title: Low oxygen saturation and mortality in an adult cohort: the Tromsø study.
abstract: BACKGROUND
  Oxygen saturation has been shown in risk score models to predict mortality in emergency medicine. The aim of this study was to determine whether low oxygen saturation measured by a single-point measurement by pulse oximetry (SpO2) is associated with increased mortality in the general adult population.
  
  
  METHODS
  Pulse oximetry was performed in 5,152 participants in a cross-sectional survey in Tromsø, Norway, in 2001-2002 ("Tromsø 5"). Ten-year follow-up data for all-cause mortality and cause of death were obtained from the National Population and the Cause of Death Registries, respectively. Cause of death was grouped into four categories: cardiovascular disease, cancer except lung cancer, pulmonary disease, and others. SpO2 categories were assessed as predictors for all-cause mortality and death using Cox proportional-hazards regression models after correcting for age, sex, smoking history, body mass index (BMI), C-reactive protein level, self-reported diseases, respiratory symptoms, and spirometry results.
  
  
  RESULTS
  The mean age was 65.8 years, and 56% were women. During the follow-up, 1,046 (20.3%) participants died. The age- and sex-adjusted hazard ratios (HRs) (95% confidence intervals) for all-cause mortality were 1.99 (1.33-2.96) for SpO2 ≤ 92% and 1.36 (1.15-1.60) for SpO2 93-95%, compared with SpO2 ≥ 96%. In the multivariable Cox proportional-hazards regression models that included self-reported diseases, respiratory symptoms, smoking history, BMI, and CRP levels as the explanatory variables, SpO2 remained a significant predictor of all-cause mortality. However, after including forced expiratory volume in 1 s percent predicted (FEV1% predicted), this association was no longer significant. Mortality caused by pulmonary diseases was significantly associated with SpO2 even when FEV1% predicted was included in the model.
  
  
  CONCLUSIONS
  Low oxygen saturation was independently associated with increased all-cause mortality and mortality caused by pulmonary diseases. When FEV1% predicted was included in the analysis, the strength of the association weakened but was still statistically significant for mortality caused by pulmonary diseases.
authors.affiliation: Department of Respiratory Medicine, University Hospital of North Norway, 9038, Tromsø, Norway. monica.linea.vold@unn.no.|Department of Community Medicine, University of Tromsø, Tromsø, Norway. monica.linea.vold@unn.no.
authors.forename: Monica Linea
authors.initials: ML
authors.lastname: Vold
authors.affiliation: Department of Respiratory Medicine, University Hospital of North Norway, 9038, Tromsø, Norway. ulf.aasebo@unn.no.|Department of Clinical Medicine, University of Tromsø, Tromsø, Norway. ulf.aasebo@unn.no.
authors.forename: Ulf
authors.initials: U
authors.lastname: Aasebø
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway. tom.wilsgaard@uit.no.
authors.forename: Tom
authors.initials: T
authors.lastname: Wilsgaard
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway. hasse.melbye@uit.no.
authors.forename: Hasse
authors.initials: H
authors.lastname: Melbye
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002318:Cardiovascular Diseases / Q000401:mortality*; D002423:Cause of Death; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D000860:Hypoxia / Q000453:epidemiology*; D008137:Longitudinal Studies; D008171:Lung Diseases / Q000401:mortality*; D008175:Lung Neoplasms / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009369:Neoplasms / Q000401:mortality*; D009664:Norway / Q000453:epidemiology; D010092:Oximetry; D016016:Proportional Hazards Models; D012042:Registries