Hemodynamic responses to cooling and warming during a continuous simulated hemorrhage ramp

Abstract

One in 10 deaths worldwide is caused by traumatic injury, and 30–40% of those trauma‐related deaths are due to hemorrhage. Currently, warming a hemorrhaging victim is the standard of care due to the adverse effects of combined hemorrhage and hypothermia on survival. However, heating can be detrimental to the maintenance of arterial pressure and cerebral perfusion during a continuous hypotensive challenge.PURPOSETo test the hypothesis that warming a normothermic individual during a continuous simulated hemorrhage ramp is harmful to the maintenance of arterial pressure and cerebral perfusion, while skin surface cooling is beneficial.METHODSTwelve men (mean ± SD: age, 29 ± 8 y; weight, 82 ± 16 kg) underwent a randomized crossover study performed over 3 separate days. Following 15 min of supine rest, 10 min of 30 mmHg of lower body negative pressure (LBNP) was applied to simulate a mild hemorrhagic challenge. With LBNP continuing, subjects were then exposed to mild whole‐body warming (WARM; mean skin temperature (Tsk): 36.4 ± 0.5°C), skin surface cooling (COOL; Tsk: 30.5 ± 0.9°C), or remained thermoneutral (NEUT; Tsk: 33.9 ± 0.6°C). Five min after the thermal provocation, a continuous LBNP ramp was applied at a rate of 5 mmHg·min−1 until pre‐syncope. Hemodynamic and thermal variables were measured continuously.RESULTSNeither average time to pre‐syncope (P = 0.14) nor the LBNP level at pre‐syncope (P = 0.09) were different between thermal conditions. However, mean arterial blood pressure was elevated (92 ± 11 mmHg; P = 0.01) during COOL across the LBNP period, relative to NEUT (83 ± 9 mmHg) and WARM (79 ± 11 mmHg) trials. Middle cerebral artery blood velocity decreased (26 ± 1 cm·sec−1; P < 0.001) to a similar extent from baseline to pre‐syncope, regardless of the thermal conditions applied.CONCLUSIONSContrary to our hypothesis, WARM did not impair LBNP tolerance or cerebral blood flow velocity. Although COOL increased blood pressure during the LBNP ramp, LBNP tolerance and cerebral perfusion were not different relative to the NEUT or WARM trials. These data indicate that mild whole‐body warming of a continuously hemorrhaging victim is not detrimental to hemodynamic stability.Support or Funding InformationProject funded by DOD‐W81XWH‐12‐1‐0152.