Determination of Cardiac Output

Name five pitfalls of the thermodilution method.	Low outputs (outputs <2.5 L/min average a 35% overestimation) Tricuspid regurgitation Improper technique (i.e., slow injection, incorrect volume) Intracardiac shunts (VSD) Extracardiac shunts (AV fistula) Cold patients Distal tip of the catheter in the main PA Changes in blood viscosity (anemia or polycythemia) Invasive insertion
What is the Fick equation?	CO = [oxygen consumption × 10]/[(AoO2 sat – PAO2 sat) × (Hgb × 1.36)]
What is the estimated value for oxygen consumption?	110–150 mL/kg/min (110 for stable patients; 150 for ICU patients)
Name at least three pitfalls of the Fick equation.	Intracardiac shunts Difficult measurement of oxygen consumption (generally estimated) Incorrect data Invasive insertion PA sample drawn too quickly, which pulls pulmonary capillary (oxygenated) blood into the sample, thus overestimating the PA saturation
In general, what PA saturation levels would be in a normal range?	A PAO2 saturation of >65% and <80% is consistent with a normal CO. A PAO2 saturation >80% is consistent with some types of left-to-right shunting, and <65% is consistent with a reduced cardiac output.
How can errors in CO determination affect SVR?	The SVR, PVR, and so on are calculated numbers, and errors in pressure or CO measurements affect these numbers. For example, a patient with a normal CO of 6.0 L/min and significant tricuspid regurgitation may have a measured CO of 3.0 L/min. This would double the calculated SVRI and may result in inappropriate treatment.