ObjectivesTo evaluate the efficacy of conventional threshold levels of coronary perfusion pressure and end-tidal CO2as predictors of resuscitability after prolonged cardiac arrest.DesignProspective, randomized, controlled animal study.SettingUniversity research laboratory.SubjectsTwenty-one Sprague-Dawley rats, including three groups of seven animals in each group.InterventionsVentricular fibrillation was untreated for 9, 12, or 15 mins. After an additional 5-min interval of precordial compression, external direct current defibrillation was attempted.Measurements and Main ResultsAll animals were successfully resuscitated after 9 mins of ventricular fibrillation but less than one half of the animals were successfully resuscitated after 15 mins of ventricular fibrillation. Each of seven animals survived for 24 hrs after 9 mins of untreated ventricular fibrillation but none of the animals survived after 15 mins of ventricular fibrillation. In this experimental setting, neither coronary perfusion pressure nor end-tidal CO2produced by precordial compression was predictive of outcomes when the animals underwent progressively longer intervals of untreated cardiac arrest.ConclusionsThe efficacy of precordial compression--as measured by coronary perfusion pressure and end-tidal CO2concentration after prolongation of untreated cardiac arrest--was not overtly compromised. However, the previously established critical threshold levels of coronary perfusion pressure and end-tidal CO2failed as predictors of resuscitability after prolonged intervals of untreated cardiac arrest.(Crit Care Med 1995; 23:1233-1236)