The effects of permissive hypercapnia on regional cerebral oxygen saturation and postoperative delirium in obese patients undergoing laparoscopic bariatric surgery: a randomized controlled trial

The aim of the study was to investigate the effect of permissive hypercapnia on regional cerebral oxygen saturation (rScO2) in obese patients undergoing sleeve gastrectomy and its association with the development of delirium. In this randomized controlled trial, 83 patients undergoing elective laparoscopic sleeve gastrectomy were randomly divided into two groups. Respiratory parameters were adjusted to achieve the target PaCO2 in each group by pressure-controlled ventilation-volume guaranteed (PCV-VG) mode. In the hypercapnia group, permissive hypercapnia was induced by the lung-protective ventilation strategy, and the target PaCO2 was set at 50 mmHg, remaining from 45 to 55 mmHg. In the normocapnia group, the target PaCO2 was set at 40 mmHg, remaining from 35 to 45 mmHg. The changes of rScO2 were recorded at various times from before induction to the end of surgery. The incidence of cerebral oxygen desaturation events (CDE), and the variables of hemodynamic, respiratory and arterial blood gas were also calculated. Furthermore, the incidence of sub-delirium and delirium, and S100β protein levels were measured within three days after surgery. The incidence of postoperative pulmonary complications (PPCs) was observed within five days after surgery. The rScO2 values in the hypercapnia group during surgery were significantly higher than those in the normocapnia group (P<0.05). Moreover, the incidence of CDE was also significantly lower. There were significant differences in peak inspiratory pressure, lung dynamic compliance, PaCO2 and pH during surgery. In addition, the outcome of subsyndromal delirium/delirium was significantly lower in the hypercapnia group than that in the normocapnia group (P<0.05). S100β protein levels were also lower in the hypercapnia group within three days after surgery (P<0.05). No difference was found in PPCs. Permissive hypercapnia can enhance cerebral oxygenation and decrease postoperative S100β protein levels in obese patients undergoing laparoscopic sleeve gastrectomy, which is beneficial for reducing the incidence of postoperative delirium.