Invasive Cardiac Output Monitoring and Pulse Contour Analysis

Invasive Cardiac Output 

Monitoring and Pulse 

Contour Analysis 

Harshad B. Ranchod 

Paediatric Intensivist 

Chris Hani Baragwanath Hospital 

COPICON 2011

Introduction 

• The primary goal of haemodynamic monitoring is to 

assess adequacy of systemic perfusion 

• The assessment of intravascular volume is one of the 

most difficult tasks in clinical medicine. 

• The question that confronts most intensive care 

providers on a daily basis is: 

• will fluid increase perfusion to end organs, or 

• will it worsen pulmonary or systemic oedema

Introduction 

• This can be especially true when treating septic patients, 

where volume expansion is often one of the 

cornerstones of early resuscitation. 

• SSG 2008 

• However, clinical studies have demonstrated that only 

about 50% of unstable critically ill patients will actually 

respond to a fluid challenge 

• Marik PE, Baram M,et al: Chest 2008; 134:172–178 

• Michard F, Teboul JL: Chest 2002; 121:2000–2008

Introduction 

• Volume overload can have dire consequences 

• such as decreased gas exchange and increased myocardial 

dysfunction. 

• Data suggests that a patient’s cumulative fluid balance 

affects outcome. 

• Wiedemann HP, et al: N Engl J Med 2006; 354:2564–2575 

• Vincent JL, et al:. Crit Care Med 2006; 34:344–353 

• Brandstrup B, et al: Ann Surg 2003; 238:641–648 

• Rivers EP: N Engl J Med 2006; 354:2598–2600

Assessment of Volume Status 

• Physical examination 

• Should never be neglected 

• There is no substitute for sequential physical 

examination to evaluate the effectiveness (or lack 

thereof) of our interventions and therapeutic 

decisions. 

• Clinical signs are, however, not as reliable or helpful 

in assessing intravascular status.

Assessment of Volume Status 

Static measures 

• The central venous pressure (CVP) and pulmonary artery 

occlusion pressure 

• poorly predict the haemodynamic response to a fluid 

challenge. 

• Other techniques for assessing intravascular volume have been 

evaluated: 

• inferior vena caval diameter 

• right ventricular end diastolic volume index 

• global end-diastolic volume index (GEDVI), etc. 

• However, the experience with these have been uniformly 

disappointing !!

Preload Responsiveness 

• Preload of the heart 

• defined as the wall stress at the end of diastole. 

• Volume/ Preload responsiveness 

• Predicts if volume administration (eg. for preload 

increase) will result in an ↑ cardiac output.


↑SV 

↓SV 

• Enomoto TM, et al; Crit Care Clin 26 

(2010) 307-321 

• If the ventricle is operating 

on the steep part of the 

curve increasing preload 

must induce an increase in 

SV (preload responsiveness). 

• If the ventricle is operating 

on the flat part of the curve 

increasing preload will not 

induce any significant 

increase in stroke volume 

(preload unresponsiveness).


• Fundamentally, the only reason to give a patient 

a fluid challenge 

• is to ↑stroke volume (SV) and ↑cardiac output 

(CO).

Preload 

• From the example shown, it 

is clear that physical 

examination and static 

markers are not an accurate 

guide to therapy. 

• Hence, this led to the 

investigation of dynamic 

indices for fluid assessment. 

• Enomoto TM, et al; Crit Care Clin 26 

(2010) 307-321


PPV 

SVV 

• Indices that have been 

shown to be predictive 

of fluid responsiveness, 

include: 

• Systolic Pressure Variation 

(SPV) and the Pulse Pressure 

Variation (PPV) 

• derived from analysis of the 

arterial waveform and 

• Stroke Volume Variation 

(SVV) 

• derived from pulse contour 

analysis 

(Michard F, Teboul JL: Chest 2002; 121:2000-2008)

Preload 

• Enomoto TM, et al; Crit Care Clin 26 (2010) 307-321 

• To assess fluid 

responsiveness, heart-lung 

interactions during 

mechanical ventilation have 

been used (in a number of 

studies)

Haemodynamic Effects of 

Mechanical Ventilation 

Early Inspiration 

↑ Intrathoracic pressure 

“squeezing” of pulmonary blood 

↑ LV preload 

↑ LV stroke volume 

↑ systolic arterial blood pressure 

Late Inspiration 

↑ Intrathoracic pressure 

↓ VR to LV and RV 

↓ LV preload 

↓ LV stroke volume 

↓ systolic arterial blood pressure 

Reuter et al., Anästhesist 2003;52: 1005-1013

↑ Variation = Volume responsiveness 

• This ↑ variation in pressures between the inspiratory 

phase and the expiratory phase 

• can be used to identify hypovolaemia and volume 

responsiveness, and 

• is the basis of indices, including stroke volume variation 

(SVV) and pulse pressure variation (PPV).

These phasic variations are increased in the 

setting of hypovolaemia for several reasons: 

1. The underfilled vena cava and right atrium 

• are more collapsible, and 

• more susceptible to ↑ intrathoracic pressure. 

2. Since venous return depends on the venous 

pressure gradient 

• hypovolaemic patients have ↓ mean circulating 

filling pressure more marked ↓ venous return 

with positive pressure ventilation.

Reasons for these exaggerated phasic 

variations in hypovolaemia : 

3. Patients who are functioning on the steep portion of 

the Frank-Starling curve 

• Larger ↓SV with ↓venous return during each positive 

pressure breath.

Pulse Contour Analysis 

• This method of measuring cardiac output is derived 

from variations in the pulse pressure/ arterial pressure 

waveform during mechanical ventilation. 

• Is based on the principle that SV can be continuously 

estimated by analysing the arterial pressure waveform. 

• Includes PPV, SVV and SPV

Parameters of Pulse Contour Analysis - SVV 

The Stroke Volume Variation 

• is the variation in stroke volume over the ventilatory cycle. 

SV max 

SV min 

SV mean 

SVV = 

SV max – SV min 

SV mean

SVV 

• Difference between the 

SV during the inspiratory 

and expiratory phases of 

ventilation, and 

• Requires a means to 

directly or indirectly 

assess SV

SVV 

• SV is calculated on 

physiological relationship 

between 

• SV and 

• area under systolic portion of 

the curve. 

• PiCCO, LiDCO and Flotrac 

monitors uses pulse contour 

analysis through a proprietary 

formula to measure cardiac 

output and SVV

Parameters of Pulse Contour Analysis - PPV 

The Pulse Pressure Variation 

•is the variation in pulse pressure over the ventilatory cycle. 

PP max 

PP min 

PP mean 

PPV = 

PP max – PP min 

PP mean

Pulse Pressure Variation 

• Arterial pulse pressure 

• is the difference between arterial 

systolic and diastolic pressure. 

• PPV 

• Based on the physiological 

relationship between Pulse 

Pressure and SV

Pulse Pressure Variation 

• PPV 

• Directly proportional to LV Stroke 

Volume. 

• Inversely related to arterial compliance. 

• Assuming that arterial compliance 

does not change during a mechanical 

breath respiratory changes in 

PPV should reflect respiratory 

changes in SV.

Use of PPV and SVV 

• Dynamic indices have repeatedly been shown to be superior to 

static measures (for determining preload responsiveness in 

critically ill patients). 

• In controlled mechanically ventilated adults with sepsis, PPV 

threshold value of 13% allowed to discriminate between : 

• preload responders to volume (PPV > 13%) from 

• Non-responders (PPV


• PPV/SVV may be helpful to monitor the 

haemodynamic effects of volume expansion 

normalization of PPV with fluid infusion. 

• Lack of improvement of the dynamic markers of 

preload after fluid challenge may be viewed as 

promoting oedema 

(Michard F, Teboul JL: Chest 2002; 121: 2000-2008) 

• To date very little data on SVV and PPV in critically 

ill children 

(Proulx F, et al; Pediatr Crit Care Med 2011; 12: 459-466)


• Recent meta-analysis 

• revealed that the diagnostic accuracy of the PPV 

(directly measured) was significantly greater (p

Limitations of Pulse Contour 

Analysis 

1. Require positive pressure, controlled 

ventilation 

• Spontaneous Respiratory Efforts (even when 

supported by the ventilator) Alter the mechanics 

such that these numbers lose their reliability 

2. Sinus rhythm is required. 

• Arrhythmias or frequent extrasystoles result in 

altered SV unreliable PPV interpretation.



3. Need Higher Tidal Volume (TV > 8ml/kg) 

• Most of the early data came from patients ventilated with at 

least 8-10 mL/kg tidal volumes. 

• In a limited series of various critical illnesses: 

• PPV less predictive of volume responsiveness when TV < 8ml/kg 

than TV > 8ml/kg 

(De Backer D, et al: (2005) Intensive Care Med 31: 517-523) 

Preisman S et al. Br J Anaesth. 2005



4. Requires invasive arterial blood pressure 

monitoring with a catheter 

• Complications of insertion (bleeding, thrombosis, etc) 

• Catheter related infections. 

• Prone to the same errors in measurement associated with 

invasive blood pressure monitoring : 

• Requires accurate calibration 

• Air bubbles in the catheter tubing, 

• Excessive tubing length, 

• Kinks in the tubing, 

• Excessively compliant tubing, etc.



5. A single value never should replace clinical 

judgment. 

• Eg. A high PPV value in a normotensive patient 

with evidence of normal tissue perfusion does not 

mean that person requires volume expansion.



6. Right Ventricular Dysfunction (or acute cor 

pulmonale) 

• may have marked ↑ RV afterload during 

inspiration high PPV observed in cases of 

preload unresponsiveness (false positives).



7. Other extremes of Ventilation MAY affect PPV 

7.1 High PEEP 

• ↑ intrathoracic and transpulmonary pressures ↑ PPV



7.2 High Respiratory Rate 

• Trial with 17 hypovolaemic patients ventilated with 

low (14-16 breaths/minute) and high (30-40 

breaths/minute) respiratory rates 

• The authors concluded that respiratory variation in SV 

and its derivates 

• is affected by respiratory rate, and 

• caution against using these indices as predictors of 

volume responsiveness at high respiratory rates. 

(De Backer D, et al. Anesthesiology 2009;100: 1092–7).



7.3 Increase in heart rate (HR) 

• ↓ PPV from 21% 4%, and 

• ↓ respiratory variation in aortic flow from 23% 

6%. 

(De Backer D, et al. Anesthesiology 2009;100: 1092–7).


7.4 HFOV 

• “CPAP with wiggle” 


• No distinct inspiratory and expiratory phases. 

• Therefore, only minimal changes in SV would occur 

during HFOV low PPV (even in fluid responsive 

patients) 

(Vincent JL (ed.) Annual Update in Intensive Care and 

Emergency Medicine 2011; pg 322-331)

13% 

or PPV

3 Categories of Commercially Available 

Haemodynamic Monitoring Systems : 

1) Calibration-dependent pulse contour analysis devices 

• Pulse Contour Cardiac Output (PiCCO) and 

• LiDCO 

2) Non-calibrated pulse contour analysis devices 

• FloTrac system 

• Pressure Recording Analytical Method (PRAM) 

• LiDCO rapid 

3) Alternative techniques 

• Doppler ultrasound methods 

• Pulse dye densitometry 

• Bioimpedance cardiography, and 

• Partial CO2 rebreathing (NiCO)

Means of measuring cardiac output 

include: 

• Pulmonary artery catheter (PAC) 

• Transpulmonary thermodilution (TD) 

• PiCCO monitor 

• Lithium dilution 

• LiDCO 

• Pulse contour analysis 

• Calibrated 

• (PiCCO, PulseCO system, LiDCO) 

• Non-calibrated 

• (Flo-trac Vigileo system)

Pulmonary Artery Catheter (PAC) 

• Used as a gold standard therefore all other 

methods are compared to this. 

• Uses different methods for calculating CO 

• Thermodilution has been most commonly 

used to measure cardiac output in the adult 

population.

Complications of PAC 

• Catheter insertion is difficult in 

• smaller patients (5-10kg) and 

• those with aberrant cardiopulmonary anatomy 

• Line-related complications 

• pneumothorax, bleeding or infections 

• Arrhythmias 

• benign and life-threatening ventricular arrhythmias and right bundle 

branch block 

• PA-related complications 

• rupture, infarction, thrombi, haemorrhage, vegetations.

Transpulmonary Thermodilution 

(TPTD) 

• Controversy surrounding PAC’s safety and 

efficacy has prompted development of newer 

less invasive techniques. 

• The PiCCO monitor is currently the only 

commercially available device that uses the 

TPTD method to measure cardiac output.

Transpulmonary Thermodilution 

(TPTD) 

• The transpulmonary thermodilution technique 

(TPTD) allows assessment of various indices 

• volumetric preload, 

• cardiac output, and 

• extravascular lung water. 

• without the need to pass a catheter through the 

right heart.

TPTD and PiCCO 

• Need a standard central venous catheter. 

• CVP is usually placed above diaphragm (IJ or SCV) 

• Can be performed using a femoral CVP. 

and 

• A specialized femoral or axillary arterial 

catheter with a thermistor at its tip is also 

required. 

• 3F or 4F arterial catheter is available for femoral 

artery cannulation in children


• A known volume of thermal indicator (ice-cold saline) is injected 

via a central venous catheter. 

• Depends on body weight (varies from 2mls – 20mls) 

• The resulting packet of cooler blood traverses the thorax and 

is sensed by a thermistor in the femoral or axillary position 

generating a TD dissipation curve. 

• Cardiac output is then calculated from the curve using the 

modified Stewart-Hamilton equation for TD. 

• The average result from three consecutive bolus injections is 

recorded.


• Manual calibrations are necessary: 

• To compensate for inter-individual differences in 

compliance and resistance of the arterial vessel 

system. 

• Frequent recalibration is necessary during 

• rapidly changing clinical conditions, 

• haemorrhage, 

• shock and 

• vasodilation 

(Gazit AZ, et al; Ped Crit Care Med 2011;12[Suppl.]:S55–S61)

PiCCO 

• PiCCO method may give incorrect thermodilution 

measurements in patients with 

• intracardiac shunts, 

• aortic aneurysm, 

• aortic stenosis, 

• pneumonectomy, 

• macro lung embolism, and 

• extracorporeal circulation (if blood is either extracted from 

or infused back into the cardiopulmonary circulation). 


PiCCO 

• It is therefore of limited use in 

• the peri-operative care of children with complex congenital 

heart defects. 

• May be useful 

• in children with normal cardiac anatomy who present with 

cardiogenic shock, or 

• in the postoperative care of children after heart 

transplantation or biventricular repair 


PiCCO 

• Use of this monitor in children is overall simple and requires 

minimal training. 

• In haemodynamically unstable patients, 

• it requires frequent recalibrations to obtain reasonable accuracy. 

• Both the PiCCO-measured dynamic and static variables were 

shown to have good correlation with CI and fluid 

responsiveness. 

Gazit AZ, et al; Ped Crit Care Med 2011;12[Suppl.]:S55–S61 

Wong HR, et al; (Pediatr Crit Care Med 2011; 12[Suppl.]:S66 –S68

Lithium Dilution / LiDCO 

• Instead of using cold injectate indicator dilution, 

methods using intravenous lithium have been 

developed to determine CO (LiDCO). 

• Lithium can be injected via central or peripheral 

venous catheters 

• Is detected in a standard radial arterial line 

• Negates the need to place a catheter across heart valves 

(PAC) or to place a femoral or axillary arterial catheter 

(TPTD). 

• A dye dissipation curve is generated

LiDCO 

• The use of this system is problematic due to the 

complexity of its calibration. 

• The available data support its use in patients with 

hyperdynamic circulation. 

• However, its validity in patients with low CO has not 

been studied. 

• Overall, it appears that more data is required before use 

of this system in critically ill children 


FloTrac Vigileo System 

• Comprised of the FloTrac sensor and a processing 

display unit (Vigileo). 

• Attempts to determine CO by pulse contour analysis 

without employing a second technique for calibration. 

• Calibration allows a way to account for changes in 

vascular compliance, which cannot be easily measured 

clinically.

FloTrac Vigileo System 

• The makers of the Flo-Trac device claim to have 

solved this calibration problem using 

• continuous self-calibration through an automatic 

vascular tone adjustment involving complex 

algorithms based on 

• mean arterial pressure, 

• age, 

• height, 

• weight, and 

• gender of patients.

FloTrac Vigileo 

• The FloTrac system, comprised of the Flotrac sensor 

and a processing display unit (Vigileo). 

• Attempts to determine CO by pulse contour analysis 

without employing a second technique for calibration. 

• Calibration allows a way to account for changes in 

vascular compliance, which cannot be easily measured 

clinically.

What else can these monitors do 

DO2 = CaO2 X Cardiac Output 

CO = HR x STROKE VOLUME (SV) 

PRELOAD CONTRACTILITY AFTERLOAD 

PPV/ SVV/ GEDVI GEF/CFI/dPmx SVRI

Contractility 

• Contractility is a measure of the performance of the 

heart muscle 

• Is a further important determinant of cardiac output. 

• Some Contractility parameters include: 

• CFI (Cardiac Function Index) 

• GEF (Global Ejection Fraction) 

• dPmx (maximum rate of the increase in pressure)

Afterload - SVRI 

• Systemic Vascular Resistance (SVR) 

• Important determinant of afterload. 

• Is the resistance the blood encounters as it flows through the 

vascular system. 

• SVR index (SVRI) – SVR indexed to BSA. 

• Normal = 1200-2400 dyn.s.cm-5.m2 

• SVRI – helps to guide catecholamine and volume 

therapies. 

• Eg. High SVR Vasoconstriction consider : 

• Decreasing vasopressors or adding vasodilator

Extravascular Lung Water (EVLW) 

• Reflects the amount of fluid in the interstitium and in 

the alveolar space. 

• Accepted normal value = < 8ml/kg 

• Paeds : may be up to 20 ml/kg. 

• EVLW > 10ml/kg pulmonary oedema (adults) 

• Is useful for differentiating and quantifying lung 

oedema

EVLW 

• May have prognostic value 

• Reports that in adult patients, mortality increases with 

increasing volumes of EVLW 

• Sakka SG, et al: (2002) Chest 122:2080-2086 

• Berkowitz DM, et al: (2008) Crit Care Med 36:1803-1809 

• EVLWi decreased significantly in survivors already at 

24 hours and remained constant thereafter 

• Sustained EVLW > 10ml/kg worse survival. 

• Lubrano R, et al: Intensive Care Med (2011) 37:124-131

Conclusion 

• The quest for the holy grail of non-invasive cardiac output 

assessment continues. 

• NO IDEAL MONITOR 

• Tailor choice of monitor by matching your requirements to information 

offered by monitor 

• Dynamic measures proving to be more useful modality 

• Our job is to learn what variables to measure, to measure them 

correctly, to institute effective therapies where available, and to 

do this with minimum patient risk.

Conclusion 

• We need to integrate all the interrelated information at 

the bedside and try to decide on the best course of 

management, based on the best available scientific 

information. 

• Know the limitations of your monitor. 

• Assess data in conjunction with clinical picture. 

MONITOR DATA IS ONLY AS GOOD AS THE 

PERSON INTERPRETING IT !!

Conclusion 

• We need to integrate all the interrelated information at 

the bedside and try to decide on the best course of 

management, based on the best available scientific 

information. 

• Know the limitations of your monitor 

• Assess data in conjunction with clinical picture 

MONITOR DATA IS ONLY AS GOOD AS THE 

PERSON INTERPRETING IT !!

Thank you.

Invasive Cardiac Output Monitoring and Pulse Contour Analysis

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