The Clinical Role of Intraoperative Core Temperature In Free Tissue Transfer

Purpose: Warming measures are routinely utilized during lengthy procedures, yet the optimal intraoperative core temperature in free tissue transfer is controversial.  Some reports suggest that mild hypothermia may reduce the incidence of pedicle thrombosis, however, other surgical disciplines have characterized significant risks associated with intraoperative hypothermia, including increased mortality and surgical site infection.  Since no major report has described the overall clinical impact of core temperature in microvascular reconstruction, this study was designed to better characterize these relationships in the setting of free tissue transfer.

Methods: A retrospective review included all free flaps performed by the plastic surgery service at a major, academic medical center on patients over 18 years of age from December 2005 to December 2010.  All information was queried from the institutional proprietary electronic medical record system and enterprise data warehouse.  Intraoperative core temperatures were measured in all patients by esophageal probe.  Median temperatures recorded over five-minute intervals were utilized to calculate a case mean (T_avg), maximum (T_max) and minimum (T_min).  Outcomes included flap failure, pedicle thrombosis and complications associated with patient and flap morbidity.  Infection was defined as clinical signs of infection involving the flap at the recipient site.  Statistical analysis utilized logistic regression and Student's t-test for comparison of means.

Results: 147 patients received 156 free flaps that met inclusion criteria.  The median T_avg, T_max and T_min were 36.5°, 37.1°, and 35.8°C, respectively.  There was one mortality [0.7%] associated with that patient's primary malignancy.  Overall, the flap failure rate was 8%[13/156].  Pedicle thrombosis occurred in 9[6%] cases and was identified in over half [7/13] of the failed flaps.  Core temperatures were not associated with overall flap failure or pedicle thrombosis, but lower T_avg was a statistically significant predictor of recipient site infection (p < 0.01) [Figure 1].  Infection occurred in 21[13%] patients who, on average, had significantly lower mean core temperatures (T_avg = 36.0°C, p < 0.01).  Risk of infection more than doubled for patients with T_max below the median value (relative risk 2.6, p < 0.05).

Conclusions: No benefit was observed with regard to pedicle thrombosis at lower core temperatures, but intraoperative hypothermia significantly increased the risk of recipient site infection.  These findings support routine intraoperative warming to maintain normothermia in the setting of free tissue transfer.