The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

Bench Study Examination of the Pressure Waveform Distal to the Endotracheal Tube (ETT) While Suction Catheter is Advanced into THE ETT. 

John S Emberger BS RRT, Joel Brown II BS RRT, Robert Locke DO, John Stefano MD, Departments of Respiratory Care and Neonatology, Christiana Care Health System, Newark DE.

Background:  Closed and open suctioning are routinely used for neonates. We examined pressure waveforms on the distal (patient) side of the ETT of an "actively breathing" neonate model while a suction catheter is in the ETT, but no suction applied.

Methods:  A neonate lung model was created simulating spontaneous breaths. The lung was enclosed in a container (Comp.=0.0018 L/cmH2O, Resist.=65 cmH2O/L/sec, Time Constant=0.117). Intermittent regulated vacuum was applied to the container, creating reproducible inspirations. A spirometer (CO2SMOPlus, Respironics) was placed distal to both the ETT and suction catheter position to capture the pressure wave distal to the ETT. Vent settings: PIP=20 cmH2O, PEEP=5 cmH2O, Rate=26, I-time=0.4 sec. A 3.0 ETT and #6 fr. suction catheters were used. Four scenarios were examined with the suction catheter in the ETT but with no suction applied:  1) Open Suctioning  2) Closed suction - Time Cycled Pressure Limited (TCPL) ventilation (VIP, Bird Medical Systems)   3) Closed suctioning - Pressure Controlled (PCV) ventilation (Evita 4, Draeger Medical)  4) Closed suctioning - Volume Targeted Pressure Limited (VTPL) ventilation (Evita 4, Draeger Medical)

Results: With the suction catheter in the ETT but no suction applied, open suctioning showed negative pressure inflections with each patient inspiratory effort. Closed suction mechanical breaths showed pressure spikes of 5 to 12 cmH2O at the start of exhalation, which lasted up to 0.2 seconds.

Conclusion: While the suction catheter is in the ETT, but with no suction applied, "actively breathing" neonates may experience short-lived pressure spikes at the start of exhalation due to passive lung recoil against expiratory resistance from the catheter. This model is passive exhalation and live neonates may even actively exhale against the expiratory resistance of the catheter creating higher pressure spikes.

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