Condensation of humidified air in the inflation line of a polyurethane cuff precludes correct continuous pressure monitoring during mechanical ventilation

Within continuously controlled limits of cuff pressure, an endotracheal tube cuff made of polyurethane (PU) prevents secretion inflow better than a conventional polyvinylchloride cuff. However, the temperature difference between ventilator gas and the air inside a PU cuff produces condensation droplets that accumulate in the cuff inflation canal. We investigated whether condensation influenced continuous cuff pressure monitoring. A PU-cuffed tube was placed into an artificial trachea and connected to a ventilator and test lung. An additional line was inserted at the distal cuff end to directly measure pressure inside the cuff. Methylene blue instillation via the inflation line mimicked condensation. Inspiratory (Pinsp) and expiratory (Pexp) pressures were continuously recorded. Six consecutive experiments were performed comparing pressures at baseline (T0) and at 24 h (T24). Shortly after dye instillation, pressures recorded at the inflation canal became permanently fixed at 25 cmH₂O. In contrast, pressures measured directly in the cuff progressively decreased (mean Pinsp 30 ± 3 vs. 20 ± 2 cmH₂O and mean Pexp 25 ± 0 vs. 12 ± 2 cmH₂O, T0 vs. T24, both P < 0.05). Thus, condensation in the inflation line of a PU-cuffed tube renders continuous cuff pressure monitoring unreliable, thereby increasing the risk for microaspiration.