Effect of end-inspiratory pause duration on respiratory system compliance calculation in mechanically ventilated dogs with healthy lungs

Abstract

Objective

To compare respiratory system compliance (C_RS), expressed per kilogram of bodyweight (C_RSBW), calculated without end-inspiratory pause (EIP) and after three EIP times (0.2, 0.5 and 1 seconds) with that after 3 second EIP (considered the reference EIP for static C_RS) and to determine the EIP times that provided C_RSBW values in acceptable agreement with static C_RSBW during controlled mechanical ventilation (CMV) in anaesthetized dogs.

Study design

Prospective, randomized, nonblinded, crossover clinical study.

Animals

A group of 24 client-owned dogs with healthy lungs undergoing surgery in lateral recumbency.

Methods

During CMV in dogs undergoing general anaesthesia, five EIPs [0 (no EIP), 0.2, 0.5, 1 and 3 seconds] were consecutively applied in random order. Tidal volume (Vt) was set at 10 mL kg^–1 and positive end-expiratory pressure (PEEP) was not applied. Respiratory rate and inspiratory time were established according to each EIP time, setting EIP between 0 and 50% of the inspiratory time. The C_RSBW was calculated as [expired Vt/(plateau pressure – PEEP)]/bodyweight and recorded every 15 seconds for 2 minutes after a 5 minute equilibration period with each EIP. One-way anova for repeated measures and the Bland–Altman analysis were used to compare C_RSBW and evaluate agreement between EIP times, respectively.

Results

The C_RSBW was significantly greater as the EIP time increased up to 1 second (p < 0.05). In the Bland–Altman analysis, none of the tested EIPs (0, 0.2, 0.5 and 1 seconds) provided 95% confidence intervals for limits of agreement within the maximum allowed difference considered for acceptable agreement with 3 second EIP.

Conclusions

and clinical relevance An EIP ≤ to 1 second does not provide a C_RSBW value in acceptable agreement with static C_RSBW in healthy dogs. Besides, the application of an EIP ≤ to 0.5 seconds underestimates the static C_RSBW to an increasing extent as the EIP time decreases.