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CRITICAL CARE AND TRAUMA

Positive End-Expiratory Pressure Improves Survival in a Rodent Model of Cardiopulmonary Resuscitation Using High-Dose Epinephrine

Conán McCaul, MB^*||, Alik Kornecki, MD^*¶, Doreen Engelberts, AHT^*, Patrick McNamara, MB^*||#, and Brian P. Kavanagh, MB^*||**

From the *Program in Physiology and Experimental Medicine, Departments of Critical Care Medicine, and Anesthesia, Hospital for Sick Children; Departments of Anesthesia, and ||Pediatrics, University of Toronto, Toronto; ¶Department of Paediatrics, Critical Care Unit, Children’s Hospital of Western Ontario, University of Western Ontario, London; #Department of Pediatrics, Hospital for Sick Children; and **Department of Physiology, and Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada.

Address correspondence and reprint requests to Dr. Brian P. Kavanagh, Department of Critical Care Medicine, Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8. Address e-mail to brian.kavanagh{at}sickkids.ca.

BACKGROUND: Multiple interventions have been tested in models of cardiopulmonary resuscitation (CPR) to optimize drug use, chest compressions, and ventilation. None has studied the effects of positive end-expiratory pressure (PEEP) on outcome. We hypothesized that because PEEP can reverse pulmonary atelectasis, lower pulmonary vascular resistance, and potentially improve cardiac output, its use during CPR would increase survival.

METHODS: Anesthetized Sprague-Dawley rats were exposed to 1 min of asphyxial cardiac arrest. Resuscitation was standardized and consisted of chest compressions, oxygen (Fio₂ 1.0), and IV epinephrine 30 µg/kg (Series 1) and 10 µg/kg (Series 2). Left ventricular function was assessed by echocardiography (Series 1), and animals were randomized to receive either 5 cm H₂O PEEP or zero PEEP at commencement of CPR and throughout resuscitation. Survival was defined as the presence of a spontaneous circulation 60 or 120 min (Series 2) after initial resuscitation.

RESULTS: There were no baseline differences between the groups. In Series 1, administration of 5 cm H₂O PEEP (Fio₂ 1.0 and 0.21) was associated with improved survival compared with zero PEEP (7/9 and 6/6 vs 0/9, P < 0.01 and <0.001, respectively). Application of 5 cm H₂O PEEP (Fio₂ 1.0) increased left ventricular end-diastolic area, systemic oxygenation, and functional residual capacity. Use of PEEP during CPR did not adversely affect left ventricular systolic function or arterial blood pressure. The outcome differences were not due to increased oxygenation because the rank order of survival was 5 cm H₂O PEEP (Fio₂ 1.0) 5 cm H₂O PEEP (Fio₂ 0.21) > zero PEEP (Fio₂ 1.0), whereas the rank order of Pao₂ was 5 cm H₂O PEEP (Fio₂ 1.0) > 5 cm H₂O PEEP (Fio₂ 0.21) zero PEEP (Fio₂ 1.0). In an additional series in which epinephrine 10 µg/kg was used (Series 2), the survival was 100% with no beneficial effects of PEEP.

CONCLUSION: In asphyxial cardiac arrest in a small rodent model, continuous application of PEEP (5 cm H₂O) during and after CPR had beneficial effects on survival that were independent of oxygenation and without adverse cardiovascular effects.