Sleep disruption has been implicated in morbidity after major surgery since 1974. Sleep-related upper airway obstruction has been associated with death after upper airway surgery and profound episodic hypoxaemia in the early postoperative period. There is also evidence for a rebound in rapid eye movement (REM) sleep that might be contributing to an increase in episodic sleep-related hypoxaemic events later in the first postoperative week. Speculation regarding the role of REM sleep rebound in the generation of late postoperative morbidity and mortality has evolved into dogma without any direct evidence to support it. The research presented in this thesis involved two main areas: a search for evidence of a clinically important contribution of REM sleep rebound to postoperative morbidity, and a re-examination of the role of sleep in the causation of postoperative episodic hypoxaemic events. To assess the latter, a relationship between airway obstruction under anaesthesia and the severity of sleep-disordered breathing was sought. In 148 consecutive sleep clinic patients, 49% of those with sleep-disordered breathing (SDB) had a number of events in non-rapid eye movement sleep (NREM) that was greater than or equal to that in REM and 51% had saturation nadirs in NREM that were equal to or worse than their nadirs in REM. This suggests SDB is not a REM-predominant phenomenon for most patients. Of 1338 postoperative deaths occurring over 6.5 years in one hospital only 37 were unexpected, most of which were one or two days after surgery with no circadian variation in the time of death, casting further doubt on the potential role of REM rebound. Five of nine subjects studied preoperatively had moderately severe SDB. Unrecognised and significant SDB is common in middle-aged and elderly patients presenting for surgery suggesting overall perioperative risk of important adverse events from SDB is probably small. In 17 postoperative patients, sleep macro-architecture was variably altered with decreases in REM and slow wave sleep while stage 1 sleep and a state of pre-sleep onset drowsiness, both associated with marked ventilatory instability, were increased. Sleep micro-architecture was also changed with an increase in power in the alpha-beta electroencephalogram range. These micro-architectural changes result in ambiguity in the staging of postoperative sleep that may have affected the findings of this and other studies. Twenty-four subjects with airway management difficulty under anaesthesia were all found to have some degree of SDB. Those with the most obstruction-prone airways while anaesthetised had a very high incidence of severe SDB. Such patients warrant referral to a sleep clinic.
| Identifer | oai:union.ndltd.org:ADTP/220737 |
| Date | January 2005 |
| Creators | Loadsman, John Anthony |
| Publisher | University of Sydney. College of Health Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English, en_AU |
| Detected Language | English |
| Rights | Copyright Loadsman, John Anthony;http://www.library.usyd.edu.au/copyright.html |
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