Identifying Risk of Postoperative Cardiorespiratory Complications in OSA.

BACKGROUND: Patients with OSA are at increased risk of postoperative cardiorespiratory complications and death. Attempts to stratify this risk have been inadequate, and predictors from large, well-characterized cohort studies are needed. RESEARCH QUESTION: What is the relationship between OSA severity, defined by various polysomnography-derived metrics, and risk of postoperative cardiorespiratory complications or death, and which metrics best identify such risk? STUDY DESIGN AND METHODS: In this cohort study, 6,770 consecutive patients who underwent diagnostic polysomnography for possible OSA and a procedure involving general anesthesia within a period of 2 years before and at least 5 years after polysomnography. Participants were identified by linking polysomnography and health databases. Relationships between OSA severity measures and the composite primary outcome of cardiorespiratory complications or death within 30 days of hospital discharge were investigated using univariable and multivariable analyses. RESULTS: The primary outcome was observed in 5.3% (n = 361) of the cohort. Although univariable analysis showed strong dose-response relationships between this outcome and multiple OSA severity measures, multivariable analysis showed its independent predictors were: age older than 65 years (OR, 2.67 [95% CI, 2.03-3.52]; P < .0001), age 55.1 to 65 years (OR, 1.47 [95% CI, 1.09-1.98]; P = .0111), time between polysomnography and procedure of ≥ 5 years (OR, 1.32 [95% CI, 1.02-1.70]; P = .0331), BMI of ≥ 35 kg/m2 (OR, 1.43 [95% CI, 1.13-1.82]; P = .0032), presence of known cardiorespiratory risk factor (OR, 1.63 [95% CI, 1.29-2.06]; P < .0001), > 4.7% of sleep time at an oxygen saturation measured by pulse oximetry of < 90% (T90; OR, 1.91 [95% CI, 1.51-2.42]; P < .0001), and cardiothoracic procedures (OR, 7.95 [95% CI, 5.71-11.08]; P < .0001). For noncardiothoracic procedures, age, BMI, presence of known cardiorespiratory risk factor, and percentage of sleep time at an oxygen saturation of < 90% remained the significant predictors, and a risk score based on their ORs was predictive of outcome (area under receiver operating characteristic curve, 0.7 [95% CI, 0.64-0.75]). INTERPRETATION: These findings provide a basis for better identifying high-risk patients with OSA and determining appropriate postoperative care.

Does OSA Increase Risk for Cancer?: A Large Historical Sleep Clinic Cohort Study.

BACKGROUND: The relationship between OSA and cancer is unclear. RESEARCH QUESTION: What is the association between OSA and cancer prevalence and incidence in a large Western Australian sleep clinic cohort (N = 20,289)? STUDY DESIGN AND METHODS: OSA severity was defined by apnea-hypopnea index (AHI) and nocturnal hypoxemia (duration and percentage at oxygen saturation < 90%) measured by in-laboratory polysomnogram. Measures of potential confounding included age, sex, BMI, smoking status, socioeconomic status, and BP. Outcomes were determined from the Western Australian cancer and death registries. Analyses were confined within periods using consistent AHI scoring criteria: January 1, 1989, to July 31, 2002 (American Sleep Disorders Association criteria), and August 1, 2002, to June 30, 2013 (Chicago criteria). We examined associations of AHI and nocturnal hypoxemia with cancer prevalence using logistic regression and cancer incidence using Cox regression analyses. RESULTS: Cancer prevalence at baseline was 329 of 10,561 in the American Sleep Disorders Association period and 633 of 9,728 in the Chicago period. Nocturnal hypoxemia but not AHI was independently associated with prevalent cancer following adjustment for participant age, sex, BMI, smoking status, socioeconomic status, and BP. Of those without prevalent cancer, cancer was diagnosed in 1,950 of 10,232 (American Sleep Disorders Association) and 623 of 9,095 (Chicago) participants over a median follow-up of 11.2 years. Compared with the reference category (no OSA, AHI < 5 events per hour), univariable models estimated higher hazard ratios for cancer incidence for mild (AHI 5-15 events per hour), moderate (AHI 15.1-30 events per hour), and severe (AHI > 30 events per hour) OSA. Multivariable analyses consistently revealed associations between age and, in some cases, sex, BMI, and smoking status, with cancer incidence. After adjusting for confounders, multivariable models showed no independent association between OSA severity and increased cancer incidence. INTERPRETATION: Nocturnal hypoxemia is independently associated with prevalent cancer. OSA severity is associated with incident cancer, although this association seems secondary to other risk factors for cancer development. OSA is not an independent risk factor for cancer incidence.

Prevalence and patterns of multimorbidity in Australian baby boomers: the Busselton healthy ageing study.

BACKGROUND AND OBJECTIVE: Chronic medical conditions accumulate within individuals with age. However, knowledge concerning the trends, patterns and determinants of multimorbidity remains limited. This study assessed the prevalence and patterns of multimorbidity using extensive individual phenotyping in a general population of Australian middle-aged adults. METHODS: Participants (n = 5029, 55% female), born between 1946 and 1964 and attending the cross-sectional phase of the Busselton Healthy Ageing Study (BHAS) between 2010 and 2015, were studied. Prevalence of 21 chronic conditions was estimated using clinical measurement, validated instrument scores and/or self-reported doctor-diagnosis. Non-random patterns of multimorbidity were explored using observed/expected (O/E) prevalence ratios and latent class analysis (LCA). Variables associated with numbers of conditions and class of multimorbidity were investigated. RESULTS: The individual prevalence of 21 chronic conditions ranged from 2 to 54% and multimorbidity was common with 73% of the cohort having 2 or more chronic conditions. (mean ± SD 2.75 ± 1.84, median = 2.00, range 0-13). The prevalence of multimorbidity increased with age, obesity, physical inactivity, tobacco smoking and family history of asthma, diabetes, myocardial infarct or cancer. There were 13 pairs and 27 triplets of conditions identified with a prevalence > 1.5% and O/E > 1.5. Of the triplets, arthritis (> 50%), bowel disease (> 33%) and depression-anxiety (> 33%) were observed most commonly. LCA modelling identified 4 statistically and clinically distinct classes of multimorbidity labelled as: 1) "Healthy" (70%) with average of 1.95 conditions; 2) "Respiratory and Atopy" (11%, 3.65 conditions); 3) "Non-cardiometabolic" (14%, 4.77 conditions), and 4) "Cardiometabolic" (5%, 6.32 conditions). Predictors of multimorbidity class membership differed between classes and differed from predictors of number of co-occurring conditions. CONCLUSION: Multimorbidity is common among middle-aged adults from a general population. Some conditions associated with ageing such as arthritis, bowel disease and depression-anxiety co-occur in clinically distinct patterns and at higher prevalence than expected by chance. These findings may inform further studies into shared biological and environmental causes of co-occurring conditions of ageing. Recognition of distinct patterns of multimorbidity may aid in a holistic approach to care management in individuals presenting with multiple chronic conditions, while also guiding health resource allocation in ageing populations.

Sleep Loss in the Hospitalized Patient and Its Influence on Recovery From Illness and Operation.

Adequate sleep is essential to health and well-being. Adverse effects of sleep loss are evident acutely and are cumulative in their effect. These include impairment of cognition, psychomotor function, and mood, as well as cardiovascular, metabolic, and immune dysfunction including proinflammatory effects and increased catabolic propensity. Such effects are counterproductive to recovery from illness and operation, yet hospitalization challenges sleep through the anxieties, discomforts, and sleep environmental challenges faced by patients, the inadequate attention given to the needs of patients with preexisting sleep disorders, and the lack of priority these issues receive from hospital staff and their leaders. Mitigation of the adverse effects of noise, light, uncomfortable bedding, intrusive observations, anxiety, and pain together with attention to specific sleep needs and monitoring of sleep quality are steps that would help address the issue and potentially improve patient outcomes.

Sequencing Analysis at 8p23 Identifies Multiple Rare Variants in DLC1 Associated with Sleep-Related Oxyhemoglobin Saturation Level.

Average arterial oxyhemoglobin saturation during sleep (AvSpO2S) is a clinically relevant measure of physiological stress associated with sleep-disordered breathing, and this measure predicts incident cardiovascular disease and mortality. Using high-depth whole-genome sequencing data from the National Heart, Lung, and Blood Institute (NHLBI) Trans-Omics for Precision Medicine (TOPMed) project and focusing on genes with linkage evidence on chromosome 8p23,1,2 we observed that six coding and 51 noncoding variants in a gene that encodes the GTPase-activating protein (DLC1) are significantly associated with AvSpO2S and replicated in independent subjects. The combined DLC1 association evidence of discovery and replication cohorts reaches genome-wide significance in European Americans (p = 7.9 × 10-7). A risk score for these variants, built on an independent dataset, explains 0.97% of the AvSpO2S variation and contributes to the linkage evidence. The 51 noncoding variants are enriched in regulatory features in a human lung fibroblast cell line and contribute to DLC1 expression variation. Mendelian randomization analysis using these variants indicates a significant causal effect of DLC1 expression in fibroblasts on AvSpO2S. Multiple sources of information, including genetic variants, gene expression, and methylation, consistently suggest that DLC1 is a gene associated with AvSpO2S.

Knowledge Gaps in the Perioperative Management of Adults with Obstructive Sleep Apnea and Obesity Hypoventilation Syndrome. An Official American Thoracic Society Workshop Report.

The purpose of this workshop was to identify knowledge gaps in the perioperative management of obstructive sleep apnea (OSA) and obesity hypoventilation syndrome (OHS). A single-day meeting was held at the American Thoracic Society Conference in May, 2016, with representation from many specialties, including anesthesiology, perioperative medicine, sleep, and respiratory medicine. Further research is urgently needed as we look to improve health outcomes for these patients and reduce health care costs. There is currently insufficient evidence to guide screening and optimization of OSA and OHS in the perioperative setting to achieve these objectives. Patients who are at greatest risk of respiratory or cardiac complications related to OSA and OHS are not well defined, and the effectiveness of monitoring and other interventions remains to be determined. Centers involved in sleep research need to develop collaborative networks to allow multicenter studies to address the knowledge gaps identified below.

Multiethnic Meta-Analysis Identifies RAI1 as a Possible Obstructive Sleep Apnea-related Quantitative Trait Locus in Men.

Obstructive sleep apnea (OSA) is a common heritable disorder displaying marked sexual dimorphism in disease prevalence and progression. Previous genetic association studies have identified a few genetic loci associated with OSA and related quantitative traits, but they have only focused on single ethnic groups, and a large proportion of the heritability remains unexplained. The apnea-hypopnea index (AHI) is a commonly used quantitative measure characterizing OSA severity. Because OSA differs by sex, and the pathophysiology of obstructive events differ in rapid eye movement (REM) and non-REM (NREM) sleep, we hypothesized that additional genetic association signals would be identified by analyzing the NREM/REM-specific AHI and by conducting sex-specific analyses in multiethnic samples. We performed genome-wide association tests for up to 19,733 participants of African, Asian, European, and Hispanic/Latino American ancestry in 7 studies. We identified rs12936587 on chromosome 17 as a possible quantitative trait locus for NREM AHI in men (N = 6,737; P = 1.7 × 10-8) but not in women (P = 0.77). The association with NREM AHI was replicated in a physiological research study (N = 67; P = 0.047). This locus overlapping the RAI1 gene and encompassing genes PEMT1, SREBF1, and RASD1 was previously reported to be associated with coronary artery disease, lipid metabolism, and implicated in Potocki-Lupski syndrome and Smith-Magenis syndrome, which are characterized by abnormal sleep phenotypes. We also identified gene-by-sex interactions in suggestive association regions, suggesting that genetic variants for AHI appear to vary by sex, consistent with the clinical observations of strong sexual dimorphism.

Perioperative management of obstructive sleep apnea in bariatric surgery: a consensus guideline.

BACKGROUND: The frequency of metabolic and bariatric surgery (MBS) is increasing worldwide, with over 500,000 cases performed every year. Obstructive sleep apnea (OSA) is present in 35%-94% of MBS patients. Nevertheless, consensus regarding the perioperative management of OSA in MBS patients is not established. OBJECTIVES: To provide consensus based guidelines utilizing current literature and, when in the absence of supporting clinical data, expert opinion by organizing a consensus meeting of experts from relevant specialties. SETTING: The meeting was held in Amsterdam, the Netherlands. METHODS: A panel of 15 international experts identified 75 questions covering preoperative screening, treatment, postoperative monitoring, anesthetic care and follow-up. Six researchers reviewed the literature systematically. During this meeting, the "Amsterdam Delphi Method" was utilized including controlled acquisition of feedback, aggregation of responses and iteration. RESULTS: Recommendations or statements were provided for 58 questions. In the judgment of the experts, 17 questions provided no additional useful information and it was agreed to exclude them. With the exception of 3 recommendations (64%, 66%, and 66% respectively), consensus (>70%) was reached for 55 statements and recommendations. Several highlights: polysomnography is the gold standard for diagnosing OSA; continuous positive airway pressure is recommended for all patients with moderate and severe OSA; OSA patients should be continuously monitored with pulse oximetry in the early postoperative period; perioperative usage of sedatives and opioids should be minimized. CONCLUSION: This first international expert meeting provided 58 statements and recommendations for a clinical consensus guideline regarding the perioperative management of OSA patients undergoing MBS.

Sleep disordered breathing and subclinical impairment of respiratory function are common in sporadic inclusion body myositis.

Relatively little is known about frequency and extent of respiratory problems in sporadic inclusion body myositis (IBM). To address this issue a study of peripheral muscle and respiratory function and related symptoms was performed in a cohort with biopsy-proven IBM. Dyspnoea, daytime sleepiness, dysphagia, spirometry, respiratory muscle strength, arterial blood gas tensions and ventilation during sleep were assessed. Sixteen patients were studied (10 males; age 68.1±9.9years; disease duration 11.9±5.0years; body mass index 28.5±4.0kg/m(2)). Four reported excessive daytime sleepiness; 8 had at least mild dysphagia; forced vital capacity was <80% predicted normal in 7; sniff nasal inspiratory pressure was reduced in 3; daytime hypoxemia was present in 9 and hypercapnia in one. Sleep study was performed in 15 and revealed sleep disordered breathing (apnoea-hypopnoea index 23.4±12.8 (range 7-50.3)events/h) in all. There were no consistent relationships between respiratory function impairment, occurrence of sleep disordered breathing, and severity of peripheral muscle weakness. Thus, asymptomatic impairment of respiratory function was common and sleep disordered breathing observed in all patients tested, irrespective of daytime respiratory function. This suggests respiratory function testing, including sleep study, should be performed routinely in IBM, irrespective of peripheral muscle function or other disease severity parameters.

Hypoglossal nerve stimulation improves obstructive sleep apnea: 12-month outcomes.

Reduced upper airway muscle activity during sleep is a key contributor to obstructive sleep apnea pathogenesis. Hypoglossal nerve stimulation activates upper airway dilator muscles, including the genioglossus, and has the potential to reduce obstructive sleep apnea severity. The objective of this study was to examine the safety, feasibility and efficacy of a novel hypoglossal nerve stimulation system (HGNS; Apnex Medical, St Paul, MN, USA) in treating obstructive sleep apnea at 12 months following implantation. Thirty-one subjects (35% female, age 52.4 ± 9.4 years) with moderate to severe obstructive sleep apnea and unable to tolerate positive airway pressure underwent surgical implantation and activation of the hypoglossal nerve stimulation system in a prospective single-arm interventional trial. Primary outcomes were changes in obstructive sleep apnea severity (apnea-hypopnea index, from in-laboratory polysomnogram) and sleep-related quality of life [Functional Outcomes of Sleep Questionnaire (FOSQ)]. Hypoglossal nerve stimulation was used on 86 ± 16% of nights for 5.4 ± 1.4 h per night. There was a significant improvement (P < 0.001) from baseline to 12 months in apnea-hypopnea index (45.4 ± 17.5 to 25.3 ± 20.6 events h(-1) ) and Functional Outcomes of Sleep Questionnaire score (14.2 ± 2.0 to 17.0 ± 2.4), as well as other polysomnogram and symptom measures. Outcomes were stable compared with 6 months following implantation. Three serious device-related adverse events occurred: an infection requiring device removal; and two stimulation lead cuff dislodgements requiring replacement. There were no significant adverse events with onset later than 6 months following implantation. Hypoglossal nerve stimulation demonstrated favourable safety, feasibility and efficacy.

High prevalence of undiagnosed obstructive sleep apnoea in the general population and methods for screening for representative controls.

PURPOSE: Undiagnosed obstructive sleep apnoea (OSA) in the community makes comparisons of OSA subjects with control samples from the general population problematic. This study aims to estimate undiagnosed moderate to severe OSA in a general population sample and to determine the capacity of questions from the Berlin questionnaire (BQ) to identify subjects without diagnosed OSA of this severity. METHODS: Using a general population sample (n = 793) with no history of OSA, case and control status for moderate-severe OSA was determined by home-based nasal flow and oximetry-derived apnoea-hypopnoea index using a cut-off value of ≥ 15 events/h to define cases. The diagnostic accuracy of the complete BQ and its component questions in identifying cases was assessed by calculating sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios and post-test probabilities. RESULTS: The age-standardised prevalence estimate of moderate-severe OSA was 9.1 % (12.4 % in men, 5.7 % in women). Sensitivity of the BQ in this population was 54 %, and specificity, 70 %. A combination of questions regarding snoring frequency and hypertension provided maximal post-test probability of OSA and greatest post-screen sample size. CONCLUSIONS: Undiagnosed OSA is highly prevalent in the Western Australian general population. While the complete BQ is a sub-optimal screening instrument for the general population, snoring frequency or hypertension can be used to screen out moderate-severe OSA from general population samples with limited reduction in sample size. As there are few general population samples available for epidemiological or genetic studies of OSA and its associated phenotypes, these results may usefully inform future case-control studies.

Elastic properties of the central airways in obstructive lung diseases measured using anatomical optical coherence tomography.

RATIONALE: Our understanding of how airway remodeling affects regional airway elastic properties is limited due to technical difficulties in quantitatively measuring dynamic, in vivo airway dimensions. Such knowledge could help elucidate mechanisms of excessive airway narrowing. OBJECTIVES: To use anatomical optical coherence tomography (aOCT) to compare central airway elastic properties in control subjects and those with obstructive lung diseases. METHODS: After bronchodilation, airway lumen area (Ai) was measured using aOCT during bronchoscopy in control subjects (n = 10) and those with asthma (n = 16), chronic obstructive pulmonary disease (COPD) (n = 9), and bronchiectasis (n = 8). Ai was measured in each of generations 0 to 5 while airway pressure was increased from -10 to 20 cm H(2)O. Airway compliance (Caw) and specific compliance (sCaw) were derived from the transpulmonary pressure (Pl) versus Ai curves. MEASUREMENTS AND MAIN RESULTS: Caw decreased progressively as airway generation increased, but sCaw did not differ appreciably across the generations. In subjects with asthma and bronchiectasis, Caw and sCaw were similar to control subjects and the Pl-Ai curves were left-shifted. No significant differences were observed between control and COPD groups. CONCLUSIONS: Proximal airway elastic properties are altered in obstructive lung diseases. Although central airway compliance does not differ from control subjects in asthma, bronchiectasis, or COPD, Ai is lower in asthma and the Pl-Ai relationship is left-shifted in both asthma and bronchiectasis, suggesting that airways are maximally distended at lower inflating pressures. Such changes reflect alteration in the balance between airway wall distensibility and radial traction exerted on airways by surrounding lung parenchyma favoring airway narrowing. Clinical trial registered with Australian New Zealand Clinical Trials Registry (ACTRN12607000624482).

Feasibility of Applying Real-time Optical Imaging During Bronchoscopic Interventions for Central Airway Obstruction.

BACKGROUND: Interventional bronchoscopists manage central airway obstruction (CAO) through dilation, tumor ablation, and/or stent insertion. Anatomical optical coherence tomography (aOCT), a validated light-based imaging technique, has the unique capacity of providing bronchoscopists with intraprocedural central airway measurements. This study aims to describe the potential role of real-time aOCT in guiding interventions during CAO procedures. METHODS: Prospective case series were recruited from patients referred for bronchoscopic management of symptomatic CAO. Preprocedure chest computed tomography (CT) scans were analyzed for relevant airway dimensions, such as stenosis caliber and length, and aided procedure planning. During bronchoscopy, an aOCT fiberoptic probe was inserted through the working channel of the bronchoscope to image the airway stenosis. From these aOCT images, stenosis dimensions were measured and compared with the preprocedure CT measurements. Preprocedure and postprocedure spirometry, Medical Research Council dyspnea score, and Eastern Cooperative Oncology Group performance status were collected to assess intervention efficacy. RESULTS: Fourteen patients were studied. CT and aOCT-based measurements of airway caliber and length correlated closely (r=0.87, P<0.001). Bland-Altman analysis showed strong agreement between measurements (mean difference 0.4±8.6 mm). The real-time nature of aOCT imaging provided the advantage of more up-to-date measurements where a delay occurred between CT and bronchoscopy or where the quality of the CT image was suboptimal. After bronchoscopy, the predicted forced expiratory flow in 1 second increased from 67±26% to 78±19% (P=0.04). Eastern Cooperative Oncology Group and dyspnea scores improved in 83% and 75% of the patients, respectively. CONCLUSIONS: aOCT provides real-time measurements of obstructing central airway lesions that can assist therapeutic interventions such as selection of endobronchial stents and airway dilatation procedures.

Using optical coherence tomography to improve diagnostic and therapeutic bronchoscopy.

Flexible bronchoscopy is a common procedure that is used in both diagnostic and therapeutic settings but does not readily permit measurement of central airway dimensions. Anatomic optical coherence tomography (a OCT), a modification of conventional optical coherence tomography (OCT), is a novel light-based imaging tool with the capacity to measure the diameter and lumen area of the central airways accurately during bronchoscopy. This study describes the first clinical use of aOCT imaging in the lower airways in three individuals with common endobronchial pathologies. During bronchoscopy, a specialized fiberoptic probe was passed through the biopsy channel of a standard flexible bronchoscope to the site of airway pathology. Airway dimensions were measured from the generated cross-sectional images in three subjects, one with subglottic tracheal stenosis (subject 1), one with malignant left main bronchus (LMB) obstruction (subject 2), and another with severe tracheomalacia (subject 3). Measured dimensions included internal airway diameter, cross-sectional area, and, in subject 1, stenosis length. Tracheal stenosis dimensions, measured using aOCT imaging, correlated with chest CT scan findings and guided the choice of airway stent (subject 1). The airway beyond a malignant obstruction of the LMB, and beyond bronchoscopic view, could be imaged using aOCT, and the distal extent of obstructing tumor identified (subject 2). The severity of newly diagnosed tracheomalacia was able to be quantified using aOCT imaging (subject 3). aOCT imaging during bronchoscopy allows accurate real-time airway measurements and may assist bronchoscopic assessment.

Influence of head extension, flexion, and rotation on collapsibility of the passive upper airway.

STUDY OBJECTIVES: To determine the effect of head posture on upper airway collapsibility and site of collapse of the passive human upper airway. DESIGN: Pharyngeal critical closing pressure (Pcrit) and site of airway collapse were assessed during head flexion, extension and rotation in individuals undergoing propofol anesthesia. SETTING: Operating theatre of major teaching hospital. PARTICIPANTS: Fifteen healthy volunteers (8 male), including 7 who were undergoing surgery unrelated to the head or neck. MEASUREMENTS AND RESULTS: Applied upper airway pressure was progressively decreased to induce variable degrees of inspiratory flow limitation and to define Pcrit. Upper airway and oesophageal pressure transducers identified the site of collapse. Genioglossus muscle activity (EMGgg) was assessed using intramuscular fine wire electrodes inserted percutaneously. Data from 3 subjects were excluded from analysis due to persistent EMGgg. In the neutral posture Pcrit was -0.4 +/- 4.4 cm H2O and collapsed most frequently in the velopharyngeal region. Relative to neutral, Pcrit increased to 3.7 +/- 2.9 cm H2O (P < 0.01) and decreased to -9.4 +/- 3.8 cm H2O (P < 0.01) when the head was flexed and extended, respectively but was unchanged by rotation (-2.6 +/- 3.3 cm H2O; n = 10; P = 0.44). The site of collapse varied, in no consistent pattern, with change in head posture in 5 subjects. CONCLUSIONS: Head posture has a marked effect on the collapsibility and site of collapse of the passive upper airway (measured by EMGgg) indicating that controlling head posture during sleep or recovery from anesthesia may alter the propensity for airway obstruction. Further, manipulating head posture during propofol sedation may assist with identification of pharyngeal regions vulnerable to collapse during sleep and may be useful for guiding surgical intervention.

Comparison of upper airway collapse during general anaesthesia and sleep.

Measurement of the collapsibility of the upper airway while a patient is awake is not a good guide to such collapsibility during sleep, presumably because of differences in respiratory drive, muscle tone, and sensitivity of reflexes. To assess whether a relation existed between general anaesthesia and sleep, we measured collapsibility of the upper airway during general anaesthesia and severity of sleep-disordered breathing in 25 people who were having minor surgery on their limbs. Anaesthetised patients who needed positive pressure to maintain airway patency had more severe sleep-disordered breathing than did those whose airways remained patent at or below atmospheric pressure. Such an association was strongest during rapid-eye-movement (REM) sleep. Our findings suggest that sleep-disordered breathing should be considered in all patients with a pronounced tendency for upper airway obstruction during anaesthesia or during recovery from it.