title: Are daytime arterial blood gases a good reflection of nighttime gas exchange in patients on long-term oxygen therapy?
abstract: OBJECTIVE
  Compare nighttime and daytime arterial blood gas values in patients undergoing long-term oxygen therapy (LTOT).
  
  
  METHODS
  We studied 39 LTOT patients with chronic airflow limitation. Oxygen from an oxygen concentrator was administered via nasal prongs until daytime blood oxygen saturation (measured via pulse oximetry [S(pO2)]) was > or = 90%. Arterial blood samples were drawn at 6:00 PM, while the subject breathed room air, and also during oxygen administration at night (3:00 AM), early in the morning (7:00 AM), and at noon. S(pO2) was measured throughout the night.
  
  
  RESULTS
  Mean patient age was 70 +/- 7 yr. All patients suffered severe chronic airflow limitation (mean forced expiratory volume in the first second 28 +/- 9% of predicted). The mean oxygen flow administered was 1.41 +/- 0.6 L/min. Mean overnight S(pO2) was 92 +/- 2.5%, with 21.5 +/- 28% of recording time under 90%. There were statistically significant differences between P(aO2), P(aCO2), and pH obtained at 3:00 AM and noon and between 7:00 AM and noon, while the patients breathed the same oxygen concentration. The differences between the 3:00 and 7:00 AM values were not significant. In 23 patients (59%) we observed a P(aCO2) increase > 10 mm Hg and/or a pH decrease to < 7.33 during that period, indicating poor response to LTOT.
  
  
  CONCLUSIONS
  Daytime arterial blood gas measurements do not reflect nighttime gas exchange. However, samples taken early in the morning (7:00 AM) do seem to reflect arterial blood gases during the night and can therefore be used for setting and monitoring nighttime oxygen flow.
authors.affiliation: Department of Pneumology, Hospital de la Santa Creu i de Sant Pau, Sant Antoni Ma Claret 167, 08025, Barcelona, Spain.
authors.forename: Julia
authors.initials: J
authors.lastname: Tárrega
authors.forename: Rosa
authors.initials: R
authors.lastname: Güell
authors.forename: Antonio
authors.initials: A
authors.lastname: Antón
authors.forename: Merce
authors.initials: M
authors.lastname: Mayos
authors.forename: Ariadna
authors.initials: A
authors.lastname: Farré
authors.forename: Francisco R
authors.initials: FR
authors.lastname: Jerez
authors.forename: Joaquín
authors.initials: J
authors.lastname: Sanchis
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D008134:Long-Term Care; D008173:Lung Diseases, Obstructive / Q000097:blood / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D010100:Oxygen / Q000097:blood*; D010102:Oxygen Inhalation Therapy; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012890:Sleep / Q000502:physiology*
chemical_list: D010100:Oxygen