Usefulness of Oximetry Paradoxus to Diagnose Cardiac Tamponade

Although echocardiography is usually diagnostic of cardiac tamponade, it may not be readily available at the point-of-care. We sought to develop and validate a measurement of respirophasic variation in the amplitude of pulse oximetry plethysmographic waveforms as a diagnostic tool for cardiac tamponade. Pulse oximetry plethysmographic waveforms were recorded, and the ratio of maximum-to-minimum measured amplitude of these waveforms from one respiratory cycle was calculated by blinded observers. Ratios from 3 consecutive respiratory cycles were then averaged to derive an "oximetry paradoxus" ratio. Cardiac tamponade was independently confirmed or excluded according to a "blinded" objective interpretation of echocardiography or right heart catheterization. Seventy four subjects were enrolled (51% men; mean age 54 ± 15 years); 19 of whom had cardiac tamponade. Oximetry paradoxus area under the curve for diagnosis of cardiac tamponade was 0.90 (95% confidence interval, 0.84 to 0.97); its diagnostic performance was superior to sphygmomanometer-measured pulsus paradoxus (area under the curve difference = 0.16, p = 0.022). In a derivation cohort (n = 37; tamponade, 9 cases), 3 diagnostic oximetry paradoxus thresholds were identified and validated in an independent validation cohort (n = 37; tamponade, 10 cases): 1.2 (100% sensitivity, 44% specificity), 1.5 (80% sensitivity, 81% specificity), and 1.7 (80% sensitivity, 89% specificity). Furthermore, oximetry paradoxus was significantly reduced after draining pericardial fluid. In conclusion, we defined and validated oximetry paradoxus as a simple and ubiquitous point-of-care test to diagnose cardiac tamponade using respirophasic changes in pulse plethysmography waveforms. This test can aid in identifying patients with cardiac tamponade, thus expediting confirmatory testing and life-saving treatment.