Measurement of cardiac output

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Measurement of cardiac output

• Dr Kavitha Lakshman

University College of Medical Sciences GTB
Hospital, Delhi
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Methods used for measurement of Cardiac Output

• Invasive
• PA catheter
• - Ficks cardiac output measurement
• - Thermodilution Technique
• - Mixed venous oximetry pulmonary catheter
• Minimally invasive
• Doppler Ultrasound
• Lithium dilution cardiac output monitoring
• Pulse contour cardiac output monitoring
• Transpulmonary thermodilution
• Non-invasive
• Bio impedence cardiac output monitoring
• Partial carbon dioxide re breathing cardiac
  output monitoring

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INVASIVE METHODS OF CARDIAC OUTPUT MEASUREMENT
(PAC)
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• PULMONARY ARTERY CATHETERISATION
• 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

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PHYSIOLOGICAL CONCEPTS OF CARDIAC OUTPUT
MEASUREMENT
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• INDICATOR DILUTION TECHNIQUE
• 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
• ? CI dt
• Where
• Q CO
• I Amount of indicator
• ? CI dt 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)

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• Other guidelines for placement waveforms
  were already discussed

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• Complication of PA catheterisation-
• Infection, endocarditis
• Thrombo embolism
• Endocardial damage, valve injury
• PA infarction
• PA rupture
• Catheter knotting
• Ventricular fibrillation, arrhythmia, RBBB

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Bolus - Thermodilution 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

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Stewart Hamilton equation is modified

• (TB TI) x K
• Q
• ? ? TB (t) dt
• Where
• Q CO
• TB Blood temp.
• TI Injectate temp.
• K Computational constant
• ? ? TB (t) dt Integral of temp. change over
  time

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• Method
• 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

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Continuous - Thermodilution CO monitoring

• Warm or cold thermal indicator
• Methods
• 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

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• Advantages
• 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

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MINIMALLY INVASIVE METHODS OF CARDIAC OUTPUT
MEASUREMENT
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Doppler Ultrasound

• 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

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• 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

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SV v x ET x CSA

• Where
• 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

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• Types of probe-Suprasternal(Ascending aorta)
• 
  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
• Its in close proximity to the aorta thereby
  minimizing signal interference

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The shape of the waveform allows Assessment of
the venticular preload, afterload and
contractility
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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
• Z

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• Advantage-
• It has the potential for continuous, beat to beat
  monitoring of cardiac output
• Disadvantage-
• Baseline calibration with known cardiac output is
  required
• Recalibration is required every 8 to 12 hrs
  Require calibration to compensate for the
  algorithms inability to independently assess the
  ever changing effects of vascular tone
• A well defined arterial pressure waveform is
  needed

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

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NON INVASIVE CARDIAC OUTPUT MEASUREMENT
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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

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• 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

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• Advantage-
• Non invasive, continuous monitoring
• Measures thoracic fluid content, left ventricular
  ejection time, cardiac index
• Disadvantage-
• Susceptibility to electrical interference
• Relies on correct placement of the electrodes

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References

• Lailu M, Kalyan RK. Cardiac output monitoring.
  Annals of Cardiac monitoring.2008 1156-61
• Jhanji S, Dawson J and Pearse R M. Cardiac output
  monitoringbasic science and clinical
  application. Anaesthesia .2008 172-78
• Rebecca A, Schroeder, Atilio B, Shahar B and
  Jonathan B. Cardiovascular Monitoring. Millers
  Anaesthesia 7th edition 1314-21
• William F Ganong, Review of medical physiology
  22nd edition 819
• Kaplan JA. Hemodynamic monitoring. Kaplans
  Cardiac Anaesthesia 5th edition 283-86
• Edward Morgan.Patient monitors. Clinical
  Anaesthesiology 4th edition 137-139

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• THANK YOU