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 (Npre) 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 (SpO2) exceeded 95% during all nights studied. The time spent at less than 90% (t90) and 85% (t85) SpO2 and the average SpO2 nadir (SpO2, 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 Npre. 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 SpO2, 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.
Infrequent control, aging of components, may compromise the accuracy of ICU ventilators. In order to assess the reliability of ventilators during their clinical use, we bench tested a group of 20 CPU1 ventilators (Ohmeda) sampled at random in several ICU units. We found major leaks in 5 ventilators, attributable to the disposable tubings used in these systems. Mean error in expired tidal volume and corresponding standard deviation (precision) were greater than 100 ml in two. Positive end expiratory pressure measurement comprised a mean error higher than 2 cm H2O in 40% of the ventilators tested. The valve opening pressure threshold was correlated to the inspiratory flow (r = 0.81) contrary to the valve opening delay (average 138 +/- 40 ms). These two parameters did not correlate with the age of the ventilator. Our study addresses the need for periodic control of ventilator performance in order to minimize the risks of errors and malfunctions.
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