Abstract 152: Intrinsic Vascular Tone may be Necessary for Successful Resuscitation from Experimental Cardiac Arrest

Abstract

Introduction: Survival rates from out-of-hospital cardiac arrest are often <10% despite performance of good quality CPR. We assessed the hypothesis that the effect of CPR on cardiac and brain perfusion may be dependent on factors other than thoracic compression force and ventilation. Methods: Eighty healthy Yorkshire pigs (29±3 kg) were anesthetized and underwent 2-4 minutes of untreated ventricular fibrillation (VF), followed by guideline based CPR, then defibrillation. “Survivors” were pigs in sinus rhythm with aortic systolic pressure ≥30 mmHg 30 minutes after defibrillation; all others were “non-survivors”. Hemodynamic, ventilatory and defibrillation parameters were measured and tested for association with survival. Results: Thirty four pigs survived (43%). During baseline and untreated VF, hemodynamic and blood gas parameters were not different between survivors and non-survivors. During CPR, compressions generated adequate left ventricular pressures in both groups (99±21 mmHg vs. 106±28 mmHg, survivors vs. non-survivors, P=ns). Compressions produced 28% higher peak aortic pressures in survivors than non-survivors (respectively 73±21 mmHg vs. 57±17 mmHg, P<0.005). During the decompression phase, nadir aortic pressures were 41% higher in survivors than non-survivors (respectively 24±7 mmHg vs. 17±5 mmHg, P<0.0001). Controlled manual bag ventilation during CPR resulted in significantly higher minute ventilation being delivered to survivors compared to non-survivors (4.8±2.3 L/min vs. 3.9±1.4 L/min, P<0.05). Coronary perfusion pressure, carotid blood flow, cerebral O 2 tension, and end tidal CO 2 were also higher in survivors. Conclusions: Guideline based CPR in a uniform population of pigs undergoing a structured cardiac arrest and resuscitation protocol does not produce consistent results. Intravascular pressures, intrathoracic pressure and critical organ flow correlate with survival. During cardiac arrest, more emphasis may need to be placed on vascular support rather than powerful compressions.