Clinical and experimental observations on cuff systems of different endotracheal tube types

Abstract

Endotracheal intubation is a very important part of the anesthesia in small animal practice, and is used every day at the Clinic during surgeries. Intubation is however associated with complications, and several of these complications relate to the pressure in the cuff‐system. These are for example pressurenecrosis of the tracheal mucosa that may appear after long‐term intubation or due to over‐inflation of the cuff, and aspiration pneumonia that occurs if the cuffpressure is too low. These many risks made us search for data that would tell us how safe the different ET types are, and how reliable the methods are that we use to estimate the cuff pressure. The goal from this was to come up with conclusions of how to perform safer intubation and limit the complications associated with it. We discussed the differences between the modern high‐volume, lowpressure (compliant) cuffs and the low‐volume, high‐pressure (stiff) cuffs. Both the fact that compliant cuffs are gentler to the tracheal structures than stiff types, and the differences in pressure that are required for efficient sealing of trachea was discussed. In our in vitro study we tested the hypothesis that there will be a difference when recording pressure values in cuffs of high‐ and low‐pressure ETs. We wanted to find signals that could indicate wall contact of the cuff, and hypothesized that the pressure curve of the cuff shows a characteristic deviation after the membrane has reached the tracheal wall. While connecting an air‐filled syringe in a syringe‐pump to each ET‐type, and injecting air into the tubes while measuring the pressure in the system with a digital manometer, we recorded a pressure curve onto a computer. We compared the results and concluded how reliable cuff pressure measurement really is in these different tube types. Like we hypothesized; both pilot balloon and pressure gauge works inaccurately in the high‐pressure cuffed tubes, thus their clinical use in everyday anesthesia procedures is a possible source of error. In low‐pressure cuffed tubes however; cuff pressure does reflect the actual relation between the cuff and the tracheal 27 wall because there will be a deviation of the pressure curve that indicates wall contact. Therefore, in aspect of controlling the cuff‐pressure; these tubes are safer to use. In our in vivo study we tested the hypothesis that ET cuff pressures routinely become too high when only using the conventional technique. The study gave data on the ability of anesthesia providers to estimate correct cuff‐pressure by palpation of the pilot balloon. This was achieved by measuring the cuff‐pressures directly with a manometer, after letting the anesthesia provider inflate a lowpressure cuff and estimate the pressure by palpating the pilot balloon to what amount of air he or she thought was correct. Results showed that only 10% of the anesthesia providers could inflate the ideal amount of 20‐25 cmH2O air into the cuff. Rest of the time, which was the majority (90%) of the cases, cuffpressure ended up too high. Thus, over‐inflation of cuffs is common at the Clinic of Surgery, and this is proved both by our measurements and by X‐rays. Accordingly, damage to the trachea may be a common complication after surgery on the Clinic. Only palpation of the pilot balloon provides unreliable control of the cuff pressure. Manometric control of cuff pressure should therefore always be considered to reduce risk caused by endotracheal intubation.