Mechanical ventilation in a critical care unit in southern Brazil: mortality risk factors

Introduction

Patients requiring mechanical ventilation (MV) have high mortality rates. In Latin America, the knowledge of mortality risk factors in patients on MV is scarce. Identification of such factors is essential to improve outcomes. The objective of our study was to determine the mortality risk factors in patients that required MV in the ICU of a general university hospital in southern Brazil.

Methods

A prospective cohort study of 1,115 adult patients admitted to the ICU who needed MV for at least 24 hours, between March 2004 and April 2007. Data were collected on each patient at the inclusion in the study and daily during the course of MV for up to 28 days. Multivariate analysis by logistic conditional regression was used.

Results

The frequency of MV was 46%; the overall and specific mortality rates were 23% and 51%, respectively. The mean (± SD) age was 57 ± 18 years; 52% were males; the mean APACHE II score was 22 ± 8.3; 69% were medical patients; the mean duration of MV was 10 ± 7.9 days; 93% were on invasive MV. The variables independently associated with increased mortality were (1) conditions present at beginning of MV: age (P = 0.04), APACHE II score (P < 0.001), acute lung injury/acute respiratory distress syndrome (ALI/ARDS) as cause of MV (P = 0.04), and gastrointestinal failure (P = 0.01); and (2) conditions occurring over the course of MV: ALI/ARDS (P < 0.001), sepsis (P = 0.007), cardiovascular (P = 0.002), renal (P < 0.001), and hepatic failure (P = 0.009), use of vasoactive drugs (P < 0.001) and opioids (P = 0.04), and duration of MV (P < 0.001). It is of note that ventilatory monitored variables included in the multivariate model were not associated with mortality.

Conclusion

In our study, the risk factors for mortality 28 days after the beginning of MV were conditions present at the beginning of MV (age, APACHE II score, ALI/ARDS as a cause of MV, and gastrointestinal failure) and conditions occurring over the course of MV (ALI/ARDS, sepsis, cardiovascular, renal and hepatic failure, use of vasoactive drugs and opioids, and duration of MV). The survival of patients on MV therefore involves conditions present at the start of MV, and conditions that occur during the MV period, including aspects related to patient management. Knowledge of these factors may permit the evolvement of early interventions that might decrease poor outcomes of patients that require MV.