Can dead space fraction predict the length of mechanical ventilation in exacerbated COPD patients?

Chronic obstructive pulmonary disease (COPD) is a condition in which there is limited airflow during expiration (exhaling, or breathing out) that is not fully reversible and usually worsens over time. The disease is estimated to kill more than 100,000 Americans each year, and costs related to care of patients with COPD are significant. Physiologically, COPD represents a disruption in ventilation and in the exchange of gases in the lungs. Laboratory tests indicate elevated CO2 levels, gradual reduction of the levels of oxygen and pH in arterial blood, and a consequent rise in the dead space fraction (DSF) of the lungs.

Patients with COPD exacerbation represent a large portion of those artificially ventilated. In an attempt to develop a prognostic tool for length of treatment, we compared the proportion of DSF to the length of mechanical ventilation (MV).

This study included 73 patients admitted to the intensive care unit (ICU) where they received MV due to exacerbation of COPD. Each patient's arterial blood gases (ABG) were measured upon admission. PeCO2 was tested using a Datex S/5 instrument. Subsequently, DSF was calculated using the Bohr equation. Statistical data was analyzed using SPSS software.

Patients included in the study were ventilated from 6 to 160 hours (average 40 +/- 47). In addition to ABG measurements, PeCO2 (expired CO2) levels were measured and DSF calculated for each patient. DSF values varied from 0.21 to 0.76 (average 0.119 +/- 0.489). No correlation was found between DSF and length of artificial ventilation.

Evaluation of DSF does not provide a factor in estimating the length of treatment for patients with acute respiratory failure due to COPD exacerbation.