title: Nonlinear Imputation of Pao2/Fio2 From Spo2/Fio2 Among Patients With Acute Respiratory Distress Syndrome.
abstract: ARDS is an important clinical problem. The definition of ARDS requires testing of arterial blood gas to define the ratio of Pao2 to Fio2 (Pao2/Fio2 ratio). However, many patients with ARDS do not undergo blood gas measurement, which may result in underdiagnosis of the condition. As a consequence, a method for estimating Pao2 on the basis of noninvasive measurements is desirable.
  
  
  
  Using data from three ARDS Network studies, we analyzed the enrollment arterial blood gas measurements to compare nonlinear with linear and log-linear imputation methods of estimating Pao2 from percent saturation of hemoglobin with oxygen as measured by pulse oximetry (Spo2). We compared mortality on the basis of various measured and imputed Pao2/Fio2 ratio cutoffs to ensure clinical equivalence.
  
  
  
  We studied 1,184 patients, in 707 of whom the Spo2 ≤ 96%. Nonlinear imputation from the Spo2/Fio2 ratio resulted in lower error than linear or log-linear imputation (P < .001) for patients with Spo2 ≤ 96% but was equivalent to log-linear imputation in all patients. Ninety-day hospital mortality was 26% to 30%, depending on the Pao2/Fio2 ratio, whether nonlinearly imputed or measured. On multivariate regression, the association between imputed and measured Pao2 varied by use of vasopressors and Spo2.
  
  
  
  A nonlinear equation more accurately imputes Pao2/Fio2 from Spo2/Fio2 than linear or log-linear equations, with similar observed hospital mortality depending on Spo2/Fio2 ratio vs measured Pao2/Fio2 ratios. While further refinement through prospective validation is indicated, a nonlinear imputation appears superior to prior approaches to imputation.
authors.affiliation: Pulmonary and Critical Care Medicine Section, Intermountain Medical Center/University of Utah School of Medicine, Murray, UT. Electronic address: samuel.brown@hsc.utah.edu.
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Brown
authors.affiliation: Pulmonary and Critical Care Medicine Section, Intermountain Medical Center/University of Utah School of Medicine, Murray, UT.
authors.forename: Colin K
authors.initials: CK
authors.lastname: Grissom
authors.affiliation: Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado School of Medicine, Aurora, CO.
authors.forename: Marc
authors.initials: M
authors.lastname: Moss
authors.affiliation: Division of Allergy, Pulmonary, and Critical Care Medicine, Vanderbilt University School of Medicine, Nashville, TN.
authors.forename: Todd W
authors.initials: TW
authors.lastname: Rice
authors.affiliation: Biostatistics Section, Massachusetts General Hospital, Boston, MA.
authors.forename: David
authors.initials: D
authors.lastname: Schoenfeld
authors.affiliation: Section of Emergency Medicine Critical Care, Department of Emergency Medicine, Brigham and Women's Hospital/Harvard Medical School, Boston, MA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Hou
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Massachusetts General Hospital, Boston, MA.
authors.forename: B Taylor
authors.initials: BT
authors.lastname: Thompson
authors.affiliation: Pulmonary and Critical Medicine Section, Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: Roy G
authors.initials: RG
authors.lastname: Brower
mesh_terms: D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D010092:Oximetry; D010313:Partial Pressure; D011379:Prognosis; D012128:Respiratory Distress Syndrome / Q000097:blood* / Q000401:mortality; D012720:Severity of Illness Index
keywords: acute respiratory distress syndrome; pulse oximetry; respiratory failure; severity scores
references.citation: JAMA. 2011 Oct 12;306(14):1574-81
references.pmid: 21976613
references.citation: Am J Respir Crit Care Med. 1994 Mar;149(3 Pt 1):818-24
references.pmid: 7509706
references.citation: Anesthesiology. 2005 Apr;102(4):715-9
references.pmid: 15791098
references.citation: N Engl J Med. 2005 Oct 20;353(16):1685-93
references.pmid: 16236739
references.citation: Crit Care Med. 2009 Apr;37(4):1317-21
references.pmid: 19242333
references.citation: Anesth Analg. 1990 Feb;70(2):195-207
references.pmid: 2105672
references.citation: JAMA. 2012 Jun 20;307(23):2526-33
references.pmid: 22797452
references.citation: Chest. 2009 Mar;135(3):662-8
references.pmid: 19029434
references.citation: Am J Respir Crit Care Med. 2010 Jul 15;182(2):133-4
references.pmid: 20634498
references.citation: Chest. 2007 Aug;132(2):410-7
references.pmid: 17573487
references.citation: Ann Emerg Med. 2012 Jan;59(1):35-41
references.pmid: 21907451
references.citation: Chest. 1985 Dec;88(6):900-5
references.pmid: 3905287
references.citation: Am J Respir Crit Care Med. 2016 Jan 1;193(1):43-51
references.pmid: 26334785
references.citation: Crit Care Med. 2009 Dec;37(12):3010-6
references.pmid: 19789456
references.citation: Chest. 2015 Dec;148(6):1477-83
references.pmid: 26271028
references.citation: N Engl J Med. 2014 Jun 5;370(23):2191-200
references.pmid: 24835849
references.citation: Chest. 2014 Nov;146(5):1155-8
references.pmid: 25367469
references.citation: J Crit Care. 2013 Aug;28(4):538.e1-7
references.pmid: 23395312
references.citation: Crit Care Med. 2012 Apr;40(4):1309-16
references.pmid: 22202709
references.citation: JAMA. 2012 Feb 22;307(8):795-803
references.pmid: 22307571
references.citation: Am J Respir Crit Care Med. 2011 Sep 1;184(5):561-8
references.pmid: 21562125
references.citation: Intensive Care Med. 1996 Jul;22(7):707-10
references.pmid: 8844239
references.citation: Pediatr Crit Care Med. 2010 Jan;11(1):12-7
references.pmid: 19561556
references.citation: J Appl Physiol Respir Environ Exerc Physiol. 1979 Mar;46(3):599-602
references.pmid: 35496
references.citation: J Hosp Med. 2013 Feb;8(2):83-90
references.pmid: 23184866
references.citation: Anesth Analg. 2007 Dec;105(6 Suppl):S18-23, tables of contents
references.pmid: 18048893
references.citation: Eur J Emerg Med. 2014 Apr;21(2):81-8
references.pmid: 23903783
references.citation: Respirology. 2015 Jul;20(5):813-8
references.pmid: 25998684
references.citation: J Appl Physiol (1985). 1989 Aug;67(2):902
references.pmid: 2793692