title: Horses Auto-Recruit Their Lungs by Inspiratory Breath Holding Following Recovery from General Anaesthesia.
abstract: This study evaluated the breathing pattern and distribution of ventilation in horses prior to and following recovery from general anaesthesia using electrical impedance tomography (EIT). Six horses were anaesthetised for 6 hours in dorsal recumbency. Arterial blood gas and EIT measurements were performed 24 hours before (baseline) and 1, 2, 3, 4, 5 and 6 hours after horses stood following anaesthesia. At each time point 4 representative spontaneous breaths were analysed. The percentage of the total breath length during which impedance remained greater than 50% of the maximum inspiratory impedance change (breath holding), the fraction of total tidal ventilation within each of four stacked regions of interest (ROI) (distribution of ventilation) and the filling time and inflation period of seven ROI evenly distributed over the dorso-ventral height of the lungs were calculated. Mixed effects multi-linear regression and linear regression were used and significance was set at p<0.05. All horses demonstrated inspiratory breath holding until 5 hours after standing. No change from baseline was seen for the distribution of ventilation during inspiration. Filling time and inflation period were more rapid and shorter in ventral and slower and longer in most dorsal ROI compared to baseline, respectively. In a mixed effects multi-linear regression, breath holding was significantly correlated with PaCO2 in both the univariate and multivariate regression. Following recovery from anaesthesia, horses showed inspiratory breath holding during which gas redistributed from ventral into dorsal regions of the lungs. This suggests auto-recruitment of lung tissue which would have been dependent and likely atelectic during anaesthesia.
authors.affiliation: Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Martina
authors.initials: M
authors.lastname: Mosing
authors.affiliation: Swisstom AG, Landquart, Switzerland.
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Waldmann
authors.affiliation: Langford Veterinary Services, University of Bristol, Bristol, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: MacFarlane
authors.affiliation: CTU Bern, University of Bern, Bern, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Iff
authors.affiliation: Veterinary University Vienna, Vienna, Austria.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Auer
authors.affiliation: Swisstom AG, Landquart, Switzerland.
authors.forename: Stephan H
authors.initials: SH
authors.lastname: Bohm
authors.affiliation: Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Regula
authors.initials: R
authors.lastname: Bettschart-Wolfensberger
authors.affiliation: School of Veterinary Science, University of Liverpool, Liverpool, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Bardell
mesh_terms: D000762:Anesthesia Recovery Period; D000768:Anesthesia, General; D000818:Animals; D001784:Blood Gas Analysis; D062485:Breath Holding; D002245:Carbon Dioxide / Q000032:analysis; D017097:Electric Impedance; D006736:Horses / Q000502:physiology*; D001239:Inhalation / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide