title: Assessment of distribution of ventilation and regional lung compliance by electrical impedance tomography in anaesthetized horses undergoing alveolar recruitment manoeuvres.
abstract: OBJECTIVE
  To examine changes in the distribution of ventilation and regional lung compliances in anaesthetized horses during the alveolar recruitment manoeuvre (ARM).
  
  
  METHODS
  Experimental study in which a series of treatments were administered in a fixed order on one occasion.
  
  
  METHODS
  Five adult Warmblood horses.
  
  
  METHODS
  Animals were anaesthetized (xylazine, midazolam-ketamine, isoflurane), placed in dorsal recumbency and ventilated with 100% oxygen using peak inspiratory pressure (PIP) and positive end-expiratory pressure (PEEP) of 20 cmH2O and 0 cmH2O, respectively. Thoracic electrical impedance tomography (EIT), spirometry and routine anaesthesia monitoring were performed. At 90 minutes after induction of anaesthesia, PIP and PEEP were increased in steps of 5 cmH2O to 50 cmH2O and 30 cmH2O, respectively, and then decreased to baseline values. Each step lasted 10 minutes. Data were recorded and functional EIT images were created using three breaths at the end of each step. Arterial blood samples were analysed. Values for left-to-right and sternal-to-dorsal centre of ventilation (COV), lung compliances and Bohr dead space were calculated.
  
  
  RESULTS
  Distribution of ventilation drifted leftward and dorsally during recruitment. Mean±standard deviation (SD) values at baseline and highest airway pressures, respectively, were 49.9±0.7% and 48.0±0.6% for left-to-right COV (p=0.009), and 46.3±2.0% and 54.6±2.0% for sternal-to-dorsal COV (p=0.0001). Compliance of dependent lung regions and PaO2increased, whereas compliance of non-dependent lung regions decreased during ARM and then returned to baseline (p<0.001). Bohr dead space decreased after ARM (p=0.007). Interestingly, PaO2correlated to the compliance of the dependent lung (r2=0.71, p<0.001).
  
  
  CONCLUSIONS
  The proportion of tidal volume distributed to dependent and left lung regions increased during ARM, presumably as a result of opening atelectasis. Monitoring compliance of the dependent lung with EIT may substitute PaO2measurements during ARM to identify an optimal PEEP.
authors.affiliation: Anaesthesiology and Perioperative Intensive Care Medicine, Department for Companion Animals and Horses, University of Veterinary Medicine, Vienna, Austria. Electronic address: tambrisko@hotmail.com.
authors.forename: Tamas D
authors.initials: TD
authors.lastname: Ambrisko
authors.affiliation: Anaesthesiology and Perioperative Intensive Care Medicine, Department for Companion Animals and Horses, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Schramel
authors.affiliation: Clinic for Horses, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Hopster
authors.affiliation: Clinic for Horses, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Kästner
authors.affiliation: Anaesthesiology and Perioperative Intensive Care Medicine, Department for Companion Animals and Horses, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Yves
authors.initials: Y
authors.lastname: Moens
mesh_terms: D000818:Animals; D017097:Electric Impedance; D006736:Horses; D008170:Lung Compliance / Q000502:physiology*; D011175:Positive-Pressure Respiration / Q000379:methods / Q000662:veterinary*; D011650:Pulmonary Alveoli / Q000502:physiology*; D012119:Respiration; D013990:Tidal Volume; D014054:Tomography / Q000379:methods / Q000662:veterinary
keywords: distribution of ventilation; electrical impedance tomography; horse; lung compliance; respiratory