Changes of endotracheal tube cuff pressure and its indicators in laparoscopic resection of colorectal neoplasms: an observational prospective clinical trial. comment on: BMC anesthesiology. 2024 Nov 13;24(1):413

Abstract

It is important to consider some of the study variables which may influence the interpretation of the paper from Cai et al. on endotracheal tube cuff pressures during laparoscopic colorectal surgery. These include cuff compliance, tracheal diameter, peritoneal insufflation pressures and the use of volume control ventilation.

Clinical trial number

Not applicable.

Dear Editor,

I read with interest the article from Cai et al. [1] reporting on the changes of endotracheal tube cuff pressure and its indicators in laparoscopic resection of colorectal neoplasms. The study provided an interesting insight into the changes in cuff pressures during pneumoperitoneum, as well as quantifying some dramatic increases in pressures seen during the study. The authors also sought to identify potential predictors for out-of-range cuff pressures during laparoscopy. However, there are some points of note which require further discussion and clarification.

First, the size of endotracheal tube (ETT) was noted to be 7.0 -7.5 for females, and 7.5 to 8.0 for males. BMI data was provided, and a size 8.0 ETT was used in only 1 patient. Additionally, the volume of air injected into the cuff of the ETT was noted to be 5-8mls in all cases prior to cuff pressure measurement. When interpreting the cuff pressures in this study it is important to consider the compliance of the cuff itself, which is dependent on the properties of the cuff material and the volume of air required to seal against the trachea, and individual patient anatomy.

A relatively undersized ETT tube which is inflated to the same measured cuff pressure as a larger ETT for a given tracheal diameter may be less compliant (where C = ΔV/P), and therefore similar external forces may result in larger pressure spikes within a less compliant cuff. Anatomical variations in tracheal calibre can affect cuff pressure [2], and would be an important potential predictor of cuff pressure variations in this study. Although this would be more challenging to measure, the use of ultrasound has previously been described for measurement of tracheal calibre, including in patients undergoing intubation for elective surgery [3,4,5] and could have been assessed with the other anatomical measurements investigated by the authors. Measurement of cuff compliance in addition to pressure alone would also have been useful in this study.

Secondly, the choice of ventilation strategy needs to be considered. Pressure controlled (PC) modes are associated with lower peak pressures during laparoscopic surgery [6, 7]. The use of volume-controlled (VC) ventilation may have influenced the cuff pressures more so than PC ventilation mode, as the inspiratory pressures may be more variable between breaths in a volume-controlled mode. Additionally, the use of a fixed I: E ratio of 1:2 may have been required to standardise the anaesthesia protocol for the purposes of the study, however prolonged I: E ratios may reduce peak pressures during laparoscopic surgery [8]. An anaesthesia protocol which used pressure-controlled ventilation and a longer inspiratory time, perhaps more reflective of true clinical practice, may have yielded lower peak cuff pressures.

Lastly, the peritoneal insufflation pressures were not reported. Higher intraperitoneal pressures during colorectal surgery can influence the respiratory mechanics and the inspiratory pressures required achieve adequate tidal volumes [9], which can in turn influence the measured internal cuff pressures.

In conclusion, it is important to consider some of the variables which may influence the interpretation of this study such as cuff compliance, peritoneal insufflation pressures and use of volume control ventilation, and their potential effects on the cuff pressures reported in this study. When searching for an anatomical measurement as a predictor for out-of-range cuff pressures, tracheal diameter should be considered an important potential marker which, if correlated with the risk of higher cuff pressures, would be easily measured with ultrasound at the bedside in clinical practice.