In-vitro endo tracheal tube cuff pressure decreases following transport via helicopter: implications for medical evacuation of military working dogs.

BACKGROUND: Altitude change impacts endotracheal tube cuff pressure (ETTCP) in human patients that are medically evacuated (MEDEVAC) via flight. While Military Working Dogs (MWD) are routinely transported via helicopter during evacuations for life threatening injuries, the effects of altitude on ETTCP have not been evaluated in veterinary medicine. This study aimed to evaluate if changes in altitude following transport in a helicopter impacts ETTCP in veterinary-grade endotracheal tubes (ETT) as seen in intubated human patients that are MEDEVAC via flight. METHODS: In an observational in-vitro study, 14 new, 11 mm polyvinyl chloride veterinary ETT were evenly divided into two groups (G1 and G2). All ETT were inflated to an initial ETTCP of 30 cmH2O at ground-level prior to the flight using one handheld manometer. All ETT were then transported together in a single helicopter flight for 1 h at varying altitudes up to 1022 m above sea level. ETTCP was measured via the same handheld manometer. In G1, ETTCP was measured twice, at inflation and following landing. In G2, ETTCP was measured at inflation and every 15 min following takeoff until landing. Altitude, barometric pressure, temperature (in and outside of the aircraft), and humidity were recorded. Groups were compared with a paired t-test (G1) and an ANOVA (f-test) followed by pairwise t-tests (G2) with significance set at p < 0.05. RESULTS: There was a 10 cmH2O or more decrease in ETTCP between the initial and final measurements in 71% and 100% ETT in G1 and G2, respectively. In G2, decreased ETTCP values became clinically relevant and statistically significant at 30 min post-takeoff. CONCLUSION: ETTCP fell below 20 cmH2O in 86% of ETT tested. During and following MEDEVAC in intubated canine patients, ETTCP should be reevaluated and adjusted.