Multi-Parameter Monitoring 2

Multi-Parameter Monitoring
Steven Lewis
Clinical Engineering
United Lincolnshire Hospital Trust

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)

Maintenance & Service Procedures
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].