Tourniquet Time and Intraoperative Hypothermia in Knee Arthroscopy: A Prospective Observational Study Comparing General and Spinal Anesthesia

Background and Objectives: Inadvertent perioperative hypothermia is common during arthroscopy, and conductive heat loss from room-temperature irrigation fluid is considered the principal mechanism. Knee arthroscopy has remained largely unstudied. We described the temperature course in knee arthroscopy without active warming, compared general with spinal anesthesia, and examined which variables were associated with heat loss. Materials and Methods: Sixty consecutive patients undergoing elective knee arthroscopy were followed prospectively: 30 received general and 30 spinal anesthesia. None was actively warmed and irrigation fluid was at room temperature. Tympanic temperature was recorded with an infrared ear thermometer before anesthesia, after induction, every 15 min to 120 min, and in recovery. Repeated measurements were analyzed with a linear mixed model; the maximum temperature decrease and the development of hypothermia were examined by multivariable regression. Results: Tympanic temperature fell significantly from 30 min onward, reaching 0.300 °C below baseline at 90 min (p < 0.001). Anesthesia type was not significant (p = 0.162), and the maximum temperature decrease did not differ significantly between groups (difference in means 0.05 °C; 95% confidence interval −0.13 to 0.23; p = 0.395). Hypothermia developed in 22 of 60 patients (36.7%), with no significant between-group difference (p = 0.592). Tourniquet time was associated with the maximum temperature decrease (β = 0.388; p = 0.003) and with the odds of hypothermia (odds ratio 1.42 per 10 min; p = 0.007), but the former was attenuated once procedure category was added (β = 0.268; p = 0.109). Recovery unit stay was shorter after spinal anesthesia (p = 0.003). Conclusions: Hypothermia affected over one third of unwarmed patients. No significant difference was detected between the anesthetic techniques. Longer tourniquet time was associated with greater heat loss and higher odds of hypothermia, although this was closely linked to procedure category and operative duration.