Do current methods for endotracheal tube cuff inflation create pressures above the recommended range? A review of the evidence

Pressure changes in the endotracheal tube cuff in otorhinolaryngologic surgery: a prospective observational study

Objective

Inflation of the endotracheal tube cuff is needed for providing ventilation. Cuff pressure should be maintained inside the appropriate range to prevent critical airway complications. The purpose of this study is to evaluate the pressure changes in the endotracheal tube cuff during otorhinolaryngologic surgery.

Design and method

This single-center observational study was conducted at Severance Hospital in Korea between April 2020 and November 2020. Patients aged >20 years scheduled to undergo otorhinolaryngological surgical procedures were enrolled. Patients undergoing planned tracheostomy and those who were slated for uncuffed endotracheal tube use were excluded. Intubation was performed after the induction of general anesthesia. A pressure transducer was connected to the pilot balloon of the endotracheal tube, and cuff pressure was continuously monitored until extubation. If the cuff pressure was not appropriate for more than 5 min, it was adjusted to the appropriate range by injecting or removing air. The percentage of time for which the cuff pressure remained within the appropriate range was calculated and defined as the time in the therapeutic range (TTR). The presumed cause for the rise or fall in cuff pressure was identified.

Results

In total 199 patients, alterations in cuff pressure outside the appropriate range occurred in 191 patients (96.0%). The mean TTR was 79.7% (SD 25.0%), and head and neck surgery had the lowest mean TTR of 69.0% compared to ear and nose surgeries (94.2 and 82.1%, respectively). Sixty-eight patients (34.2%) demonstrated inadequate endotracheal tube cuff pressure for more than 20% of the total anesthesia time. Twenty-six patients (13.1%) demonstrated optimal endotracheal tube cuff pressure for less than 50% of the total anesthesia time. The causative factors inducing inappropriate cuff pressure were found to vary, including positional changes, surgical procedure, anatomical manipulation, and anesthetic procedure.

Conclusion

In otorhinolaryngologic surgery, cuff pressure increased or decreased outside the appropriate range due to various factors. Therefore, we suggest close continuous monitoring of cuff pressure during anesthesia for otorhinolaryngologic surgery.

Clinical trial registration

clinicaltrials.gov, identifier NCT03938493.

Bronchial blockers under pressure: in vitro model and ex vivo model

BACKGROUND

Pressures (Pe) exerted by bronchial blockers on the inner wall of the bronchi may cause mucosal ischaemia. Our aims were as follows: (i) to compare the intracuff pressure (Pi) and Pe exerted by commercially available bronchial blockers in an in vitro and an ex vivo model; (ii) to investigate the influence of both the inflated intracuff volume and cuff diameter on Pe; and (iii) to estimate the minimal sealing volume (VSmin) and the corresponding Pe for each bronchial blocker studied.

METHODS

The Pe exerted by seven commercial bronchial blockers was measured at different inflation volumes using a custom-designed system using in vitro and ex vivo animal models with two internal diameters (12 and 15 mm).

RESULTS

In the same conditions, Pi was significantly lower than Pe (P<0.05), and Pe was higher in the in vitro model than in the ex vivo model. The Pe increased with the inflated volume, with use of the small-diameter model (P<0.05). Ex vivo models needed a higher minimal sealing volume than the in vitro models, and this volume increased with the diameter (e.g. the VSmin at a positive pressure of 25 cm H2O required a Pe ranging from 12 to 78 mm Hg on the 15 mm ex vivo model and from 66 to 110 mm Hg on the 12 mm ex vivo model).

CONCLUSIONS

The Pi cannot be used to approximate Pe. The diameter of the model, the inflated volume, and the bronchial blocker design all influence Pe. A pressure higher than the critical ischaemic threshold (i.e. 25 mm Hg) was needed to prevent air leak around the cuff in the in vitro and ex vivo models.

Design and characterization of a measurement system for monitoring pressure exerted by bronchial blockers: In vitro trials

Bronchial blockers (BBs) allow occluding the bronchial duct and collapsing the "dependent" lung in a number of thoracic surgery. The occlusion is obtained through a cuff that, inflated with a proper air volume, exerts a pressure, Pe, on the inner wall of the mainstem bronchus. In this work a measurement chain, based on two piezorestistive force sensors, was developed and calibrated to measure Pe exerted by six BBs, as a function of inflated volume on in vitro models (two latex ducts with diameters similar to the ones of the adult mainstem bronchi: 12 mm and 15 mm). Pe showed wide changes considering different BBs, and significantly increases with the decrease of the model's diameter, at the same inflated volume. Lastly, the minimum occlusive volume (MOV) to sail the two models was estimated for each BB. These experiments were performed by applying a pressure difference across the cuff of 25 cmH2O, in order to simulate the worst condition in a clinical scenario. Results show that MOV depends on both the type of BB and the duct diameter. The knowledge of this volume allows estimating the minimum value of Pe exerted by BBs to avoid air leakage.