Journal: Crit Care Med 35(7):1660-1666, 2007. 32 References
Reprint: Dept of Internal Medicine, Division of Pulmonary and Critical Care Medicine, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 (O Gajic, MD)
Faculty Disclosure: Abstracted by R. Klotz, who has nothing to disclose.
Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS), are major problems in critically ill patients. Although sepsis, aspiration, and pneumonia are the most common underlying risk factors for the development of ALI/ARDS, iatrogenic insults, including transfusion and mechanical ventilation, may also contribute to its development. The authors recently reported that both ventilation with high tidal volume and transfusion of blood products were important risk factors for the development of ALI/ARDS in mechanically ventilated patients who did not have ALI/ARDS at the outset.
The authors report the effects of two interdisciplinary quality improvement interventions aimed at eliminating the use of inappropriately large tidal volumes and unnecessary RBC transfusion. They hypothesized that intervention would decrease the frequency of iatrogenic ALI/ARDS and improve outcomes of mechanically ventilated patients who did not suffer from ALI/ARDS from the outset.
Three ICUs were screened for patients who were mechanically ventilated > 48 hours but did not have ALI/ARDS or pulmonary edema at the onset of mechanical ventilation. The main outcome of interest was the development of ALI/ARDS according to the American-European Consensus Conference definition (the reader is referred to the article for the full definition). Secondary outcome variables were hospital mortality, duration of mechanical ventilation and ICU length of stay, and ventilator-free days calculated to day 28 after intubation.
The protocol limited tidal volumes to a maximum of 10 mL/kg predicted body weight (PBW) in all patients receiving invasive ventilation with a recommendation to use 6-8 mL/kg PBW for patients at risk of ALI/ARDS. In addition, an algorithm for evidence-based RBC transfusion that was subsequently incorporated as a decision support within the institutional computerized order entry (CPOE).
Data were collected prospectively from three adult ICUs over a one-year period and compared with a historical cohort of patients who were treated in the same ICUs before protocol introduction. Demographics, admission diagnosis, length of hospital and ICU stay, duration of mechanical ventilation, past medical history, and physiologic and laboratory variables were entered into the APACHE III database in the same manner during both study periods. Sepsis was defined according to standard criteria. Aspiration was defined as witnessed or strongly suspected aspiration of gastric contents into the airways. Alcohol abuse was defined as known/reported intake of three or more alcoholic drinks daily. Tobacco abuse was defined as a known history of smoking > one-pack year. Transfusion of packed RBCs 24 hours before intubation and during the first 24 hours of mechanical ventilation was recorded. Ventilation variables were recorded every 15 minutes in all ICUs during the protocol period. The frequency of ALI/ARDS was calculated per number of patients ventilated for ≥ 48 hours.
A total of 375 patients (212 before and 163 after the introduction of the quality improvement intervention) met inclusion criteria. The second group had a lower frequency of sepsis, a trend toward lower median glucose levels, lower frequency of pneumonia, and younger age. After intervention, there was a marked reduction in tidal volumes and airway pressures and percentage of transfused patients. During hospitalization, the percentage of transfused patients decreased from 83% to 71%. After intervention, higher positive end-expiratory pressure and rate settings, more often combined with pressure-controlled modes was used. The frequency of ALI/ARDS decreased in the postintervention period.
Aspiration, acidosis, ventilation with high tidal volumes, and RBC transfusion were identified as important risk factors in the development of ALI/ARDS. A higher glucose level during the first 24 hours of mechanical ventilation was associated with a decreased risk of ALI/ARDS. The duration of mechanical ventilation, ICU stay and ICU and hospital mortality also decreased during the second period.
The introduction of protocols for protective mechanical ventilation and restrictive transfusion effectively decreased high tidal volumes, airway pressures, and the percentage of mechanically ventilated patients exposed to RBC transfusion in the three ICUs of the author’s institution. These changes were associated with a reduction in the frequency of ALI/ARDS and overall improved outcomes of these patients.
The authors conclude that further studies will be needed to determine optimal ventilator settings and transfusion thresholds for specific groups of mechanically ventilated patients. |
