Synchronous and Asynchronous Ventilation during Cardiopulmonary Resuscitation

Melker RJ, Cavallaro D Annals of Emergency Medicine 1983 Page 142

During CPR, ventilation is interposed after every fifth compression. Inspiratory time for ventilation is 0.5 sec. High flow and airway pressure results, increasing the likelihood of gastric insufflation. Low flow would decrease this risk, but would increase inspiratory time requiring ventilation during both compression and release. This study compares interposed synchronous ventilation (ISV) and asynchronous ventilation (ASV) during CPR. Eight swine (50-70 kg) were anesthetized. After tracheostomy, catheters were placed to measure pulmonary artery and aortic pressure. Common carotid artery flow, airway flow, tidal volume, airway pressure, and arterial and mixed venous blood gases were measured. Intrapulmonary shunt fraction was also calculated. Cardiac arrest was then induced and CPR started at 60 compressions/minute. Five minute periods of ISV and ASC were randomized. Adequacy of ventilation was judged by chest excursion. During ISV, inspiratory time was 0.5 seconds at 12 breaths/minute. During ASV, inspiratory time average 1.5 seconds and 13 breaths/minute. No statistical differences were found in aortic pressure, tidal volume, blood gases or shunt. However, order-dependent differences in common carotid artery flow were found. When ISV was performed first, carotid flow during ASV was significantly better (14.8 vs. 30.8 ml/min P<.01). When ASV was performed first, ISV was no better (19.4 vs. 21.0 ml/min). Airway pressure was statistically significantly lower during ASV than ISV (24 mmHg vs. 34.8 mmHg P<.001). Carotid flow was significantly better with ASV when ISV was used first. Airway pressure was always lower with ASV - an advantage in victims with an unprotected airway. Further study is necessary to differentiate effects caused by duration of CPR from effects of respiratory patterns on blood flow and ventilation.