Role of adenosine triphosphate (ATP) in trauma-induced and elective hypothermia

BACKGROUND: In trauma patients hypothermia is a frequent event. According to the literature the majority of trauma patients are presenting a core temperature of less than 34 degrees C at admission. In contrast to the benefit of hypothermia in elective surgery, clinical experience with hypothermia in trauma patients has identified hypothermia to be one major cause of severe posttraumatic complications. It was hypothetized that this diverse effect of hypothermia is related to depletion of high energy phosphates like adenosine-tri-phosphate (ATP) in trauma patients. To verify this hypothesis the relation of ATP plasma levels and hypothermia was examined in a clinical study. METHODS: Three different groups of patients were under study. The first group (group A, normothermic control group) included patients (n = 15) undergoing elective surgery of the lower limb with a mean operation time of 113 minutes. The second study group, hypothermic control (group B), comprised patients (n = 15) that were subjected to elective coronary artery bypass operation under hypothermia (31 degrees C for 48 minutes, mean total operation time being 205 minutes). The third study group (group C) included trauma patients (n = 23, mean ISS of 24.7). At the time of admission 10 patients presented a core temperature > or = 34 degrees C (group C1, mean ISS 25.2, mean TA 34.5 degrees C), 13 patients presented a TA < 34 degrees C (group C2, mean ISS 26.0, mean TA 32.9 degrees C). In both groups of surgical patients the ATP plasma level was measured preoperatively, at 2 hr, 4 hr and 24 hr postoperatively. In trauma patients this measurement was performed at admission and 24 hours later. Within the same schedule body core temperature was recorded and the clinical course was documented as well. RESULTS: Elective limb surgery in normothermic patients resulted only in a transient decrease in ATP plasma levels (preoperative: 87.8 mumol/dl, 4 hr postoperative: 52.0 mumol/dl). At 24 hours the ATP plasma level (62.6 +/- 10.0 mumol/dl) has increased towards baseline level. Elective hypothermia in patients subjected to coronary bypass also resulted only in a transient decrease in ATP plasma levels. During the operation period, including hypothermia, the ATP plasma level was comparable (50.4 mumol/dl) to group A and also returned back towards normal values at 24 hours (58.2 mumol/dl). All trauma patients revealed a significant low ATP plasma level at admission as compared to both control groups. Looking at subdivided groups the most significant drop in ATP plasma level (28.5 mumol/dl) was noted in patients presenting an initial core temperature < 34 degrees C and ISS > 30. Even 24 hours later the ATP level of this subgroup was significantly diminished despite a rise up to 44.4 mumol/dl. In contrast an only moderate drop in ATP plasma concentration (59.2 mmol/dl) was noted in the group of TA > or = 34 degrees C and ISS < 20. This group revealed almost normal values (68.3 mmol/dl) 24 hours after trauma. Beside hypothermia the metabolic state, reflected by the plasma lactate levels, significantly influenced the ATP plasma levels, as high lactate levels were paralleled by low ATP levels. Also the over all outcome was related to injury severity and hypothermia. CONCLUSION: Hypothermia in elective surgery, established by active cooling, preserves the ATP storage and maintains an aerobic metabolism, which both contribute to the beneficial effect of hypothermia in ischemia/reperfusion in cardiovascular surgery. However, in trauma patients hypothermia is caused by insufficient heat production due to utilization of ATP under anaerobic metabolic conditions. Low ATP plasma levels combined with hypothermia seem to be a predisposition for posttraumatic complications like organ failure.