Letters to the Editor
The modern polyvinylchloride endotracheal tube (ET) has a large cuff that conforms to the shape of the trachea and can seal it with a low pressure. This large-volume, low-pressure cuffed ET design has, therefore, largely replaced the older red rubber ET which has a small-volume, high-pressure cuff that predisposes to tracheal ischemic complications, particularly during long-term use (1).
The new intubating laryngeal mask endotracheal tube (ILM-ET) is an ET used in conjunction with the LMA-Fastrach™ Laryngeal Mask (Euromedical) for blind and fiberoptic-guided tracheal intubation. No specific information is currently available regarding the compliance characteristics of the ILM-ET cuff, which appears to be relatively small. Therefore, this study was designed to measure the compliance of the cuff of the ILM-ET and to compare it with that of the cuff of the polyvinylchloride and red rubber ET.
Four size 7.5-mm (inside diameter) of each ET type was tested. The cuff of each tube was incrementally inflated in air, and the corresponding cuff pressure was measured using a calibrated pressure manometer.
The ILM-ET cuff clearly exhibited high-pressure characteristics (Figure 1). At cuff volumes used during routine clinical practice, cuff pressure approached 100 mm Hg.
During inflation of a low-volume, high-pressure cuff, part of the cuff pressure is consumed in stretching the cuff wall itself. The pressure inside such a cuff is, therefore, higher than the pressure exerted on the tracheal mucosa (CT pressure) by the amount of pressure needed to maintain cuff inflation (2). Nonetheless, when using a low-volume, high-pressure cuffed ET, such as the ILM-ET, it is prudent to attempt to limit the CT pressure. Knowlson and Bassett (3) demonstrated that this could be achieved by inflating the cuff to the minimal volume that sealed the trachea (minimal occlusion volume [MOV]). The authors performed in vivo measurements of CT pressure in patients undergoing anesthesia with a low-volume, high-pressure cuff in place. The CT pressure ranged between 25 and 40 mm Hg at MOV, with a peak inflation pressure of 15 mm Hg and rose rapidly to very high levels with further increments in cuff volume. They concluded from their findings that low-volume, high-pressure cuffs were capable of sealing the trachea with reasonably low CT pressures as long as the cuff was maintained at MOV.
The high-pressure characteristics of the cuff of the ILM-ET can be used as an argument against its long term use. Other problems which can be encountered during the long term use of the ILM-ET are the susceptibility to biting and the potential for accumulation of secretions at the reduced-caliber tube tip.
In conclusion, the cuff of the ILM-ET is a low-volume, high-pressure cuff. It is, therefore, important when using this ET to maintain its cuff volume at MOV.
Esme Riley MD
Kerry DeGroot MD
Medhat Hannallah MD, FFARCS
1. Guyton D. Endotracheal and tracheostomy tube cuff design: influence on tracheal damage. In: Civetta J, Taylor R, Kirby R, eds. Critical care update. Vol 1, No. 3. Philadelphia: JB Lippincott, 1990:1–10.
2. Megee P. Endobronchial cuff pressures of double-lumen tubes. Anesth Analg 1991; 72: 265–6.
3. Knowlson G, Bassett H. The pressures exerted on the trachea by endotracheal inflatable cuffs. Br J Anaesth 1970; 42: 834–8.