Effect of nitrous oxide on propofol requirement during target-controlled infusion for oocyte retrieval

Oocyte (egg) retrieval for in-vitro fertilization is a relatively short procedure, usually performed as an outpatient. Propofol is a suitable anesthetic agent. Target-controlled infusion is a recently developed system that aids rapid recovery from propofol anesthesia. This study sought to determine the target concentration of propofol required to prevent movement in 50% (Cp50) and 95% (Cp95) of women during oocyte retrieval, and investigated whether supplemental nitrous oxide (N2O) modified the Cp50 and Cp95.

Forty-seven women scheduled for oocyte retrieval were randomly selected to receive either O2-air mixture (control group; n = 23) or 50% O2-N2O mixture (Nitrous oxide group; n = 24). Propofol was infused using a target-controlled infusion system with the concentration determined by up-down sequential allocation using 0.5 microg/mL step size. Transvaginal oocyte retrieval was performed after reaching target blood concentration. Patient responses to oocyte retrieval were noted as either no movement or movement.

Using target-controlled infusion the Cp50 was 4.1 microg/mL in the control group and 3.3 microg/mL in the nitrous oxide group. Calculated Cp95 values were 4.0 microg/mL and 5.1 microg/mL with and without 50% nitrous oxide respectively.

The Cp50 value for target-controlled infusion propofol during oocyte retrieval was significantly reduced by a factor of 1.24 (95% CI 1.07-1.44) with the use of 50% nitrous oxide.