Cardiac output factors governing and measurement

Cardiac output factors governing and measurement

1. Cardiac Output: Factors Governing and Measurement Presenter: Dr. Suresh Pradhan Moderator: Prof. PK Datta

2. Cardiac Output is the amount of blood pumped by the heart per unit of time is the product of the stroke volume (SV) and the heart rate (HR) is also the quantity of blood that flows through the circulation is pivotal in maintaining arterial BP (BP=CO X SVR) and oxygen delivery

3. varies widely with the level of activity of the body following factors directly affect cardiac output the basic level of body metabolism whether the person is exercising the person’s age the size of the body

4. for young, healthy men, resting cardiac output averages about 5.6 L/min for women, this value is about 4.9 L/min with exercise it may rise to 35 L/min

5. Cardiac Index cardiac output is frequently stated in terms of the cardiac index is the cardiac output per square meter of body surface area average human being who weighs 70 kilograms has a body surface area of about 1.7 square meters, which means that the normal average cardiac index for adults is about 3 L/min/m 2 of body surface area

6. Variation of Cardiac Index with age

7. Distribution of Cardiac Output

8. Factors Governing determined by four factors two factors that are intrinsic to the heart heart rate myocardial contractility two factors that are extrinsic to the heart but functionally couple the heart and the vasculature preload afterload

9. Heart rate is defined as the number of beats per minute is mainly influenced by the autonomic nervous system increase in heart rate escalate cardiac output as long as ventricular filling is adequate during diastole

10. Myocardial Contractility can be defined as the intrinsic level of contractile performance that is independent of loading conditions intrinsic ability of the heart to adapt to increasing volumes of inflowing blood is called the Frank Starling mechanism of the heart Or, stated another way: Within physiological limits, the heart pumps all the blood that returns to it by way of the veins

11. Factors that modify contractility are Exercise Adrenergic stimulation Changes in pH Temperature Drugs such as digitalis

12. Preload is defined as the ventricular load at the end of diastole, before contraction has started first described by Starling, a linear relationship exists between sarcomere length and myocardial force in clinical practice, surrogate representatives of left ventricular volume such as pulmonary wedge pressure or central venous pressure are used to estimate preload with the development of transesophageal echocardiography a more direct measure of ventricular volume is available

13. Afterload is defined as systolic load on the LV after contraction has begun aortic compliance is an additional determinant of afterload aortic compliance is the ability of the aorta to give way to systolic forces from the ventricle changes in the aortic wall (dilation or stiffness) can alter aortic compliance and thus afterload

14. pathologic conditions that alter afterload are aortic stenosis and chronic hypertension both impede ventricular ejection, thereby increasing afterload

15. Preload and afterload can be thought of as the wall stress that is present at the end of diastole and during left ventricular ejection, respectively

16. Effects of Intravenous Anaesthetic agents on CO CO reduced by Propofol > Thiopentone >Etomidate secondary to decreased contractility Propofol also causes vasodilatation and bradycardia

17. Effects of Inhalational Anaesthetic agents on CO CO reduced by Enflurane >Halothane>Isoflurane/ Desflurane >Sevoflurane>N 2 O Secondary to direct myocardial depression inhibition of the sympathetic nervous system outflow altered baroreceptor activity

18. Measurement of Cardiac Output AIM : hemodynamic monitoring and support in the critically ill so as to optimize oxygen delivery to the tissues oxygen delivery is determined by Cardiac Output and amount of oxygen carried in the blood allows us to assess the blood flow to the tissues, and provides information on how to best support a failing circulation

19. Why should we measure? three major factors have driven efforts to measure cardiac output in clinical practice the recognition that in many critically ill patients, low cardiac output leads to significant morbidity and mortality the clinical assessment of cardiac output is unreliable / inaccurate

20. newer techniques for measurement of cardiac output are less invasive than Pulmonary Arterial Catheterization monitoring and thus might provide benefit to many patients without the attendant risks associated

21. Where should we monitor? high risk critically ill surgical patients in whom large fluid shifts are expected along with bleeding and hemodynamic instability an important component of goal directed therapy (GDT), i.e. , when a monitor is used in conjunction with administration of fluids and vasopressors to achieve set therapeutic endpoints thereby improving patient care and outcome

22. Signs of inadequate oxygen delivery acidosis elevated lactate oliguria low superior vena cava oxygen saturation

23. Measurement True non-invasive Low-invasive Invasive

24. True noninvasive Clinical Examination Trans Thoracic Echocardiography (TTE) Bioimpedance Cardiography (ICG) Thoracic ICG Whole-body or Regional ICG Bioreactance Applied Fick’s Principle Partial gas rebreathing Pulsed dye densitometry Endotracheal Cardiac Output Monitor (ECOM) Photoelectric plethysmography

25. Low-invasive Trans Esophageal Echocardiography (TEE) / Esophageal Doppler Arterial Pulse contour analysis ( PiCCO and FloTrac) Pulse power analysis : Lithium dilution CO ( LiDCO )

26. Invasive Pulmonary Artery Catheter (PAC) (Dye, Thermodilution ) (intermittent/ continuous) Fick Principle

27. Factors affecting selection of cardiac output monitoring devices

28. Features of an ideal Cardiac Output monitor safe and accurate give measurements that are reproducible quick and easy to use (both in terms of set-up and interpretation of information) operator independent (i.e. the skill of the operator doesn’t affect the information collected) provide continuous measurement reliable during various physiological states

29. TRUE NON-INVASIVE TECHNIQUES

30. Clinical Examination clinical signs of cardiac output pertain to the state of end-organ tissue perfusion no single clinical sign can be used to make an accurate assessment of cardiac output however, if used together they can be useful in estimation of cardiac output

31. Clinical signs include: Skin colour Capillary Refill Time Heart Rate Skin temperature Core-peripheral temperature difference Urine Output Mental State

32. Clinical Examination Assess adequacy End organ perfusion Brain (confusion, altered consciousness) Kidney (UO) Tissues (lactate) Skin (CRT) BP correlates poorly

33. Lactate produced by anaerobic metabolism an indicator of tissue hypoperfusion measured in the laboratory, and most modern blood gas machines now give a lactate value as part of arterial blood gas analysis can be used to monitor therapy, as it will fall as oxygen delivery improves, and as liver perfusion increases

34. Trans Thoracic Echocardiography (TTE) Echocardiography is cardiac ultrasound can be used to estimate Cardiac Output by direct visualization of the contracting heart in real time gaining acceptance as one of the safest and most widely used cardiac output monitors in the critically ill

35. be used to assess cardiac output (intermittently) The USCOM TM device (USCOM, Sydney, Australia) targets the pulmonary and aortic valves accessed via the parasternal and suprasternal windows in order to assess cardiac output completely non-invasively

36. Transthoracic Approach: non-invasive quick allows for measurement of the ventricles, visualization of the valves, estimation of ejection fraction disadvantages of user dependent possible interference from bone, lung and soft tissues non-continuous

37. Impedance Cardiography (ICG) is a noninvasive technology for measuring total electrical conductivity of the human body and its changes over time to process continuously a number of hemodynamic parameters such as Stroke Volume (SV) Heart Rate (HR) Cardiac Output (CO) Body water Total peripheral Resistance (TPR) Cardiac Power (CP)

38. Two basic technologies are currently in use for impedance cardiography : Thoracic ICG , were the sensors are placed on the root of the neck and the lower part of the chest Whole-body or Regional ICG , were four pairs of sensors are used, one pair on each limb

39. in Whole-body Impedance Cardiography, peripheral volumetric signal is borne throughout the length of the arterial tree in Thoracic ICG waveform is generated by multiple sources including the aorta, lungs, vena cava, and artifacts due to heart movement the peripheral systolic impedance changes are more reliable than the thoracic impedance changes for calculating the cardiac Stroke Volume

40. first described by Kubicek and colleagues is based on changes in electrical impedence occurring with ejection of blood during cardiac systole disposable electrodes are applied to the skin continuous current is applied

41. bioimpedance CO is computed for each cardiac cycle and continuously displayed as an average value over several heartbeats bioimpedance measurement leads to calculation of SV electrode placement and appropriate contact with the skin are important sources of error

42. SV= ρL 2 x VET x max dZ / dT Z o 2 Where, SV= stroke volume ρ= specific resistivity of blood L= thoracic length Z o = basal thoracic impedence VET= ventricular ejection time Max dZ / dT = max change in impedence time during systole upstroke

43. Bioreactance newer and more accurate technology (NICOM device, Cheetah medical, Portland, Oregon) based on Bioreactance or the Phase Shifts that occur when an alternating current is passed through the thorax when an alternating current (AC) is applied to the thorax, the thoracic pulsatile blood flow through the large arteries causes the amplitude of the applied thoracic voltage to change

44. also causes a time delay or Phase Shift between the applied current and the measured voltage AC current to the thoracic cavity is applied via four transmitting sensors detection of the phase shifts is done with an additional four receiving sensors

45. extensive research has shown that the Phase Shifts are tightly correlated with stroke volume by accurately and continuously measuring Phase Shifts this technology is able to determine the stroke volume

46. Phase Shift

47. Applied Fick’s Principle Partial Gas Rebreathing Cardiac Output can be estimated by using the Fick’s principle with carbon dioxide as the marker gas ( Berton & Cholley 2002, Mathews & Sigh 2008) Partial CO 2 rebreathing called NICO TM system ( Novametrix Medical Systems, Wallingford, Conn, United States)

48. is based on the application of the Fick’s principle to carbon dioxide, in order to estimate cardiac output non-invasively the monitor consists of a carbon dioxide sensor, a disposable airflow sensor and a pulse oximeter VCO 2 -CO 2 consumption is calculated from minute ventilation and its carbon dioxide content the arterial CO 2 content (CaCO 2 ) is estimated from end-tidal carbon dioxide

49. The Fick equation for carbon dioxide is: CO=VCO 2 /CvCO 2 -CaCO 2 where VCO 2 , CvCO 2 , CaCO 2 are CO 2 consumption, venous CO 2 concentration and arterial CO 2 concentration respectively

50. Major limitation--tracheal intubation with fixed ventilator setting is required not very accurate in patients with severe chest trauma significant intrapulmonary shunt high CO states low minute ventilation

51. Pulsed dye densitometry allows intermittent cardiac output measurement based on transpulmonary dye dilution with transcutaneous signal detection adapted from pulse oximetry (pulsed dye densitometry) the concentration of indocyanine green is estimated in the arterial blood flow by optical absorbance measurements after its venous injection Cardiac Output is calculated from the dye dilution curve according to the Stewart Hamilton principle

52. The results are altered by vasoconstriction interstitial edema movement ambient light artefacts

53. Endotracheal Cardiac Output Monitor (ECOM) ECOM (Con-Med, Irvine, Calif, United States) measures CO using impedance plethysmography is based on the principle of bioimpedance current is passed through electrodes attached to endotracheal tube shaft and cuff current is passed from electrode on the shaft of endotracheal tube and change in impedance secondary to aortic blood flow is detected by electrode on the cuff

54. an algorithm calculates SV based on impedance changes and CO can be calculated impedance is affected by aortic blood flow Limitations: electrocautery affects its accuracy coronary blood flow is not calculated is still adequately not validated in humans is costly and has not become very popular

55. Photoelectric Plethysmography is a completely non-invasive pulse pressure analysis device that assesses pulse pressure using photoelectric plethysmography in combination with a volume-clamp technique (inflatable finger cuff) Nexfin HD (BMEYE B.V, Amsterdam, Netherlands) Cardiac Output is derived by Modelflow method very few validation studies to state its efficacy

56. LOW-INVASIVE TECHINQUES

57. Trans Esophageal Echocardiography (TEE) / Doppler a widely used monitor in perioperative setting is an important tool for the assessment of cardiac structures, filling status and cardiac contractility aortic pathology can also be detected by TEE Doppler technique is used to measure CO by Simpson’s rule measuring SV multiplied by HR

58. Measurement can be done at the level of pulmonary artery, mitral or aortic valve TEE can quantify Cardiac Output more precisely by measuring both the velocity and the cross-sectional area of blood flow at appropriate locations in the heart or great vessels i.e. flow = CSA X Velocity SV= flow X ET ( Systolic Ejection time) CO=SV X HR

59. Advantages Minimally invasive Minimal interference form bone, lungs and soft tissue (as seen with transthoracic route) Quickly inserted and analyzed Little training required Very few complications

60. Disadvantages May require sedation User dependent Interference from surgical instruments eg . NG tube, Diathermy impairs signal Depends on accurate probe positioning

61. Probe may detect other vessels e.g. intracardiac /intrapulmonary Contraindicated in Esophageal Surgeries Assumes a constant percentage of cardiac output ( approx 70%) enters the descending aorta. May therefore be inaccurate in a hypovolaemic patient where flow may be redirected to the cerebral circulation

62. Arterial Pulse contour analysis is based on the principle that SV can be continuously estimated by analyzing the arterial pressure waveform obtained from an arterial line characteristics of the arterial pressure waveform are affected by interaction between SV and vascular compliance aortic impedance peripheral arterial resistance

63. for reliable Cardiac Output measurement using all devices that employ pulse pressure analysis technology, optimal arterial waveform signal is a prerequisite severe arrhythmias may reduce the accuracy of cardiac output measurement the use of an intra-aortic balloon pump precludes adequate performance of the device limited accuracy during periods of hemodynamic instability, i.e. rapid changes in vascular resistance

64. PICCO system the PiCCO system (PULSION medical system, Munich, Germany) was the first pulse contour device introduced was replaced with PiCCO2 in 2007 requires both central venous (femoral or internal jugular) and arterial cannulation (femoral/radial) Indicator solution injected via central venous cannula and blood temperature changes are detected by a thermistor tip catheter placed in the artery

65. it combines pulse contour analysis with the transpulmonary thermodilution CO to determine hemodynamic variables it requires manual calibration every 8 h and hourly during hemodynamic instability

66. accuracy may be affected by: vascular compliance aortic impedence peripheral arterial resistance air bubble, clots inadequate indicator valvular regurgitation aortic aneurysm significant arrhythmia rapidly changing temperature

67. FloTrac system FloTrac (Edwards LifeSciences , Irvine, United States) is a pulse contour device introduced in 2005 is a minimally invasive method as it requires only an arterial line (femoral or radial) the system does not need any external calibration, is operator independent and easy to use it is based on the principle that there is a linear relationship between the pulse pressure and SV

68. Pressure recording analytical method (PRAM) PRAM – MostCare ® ( Vytech , Padova , Italy), which is based on mathematical assessment of the pressure signal obtained from an arterial line without calibration similar to other devices that use pulse contour analysis, the accuracy of PRAM derived cardiac output is affected by the quality of the pressure signal by factors that interfere with the ability to detect a pressure signal

69. EV1000 / Volume view a new calibrated pulse wave analysis method ( VolumeView ™/EV1000™, Edwards Lifesciences, Irvine, CA, United States) is based on pulse pressure analysis, which is calibrated by transpulmonary thermodilution is currently under trial its comparison with PICCO2 system in critically ill patients found comparable results very few studies are available for its validation

70. Pulse power analysis is based on the principle that change of the blood pressure about the mean is directly related to the SV various factors affect its accuracy like compliance of the arterial tree wave reflection damping of the transducer aortic systolic outflow

71. Lithium dilution CO ( LiDCO ) LiDCO (Cambridge, United Kingdom) system combines pulse contour analysis with lithium indicator dilution for continuous monitoring of SV and SV variation is a minimally invasive technique first described in 1993 requires a venous (central or peripheral) line and an arterial catheter

72. a bolus of lithium chloride is injected into venous line and arterial concentration is measured by withdrawing blood across disposable lithium sensitive sensor containing an ionophor selectively permeable to Li CO is calculated based on Li dose and area according to the concentration time circulation requires calibration every 8 h and during major hemodynamic changes

73. is contraindicated in patients on Li therapy calibration is affected by neuromuscular blockers as quaternary ammonium residue causes electrode to drift accuracy is affected by aortic regurgitation Intra aortic balloon pump Damped arterial line Post aortic surgery Arrhythmia intra or extracardiac shunts

74. INVASIVE TECHINQUES

75. Pulmonary Artery Catheterization pulmonary artery catheter (PAC) as a monitor to measure flow and pressure was developed by Dexter and modified later on by Swan et al to measure CO and central filling pressures is still considered as gold standard monitor to measure CO since 1970’s it has been used as a monitoring tool in high risk surgeries and critical care units

76. The Swan Ganz Catheter Most popular design with 5 lumens, 7.5 F catheter, 110 cm long Distal lumen : at tip of catheter, lies in a branch of the pulmonary artery, connected to a pressure transducer. Yellow port: distal PA port Balloon lumen : permits introduction of 1.5 ml of air into the balloon at the distal tip. Red port: balloon port

77. Thermistor lumen : bead situated 4 cm from the tip of the catheter and measures temperature Proximal lumen : 25 cm from tip, lies in right atrium, measures central venous pressure (CVP) Blue port: proximal to the PA port ; CVP port Clear port/ white port : 30 cm from the tip and used to inject drug

78. Use of the Catheter sampling of mixed venous blood measurement of cardiac output using thermodilution assessment of CVP derivation of other cardiovascular indices, such as the pulmonary vascular resistance, oxygen delivery and uptake

79. arrhythmias on insertion pneumothorax pulmonary artery rupture balloon rupture valve injury pulmonary infarction infection thrombosis leading to embolism knotting of catheter in right ventricle

80. Complications

81. various technical errors may lead to false readings like loss of injectate variability of temperature thermistor malfunction clot over catheter tip coiling of catheter or timing of injectate > 4 seconds intracardiac shunts, mechanical ventilation or valvular dysfunction may lead to incorrect readings

82. Thermodilution A cold solution of D/W 5% or normal saline (temperature 0°C) is injected into the right atrium from a proximal catheter port this solution causes a decrease in blood temperature in right heart and flows to the pulmonary artery where the temperature is measured by a thermistor placed in the pulmonary artery catheter

83. the thermistor records the change in blood temperature with time and sends this information to an electronic instrument that records and displays a temperature-time curve / thermodilution curve

84. The Cardiac Output can be derived from the Modified Stewart-Hamilton conservation of heat equation CO= V 1 ( Tb- T1) K 1 K 2 ξ ΔTb (t) dt Where, V 1 = injectate volume in ml Tb= temperature of pulmonary artery blood T1= injectate temperature °C K 1 = density factor K 2 = computation constant taking in account the catheter deadspace and heat exchange in transit ; both computation constant Denominator: change in temp and change in time: corresponds to the area under thermodilution curve

85. The degree of change is inversely proportional to cardiac output Temperature change is minimal if there is a high blood flow but high if flow is low

86. Accurate measurements of cardiac output depend on: rapid and smooth injection precisely known injectant temperature and volume correct entry of the calibration factors for the specific type of PAC into the cardiac output computer avoidance of measurements during electrocautery

87. Continuous thermodilution cardiac output using an electric heating coil to warm the pulmonary artery blood removes errors associated with fluid injectate techniques But there is the need to average the smaller signal over a longer time interval

88. Dye dilution/ Indicator dilution Based on the observation that, for a known amount of indicator introduced at one point in the circulation, the same amount of indicator should be detectable at a downstream point Indocyanine green injected through a Central venous catheter and its appearance in arterial system detected by a densitometer. the area under dye indicator curve is related to Cardiac Output

89. CO is calculated using the Stewart-Hamilton equation: CO = cardiac output Q = amount of indicator injected ∫C dt = the integral of indicator concentration over time Blood flow is directly proportional to the amount of the indicator delivered

90. Fick Principle Adolfo Fick in 1870: the blood flow to an organ per unit time is calculated by the ratio of consumption of marker by that organ to the difference between arterial and venous content of that marker Fick used oxygen as the marker CvO 2 and CaO 2 measured by PAC and arterial line in place Oxygen consumption from the difference between the oxygen content in inspired and expired gas

91. Integrative concept for the use of cardiac output monitoring devices

92. Advantages and disadvantages of methods of cardiac output monitoring

93. THANK YOU!!!