[Inhalation anesthesia in the cat: Development of cuff pressure when using nitrous oxide].

Objective: During inhalation anesthesia with nitrous oxide in oxygen the pressure in the cuff of the endotracheal tube may increase due to diffusion of nitrous oxide into the cuff. The aim of the study was to investigate the development of cuff pressure during nitrous oxide anesthesia under clinical conditions in feline patients and to identify possible influencing factors such as tube size and gas flow rate.

Material And Methods: The prospective study included cats scheduled for inhalation anesthesia with nitrous oxide for a minimum duration of 60 minutes at the Department for Small Animals of the University of Leipzig. Cuff pressure was adjusted with a cuff manometer and its development was recorded.

Results: In total, the cuff pressure values of 24 cats were recorded. Animals were allocated into groups by tube size (ID 4.0 mm and ID 4.5 mm) and by fresh gas flow rate: low flow rate (0.6 l/min) and high flow rate (3 l/min). During anesthesia, cuff pressure increased over time, with statistical significance occurring from 45 minutes onwards in comparison to the initial cuff pressure (p=0.005). After 60 minutes, there was a mean cuff pressure increase of 3 cmHO. Despite this moderate mean increase, highly variable pressure values up to 48 cmHO in individual animals were recorded. No cat reached the termination criterion of 60 cmHO cuff pressure. Effects of tube size (p=0.63) and flow rate (p=0.334) on the cuff pressure were not evident.

Conclusion: After a period of 45 minutes of nitrous oxide administration, a significant increase in cuff pressure occurs in the cat. However, tube size and total gas flow rate do not seem to influence the cuff pressure development.

Clinical Relevance: When using nitrous oxide during inhalation anesthesia, regular cuff pressure evaluation and correction are necessary and hence recommended in feline patients. As individual pressure changes may be highly variable, no fixed recommendations for optimal management are possible.