Validation of the Deltatrac Metabolic Cart for Measurement of Dead-Space-to-Tidal-Volume Ratio

INTRODUCTION: Determination of the volume of respiratory dead space can be clinically useful. Measurements made with a Deltatrac metabolic cart were used to determine dead-space-to-tidal-volume ratio (V_D/V_T) and were compared to V_D/V_T determination by a standard method using a Douglas bag. MATERIALS & METHOD: Thirty studies were performed on 26 mechanically ventilated patients in the Medical/Surgical Intensive Care Unit. V_D/V_T was calculated using the Enghoff modification of the Bohr equation. RESULTS: Values obtained using the Douglas bag ranged from 0.37 to 0.74. Simultaneous measurements using the metabolic cart ranged from 0.40 to 0.78. The correlation coefficient was 0.92, the mean difference was 0.004 and the standard deviation of the difference was 0.034. CONCLUSION: These data show that the metabolic cart is as accurate as the Douglas-bag method for determination of V_D/V_T.