Discussion
In our study, we observed that the amount of propofol administered to patients during the transvaginal oocyte retrieval procedure was higher when administered as an infusion with BIS monitoring, compared to the administration as bolus doses according to the clinical conditions of the patients.
There are studies showing that the success of the oocyte retrieval process does not change with the applied anesthesia methods [5, 14, 15]. But there is increasing concern about the potential detrimental effects of different types of anesthesia on the quality of the oocytes and, consequently, on the reproductive outcome [3]. Since it has been shown that exposure to anesthetic drugs, especially for a long time, has negative effects on fertilization [8, 16], it is recommended that the oocyte should be exposed to anesthetic agents at a minimum level [16, 17]. Therefore, it is critical to administer the appropriate agent at the appropriate dose and duration in anesthesia [18].
Propofol is one of the most preferred drugs for anesthesia in oocyte retrieval, due to its short onset time and rapid recovery from anesthesia [13]. Nevertheless, there are conflicting results regarding the effect of propofol used in oocyte retrieval on fertilization. In their 1997 editorial, Hein and his colleagues ask the following question: ”What we do really know about propofol’s effects on human reproduction?” [19]. It seems very difficult to find the exact answer to this question. The results of studies are confusing.
Alsalili et al., in their study on the effect of propofol on oocyte maturation and fertilization, concluded that although propofol did not affect fertilization, high propofol concentrations could impair in vitro oocyte maturation in mice [20]. Although Ben-Shlomo et al. could not show a relationship between the duration of anesthesia and propofol concentrations in the follicular fluid [21], Janssenwillen et al. conducted a study on mouse oocytes and showed that propofol accumulates in the follicular fluid in a dose- and time-dependent manner [6]. They suggested caution in the clinical use of propofol during oocyte retrieval [6]. Similarly to animal studies, it was determined that propofol accumulates in the follicular fluid depending on the dose and duration in studies conducted in humans [7, 8]. Considering the possible adverse effects on fertility during anesthesia, it is recommended to limit the total dose and duration of propofol administration [7, 8].
In previous studies, it has been demonstrated that using BIS monitoring reduces the amount of anesthetic drug used [9, 12]. It was also stated in these studies that the recovery of patients after anesthesia was faster [9, 12].
Gan et al. demonstrated that adding BIS monitoring to standard anesthesia practice reduced the propofol infusion rate and the total amount of propofol used. In our study, we could not observe similar results in general anesthesia applied with BIS monitoring. In their study, Gan et al. adjusted their propofol infusions to reach the target BIS value of 45-60, but they allowed the BIS value to increase to 60-75 in the last 15 minutes of the case. Considering that our target value for BIS value is in the range of 40-60 and the average procedure time is 16 minutes in our study, it is understood that the target BIS values are very different from the study of Gan et al. [9]. They also showed that BIS facilitates the titration of propofol, which improves patients’ recovery from anesthesia [9]. In the postoperative period, the time to reach the PADSS≥9 value, which was considered suitable for discharge, was longer in the group BIS than in the group bolus in our study. This result is not surprising considering that the total dose of propofol used was higher in the group BIS than in the bolus group.
Luginbühl et al. reported that BIS monitoring reduced propofol use and accelerated recovery after propofol anesthesia. In this study, it was stated that the drug concentration was adjusted to keep the BIS between 45-55 during the surgery in patients with BIS monitoring. However, if the BIS increased above the target level, they preferred to apply muscle relaxants before increasing the drug concentration [12]. It is not surprising that the amount of propofol used with this method is low. In our study, the highest targeted BIS value was 60 during the procedure, and propofol infusion rate was increased instead of giving muscle relaxants when the BIS value of the patients exceeded the target value. In addition, in the above-mentioned study, the BIS value was allowed to rise up to 65 in the last 15 minutes of the procedure. In this case, it can be said that the target BIS value in our study is completely different from this study. Therefore, it was inevitable that we would come to a different conclusion from Luginbuhl et al. [12].
Based on the results of our study, is it realistic to say that the amount of propofol used increased by using BIS, contrary to the results of previous studies? Or should a more appropriate target be determined for BIS value during anesthesia for oocyte retrieval? Circeo et al. observed that the mean BIS ranged from 47 to 53 during oocyte retrieval, and they recommended this range as a target. However, artificial airway insertion was not used in any patient in this study [1]. Since we are used to insert laryngeal masks under general anesthesia in all patients during oocyte retrieval, we targeted the BIS value within the recommended range of 40-60 for general anesthesia.
In the present study, the patients in the bolus group were given propofol according to their clinical responses, without BIS monitoring. Patients were questioned about their satisfaction before being discharged after the procedure. Fifty-nine patients in this group said that they were very satisfied with the anesthesia, while the other two patients said they were satisfied. No patient was dissatisfied with the anesthesia method applied. This finding shows that even if propofol is given according to the clinical response of the patient without BIS monitoring, patient satisfaction is high and sufficient depth of anesthesia can be provided for the patient.
We did not use BIS in the group bolus, so we cannot recommend the BIS value that should be targeted for oocyte retrieval based on the results of our study. Considering these findings, we think that the targeted BIS value should be reconsidered for patients undergoing oocyte retrieval under general anesthesia.
In the present study, we could not confirm our hypothesis that we could reduce the amount of propofol administered for general anesthesia in patients undergoing transvaginal oocyte retrieval procedure for IVF treatment, when BIS is targeted in the 40-60 range. This brought us to the conclusion that further studies with more specific methodology and larger series are needed to determine the appropriate target value in the depth of anesthesia when BIS is used during anesthesia for oocyte retrieval.
Intraoperatively, we were unable to use a double-blind study design. The anesthesiologist who administered the anesthesia and recorded the results during the procedure was not blind. This is a major limitation of our study.