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

Objective To compare respiratory system compliance (CRS), expressed per kg of bodyweight (CRSBW), 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 CRS) and to determine the EIP times that provided CRSBW values in acceptable agreement with static CRSBW during controlled mechanical ventilation (CMV) in anaesthetised dogs. Study design Prospective, randomised, 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. The tidal volume (VT) was set at 10 mL kg-1 and positive end-expiratory pressure (PEEP) was not applied. The respiratory rate and the inspiratory time were established according to each EIP time, setting EIP between 0 and 50% of the inspiratory time. The CRSBW 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. The one-way ANOVA for repeated measures and the Bland-Altman analysis were used to compare CRSBW and evaluate agreement between EIP times, respectively. Results The CRSBW 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 CRSBW value in acceptable agreement with static CRSBW in healthy dogs. Besides, the application of an EIP ≤ to 0.5 seconds underestimates the static CRSBW to an increasing extent as the EIP time decreases.