C. G. Morgan1, E. N. Hathaway2, L. E. Neidert1, L. Schaub1, J. J. Glaser1 1Naval Medical Research Unit San Antonio,JBSA-Ft. Sam Houston, TX, USA 2Brooke Army Medical Center,JBSA-Ft. Sam Houston, TX, USA
Introduction: Tactical Combat Casualty Care (TCCC) guidelines for hemorrhage recommend resuscitation to systolic blood pressure (SBP) 80-90mmHg, only fully resuscitating after surgical hemostasis. Success depends on rapid transport to definitive care, within the ‘golden hour’. Future conflicts may demand longer prehospital/transport times. We sought to determine safety of prolonged permissive hypotension (PH) over 6 hours.
Methods: Adult male swine were randomized to 1) hemorrhage + hypotension 2) hypotensive sham 3) anesthesia sham. Group 1 (G1) underwent hemorrhage to mean arterial blood pressure (MAP) 30mmHg for 30 min followed by 6 hr prolonged field care (PFC) with goal SBP 85±5mmHg maintained with crystalloid. Animals were then resuscitated with whole blood simulating hospital care, and observed for 24 hrs. Group 2 (G2) was bled to SBP 85±5mmHg during PFC then recovered. Group 3 (G3) underwent anesthesia only. Physiologic variables, blood, tissue samples, and neurologic (Tarlov) scores were collected. Significance = p<0.05.
Results: Survival of all groups was 100% at 24 hrs, with no significant differences in Tarlov score (G1: 6.2±6.8, G2: 2.5±4.5, G3: 0.0±0.0). Mean blood loss after hemorrhage was 37.2±7.3%. At PFC Hr 1 G1 lactate level (mmol/L) was significantly higher than G2 and G3 (5.1±2.2 vs 2.6±1.8 vs 2.1±1.1) and at PFC Hr 2 and PFC Hr 4 compared to G3 (PFC Hr 2: 5.7±2.9 vs 1.6±0.5; PFC Hr 4: 4.0±2.4 vs 1.3±0.1). Crystalloid requirement (mL) to maintain blood pressure in PFC was significantly higher in G1 than G2 and G3 (G1: 4728±1410 vs G2: 1214±608 vs G3: 155±347). PaO2/FiO2 ratio remained above 300 in all groups throughout.
Conclusion: After 6 hrs, a prolonged PH strategy showed no detrimental effect on survival or neurologic outcome despite the increased ischemic burden of hemorrhage. Significant fluid volume was required to maintain SBP- a potential logistic burden for prehospital care. Further work to define maximum allowable time of PH is needed.
