We provide information that we believe should allow the establishment of rational guidelines for discontinuing, with physician supervision, unsuccessful prehospital CPR. Goldberg has advocated that CPR be terminated only after evidence of brain or cardiac death has persisted for more than one hour of adequately applied advanced CPR. This recommendation was made for inhospital resuscitation and does not reflect the limited capabilities of basic and advanced CPR techniques to sustain life outside the hospital. In addition, White and associates have demonstrated that after resuscitation from prolonged cardiac arrest, cerebral cortical blood flow is reduced severely. This state of hypoperfusion may last up to 18 hours. Because this condition can result in extensive neurologic damage, it may explain the poor survival rates after prolonged resuscitation. We propose that CPR be terminated in the ED when, despite adequate rescue attempts (intubation, defibrillation, IV medications, CCCM en route) by those responding at the scene of cardiac arrest, intrinsic cardiac activity has not been achieved in patients brought to the hospital with asystole or bradyarrhythmia. Additionally patients who have had advanced prehospital CPR for more than 45 minutes without generation of any intrinsic cardiac activity are not resuscitatable by current standard techniques, and CPR may be discontinued. These criteria must not be used for victims of hypothermia before a core temperature of 35 C to 36.1 C is achieved by active core rewarming during CPR. The available data suggest that if these criteria are implemented, many unproductive hospital-based resuscitative efforts can be eliminated without jeopardizing potential survivors.(ABSTRACT TRUNCATED AT 250 WORDS)