Objective: This paper aims to highlight the physical principles of pressure and flow dynamics underlying endotracheal suctioning, to demonstrate these on a simple illustrative model and to discuss the clinical implications of these principles for paediatric practice.
Design: Prospective in vitro study.
Setting: Paediatric intensive care unit of a tertiary, academic hospital.
Measurements and main results: The peak pressure change (DeltaP) obtained in a "bag-in-box" model was recorded during suctioning, using different combinations of endotracheal tube (ETT) and catheter sizes, different suction pressures and techniques. Suction was also performed on three different consistencies of gelatine, using a range of suction catheter sizes and vacuum pressures. The mass of gelatine suctioned per second was calculated. A large DeltaP was measured when using neonatal-sized ETTs. There was a linear relationship (r=0,8, p<0.05) between DeltaP and the ratio of external catheter area to area difference (internal ETT area-external catheter area). Significantly greater DeltaP was measured when using a short versus long suction catheter ( p<0.001) and when applying suction for longer duration ( p<0,001) and with higher vacuum pressures ( p<0.05). The amount of mucus suctioned in a given time was related to catheter size, suction pressure and mucus density.
Conclusion: Applied clinically, these results indicate that intrapulmonary pressure changes generated by the endotracheal suctioning of intubated neonates are likely to be considerable, possibly translating into loss of lung volume.