Study objective: To compare CPR with chest compressions plus ventilatory support (CC+V) and chest compressions alone (CC). Design: Prospective, randomized study. Setting: Research laboratory. Interventions: After 2 minutes of ventricular fibrillation, 18 domestic swine (20 to 35 kg) were treated first with CC or CC+V for 10 minutes, then with standard advanced cardiac life support. Results: Hemodynamics, survival, and neurologic outcome were determined. All 8 swine subjected to CC+V and all 10 subjected to CC showed return of spontaneous circulation. One animal in each group died within 1 hour. Seven of 8 animals in the CC+V group survived for 24 and 48 hours, compared with 9 of 10 CC animals at 24 hours and 8 of 10 at 48 hours. All 48-hour survivors were neurologically normal. Conclusion: In this experimental model of bystander CPR, we could not detect a difference in hemodynamics, 48-hour survival, or neurologic outcome when CPR was applied with and without ventilatory support. [Berg RA, Wilcoxson D, Hilwig RW, Kern KB, Sanders AB, Otto CW, Eklund DK, Ewy GA: The need for ventilatory support during bystander CPR. Ann Emerg Med September 1995;26:342-350.]