Continuous Noninvasive Determination of Pulsus Paradoxus: A Pilot Study

OBJECTIVE: To evaluate two methods of continuous, noninvasive monitoring of pulsus paradoxus (PP). METHODS: A single-subject, nonblind assessment was conducted of the ability of noninvasive monitoring techniques to measure experimentally induced PP. Variable degrees of PP were induced in a healthy adult breathing through a one-way valve to which a series of external airway resistances were added. Intra-arterial pressure (IAP), finger arterial blood pressure (FINAP), pulse oximeter pulse waveform, and chest wall motion were continuously recorded. For each resistance, PP was calculated from the IAP (PPIAP) and the FINAP (PPFINAP) recordings. PP was measured manually (PPmanual) in the opposite arm. The percentage pulse waveform decrease on inspiration (%PWDpleth) was derived from the oximeter pulse waveform. These measurements were compared with the PPIAP. Bias was assessed as the mean difference between PP measures. RESULTS: PPFINAP was highly correlated with PPIAP (r = 0.96; 95% CI 0.93 to 0.98; p < 0.0001). There was a weak correlation between PPmanual and PPIAP (r = 0.27; 95% CI -0.05 to 0.55; p = 0.0963). The %PWDpleth correlated with PPIAP (r = 0.59, 95% CI 0.32 to 0.78; p = 0.0002). Bias was -1.515 +/- 5.6 mm Hg between PPIAP and PPFINAP; and -4.508 +/- 23.4 mm Hg between PPIAP and PPmanual. CONCLUSION: An accurate and continuous PP can be measured noninvasively using a FINAP monitor. This method has much better agreement with IAP measurements than do manual measurements. The qualitative information provided by the oximeter pulse waveform is less accurate than that provided by the FINAP monitor, but is a potentially useful screening tool for detection of significant PP.