This document summarizes different methods for measuring cardiac output, including clinical assessment, minimally invasive techniques, and invasive pulmonary artery catheterization. Clinical assessment involves evaluating end organ perfusion rather than direct cardiac output measurements. Minimally invasive techniques discussed include thoracic bioimpedance and esophageal Doppler. Invasive pulmonary artery catheterization provides direct cardiac output measurements via thermodilution but carries risks of complications. The document evaluates the advantages, limitations, and evidence for various cardiac output monitoring methods.

1. Cardiac output
monitoring
Dr Karen Orr
ST6 anaesthetics/ICM
Altnagelvin ICM study day 7/11/13

2. Cardiac output
•
Volume of blood ejected from the left ventricle per minute
•
Depends on preload, contractility, heart rate and
afterload
•
CO = HR x SV
•
MAP = CO x SVR

3. Methods of measuring CO
•
Clinical
•
Minimally-invasive
•
Invasive

4. Clinical
•
Assess adequacy rather than "numbers"
•
End organ perfusion
•
•
Kidney (UO)
•
Tissues (lactate)
•
•
Brain (confusion, altered consciousness)
Skin (CRT)
BP correlates poorly...but...narrowed pulse pressure may have
some value

5. •
Increased intrathoracic pressure during inspiration
•
Reduced venous return therefore reduced SV and BP
•
More pronounced during MV

6. Minimally invasive

7. Efficacy compared to PAFC?????

8. Fick principle
•
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
•
CO = VCO2/ CaCO2- CvCO2
•
CO2 production can be measured via sensors on breathing
circuit
•
CO2 content in mixed venous and arterial blood
•
Reduced accuracy in sicker patients, severe chest trauma, intra
pulmonary shunt, low MV and high CO

9. Thoracic bio-impedance
•
Ejection of blood from LV into aorta is associated with changes in
electrical impedance of the thoracic cavity
•
High frequency, low voltage AC is applied
•
Adv- minimally invasive
•
Correlates relatively well in healthy people but not in unwell
patients (0.29L/min)
•
Reduced reliability in advanced age, perioperative fluid shifts,
pulmonary oedema, MI, patient movement and electrical
interference

10. Oesophageal Doppler
•
Continuous, real time monitoring
•
Shift in frequency of reflected sound waves
changes proportionally with change in velocity
•
V = 2 x transmitted frequency/ velocity of US in
blood x Doppler shift x cosine theta

11. Assumptions
•
70% of blood enters descending aorta
•
Blood flow is uniform and maximal
•
Cross sectional area is constant (calculated using
formula dependent on age, sex and height)

12. Measured variables
•
CO
•
SV (stroke distance x aortic root diameter)
•
Stroke distance is AUC x HR
•
FTc (corrected flow time): indicates preload
•
Peak velocity: indicates contractility
•
HR

14. Contraindications
•
Oesophageal varices
•
IABP
•
Severe coarctation
•
Known oesophageal pathology

15. Limitations
•
Intubated patients
•
Probe must be as close as possible to parallel to aorta
•
Operator dependent
•
Learning curve for operator
•
Probe displacement

16. Evidence for use
•
Reduced post operative complications, cost, CVC
use and hospital LOS when used in high risk
surgical patients
•
No change in mortality in either surgical or ICU pts
•
Recommended by NICE for high risk surgical pts

17. •
Small study (12 pts) comparing PAFC and OD in
adult sepsis in ICU: good correlation with CI but
poor with preload and SVR

18. Pulse contour analysis
•
Relate the contour of the arterial pressure waveform
to SV and SVR
•
An algorithm is use to determine CO and produce a
continuous readout
•
Provide info on CO/ SVR etc but also SVV as a
measure of fluid responsiveness
•
SVV is the difference between max and min SV
across the respiratory cycle

19. PiCCO
•
Thermistor tipped femoral arterial line
•
Standard central line is used to calibrate using
thermodilution
•
Correlates strongly with PAFC readings in both
controls and patients with abnormal physiology
(less than 0.29L/min)

20. FloTrac
•
Standard arterial catheter
•
Algorithm is used based on age, height, gender, weight and
waveform characteristics
•
No external calibration
•
Conflicting evidence for accuracy compared with PiCCO and
PAFC
•
One study showed CO underestimated by up to 2L/min in 40%
of readings
•
Main advantage is ease of use

21. LiDCO
•
Pulse power analysis (based on law of conservation of mass)
•
Assumes that net power equates to net flow
•
Standard arterial line +/- CVL
•
Calibrated using lithium dilution
•
Good correlation with PAFC across a range of values (error of
<0.11L/min)
•
Contraindicated in chronic lithium use, recent NDNMB, early
pregnancy

22. Limitations
•
Rely on optimal arterial signal
•
Arrhythmias
•
IABP
•
Severe aortic regurg
•
Changes in SVR

23. Invasive

24. Pulmonary artery flotation
catheter
•
Dye dilution (known quantity of indocyanine green with
timed samples)
•
Thermodilution (continuous- heated coil or intermittentknown volume of cold saline injected via RA with distal
thermistor at the tip)
•
PACWP (surrogate for LVEDP)
•
Modified Stewart Hamilton equation

26. Limitations
•
Right and left ventricular output may differ in the presence of
an cardiac shunt
•
Tricuspid or pulmonary valve regurg may cause
underestimation of CO
•
MV causes variation in CO depending on point in respiratory
cycle
•
Tip of catheter in west zone 1 or 2
•
Mitral stenosis

27. Advantages
•
Right and left sided pressures
•
SvO2
•
Core temperature
•
Multi lumen infusion port
•
Provides angiographic access

28. Complications
•
Associated with CVL (arterial puncture, nerve injury,
embolism, pneumothorax)
•
Associated with catheterisation (arrhythmias, RV
rupture)
•
Associated with prolonged catheter insertion (PA
rupture, pulmonary infarction, thrombosis, stenosis)
•
PACMAN trial 10% incidence, ESCAPE trial 5%

29. The evidence
•
No effect on mortality, LOS, or cost of care in either
general ICU or high risk surgical patients
•
No effect on surgical outcomes when used preoperatively to optimise haemodynamics

30. What about cardiac surgery?
•
Increased mortality and end organ complications in
propensity matched obs study
•
Authors recognise need for RCT

31. Device comparison