The ultimate goal of managing systemic hypertension (SH) is to prevent target organ damage.
Depending on the patient’s risk category – based on their systolic and diastolic pressures – it will determine whether acute, emergency interventions or chronic, long-term management will be required.
Various medications are available to manage hypertension. The choice of which drug class(es) to use will be dependent on the individual patient.
Monitoring
Close monitoring is crucial after commencement of therapy, as well as each time after a change in medication dosages. Long-term monitoring of the potential side effects of hypertensive therapy is also critical.
The prognosis of SH can be variable and dependent on a multitude of factors. For this reason, it is important all underlying diseases are managed appropriately to prevent further destabilisation and of the blood pressure.
The level of intervention required for SH is based on the risk category of the patient. The American College of Veterinary Internal Medicine has developed a four risk category – I (minimal), II (mild), III (moderate) and IV (severe) – to help determine the risks of future target organ damage to the brain, eyes, heart and kidneys.
- Risk Category I: systolic arteriolar pressure (SAP) under 150mmHg, diastolic arteriolar pressure (DAP) under 95mmHg.
- Risk Category II: systolic blood pressure 150mmHg to 159mmHg, DAP 95mmHg to 99mmHg.
- Risk Category III: SAP 160mmHg to 179mmHg, DAP 100mmHg to 119mmHg.
- Risk Category IV: SAP more than 180mmHg, DAP more than 120mmHg.
Severe cases
Emergency treatment is rarely indicated, except in patients exhibiting per-acute signs of target organ damage. These are the patients with signs of acute blindness, retinal detachment, per-acute onset of neurological signs or congestive heart failure precipitated by the development of hypertension. The goal is to achieve an overall SAP of under 160mmHg or a 50mmHg decrease from the baseline SAP.
Although not commonly used, nitroprusside can be used in acute severe situations. It is crucial the blood pressure is frequently monitoring as severe hypotension can result. Nitroprusside causes immediate peripheral arterial and venous vasodilation when given intravenously. A starting dose of 1ug/kg/min to 2.5ug/kg/min IV can be used. If this does not achieve the desired decrease in SAP, this dose can be increased in increments of 2ug/kg/min every 30 minutes until a maximum of 10ug/kg/min to 15ug/kg/min IV is reached.
It should be noted nitroprusside is very short acting – the blood pressure will return to pre-treatment levels within 1 to 10 minutes following cessation of therapy. Therapy should also not continue longer than 24 hours.
Chronic therapy
For most patients, chronic therapy generally involves the use of calcium channel blockers and angiotensin converting-enzyme (ACE) inhibitors.
Calcium channel blockers
Calcium channel blockers reduces blood pressure by a combination of peripheral vasodilation, as well as negative chronotropic and inotropic effects that, in turn, reduce cardiac output. It reduces blood pressure by approximately 40mmHg to 50mmHg and is the first choice of drug for as an antihypertensive.
Amlodipine is the most commonly used calcium channel blocker and the dose is 0.2mg/kg to 0.5mg/kg PO q12hrs to 24hrs (0.7mg/cat/day to 1.2mg/cat/day). Electrolytes must be monitored when calcium channel blockers are used as hypokalaemia is a common side effect.
ACE inhibitors
Angiotensin-converting-enzyme (ACE) inhibitors lower blood pressure by reducing peripheral vascular resistance and stroke volume by preventing the conversion of angiotensin I to angiotensin II.
Compared to calcium channel blockers, ACE inhibitors are less effective as a monotherapy as they only reduces blood pressure by 5mmHg to 15mmHg, making them ineffective in patients with severe hypertension (SAP more than 240mmHg).
Despite this, ACE inhibitors can be potentially beneficial in patients that have concurrent proteinuria and can be used in combination with calcium channel blockers. Examples are enalapril (0.5mg/kg PO q12hrs to 24hrs) and benazepril (0.25mg/kg to 1mg/kg PO q24hrs). Although most mild to moderate cases can be managed with one class of drug alone, most severely hypertensive patients will require a combination of these two.
Alternate medications
Other classes of drugs that may be used to help manage hypertension include hydralazine, beta adrenergic blockers and diuretics. These classes of drugs are often reserved as alternatives, as these medications have comparably more side effects than calcium channel blockers and ACE inhibitors.
Ongoing assessment
Long-term management of hypertensive patients require regular physical examinations, fundic examinations, and monitoring of blood pressures, as well as blood and urine tests to assess for target organ damage and side effects of the drugs. After institution of antihypertensive therapy, the patient should be revaluated within 7 to 10 days. This is the same if the patient requires any medication dosage adjustments.
For patients with severe hypertension, or those with rapid onset of target organ damage clinical signs, these patients will need reassessments every one to three days. All patients on hypertensive treatments are at risk of hypotension; therefore, any unusual clinical signs should prompt an immediate veterinary reassessment.
Prognosis
Prognosis of SH is variable and is dependent on a combination of factors:
- the presence of target organ damage
- the ability to identify and manage the underlying diseases
- the severity of hypertension
- the effectiveness of the hypertensive treatment
There is also a correlation with the degree of proteinuria with hypertension; if there is no improvement in urine protein: creatinine ratio despite treatment, the prognosis is poor.
Return of vision after retinal detachment is poor, despite rapid correction of hypertension and reattachment of retina. Hypertensive encephalopathy carries a better prognosis with patients being able to return to normal if the hypertension is corrected rapidly.
Summary
SH is a common sequalae to a multitude of systemic diseases. Blood pressure should always be checked as part of the wellness exam in any geriatric patient, and especially in patients with other systemic diseases.
With prompt identification and management, target organ damage can be prevented and the overall prognosis of the patient improved.
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