[Evaluation value of oxygenation index of mechanical ventilation on the prognosis of patients with ARDS: a retrospective analysis with 228 patients].

OBJECTIVE

To investigate the evaluation value of oxygenation index at different times of mechanical ventilation (MV) on the prognosis of patients with acute respiratory distress syndrome (ARDS).

METHODS

A retrospectively analysis was conducted. A total of 228 patients with ARDS admitted to Department of Emergency of China Medical University Affiliated First Hospital from February 2014 to June 2016 were enrolled. All patients underwent MV treatment, and recruitment maneuver (RM) was performed by pressure-controlled ventilation (PCV) 30 minutes after the implementation of the protective ventilation strategy. Arterial blood gas analysis was performed at MV immediately, after RM and at 6, 12, 24 hours of MV, and oxygenation index was calculated. Vital signs, laboratory data, ultrasonic echocardiography, sequential organ failure assessment (SOFA) score, duration of MV, and ventilator related parameters of patients were collected. The patients were divided into survivors and non-survivors according to the prognosis of 28 days. The survivors were subdivided into high and low oxygenation group (oxygenation index was ≥ 150 mmHg and < 150 mmHg, respectively, 1 mmHg = 0.133 kPa). Differences in clinical indicators between survivors and non-survivors were compared. The correlation between the oxygenation index after RM and the oxygenation index at each time after MV was analyzed by bivariate correlation analysis. Receiver operating characteristic (ROC) curve was plotted to analyze predictive value of oxygenation index measured at different times for the 28-day outcome of patients with ARDS.

RESULTS

Among 228 patients, 99 patients died within 28 days, and 129 survived, with mortality rate of 43.4%. (1) The oxygenation index after RM and at 6, 12, 24 hours after MV in survivors and non-survivors showed a continuously increased tendency, which was significantly lower in non-survivors than that in survivors (all P < 0.05). There was no significant difference in the duration of MV between high oxygenation group and low oxygenation group at MV immediately and after RM, but the duration of MV in high oxygenation group was significantly shorter than that of the low oxygenation group at 6, 12, 24 hour of MV (all P < 0.01). (2) After ventilation for 24 hours, serum creatinine (SCr), brain natriuretic peptide (BNP), lactate (Lac), right ventricular internal diameter, and SOFA score in non-survivors were significantly higher than those of survivors, and arterial partial pressure of oxygen (PaO), platelet (PLT) and right ventricular ejection fraction (RVEF) were significantly lower than those of survivors (all P < 0.05). (3) After 24 hours ventilation, positive end-expiratory pressure (PEEP), tidal volume (VT), and minute ventilation (VE) in non-survivors were significantly higher than those of survivors, and static compliance of thorax (Cdyn) was significantly lower than that of survivors (all P < 0.01). (4) It was shown by correlation analysis that the oxygenation index after RM was positively correlated with those at 6, 12, 24 hours of MV (r values were 0.856, 0.765, and 0.758, respectively, all P < 0.001). (5) It was shown by ROC curve that the area under the ROC curve (AUC) of the oxygenation index after RM for predicting 28-day prognosis was 0.688. When the cut-off value was 80.75 mmHg, the sensitivity was 97.7%, and the specificity was 42.4%, which could only be used for preliminary judgment of prognosis. The AUC of oxygenation index at 6, 12, 24 hours of MV for 28-day survival of ARDS patients were 0.719, 0.727, 0.754, respectively. When the cut-off values were 171.50, 192.14, and 161.75 mmHg, the sensitivity was 69.8%, 67.4%, 86.0%, and the specificity was 78.8%, 78.8%, and 63.6%, respectively. It indicated that the predictive value was higher, and no significant difference was found among the oxygenation index at different time points.

CONCLUSIONS

The oxygenation index after the early stage of RM can preliminarily determine the prognosis of patients. The predictive value of oxygenation index after MV for 28-day survival of ARDS patients was higher, so the oxygenation index measured at 6 hours of MV may be considered to evaluate the prognosis of patients with ARDS.