The use of electrical impedance tomography to assess distribution of ventilation in equine medicine

Muriel Sacks

Background: The non-invasive real-time imaging modality electrical impedance tomography (EIT) detects alterations of tissue impedance within the thorax. While EIT has been used to document the distribution of ventilation in anaesthetised horses, there is little information on clinical implications of EIT in equine medicine. The aim of this thesis was to confirm the hypothesis that EIT is a useful tool for monitoring alterations in ventilation caused by cardiac disease in adult horses and during clinical interventions in foals. Animals: Fourteen adult horses (healthy: 8, mean (± SD) age of 10.5 (± 2.8) years; cardiac disease: 4 compensated, 2 decompensated, mean (± SD) age of 18.0 (± 11.5) years), six healthy foals with a median age of 23 days (range 8 to 29 days). Material and methods: Two prospective research studies collecting EIT data in 1) standing adult horses with and without left-sided cardiac volume overload (LCVO), and 2) foals undergoing sedation, body position change and administration of positive pressure support ventilation (PPSV). Data was analysed for conventional EIT variables including ventral to dorsal (COVVD) and right to left centers of ventilation, silent spaces and right to left ventilation ratio, and for non-conventional variables such as ventilated right (VAR) and left (VAL) lung area and linear-plane distribution variables (avg-max VZLine, VZLine). Statistical tests were applied in accordance with individual data sets and study design, with significance determined at p < 0.05. Results: Compared to healthy horses, horses with LCVO had significantly smaller VAL (p = 0.016) and greater VAR (p = 0.037), smaller avg-max VZLLine (p = 0.003) and VZLLine (p = 0.013). In foals, diazepam sedation did not cause significant changes to distribution of ventilation. Right lateral recumbency led to a significant decrease in right to left ratio (p = 0.0017). In dorsal recumbency, increasing levels of PPSV led to a significant increase in COVVD (p = 0.0009). Conclusions: EIT can demonstrate changes in ventilation distribution in horses with cardiopulmonary disease as well as during clinical interventions in foals and therefore embodies a promising clinical tool for the monitoring of subtle pulmonary changes in horses with cardiac disease, as well as identifying ventilation shifts in foals.

The use of electrical impedance tomography to assess distribution of ventilation in equine medicine

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