MEASUREMENT OF CARDIAC OUTPUT

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1. MEASUREMENT OF CARDIAC OUTPUT PRESENTOR- Dr. K. AMUDHA LAKSHMI M.B.B.S.,D.O.,M.D

2. INTRODUCTION HISTORY METHODS OF MEASURING CARDIAC OUTPUT INVASIVE METHODS NON INVASIVE METHODS SUMMARY REFERENCES

3. INTRODUCTION Cardiac output is the volume of blood pumped into the aorta each minute by the ventricle It is the determinant of global oxygen transport to the body It reflects the efficiency of cardiovascular system

4. HISTORY ADOLPH EUGEN FICK(1829-1901) 1855 – Introduced Fick’s law of diffusion 1870- was the first one to develop a technique for measuring cardiac output i.e Direct Fick method.

5. DYE DILUTION METHOD Introduced by G.N.STEWART in 1897 Extended by W.F.HAMILTON in 1932 G.N.STEWART

6. INGE EDLER - FATHER OF ECHOCARDIOGRAPHY CARL HELMUTH HERTZ discovered echocardiography in 1950 INGE EDLER CARL HELMUTH HERTZ

7. CHRISTIAN DOPPLER , an astronomer in 19th century discovered the principles of Doppler

8. CARDIAC OUTPUT MEASUREMENT AIM : Hemodynamic monitoring In Critically ill patients, to optimize oxygen delivery to the tissues Oxygen delivery is determined by cardiac output Assess the blood flow to the tissues & helps to support a failing circulation

9. WHY SHOULD WE MEASURE? In many critically ill patients ,low cardiac output leads to significant morbidity & mortality. The clinical assessment of cardiac output is unreliable / inaccurate

10. WHEN SHOULD WE MONITOR? High risk critically ill surgical patients - large fluid shifts, bleeding & hemodynamic instability expected Goal directed therapy (GDT) i.e To set therapeutic endpoints thereby improving patient care & outcome

11. FEATURES OF IDEAL CARDIAC OUTPUT MONITOR Safe & accurate Quick & easy Operator independent i.e the skill of the operator doesn’t affect the information collected Provide continuous measurement Reliable during various physiological states

12. METHODS OF MEASURING CARDIAC OUTPUT INVASIVE Fick’s method Dye Diltuion method Thermodilution Cineradiographic technique X ray method NON – INVASIVE Endotracheal cardiac output monitor (ECOM) TTE/Trans thoracic echocardiography TEE/Trans esophageal echocardiography- D oppler Pulse pressure method Method employing inhalation of Inert gases

13. FACTORS AFFECTING SELECTION OF CARDIAC OUTPUT MONITORING DEVICES Institution Type of institution Availability of monitoring techniques Level of standardization Potential integration into existing monitor systems Level of experience

14. Devices Invasiveness Handling Technical limitations Validity ,accuracy & repeatability Availability of additional hemodynamic information

15. Patient Severity of specific diseases Heart rhythm Contraindications Type of intervention Type of treatment protocol

16. METHODS OF MEASURING CARDIAC OUTPUT SIMPLE METHOD CO(L/min)=HR(beats/min)x SV(L/beat) SV :stroke volume- volume ejected during each beat. CO(cardiac output at rest)=5-6L/min HR(Heart rate)=72 beats/min, SV=0.07 L/min(70ml)

17. INVASIVE METHODS

18. FICK’S PRINCIPLE   It states that the amount of a substance taken up by an organ (or by the whole body) per unit of time is equal to the arterial level of the substance (A) minus the venous level (V) times the blood flow (F), i.e Q=A- VxF Or F=Q/A-V

19. This principle can be used only in situations in which the arterial blood is the sole source of the substance taken up. The Fick’s principle can be used to measure cardiac output by two methods: Direct method Indirect method.

20. FICK’S PRINCIPLE (DIRECT METHOD) Cardiac output = O2 taken by the lungs ml/min/AO2-VO2

21. Amount of O2 uptake/min - spirometer Mixed venous blood(VO2)-The cardiac catheter is inserted into brachial vein subclavian vein right atrium right ventricle pulmonary artery. Systemic arterial blood(AO2)-brachial or femoral artery

22. Cardiac output = O2 taken by the lungs ml/min/AO2-VO2 =200ml/min/200-160 ml =200/40 =5 L/min

23. Pulmonary blood flow=amount of O2 taken by the lungs/min/PVO2-PAO2 O2 uptake is 250 ml/min, PVO2 is 19 ml/100 ml and PAO2 is 14 ml/100 ml, then Cardiac output=250x100/19-14 =25000ml/min/5 =5000ml/min =5L/min

24. ADVANTAGES Result is accurate No chemical is injected

25. DISADVANTAGES OF FICK’S PRINCIPLE (DIRECT METHOD) Catheterization should be done by expert hands Hospitalization is required It is an invasive technique, so there are risks of infection and haemorrhage. The cardiac output estimated may be somewhat higher than normal as the patient becomes conscious of the whole technique.

26. Simultaneous measurement of oxygen consumption makes the process difficult. A fatal complication like ventricular fibrillation may occur if the indwelling catheter irritates the ventricular walls, especially when the cardiac output is being measured during heavy exercise. Difficult to measure in ambulatory patients

27. FICK’S PRINCIPLE (INDIRECT METHOD)   In this method, arterial puncture and right heart catheterization are avoided and CO2 excretion by the lungs is used instead of O2 uptake CO2 excretion by the lungs - spirometry Arterial CO2 (PACO2) is estimated from alveolar air Mixed venous blood CO2 (PVCO2) is estimated by rebreathing into a closed bag.

28. With rebreathing , the CO2 in the bag will come into equilibrium with the venous blood in lungs. The breathing should be done in an interrupted manner so that the blood level of CO2 is not increased. According to Fick’s principle: Cardiac output=CO2 output/min/PACO2-PVCO2

29. INDICATOR OR DYE DILUTION METHOD /HAMILTON’S DYE DILUTION METHOD Principle   Introduced by G. N. Stewart in 1897 and extended by W. F. Hamilton in 1932, is a variation of the Fick procedure.

30. The blood flow in l/min (F) is given by the following formula: F=Q/Ct F = Blood flow in l/min Q = Quantity of the dye injected C = Mean concentration of dye t = Time duration in seconds of the first passage of dye through the artery.

31. Prerequisites for an Ideal indicator (Dye) It should be nontoxic. It must mix evenly in the blood. It should be relatively easy to measure its concentration. It should not alter the cardiac output or hemodynamics of blood flow. Either it must not be changed by the body during mixing period or the amount changed must be known. The dye commonly used is Evans blue (T-1824) or radioactive isotopes or cardiogreen .

32. Procedure- Injection of dye A few millilitre of venous blood is withdrawn from the antecubital vein and it is mixed with 5 mg Evans blue dye. The blood containing dye is then injected rapidly into the vein.

33. Estimation of duration of first passage of dye (t) and mean concentration (C) of dye in arterial blood. Serial samples of arterial blood from the brachial artery are taken every 2s and the dye concentration is determined by photo colorimetry Dye concentration is plotted on a semi-log paper

34. AG=C AE=t

35. F=Q/Ct Amount of dye injected (Q) is 5 mg Time duration for first circulation is 40 s Mean concentration of dye (C) = 15 mg/l, then Cardiac output=Qx60/ Cxt =5x60/15x40 =300/60 =5L/min

36. Investigating cardiac septal defects not used ADVANTAGES Accurate method DISADVANTAGES Procedure should not be repeated in short time

37. THERMODILUTION METHOD Principle .  It is also an indicator dilution technique in which instead of a dye, ‘ cold saline ’ is used as an indicator. The cardiac output is measured by determining the resultant change in the blood temperature in pulmonary artery. The change in temperature is inversely proportional to the amount of blood flowing through the pulmonary artery.

38. PROCEDURE   In this technique, two thermistors , one each in the inferior vena cava and pulmonary artery are placed with the help of cardiac catheter.

39. A known volume of sterile cold saline is then injected into the inferior vena cava. Temperature of the blood entering the heart from inferior vena cava and that of the blood leaving the heart via pulmonary artery is determined by the thermistors .

40. F=V1x(TB-TI)/ ΔTB xt F – blood flow in litre per second VI – volume of the injectate TB and TI – Temperature of blood and injectate , respectively ΔTB – mean change in the pulmonary artery blood t – duration of first passage of injectate in seconds.

41. ADVANTAGES Saline is harmless Cold is dissipated, so recirculation is not a problem Withdrawal of blood for sampling is not required Can be repeated many times Preferred for infants and small children in whom the blood volume is limited & saline is non toxic Useful in severely sick patients DISADVANTAGES Cardiac catheterization required

42. X-RAY METHOD Radio-opaque dye is injected intravenously Size of heart detected from serial x-rays in systole & diastole Cardiac output measured using computer programmes.

43. CINERADIOGRAPHY Diagnostic technique in which a camera is used to record images of internal body structures produced through radiography or fluoroscopy Takes high speed X-ray motion pictures

44. ANGIOGRAPHY Visualizes coronary arteries, also m easures End diastolic & End systolic volume Cardiac output=(EDV-ESV) xHR

45. NON INVASIVE METHODS

46. ENDOTRACHEAL CARDIAC OUTPUT MONITOR(ECOM)/IMPEDENCE CARDIOGRAPHY ECOM measures cardiac output using impedance plethysmography Is based on the principle of bio-impedance . Current is passed through electrodes attached to endotracheal tube shaft & cuff Change in impedance secondary to aortic blood flow is detected by electrode on the cuff.

47. An algorithm calculates stroke volume on impedance changes & cardiac output can be calculated Impedance affected by aortic blood flow LIMITATIONS Electrocautery affects its accuracy Coronary blood flow is not calculated Is not validated in humans Is costly & has not become very popular

48. ECHO ECHOCARDIOGRAPHY

49. DELIVERY ROUTES TRANSTHORACIC WINDOW Left parasternal Apical Subcostal Right parasternal Suprasternal Posterior thoracic TRANSESOPHAGEAL INTRAVASCUAR Intracardiac Intracoronary EPICARDIAL

50. TRANS THORACIC ECHOCARDIOGRAPHY/ CARDIAC ULTRASOUND   Echocardiography refers to ultrasonic evaluation of cardiac functions. It is a non-invasive technique that does not involve injections or insertion of a catheter. It involves B-scan ultrasound at a frequency of 2.25 MHz using a transducer which also acts as receiver of the reflected waves.

51. The reflections are recorded in a photosensitive paper using an oscilloscope . The thickness & movement of the ventricular walls, chambers, septum, and valves during the cardiac cycle.

52. When combined with Doppler techniques, can be used to measure velocity and volume of flow through the valves. Also Evaluates end-diastolic volume (EDV), end-systolic volume (ESV), cardiac output (CO) and valvular defects.

53. ACOUSTIC WINDOWS Para sternal -long axis & short axis views Apical-4 chamber & 2 chamber views Sub costal- 4 chamber view Suprasternal view

54. MODALATIES OF ECHO CONVENTIONAL ECHO Two dimensional echo (2-D echo) Motion mode echo ( M- mode echo) DOPPLER ECHO Continuous wave (CW) doppler Pulsed wave(PW) doppler Colour flow(CF) doppler

55. TWO DIMENSIONAL ECHO M- MODE ECHO

56. ADVANTAGES Non-invasive Quick Allows for measurement of the ventricles, visualization of the valves ,estimation of ejection fraction DISADVANTAGES User dependent Possible interference from bone ,lung & soft tissues

57. TRANS ESOPHAGEAL ECHOCARDIOGRAPHY (TEE)/DOPPLER Provides information on the velocity, direction, and character of blood flow, just as police radar monitors traffic. Information is obtained with the beam parallel to the flow of blood. Can continuously monitor the velocity of flowing blood in a blood vessel or part of the heart.

58. The strength of the returning signal, which depends on the number of red blood cells moving at that velocity. Can distinguish the character of flow: laminar versus turbulent.

59. Blood moves through the mitral valve and into the left ventricle during diastole. Because blood is flowing toward the transducer , its velocity is encoded as red . Blood moves out of the ventricle and toward the aortic valve during systole. Because blood is flowing away from the transducer , its velocity is encoded as blue .

60. A magnetic resonance scanner can also be used in two-dimensional phase-contrast mapping to yield quantitative measurements of blood flow velocity.

61. ADVANTAGES Minimally invasive Minimal interference from bone, lungs & soft tissues Quickly inserted & analyzed Little training required Very few complications DISADVANTAGES May require sedation User dependent Probe may detect other vessels e.g intracardiac ,intrapulmonary vessels Contraindicted in esophageal surgeries Depends on accurate probe positioning

62. Ballistocardiography method   This method is not used practically . Refers to graphical record of the pulsations created due to ballistic recoil of the pumping heart. The ballistic recoil occurs in accordance with Newton’s third law of motion , i.e. when heart pumps blood into aorta and pulmonary artery, recoil of the body occurs in the opposite direction. This is similar to that of ballistic recoil when a bullet is fired from the rifle.

63. The ballistic recoil pulsations can be recorded graphically by making the subject to lie on a suspended bed movable in the long axis of the body. The cardiac output is determined by analyzing the graph obtained. Not an accurate one

64. PULSE PRESSURE METHOD Pulse pressure -Difference between systolic & diastolic pressures provides rough idea about cardiac output

65. METHOD EMPLOYING INHALATION OF INERT GASES Also called foreign gas re-breathing In this technique, an inert gas which dissolves in plasma but does not combine with Hb or other constituents of the blood is used as an indicator. Gases- nitrous oxide,CO2 and acetylene The pulmonary blood flow is determined by The quantity of gas absorbed in the given time The partial pressure of the gas in the alveolar air The solubility of the gas (a known factor).

66. SUMMARY INVASIVE Pulmonary artery catheter ( Fick’s method, Dye, Thermodilution ) Cineradiographic technique X-ray method NON – INVASIVE Endotracheal cardiac output monitor (ECOM) TTE/Trans Thoracic echocardiography TEE/Trans esophageal doppler Pulse pressure method Method employing inhalation of Inert gases METHODS OF MEASURING CARDIAC OUTPUT

67. REFERENCES GUYTON AND HALL- Text Book of Medical Physiology-13 th International edition. GANONG ‘S Review of Medical Physiology 26 th edition. Text book of medical Physiology- INDHU KHURANA 2 nd edition Comprehensive Text Book of Medical Physiology- G.K. PAL 2 nd edition BERNE & LEVY -Text book of Medical Physiology 1 st edition BORON -Text book of Medical Physiology 3 rd edition BRAUNWALD’S Text book of Heart Disease 11th edition