Impact of timing of preoperative gabapentin administration on postoperative somnolence.

Context: Enhanced Recovery After Surgery (ERAS) is a multimodal protocol aimed to improve quality of postoperative recovery, minimize complications, and optimize overall self-regulation. Preoperative gabapentin decreases postoperative pain but can be associated with prolonged postoperative somnolence and respiratory depression risk. Although it is known that gabapentin affects the postoperative course, it is unclear if the timing of preoperative administration affects this finding.

Objectives: This study aims to assess the optimal preoperative timing for gabapentin administration in patients undergoing gynecologic surgery to minimize postoperative somnolence risk.

Methods: A retrospective cohort study evaluated patients who underwent major gynecologic surgery and received preoperative gabapentin. Patients were grouped based on timing from gabapentin administration to surgical incision (<4 h group vs. ≥4 h group). Preoperative, intraoperative, and postoperative data were abstracted and compared. Univariate associations between the timing of gabapentin administration and the patient and surgical characteristics and outcomes were tested utilizing two-sample equal-variance t-tests, linear model ANOVA, or Fisher's exact tests. Associations between the timing of gabapentin administration and the time until the Richmond Agitation Sedation Scale (RASS) score of 0 were modeled utilizing linear regression, adjusted for age, initial postoperative anesthesia care unit (PACU), RASS score, and postoperative narcotics.

Results: Each group contained 127 patients. Demographics were similar except for age (<4 h group mean=44.2 years; ≥4 h group mean=40.5 years; p=0.021), chronic pain (<4 h group=17.6%; ≥4 h group=43.3%; p<0.001), and surgical indication (<4 h group=pelvic pain [29.1%]; ≥4 h group=pelvic pain [51.2%]; p=0.007). The <4 h group had a similar postoperative narcotic administration (<4 h group mean morphine milligram equivalents [MME]=3.667; ≥4 h group mean MME=4.833; p=0.185). The minutes from surgical closure until the patient received a RASS score of 0 and initial PACU pain score (Visual Analogue Scale [VAS]) were similar. The initial PACU oxygen administration volume, hours from surgical closure until the patient transitioned to room air, and initial PACU respiratory rate were similar. The PACU duration, admission secondary to somnolence, and initial PACU Glasgow Coma Scale (GCS) score showed no difference. Postoperative nausea/vomiting was decreased in the ≥4 h group (<4 h group=24.4%; ≥4 h group=13.4%; p-value=0.036), and urinary retention (<4 h group=14.2%; ≥4 h group=5.5%; p-value=0.033) was decreased in the ≥4 h group.

Conclusions: The timing of gabapentin administration less than or more than 4 h preoperatively in patients 18 years does not significantly affect postoperative somnolence or respiratory depression. Further, it does not have a significant effect on GCS scores or VAS scores.