In total, 436 trauma patients admitted in ICU were studied. Patients characteristics, outcomes, and comparison between AKI and no AKI groups are summarized in table and . All the patients were mechanically ventilated. Eighty percent of patients were male, with a median age of 37 years (IQR 23-55). The majority had blunt trauma (95%) caused by road traffic accidents (67%). Mean ISS and RTS was 27.3 (SD = 11.4) and 5.7 (SD = 1.4), respectively. Renal trauma had an incidence of 2.5% in our cohort (11 patients), with a similar distribution in the AKI and non AKI groups.
AKI patient's characteristics
The highest RIFLE class was obtained using serum creatinine in 98.6% of patients and using urine output in 1.4% of patients (3 patients only). In 76.1% of the patients the baseline serum creatinine was calculated using the MDRD equation because a record with previous baseline levels was not present for most of the patients. Concerning urinary output all patients except the 3 mentioned had more than 0.5 ml/Kg/h of diuresis. In all other patients what gave the RIFLE class of Risk, Injury or Failure was the increase from the basal level of creatinine to the maximum level of creatinine achieved during the entire length in ICU according to the criteria defined in table [7
AKI occurred in 217 patients (50%) but only 8% developed class F. No differences in age, gender, type of injury, mechanism of injury, TRISS, SAPS II, incidence of different body regions involved or RTS were found between patients with and without AKI. The severity of trauma, assessed by ISS, was higher in the AKI group (28.4 ± 11.8 vs. 26.21 ± 10.9, p = 0.045). In the subgroup of patients with AKI, 47% had a maximum RIFLE class of Risk, 36% had Injury, and 17% had Failure.
In terms of outcomes, none of the patients in our study required renal replacement therapy during ICU or hospital stay, and no patients reached the RIFLE outcome classes L or E. All patients that survived returned to normal levels of creatinine and diuresis. Increasing severity of AKI was associated with a significant increase in ICU length of stay (p = 0.044). Length of hospital stay also tended to increase with severity of AKI, but the differences had no statistical significance. We were not able to relate an increase in mortality to the severity of AKI. Overall trauma patient mortality was 30% and was significantly higher for patients without AKI. Regarding late mortality, no differences were found between the AKI and No AKI groups (18% versus 22%, p = 0.315). When stratified by RIFLE category the crude mortality was 23% for Risk, 19% for Injury, and 22% for Failure.
To better understand mortality distribution we divided the mortality into early (less than two days) and late categories. We found a significantly higher proportion of mortalities in the first two days in the group of patients without AKI (79% of early deaths are in the No AKI group). We also found a significantly higher incidence of intracranial hypertension and a higher proportion of mortality due to intracranial hypertension in the No AKI group of patients.