Comparison of early and late time-controlled adaptive ventilation on pulmonary gas exchange in anesthetized horses.

OBJECTIVE

To compare early versus late time-controlled adaptive ventilation (TCAV) for setting airway pressure release ventilation (APRV) on arterial oxygenation in dorsally recumbent anesthetized horses.

STUDY

DESIGN

A crossover, nonrandomized, experimental study.

ANIMALS: Six healthy adult horses.

METHODS

Each horse underwent two anesthetics: 1) volume-controlled ventilation (VCV) began for 30 minutes before switching to APRV using the TCAV method (late TCAV, TCAVL); and 2) ventilation began immediately with TCAV (early TCAV, TCAVE). The study lasted 180 minutes, with arterial blood gases and respiratory mechanics recorded at T0 and every 30 minutes. Electrical impedance tomography (EIT) was performed at T0, T30, T90 and T180 to calculate mid-cranial regional ventilation. A two-way repeated measures analysis of variance was used for comparisons. Lung ultrasound (LUS) images were obtained from three horses at baseline (before anesthesia) and at T30, T60, T120 and T180 during each crossover to calculate a mid-caudal LUS score. No statistical analysis was performed on ultrasound data.

RESULTS

TCAVE showed significantly higher partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2/FiO2) than TCAVL, whereas TCAV did not significantly affect it compared with VCV in the TCAVL group. TCAVE resulted in significantly higher tidal volumes (VT)than TCAVL, whereas in the TCAVL group, TCAV reduced VT compared with VCV. No significant differences were found in respiratory system compliance or airway driving pressure. Both TCAVE and TCAVL significantly improved dorsal lung ventilation on EIT, but TCAVL failed to reverse caudal atelectasis and consolidation seen on LUS, whereas TCAVE appeared to prevent it.

CONCLUSIONS AND CLINICAL RELEVANCE: TCAVE improved oxygenation and regional ventilation, whereas TCAVL failed to improve respiratory mechanics or oxygenation compared with VCV.