Mannitol improves cerebral oxygen content and postoperative recovery after prolonged retroperitoneal laparoscopy

Prolonged pneumoperitoneum has cerebral adverse effects that may delay recovery and cause postoperative cognitive changes. The purpose of this study was to investigate the effect of mannitol infusion after pneumoperitoneum initiation on cerebral oxygen balance and quality of postoperative recovery in patients undergoing prolonged retroperitoneal laparoscopy.

Forty patients scheduled for retroperitoneal laparoscopic radical excision of prostatic carcinoma were randomly divided into two groups (n = 20, each) to receive either 0.5 g/kg of 20% mannitol 150 min after the initiation of pneumoperitoneum or an equal volume of 0.9% normal saline. After surgery, time to extubation and recovery time were recorded. The Observer's Assessment of Alertness/Sedation (OAA/S) scale was used to assess the quality of recovery. The Mini-Mental State Exam (MMSE) was given to test cognitive function preoperatively and at 1, 2, and 3 h after extubation. Blood samples from the jugular bulb and the radial artery were collected for blood gas analysis before CO2 insufflation and at 10, 60, and 180 min after insufflation.

In the control group (without mannitol), the difference between arterial and venous oxygen content (CaO2-CvO2) before insufflation (6.21 ± 2.58 mL/dL) was significantly greater than it was 3 h after insufflation (2.63 ± 1.29 mL/dL; p < 0.05). Furthermore, 3 h after insufflation, the CaO2-CvO2 also was higher in the group that had been administered mannitol (5.93 ± 1.98 mL/dL) than it was in the control group at that time (p < 0.05). Lactic acid in both arterial and jugular venous blood of the control group at 3 h postinsufflation (2.39 ± 0.89 and 2.51 ± 0.72 mg/dL, respectively) had increased significantly from the preinsufflation values (1.18 ± 0.82 and 1.1 ± 0.85 mg/dL). In the group that received mannitol, the lactic acid levels 3 h postinsufflation were essentially the same as the preinsufflation values. The recovery and extubation times in those receiving mannitol (12.19 ± 2.12 and 20.14 ± 3.62 min, respectively) were significantly shorter than in the control group (21.25 ± 3.61 and 28.79 ± 4.73 min; p < 0.05). The OAAS scores of the mannitol group at the time of extubation and 10 min afterward was significantly higher than these scores in the control group (p < 0.05). One hour and 2 h after extubation, the cognitive function score of the mannitol group was significantly higher than for the control group (p < 0.05).

After prolonged retroperitoneal laparoscopy, there is an imbalance between oxygen supply and demand. A small dose of mannitol can effectively improve cerebral oxygen metabolism, recovery, and cognitive function after the operation.