Potential Inadequacy of Automatic Tube Compensation to Decrease Inspiratory Work Load After at Least 48 Hours of Endotracheal Tube Use in the Clinical Setting

Abstract

BACKGROUND: Endotracheal tubes (ETTs) impose a substantial respiratory work load on mechanically ventilated patients. Automatic tube compensation (ATC) should overcome this flowdependent resistive work load; however, ETT resistance can be increased by tracheal secretions or ETT deformities. Our bench study investigated whether ATC provides effective respiratory work load relief in used ETTs. METHODS: We enrolled 20 critically ill patients requiring mechanical ventilation for longer than 48 hours. After extubation, we collected the used ETTs and measured the pressure-time products (PTPs) by using a bellows-in-a-box lung model that simulated spontaneous breathing, at a respiratory rate of 10 breaths/min, inspiratory time of 1.0 s, and tidal volumes (V T ) of 300 mL, 500 mL, and 700 mL. The ventilator was set at ATC 100% with PEEP of 5 cm H 2 O and F IO 2 of 0.21. The flow and airway pressure at the proximal (P aw ) and distal (P tr ) ends of the ETT were recorded, and the PTP integrated from P tr analyzed. RESULTS: PTP values increased with V T during ATC. Even at 100% ATC the ventilator did not completely compensate for the PTP imposed by the ETT. In used ETTs, peak flow and peak P aw were lower and PTP values were greater than in new ETTs. As V T increased, the percentage difference in the PTP values between the new and used ETTs increased. CONCLUSIONS: ATC does not necessarily compensate for an ETT-imposed respiratory work load. ETT configuration changes and tracheal secretions can increase ETT resistance and decrease the ability of ATC to compensate for the increased respiratory work load.

Management of the Artificial AirwayDiscussion

“…[50][51][52] Oto et al 53 found that reduction in ETT resistance precludes the automatic tube compensation ventilator feature from completely overcoming ETT resistance. It also reinforces the fact that humidification devices should be chosen based on suspected duration of use, patient condition, and presence of thick secretions.…”

Pediatric extubation readiness tests should not use pressure support

“…15 L/min through 3.5 ETT has higher resistance than 15 L/min through 6.0 ETT), but children with 3.5 ETT generally breathe at lower flow rates than those who have 6.0 ETT [9]. Several studies demonstrate that PS or Automatic endotracheal Tube Compensation (ATC) overcome imposed resistance from the ETT or ventilator circuits [3,5,[10][11][12][13]. However, these studies do not factor in the resistance of the natural airway, and have not routinely measured the difference between effort of breathing before and after extubation.…”

Micropatterned Endotracheal Tubes Reduce Secretion-Related Lumen Occlusion

“…5,18,31,49,51 Luminal narrowing due to secretion buildup correlates with increased airflow resistance that leads to increased work of breathing for the patient. 32,51 Physicians commonly evaluate suitability for extubation by conducting spontaneous breathing trials where the patient must breathe through the ETT. Reduction in ETT internal diameter caused by secretion accumulation results in significant increases in diaphragmatic effort, decreases in tidal volume and disruption in breathing patterns during weaning procedures.…”