Do we need inbuilt pressure monitoring systems across all cuffed airway devices?

We read with interest the bi-national survey by Lee et al. on the practice of cuff pressure monitoring of endotracheal tubes and supraglottic airway devices (SADs), highlighting the need for ongoing education related to this practice. ¹ We recently published a prospective observational study (n = 150) assessing the predictors of early postoperative pharyngolaryngeal complications arising from cuffed SADs, which found an overinflation rate of 62%. ² During this previous study, manometers were available in every operating room and two-thirds of our assessed cuffed SADs (96/150) were of the inbuilt pressure indicator type. Yet 63% (61/96) had been overinflated. ²

We have since conducted a departmental survey between March and April 2018 and would like to report our results, which also support the findings of Lee et al. ¹ A questionnaire survey was distributed to all the consultant anaesthetists (n = 35) and the anaesthetic nursing staff (n = 24) of our department. The survey was approved by the Human Research Ethics Committee of the Central Adelaide Local Health Network (reference no: Q20171003). The paper-based anonymous questionnaire survey had three questions containing multiple choice and free-text answering options. The devices with inbuilt pressure indicators were introduced in our department one month before commencing our study.

The three questions asked were:

Do you routinely monitor SAD cuff pressure? Yes/no

If you do not monitor cuff pressure, what are your reasons and beliefs behind it (multiple responses allowed): (a) relying on correct volume of air injected; (b) relying on pilot balloon tactile assessments; (c) not a believer that cuff pressure monitoring reduces pharyngolaryngeal complications; (d) a good seal matters more than the volume of air and the pressure generated in the cuff; (e) do not measure for a short duration procedure; (f) postoperative pharyngolaryngeal complications are not significant enough; or (g) other reasons.

Are you aware that the first-generation SADs used in our department have an inbuilt pressure monitor? Yes/no

Responses were collected from 31 of the 35 (88%) consultant anaesthetists and all 24 anaesthetic nurses. Only 25% (8/31) of the anaesthetic consultants and 33% (8/24) of the anaesthetic nurses reported routine monitoring of cuff pressure. Eighty three percent of the consultants (26/31) and 92% (22/24) of the anaesthetic nurses were aware the first-generation SADs used in our department had an inbuilt pressure monitor (admittedly there may have been inadequate education within the department when this new device was introduced). In total, 55% (17/31) of anaesthetists and 54% (13/24) of nurses responded they were relying on the volume of air injected in the cuff. Then 16% (5/31) of consultants and 25% (6/24) of anaesthetic nurses responded they were relying on the pilot balloon palpation technique. Overall, 35% (11/31) of consultants and 12.5% (3/24) of nurses reported they do not measure cuff pressure for short duration procedures. Of the anaesthetic consultants, 16% (5/31) felt that postoperative pharyngolaryngeal complications were not sufficiently significant to warrant routine manometry of the cuff. Choosing the SAD based on weight to reduce the inflating volumes, using lowest volume before a leak and checking for cuff leak with adjustable pressure limiting valve at 20 cmH₂O were the other reasons cited.

Various barriers and myths have been recognised in adopting routine manometry with cuffed SADs, as summarised by Bick et al. ³ These include: non-availability of manometers in every operating room, relying on recommended volumes of inflation, trusting pilot balloon palpation to estimate cuff pressures, accepting a high volume as far as good seal is achieved, lack of recognition of postoperative sore throat as a significant morbidity factor related to cuff pressure and a lack of awareness that more serious complications such as cranial nerve injuries can result from cuff overinflation. ³

Half of the consultants responded they would rely on set volumes for cuff inflation. In total, 16% reported trusting pilot balloon palpation and a similar proportion felt the pharyngolaryngeal complications were insignificant. However, inflating with recommended volumes can result in intracuff pressures as high as 200 cmH₂O. ⁴ These volume recommendations were originally based on the distending properties of the surface material of SADs, without taking into account the configuration of oropharyngeal mucosa and the pressure points generated inside the oral cavity. ³ With regard to balloon palpation, other studies have shown that anaesthetists, regardless of experience, are poor at judging the cuff pressures by a palpation technique, and hence trusting tactile assessment has been discouraged. ³

Although pharyngolaryngeal complications such as a sore throat are usually self-limiting, they can add significantly to post-anaesthetic morbidity. Limiting the cuff pressures to <60 cmH₂O can also prevent rare but serious adverse events such as cranial nerve injuries. ⁵ Our survey and our previous prospective study ² clearly reveal the uptake of cuff pressure monitoring is suboptimal. Others have reported that in the absence of routine manometry, the overinflation rate of cuffed SADs may be as high as 95%. ⁷ Another recent audit (2018) reported a 95% rate of overinflation. ⁸

There is increasing recognition that postoperative pharyngolaryngeal complications are directly linked to overinflation of cuffed SADs, and an editorial by Bick et al. has called for routine manometry as standard of care while using cuffed SADs. ³ Similar recommendations are in place from governing bodies such as the Association of Anaesthetists of Great Britain and Ireland. ⁶ Manometry may not be available universally and, being reusable, monitoring devices warrant adequate infection control measures. ⁹ It is worth emphasizing that dynamic changes in intracuff pressure can be expected with modifications in the position of the head and neck, use of N₂O and muscle relaxants. Hence, cuff pressure should be checked during vulnerable periods. The devices with an inbuilt pressure-monitoring system offer a viable alternative to ensure that the 60 cmH₂O mark is not breached. Further, they provide continuous real-time feedback of intracuff pressure dynamics. In our opinion, inbuilt pressure monitoring systems should be mandatory across all cuffed airway devices.