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Monitoring changes in distribution of pulmonary ventilation by functional electrical impedance tomography in anaesthetized ponies

Auer, U., Schramel, J.P., Moens, Y.P., Mosing, M. and Braun, Ch. (2018) Monitoring changes in distribution of pulmonary ventilation by functional electrical impedance tomography in anaesthetized ponies. Veterinary Anaesthesia and Analgesia, 46 (2). pp. 200-208.

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To assess changes in the distribution in pulmonary ventilation in anaesthetized ponies using Electrical Impedance Tomography (EIT).

Study design

Prospective experimental study


Eight adult ponies geldings


General anaesthesia was induced and maintained using isoflurane in oxygen with volume-controlled ventilation [tidal volume (10 mL kg-1), respiratory rate (8 – 12 breaths minute-1)] to maintain end-tidal carbon dioxide between 35 and 40 mmHg (4.66–5.32 kPa). Regional distribution of ventilation was assessed with EIT (plane of 5th to 6th intercostal space) at 30, 60 and 90 minutes after intubation. The resulting functional images were divided into four regions of interest (ROI, A - D) to determine 1) the ratio of tidal volume distribution between dependent to non-dependent lung (D/ND), 2) changes in distribution within the lungs in latero-lateral direction. The centre of ventilation (COV) was calculated. The dimension of the chest in latero-lateral (W) and dorso-ventral (H) direction was measured at the height of the withers and the W/H ratio was calculated. The influence of time on D/ND ratio, COV and ROI A – D were analysed with ANOVA followed by post-hoc Bonferroni tests. Pearson correlation coefficient and the coefficient of determination (r2) were calculated to evaluate the relationship between W/H ratio and D/ND ratio, and COV. Statistical significance was set at p < 0.05.


The median D/ND ratio (T30 to T90) was 0.67 (0.40 -1.01) and for COV 31.15% (11.20-45.20), confirming the expected uneven distribution of ventilation. The D/ND ratio had a moderate negative correlation with the W/H ratio (r = -0.68, r2 = 0.46, p = 0.000), while the COV did not correlate with the W/H ratio (r = -0.04).


and clinical relevance: Uneven ventilation in mechanically ventilated right laterally recumbent anaesthetised ponies occurs within thirty minutes and changed little over the following 60 minutes.

Item Type: Journal Article
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Publisher: Elsevier Ltd.
Copyright: © 2018 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia
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