title: Supplemental oxygen impairs detection of hypoventilation by pulse oximetry.
abstract: OBJECTIVE
  This two-part study was designed to determine the effect of supplemental oxygen on the detection of hypoventilation, evidenced by a decline in oxygen saturation (Spo(2)) with pulse oximetry.
  
  
  METHODS
  Phase 1 was a prospective, patient-controlled, clinical trial. Phase 2 was a prospective, randomized, clinical trial.
  
  
  METHODS
  Phase 1 took place in the operating room. Phase 2 took place in the postanesthesia care unit (PACU).
  
  
  METHODS
  In phase 1, 45 patients underwent abdominal, gynecologic, urologic, and lower-extremity vascular operations. In phase 2, 288 patients were recovering from anesthesia.
  
  
  METHODS
  In phase 1, modeling of deliberate hypoventilation entailed decreasing by 50% the minute ventilation of patients receiving general anesthesia. Patients breathing a fraction of inspired oxygen (Fio(2)) of 0.21 (n = 25) underwent hypoventilation for up to 5 min. Patients with an Fio(2) of 0.25 (n = 10) or 0.30 (n = 10) underwent hypoventilation for 10 min. In phase 2, spontaneously breathing patients were randomized to breathe room air (n = 155) or to receive supplemental oxygen (n = 133) on arrival in the PACU.
  
  
  RESULTS
  In phase 1, end-tidal carbon dioxide and Spo(2) were measured during deliberate hypoventilation. A decrease in Spo(2) occurred only in patients who breathed room air. No decline occurred in patients with Fio(2) levels of 0.25 and 0.30. In phase 2, Spo(2) was recorded every min for up to 40 min in the PACU. Arterial desaturation (Spo(2) < 90%) was fourfold higher in patients who breathed room air than in patients who breathed supplemental oxygen (9.0% vs 2.3%, p = 0.02).
  
  
  CONCLUSIONS
  Hypoventilation can be detected reliably by pulse oximetry only when patients breathe room air. In patients with spontaneous ventilation, supplemental oxygen often masked the ability to detect abnormalities in respiratory function in the PACU. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilatory abnormalities, but only in the absence of supplemental inspired oxygen.
authors.affiliation: H. Lee Moffitt Cancer Center, 12902 Magnolia Dr, Suite 2194 Anesthesia, Tampa, FL 33612, USA.
authors.forename: Eugene S
authors.initials: ES
authors.lastname: Fu
authors.forename: John B
authors.initials: JB
authors.lastname: Downs
authors.forename: John W
authors.initials: JW
authors.lastname: Schweiger
authors.forename: Rafael V
authors.initials: RV
authors.lastname: Miguel
authors.forename: Robert A
authors.initials: RA
authors.lastname: Smith
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007040:Hypoventilation / Q000097:blood* / Q000175:diagnosis* / Q000628:therapy; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010102:Oxygen Inhalation Therapy; D011446:Prospective Studies