Dead space washout by intentional leakage flow during conventional ventilation of premature infants-an experimental study

Abstract

Objective: Invasive mechanical ventilation poses a strong risk factor for the development of chronic lung disease in preterm infants. A reduction of the dead space as part of the total breathing volume would reduce the ventilation effort and thereby lower the risk of ventilator-induced lung injuries. In this experimental study, we compared the efficacy of mechanical dead space washout via uncontrolled and controlled leakage flow in their ability to eliminate CO₂ during conventional ventilation in preterm infants.

Methods: Three frequently used neonatal ventilators, operating under standard conventional ventilating parameters, were individually connected to a test lung. To maintain a constant physiological end-expiratory pCO₂ level during ventilation, the test lung was continuously flooded with CO₂ . A side port in the area of the connector between the endotracheal tube and the flow sensor allowed breathing gas to escape passively or in a second experimental setup, regulated by a pump. Measurements of end-expiratory pCO₂ were taken in both experiments and compared to end-expiratory pCO₂ levels of ventilation without active dead space leakage.

Results: Following dead space washout, a significant reduction of end-expiratory pCO₂ was attained. Under conditions of uncontrolled leakage, the mean decrease was 14.1% while controlled leakage saw a mean reduction of 16.1%.

Conclusion: Washout of dead space by way of leakage flow is an effective method to reduce end-expiratory pCO₂ . Both controlled and uncontrolled leakage provide comparable results, but precise regulation of leakage allows for a more stable ventilation by preventing uncontrolled loss of tidal volume during inspiration.

Keywords: dead space washout; leakage flow; mechanical ventilation; preterm infant.

Figure 1

Diagram of the test setting with (1) conventionally ventilated test lung, (2) endotracheal tube, (3) end‐expiratory measurement of pCO₂, (4) endotracheal tube connector, (5) Flow sensor, (6) expiratory limb of ventilation tubes, (7) inspiratory limb of ventilation tubes, (8) leakage flow through the leakage tube for dead space washout, (9) continuously CO₂ flooding of the test lung. Arrows indicate direction of airflow within the circuit. The double arrow symbolizes the movement of the test lung, the remaining arrows symbolize the direction of flow of the respiratory gas at the corresponding points

Figure 2

Graph of mean end expiratory pCO₂ values with controlled, uncontrolled and without leakage, averaged over all ventilators used. Error bars represents the 95% confidence intervals of the means