Measurement of cardiac output
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Measurement of cardiac output. Dr Kavitha Lakshman. University College of Medical Sciences & GTB Hospital, Delhi. Methods used for measurement of Cardiac Output. Invasive PA catheter - Fick’s cardiac output measurement - Thermodilution Technique

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Measurement of cardiac output

Measurement of cardiac output

Dr Kavitha Lakshman

University College of Medical Sciences & GTB Hospital, Delhi

Methods used for measurement of cardiac output
Methods used for measurement of Cardiac Output


PA catheter

- Fick’s cardiac output measurement

- Thermodilution Technique

- Mixed venous oximetry pulmonary catheter

Minimally invasive

  • Doppler Ultrasound

  • Lithium dilution cardiac output monitoring

  • Pulse contour cardiac output monitoring

  • Transpulmonarythermodilution


  • Bio impedence cardiac output monitoring

  • Partial carbon dioxide re breathing cardiac output monitoring


  • First used by Swan, Ganz for hemodymamic monitoring of patients

  • PAC can be placed from any central venous cannulation sites, but right internal jugular vein is most commonly used.

  • Standard PAC is 7.0 to 9.0 Fr in circumference, 110 cm long, has 4 internal lumens


  • Tracer substance is injected into the bloodstream – concentration change measured at a downstream site

  • Indocyanin green most commonly used dye

  • Stewart Hamilton Equation

  • I

  • Q =

  • ∫ CIdt

  • Where

  • Q = CO

  • I = Amount of indicator

  • ∫ CIdt = Integral of indicator concentration over time

  • Drawbacks of indicator dilution method

  • Limited to cardiac catheterization laboratories

  • Continuous withdrawal of arterial blood to plot the dye concentration curve

  • Dye needs regular injections (can accumulate)

Complication of PA discussedcatheterisation-

Infection, endocarditis

Thrombo embolism

Endocardial damage, valve injury

PA infarction

PA rupture

Catheter knotting

Ventricular fibrillation, arrhythmia, RBBB

Bolus thermodilution cardiac output monitoring
Bolus - discussedThermodilution Cardiac Output Monitoring

  • Variant of indicator dilution technique

  • Iced indicator/ room temperature indicator (bolus)- 10 ml or 0.15ml/kg in children

  • Advantages

    • Performed quickly, repeatedly

    • Does not require advanced diagnostic or technical skills

    • Uses non-toxic, non-accumulative indicator

Stewart hamilton equation is modified
Stewart Hamilton equation is modified discussed

(TB – TI) x K

Q =

∫  TB (t) dt


Q = CO

TB= Blood temp.

TI= Injectate temp.

K = Computational constant

∫  TB (t) dt = Integral of temp. change over time

Method discussed

Volume of ice cold or room temperature fluid is injected as bolus

Change in pulmonary artery blood temperature is recorded

Source of error

Intra or extra-cardiac shunt

Tricuspid or pulmonary valve regurgitation

Inadequate delivery of indicator

Thermister malfunction

Unrecognised blood temperature fluctuation

Respiratory cycle influence

Continuous thermodilution co monitoring
Continuous - discussedThermodilution CO monitoring

Warm or cold thermal indicator


Release of small quantity of heat from a 10 cm thermal filament incorporated into right ventricular portion of a PAC approx. 15-20 cm from catheter tip

Heating filament is cycled on & off

Thermal signal measured

CO derived from cross-correlation of measured pulmonary artery temp.

Displayed value of CO is updated every 30-60 sec & represents the average value for cardiac output measured over 3-6 min

Advantages discussed

  • External system for cold fluid injection is not required

  • Fewer measurement error

  • Less risk of fluid overload and infection

  • Measures average CO value - derived over several mins

  • Beat-to-beat variation in SV that occur during single respiratory cycle are equally represented

    In contrast bolus technique measures cardiac output values depending on phase of respiration

Doppler ultrasound
Doppler Ultrasound discussed

  • Doppler principle

  • When USG waves strike moving objects, these waves are reflected back to their source at a different frequency, termed the Doppler shift frequency that is directly related to the velocity of moving object and the angle at which the USG beam strikes these objects

  • Red blood cells serve as moving object target

2 discussed

  • Where

  • f = Doppler shift frequency

  • v = Velocity of red blood cell targets

  • f0 = Transmitted USG beam frequency

  • 0 = Angle b/w the USG beam and the vector of RBC flow

  • C = Velocity of USG in blood (approx. 1570 m/sec)

  • Cosine 0 = 1 as long as angle of insonation is small

Sv v x et x csa
SV = v x ET x CSA discussed


SV = Stroke volume

v = Spatial average velocity of blood flow (cm/sec)

ET = Systolic ejection time

CSA = Cross-sectional area of vessel

-Estimated CSA close to the mean value during systole obtained from a nomogram stored in the computer

-Measured CSA using an M mode echo transducer incorporated in the probe

  • Types of probe-Suprasternal(Ascending aorta) discussed

    Esophageal(Descending aorta)

  • Suprasternal probe position instability limited their use for extended period of time

  • Esophageal probes have 2 advantage over the suprasternal probe

  • Smooth muscle tone of the oesophagus maintains the probe position

  • It’s in close proximity to the aorta; thereby minimizing signal interference

The shape of the waveform allows discussed

Assessment of the

venticular preload,

afterload and contractility

Pulse contour cardiac output monitoring

  • Cardiac output is determined through analysis of arterial pressure wave form obtained from an arterial catheter or from a non invasive finger blood pressure waveform

  • CO is measured on a beat to beat basis

  • Wesseling and colleagues devised an algorithm for the calculation of SV from aortic impedence and changes in arterial pressure during systole

  • SV=∫ dP/dt


Advantage discussed-

  • It has the potential for continuous, beat to beat monitoring of cardiac output


  • Baseline calibration with known cardiac output is required

  • Recalibration is required every 8 to 12 hrs Require calibration to compensate for the algorithm’s inability to independently assess the ever changing effects of vascular tone

  • A well defined arterial pressure waveform is needed

  • Pulse contour cardiac output estimation without external calibration(Flo Trac)

  • Doesn’t require external calibration

  • The algorithm works on the principle that SV is directly proportional to pulse pressure and inversely proportional to aortic compliance

  • The aortic pressure is sampled at 100Hz analysed and updated every 20 sec

  • SV =K(SdAP)

  • The standard deviation-SdAP is proportional to the pulse pressure, which is proportional to SV. K is the constant derived from patient characteristics as described by Langewouler and co workers

Bioimpedence cardiac output monitoring

  • Developed by Kubiceck and NASA researchers in 1960s

  • Based on changes in electrical resistance of the thoracic cavity occurring with change in aortic blood volume during systole & diastole

  • 4Pairs -Each pair of electrode consists of a transmitting and a sensing electrode

  • Two pairs are applied to the base of the neck on opposite sides, two pairs are applied to the lateral aspect of the thorax at the level of the xiphoid process on opposite sides

The electrodes mark the upper and lower boundaries of the thorax

An alternating current of low amplitude and high frequency is applied which is sensed by electrodes placed over the neck & lateral aspect of the chest.

Volume of thorax is calculated according to the height, weight and gender

Advantage- thorax

Non invasive, continuous monitoring

Measures thoracic fluid content, left ventricular ejection time, cardiac index


Susceptibility to electrical interference

Relies on correct placement of the electrodes

References thorax

  • Lailu M, Kalyan RK. Cardiac output monitoring. Annals of Cardiac monitoring.2008; 11:56-61

  • Jhanji S, Dawson J and Pearse R M. Cardiac output monitoring:basic science and clinical application. Anaesthesia .2008; 172-78

  • Rebecca A, Schroeder, Atilio B, Shahar B and Jonathan B. Cardiovascular Monitoring. Miller’s Anaesthesia: 7th edition: 1314-21

  • William F Ganong, Review of medical physiology 22nd edition: 819

  • Kaplan JA. Hemodynamic monitoring. Kaplan’s Cardiac Anaesthesia 5th edition: 283-86

  • Edward Morgan.Patient monitors. Clinical Anaesthesiology 4th edition: 137-139

THANK YOU thorax