Check to see that at least three values were averaged and that the range of these values is no greater than 20% of the mean. Check the chest x-ray; is the distal tip of the catheter in the pulmonary artery and the proximal port in the right atrium? Check to see if the computer is calibrated to the proper temperatures. Finally, if the computer can display the time versus temperature curve, check to see that the curve is shaped properly (see figure below).
Typical time versus fall-in-temperature curve obtained from a thermodilution cardiac output computer. The curve rises steeply, then falls slowly. The downsloping limb of the curve is not perfectly concave, indicating some early recirculation of the indicator (cold saline).
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This tracing was obtained from a patient with heart failure; the recirculation is probably the result of tricuspid regurgitation, and does not affect the accuracy of the cardiac output determination.
Does pulmonary artery catheterization really help?
Despite widespread use of these devices in intensive care units, some physicians point out that few if any studies have shown that their use decreases mortality and that randomized studies have not been widely performed. Proponents point out that many studies have shown that clinical data predict wedge pressure poorly and that insertion of the catheter changes management plans frequently. In at least one study of critically ill postoperative patients, management based on cardiac output data improved survival. The truth lies somewhere between. Pulmonary artery catheterization at the bedside is not without risk. It should be used only after careful consideration of its possible benefits and with thorough knowledge of its capabilities.