The effects of high, normal and low flow anesthesia methods on postoperative cognitive functions in rhinoplasty patients undergoing hypotensive anesthesia

Aim: Different flow techniques can be used for general anesthesia and low flow anesthesia trends are increasing nowadays. Low flow anesthesia modalities have a numerous positive impacts, including ecology, economy and patient care. But flow rates between 2 L/min and 6 L/min are still commonly used. To increase the surgical area awareness, lower the blood loss and complication rates, controlled hypotension is a useful modality among rhinoplasty cases. The number of studies conducted on the positive effects of anesthesia techniques and drugs that enable rapid recovery of cognitive functions are increasing. The Montreal Cognitive Assessment test (MoCA) is used commonly for evaluating the early stages of cognitive functions and studies have shown that it is superior to the other tests. It is suggested that these differing flow modalities and controlled hypotension procedures might have variating effects on cognitive functions. Thus our aim in this study was to evaluate the effects of Low, Normal and High flow rate anesthesia with controlled hypotension on cognitive dysfunction. Material and methods: This study was conducted following the approval of the Erzincan Binali University ethics committee. A total of 150 patients between the ages 18-65 which were planned for +2 hours of elective rhinoplasty, among ASA Class I and II were included to our study. It was planned as a prospective observational study. Patients were divided into 3 groups according to the flow rate: low flow anesthesia (1 L/min) group as "Group D" (n=50), high flow rate (4 L/min) group as "Group Y" (n=50), and normal flow rate (2 L/min) group as "Group N" (n=50). In order to create controlled hypotension among patients remifentanyl infusion was given to ensure a mean arterial pressure between 60-70 mmHg. The vital signs of the patients were recorded preoperatively, at the 0th, 30th, 60th, and 120th minutes after intubation. MoCA test was performed on patients as following: the first hour preoperatively; the 1st hr, 24th hr, and 1st month postoperatively. Results: No statistically significant difference was found among vital signs between the flow groups. A significant difference was found between mean arterial pressure and peak heart rate in the preoperative and postoperative 0th min groups; as well as the postoperative 0th min and 30th min groups. No significant difference was found among flow groups according to the MoCA results. The comparative results between the conduction periods of MoCA test was as following: no significant difference between preoperative and postoperative 24th hr, or between postoperative 24th hr and 1 month among normal and high flow rate groups. In contrast there 4 was a significant difference among the low flow rate group with the aforementioned periods (p<0.05). Conclusions: As we induced controlled hypotension with varying flow rates of anesthesia in this study, we determined that postoperative cognitive functions were better preserved with low flow anesthesia. We strongly argue that low flow anesthesia modalities should be used more widely in routine practice.