This document discusses hemodynamic monitoring in critically ill patients, focusing on cardiac output, fluid status, and volume responsiveness assessment techniques. It outlines invasive and non-invasive methods for measuring cardiac output, including the Fick principle and pulmonary artery thermodilution, while highlighting their limitations. Additionally, it presents alternative assessments like inferior vena cava diameter variation and passive leg raising tests to evaluate fluid responsiveness.

1. HEMODYNAMICS MONITORING IN CRITICALLY ILL
PATIENTS: ASSESSMENT OF FLUID STATUS AND
MEASURES OF VOLUME RESPONSIVENESS
Bassel Ericsoussi, MD
Pulmonary & Critical Care Specialist

2. Measuring Cardiac Output
• The function of the heart is to transport blood
to deliver oxygen to the cells of the body to
ensure their survival and proper function and
to remove the cellular wastes
– Cardiac Output (CO) = SV × HR
– Ejection Fraction (EF) = (SV / EDV) × 100%
– Stroke Volume (SV) = EDV – ESV
– Cardiac Index (CI) = CO / Body Surface Area (BSA)

3. Measuring Cardiac Output
Invasive methods are well accepted, but there is
increasing evidence that these methods are
neither accurate nor effective in guiding therapy
An accurate and non-invasive measurement of
CO is the best method of cardiovascular
assessment

4. Measuring Cardiac Output
The Fick Principle
• First described by Adolf Fick in 1870
• The rate at which oxygen is consumed is a
function of the rate of blood flows and the
rate of oxygen picked up by the red blood cells
• VO2 = CO x (CA – CV)
• CO = VO2 / (CA – CV)
– (CA – CV) Arteriovenous oxygen difference

5. Measuring Cardiac Output
The Fick Principle
• VO2 = CO x (CA – CV)
• CO = VO2 / (CA – CV)
– (CA – CV) Arteriovenous oxygen difference
• VO2 calculated using an assumed oxygen
consumption
• CaO2 = Hb x 1.34 x SaO2 + 0.003 PaO2
• CvO2 = Hb x 1.34 x SvO2 + 0.003 PvO2

6. Measuring Cardiac Output
The Fick Principle
• Invasive
• Requires time for the sample analysis
• Accurate oxygen consumption samples are
difficult to acquire

7. Measuring Cardiac Output
Pulmonary Artery Thermodilution
• Injection of 10 ml of cold glucose into the pulmonary
artery and measuring the temperature distally using
the same catheter with temperature sensors set apart
at a known distance 6–10 cm
• Calculate the Cardiac Output from a measured
time/temperature curve (The "thermodilution curve")
– low CO registers temperature change slowly
– high CO registers temperature change rapidly
– The degree of change in temperature is directly
proportional to the CO
• 3-4 passes are usually averaged to improve accuracy

8. Measuring Cardiac Output
Pulmonary Artery Thermodilution
• The Swan - Ganz catheter or PAC, was
introduced to clinical practice in 1970
• Due to hospital acquired infection, we don’t
use continuous invasive cardiac monitoring in
the Intensive Care Unit.
• Use of the PAC is still useful in right heart
study in the cardiac catheterization laboratory
today.

9. Measuring Cardiac Output
Pulmonary Artery Thermodilution
• PAC use is complicated by
– arrhythmias
– infection
– pulmonary artery rupture
– right heart valve damage
• Recent studies in patients with critical
illness, sepsis, acute respiratory failure and
heart failure suggest use of the PAC does not
improve patient outcomes

10. CVP AS A MARKER OF INTRAVASCULAR
VOLUME STATUS AND RESPONSE TO FLUIDS
• CVP is NOT RELIABLE for judging intravascular volume status
• A low CVP generally can be relied upon as supporting positive
response to fluid loading
• Target CVP 8–12 mmHg
• Higher target CVP of 12-15 mmHg should be achieved
–
–
–
–
Mechanically ventilated patients
Decreased ventricular compliance
Pulmonary artery hypertension
Increased abdominal pressure

12. Assessment of Fluid Status and Measures of
Volume Responsiveness
Passive Leg Raising and Artery Peak Velocity
• Doppler evaluation of arterial peak velocity
variation
In the responder patient, passive leg raising
induced an increase of arterial peak velocity by
15%

15. Assessment of Fluid Status and
Measures of Volume Responsiveness
IVC Diameter Variation
• Measure proximal IVC AP diameter 3 cm from the RA
• Spontaneous breathing
 > 50% decrease in the IVC diameter with inspiration
predicts responsiveness to volume expansion
• Positive pressure ventilation
 > 12% increase in the IVC diameter with inspiration
predicts responsiveness to volume expansion
Max D – min D / average D > 12%
Max D - min D / min D > 18%

16. IVC Evaluation
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17. Normal: IVC diameter 1-3 cm
• Subcostal view of the IVC passing through the liver and
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draining into the rightBassel Ericsoussi, MD
atrium.

18. Volume Responsive: IVC diameter <1 cm
Bassel Ericsoussi, MD
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19. Not Responsive: IVC diameter >3 cm
Bassel Ericsoussi, MD
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20. Assessment of Fluid Status and
Measures of Volume Responsiveness
Pulse pressure variation

21. LIMITATIONS OF IVC AND PULSE
PRESSURE VARIATIONS
• All patients must be:
– Passively ventilated – heavily sedated
– Large tidal volume 10-12 ml/kg
– Off vasopressors
– Sinus rhythm
– Absence of increased abdominal pressure
• Good luck finding these patient
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22. Assessment of Fluid Status and
Measures of Volume Responsiveness
Passive Leg Raising and Stroke
Volume Variation
• Straight leg raising test: Can be done on any patient
– Sinus or irregular rhythm
– Spontaneous breathing or on ventilator
– On pressors or off pressors
• Use apical 5 chamber view and measure the aortic blood flow (stroke
volume)
• Raise legs to 45 degree (you have just given a “blood bolus” 500 ml blood
in legs returned to the heart)
• Wait 30-60-90 sec (highest values within 90 sec)
• Recheck the stroke volume
– SVV > 12%
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23. Statistical Analysis Of Arterial Pressure
Flotrac/Vigileo
• By analyzing the shape of the arterial pressure
waveform, the effect of vascular tone is
assessed allowing calculation of SV.
• Cardiac Output (Q) is then derived utilizing the
equation Q=HR*SV.
• While these invasive arterial monitors do not
require intracardiac catheterisation from a
pulmonary artery catheter, they do require an
arterial line and are invasive.

24. Statistical Analysis Of Arterial Pressure
Flotrac/Vigileo
• Disadvantages
– Inability to provide data regarding right-sided heart
pressures, or mixed venous oxygen saturation
– The measurement of pressure in the artery to
calculate the flow in the heart is irrational and of
questionable accuracy
– Arterial pressure monitoring is limited in patients off
ventilation, in atrial fibrillation, in patients on
vasopressors and in patients with a dynamic
autonomic system such as in sepsis