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 oneway 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 (PP_IAP) and the FINAP (PP_FINAP) recordings. PP was measured manually (PP_manual) in the opposite arm. The percentage pulse waveform decrease on inspiration (%PWD_pleth) was derived from the oximeter pulse waveform. These measurements were compared with the PP_IAP. Bias was assessed as the mean difference between PP measures. Results: PP_FINAP, was highly correlated with PP_IAP (r = 0.96; 95% CI 0.93 to 0.98; p < 0.0001). There was a weak correlation between PP_manual and PP_IAP (r = 0.27; 95% CI -0.05 to 0.55; p = 0.0963). The %PWD_pleth correlated with PP_IAP (r = 0.59, 95% CI 0.32 to 0.78; p = 0.0002). Bias was -1.515 ± 5.6 mm Hg between PP_IAP and PP_FINAP; and -4.508 ± 23.4 mm Hg between PP_IAP and PP_manual. 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.