Dead space free flow sensor reduces the ventilation effort in very low birth weight infants: an experimental study

Introduction

Bronchopulmonary dysplasia is a serious side effect of long-term ventilation in very low birth-weight infants, high tidal volumes being the main cause. However, technical dead space represents the biggest part of the necessary tidal volume. Therefore we studied whether reducing dead space could also reduce the ventilation effort.

Methods

The time needed to eliminate CO₂ by mechanical ventilation from a 'preterm infant test lung' flooded with CO₂ was measured. Four different Y-pieces (three with flow sensor: integrated [A], small dead space [B], dead-space free (our patent) [C] and one without flow sensor [D]) either connected or not connected to an enclosed suction device were used. Mechanical ventilation was standardized using a ventilation rate of 60/min, a PIP of 16 mbar, a PEEP of 3.5 mbar and a flow of 10 l/min. A capnograph in the expiration-part of the ventilation tube measured CO₂ concentrations. The test series were repeated 10 times and the mean (± SD) was used for statistical analysis.

Results

CO₂ elimination time was: in A, 47.7 (± 0.82) s with enclosed suctioning device, without 45.5 (± 1.18) s; in B, 42.5 (± 1.27) and 41.1 (± 0.99) s; in C, 37.5 (± 1.18) and 37.4 (± 0.97) s; and in D, 38.3 (± 1.16) s and 36.8 (± 0.79) s, respectively.

Conclusion

The use of the Y-piece with the patented dead space free flow sensor shows the same CO₂ elimination time as the Y-piece without flow sensor. This reduced the ventilation effort by 20% compared with the Y-pieces with integrated flow sensor and by 10% with the flow sensor with small dead space. This might also reduce the incidence of bronchopulmonary dysplasia.