Exogenous Sex Hormones and Postoperative Nausea and Vomiting Risk in Transgender Patients.

[BACKGROUND] Postoperative nausea and vomiting (PONV) remain a significant consideration in perioperative care; however, the incidence and risk factors of PONV in transgender patients are poorly understood. This study investigated the rates of PONV in transgender patients receiving gender-affirming hormone therapy (GAHT) compared to cisgender patients. We postulate that exogenous testosterone GAHT reduces the risk of PONV while exogenous estrogen GAHT increases the risk of PONV.

[METHODS] This retrospective cohort study was conducted using the TriNetX database. Patients were divided into 2 groups: transgender and cisgender. Separate analyses were performed for hysterectomies (transgender male [assigned female at birth, AFAB] versus cisgender female), orchiectomies (transgender female [assigned male at birth, AMAB] versus cisgender male), and augmentation mammoplasties (transgender female [AMAB] versus cisgender female). Propensity score matching was performed for age, race, and ethnicity (White, Black, Hispanic, or Latino), which were treated as social and demographic variables as recorded in the database, nicotine dependence, and tobacco use. The primary outcome was the administration of a rescue antiemetic, defined as droperidol, promethazine, dimenhydrinate, metoclopramide, and prochlorperazine, on the day of or day following surgery.

[RESULTS] Following hysterectomy, there was a significant difference in the risk of rescue antiemetic use between transgender males (AFAB) taking testosterone GAHT (62.11%, 1031 of 1660) and cisgender females (65.90%, 1094 of 1660) (P = .0227). Following orchiectomy, there was a significant difference in the risk of rescue antiemetic use between transgender females (AMAB) taking estrogen GAHT (51.15%, 445 of 870) and cisgender males (36.78%, 320 of 870) (P < .0001). Following augmentation mammoplasty, there was a significant difference in the risk of rescue antiemetic use between transgender females (AMAB) taking estrogen GAHT (53.29%, 356 of 668) and cisgender females (43.71%, 292 of 668) (P = .0005).

[CONCLUSIONS] Transgender female (AMAB) patients on estrogen GAHT required rescue antiemetics more often than cisgender males and cisgender females after orchiectomies and augmentation mammoplasties. Transgender male (AFAB) patients on testosterone GAHT required rescue antiemetics less often than cisgender females after hysterectomies. These findings underscore the need for individualized perioperative care and antiemetic prophylaxis to promote equitable anesthetic care for transgender patients. This study's retrospective design limits causal inference and is subject to coding errors and residual confounding. Prospective studies with detailed perioperative and hormonal data are needed to validate these findings and clarify how the timing, dosage, and duration of GAHT influence PONV risk.