Daytime hypercapnia in obstructive sleep apnea syndrome

Chest. 2007 Dec;132(6):1832-8. doi: 10.1378/chest.07-0673.


Background: The pathogenesis of daytime hypercapnia (Paco2 >or= 45 mm Hg) may be directly linked to the existence of obstructive sleep apnea syndrome (OSAS) per se, although only some patients with OSAS exhibit daytime hypercapnia.

Objective: To investigate the prevalence of daytime hypercapnia in patients with OSAS; the association of daytime hypercapnia and obesity, obstructive airflow limitation, restrictive lung impairment, and severity of sleep apnea; and the response to continuous positive airway pressure (CPAP) therapy in a subset of subjects.

Methods: The study involved 1,227 patients with OSAS who visited a sleep clinic and were examined using polysomnography. As for the response to CPAP therapy, the patients were considered good responders if their daytime Paco2 decreased >or= 5 mm Hg and poor responders if it decreased < 5 mm Hg.

Results: Fourteen percent (168 of 1,227 patients) exhibited daytime hypercapnia. These patients had significantly higher body mass index (BMI) and apnea-hypopnea index (AHI) values compared with normocapnic patients, while percentage of predicted vital capacity (%VC) and FEV(1)/FVC ratio did not differ between the two groups. Logistic regression analysis showed that only AHI was a predictor of daytime hypercapnia (p < 0.0001), while BMI (p = 0.051) and %VC (p = 0.062) were borderline predictors of daytime hypercapnia. Daytime hypercapnia was corrected in some patients (51%, 19 of 37 patients) with severe OSAS after 3 months of CPAP therapy.

Conclusion: The pathogenesis of daytime hypercapnia may be directly linked to sleep apnea in a subgroup of patients with OSAS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chi-Square Distribution
  • Continuous Positive Airway Pressure
  • Female
  • Humans
  • Hypercapnia / blood*
  • Hypercapnia / epidemiology
  • Hypercapnia / physiopathology
  • Hypercapnia / therapy
  • Linear Models
  • Logistic Models
  • Male
  • Middle Aged
  • Obesity / complications
  • Oxygen / blood
  • Polysomnography
  • Prevalence
  • Respiratory Function Tests
  • Sleep Apnea, Obstructive / blood*
  • Sleep Apnea, Obstructive / physiopathology
  • Sleep Apnea, Obstructive / therapy
  • Treatment Outcome


  • Oxygen