Risk factors for the deterioration of oxygenation ratio in ventilated intensive care unit patients: a retrospective cohort study.
OBJECTIVE
The aim of the study is to determine which factors are associated with the deterioration of Pao(2)/fraction of inspired oxygen (Fio(2)) ratio in patients with normal oxygenation at admission and ventilated according to a lung protective ventilation strategy.


METHODS
Retrospective cohort study of ventilated (>/=3 days) intensive care unit patients with an admission Pao(2)/Fio(2) ratio of 300 mm Hg or higher (n = 105). Patients who developed lung injury (Pao(2)/Fio(2) ratio, <300 mm Hg) on day 7 (n = 37) were compared to those who did not (n = 68), with regard to ventilator settings, gas exchange variables, and lung injury risk factors.


RESULTS
Mean +/- SD of administered tidal volume was 7.9 +/- 1.3 mL/kg. Patients who developed lung injury were older (P = .019), had lower Pao(2) (P = .009), higher Paco(2) (P = .045), and lower Pao(2)/Fio(2) ratio (P = .002) at admission. Postoperative state (Hazard risk [HR], 5.1) and controlled ventilation mode (HR, 4.3) were identified as independent risk factors. Lung injury-free time was shorter in patients with low initial Pao(2)/Fio(2) ratio (odds ratio, 1.7; P = .039). This effect was not only caused by the baseline difference, as the decrease in Pao(2)/Fio(2) ratio was more pronounced in patients who developed lung injury compared to those who did not (P = .008).


CONCLUSIONS
Lung injury exacerbates during mechanical ventilation. In patients treated with a mean tidal volume of 7.9 mL/kg, controlled ventilation is a major risk factor.
Fick
Ilma W F
IW
Radboud University Nijmegen Medical Center, PO-Box 9101, 6500HB Nijmegen, The Netherlands.
Tijdink
Myrthe M
MM
Halbertsma
Feico J J
FJ
van der Hoeven
Johannes G
JG
Pickkers
Peter
P
D015331:Cohort Studies; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D055370:Lung Injury / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D012121:Respiration, Artificial / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors; D013990:Tidal Volume; D016896:Treatment Outcome
D010100:Oxygen