High blood pressure in cats: the silent killer (Proceedings)

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High blood pressure in cats: the silent killer (Proceedings)

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Aug 01, 2011

Why should I measure blood pressure?

     • Many of the diseases seen in everyday practice can cause high blood pressure:
         – Hyperthyroidism
         – Diabetes mellitus
         – Renal, hepatic, and cardiac insufficiency
         – Hyperadrenocorticism
         – Obesity
         – Neoplasia – pheochromocytoma; mineralocorticoid-secreting tumor (primary hyperaldosteronism) Uncommon in cats.
     • Some of the drugs/nutraceuticals used can cause high blood pressure:
         – Drugs – phenylpropanolamine (PPA), phenylephrine, theophylline, aminophylline, glucocorticoids, erythropoietin, nonsteroidal anti-inflammatory drugs (NSAIDs)
         – Supplements – Ma huang (Ephedra sinica)
         – IV fluid therapy can contribute to high blood pressure.
     • Many of the clinical signs seen every day could be due to high blood pressure:
         – Acute blindness (due to retinal hemorrhage/detachment)
         – Hyphema
         – Dilated pupils
         – Increased tortuosity of retinal vessels
         – Decreased/ increased appetite
         – Vomiting
         – Increased water consumption
         – Increased urination
         – Weight loss
         – Lethargy
         – Heart murmur
         – Seizures
         – Collapse/ Syncope
         – Abnormal behavior
         – Proteinuria
         – Epistaxis
         – Hematuria
     • High blood pressure can be a "silent killer"
         – No overt clinical signs may be noticed.
         – Can be the primary problem – "essential" hypertension – with no underlying cause.

The time to diagnose high blood pressure is before damage is done. Retinal hemorrhages and detachment can be avoided in a well-managed feline patient. I recommend that Doppler ultrasonic blood pressure measurements begin in all patients at an early age as part of their health care program. That helps the veterinarian establish a baseline for each individual cat. Senior cats, which have a greater risk of developing diseases that cause high blood pressure, should have their blood pressure checked every 6 months. Once a cat has been diagnosed with a disease that can cause high blood pressure (ex: Chronic kidney disease), blood pressure measurements should occur at least every 3 months or sooner if any concerns arise. Your clients are well educated about high blood pressure, so it is easy for them to understand the importance of blood pressure control in their cats.

How do I measure blood pressure?

     • Direct arterial measurement
         – Impractical for routine monitoring
         – Useful during prolonged procedures performed under anesthesia
     • Indirect measurement
         – Doppler ultrasonic method - preferred method for cats
         – Oscillometric method –automatic, useful during anesthesia, use upper forelimb for best results.

Blood pressure measurement: Technique tips

     • Animal positioning
         – Minimal restraint
         – Minimal stress
         – Sitting
         – Lateral recumbency
         – May be performed in the exam room with the client or in a separate area.
         – **Measurement must be made at the level of the heart.**

While we try to perform blood pressure measurements under these ideal situations, there are exceptions to the rule. Some cats are "difficult to handle", but still need to have their blood pressure measured. An accurate blood pressure measurement can be obtained, even on a cat that is trying to "eat you alive".

     • Cuff placement
         – Cats – tail (median coccygeal artery), fore limb (median artery), rear limb (dorsal metatarsal artery)
         – Use the "up" leg
     • Cuff selection
         – Width of the cuff should be 40% of the circumference of the measurement
         – site (tail, leg)
         – Cuff too small or too loose – falsely elevates the readings
         – Cuff too large or too tight – falsely lowers the readings
     • Doppler Probe - use water or alcohol to separate the hair and apply gel to pick up signal. Shave a small patch of hair as needed.
         – Obtain a series of 3-5 readings, with at least 30 seconds between readings to allow recirculation

Now what?

     • Blood pressure measurements – Normal systolic reading
         – Goal: Less than or equal to 145 mmHg
         – Prevention of organ damage (Kidneys, Heart, Eyes, Brain, etc)

How do I manage high blood pressure?

     • Drug therapy – may require single or multiple drug regimen
         – Calcium channel-blocking agents
              o Amlodipine (Norvasc) 0.625 – 1.25 mg/cat/day PO
              o Diltiazem 0.5-2.5 mg/kg PO q.8h; sustained release (Cardizem CD) 10 mg/kg PO q.24h
         – Angiotensin-converting enzyme (ACE) inhibitors
              o Enalapril 0.25 - 0.5 mg/kg PO q.12-24h
              o Benazapril 0.25-0.5 mg/kg PO q.12-24h
         – Beta-blockers
              o Atenolol 6.25 – 12.5 mg PO q. 12-24h
         – Diuretics
              o Furosemide 1-2 mg/kg PO q.12h
              o Spironolactone 1-2 mg/kg PO q.12h
         – Other drugs to consider: Pimobendan (Vetmedin)???
     • Continued monitoring
         – Identify cause of high blood pressure
              o Obtain complete database: CBC, biochemistry profile, serum T4, urinalysis, FeLV/FIV, imaging studies as indicated
         – Start drug therapy for high blood pressure control and address other diseases.
         – Reevaluate the patient in 7 days to make sure the drug is working and that the patient is handling the drug well.
              o Measure blood pressure.
              o Check renal enzymes.
         – If blood pressure is still too high or renal enzymes are elevated, adjust drug therapy and reevaluate in 7 days.
         – If blood pressure is well controlled and renal enzymes are normal/stable, reevaluate in 30 days. This gives the patient time to equilibrate on this dose.
         – Reevaluate blood pressure every 3-6 months.

Selected readings

Belew AM, Barlett T, Brown SA: Evaluation of the white-coat effect in cats. J Vet Intern Med 13:134-142, 1999.

Brown S, Atkins C, Bagley R, et al: Guidelines for the identification, evaluation and management of systemic hypertension in dogs and cats. J Vet Intern Med 21(3):542-58, 2007.

Chetboul V, Lefebvre HP, Pinhas C, et al: Spontaneous feline hypertension: clinical and echocardiographic abnormalities, and survival rate. J Vet Intern Med 17:89-95, 2003.

Elliott J, Barber PJ, Syme HM, et al: Feline hypertension: clinical findings and response to antihypertensive treatment in 30 cases. J Small Anim Pract 42:122-129, 2001.

Grandy JL, Dunlop CI, Hodgson DS, et al: Evaluation of the doppler ultrasonic method of measuring systolic arterial blood pressure in cats. Am J Vet Res 53:1166-1169, 1992.

Henik RA: Diagnosis and treatment of feline systemic hypertension. Comp Cont Educ Pract Vet 19(2): 163-179, 1997.

Hypertension Consensus Panel, American College of Veterinary Internal Medicine (report), in Proceedings. 20th Annual Vet Med Forum, 2002.

Jepson RE, Elliott J, Brodbelt D, et al: Effect of control of systolic blood pressure on survival in cats with systemic hypertension. J Vet Intern Med 21(3):402-9, 2007.

Littman MP: Spontaneous systemic hypertension in 24 cats. J Vet Intern Med 8: 79-86, 1994.

Maggio F, DeFrancesco TC, Atkins CE, et al: Ocular lesions associated with systemic hypertension in cats: 69 cases (1985-1998). J Am Vet Med Assoc 217:695-702, 2000.

Nelson OL, Reidesel E, Ware WA, et al: Echocardiographic and radiographic changes associated with systemic hypertension. J Vet Intern Med 16:418-425, 2002.

Pascoe PJ, Ilkiw JE, Stiles J, et al: Arterial hypertension associated with topical ocular use of phenylephrine in dogs. J Am Vet Med Assoc 205:1562-1564, 1994.

Sansom J, Rogers K, Wood JLN, et al: Blood pressure assessment in healthy cats and cats with hypertensive retinopathy. Am J Vet Res 65:245-252, 2004.

Snyder PS, Sadek D, Jones GL: Effect of amlodipine on echocardiographic variables in cats with systemic hypertension. J Vet Intern Med 15:52-56, 2001.

Sparkes AH, Caney SMA, King MCA, et al: Inter- and intraindividual variation in Doppler ultrasonic indirect blood pressure measurements in healthy cats. J Vet Intern Med 13:314-318, 1999.