Measurement of tidal volume using Respiratory Ultrasonic Plethysmography in anaesthetized, mechanically ventilated horses

Abstract

ObjectiveTo compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses. Study designProspective randomized experimental study. AnimalsFive experimental horses. MethodsFive horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg−1) and positive end-expiratory pressures (PEEP) (0, 10, 20 cm H2O). Baseline ventilation mode (tidal volume = 15 mL kg−1, PEEP = 0 cm H2O) was applied for 4 minutes between all treatments. Spirometry and RUP data were downloaded to personal computers. Linear regression analyses (RUP versus spirometric tidal volume) were performed using different subsets of data. Additonally RUP was calibrated against spirometry using a regression equation for all RUP signal values (thoracic, abdominal and combined) with all data collectively and also by an individually determined best regression equation (highest R2) for each experiment (horse versus recumbency) separately. Agreement between methods was assessed with Bland-Altman analyses. ResultsThe highest correlation of RUP and spirometric tidal volume (R2 = 0.81) was found with the combined RUP signal in horses in lateral recumbency and ventilated without PEEP. The bias ± 2 SD was 0 ± 2.66 L when RUP was calibrated for collective data, but decreased to 0 ± 0.87 L when RUP was calibrated with individual data. Conclusions and clinical relevanceA possible use of RUP for tidal volume measurement during IPPV needs individual calibration to obtain limits of agreement within ± 20%.