Permissive hypoventilation equally effective to maintain oxygenation as positive pressure ventilation after porcine class III hemorrhage and whole blood resuscitation

Abstract

Background: Prehospital anesthesia may lead to circulatory collapse after severe hemorrhage. It is possible that permissive hypoventilation, refraining from tracheal intubation and accepting spontaneous ventilation, decreases this risk, but it is not known if oxygen delivery can be maintained. We investigated the feasibility of permissive hypoventilation after class III hemorrhage and whole blood resuscitation in three prehospital phases: 15 min on-scene, 30 min whole blood resuscitation, and 45 min after. Study Design and Methods: 19 crossbred swine, mean weight 58.5 kg, were anesthetized with ketamine/midazolam and hemorrhaged to a mean (SD) 1298 (220) mL (33%) and randomized to permissive hypoventilation (n = 9) or positive pressure ventilation with FiO2 21% (n = 10). Results: In permissive hypoventilation versus positive pressure ventilation, indexed oxygen delivery (DO2I) decreased to mean (SD) 4.73 (1.06) versus 3.70 (1.13) mL min−1 kg−1 after hemorrhage and increased to 8.62 (2.09) versus 6.70 (1.56) mL min−1 kg−1 at completion of resuscitation. DO2I, indexed oxygen consumption (VO2I), and arterial saturation (SaO2) did not differ. Permissive hypoventilation increased the respiratory rate and increased pCO2. Positive pressure ventilation did not deteriorate circulation. Cardiac index (CI), systolic arterial pressure (SAP), hemoglobin (Hb), and heart rate did not differ. Discussion: Permissive hypoventilation and positive pressure ventilation were equally effective to maintain oxygen delivery in all phases. A respiratory rate of 40 was feasible, showing no signs of respiratory fatigue for 90 min, indicating that whole blood resuscitation may be prioritized in select patients with severe hemorrhage and spontaneous breathing.