Microaspirations during mechanical ventilation: polyurethane versus polyvinyl cuffed endotracheal tubes

Introduction

Mechanically ventilated (MV) patients are prone to develop ventilator-associated pneumonia. One of the major risk factors is microaspirations of supraglottic secretions past the endotracheal tube cuff (usually in polyvinyl (PV)). A novel polyurethane (PUE) cuff was designed to minimize these leakages. We therefore compared the sealing capacities of the two tubes in MV patients.

Methods

Twenty-nine consecutive MV patients (mean age ± SD: 68 13, 21 males), were randomly allocated to receive either a PV (HI-LO Evac, Mallinckrodt) or a PUE (SEALGUARD Evac, Mallinckrodt) cuffed endotracheal tube (size: 9 for men; 8 or 8.5 for women, as a rule). We excluded patients with emergency intubation, unstable haemodynamics, severe respiratory failure or patients with history of tracheal/laryngeal disease. In each patient, cuff pressure was maintained at 30 cmH₂O, and ventilator parameters were set to plateau pressure ≤30 cmH₂O; patients were fasting and placed in a strict semirecumbent position (45°). Radioactivity of tracheal aspirates was assessed sequentially (hourly samplings from T0 to T6 hours, then T8 hours and T12 hours) after injection of 74 MBq ^99mTc-DTPA diluted in 5 ml of 0.9% NaCl just above the cuff via the aspiration channel of the tube. Additionally, kinetics of respiratory tract contamination was followed by simultaneous pulmonary images using scintillation camera. Data were blindly analysed by nuclear physicians. The study was approved by the hospital ethics committee and informed consent was obtained from relatives.

Results

Sixteen PUE and 13 PV cuffed tubes were compared. The study was performed 3.2 ± 2.8 days after intubation and 8.3 ± 9.6 days after ICU admission (mean ± SD). Ventilator parameters were the following: volume control or pressure support but one on T tube, FiO₂ was 0.43 ± 0.14, PEEP 6 ± 2 cmH₂O. Leakages were observed in 11/29 patients (38%), with similar rate of aspiration in PUE (5/16) and PV (6/13) groups (P = NS). Leakages were more frequently observed in female (7/8) than in male patients (4/21) (P < 0.001). There was a trend to decreased frequency of aspiration in patients with larger tubes (size 9 vs 8.5: P = 0.062).

Conclusions

Both PUE and PV cuffed endotracheal tubes are poorly effective in preventing microaspirations in MV patients. Tube size and/or gender may be more important than cuff composition in the prevention of aspiration during MV.