Early evolution of arterial oxygenation in severe community-acquired pneumonia: a prospective observational study.
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.
Wu
Chien Liang
CL
Division of Pulmonary and Critical Care Medicine, Mackay Memorial Hospital, 10449 Taipei, Taiwan. wuchienliang100@pchome.com.tw
Lin
Fung J
FJ
Lee
Shih Yi
SY
Lee
Chao Hsien
CH
Peng
Ming Jen
MJ
Chen
Pei Jan
PJ
Kuo
Hsu Tah
HT
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
D010100:Oxygen