title: Early evolution of arterial oxygenation in severe community-acquired pneumonia: a prospective observational study.
abstract: OBJECTIVE
  Acute respiratory failure requiring mechanical ventilation in severe community-acquired pneumonia has been shown to be a significant negative prognostic factor. We analyzed the early evolution of the Pao(2)/Fio(2) ratio and evaluated its clinical value as an outcome predictor.
  
  
  METHODS
  This is a prospective study conducted in a tertiary referral hospital. In 62 adult patients requiring early mechanical ventilation due to severe community-acquired pneumonia, we measured serial changes in Pao(2)/Fio(2) ratio and other clinical variables within the first 48 hours of mechanical ventilation and compared the difference between survivors and nonsurvivors.
  
  
  RESULTS
  The initial Pao(2)/Fio(2) ratio was lower in nonsurvivors (n = 27) than in survivors (n = 35) (158.0 +/- 55.8 vs 117.9 +/- 50.6, P = .025). Over the next 48 hours, the ratio increased significantly in survivors but not in nonsurvivors (analysis of variance, P < .001). An increase in Pao(2)/Fio(2) ratio greater than 56 mm Hg had a sensitivity of 75% and a specificity of 81% of survival. A definite causative pathogen was identified in 36 patients (58%) and the 3 most commonly isolated pathogens were Streptococcus pneumoniae, Staphylococcus aureus, and Klebsiella pneumoniae. Ten patients received inadequate initial empirical antimicrobial therapy, in which the Pao(2)/Fio(2) ratio change was significantly less than those who were adequately treated (analysis of variance, P < .001). Mortality was much higher (86% [6/7]) in patients who received inadequate antibiotics and where Pao(2)/Fio(2) ratio change was less than 56 mm Hg. On multivariate analysis, trend changes in Pao(2)/Fio(2) ratio over 48 hours, shock, and Acute Physiology and Chronic Health Evaluation II score were documented to be independent predictors of mortality.
  
  
  CONCLUSIONS
  A progressive improvement of Pao(2)/Fio(2) ratio during the first 48 hours of mechanical ventilation indicates favorable outcome. Serial measurement of this ratio should be considered in decision making for therapeutic strategy.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Mackay Memorial Hospital, 10449 Taipei, Taiwan. wuchienliang100@pchome.com.tw
authors.forename: Chien Liang
authors.initials: CL
authors.lastname: Wu
authors.forename: Fung J
authors.initials: FJ
authors.lastname: Lin
authors.forename: Shih Yi
authors.initials: SY
authors.lastname: Lee
authors.forename: Chao Hsien
authors.initials: CH
authors.lastname: Lee
authors.forename: Ming Jen
authors.initials: MJ
authors.lastname: Peng
authors.forename: Pei Jan
authors.initials: PJ
authors.lastname: Chen
authors.forename: Hsu Tah
authors.initials: HT
authors.lastname: Kuo
mesh_terms: D000368:Aged; D017714:Community-Acquired Infections / Q000175:diagnosis* / Q000382:microbiology / Q000401:mortality / Q000628:therapy; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D015999:Multivariate Analysis; D010100:Oxygen / Q000097:blood*; D011014:Pneumonia / Q000175:diagnosis* / Q000382:microbiology / Q000401:mortality / Q000628:therapy; D011379:Prognosis; D011446:Prospective Studies; D012372:ROC Curve; D012121:Respiration, Artificial; D016019:Survival Analysis
chemical_list: D010100:Oxygen