Failure of recommended in vitro tests to detect a leak in flexometallic endotracheal tube cuff system: Are we really safe?

Sir,

We wish to report an interesting case where malfunctioning of a flexometallic endotracheal tube (ETT) went undetected even though the recommended routine checking for its proper functioning was done preoperatively.

A 24-year-old woman, American Society of Anesthesiologists grade I, was posted for L4-L5 lumbar discectomy surgery, to be done in prone position. After a standard safety check of anesthesia equipment, standard monitors were applied. General anesthesia was induced using standard anesthesia technique as per our hospital protocol. The trachea was intubated with a flexometallic tube (UnoflexTM) of size 7 mm ID. The ETT cuff was inflated with 6 mL of air and the ETT was fixed after confirmation of bilateral equal air entry. Ten minutes following intubation, while we were preparing to turn the patient prone, the cuff of the ETT got deflated. We reinflated the cuff, which almost immediately deflated again, implying some leak in the ETT cuff system. We replaced the ETT with another 7 mm ID flexometallic tube. The patient was positioned prone and the surgery went uneventfully. Following surgery, the patient recovered well from anesthesia.

Prior to use, the flexometallic ETT had appeared to function normally. Its cuff getting deflated 10 min following intubation was a bit surprising. We thus carefully examined it again, for functioning of its cuff system. The ETT had been used twice before. When we inflated its cuff, there was no leak and it remained inflated. No air bubbles were seen upon immersing the ETT in a bowl filled with water. No cuff leak was observed when concavity was maintained along the internal inflation lumen [Figure 1], which was the tube's natural shape.

Figure 1

Flexometallic endotracheal tube with inflated cuff, immersed in a bowl of water. The tube is in its natural shape, that is, concavity maintained at internal inflation lumen. No air bubbles or cuff leak seen

However, when this tube was straightened, its cuff got deflated. Air bubbles were seen to emanate from a point 18 cm from the ETT tip at the internal inflation lumen [Figure 2]. This was a possible simulation of probably what could have happened while we were about to position our patient prone. While the patient's head was held, stabilizing the ETT, extension of neck occurred because of which the flexometallic tube might have got straightened, exposing the occult defect causing cuff deflation.

Figure 2

The same flexometallic endotracheal tube with inflated cuff, straightened while immersed in a bowl of water. Air bubbles appear from a point 18 cm from the endotracheal tube tip, demonstrating a leak in cuff system

Intraoperative cuff deflation of the ETT may necessitate a change in the ETT. This is not only at times technically difficult but is fraught with risks putting patient safety at stake. It is thus mandatory to subject these tubes to in vitro tests for confirming the integrity of their cuff system prior to use. Although the standard tests recommended are able to detect most of these defects arising either due to reuse or a manufacturing defect, some may still escape as seen in our case and have been reported by Arya et al.,[1] and Tamakawa et al.,[2] We would like to highlight that flexing the ETT in different directions may expose occult defects atleast in some cases. It may be prudent to incorporate this simple test as a part of routine checking of endotracheal tubes, especially flexometallic tubes, to increase patient safety. This is particularly important as these tubes are often reused for economic reasons.