title: Cardiovascular, respiratory and metabolic responses to apnea induced by atlanto-occipital intrathecal lidocaine injection in anesthetized horses.
abstract: OBJECTIVE
  To determine physiologic responses to apnea-induced severe hypoxemia in anesthetized horses.
  
  
  METHODS
  Prospective experimental study.
  
  
  METHODS
  Six university-owned horses with a median (range) body weight of 500 (220-510) kg and aged 13.5 (0.8-24.0) years scheduled for euthanasia.
  
  
  METHODS
  Xylazine-midazolam-ketamine-anesthetized horses breathing room air spontaneously were instrumented with a facial artery catheter for pressure measurement and blood sampling, and were made apneic with atlanto-occipital intrathecal lidocaine (4 mg kg-1). Cardiopulmonary, biochemical and hematologic variables were recorded before (baseline) and every minute for 10 minutes after lidocaine injection.
  
  
  RESULTS
  PaO2values were: baseline, 55 mmHg (7.3 kPa); 1 minute, 28 mmHg (3.8 kPa); 2 minutes, 18 mmHg (2.4 kPa); 3 minutes, 15 mmHg (2.0 kPa), and 4-10 minutes, (8-11 mmHg (1.1-1.5 kPa). PaCO2values were: baseline, 50 mmHg (6.7 kPa); 1 minute, 61 mmHg (8.1 kPa), and 2-10 minutes, 64-66 mmHg (8.5-8.8 kPa). Base excess values at baseline, 1 minute and 2-10 minutes were 5.3 mmol L-1, 6.5 mmol L-1and 7.0-8.1 mmol L-1, respectively. Pulse rates at baseline, 1 minute and 2-7 minutes were 36, 53 and 54-85 beats minute-1, respectively. Asystole occurred at 8 minutes. Pulse pressures were 50 mmHg at baseline and 1 minute, and 39 mmHg, 31 mmHg, 22 mmHg, 17 mmHg and 1-9 mmHg at 2, 3, 4, 5 and 6-10 minutes, respectively. Lactate was 0.9 mmol L-1at baseline, progressively increasing to 1.7-2.4 mmol L-1at 7-10 minutes. Packed cell volume increased after 7 minutes of apnea. There were no other major changes.
  
  
  CONCLUSIONS
  Apnea immediately exacerbated hypoxemia and hypercapnia and rapidly caused hemodynamic instability. Apnea in hypoxemic anesthetized horses is associated with a serious risk for progress to cardiovascular collapse.
authors: Department of Surgical and Radiological Sciences, University of California, Davis, CA, USA. guede003@umn.edu.|Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN, USA. guede003@umn.edu.
authors: Alonso
authors: A
authors: Guedes
authors: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors: Monica
authors: M
authors: Aleman
authors: International Animal Welfare Training Institute, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors: Eric
authors: E
authors: Davis
authors: William R Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors: Caitlin
authors: C
authors: Tearney
mesh_terms: D000758:Anesthesia / Q000662:veterinary; D000777:Anesthetics / Q000008:administration & dosage*; D000818:Animals; D001049:Apnea / Q000139:chemically induced / Q000662:veterinary*; D002319:Cardiovascular System / Q000187:drug effects; D005260:Female; D006736:Horses; D000860:Hypoxia / Q000209:etiology / Q000662:veterinary*; D007278:Injections, Spinal / Q000662:veterinary; D008012:Lidocaine / Q000008:administration & dosage*; D008297:Male; D011446:Prospective Studies; D012119:Respiration / Q000187:drug effects
chemical_list: D000777:Anesthetics; D008012:Lidocaine
keywords: heart rate; hypercapnia; hypotension; hypoxia; mortality