Canis ISSN: 2398-2942

Blood pressure: direct measurement

Synonym(s): Invasive arterial blood pressure monitoring

Contributor(s): John Dodam

Introduction

Rationale

  • Arterial blood pressure is the product of stroke volume, heart rate and total peripheral resistance.
  • There is some variation between published values for 'normal' arterial blood pressure in different sources. Suggested values: systolic pressure 105-145 mmHg; diastolic pressure 55-85 mmHg; mean arterial pressure 90-110 mmHg.
    Mean pressure is the hydrostatic intravascular pressure in the vessel during one complete cardiac cycle, NOT the arithmetic mean of the systolic and diastolic pressures
  • Almost all general anesthetic drugs and some premedicant drugs cause hypotension by affecting one or more of the following factors: total peripheral resistance, stroke volume, heart rate. Their effects are often dose related.
  • Adequate arterial blood pressure is necessary to maintain sufficient tissue perfusion to avoid cellular damage and/or death.
  • In anesthetic monitoring, mean arterial pressure should be maintained above 70 mmHg.

Uses

  • Accurate monitoring of arterial blood pressure enables appropriate corrective measures to be taken to ensure adequate tissue perfusion if hypotension develops.
  • Particularly beneficial in animals which are hypovolemic prior to surgery, have pre-existing cardiovascular system disease, or are undergoing procedures where significant blood loss or large fluctuations in blood pressure are anticipated.
  • Mean arterial pressure and cardiac output are maintained at normal levels until 10% of circulating blood volume has been lost.
  • Mean arterial blood pressure is maintained by constriction of arterioles at deficits of circulating blood volume between 10 and 20%, but cardiac output is reduced.
  • At deficits of circulating blood volume in excess of 20%, mean arterial blood pressure is no longer maintained and hypotension develops.

Pros

  • Most accurate estimation of arterial blood pressure.
  • Equipment required for determination of mean arterial pressure alone is inexpensive compared with that for oscillometric indirect technique.
  • Arterial cannulae can also be used to collect samples for blood gas analysis.

Cons

  • Requires arterial cannulation with attendant risks, eg hemorrhage, sepsis, thromboembolism.
  • Arterial cannulation technique requires practice.
    Gain practice on a peripheral artery in medium to large breeds after anesthesia has been induced, eg dorsal pedal (metatarsal) artery. Pressure dressing can be used to control any hemorrhage/hematoma formation more easily than in larger, more proximal vessels.
  • Equipment required to display and record systolic, diastolic and mean arterial blood pressure is expensive.

Alternatives - indirect techniques

Preparation

  • Collect all necessary equipment.
  • Prepare selected site aseptically.

Requirements

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Procedure

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Further Reading

Publications

Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Bodey A R & Rampling M W (1999) Comparison of hemorrheological parameters and blood pressure in various breeds of dog. JSAP 40(1), 3.
  • Bodey A R, Young L E, Bartram D H, Diamond M J & Michell A R (1994) A comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in anesthetised dogs, using tail and limb cuffs. Res in Vet Sci 57, 265-269.
  • Kittleson M D & Olivier N B (1983) Measurement of systemic arterial blood pressure 13. Vet Clin of N Am - Small Anim Pract, 321-336.


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