Minimally invasive Cardiac output Monitoring

Presentation on minimally cardiac output monitoring in critical care units

1. Minimally invasive Cardiac output monitoring

2. Cardiac output Cardiac output (CO) is the volume of blood ejected by each ventricle per minute and is the product of stroke volume and heart rate. SV depends on preload, contractility, heart rate and afterload CO= SV x HR (L/min) CI = SV x HR/BSA (L/min/m2) Normal CI = 2.5-4.2 Thermodilution method using pulmonary artery catheter (PAC) is till date considered as gold standard method.

3. Clinical Assessment of Cardiac Output Assess adequacy rather than “numbers” End organ perfusion Brain (Confusion, altered consciousness) Kidney(UO) Tissues(lactate) Skin(CRT) BP correlate poorly ….but….narrowed pulse pressure may have some value

4. Methods of CO monitoring Here are various methods of CO monitoring based on Fick principle, Thermodilution, Doppler, P ulse contour analysis

5. Fick Principle Adolf Eugen Fick (1829-1901) in 1870, was the first to measure cardiac output Amount of a substance taken up by an organ per unit time is equal to the arterial minus the venous concentration multiplied by blood flow VO2 = (CO x Ca) – (CO x Cv) Therefore, CO = VO2/(Ca-Cv) VO2 = oxygen consumption/min, Cv = oxygen content of blood taken from pulmonary artery (deoxygenated), Ca = oxygen content of blood taken from a peripheral artery (oxygenated) Reduced accuracy in sicker patients, severe chest trauma, intra pulmonary shunt, low MV and high CO

6. Pulse contour analysis Based on the principle that area under the systolic part of the arterial pressure waveform is proportional to the SV CO was proportional to arterial pulse pressure IN this method the area is measured post diastole to end of ejection phase divided by aortic impedance that measures SV

7. Classification of cardiac output monitoring Invasive PA catheter Minimally invasive Lithium dilution CO (LiDCO) Pulse contour analysis CO (PiCCO and FloTrac) Esophgeal Doppler (ED) Transesophgealechocardiography (TEE) Non-invasive Partial gas rebreathing Endotrachealcardiac output monitor (ECOM) Doppler method and Photoelectric plethysmography

8. An ideal CO monitor should be Minimally or non-invasive Continuous Cost effective Reproducible Reliable during various physiological states and Have fast response time

9. Minimally invasive Methods LiDCO PICCO Flo Trac TEE Esophageal doppler

10. LiDCO (Lithium dilution cardiac output) LiDCO system combines pulse contour analysis with lithium indicator dilution for continuous monitoring of SV and SV variation (SVV). A bolus of lithium chloride is injected into venous (central or peripheral) line and arterial concentration is measured by with drawing blood across disposable lithium sensitive sensor containing an ionophore selectively permeable to Lithium CO is calculated based on Lithium dose and area according to the concentration time circulation.

11. LiDCO (Lithium dilution cardiac output) It requires calibration every 8 hours and during major hemodynamic changes. It is contraindicated in patients on Lithium therapy. Its accuracy is affected by : Aortic regurgitation, Intraaortic balloon pump(IABP), Post aortic surgery, Arrythmia and intra or extracardiac shunts. In relation with PAC ,found good correlation with PAC by Linton et al.

12. PiCCO (Pulse index continuous CO) It combines pulse contour analysis with the transpulmonary thermodilution CO to determine hemodynamic variables It 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 thermistor tip catheter placed in the artery.

13. PiCCO (Pulse index continuous CO) It requires manual calibration every 8 hours and hourly during hemodynamic instability. It accuracy may be affected by: Vascular compliance, Aortic aneurysm peripheral arterial resistance Arrhythmia Rapidly changing temperature Studies have found good correlation with PAC during coronary artery bypass grafting

14. FloTrac System FloTrac is a pulse contour device introduced in 2005 It is 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

15. FloTrac System Accuracy is affected in patients with significant Arrhythmias IABP Morbid obesity Various studies have validated the efficacy of FloTrac with PAC and find good correlation However in patients with low SVR undergoing liver transplantation or septic shock it is not found as accurate as PAC

16. Esophageal doppler As aorta is considered as cylinder the flow can be measured by multiplying cross sectional area and velocity. Major limiting factor is that it measured flow in descending thoracic aorta which is 70% of total flow , a correction factor to be added to compensate aortic arch flow. More over discrepancies in flow may be seen in aortic coarctation, aneurysm or crossclamp, IABP. Various studies have compared ED with PAC and found good agreement

17. TEE TEE now been a widely used monitor in perioperative setting. Important tool for the assessment of cardiac structures, filling status and cardiac contractility. Doppler technique is used to measure CO by Simpson's rule measuring SV multiplied by HR. Flow is measured by area under the Doppler velocity waveform that gives VTI ( VELOCITY TIME INTERFERANCE)

18. TEE Measurement can be done at the level of pulmonary artery, mitral or aortic valve. TEE views used for measurement are midesophageal aortic long axis view and deep transgastric long axis view with pulsed and continuous wave Doppler respectively. It is a useful tool in hemodynamically unstable patient under mechanical ventilation.

19. Comparison of methods of measuring CO

20. Thank you