title: Prediction of arterial oxygen partial pressure after changes in FIO₂: validation and clinical application of a novel formula.
abstract: BACKGROUND
  Existing methods allow prediction of Pa(O₂) during adjustment of Fi(O₂). However, these are cumbersome and lack sufficient accuracy for use in the clinical setting. The present studies aim to extend the validity of a novel formula designed to predict Pa(O₂) during adjustment of Fi(O₂) and to compare it with the current methods.
  
  
  METHODS
  Sixty-seven new data sets were collected from 46 randomly selected, mechanically ventilated patients. Each data set consisted of two subsets (before and 20 min after Fi(O₂) adjustment) and contained ventilator settings, pH, and arterial blood gas values. We compared the accuracy of Pa(O₂) prediction using a new formula (which utilizes only the pre-adjustment Pa(O₂) and pre- and post-adjustment Fi(O₂) with prediction using assumptions of constant Pa(O₂)/Fi(O₂) or constant Pa(O₂)/Pa(O₂). Subsequently, 20 clinicians predicted Pa(O₂) using the new formula and using Nunn's isoshunt diagram. The accuracy of the clinician's predictions was examined.
  
  
  RESULTS
  The 95% limits of agreement (LA(95%)) between predicted and measured Pa(O₂) in the patient group were: new formula 0.11 (2.0) kPa, Pa(O₂)/Fi(O₂) -1.9 (4.4) kPa, and Pa(O₂)/Pa(O₂) -1.0 (3.6) kPa. The LA(95%) of clinicians' predictions of Pa(O₂) were 0.56 (3.6) kPa (new formula) and -2.7 (6.4) kPa (isoshunt diagram).
  
  
  CONCLUSIONS
  The new formula's prediction of changes in Pa(O₂) is acceptably accurate and reliable and better than any other existing method. Its use by clinicians appears to improve accuracy over the most popular existing method. The simplicity of the new method may allow its regular use in the critical care setting.
authors.affiliation: Division of Anaesthesia and Intensive Care, University of Nottingham, Queen's Medical Centre, Nottingham, UK.
authors.forename: H M
authors.initials: HM
authors.lastname: Al-Otaibi
authors.forename: J G
authors.initials: JG
authors.lastname: Hardman
mesh_terms: D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D005260:Female; D006801:Humans; D007385:Intermittent Positive-Pressure Ventilation / Q000379:methods* / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage / Q000378:metabolism*; D010102:Oxygen Inhalation Therapy; D010313:Partial Pressure; D011237:Predictive Value of Tests; D015203:Reproducibility of Results
chemical_list: D010100:Oxygen