Use of Remifentanil for Open in utero Fetal Myelomeningocele Repair Maintains Uterine Relaxation with Reduced Volatile Anesthetic Concentration.

INTRODUCTION Open fetal repair of myelomeningocele (MMC) is an option for prenatally diagnosed spina bifida. Historically, high-dose volatile anesthetic was used for uterine relaxation but is associated with fetal cardiovascular depression. We examined the impact of administering a supplemental remifentanil infusion on the concentration of inhaled anesthetic required for intraoperative uterine relaxation. METHODS We retrospectively analyzed 22 consecutive patients who underwent open fetal MMC repair with desflurane anesthesia from 2014 to 2018. The anesthetic protocol was modified to include high-dose opioid with remifentanil in 2016. We examined intraoperative end-tidal desflurane concentrations, vasopressor use, incidence of umbilical artery Doppler abnormalities, and incidence of preterm labor and delivery. RESULTS Patients (n = 11) who received desflurane and remifentanil (Des/Remi) were compared to patients (n = 11) who received desflurane (Des) alone. Intraoperatively, the maximum end-tidal desflurane required to maintain uterine relaxation was lower in the Des/Remi group (7.9 ± 2.2% vs. 13.1 ± 1.2%, p < 0.001). The mean phenylephrine infusion rate was also lower in the Des/Remi group (36 ± 14 vs. 53 ± 10 mcg/min, p = 0.004). DISCUSSION Use of opioid with supplemental remifentanil was associated with lower volatile anesthetic dosing and decreased vasopressor use; fetal outcomes were not different. Remifentanil may allow for less volatile anesthetic use while maintaining adequate uterine relaxation.