Large difference between Enghoff and Bohr dead space in ventilated infants with hypoxemic respiratory failure

Ventilated neonates with hypoxemic respiratory failure (HRF) may show a ventilation-perfusion (V/Q) mismatch.

To evaluate the difference between the Bohr (V_{d, Bohr} ) and Enghoff (V_{d, Enghoff} ) dead spaces in infants by using volumetric capnography based on ventilator graphics and capnograms.

This study enrolled 46 ventilated infants (mean birth weight, 2239 ± 640 g; mean gestational age, 35.5 ± 3.3 weeks). We performed volumetric capnography and calculated V_{d, Bohr} and V_{d, Enghoff} when arterial blood sampling was necessary for treatment. According to the oxygenation index (OI) based on the Montreux definition of neonatal acute respiratory distress syndrome, each measurement was classified into the HRF (OI ≥ 4) or control (OI < 4) group. Then, a regression analysis was performed to evaluate the correlation between the OI and the difference between V_{d, Enghoff} and V_{d, Bohr} .

The median V_{d, Enghoff} /tidal volume (V_T ) was significantly higher in the HRF group (0.55 [interquartile range, 0.47-0.68]) than in the control group (0.46 [0.37-0.57]). The HRF group showed a larger difference between V_{d, Enghoff} /V_T and V_{d, Bohr} /V_T than the control group (median, 0.22 [0.15-0.29] vs. 0.10 [0.06-0.14], respectively). Moreover, the regression analysis of the relationship between OI and V_{d, Enghoff} /V_T  - V_{d, Bohr} /V_T showed a positive correlation (r = .60, p < .001).

Ventilated neonates with hypoxemic respiratory failure showed a large difference between V_{d, Enghoff} and V_{d, Bohr} , possibly reflecting a low V/Q mismatch and right-to-left shunting.