Late postoperative hypoxaemia

摘要

Major surgery may be followed by complications such as myocardial infarction, wound infection, impaired wound healing, and mental disturbances, which can not only be explained by imperfections in surgical technique but rather may be due to increased organ demands caused by the endocrine metabolic response to surgical trauma (Kehlet 1988). Hypoxaemia, leading to decreased oxygen supply to body organs, may be an amplifying or precipitating factor in the above mentioned postoperative morbidity parameters. It is important to distinguish between hypoxia, which is determined by the supply/demand ratio of oxygen in peripheral tissue, and hypoxaemia, which simply means lowered arterial oxygen content (Gilston 1991). This review will deal with hypoxaemia in the late postoperative period, that is when the patient is back in the surgical ward, and usually without intensive monitoring. Episodic hypoxaemia is detectable with continuous monitoring and has therefore only recently been demonstrated. Continuous non-invasive monitoring of the arterial oxygen status has been possible since the early 1980's where pulse oximetry became widely available. The first study to monitor patients continuously for 16 hours in the post anaesthesia care unit was published in 1985 showing that a high number of sudden hypoxaemic events occurred in the first eight hours after surgery (Catley et al. 1985). These events were only seen when the patients were sleeping, and were usually related to ventilatory dysrythmias such as obstructive apnoeas and hypoventi-lation (Catley et al. 1985). Subsequently, studies describing episodic hypoxaemia in the late postoperative period were published (Knill et al. 1987, Rosenberg et al. 1989). These studies showed almost no hypoxaemic episodes on the first postoperative night whereas the second and third postoperative nights were characterized by a significant increase in episodic hypoxaemia compared with the preoper-ative night (Knill et al. 1987, Rosenberg et al. 1989).