RISK-FACTORS FOR OXYGEN DESATURATION DURING SLEEP, AFTER ABDOMINAL-SURGERY

The postoperative period after major abdominal surgery is known to be a period of increased episodic oxygen desaturation. In order to assess the risk factors for episodic desaturation, we have studied 29 surgical patients using pulse oximetry during the preoperative night (N(pre)) when they received benzodiazepine premedication and breathed-air, and also during the first three nights after operation when they received nasal oxygen supplementation. Modal oxygen saturation (Sp(O2)) exceeded 95% during all nights studied. The time spent at less than 90% (t90) and 85% (t85) Sp(O2), and the average Sp(O2), nadir (Sp(O2,nadir)) did not differ each night. Heart rate was greater (mean 90. 1 (SD 16.6) vs 68.2 (12.0) beat min-1, P < 0.001) during the second night after operation (N2) than during N(pre). Before operation, the number of desaturations, t90 and t85 correlated with pharyngeal hypertrophy (P = 0.003, P = 0.002, P = 0.001, respectively). At the same time, t90 and t85 correlated with body mass index (P = 0.02 and P = 0.05, respectively). During N2, t90 correlated with radiological lung consolidation (P = 0.05) and Sp(O2,nadir) correlated with FEV1 (P = 0.03). We conclude that there are several mechanisms responsible for oxygen desaturation and that these mechanisms differ before and after surgery.