THE "ABC'S" OF CARDIOPULMONARY RESUSCITATION WITHOUT THE "B" IN A SWINE MODEL

Abstract

S140 INTRODUCTION: We reported that application of CPAP during precordial compression will provide sufficient tidal ventilation even without intermittent positive pressure ventilation. [1] We have observed increased carotid blood flow and aortic blood pressure during precordial compression and CPAP (CPRCPAP) compared to conventional-CPR (CPRC).2 The objective of this study was to compare the success of defibrillation and restoration of spontaneous circulation during CPRC versus CPRCPAP. METHODS: Twenty-four anesthetized, tracheally intubated pigs (24 +/- 3 kg) underwent appropriate instrumentation to determine aortic blood pressure, arterial blood gas tensions and pH, PETCO2, and minute ventilation. An electromagnetic, in-line flow probe was placed in the left carotid artery to measure blood flow. Ventricular fibrillation was induced by an electric shock, after measurement of baseline data. Animals were given epinephrine (20 mg/kg IV immediately and q5min), then randomly were assigned to receive five or ten min trials of CPRC or CPRCPAP (FIO2=1.0) at a compression rate of 80/minute with a sternal pneumatic compressor. During CPRC, intermittent positive pressure ventilation (12mL/kg) for 1.5sec was given after every fifth compression. During CPRCPAP, CPAP (20 +/- 3 cmH2 O) was adjusted to equal the animal's baseline spontaneous ventilation. Defibrillation was attempted with DC countershock and when successful, data were collected 30min later. Measurement data are summarized as mean +/- 1SD and were compared with a two-factor analysis of variance and Scheffe's test. Defibrillation success rate was compared with Fishers exact test. RESULTS: There were no differences in resuscitation success between animals who received CPRC versus CPRCPAP after five (5/6 vs. 5/5, P=.52) or ten (1/6 vs. 2/7, P=.88) minutes of CPR. There were no intergroup differences in carotid blood flow (CBF), aortic blood pressure during chest compression (BPComp) and relaxation (BPRelax), PETCO2, arterial blood gases or pHa between animals who were or were not resuscitated. There were no intergroup differences in measured variables of the animals who were resuscitated. Variables reflecting cardiovascular function during ventricular fibrillation and CPR are summarized in Table 1 (*p<.06 vs. CPRC at 5min).Table 1DISCUSSION: We observed that defibrillation success during CPR was independent of ventilation technique. Systemic blood pressure was greater after 5min in animals, who received CPRCPAP versus CPRC, which coincides with previous observations that positive airway pressure, applied coincidently with chest compression, increases blood pressure and flow. We conclude that application of CPAP during chest compression obviates the need for intermittent mechanical ventilation, without compromising cardiovascular function or success of resuscitation. This study was supported by the Laerdal Foundation for Acute Medicine.