title: The effect of two different intra-operative end-tidal carbon dioxide tensions on apnoeic duration in the recovery period in horses.
abstract: OBJECTIVE
  To compare the effect of two different intraoperative end-tidal carbon dioxide tensions on apnoeic duration in the recovery period in horses.
  
  
  METHODS
  Prospective randomized clinical study.
  
  
  METHODS
  Eighteen healthy client-owned adult horses (ASA I-II) admitted for elective surgery. Horses were of a median body mass of 595 (238-706) kg and a mean age of 9 ± 5 years.
  
  
  METHODS
  A standardized anaesthetic protocol was used. Horses were positioned in dorsal recumbency and randomly allocated to one of two groups. Controlled mechanical ventilation (CMV) was adjusted to maintain the end-tidal carbon dioxide tension (Pe'CO2 ) at 40 ± 5 mmHg (5.3 ± 0.7 kPa) (group 40) or 60 ± 5 mmHg (8.0 ± 0.7 kPa) (group 60). Arterial blood gas analysis was performed at the start of the anaesthetic period (T0), at one point during the anaesthetic (T1), immediately prior to disconnection from the breathing system (T2) and at the first spontaneous breath in the recovery box (T3). The time from disconnection from the breathing system to return to spontaneous ventilation (RSV) was recorded. Data were analysed using a two sample t-test or the Mann-Whitney U-test and significance assigned when p < 0.05.
  
  
  RESULTS
  Horses in group 60 resumed spontaneous breathing significantly earlier than those in group 40, [52 (14-151) and 210 (103-542) seconds, respectively] (p < 0.001). Arterial oxygen tension (PaO2 ), pH, base excess (BE) and plasma bicarbonate (HCO3-) were not different between the groups at RSV, however, PaO2 was significantly lower in group 60 during (T1) and at the end of anaesthesia (T2).
  
  
  CONCLUSIONS
  Aiming to maintain intra-operative Pe'CO2 at 60 ± 5 mmHg (8.0 ± 0.7 kPa) in mechanically ventilated horses resulted in more rapid RSV compared with when Pe'CO2 was maintained at 40 ± 5 mmHg (5.3 ± 0.7 kPa).
authors.affiliation: Small Animal Teaching Hospital, University of Liverpool, Neston, UK.
authors.forename: Kate R
authors.initials: KR
authors.lastname: Thompson
authors.affiliation: Philip Leverhulme Equine Hospital, University of Liverpool, Neston, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bardell
mesh_terms: D000758:Anesthesia / Q000662:veterinary*; D000762:Anesthesia Recovery Period; D000818:Animals; D001049:Apnea / Q000209:etiology / Q000517:prevention & control / Q000662:veterinary; D002245:Carbon Dioxide; D006736:Horses; D007430:Intraoperative Care / Q000662:veterinary*; D010313:Partial Pressure; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial / Q000662:veterinary*
chemical_list: D002245:Carbon Dioxide
keywords: apnoea; horses; hypercapnia; recovery period; ventilation