structures. 

Higher frequencies have a shorter wavelength and are therefore capable of reflecting and 

scattering off smaller structures giving higher resolution, however, the use of high frequencies 

is limited by their greater attenuation (loss of signal strength) in tissue and thus shorter depth 

of penetration limiting the depth when producing an image. Lower frequencies produce less 

resolution but image deeper into the body. For this reason, different ranges of frequency are 

used for examining different parts of the body values typically used are: 

 

 

 

 

 

 

2.5 MHz - deep abdomen, obstetric and gynaecological imaging 

3.5 MHz - general abdomen, obstetric and gynaecological imaging 

5.0 MHz - vascular, breast, pelvic imaging 

7.5 MHz - breast, thyroid 

10.0 MHz - breast, thyroid, superficial veins, superficial masses, musculoskeletal 

imaging. 

15.0 MHz - superficial structures, musculoskeletal imaging. 

(Morgan, 2015)

Transducer 

Ultrasound waves are produced by a transducer (a hand-held probe), which can both emit 

ultrasound waves, as well as detect the ultrasound echoes reflected back. The probe produces 

the ultrasound waves and receives the echoes using a principle called the piezoelectric effect. 

Inside the probe there are one or more piezoelectric crystals, piezoelectric crystals are able to 

produce sound waves when an electric current passes through them, but can also work 

in reverse, producing electricity when a sound wave hits them. This happens as the mechanical 

and electrical energy causes them to change shape, by contracting or expanding. 

When used in an ultrasound scanner, the transducer sends out a directed beam of sound waves 

into the body, and the sound waves are reflected back to the transducer from the tissues and 

organs in the path of the beam. When these echoes hit the transducer, they generate electrical 

signals that the ultrasound scanner converts into images of the tissues and organs. 

The probe has a sound absorbing substance to eliminate back reflections from the probe itself, 

and an acoustic lens to help focus the emitted ultrasound waves. 

Ultrasound Techniques 

The echo principle forms the basis of all common ultrasound techniques. The distance between 

the transducer and the reflector or scatterer in the tissue is measured by the time between the 

emission of a pulse and reception of its echo. Additionally, the intensity of the echo can be 

measured. With Doppler techniques, comparison of the Doppler shift of the echo with the 

emitted frequency gives information about any movement of the reflector. The various 

ultrasound techniques used are described below. 

A-mode 

A-mode (A-scan, amplitude modulation) is a one-dimensional examination technique in which a 

transducer with a single crystal is used. The echoes are displayed on the screen along a time 

(distance) axis as peaks proportional to the intensity (amplitude) of each signal. The method is 

rarely used today, as it conveys limited information, e.g. measurement of distances. For an 

example, ophthalmologists can use it to measure the diameter of the eye ball 

B-mode 

B-mode (brightness modulation) is a similar technique, but the echoes are displayed as points of 

different grey-scale brightness corresponding to the intensity (amplitude) of each signal. 

B-scan, 2D 

The arrangement of many (e.g. 256) one-dimensional lines in one plane makes it possible to 

build up a two-dimensional (2D) ultrasound image (2D B-scan). The single lines are generated 

one after the other by moving (rotating or swinging) transducers or by electronic multi-element 

transducers. 

Electronic transducers are made from a large number of separate elements arranged on a plane 

(linear array) or a curved surface (curved array). A group of elements is triggered 

simultaneously to form a single composite ultrasound beam that will generate one line of the 

image. The whole two-dimensional image is constructed step-by-step, by stimulating one group 

after the other over the whole array. 

The lines can run parallel to form a rectangular (linear array) or a divergent image (curved 

array)

Three- and four-dimensional techniques 

The main prerequisite for construction of three-dimensional (3D) ultrasound images is very fast 

data acquisition. The transducer is moved by hand or mechanically perpendicular to the 

scanning plane over the region of interest. 

The collected data are processed at high speed, so that real-time presentation on the screen is 

possible. This is called the four-dimensional (4D) technique (4D = 3D + real time). The 3D image 

can be displayed in various ways, such as transparent views of the entire volume of interest or 

images of surfaces, as used in obstetrics and not only for medical purposes. It is also possible to 

select two-dimensional images in any plane, especially those that cannot be obtained by a 2D B- 

scan. 

M-mode or TM-mode 

Fig 1 - 3D Ultrasound scan Image 

M-mode or TM-mode (time motion) is used to analyse moving structures, such as heart valves. 

The echoes generated by a stationary transducer (one-dimensional B-mode) are recorded 

continuously over time. 

The ultrasound images can show: 

Presence, position, size and shape of organs. 

Stasis, concretions and dysfunction of hollow organs and structures. 

Tumour diagnosis and differentiation of focal lesions. 

Inflammatory diseases. 

Metabolic diseases causing macroscopic alterations of organs. 

Abnormal fluid collection in body cavities or organs, including ultrasound-guided 

diagnostic and therapeutic interventions; 

Evaluating transplants; 

Diagnosis of congenital defects and malformations. 

Additionally, ultrasound is particularly suitable for checks in the management of chronic 

diseases and for screening, because it is low risk, comfortable for patients and cheaper than 

other imaging modalities. (World Health Organization, 2011) 

Signal Processing and image capture 

The main ultrasound system takes care of processing signals from the ultrasound probe and 

capturing and recording images. The computer based system runs dedicated software that 

controls the ultrasound probes, processes the signal returned from the probe, displays the 

image and allows the image to be captured on internal storage or sent through the hospital 

network


A visual inspection paying attention to the case, cables, any foot pedals and the ultrasound 

probe should be carried out, also checking that any ventilation grilles are free from dust/debris. 

The ultrasound system should be running quietly when switched on and a check that all the 

buttons are functioning and the screen displays a clear image. 

Check for ‘dropout’ (i.e. crystal failure) on all probes using a paperclip ensuring that it is 

displayed as expected. If an ultrasound phantom is available confirm the following; 

 

 

Image quality (uniformity, no axial banding, excessive noise etc.) 

Ultrasound phantom targets imaged as expected. 

An EST should then be performed on the system with the probe placed in a saline solution with 

the applied part lead.

Bibliography 

Morgan, D. M. A., 2015. Ultrasound Frequencies, s.l.: NIBIB. 

NIBI, 2012. National Institute of Biomedical Imaging. [Online] 

Available at: http://www.nibib.nih.gov/science-education/science-topics/ultrasound 

[Accessed 2016]. 

Stern, B., 2016. Basic Concepts of Utrasound Scanning. [Online] 

Available at: http://www.yale.edu/ynhti/curriculum/units/1983/7/83.07.05.x.html 

[Accessed 2016]. 

World Health Organization, 2011. Manual of Diagnostic Ultrasound. 2nd ed. Geneva: WHO Press.

Electro-Surgery Equipment 

Steven Lewis 



Electro-Surgery 

Electro-surgery is the application of a high-frequency electric current to biological tissue as a 

means to cut, coagulate (form blood clots), desiccate (remove water), or fulgurate (destroy and 

remove) tissue. Its benefits include the ability to make precise cuts with limited blood loss. 

Electrosurgical devices are frequently used during surgical operations in hospital operating 

rooms or in outpatient procedures. 

Electro-surgery is performed using an electrosurgical generator (also referred to as a power 

supply or waveform generator), in a circuit made up of an active electrode, the patient and an 

active return electrode. The tissue is heated by an AC current; the AC current is used to directly 

heat the tissue itself, whereas in electro-cautery the tip of the instrument is heated. 

Fig 1 – Mono-polar Electro-surgery 

Fig 2 – Bi-polar Electro-surgery 

Standard electrical current alternates at a frequency of 50Hz, at this frequency the current 

transmitted to the body tissue would cause excessive neuromuscular stimulation and possibly 

electrocution. Nerve and muscle stimulation cease at 100 kHz so at frequencies above this, 

typically 200 kHz – 3.3 MHz, electro-surgery can be performed with the energy passing through 

the patient with minimal neuromuscular stimulation and no risk of electrocution meaning 

electro-surgery can be performed safely.

Mono-polar 

Mono-polar is the most commonly used electro-surgical mode. In mono-polar electro-surgery, 

the active electrode is in the surgical site, with the patient return electrode somewhere else on 

the patient’s body. The current passes through the patient as it completes the circuit from the 

active electrode to the return electrode. The return electrode placement should be on 

conductive tissue over a large surface area to prevent a build-up of heat which could potentially 

cause a burn. Other factors that may cause the return electrode to be compromised are 

excessive hair, adipose tissue (fat), bony prominences, fluid invasion, metal implants and scar 

tissue. 

Fig 3 – Patient return electrode placement 

Return Electrode Contact Quality Monitoring (RECQM) 

RECQM was developed to protect patients from burns due to inadequate contact of the return 

electrode pad site by using a split plate system. RECQM equipped generators actively monitor 

the amount of impedance between the two split plates. If the impedance is high, due to poor 

contact on either side of the split plate, the electrosurgical unit will alarm to warn the clinical 

user of the problem. If the impedance between the two plates is very high or not symmetrical 

the unit will alarm and the system will deactivate the generator before an injury can occur 

Fig4 – Return Electrode Contact Quality Monitoring 

(RECQM)

Bi-polar 

In bipolar electro-surgery, both the active electrode and return electrode functions are 

performed at the site of the surgery. The tines of the forceps perform the active & return 

electrode with only the tissue being grasped included in the circuit. As one of the tines of the 

forceps performs the return function no patient return electrode is needed. Bipolar diathermy 

is perceived to be safer as the current pathway is much shorter than that utilised in mono-polar 

diathermy. Bipolar diathermy is generally utilised in the following situations: 

 

 

 

 

When coagulation only is required. 

When coagulation is required in peripheral areas of the body such as hands or feet or 

other areas where channelling (tissue damage caused by heat) may occur. 

In procedures where pinpoint or micro coagulation is required. 

When a patient has a pacemaker in situ. 

Electrosurgical Modes 

Electrosurgical generators are able to produce a variety of electrical waveforms. As waveforms 

change, so will the corresponding tissue effects. Using a constant waveform, like cut, the 

surgeon is able to vaporize or cut tissue. This waveform produces heat very rapidly. 

Using an intermittent waveform, like coagulation, causes the generator to modify the waveform 

so that the duty cycle (on time) is reduced. This interrupted waveform will produce less heat. 

Instead of tissue vaporization, a coagulum is produced. 

A blended current is not a mixture of both cutting and coagulation current but rather a 

modification of the duty cycle. In the example below, as you go from Blend 1 to Blend 3 the 

duty cycle is progressively reduced. A lower duty cycle produces less heat. Consequently, Blend 

1 is able to vaporize tissue with minimal haemostasis whereas Blend 3 is less effective at cutting 

but has maximum haemostasis. 

Fig 5 – Electrosurgical Modes 

The only variable that determines whether one waveform vaporizes tissue and another 

produces a coagulum is the rate at which heat is produced. High heat produced rapidly causes 

vaporization. Low heat produced more slowly creates a coagulum. 

Any one of the five waveforms can accomplish both tasks by modifying the variables that impact 

tissue effect.

The electrosurgical generator or unit can produce three distinct surgical effects, known as 

fulguration, desiccation and cutting. The electrosurgical generator creates different wave forms 

which are determined by the setting on the machine, universally known as COAG, CUT and 

BLEND. The settings and desired effects are linked as follows: 

Cutting 

The CUT waveform is a continuous waveform at a lower voltage but higher current than COAG. 

This creates a high density of current in a specific tissue area within a short period of time 

causing cellular fluid to burst into steam and disrupt the structure which results in vaporisation 

of tissue. This results in cell explosion due to the localised but intense heat 

Coagulation 

Fig 6 – Electrosurgical Cut 

Coagulation is performed using waveforms with a lower average power, generating insufficient 

heat for explosive vaporisation, but performing a thermal coagulum instead. 

Fulguration 

When the COAG waveform is used at a high power setting it will create the effect known as 

fulguration. The high power generates sparks which create intermittent heating of tissue 

causing cells to dry out quickly rather than explode into steam. In fulguration mode the 

electrode is held away from the tissue so that when the air gap between the electrode and the 

tissue is ionised an electric arc discharge develops. Fulguration coagulates and chars the tissue 

over a wide area. In this application the burning of the tissue is more superficial; therefor this 

technique is used for very superficial or protrusive lesions such as skin tags. 

Desiccation 

Fig 7 – Electrosurgical Coagulate 

Electrosurgical desiccation occurs when the electrode is in direct contact with the tissue. 

Desiccation is achieved most efficiently with the cutting current. By touching the tissue with the 

electrode, the current concentration is reduced. Less heat is generated and no cutting action 

occurs. The cells dry out and form a coagulum rather than vaporize and explode.

Many surgeons routinely cut with the coagulation current. Likewise, you can coagulate with the 

cutting current by holding the electrode in direct contact with tissue. It may be necessary to 

adjust power settings and electrode size to achieve the desired surgical effect. The benefit of 

coagulating with the cutting current is that you will be using far less voltage. Likewise, cutting 

with the cut current will also accomplish the task with less voltage. This is an important 

consideration during minimally invasive procedures. 

Variables Impacting Tissue Effect 

In addition to waveform and power setting, other variables impact tissue effect. They include: 

Size of the electrode: The smaller the electrode, the higher the current concentration. 

Consequently, the same tissue effect can be achieved with a smaller electrode, even though the 

power setting is reduced. 

Time: At any given setting, the longer the generator is activated, the more heat is produced. And 

the greater the heat, the farther it will travel to adjacent tissue (thermal spread). 

Manipulation of the electrode: This can determine whether vaporization or coagulation 

occurs. This is a function of current density and the resultant heat produced while sparking to 

tissue versus holding the electrode in direct contact with tissue. 

Type of Tissue: Tissues vary widely in resistance. 

Eschar: Eschar (dead tissue produced by a thermal burn) is relatively high in resistance to 

current. Keeping electrodes clean and free of eschar will enhance performance by maintaining 

lower resistance within the surgical circuit. 

Fig 8 – Electrosurgical Mode Effects

Argon-Enhanced Electro-surgery 

Argon-enhanced electro-surgery incorporates a stream of argon gas to improve the surgical 

effectiveness of the electrosurgical current. 

Argon gas is inert and non-combustible, making it a safe medium through which to pass 

electrosurgical current. Electrosurgical current easily ionizes argon gas, making it more 

conductive than air. This highly conductive stream of ionized gas provides the electrical current 

an efficient pathway. 

There are many advantages to argon-enhanced electrosurgical cutting and coagulation. 

 

 

 

 

 

Non-combustible 

Decreased smoke & odour 

Non-contact in coagulation mode 

Decreased blood loss. 

Decreased tissue damage 

Fig 9 – Argon enhanced electro-surgery 

Surgical Smoke 

Surgical smoke is created when tissue is heated and cellular fluid is vaporized by the thermal 

action of an energy source. Viral DNA, bacteria, carcinogens and irritants are known to be 

present in electrosurgical smoke. Universal precautions indicate a smoke evacuation system 

should be used. The National Institute of Occupational Safety and Health (NIOSH) and the 

Centre for Disease Control (CDC) have also studied electrosurgical smoke at length. The 

organisations concluded: “Research studies have confirmed that this smoke plume can contain 

toxic gases and vapours such as benzene, hydrogen cyanide, formaldehyde, bio-aerosols, dead 

and live cellular material (including blood fragments) and viruses.” 

When electro-surgery is used in the context of minimally invasive surgery, it raises a new set of 

safety concerns. Two of these are insulation failure and direct coupling of current. 

Direct Coupling 

Direct coupling occurs when the user accidentally activates the generator while the active 

electrode is near another metal Instrument (scopes, graspers, etc.). Electrical current will flow 

from the first conductor into the secondary one and energize it. This energy will seek a pathway 

to complete the circuit to the patient return electrode. There is potential for significant patient 

injury.

Insulation Failure 

Many surgeons routinely use the coagulation waveform. This waveform is comparatively high 

in voltage. This voltage can spark through compromised insulation. Also, high voltage can cause 

breaks in weak insulation. Breaks in insulation can create an alternate route for the current to 

flow. If this current is concentrated, it can cause significant injury. Also radio frequency is not 

always confined by insulation and current leakage does occur. It is recommended that Cords 

not be wrapped around metal instruments and Cords not be bundled together. 

Fig 10 – Possible injury through compromised 

insulation 

Further precautions to take for safe use are; the electrosurgical device should not be used in the 

presence of flammable agents such as alcohol and /or tincture based (alcoholic extract of plant 

or animal) agents. 

Use of electrosurgical devices should be avoided in oxygen enriched environments 

Active electrodes should be placed in clean, dry, well insulated safety holsters when not in use 

to avoid any accidental injury if the generator is accidently activated. 

Maintenance and service procedures 

Maintenance procedures should include a thorough visual inspection of all elements of the 

electrosurgical device. 

Error logs should be checked and any regular or serious errors should be rectified. 

The system that checks pad resistance should be checked to ensure the correct errors occur at 

the correct resistances. 

The power output should be checked across all setting at various levels and effects. 

Argon plasma units should be checked alongside the correct electrosurgical device. 

Flow rates of the argon gas output should be measured. All functions should be checked. 

A full electrical safety test should be carried out, it is important to consult the service manual/ 

protocol to ensure the unit is in the correct mode to ensure the output relays are all closed for 

the duration of the safety test.

Bibliography 

Covidien, 2014. Principles in Electro-surgery. [Online] 

Available at: http://www.asit.org/assets/documents/Prinicpals_in_electrosurgery.pdf 

[Accessed July 2015]. 

EBME, 2009. EBME - Apnoea Alarms. [Online] 

Available at: http://www.ebme.co.uk/articles/clinical-engineering/6-apnoea-alarms 

[Accessed March 2014]. 

Gov.uk, 2014. Electro-surgery Equipment Safety. [Online] 

Available at: 

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/403384/Ele 

ctro-surgery_equipment_safety_poster.pdf 


MHRA, n.d. Electrosurgical Module. [Online] 

Available at: info.mhra.gov.uk/learning/ESUGenericModule/player.html 


NATN, 2013. Electro-surgery managing the risk – National Association of Theatre Nurses. [Online] 

Available at: www.afpp.org.uk/filegrab/electrosurgeryguidance.pdf?ref=5 

[Accessed July 2015].

Multi-Parameter Monitoring 

Steven Lewis 



Multi-parameter Monitors 

Multi-parameter Monitors are intended to be used for monitoring, displaying, reviewing, storing 

and the transferring of multiple physiological parameters including, ECG, heart rate (HR), 

respiration (Resp), temperature (Temp), SPO 2 (pulse oxygen saturation), pulse rate (PR), noninvasive 

blood pressure (NIBP), invasive blood pressure (IBP), cardiac output (C.O.), airways 

gases such as; carbon dioxide (CO 2), oxygen (O 2), anaesthetic gas (AG). 

Monitoring vital signs for example; a patient’s blood pressure, pulse rate, and respiration rate is 

a crucial aspect of patient care in hospital. Vital signs indicate a patient’s clinical condition, are 

necessary to calculate national early warning scores (NEWS) and used to determine the 

monitoring, escalation and interventions that are required subsequently. 

In a hospital setting, patient monitoring is used in operating theatres, intensive care and critical 

care units, and many other critical and non-critical areas. 

Continuous multi-parameter monitoring has shown to be an effective mechanism for triggering 

early detection of changes in a patient’s condition by notifying the nursing staff that the patient 

needs attention. This is beneficial as by assessing the situation sooner and making the right 

clinical decision to intervene as appropriate. 

In addition to monitoring patients on an individual basis, the remote observation of multiple 

patients is possible through central patient monitoring systems. These monitoring systems are 

typically made up of networked machines consisting of one or more sensors, display devices, 

processing components, and communication links for displaying or recording the results 

elsewhere through the network. For portable monitors or in areas where a hard wired network 

is not practical wireless monitors are used, the signal is sent from the telemetry unit and picked 

up by aerial’s located around the hospital. This is particularly useful for areas such as Accident & 

Emergency and Coronary Care Unit or where multiple areas need to monitor the same patient at 

the same time or while a patient is being transported from one area to another. 

In non-critical areas the signs being monitored will predominantly be Heart Rate, SPO 2, Blood 

Pressure and ECG. In a critical care area such as ICU or an operating theatre, further signs will 

be monitored these may include; Invasive Blood Pressure (IBP), Respiration Rate and airways 

gases such as CO 2, O 2, and other gases that may be respired such as anaesthetic gases during a 

surgical procedure. 

Respiration Rate 

The function of the respiratory system is to supply adequate oxygen to the tissues and to 

remove the waste product carbon dioxide. This is achieved with the inspiration and expiration 

of air. With each breath there is a pause after expiration. The rate of respiration will vary with 

age and gender. A respiratory rate of 12-18 breaths per minute in a healthy adult is considered 

normal. Rates outside of this normal range can be classed as; 

 

 

 

 

 

Tachypnoea: the rate is regular but over 20 breaths per minute. 

Bradypnoea: the rate is regular but less than 12 breaths per minute. 

Apnoea: there is an absence of respiration for several seconds - this can lead to 

respiratory arrest. 

Dyspnoea: difficulty in breathing, the patient gasps for air. 

Cheyne-Stokes respiration: the breathing gets increasingly deeper then shallower, 

very slow and laboured with periods of apnoea. This type of breathing is often seen in 

the dying patient.

Hyperventilation: patients may breathe rapidly due to a physical or psychological 

cause, for example if they are in pain or panicking. Hyperventilation reduces the carbon 

dioxide levels in the blood, causing tingling and numbness in the hands; this may cause 

further distress. In adults, more than 20 breaths a minute is considered moderate, more 

than 30 breaths is severe. (Mallett & Dougherty, 2004) 

Multi-parameter monitors have a function to measure the respiration rate of the patient. This is 

the number of breaths the patient takes per minute. Most multi-parameter monitors record this 

by monitoring the resistance between two ECG electrodes connected to the patient. As the 

patient breaths in and the chest expands the resistance between the two electrodes increases 

and then decreases as the patient exhales and the chest contracts. Others ways to monitor 

respiration could be using capnography which involves CO 2 measurements, referred to as EtCO 2 

or end-tidal carbon dioxide concentration. The respiratory rate monitored as such is called 

AWRR or airway respiratory rate. Other monitors may record spirometry flow volume loops, 

which will show the flow, volume and time taken to inhale and exhale, or it may be monitored 

by simply counting the number of breaths in one minute by recording how many times the chest 

rises. 

Capnography 

Capnography is the measurement of carbon dioxide (CO 2) in exhaled breath; capnography gives 

medical professionals another tool for determining whether blood is flowing to vital organs like 

the heart and brain. CO 2 levels reflect cardiac output and pulmonary blood flow; as the gas is 

transported by the venous system to the right side of the heart and then pumped to the lungs by 

the right ventricles. 

Capnography is particularly important during surgery, where patients are continuously 

monitored while under anaesthesia to ensure safety. In addition to its use in surgical settings, 

capnography can help physicians and emergency medical personnel determine whether a 

patient is having a heart attack or hyperventilating. It can also help them determine whether 

CPR is working. 

The two primary methods used for measuring CO 2 in expired air are mass spectroscopy and 

infrared spectroscopy. In mass spectroscopy gases and vapours of different molecular weights 

are separated and a breakdown of what gases and percentages can be displayed. 

End tidal Carbon Dioxide (EtCO 2) is the partial pressure or maximal concentration of carbon 

dioxide at the end of an exhaled breath, which is expressed as a percentage of CO 2 or in mmHg. 

Infrared (IR) spectroscopy uses an EtCO 2 sensor to continuously monitor the carbon dioxide 

that is inspired and exhaled by the patient. It is usually presented as a graph of expiratory CO 2 

against time, or less commonly against expired volume. 

The EtCO 2 sensor consists of an infrared source, a chamber through which the gas sample 

passes, and a photo-detector. When the expired CO 2 passes between the beam of infrared light 

and photo-detector it leads to a reduction in the amount of light falling on the sensor, this is due 

to the principle that CO 2 absorbs infrared radiation. The absorbance is proportional to the 

concentration of CO 2 in the gas sample. (Physio-Control, 2013) 

Capnometers can be categorised based on the sensing device location. The gas samples can be 

analysed by mainstream or side-stream techniques.

Mainstream capnometers are in-line with the patient tubing; the housing is heated to prevent 

condensation. The advantage of mainstream analysis is that it gives a real-time measurement 

(i.e., an immediate response rate of

eat, and a waveform (a graph of pressure against time) can be displayed. 

The components of an intra-arterial monitoring system can be viewed as three main parts: 

 

 

 

The measuring apparatus 

The transducer 

The monitor 

The measuring apparatus consists of an arterial cannula connected to tubing containing a 

continuous column of saline. The pressure waveform of the arterial pulse is transmitted via the 

column of fluid, to a pressure transducer, in the case of intra-arterial monitoring the transducer 

consists of a flexible diaphragm which in turn moves strain gauges converting the pressure 

waveform into an electrical signal. Monitors amplify the output signal from the transducer, filter 

the noise and also display the arterial waveform in real time on a screen. They also usually give 

a digital numeric display of systolic, diastolic and mean arterial blood pressure (MAP). 

The arterial line is also connected to a flushing system consisting of a bag of saline pressurised 

to 300 mm/Hg via a flushing device. 

Fig 3 – Invasive Blood Pressure being monitored 

For a pressure transducer to read accurately, atmospheric pressure must be discounted from 

the pressure measurement. This is done by exposing the transducer to atmospheric pressure 

and calibrating the pressure reading to zero. A transducer should be zeroed several times per 

day to eliminate any baseline drift. 

The pressure transducer must be set at the appropriate level in relation to the patient in order 

to measure blood pressure correctly. This is usually taken to be level with the patient’s heart. 

Failure to do this results in an error due to hydrostatic pressure (the pressure exerted by a 

column of fluid – in this case, blood) being measured in addition to blood pressure. This can be 

significant – every 10cm error in levelling will result in a 7.4mmHg error in the pressure 

measured; a transducer too low over reads, a transducer too high under reads. 

IBP monitoring has numerous advantages; IBP allows continuous ‘beat-to-beat’ blood pressure 

monitoring. This is useful in patients who are likely to display sudden changes in blood pressure 

(e.g. vascular surgery), patients who require close control of blood pressure (e.g. head injured 

patients), or in patients receiving drugs to maintain blood pressure. 

The IBP technique also allows accurate blood pressure readings at very low pressures, for 

example in shocked patients. 

An invasive blood pressure reading could also allow for improvement of patient comfort if blood 

pressure monitoring is required for a long period of time. IBP monitoring avoids the trauma of 

repeated cuff inflations. 

Other advantages include that the arterial cannula is convenient for repeated arterial blood 

sampling, for instance for arterial blood gases. (Jones, 2009)


Invasive Blood Pressure 

This is checked using a patient simulator at various pressures, it is essential that a zeroing 

procedure is performed before any measurements are taken. 

Respiration Rate 

This is also checked using a patient simulator at various rates to ensure accuracy. 

Capnography & Airways Gases 

Capnograpy can be tested by attaching an ETCO 2 circuit and breathing into the airway adapter at 

a set rate, the rise and fall of the CO 2 graph will be displayed on the monitor. The accuracy of 

any measured airways gases is also to be checked by attaching a cylinder filled with various 

gases such as; O 2, CO 2, nitrogen and typically an anaesthetic gas at set percentages. The monitor 

should show the levels of the various gases, if the values displayed are not correct a calibration 

procedure should be carried out.

Bibliography 

EBME, 2014. Capnography. [Online] 

Available at: http://www.ebme.co.uk/articles/clinical-engineering/16-capnometrycapnography 

[Accessed December 2015]. 

Fukuda Denshi UK, 2014. DS-8500 System Maintenance Manual V.09 (2014). V 9 ed. Tokyo: 

Fukuda Denshi. 

Jones, A., 2009. Physical Principles of Intra-Arterial Blood Pressure Measurements, Salford: s.n. 

Mallett , J. & Dougherty, L., 2004. The Royal Marsden Hospital Manual of Clinical Nursing 

Procedures. 6th ed. Oxford: Blackwell Science. 

Paramedicine, 2000. End Tidal CO2. [Online] 

Available at: http://www.paramedicine.com/pmc/End_Tidal_CO2.html 

[Accessed October 2015]. 

Physio-Control, 2013. Lifepak® 20e Defibrillator Service/User manual. 

Tilakaratna, P., 2014. How Equipment Works. [Online] 

Available at: http://www.howequipmentworks.com/capnography/ 

[Accessed December 2015].

Neonatal Phototherapy 

Steven Lewis 



Neonatal Phototherapy 

Jaundice is one of the most common conditions needing medical attention in newborn babies. 

Jaundice refers to yellow colouration of the skin and the sclerae (white outer coat of the 

eyeball). The yellow coloration of the skin and sclera in newborns with jaundice is the result of 

an accumulation of unconjugated bilirubin. In most infants, unconjugated bilirubin reflects a 

normal transitional phenomenon. However, in some infants, serum bilirubin levels may rise 

excessively, a condition known as hyper-bilirubinaemia, which can be cause for concern 

because unconjugated bilirubin is neurotoxic and can cause death in newborns and lifelong 

neurologic complications (bilirubin encephalopathy) in infants who survive. The term 

kernicterus is used to denote the clinical features of acute or chronic bilirubin encephalopathy. 

Newborns are especially vulnerable to hyper-bilirubinemia induced neurological damage and 

therefore must be carefully monitored for alterations in their serum bilirubin levels. (GOSH, 

2014) 

Neonatal phototherapy is a widely used and accepted form of treatment for neonatal hyperbilirubinaemia. 

Effective phototherapy needs to satisfy three important criteria; effective 

spectrum, sufficiently high irradiance and large effective treatment area. The aim of 

phototherapy is to lower the concentration of circulating bilirubin or keep it from increasing. 

Phototherapy achieves this by using light energy to change the shape and structure of bilirubin, 

converting it to molecules that can be easily excreted. 

Fig 1 – Effect of Blue Light on Bilirubin 

Bilirubin absorbs light most strongly in the blue region of the spectrum near 460nm. Only 

wavelengths that penetrate tissue and are absorbed by bilirubin have a phototherapeutic effect. 

Phototherapy units with outputs predominantly in the 460-490nm blue region of the spectrum 

are the most effective for treating hyper-bilirubinaemia. 

Blue light (400-480nm) has the potential to cause photochemical induced retinal injury, usually 

during therapy the neonate’s eyes will be covered using commercial or in-house eye protection. 

The baby’s temperature must also be carefully monitored during treatment because there may 

be increased heat from the phototherapy lamps. (Wentworth, 2005)

Maintenance and Service Procedures 

Phototherapy units require a thorough visual inspection, a light output check every 3-6 months 

and a filter clean and electrical safety test. During service or maintenance procedures it is 

important to wear the correct PPE; in this case the most important piece is the correct eye 

protection, and safety glasses that block the blue light from entering the eye should be worn. 

Fig 2 – Example of Blue Light Blocking Glasses (Amber Lens) 

Bibliography 

GOSH, 2014. GOSH - Neonatal Jaundice and Phototherapy. [Online] 

Available at: http://www.gosh.nhs.uk/health-professionals/clinical-guidelines/neonataljaundice-and-phototherapy 

[Accessed August 2015]. 

NHS, 2013. Jaundice Newborns & Phottherapy. [Online] 

Available at: http://www.nhs.uk/conditions/jaundice-newborn/pages/treatment.aspx 


NICE, 2014. NICE Guidance. [Online] 

Available at: https://www.nice.org.uk/guidance/cg98/chapter/Introduction 


Wentworth, S. D., 2005. Neonatal Phototherapy, Cardiff: Rookwood.

Video Stacks & Endoscopy 

Systems 

Steven Lewis 



Endoscopy Systems & Video Stacks 

Endoscopy is a minimally invasive medical procedure directly visualising any part of the inside 

of the body using an endoscope, this will be used with a stack containing various equipment 

such as a monitor, light source, insufflator, camera, and printer all connected through an 

isolation transformer. These stacks are used in theatres and various clinics, such as Ear, Nose, 

and Throat (ENT). 

Endoscopes 

An endoscope is a long, thin, rigid or flexible tube that consists of two or three main optical 

cables, each of which comprises up to 50,000 separate optical fibres (made from optical-quality 

glass or plastic). One or two of the cables carry light down into the patient's body; another one 

carries reflected light (the image of the patient's body) back up to the physician's eyepiece (or 

into a camera, which can display it on a monitor). 

The optics of an endoscope are similar to those in a telescope. At the remote (distal) end, there 

is an objective lens, which links to one or more bendy sections of fibre-optic cable that carry the 

light back out of the patient's body to a second lens in an eyepiece or to a camera, which can be 

manipulated to adjust the focus. 

Endoscopes can be inserted into the body through a natural opening, such as the mouth and 

down the throat, or through the anus. Alternatively, an endoscope can be inserted through a 

small surgical cut made in the skin (known as keyhole surgery). Images of the inside of the body 

are relayed to a Monitor. The instrument may not only provide an image for visual inspection 

and photography, but may also be capable of taking biopsies or the retrieval of foreign objects. 

Some of the most commonly used types of endoscope include: 

 

 

 

 

Colonoscopes: used to examine the large intestine (colon). 

Gastroscopes: used to examine the oesophagus and stomach. 

Endoscopic Retrograde Cholangiopancreatography (ERCP): used to check for 

gallstones. 

Broncoscopes: used to examine the lungs and airways. 

Other types of endoscope include: 

 

 

 

Arthroscopes: used to examine joints. 

Hysteroscopes: used to examine the womb (uterus). 

Cystoscopes: used to examine the bladder. 

Endoscopy can involve; 

 

 

 

 

The Gastrointestinal Tract (GI tract): oesophagus, stomach and duodenum 

(esophagogastroduodenoscopy), small intestine, colon, (colonoscopy, proctosigmoidoscopy). 

The Respiratory Tract: the nose (rhinoscopy), the lower respiratory tract 

(bronchoscopy), the urinary tract (cystoscopy). 

The Female Reproductive System: The cervix (colposcopy), the uterus 

(hysteroscopy), the Fallopian tubes (Falloscopy). 

Normally closed body cavities (through a small incision): the abdominal or pelvic 

cavity (laparoscopy), the interior of a joint (arthroscopy), Organs of the chest 

(thoracoscopy and mediastinoscopy).

An endoscopy is normally carried out while a patient is conscious. It is not usually painful, but 

can be uncomfortable, so a local anaesthetic or sedative may be given. 

The exception is keyhole surgery, such as a laparoscopy or an arthroscopy, which are performed 

under general anaesthetic. (Martin, 2014) 

Endoscopy procedures are usually safe, and the risk of serious complications is low. Possible 

complications of an endoscopy include an infection in the part of the body that the endoscope is 

used to examine, damage to the body part which may in turn cause excessive bleeding. 

Monitors 

Monitors used on modern video stacks are high quality high definition (HD) flat panel screens, 

with excellent colour reproduction and a wide viewing angle. Most will have various video 

connections on the back such as S-Video, BNC, DVI, HDMI, etc. Some older video stacks may 

have a non HD flat panel monitor or a CRT monitor. 

Light Source & Lamps 

The light source may form part of a video or endoscopic stack, be a stand-alone unit often used 

in ENT procedures, or be attached to a microscope providing illumination to the area under 

investigation, the light is usually transmitted via a fibre optic cable to the lens end of a scope. 

High-Intensity Discharge Lamps 

High Pressure Sodium (HPS), Metal Halide, Mercury Vapour and Self-Ballasted Mercury Lamps 

are all high intensity discharge lamps (HID). Compared to fluorescent and incandescent lamps, 

HID lamps produce a large quantity of light from a relatively small bulb. 

HID lamps produce light by striking an electrical arc across tungsten electrodes housed inside a 

specially designed inner glass tube. This tube is filled with both gas and metals. The gas aids in 

the starting of the lamps, then, the metals produce the light once they are heated to a point of 

evaporation. High intensity discharge lamps, such as xenon, are ubiquitous within the field of 

endoscopy for minimally invasive surgery and diagnosis. Coupling light into a small diameter 

fibre bundle is difficult, so an extremely bright light source is required. Historically, the light 

source of choice has been the 180 to 300 W xenon lamp, which could deliver 1,000+ lumens of 

light at the distal end of the fibre bundle. While xenon bulbs achieve the technical requirements 

for endoscopy, they have a very short life, 500 - 1,000 hours, and can be expensive. 

LED Lighting 

The medical device industry is constantly changing. New technologies and products enter the 

market, replacing outdated or inefficient equipment. LED lighting is one of these, and there are 

numerous benefits in using LEDs for medical illumination applications including; longer life, less 

heat, dynamic control, lower energy consumption, and in many cases, lower cost. LED 

technology has improved significantly over the years, and is currently being integrated into 

medical devices, including surgical lighting, exam lights, phototherapy, and endoscopy. Ongoing 

advancements in LEDs that are driving the technology’s use in medical devices include 

improvement in light intensity, product size and weight; long-term reliability, and 

heat/temperature management, a line of high performance LEDs optimised to displace xenon 

technology for endoscopy have been developed.

Fibre Optic 

The light in a fiber-optic cable travels through the core by constantly bouncing from the 

cladding (mirror-lined walls), a principle called total internal reflection. The cladding does not 

absorb any light from the core, enabling the light wave to travel great distances. 

Fig 1 - Fibre Optic Cable 

Light source intensity is either adjusted manually via a dial or slider on the unit. If a camera and 

processor are attached they can monitor the amount of light at the scope end and adjusts the 

intensity automatically. 

Different wavelengths of light are needed for different procedures; 

Auto Fluorescence Imaging (AFI) is based on the detection of natural tissue fluorescence 

emitted by endogenous molecules (fluorophores) such as collagen, flavins, and porphyrins. 

After excitation by a short-wavelength light source, mucosal tissue emits a green fluorescence. 

A difference in the intensity of this fluorescence is seen between healthy and unhealthy tissue. 

These colour differences in fluorescence emission can be captured in real time during 

endoscopy and used for lesion detection or characterisation. 

Narrow Band Imaging (NBI) is a powerful optical image enhancement technology that 

improves the visibility of blood vessels and other structures on the bladder mucosa. This makes 

it an excellent tool for diagnosing bladder cancer during cystoscopy. 

White light is composed of an equal mixture of wavelengths. The shorter wavelengths only 

penetrate the top layer of the mucosa, while the longer wavelengths penetrate deep into the 

mucosa. NBI light is composed of just two specific wavelengths that are strongly absorbed by 

haemoglobin. 

The shorter wavelength in NBI is 415 nm light, which only penetrates the superficial layers of 

the mucosa. This is absorbed by capillary vessels in the surface of the mucosa and shows up 

brownish on the video image. This wavelength is particularly useful for detecting tumours, 

which are often highly vascularised. The second NBI wavelength is 540 nm light, which 

penetrates deeper than 415 nm light. It is absorbed by blood vessels located deeper within the 

mucosal layer, and appears cyan on the NBI image. This wavelength allows a better 

understanding of the vasculature of suspect lesions. (Olympus, 2014) 

Fig 2 – Absorption of Narrow Band Illumination

Insufflator 

An Insufflator provides distension of the required cavity for diagnostic or operative procedures. 

The insufflator pumps CO 2 into the cavity to a set pressure, this stretches the area being worked 

on making it easier to manipulate tools, assess the surgical site or perform the operative 

procedure. The maximum pressures of cavity’s should be observed when using an insufflator to 

prevent any problems, for example, Prolonged intra-abdominal pressures greater than 20mmHg 

should be avoided as they can cause any of the following problems; 

 

 

 

Decreased respiration due to pressure on the diaphragm. 

Decreased venous return. 

Decreased Cardiac output. 

CO 2 is now preferred over air as CO 2 is absorbed 150 times faster than the nitrogen in air, and is 

promptly eliminated via the lungs. This also means that patients are not subjected to extended 

discomfort from bloating and cramping. 

Camera System 

The camera on a video stack consists of two parts, the camera head, where scopes and light 

guides are attached, and a processer unit which feeds the image taken by the camera to a 

monitor, image capture device or printer. 

The aperture opens and closes to control how much light travels from the subject through a 

series of curved lens and through coloured filters focused on a digital sensor, which converts it 

into a digital (numerical) format. This is then processed and fed to the image capture system, 

monitor and printer. 

Image Capture System 

Image capture systems are image management systems that have the ability to record images 

and videos to their internal hard drive. They can also be connected to the hospital network 

where they can be integrated with PACS and other similar systems. 

Many image capture systems are generally windows based systems with a dedicated user 

interface. Very little maintenance of this system is required, at ULHT the only thing in the way 

service and repair we carry out is to take an image of the hard-drive at acceptance in case of any 

faults during its life, functional and visual checks and electrical safety testing. 

Isolation Transformer 

An isolation transformer is a transformer used to transfer electrical power from a source of 

alternating current (AC) power to some equipment or device while isolating the powered device 

from the power source, usually for safety reasons. Isolation transformers are used to protect 

against electric shock, to suppress electrical noise in sensitive devices, or to transfer power 

between two circuits which must not be connected. All true transformers are isolating as the 

primary and secondary are not connected physically but only by induction. However, in an 

isolation transformer the windings are completely insulated from each other to ensure good 

isolation.

In a normal supply the earth conductor is referenced to the neutral 

connector at source, which gives a potential voltage between live 

and earth of 240V. This means that touching either the live or 

neutral makes you part of the return path and can result in 

electrocution. 

With an isolation transformer the output voltage is not referenced 

to ground, so you could safely touch the live conductor and ground 

and not received a shock. This system is safer but if there is a fault, 

the operator touched both live and neutral connections or there 

was capacitive coupling between the secondary windings and 

earth. This would allow current to flow from either of the 

secondary connections through the operator/ patient to ground 

and electrocution could still occur. 


Endoscopes 

These are generally managed by the user, this includes cleaning. 

Cameras and Image Capture devices 

Cameras should have visual inspection and function test, checking image quality and focus also 

ensuring the various buttons work as they should. 

Image capture devices should also be visually inspected paying attention to the screen and case 

all functions should then be checked including the touch screen responds if applicable. This 

should then be safety tested. 

Light Sources 

A thorough visual inspection to include the case, mains lead, and the bulb for any 

damage/pitting should be performed. A filter clean/change and an electrical safety test are 

often all that is required. 

Light sources that used arc lamps or HID lamps require a scheduled lamp change, usually at 

approx. 500 hours of use. 

Before HID lamps are disposed of in an appropriate manner the xenon gas should be discharged. 

Insufflators 

A Visual inspection should be performed taking special care to inspect any gas connections and 

hoses including the pin index. 

A Check of output pressure and flow rates for conformity and accuracy against manufacturer’s 

specification. Check all controls work and that any alarms sound, including excess pressure and 

empty cylinder alarm. 

An Electrical Safety Test (EST) should then be completed to the appropriate standard.

Bibliography 

Blackwell Publishing, 2014. Basic Endoscopic Equipment. [Online] 

Available at: https://www.blackwellpublishing.com/xml/dtds/4- 

0/help/10003420_chapter_1.pdf 

[Accessed December 2015]. 

Martin, T., 2014. Principles of Gastrointestinal Endoscopy. Surgery (Oxford), 32(3), pp. 139-144. 

Olympus, 2014. Olympus - Narrow Band Imaging. [Online] 

Available at: 

http://www.olympus.co.uk/medical/en/medical_systems/applications/urology/bladder/narro 

w_band_imaging__nbi_/narrow_band_imaging__nbi_.html 

[Accessed Febuary 2014]. 

ustudy, 2011. Endoscopy Working Principle. [Online] 

Available at: http://www.ustudy.in/node/5066 

[Accessed December 2015].

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