In normal patients, progression of core hypothermia after induction of general anesthesia is usually halted by reemergence of thermoregulatory vasoconstriction. In diabetic patients with impaired peripheral neurovascular function, this thermoregulatory mechanism may not reappear. To determine the extent to which diabetic patients may be at greater risk of intraoperative hypothermia, Kitamura et al. compared the threshold for intraoperative vasoconstriction in diabetic and nondiabetic patients scheduled for elective abdominal surgery.
The diabetic (n = 27) and nondiabetic (n = 36) patients were divided into younger (less than 60 years old) and older (more than 60 years old) groups. Autonomic function was assessed in all participants before the study using three standard noninvasive tests: heart rate variation at deep periodical breathing, Valsalva’s maneuver, and head-up tilt. Anesthetic techniques were standardized for each patient, using fentanyl/propofol for induction and vecuronium to facilitate endotracheal intubation. Intraoperative monitoring included blood glucose levels, core temperature measured continuously at the tympanic membrane, mean skin temperature, and fingertip blood flow. Patients were covered with a single surgical drape in a 23°C environment, and rewarmed after the study with a forced-air warmer. Most of the procedures (70–90%) lasted more than 2 h, with mean blood loss at 265 ml. Changes in core temperature were similar in all groups at 75 min after induction of anesthesia, but from 120 min onward, the core temperature of diabetics with previously established autonomic dysfunction was significantly lower, decreasing to 34.6°C at 180 min. The researchers found that the vasoconstriction threshold decreased in relation to autonomic insufficiency in the diabetic patients. Thermoregulatory vasoconstriction was also more inhibited in the elderly than in the younger control patients.
By combining three tests of autonomic response, the authors believed they obtained a higher specificity for defining dermatosympathetic responses in diabetics. Accordingly, a simple form of autonomic screening combined with the clinical history might provide useful information to the anesthesiologist when planning anesthetic management of the diabetic patient.