Adenosine-triphosphate (ATP) in accidental and elective hypothermia

Background: In trauma patients hypothermia is a frequent event. According t o the literature the majority of trauma patients are presenting a core temp erature 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 adeno sine-tri-phosphate (ATP) in trauma patients. To verify this hypothesis the relation of ATP plasma levels and hypothermia was examined in a clinical st udy. Methods: Three different groups of patients were under study. The first gro up (group A, normothermic control group) included patients (n = 15) undergo ing elective surgery of the lower limb with a mean operation time of 113 mi nutes. The second study group, hypothermic control (group B), comprised pat ients (n = 15) that were subjected to elective coronary artery bypass opera tion under hypothermia (31 degrees C for 48 minutes, mean total operation t ime being 205 minutes). The third study group (group C) included trauma pat ients (n = 23, mean ISS of 24.7). At the time of admission 10 patients pres ented a core temperature greater than or equal to 34 degrees C (group C1, m ean ISS 25.2, mean TA 34.5 degrees C), 13 patients presented a TA <34 degre es C (group C2, mean ISS 26.0, mean TA 32.9 degrees C). In both groups of s urgical patients the ATP plasma level was measured preoperatively, at 2 hr, 4 hr and 24 hr postoperatively. In trauma patients this measurement was pe rformed 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 mu mol/dl, 4hr postoperative: 52.0 mu mol/dl). At 24 hours the ATP plasma level (62.6 +/- 10.0 mu mol/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 hypot hermia, the ATP plasma level was comparable (50.4 mu mol/dl) to group A and also returned back towards normal values at 24 hours (58.2 mu mol/dl). All trauma patients revealed a significant low ATP plasma level at admission a s compared to both control groups. Looking at subdivided groups the most si gnificant drop in ATP plasma level (28.5 mu mol/dl) was noted in patients p resenting an initial core temperature <34 degrees C and ISS>30. Even 24 hou rs later the ATP level of this subgroup was significantly diminished despit e a rise up to 44.4 mu mol/dl. In contrast an only moderate drop in ATP pla sma concentration (59.2 mmol/dl) was noted in the group of TA greater than or equal to 34 degrees C and ISS<20. This group revealed almost normal valu es (68.3 mmol/dl) 24 hours after trauma. Beside hypothermia the metabolic s tate, 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 cause d 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.