Hypertensive Crisis

Chapter 42 Hypertensive Crisis



Scott Brown, VMD, PhD, Diplomate (ACVIM)



KEY POINTS



• Emergency antihypertensive therapy is indicated only when there is end-organ damage likely to produce significant permanent abnormalities without rapid lowering of blood pressure (BP).

• Diagnosis and management of hypertension must be based on measurement of the patient’s BP following a standard protocol, and a thorough physical examination should be performed concurrently to assess end-organ damage.

• The primary goal of emergency antihypertensive therapy is to reduce the magnitude, severity, and likelihood of further end-organ damage.

• To resolve a hypertensive crisis, systolic BP should be lowered to 110 to 150 mm Hg, generally within 4 to 12 hours, using parenteral or oral pharmacologic agents.


RATIONALE FOR EMERGENCY MANAGEMENT


Elevations of systemic arterial BP can injure tissues, referred to as end-organ damage. The end organs affected by elevated BP include the kidney, cardiovascular system, eye, and brain. A hypertensive crisis mandating emergency therapy occurs whenever there is end-organ damage that is likely to produce significant permanent abnormalities unless BP is lowered immediately. In veterinary patients, the end organs affected by this type of damage are usually the eyes and brain (Table 42-1).



Table 42-1 Hypertensive End-organ Damage

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END-ORGAN DAMAGE



Ocular


Ocular lesions are observed in many animals with systemic hypertension; reported prevalence rates are as high as 100%.1-6 The syndrome of hypertensive ocular injury is most often termed hypertensive retinopathy.2,4,7,8 Sudden onset of blindness, intraocular hemorrhage, and retinal detachment are the most common indications for emergency lowering of BP. Other ocular lesions associated with high BP include retinal vessel tortuosity, edema, and retinal degeneration. Effective antihypertensive treatment can lead to retinal reattachment, although restoration of vision is not common and subsequent retinal degeneration leading to blindness may occur. Hypertensive ocular injury has been reported at systolic BP as low as 168 mm Hg,3 and there is a substantially elevated risk of occurrence when systolic BP exceeds 180 mm Hg, particularly when this occurs suddenly.6,8



Neurologic


Neurologic clinical signs are frequently in hypertensive dogs and cats. Signs include altered mentation, disorientation, lethargy, seizures, balance disturbances, head tilt, nystagmus, behavioral abnormalities, and focal neurologic defects. Hypertensive encephalopathy9 is a complication justifying rapid lowering of BP that has been reported in dogs5 and cats,4,7,10,11 occurring as a well-described entity in humans characterized by white matter edema and vascular lesions.12 Hypertensive encephalopathy also occurs after renal transplantation in humans13 and is a cause of otherwise unexplained death in cats.10 Hypertensive encephalopathy is more likely to occur with a sudden rise of BP or a systolic BP that exceeds 180 mm Hg.14 This syndrome, in its early phases, is rapidly responsive to lowering of BP.10,14 Hemorrhagic and ischemic stroke are observed in dogs and cats, and these conditions may generally be distinguished from hypertensive encephalopathy by virtue of their slow and incomplete response to lowering BP. Before treating hypertension in the patient with evidence of intracranial disease, a Cushing reflex in response to increased intracranial pressure must be distinguished from neurologic injury secondary to hypertension (see Chapter 100, Intracranial Hypertension).



Renal


In the kidney, hypertensive injury generally manifests as an enhanced rate of decline of renal function, early renal death, and proteinuria. Proteinuria is a marker of hypertensive nephropathy in humans,15 and severity was directly related to degree of elevation of BP in an experimental study of chronic kidney disease in cats.14 Malignant hypertension is a syndrome of severe, progressive elevations of BP causing end-organ damage that is often associated with kidney disease and is a recognized cause of rapidly progressive renal injury in rats and people, necessitating quick reductions in BP. However, hypertensive damage to the canine and feline kidneys is almost always a slow and insidious process requiring weeks to years to fully manifest, and is thus rarely a rationale for emergency therapy in dogs and cats.



Cardiovascular


Cardiac changes in hypertensive animals may include systolic murmurs and cardiac gallops16 and left ventricular hypertrophy.1,4,16,17 Although cats with previously undiagnosed hypertension may unexpectedly develop signs of congestive heart failure after receiving fluid therapy, heart failure and other serious complications are infrequent4,7,18 and slow to develop. Although vascular injury within the eye or central nervous system is a rationale for emergency therapy, cardiac changes rarely mandate rapid reductions in BP.



PATIENTS AT RISK FOR HYPERTENSION


There are at least two primary indications for evaluating BP in a patient. First, BP should be measured in patients with clinical abnormalities consistent with hypertensive end-organ damage; the presence of unexplained clinical findings that are associated with systemic hypertension should lead to BP measurement at the time of diagnosis. For emergency treatment, this generally includes clinical signs of hypertensive retinopathy or hyphema and unexplained intracranial neurologic signs (e.g., seizures, altered mentation, focal neurologic deficits). A second indication for BP measurement is the presence of diseases or conditions casually associated with secondary hypertension (e.g., chronic kidney disease, feline hyperthyroidism, diabetes mellitus, and hyperadrenocorticism) or the use of therapy that may elevate BP (e.g., sympathetic agonists or intensive fluid therapy). A thorough physical examination, including funduscopic evaluation, cardiac auscultation, and neurologic examination, should concurrently be performed in these at-risk populations to assess for end-organ damage. Abnormalities of the urinary (e.g., microalbuminuria, proteinuria, azotemia, or structural changes in the kidney) and cardiovascular (e.g., unexplained left ventricular hypertrophy, gallop rhythm, arrhythmia, or systolic murmur) systems also indicate BP measurement.

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Hypertensive Crisis
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