IntroductionAirway compromise is the second leading cause of potentially survivable death on the battlefield, indicating a need for improved airway management approaches. Over‐ventilation of the lungs is a complication associated with prolonged use of mechanical ventilation, but few studies have examined the consequence of acute, pre‐hospital over‐ventilation. Therefore, the goal of this study was to determine the effect of acute hyperventilation on the morbidity of hemorrhaged swine.Materials and MethodsFemale Yorkshire pigs (40–50 kg) were anesthetized with isoflurane, instrumented for hemodynamic measurements and blood draws, and switched to IV anesthesia with midazolam and ketamine. Following baseline recording, 25% blood volume by weight was removed, followed by 1 hour of: spontaneous breathing (n=8), “normal” bag ventilation (6 L minute volume, n=9), bag hyperventilation (20 L minute volume, n=8), or mechanical ventilation (n=8). The pigs were then allowed to wake up from anesthesia, recovered for 24 hours, and euthanized for blood and tissue collections.ResultsHemorrhage significantly decreased mean arterial pressure (P<0.001), cardiac output (P<0.001), and stroke volume (P=0.004), but increased heart rate (P<0.001). Ventilation following hemorrhage did not have any further impact on hemodynamic variables, except a significant increase in heart rate in those that underwent bag hyperventilation as compared to spontaneous breathing, normal bag ventilation, and mechanical ventilation groups (24±5 bpm, vs −7±7, 9±11, and 2±2 bpm), respectively. Following ventilation, blood lactate levels were significantly elevated compared to baseline in all groups. The change was significantly greater in those that underwent hyperventilation than in spontaneous breathing, normal bag ventilation, and mechanical ventilation groups (7.9±0.7 mmol/L, vs 4.1±0.6, 5.9±0.4, and 5.4±1 mmol/L), respectively. Blood lactate levels returned to baseline levels by 24 h in all groups. Wet to dry lung weight ratios were also not significantly different between groups, an indication that any edema caused by over‐inflation dissipates by 24 hours.DiscussionThis study was undertaken on the premise that over‐inflation of the lungs, even acutely, would result in significant barotrauma and negative downstream physiological effects. Preliminary results, however, indicate that hemorrhage followed by acute hyperventilation does not affect hemodynamic variables or increase morbidity in mildly hemorrhaged swine. Ongoing studies include histological evaluation of tissue samples, assessment of blood markers for tissue damage, and measurement of plasma cytokine levels to more fully discern the presence of any lasting detrimental physiological effects to the lung or to systemic physiology.Support or Funding InformationUSAMRDC Tactical Combat Casualty Care Research Program