Supplemental oxygen reduces serotonin levels in plasma and platelets during colorectal surgery and reduces postoperative nausea and vomiting.

Background And Objective: it has been shown that supplemental oxygen reduces the incidence of postoperative nausea and vomiting (PONV) in patients undergoing colon surgery. Serotonin is a potent trigger of PONV. Theoretically, supplemental oxygen decreases gut ischaemia during surgery and in this way minimizes the release of serotonin. We investigated the release of serotonin during and after colorectal surgery with normal and supplemental oxygen administration.

Methods: patients (n = 53) undergoing colon surgery were randomly assigned to one of two intraoperative ventilation regimens: group A (n = 30) received 80% oxygen and 20% nitrogen mixed with desflurane and group B (n = 23) received 30% oxygen and 70% nitrogen mixed with desflurane. To verify oxygenation status, we measured the arterial oxygen partial pressure (pO2) by blood gas analysis and the intramuscular tissue oxygenation using a polarographic microoxygen sensor (Licox, GMS, Mielkendorf, Germany). Serotonin levels in plasma and in platelets were measured using high-performance liquid chromatography (HPLC) before the beginning of surgery (T0), at the end of surgery (T1), and 2 h (T2), 8 h (T3) and 24 h (T4) postoperatively. PONV was assessed in the early (0-4 h) and overall (0-24 h) postoperative period by an anaesthesiologist unaware of patients' treatment regime.

Results: at T1, T2 and T3, serotonin levels were significantly (T1 '80% group' 80 ± 68.2 vs. '30% group' 147 ± 130.5; T2 '80% group' 78.4 ± 61 vs. '30% group' 139 ± 103; T3 '80% group' 76.2 ± 49.5 vs. '30% group' 124 ± 73.7; P < 0.05) reduced in the '80% oxygen group'. Patients in the '80% group' showed a significantly higher pO2 and subcutaneous tissue oxygenation (ptO2). The overall incidence of PONV was significantly reduced in the '80% oxygen group' ('80% group' 7% vs. '30% group' 35%).

Conclusion: an inspired oxygen fraction of 0.8 reduces serotonin levels significantly and decreases PONV significantly in patients undergoing colon surgery.