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