Felis ISSN 2398-2950

Anesthetic monitoring: blood pressure (direct pressure)

Synonym(s): Invasive arterial blood pressure monitoring

Contributor(s): John Dodam



  • 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.
  • Systolic blood pressure should not exceed 170 mm Hg, and diastolic pressure should not exceed 100 mm Hg. When systolic blood pressure is less than 90 mm Hg, or when mean blood pressure is less than 60-70 mm Hg, an animal is considered to be hypotensive.
    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. In cats, mean blood pressure can be expected to range from 85 mm Hg when the animal is in a light plane of anesthesia (~1.6% end-tidal isoflurane concentration) to 53 mm Hg when in a deep plane of anesthesia (~ 3.2% end tidal isoflurane concentration).
  • Adequate arterial blood pressure is necessary to maintain sufficient tissue perfusion to avoid cellular damage and/or death.
  • During anesthesia, mean arterial pressure should be maintained above 70 mmHg.
  • 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  • At deficits of circulating blood volume in excess of 20%, mean arterial blood pressure is no longer maintained and hypotension develops.
    Direct arterial blood pressure monitoring is rarely used in the domestic cat due to the technical difficulties associated with placing and maintaining a femoral artery catheter.


  • 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.


  • 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.


  • Requires arterial cannulation with attendant risks, eg hemorrhage, sepsis Shock: septic, thromboembolism Thromboembolism: aorta.
  • Peripheral arterial cannulation is extremely difficult in the cat. Often a surgical approach must be employed to gain access to the artery.
  • High degree of technical difficulty.
  • High complication rate.
  • Equipment required to display and record systolic, diastolic and mean arterial blood pressure is expensive.

Alternatives - indirect techniques


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


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Kittleson M D & Olivier N B (1983) Measurement of systemic arterial blood pressure. Vet Clin of N Am Small Anim Pract 13 (2), 321-336 PubMed.

Other sources of information

  • Trim CM (1994) Monitoring the anesthetized cat. In: Anaesthesia of the Cat. Hall LW and Taylor PM, eds. Bailli√®re Tindall, London. pp 199-209.