title: Regional distribution of ventilation in horses in dorsal recumbency during spontaneous and mechanical ventilation assessed by electrical impedance tomography: a case series.
abstract: OBJECTIVE
  To evaluate the regional distribution of ventilation in horses during spontaneous breathing and controlled mechanical ventilation (CMV) using electrical impedance tomography (EIT).
  
  
  METHODS
  Prospective, experimental case series.
  
  
  METHODS
  Four anaesthetized experimental horses.
  
  
  METHODS
  Horses were anaesthetized with isoflurane in an oxygen-air mixture and medetomidine continuous rate infusion, placed in dorsal recumbency with an EIT belt around the thorax, and allowed to breathe spontaneously until PaCO2reached 13.3 kPa (100 mmHg), when volume CMV was started. For each horse, the EIT signal was recorded for at least 2 minutes immediately before (T1), and at 30 (n = 3) or 60 (n = 1) minutes after the start of CMV (T2). The centre of ventilation (CoV), dependent silent spaces (DSS) (likely to represent atelectatic lung areas), non-dependent silent spaces (NSS) (likely to represent lung areas with low ventilation) and total ventilated area (TVA) were evaluated. Cardiac output (CO) was measured and venous admixture and oxygen delivery (DO2) were calculated at T1 and T2. Data are presented as median and range.
  
  
  RESULTS
  After the initiation of CMV, the CoV moved ventrally towards the non-dependent lung by 10% [from 57.4% (49.6-60.2%) to 48.3% (41.9-54.4%)]. DSS increased [from 4.1% (0.2-13.9%) to 18.7% (7.5-27.5%)], while NSS [21.7% (9.4-29.2%) to 9.9% (1.0-20.7%)] and TVA [920 (699-1051) to 837 (662-961) pixels] decreased. CO, venous admixture and DO2also decreased.
  
  
  CONCLUSIONS
  In spontaneously breathing anaesthetized horses in dorsal recumbency, ventilation was essentially centred within the dependent dorsal lung regions and moved towards non-dependent ventral regions as soon as CMV was started. This shows a major lack of ventilation in the dependent lung, which may be indicative of atelectasis.
authors.affiliation: Equine Department, Section of Anaesthesiology, Vetsuisse Faculty, University of Zürich, Zürich, Switzerland.
authors.forename: Martina
authors.initials: M
authors.lastname: Mosing
authors.affiliation: Equine Department, Section of Anaesthesiology, Vetsuisse Faculty, University of Zürich, Zürich, Switzerland. Electronic address: chm062@mail.usask.ca.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Marly-Voquer
authors.affiliation: Langford Veterinary Services, University of Bristol, Bristol, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: MacFarlane
authors.affiliation: School of Veterinary Science, Leahurst Campus, University of Liverpool, Neston, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bardell
authors.affiliation: Swisstom AG, Landquart, Switzerland.
authors.forename: Stephan H
authors.initials: SH
authors.lastname: Böhm
authors.affiliation: Equine Department, Section of Anaesthesiology, Vetsuisse Faculty, University of Zürich, Zürich, Switzerland.
authors.forename: Regula
authors.initials: R
authors.lastname: Bettschart-Wolfensberger
authors.affiliation: Swisstom AG, Landquart, Switzerland.
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Waldmann
mesh_terms: D000758:Anesthesia / Q000379:methods / Q000662:veterinary; D018685:Anesthetics, Inhalation; D000818:Animals; D017097:Electric Impedance; D006734:Horse Diseases / Q000503:physiopathology; D006736:Horses; D007530:Isoflurane; D008168:Lung / Q000502:physiology*; D020926:Medetomidine; D056888:Patient Positioning / Q000379:methods / Q000662:veterinary; D011446:Prospective Studies; D001261:Pulmonary Atelectasis / Q000503:physiopathology / Q000662:veterinary; D012119:Respiration; D012121:Respiration, Artificial / Q000379:methods / Q000662:veterinary*; D014054:Tomography
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane; D020926:Medetomidine
keywords: anaesthesia; controlled mechanical ventilation; distribution of ventilation; electrical impedance tomography; horse; lung aeration