Does Mean Body Temperature Matter in the Amout of Intraoperative Blood Loss During Bimaxillary Orthognathic Surgery?
Introduction:
Intraoperative hypothermia during major head and neck surgery occurs secondary to general anesthesia associated alterations in thermoregulation and body heat distribution. Studies have shown that intraoperative hypothermia can increase intraoperative blood loss secondary to coagulopathy.1-3 No such study has been performed to evaluate intraoperative blood loss and thermal regulation in the orthognathic surgery patient population. It is hypothesized, that intraoperative hypothermia will increase quantitative intraoperative blood loss in bimaxillary orthognathic surgery patients.
Methods:
This retrospective study included bimaxillary orthognathic surgery patients from 2008 to 2012, which were treated at the Virginia Commonwealth University Department of Oral and Maxillofacial Surgery. Data collected includes patient demographics, mean arterial pressure (MAP), mean body temperature (MBT), total intraoperative blood loss (TBL), and total operative time (TOT). Patients with craniofacial syndromes, cleft lip and/or palate, hematologic disorders and/or anti-coagulation therapy, single-jaw orthognathic surgery, and previous maxilla and/or mandible surgery were excluded in the study. In the first part of the analysis, patients were stratified by MBT into the hypothermic group (MBT <97.7° F) and the hyperthermic group (MBT >97.7° F). In the second part of the analysis, patients were stratified based on TBL: TBL <500 mL (Group A), TBL between 500-900 mL (Group B), and TBL >900 mL (Group C). Statistical analysis was performed via two-way ANOVA study (StatPlus:mac LE, AnalystSoft Inc.)
Results:
In the study, 70 patients were identified as meeting the previously outlined criteria (36 patients in the hypothermic group and 34 patients in the hyperthermic group). The hypothermic group was found to have a statistically significant reduction in TBL when compared to the hyperthermic group (492 mL vs. 600 mL, p < 0.05). There was no statistically significant difference between the TOT and the MAP between these two groups (p > 0.05). When the patients were stratified by TBL, there was no statistically significant difference in the TOT between Group A and Group B (355 minutes vs. 413 minutes, p > 0.05), but there was a significant difference in TOT between Group B and Group C (413 minutes vs. 511 minutes, p < 0.05). The MBT between Group A and Group B (96.1° F vs. 97.3° F, p < 0.05) is statistically significant, but the MBT between Group B and Group C (97.3° F vs. 97.2° F, p > 0.05) is not. There was no statistically significant difference among Group A, B, and C regarding MAP (p > 0.05).
Discussion:
Based on this study, it is shown that with a MBT <97.7° F TBL is decreased compared to a MBT >97.7° F, independent of TOT and MAP. This reduction in TBL is contradictory to the proposed hypothesis and is likely secondary to hypothermia-associated vasoconstriction. Unlike the study by Sumer et al, the minimal amount of hypothermia produced in these bimaxillary orthognathic surgeries was not significant enough to cause coagulopathy.3 The increased TBL in Group C when compared to Group B, even though they have similar MBT, is likely due to the excessive TOT of Group C. This study shows the importance of managing MBT in bimaxillary orthognathic surgery.
References:
1. Slotman GJ, Jed EH, Burchard KW. Adverse effects of hypothermia in postoperative patients. Am J Surg. 1985; 149(4): 495-501.
2. Schmied H, Kurz A, Sessler DI, Kozek S, Reiter A. Mild hypothermia increases blood loss and transfusion requirements during total hip arthroplasty. Lancet. 1996; 347(8997): 289-292.
3. Sumer BD, Myers LL, Leach J, Truelson JM. Correlation between intraoperative hypothermia and perioperative morbidity in patients with head and neck cancer. Arch Otolaryngol Head Neck Surg. 2009; 135(7): 682-686.