Equis ISSN 2398-2977

Anesthesia: monitoring - cardiac output and blood pressure

Contributor(s): Dennis R Gieser, Matthew Gurney, Craig Johnson, G Mark Johnston, Vetstream Ltd


  • Measurement of arterial blood pressure is an important monitoring tool in equine anesthesia.
  • Arterial blood pressure should be maintained above 60-70 mmHg to reduce the risk of developing anesthetic related myopathies/neuropathies   Anesthesia: peri-operative complications - post-operative myopathy  .
  • Measurement of cardiac output is technically difficult and the equipment is expensive. It is currently limited to a research tool at present in the veterinary field.
  • Arterial blood pressure does not equate to cardiac output, but can give a good indication of cardiovascular performance. 
  • Arterial blood pressure = cardiac output x systemic vascular resistance.
  • In general, raised blood pressure is associated with increased cardiac output, increased peripheral resistance or a lighter anesthesia. Under anesthesia a sudden increase in mean arterial pressure often precedes movement.
  • In most cases, hypotension   Anesthesia: peri-operative complications - hypotension   is associated with decreased cardiac output as a result of myocardial depression, eg due to anesthesia being too deep, endotoxic shock or acidosis.
  • All inhalational anesthetic agents cause a dose dependent hypotension.
  • Hypotension may also be associated with arrhythmias, eg bradycardia   Heart: sinus bradycardia  , sinus arrest   Heart: sinus block  , atrioventricular block   Heart: atrioventricular block - 1st degree    Heart: atrioventricular block - 2nd degree  , or ventricular tachycardia   Heart: ventricular tachycardia  , or reduced venous return (due to positioning of the horse, hypovolemia or abdominal distension).
  • Some premedicant drugs   Anesthesia: premedication - overview  can cause hypotension.
  • Measurement of arterial blood pressure   Cardiovascular: blood pressure monitoring  can be by either direct or indirect methods.

Arterial blood pressure

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Central venous pressure (CVP)

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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Menzies-Gow N J (2008) Effects of sedation with acepromazine on echocardiographic measurements in eight healthy thoroughbred horses. Vet Rec 163 (1), 21-25 PubMed.
  • Barr E D, Clegg P D, Senior J M & Singer E R (2005) Destructive lesions of the proximal sesamoid bones as a complication of dorsal metatarsal artery catheterization in three horsesVet Surg 34 (2), 159-166 PubMed.
  • Trim C M (1998) Monitoring during anesthesia - techniques and interpretation. Equine Vet Educ 10 (4), 207-218 VetMedResource.
  • Jones J L (1996) Invasive monitoring techniques in anesthetized animals. Vet Med, 326 VetMedResource.
  • Jones J L (1996) Non-invasive monitoring techniques in anesthetized animals. Vet Med, 337 VetMedResource.
  • Keegan R D, Greene S A (1994) Equine anesthesia; blood pressure and monitoring - a review. Equine Pract 16 (7), 26.
  • Riebold T W (1990) Monitoring Equine Anesthesia. Vet Clin North Am Equine Pract (3), 607-624 PubMed.
  • Young S (1989) Monitoring the anesthetized horse. Equine Vet Educ 1, 45-49.

Other sources of information

  • Taylor P M & Clarke K W (2005) Handbook of Equine Anesthesia. 3rd edn. W B Saunders, UK.
  • Hubbell J A E (1991) Monitoring. In: Equine Anesthesia Monitoring & Emergency Therapy. Eds: Muir W W & Hubbell J A E. Mosby. pp 153-179. ISBN: 0-8016-3576-4.
  • McDonell W N & Dyson D H (1990) Monitoring the anesthetized horse. In: Current Practice of Equine surgery. Eds N A White & J N Moore. Lippincott. pp 87-93. ISBN: 0-397-50937-5.