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Blood pressure: A critical factor (Proceedings)


Let's look at the applicability of measuring blood pressure, methods of assessment and the interpretation of results in clinical practice.

It has been stated that: "Systemic hypertension associated with kidney disease is a very real problem, and has been diagnosed in over 60% of cats with chronic renal disease. Hypertension can have multi-systemic effects if left untreated, including left ventricular hypertrophy and cardiac failure, retinal detachment and blindness, cerebrovascular hemorrhage, and progression of renal dysfunction." (Rosemary Henik, DVM, MS, DACVIM) While this is true, let's look at the applicability of measuring blood pressure, methods of assessment and the interpretation of results in clinical practice.

Key points

1. Systemic arterial pressure is the pressure within the arteries and arterioles

2. Systolic pressure refers to the pressure when the aortic valve is open and the heart is ejecting blood (120 mmHg)

3. Diastolic pressure refers to the pressure when the aortic valve is closed and the heart is resting (80 mmHg)

4. Mean arterial pressure is closer to diastolic as the heart spends most of its time resting in diastole (90 mmHg)

5. Excitation, stress and pain can *transiently* raise the values, but as there are mechanisms in place to limit the elevations, consistent systolic values exceeding 170 mm Hg (range 168-180) are accepted as reflecting hypertension.1-9

6. To minimize the effects of "white coat syndrome", allow the patient to acclimate to the environment for ten minutes before measuring BP. Measure BP before performing any other evaluations (TPR, examination, etc.) Take measurements over several minutes until a series of five values are obtained that vary by no more than 10 mm Hg.

7. A mean arterial pressure of >60 mmHg are necessary to maintain perfusion to the brain, heart and kidneys.

8. Doppler measurement of systolic pressure underestimates values obtained by direct invasive measurement of arterial pressure. This may be corrected by the equation: Doppler + 14 mm Hg = direct systolic pressure.

Whose blood pressure should we measure?

Non-invasive, indirect arterial measurements of blood pressure should be made in all anesthetized, critical or high-risk patients to detect and monitor management of hypotension. This technique should be used widely as a screening method for the pre-clinical detection of hypertension in patients with renal disease, hyperthyroidism, ocular changes consistent with hypertension, a cardiac murmur, or left ventricular hypertrophy, neurological dysfunction and all cats over eight years of age.

How to measure

In an anesthetized patient, Doppler or oscillometric methods are reliable. In conscious cats, oscillometric measurements using devices reported in published papers do not correlate with radiotelemetrically obtained values; Doppler, PetMap or Memo methodology should be used. To minimize the effects of "white coat syndrome", allow the patient to acclimate to the environment for ten minutes before measuring BP. Measure BP before performing any other evaluations (TPR, examination, etc.). Use of forelimb or hindlimb is equally valid. It is very important to use the appropriate cuff size. The cuff chosen must measure 40% of the circumference of the limb at the cuff placement site (see attached table). Shaving helps achieve good probe contact but is not essential. In fact, I do not recommend shaving a conscious patient as this raises their fear level. Wetting the fur in the metatarsal or metacarpal area with alcohol is adequate. It is important to avoid alcohol touching the probe; use gel generously. Gentle inflation and deflation of the cuff will reduce strangeness of the experience for the patient. Use of a stereo headset will help reduce noise for the cat as well as make it easier for the operator to hear the signal. Take measurements over several minutes until a series of five values are obtained that vary by no more than 10 mm Hg. Record the limb and cuff size used, for future comparisons, in the medical record.

Causes of artificially high values: fear, noise and the sensation of the cuff inflating and deflating.... be quiet, use headset and inflate gently; take the readings on the client's lap whenever possible. Using a cuff that is too small will also cause artificially high BP readings.

Other methods of measurement

* Oscillometric measurement (Critikon, Dinamap, Datascope Passport) is not reliable in conscious cats and small dogs (<25 lbs). These are appropriate for monitoring anesthetized patients.

* Central Venous Pressure (CVP) measurement:

CVP an easy, cheap and is an under-utilized technique and is the most accurate, but requires invasive procedure and is not an out patient procedure. While it reflects right atrial pressure associated with volume changes, arterial BP assesses adequacy of perfusion of vital tissues.

Causes of hypertension

Chronic renal insufficiency (of unspecified types) and hyperthyroidism are undisputedly the most common disease conditions associated with hypertension in older cats. In sixteen studies, the percentage of hypertensive patients with these two underlying causes varies quite widely. For hypertensive cats the incidence of CRI is between 41 and 92%. Hyperthyroidism is found in 8-87% of hypertensive cats. The corollary of this is that approximately 60% of cats with CRI and 40-60% of cats with hyperthyroidism are hypertensive. Thus, it is logical to recommend that blood pressure monitoring be part of the examination of any feline patient with renal disease, hyperthyroidism, ocular changes reflective of hypertension, a cardiac murmur or echocardiographic changes shown to be associated with increased afterload, epistaxis, or neurological dysfunction as well as all cats over 8 years of age. Less common causes of hypertension include excessive dietary sodium, pheochromocytoma and as an uncommon adverse effect in erythropoeitin therapy. Whether idiopathic or "essential" hypertension occurs in cats is unknown. Unlike humans, diabetes mellitus does not appear to predispose cats to hypertension.

While there is an increased incidence of hypertension inducing disease in senior cats, an increase in blood pressure has also been shown to occur in healthy cats associated with increasing age.

Pathogenesis of hypertension

When hypertension occurs in feline chronic renal disease (CRD), the speculated mechanism of action involves the renin-angiotensin-aldosterone (RAA) axis. Interestingly, in the few studies that have looked at this, results, and therefore, interpretation, vary. One paper speculates that the cause for hypertension is due to RAA changes. Another shows a lack of difference in plasma renin activity as well as angiotensin levels between cats with CRD and normal cats. This same paper reports a significantly higher aldosterone level in hypertensive CRD cats. A third paper, which compared a small number of Persian cats with polycystic kidney disease (PKD) to normal cats cites a higher aldosterone: renin ration in half of the PKD cats. Of interest is the finding in this paper that the cats with PKD had only slightly higher BP levels than normal cats. A different paper studying PKD patients showed normotension in both PKD and normal cats. This implies, albeit in a very small number of patients, that PKD does not result in hypertension, a situation that is different from other forms of chronic renal disease.

In hyperthyroid cats, the mechanism of hypertension appears to be due to high cardiac output. In fact, unless hyperthyroidism is accompanied by chronic renal insufficiency, the degree of hypertension is mild. Therapy directed towards controlling hyperthyroidism is usually all that is required to control hypertension in these cats. If inadequate, then the hyperdynamic state should be addressed using a beta-blocker to dampen the inotropic effect and tachycardia induced by thyroid hormones.

When renal insufficiency is part of, or the sole cause of, the hypertension, reduction of arteriolar constriction may be achieved using amlodipine through its action blocking calcium channels in peripheral vasculature.

The most obvious clinical effects of hypertension are those affecting the ocular structures: retinal hemorrhage, hyphema and retinal detachment resulting in visibly obvious changes in the appearance of the cat's eye (persistent papillary dilation or hyphema) or an acute onset of blindness. Hypertension affects other tissues, which also have a rich arteriolar supply, cardiovascular and renal structures.

Persistence in hypertension results in an increased afterload for the heart. This results in concentric hypertrophy. If the hypertrophy is more than mild, especially if it is severe, then the trophic effect of hyperthyroidism should be suspected. Indeed, two papers evaluating the effects of systemic hypertension on cardiovascular parameters showed mild left ventricular hypertrophy, subtle asymmetrical hypertrophy with thicker interventricular septum, and distal aortic root measurements that were greater in hypertensive cats compared to age-matched, older healthy cats.

The effects of hypertension on the kidneys of cats appear to be somewhat different than what has been recognized in dogs and humans. The feline pre-glomerular vessels are more resistant to the detrimental effects of hypertension and are able to compensate better than in those other species. While albuminuria (but not increases in urine protein: creatinine ratios) correlates with hypertension in experimentally induced renal failure (9/10 nephrectomy remnant kidney model34), this effect has not been documented in hypertensive cats to date.

The situation with chronic renal insufficiency (CRWSAVAI) as a cause of hypertension is being studied intensively. Cats with CRI lose the normal auto regulatory capacity of the glomerular arterioles. This may not only cause systemic hypertension (50-60% of cats with CRI?) but also promote progression of renal insufficiency through glomerular injury. Treatment of hypertension should be considered in cats whose systolic BP is consistently > 170 mm Hg. Amlodipine is the most efficacious agent (0.625 mg/cat PO q24h, titrate up as needed) as it has a direct effect on the calcium channels of the peripheral vasculature. Angiotensin-converting enzyme inhibitors (ACEI) will have overall effect of reduced vasoconstriction of efferent arteriole that can increase overall renal flow, reduce glomerular hypertension (beneficial in the case of renal protein loss) but can at the same time reduce driving force for GFR by which we may create, in essence, a pre-renal azotemia. If ACEI are used, monitor BUN and creatinine after 1 or 2 doses and respond accordingly. Beta-blockers reduce renin secretion, which will have same net effect. Combination therapy using amlodipine along with an ACEI may be advantageous by reducing BP via the systemic vasodilation (preglomerular) while also dilating efferent arterioles (post-glomerular), thereby balancing the effects on GFR and on glomerular capillary pressure.

Benazepril (an ACEI) is currently undergoing a large, multi-institutional study to assess its effects on CRI in cats. Interim results for this study (presented September, 2001, WSAVA, ACVIM 2002) show that using benazepril or placebo didn't make any significant difference in survival time for all CRI cats. For cats with urinary protein loss (urine protein/creatinine), benazepril treated cats had longer survival times and better appetite than placebo treated urinary protein losing cats. Benazepril was well tolerated by all cats. Subsequent studies have not shown compelling reasons to use this agent routinely in CRI.

When to treat

Normal values are ~120mm Hg systolic, but due to fear-induced hypertension, reassess when the values are consistently above 170 mmHg.

How to treat

1. identify and treat the underlying cause;

2. medical management? ONLY if you can and will monitor the BP. Classes of drugs used in the treatment of hypertension include diuretics, ACE inhibitors, beta-blockers, calcium channel blocker, and vasodilators. The drug chosen must depend on the underlying cause as well as the hydration status, renal and cardiac function and response to therapy. Of ten papers reporting studies of therapies for the treatment of hypertension in cats, eight evaluated efficacy or safety and efficacy of amlodipine. Three evaluated other agents (propranolol, enalapril, captopril, furosemide).29,33,34 The conclusion can be made that amlodipine is safe and effective when used long-term at a dose of 0.625 mg/cat/day (or 1.25 mg/cat/day to effect in cats weighing more than 5 kg) at the average dose of 0.18 ± 0.03 mg/kg PO q24h.2-4,7,25,34,35 The other agents had a high incidence of side effects and were not reliably effective in reducing blood pressure.

3. sodium restriction in diet?

4. weight reduction if obese or overweight

MONITOR! after 5-7 days and adjust dose if necessary, check again in 2-3 weeks ....then every two to three months. Monitoring is essential, as over treatment, causing hyPOtension could cause acute renal failure or cardiac collapse and coma. Recheck appointments should include assessment of heart rate and function, hydration, body weight, general condition and quality of life, renal values, urinalysis, ophthalmic and neurologic status.

Causes of hypotension

Anesthesia commonly causes hypotension. Mean arteriolar BP must be above 60 mm Hg (approx 80-90 systolic BP) to provide adequate perfusion to the brain, heart and kidneys. If this is not achieved, organ dysfunction will result. Monitoring the blood pressure of anesthetized patients along with other parameters allows for appropriate and timely adjustment of anesthetic depth, fluid support and the use of supportive drugs. One paper showed a dramatic decrease in cardiac parameters along with blood pressure when 2.0 minimum alveolar concentration (MAC) isoflurane was compared to 1.30 MAC in cats. Despite assisted ventilation, cardiac indices remained impaired.

Other causes of hypotension include hypoperfusion due to pain, hypovolemia,, cardiac arrhythmias, heart failure, blood loss, sepsis, DIC. Causes of artificially low values: using a cuff that is too large and is occluding the artery, taping the cuff too snugly.

Treatment of hypotension: treat the underlying cause (provide analgesia, reduce the inhalant anesthetic flow, use appropriate antibiotics, etc.) and support hypovolemia with oxygen, fluids (crystalloids, colloids), dopamine or dobutamine. Refractory hypotension, with or without cardiovascular collapse, development of respiratory disease, or disseminated intravascular coagulation (DIC) are all associated with a poor prognosis in patients with septic peritonitis, thus recognition, treatment and monitoring of hypotension is of critical importance in caring for these patients.


1. Sansom J, Barnett KC, Dunn KA et al.: Ocular disease associated with hypertension in 16 cats. J Small Anim Pract 35[12]: 604-611 1994.

2. Henik RA, Snyder PS, Volk LM: Treatment of Systemic Hypertension in Cats With Amlodipine Besylate. J Am Anim Hosp Assoc 33[3]: 226-234 1997.

3. Henik RA: Diagnosis and Treatment of Feline Systemic Hypertension. Compend Contin Educ Pract Vet 19[2]: 163-179 1997.

4. Henik RA: Systemic hypertension and its management. Vet Clin North Am Small Anim Pract 27[6]: 1355-72 1997.

5. Sansom J, Rogers K, Wood JL: Blood pressure assessment in healthy cats and cats with hypertensive retinopathy. Am J Vet Res 65[2]: 245-52 2004.

6. Syme HM, Barber PJ, Markwell PJ wt al: Prevalence of Systolic Hypertension in Cats with Chronic Renal Failure at Initial Evaluation. J Am Vet Med Assoc 220[12]:1799-1804 2002.

7. Chastain CB, Panciera D, DVM, MS, Dipl. ACVIM; Elliott J, Barber PJ, Syme HM, et al.: Feline Hypertension: Clinical Findings and Response To Antihypertensive Treatment in 30 Cases Sm Anim Clin Endocrinol 12[2]:5 2002 J Sm Anim Pract 42:122-129 2001.

8. Sennello KA, Schulman RL, Prosek R et al: Systolic Blood Pressure in Cats with Diabetes Mellitus. J Am Vet Med Assoc 223[2]: 198-201 2003.

9. Nelson OL, Reidesel E, Ware WA et al: Echocardiographic and Radiographic Changes Associated with Systemic Hypertension in Cats. J Vet Intern Med 16[4]: 418-425 2002.

10. Grandy JL, Dunlop CI, Hodgson DS: Evaluation of the Doppler ultrasonic method of measuring systolic arterial blood pressure in cats. Am J Vet Res 53[7]: 1166-1169 1992.

11. Grosenbaugh DA, Muir WW: Blood Pressure Monitoring. Vet Med 93[1]: 48-59 1998.

12. AAFP and AFM: Panel Report On Feline Senior Health Care. Compend Contin Educ Pract Vet 21[6]: 531-539 1999.

13. Caulkett NA, Cantwell SL, Houston DM: A comparison of indirect blood pressure monitoring techniques in the anesthetized cat. Vet Surg 27[4]: 370-7 1998.

14. Pedersen KM, Butler MA, Ersboll AK et al: Evaluation of an Oscillometric Blood Pressure Monitor for Use in Anesthetized Cats. J Am Vet Med Assoc 221[5]: 646-650 2002.

15. Belew AM, Barlett T, Brown SA: Evaluation of the White-Coat Effect in Cats. J Vet Intern Med 13[2]: 134-142 1999.

16. Sparkes AH, Caney SMA, King MCA: Inter- and Intraindividual Variation in Doppler Ultrasonic Indirect Blood Pressure Measurements in Healthy Cats.. J Vet Intern Med 13[4]: 314-318 1999.

17. Branson KR, Wagner-Mann CC, Mann FA: Evaluation of an oscillometric blood pressure monitor on anesthetized cats and the effect of cuff placement and fur on accuracy. Vet Surg 26[4]: 347-53 1997.

19. de Laforcade AM, Rozanski EA: Central venous pressure and arterial blood pressure measurements. Vet Clin North Am Small Anim Pract 31[6]: 1163-74, 2001.

19. Kobayashi DL, Peterson ME, Graves TK et al: Hypertension in cats with chronic renal failure or hyperthyroidism. J Vet Intern Med 4[2]: 58-62 1990.

20. Lesser M, Fox PR, Bond B: Non-invasive blood pressure evaluation in cats with left ventricular hypertrophic diseases. J Vet Intern Med 4[2]: 117 1990 ACVIM 8th Annual Forum.

21. Littman MP: Spontaneous systemic hypertension in cats. J Vet Intern Med 4[2]: 126 1990 ACVIM 8th Annual Forum.

22. Jean Stiles J, Polzin DJ, Bistner SI: The Prevalence of Retinopathy in Cats with Systemic Hypertension and Chronic Renal Failure or Hyperthyroidism. J Am Anim Hosp Assoc 30[6]: 564-572 1994.

23. Littman MP: Spontaneous Systemic Hypertension in 24 Cats. J Vet Intern Med 8[2]: 79-86 1994.

24. Jensen J, Henik RA, Brownfield M et al: Plasma renin activity and angiotensin I and aldosterone concentrations in cats with hypertension associated with chronic renal disease. Am J Vet Res 58[5]: 535-40 1997.

25. Elliott J, Barber PJ, Syme HM et al: Feline hypertension: clinical findings and response to antihypertensive treatment in 30 cases. J Small Anim Pract 42[3]: 122-9 2001.

26. Chetboul V, Lefebvre HP, Pinhas C et al: Spontaneous Feline Hypertension: Clinical and Echocardiographic Abnormalities, and Survival Rate. J Vet Intern Med 17[1]: 89-95 2003.

27. Mishina M, Watanabe T, Fujii K et al: Non-invasive blood pressure measurements in cats: clinical significance of hypertension associated with chronic renal failure. J Vet Med Sci 60[7]: 805-8 1998.

28. Turner JL, Brogdon JD, Lees GE et al: Idiopathic hypertension in a cat with secondary hypertensive retinopathy associated with a high-salt diet. J Am Anim Hosp Assoc 26[6]: 647-651 1990.

29. Maher ER Jr, McNiel EA: Pheochromocytoma in dogs and cats. Vet Clin North Am Small Anim Pract 27[2]: 359-80 1997.

30. Cowgill LD, James KM, Levy JK et al: Use of Recombinant Human Erythropoietin for Management of Anemia in Dogs and Cats with Renal Failure. J Am Vet Med Assoc 212[4]: 521-528 1998.

31. Bodey AR, Sansom J: Epidemiological study of blood pressure in domestic cats. J Small Anim Pract 39[12]: 567-73 1998.

32. Pedersen KM, Pedersen HD, Haggstrom J et al: Increased Mean Arterial Pressure and Aldosterone-to-Renin Ratio in Persian Cats with Polycystic Kidney Disease. J Vet Intern Med 17[1]: 21-27 2003.

33. Miller RH, Lehmkuhl LB, Smeak DD et al: Effect of enalapril on blood pressure, renal function, and the renin-angiotensin-aldosterone system in cats with autosomal dominant polycystic kidney disease. Am J Vet Res 60[12]: 1516-25 1999.

34. Mathur S, Syme H, Brown CA et al: Effects of the calcium channel antagonist amlodipine in cats with surgically induced hypertensive renal insufficiency. Am J Vet Res 63[6]: 833-9 2002.

35. Snyder PS: Amlodipine: A Randomized, Blinded Clinical Trial in 9 Cats with Systemic Hypertension. J Vet Intern Med 12[3]: 157-162 1998.

36. Mazzaferro E, Wagner AE: Hypotension During Anesthesia in Dogs and Cats: Recognition, Causes, and Treatment. Compend Contin Educ Pract Vet 23[8]: 728-737 2001.

37. Hodgson DS, Dunlop CI, Chapman PL et al: Cardiopulmonary effects of anesthesia induced and maintained with isoflurane in cats. Am J Vet Res 59[2]: 182-5 1998.

38. Smith JD, Allen SW, Quandt JE et al: Indicators of postoperative pain in cats and correlation with clinical criteria.. Am J Vet Res 57[11]: 1674-8 1996.

39. Rudloff E, Kirby R: Hypovolemic Shock and Resuscitation. Vet Clin North Am Small Anim Pract 24[6]: 1015-1039 1994.

40. King LG: Postoperative complications and prognostic indicators in dogs and cats with septic peritonitis: 23 cases (1989-1992). J Am Vet Med Assoc 204[3]: 407-414 1994.

41. Weeren FR, Muir WW: Clinical aspects of septic shock and comprehensive approaches to treatment in dogs and cats. J Am Vet Med Assoc 200[12]: 1859-1870 Jun 15'92 Reports from Symposia on Circulatory Shock and CPR.

42. Haskins SC: Management of septic shock. J Am Vet Med Assoc 200[12]: 1915-1924 Jun 15'92 Reports from Symposia on Circulatory Shock and CPR.

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