Using a Cox proportional hazard model , V ( D ) / V ( T ) was associated with a trend toward higher mortality ( HR = 4.37 [ CI 0.99-19 .32 ] , P = .052 ) that became significant when the analysis was adjusted for daily oxygenation index ( HR = 1.74 [ 95 % CI 1.12-3 .35 ] P = .04 ) .