Preliminary evaluation of the effects of a 1:1 inspiratory-to-expiratory ratio in anesthetized and ventilated horses |
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| Institution: | 1. Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA;2. School of Veterinary Medicine, Murdoch University, Perth, WA, Australia;3. Pharmacology and Toxicology, Facultad de Ciencias Veterinarias, Universidad Católica de Córdoba, Córdoba, CD, Argentina;4. Departamento de Medicina Intensiva, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile;5. Section of Veterinary Clinics and Animal Production, Department of Emergency and Organ Transplantation D.E.O.T., \"Aldo Moro\" University of Bari, Bari, Italy;6. Systems and Computer Engineering, Carleton University, Ottawa, ON, Canada |
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| Abstract: | ObjectiveTo describe some cardiorespiratory effects of an inspiratory-to-expiratory (IE) ratio of 1:1 compared with 1:3 in ventilated horses in dorsal recumbency.Study designRandomized crossover experimental study.AnimalsA total of eight anesthetized horses, with 444 (330–485) kg body weight median (range)].MethodsHorses were ventilated in dorsal recumbency with a tidal volume of 15 mL kg–1 and a respiratory rate of 8 breaths minute–1, and IE ratios of 1:1 (IE1:1) and 1:3 (IE1:3) in random order, each for 25 minutes after applying a recruitment maneuver. Spirometry, arterial blood gases and dobutamine requirements were recorded in all horses during each treatment. Electrical impedance tomography (EIT) data were recorded in four horses and used to generate functional EIT variables including regional ventilation delay index (RVD), a measure of speed of lung inflation, and end-expiratory lung impedance (EELI), an indicator of functional residual capacity (FRC). Results were assessed with linear and generalized linear mixed models.ResultsCompared with treatment IE1:3, horses ventilated with treatment IE1:1 had higher mean airway pressures and respiratory system compliance (p < 0.014), while peak, end-inspiratory and driving airway pressures were lower (p < 0.001). No differences in arterial oxygenation or dobutamine requirements were observed. PaCO2 was lower in treatment IE1:1 (p = 0.039). Treatment IE1:1 resulted in lower RVD (p < 0.002) and higher EELI (p = 0.023) than treatment IE1:3.Conclusions and clinical relevanceThese results suggest that IE1:1 improved respiratory system mechanics and alveolar ventilation compared with IE1:3, whereas oxygenation and dobutamine requirements were unchanged, although differences were small. In the four horses where EIT was evaluated, IE1:1 led to a faster inflation rate of the lung, possibly the result of increased FRC. The clinical relevance of these findings needs to be further investigated. |
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| Keywords: | electrical impedance tomography in horses equine mechanical ventilation equine respiratory mechanics inspiratory-to-expiratory ratios |
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