Abstract & Commentary
Recognizing Underuse of Lung-Protective Ventilation in Acute Lung Injury: What Can We Do Differently?
By Betty Tran, MD, MS, Assistant Professor of Medicine, Pulmonary and Critical Care Medicine, Rush University Medical Center, Chicago, is Associate Editor for Critical Care Alert.
Dr. Tran reports no financial relationships relevant to this field of study.
Synopsis: Clinical factors associated with underuse of lung-protective ventilation among patients with acute lung injury include older age, shorter height, white race, less severe illness, lower serum bicarbonate levels, shorter ICU stay, and use of non-volume-targeted ventilation.
Source: Walkey AJ, Wiener RS. Risk factors for underuse of lung-protective ventilation in acute lung injury. J Crit Care 2012;27:323.e1-9.
Although lung-protective ventilation (LPV) is widely acknowledged as one of the few interventions currently available that improves survival in patients with acute lung injury (ALI), it is poorly adopted in practice. Identification of barriers in utilizing LPV is the first step toward designing interventions that could result in improved patient outcomes in ALI.
Walkey et al conducted a secondary analysis of the Acute Respiratory Distress Syndrome Clinical Trials Network (ARDSNet) trial data from 1995 through 2005 using baseline patient clinical and demographic data before randomization. Of the 1385 study participants with ALI, only 430 (31.2%) received LPV, defined as a tidal volume ≤ 6.5 mL/kg predicted body weight (PBW) based on height and sex. The average tidal volume during pre-enrollment in the study was 7.65 ± 1.82 mL/kg PBW, with a range of delivered tidal volumes being twice that of predicted lung protective tidal volumes.
Factors associated with the underuse of LPV were older age, shorter height, white race, less severe illness (defined by lower Simplified Acute Physiology II and radiographic lung injury scores), lower serum bicarbonate levels, shorter ICU stay prior to study enrollment, and use of non-volume targeted mechanical ventilation. The authors reported similar results in their sensitivity analyses using a tidal volume of ≤ 8 mL/kg PBW, which was used in the ARDSNet trial if patients were breath stacking or dyssynchronous on the ventilator as long as plateau pressures remained < 30 cm H2O, and using mL/kg PBW as a continuous variable. Notably, the authors observed that tidal volumes of 450 mL for men and 350 mL for women qualified as LPV for more than 80% of both men and women.
This is the first published study adequately powered to identify risk factors for the underuse of LPV in patients with ALI. Its findings support and expand results from prior smaller studies that identified several factors contributing to the underuse of LPV, including underrecognition of ALI due to perception of patients being less severely ill, difficulties in calculating PBW, and discomfort with untoward effects of LPV (e.g., hypercapnia, hypoxemia, and acidosis).
Although the patient-level risk factors identified in this study are not modifiable per se, their identification highlights common, often unconscious biases in our use of LPV and simple interventions that could improve adherence. First, it is necessary to acknowledge that ALI should be in the differential diagnosis for any patient presenting with acute hypoxic respiratory failure having imaging consistent with diffuse pulmonary edema, regardless of the underlying severity of illness. For those who meet the definition of ALI/ARDS as recently updated in the Berlin Definition,1 LPV improves outcomes regardless of lung injury severity. Second, increased attentiveness to the ARDSNet protocol, accurate assessments of height, and monitoring of tidal volumes delivered with pressure-targeted ventilation modes are needed in the ICU.
Finally, the development of accessible systematic protocols may improve adherence to LPV by taking decision making out of the hands of the physician, a strategy already shown to be successful in other areas of critical care. Examples include defaulting to lower tidal volumes (450 mL for men and 350 mL for women as suggested by this study) for patients at risk for ALI, attaching charts with precalculated 6 mL/kg PBW tidal volumes and ARDSNet protocols to every ICU ventilator, and incorporating a surveillance system for ALI and LPV use either electronically or as part of ICU rounding checklists. Further studies are needed to confirm whether these interventions will result in improvement of LPV adherence and patient outcomes.
- The ARDS Definition Task Force. Acute respiratory distress syndrome: The Berlin definition. JAMA 2012;307:2536-2533.