Assessment of Bohr and Enghoff Dead Space Equations in Mechanically Ventilated Children.

BACKGROUND

Recent findings suggest that using alveolar P (P ) estimated by volumetric capnography in the Bohr equation instead of P (Enghoff modification) could be appropriate for the calculation of physiological dead space to tidal volume ratio (V/V and V/V, respectively). We aimed to describe the relationship between these 2 measurements in mechanically ventilated children and their significance in cases of ARDS.

METHODS

From June 2013 to December 2013, mechanically ventilated children with various respiratory conditions were included in this study. Demographic data, medical history, and ventilatory parameters were recorded. Volumetric capnography indices (NM3 monitor) were obtained over a period of 5 min preceding a blood sample. Bohr's and Enghoff's dead space, S2 and S3 slopes, and the S2/S3 ratio were calculated breath-by-breath using dedicated software (FlowTool). This study was approved by Ste-Justine research ethics review board.

RESULTS

Thirty-four subjects were analyzed. Mean V/V was 0.39 ± 0.12, and V/V was 0.47 ± 0.13 ( = .02). The difference between V/V and V/V was correlated with P /F and with S2/S3. In subjects without lung disease (P /F ≥ 300), mean V/V was 0.36 ± 0.11, and V/V was 0.39 ± 0.11 ( = .056). Two children with status asthmaticus had a major difference between V/V and V/V in the absence of a low P /F .

CONCLUSIONS

This study suggests that V/V and V/V are not different when there is no hypoxemia (P /F > 300) except in the case of status asthmaticus. In subjects with a low P /F , the method to measure V/V must be reported, and results cannot be easily compared if the measurement methods are not the same.