2005 OPEN FORUM Abstracts
Automatic Tube Compensation: Is It Safe and Effective For Neonatal and Pediatric Patients?
David W. Southwick, C.R.T., Jody Lester, MEd R.R.T., and Randal Rose. Boise State University - Boise, Idaho
Rationale:In modern mechanical ventilators Automatic Tube Compensation (ATC), also known as Automatic Airway Compensation (AAC), is designed to deliver the set pressure to the distal end of an artificial airway thereby compensating for the resistance of the endotracheal tube (ETT) or tracheostomy tube. The effects of ATC for neonatal and pediatric patients, using appropriately sized endotracheal tubes, have not been well documented. It is hypothesized, due to the higher resistance of smaller endotracheal tubes used in neonatal and pediatric patients, that mechanical compensation for the increased resistance would benefit the neonatal and pediatric patient.
Methods:We studied two ventilators: Viasys Avea (VA), Dräger Evita 2 (DE). Peak and mean pressures were measured at each end of a 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 mm ETT connected to a mechanical test lung. Each ventilator was placed in Continuous Positive Airway Pressure mode (CPAP) at 3 cm H2O and Pressure Support Ventilation (PSV) of 5, 10, 15, and 20 cmH2O. The target Tidal Volume (VT) was 5 ml/Kg, Inspiratory time (TI) of 0.3 seconds. The appropriate ETT size was entered during ventilator set up. ATC compensation was set at 100%. The drive ventilator for spontaneous breath generation was set at a rate of 25, PEEP of 0.0 cm H2O, Inspiratory Pause 0.0 seconds, Peak Flow 75 L/min, and an I:E ratio of 1:10. The drive lung was set with a compliance of 0.02 L/cm H2O with a measured resistance of 5.6 cm H20/L/Sec. The neonatal/pediatric test lung was set with a compliance of 0.002 L/cm H2O and a resistance of 20 cm H2O/L/sec. All data was collected using calibrated flow and pressure transducers, and the resultant data was evaluated via computer.
Results:Both ventilators provided ATC to the test lung, however there was a marked difference in the measured pressures provided by the ventilators when ATC was active. The VA provided a distal pressure of 11.5 (PSV 5) and 25 cm H2O (PSV 20) for the 3.0 ETT, with no significant change in pressure when AAC was activated. Similarly the 5.0 ETT distal pressures were 8.5 (PSV 5) and 21 cm H2O (PSV 20) and slightly higher with AAC active at 9.5 (PSV 5) and 24 cm H2O (PSV 20). The DE provided a distal pressure of 9 (PSV 5) and 24 cm H2O (PSV 20) for the 3.0 ETT, and pressures increased with ATC active to 11 (PSV 5) and 36 cm H2O (PSV 20). The distal pressures for the 5.0 ETT, with ATC off were 9.5 (PSV 5) and 25.5 (PSV 20), the distal pressure changed to 10 (PSV 5) and 26.5 (PSV 20) when ATC was applied.
Conclusions: The VA demonstrated minimal pressure changes during AAC targeted breaths. The authors cannot demonstrate an advantage for the use of AAC with neonatal and pediatric sized endotracheal tubes while using the VA. The DE demonstrated similar results with the larger sized endotracheal tubes, which resulted in minimal changes in distal pressure when ATC was active. However, there was a marked correlation between the smaller endotracheal tubes and the significance of higher than set pressures delivered to the distal end of the ETT during an ATC targeted breath. This was more remarkable as the pressure support was increased. The authors suggest caution when applying ATC on the DE to endotracheal tubes of size 2.5 to 5.0 mm due to the high pressures delivered to the distal end of the ETT.