Wednesday October 8, 2008
Risk of death in ARDS - dead space fraction

Severity of hypoxemia, imaging and none of the single variable is predictive of risk of death in acute respiratory distress syndrome (ARDS) when measured early in the course of the disease. However the quintile of dead space fraction correlated well with later mortality in a few observational studies and in at least prospective study. The dead space fraction was independent risk factor for death.

dead-space fraction = (PaCO2 – PeCO2) ÷ PaCO2

PeCO2 is a mean expired carbon dioxide fraction and is measured with a bedside metabolic monitor. Metabolic monitoring (metabolic cart) is noninvasive and is used widely for metabolic and nutritional assessment.

Study Details

The dead-space fraction was prospectively measured in 179 intubated patients, a mean (±SD) of 10.9±7.4 hours after the ARDS had developed. Additional clinical and physiological variables were analyzed with the use of multiple logistic regression. The study outcome was mortality before hospital discharge.


Results

• The mean dead-space fraction was markedly elevated (0.58±0.09) early in the course of the ARDS and was higher among patients who died than among those who survived (0.63±0.10 vs. 0.54±0.09)
• The dead-space fraction was an independent risk factor for death: for every 0.05 increase, the odds of death increased by 45 percent
• The only other independent predictors of an increased risk of death were the Simplified Acute Physiology Score II, an indicator of the severity of illness and quasistatic respiratory compliance

Conclusions: Increased dead-space fraction is a feature of the early phase of the acute respiratory distress syndrome. Elevated values are associated with an increased risk of death



Pulmonary Dead-Space Fraction as a Risk Factor for Death in the Acute Respiratory Distress Syndrome - NEJM,Volume 346:1281-1286, Number 17, April 25, 2002