HEMODYNAMICS DURING CPR

Abstract

S141 INTRODUCTION: During CPR, airway pressure and ventilator pattern may have a dramatic effect on arterial blood pressure and flow. This may explain why attempts to define the ideal rate and time of chest compression have led to conflicting results. Thus, we chose to hold airway pressure constant, in order to examine the effect of variable chest compression and rate on hemodynamic function during CPR. METHODS: Sixteen anesthetized, tracheally intubated pigs (28 +/- 3 kg) underwent appropriate instrumentation to determine aortic blood pressure and carotid blood flow. Ventricular fibrillation was induced by an electric shock. Chest compression time (0.25, 0.3 and 0.4s) and rate (40, 60, 80, 100, 120/min) were varied randomly at 30 sec intervals with a computer program driven sternal pneumatic compressor. Compression force was adjusted to result in a sternal displacement of [similar]25% of the anteroposterior diameter. CPAP (20 cmH2 O) was applied with 100% oxygen. Carotid blood flow and aortic blood pressure during chest compression were recorded during each compression time and rate trial. Blood pressure data are summarized as mean +/- 1SD and were compared using a repeated measures analysis of variance. Carotid blood flow values were compared using Friedman's repeated measures ANOVA. RESULTS: There were no differences in BPComp (58 +/- 12 mmHg) and BPRelax (22 +/- 13 mmHg) with varied chest compression time and rate; thus, data were pooled. Carotid blood flow values were similar during CPR and are summarized in Figure 1.Figure 1DISCUSSION: We found that application of CPAP during chest compression will provide sufficient tidal ventilation, even without intermittent positive pressure ventilation.1 We observed greater carotid blood flow and aortic blood pressure during precordial compression and CPAP than during conventional-CPR.2 Assuming the carotid blood flow was a consistent fraction of the total blood flow, we observed no significant advantage of varied chest compression time and rate in the range studied. With a chest compression rate of at least 40/min, blood flow may be more dependent on the filling and emptying time constants of the intrathoracic vasculature.