• R D Warters, S J Allen, and A S Tonnesen.
• Department of Anesthesiology, The University of Texas Medical School, Houston 77030, USA.
• Crit. Care Med. 1997 Feb 1; 25 (2): 227-30.

ObjectivesTo directly measure airway pressures proximal and distal to endotracheal tubes during conventional synchronized intermittent mandatory ventilation (SIMV) and pressure controlled-inverse ratio ventilation (PC-IRV), and to compare them with these values measured by the ventilator.DesignProspective, nonrandomized study.SettingSurgical intensive care unit at a trauma center.PatientsGroup 1: Eight intubated adult patients connected to mechanical ventilators in the SIMV mode were studied. All patients required mechanical ventilation following traumatic injuries. Group 2: Five intubated adult patients with adult respiratory distress syndrome connected to mechanical ventilators were studied.InterventionsA small polyethylene catheter was threaded through each endotracheal tube such that it could be positioned to measure pressures proximal and distal to the tubes.Measurements And Main ResultsDuring SIMV, a significant pressure gradient exists across endotracheal tubes. In addition, although initiation of PC-IRV did lead to a lower peak airway pressure measured proximally, intratracheal peak airway pressure was unchanged.ConclusionsA pressure gradient exists during inspiration from the ventilator to the trachea in mechanically ventilated patients. Tracheal pressures cannot be predicted from proximal airway pressure monitors because of marked variation in endotracheal tube resistance in vivo. Initiation of PC-IRV does not result in a decrease in peak airway pressure when measured intratracheally.

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