NEJM - KCLIP: Incidence and Outcomes of Acute Lung Injury (ALI)

A prospective population-based study of King County in Seattle, the 13th largest county in the US with > 1.8 million residents. During the period from 4/1999 to 7/2000, a total of 1,113 King County residents >15yo who underwent mechanical ventilation met the American-European Consensus Conference on ARDS definition of ALI.

Only arterial blood gas measurements obtained while the patient was intubated
were assessed. The arterial blood gas values with the worst PaO2:FiO2 ratio,
regardless of the positive end-expiratory pressure, were used to assess
oxygenation for each 24-hour period.

Because the PaO2: FiO2 ratio becomes an increasingly unreliable assessment of shunt when the FiO2 is below 0.40, the ratio was used to assess oxygenation only when the FiO2 was 0.40 or more.

Risk factors present during the four days before the onset of ALI: severe sepsis (sepsis with a suspected pulmonary source, sepsis with a suspected nonpulmonary source or an unidentified source), severe trauma (with an Injury Severity Score > 15), witnessed aspiration, transfusion of > 15 units of blood within a 24-hour period, drug overdose, pancreatitis, near-drowning, and inhalation injury.

Outcomes:
In-hospital mortality, ICU LOS, etc.

Analysis:
Pearson chi-square, Mann-Whitney, t-test.

Conclusions
1. The incidence of ALI is 2.5~5.0x as high as previously believed, with age-adjusted incidence of 86 /100,000 person-years. Mortality is about 39%.
2. The incidence of ARDS is 2~40x as high as previously believed, with age-adjusted incidence of 64 /100,000 person-years. Mortality is about 41%.
3. The most common risk factor for developing ALI is severe sepsis with pneumonia (46%), f/b severe sepsis with suspected nonpulmonary source (33%).

Accompanying editorial raises 2 points worth considering:

• Why is the incidence in this study seemingly higher than in others? Is this possibly a reflection of US Hospitals overusing ICU beds?
• While the main outcome measured was in-hospital mortality, post D/C morbidity is high and the logistics of care need to be carefully arranged.

medicine statistics pulmonology ARDS ALI