Introduction

• 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

Central venous pressure (CVP)

Further Reading

Publications

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 horses. Vet 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 6 (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.