Effect of sex differences in remifentanil requirements for inhibiting the response to a CO(2) pneumoperitoneum during propofol anesthesia: an up-and-down sequential allocation trial

BACKGROUND: A CO(2) pneumoperitoneum during a laparoscopic procedure causes violent hemodynamic changes. However, the remifentanil required to inhibit the cardiovascular response to a CO(2) pneumoperitoneum combined with propofol remains unknown. Moreover, the sex of the patient may influence the response to opioids, which can affect this requirement. The main objective of this study was to compare the required median effective concentration (EC(50)) of remifentanil for inhibiting the cardiovascular response to a CO(2) pneumoperitoneum between female and male patients during propofol anesthesia. METHODS: The current study is an up-and-down sequential allocation trial. Forty-six patients with American Society of Anesthesiologists physical status I or II, a body mass index 18 to 30 kg/m(2), aged 20 to 60 years, and scheduled for laparoscopic surgery were enrolled. Induction of anesthesia was performed by target-controlled infusion. The effective effect-site concentration (Ce) of propofol was 4 μg/ml. The Ce of remifentanil was initially 4 ng/ml and then adjusted to a predetermined level after I-gel laryngeal mask airway insertion. The Ce of remifentanil for each patient was determined by the response of the previous patient using the modified Dixon “up-and-down” method. The first patient received remifentanil at 5.0 ng/ml Ce, and the step size between patients was 0.5 ng/ml. RESULTS: Patients characteristics including age, body mass index, American Society of Anesthesiologists physical status, type of surgery and surgery duration, were comparable between male and female patients. The EC(50) of remifentanil required to inhibit the response to a CO(2) pneumoperitoneum based on the Dixon “up-and-down” method in women (4.17 ± 0.38 ng/ml) was significantly lower than that in men (5.00 ± 0.52 ng/ml) during propofol anesthesia (P = 0.01). CONCLUSIONS: The EC(50) of remifentanil required to inhibit the response to a CO(2) pneumoperitoneum was lower in women than in men during propofol anesthesia. TRIAL REGISTRATION: The study was registered at http://www.chictr.org.cn (ChiCTR-IOR-17011906, 8th, July, 2017).