Pulsus paradoxus: definition and relation to the severity of cardiac tamponade.
Based on 101 control patients, the 95% confidence limit for the inspiratory decrease in arterial systolic pressure (delta SYST, mm Hg) and the percentage decrease in arterial systolic pressure (% delta SYST = delta SYST/expiratory systolic pressure) were determined to be 12 mm Hg and 9%, respectively. In 65 patients with pericardial effusion, the severity of cardiac tamponade was estimated on the basis of the percentage increase in cardiac output resulting from pericardiocentesis: absent = less than 20% (n = 24), mild = 20% to 49% (n = 9), and moderate or severe = greater than or equal to 50% (n = 32). The accuracy of a delta SYST greater than 12 mm Hg and % delta SYST greater than 9% in the identification of tamponade was 92% and 97%, respectively. A % delta SYST greater than 15% with relative hypotension (expiratory systolic pressure less than or equal to 120 mm Hg) or a delta SYST greater than 25 mm Hg or inspiratory pulse obliteration was found in 31 of 32 patients with moderate or severe tamponade compared to 2 of the 33 remaining patients. We conclude that the inspiratory decline in arterial systolic pressure can be used to accurately estimate the level of hemodynamic embarrassment resulting from pericardial effusion.