Noninvasive cardiac output determination using applanation tonometry-derived radial artery pulse contour analysis in critically ill patients

Conventional thermodilution cardiac output (CO) monitoring is limited mainly to intensive care units and operating rooms because it requires the use of invasive techniques. To reduce the potential for complications and to broaden the applicability of hernodynamic monitoring, noninvasive methods for CO determination are being sought. Applanation tonometry allows noninvasive CO estimation through pulse contour analysis, but the method has not been evaluated in critically ill patients. We therefore performed noninvasive radial artery applanation tonometry in 49 critically ill medical intensive care unit patients and compared CO estimates to invasive CO measurements obtained using a pulmonary artery catheter or the PiCCO (R) transpulmonary thermodilution system. One-hundred-sixteen measurements were performed, and patients were receiving vasopressor support during 78 measurements. When the data were analyzed with bias and precision statistics, a large bias of 2.03 L center dot min(-1)center dot m(-2) and a high percentage error of 85% were found between the invasive measurements and applanation tonometry-derived CO estimates, with the noninvasive CO results being significantly lower than the invasive ones (P < 0.001). There Was no significant difference in bias between the patients who were receiving vasopressor support and those who were not (P = 0.874) or between patients with good and poor applanation tonometry pressure waveform signal quality (P = 0.071). Whereas a significant increase in the invasively determined CO was observed when a fluid bolus was administered (n = 7, P = 0.016), these changes were not reflected by the noninvasive method. We conclude that radial artery applanation tonometry is not suitable to determine CO in critically ill hemodynamically unstable patients.