The norm of blood pressure in a cat and how to measure it. Hypertension - high blood pressure in cats Venous hypertension in cats treatment and prevention

The authors): A.V. Girshov, veterinarian, S.A. Luzhetsky, veterinarian
Organization(s):"Clinic of Neurology, Traumatology and Intensive Care of Dr. Sotnikov V.V.", St. Petersburg
Journal: №5-6 - 2013

annotation

Feline systemic arterial hypertension as a systemic circulatory pathology is often recorded in older cats (over 14 years of age). It has been established that this pathology is often associated with chronic renal failure and hyperthyroidism. At the same time, the possibility of developing an idiopathic genesis of an increase in peripheral vascular resistance and developing endothelial dysfunction is not ruled out.

The clinical picture of systemic arterial hypertension is usually caused by damage to the vessels of target organs (brain, heart, kidneys, eyes) with the development of serious neurological, ophthalmological, cardiological and nephrological disorders in an uncontrolled course.

Specific antihypertensive drugs can significantly improve target organ function and long-term prognosis in these cats. The main goal of treatment is to prevent further damage to the microvasculature of the target organs. The range of possible antihypertensive drugs is quite diverse and includes a large number of drugs from different pharmacological groups. To date, the drugs of choice in the treatment of arterial hypertension in cats are ACE inhibitors and calcium channel blockers from the dihydropyridine group (amlodipine). The use of combined antihypertensive therapy with the inclusion of an ACE inhibitor and amlodipine seems to be highly effective, in which the maximum angioprotection for target organs is achieved.

Feline systemic hypertension is systemic circulatory pathology, which is often recorded in older cats (over 14 years). This pathology is often associated with chronic renal failure and hyperthyroidism. But there is also the possibility of the development of idiopathic increasing of peripheral vascular resistance and developing endothelial dysfunction. Clinical manifestation of systemic arterial hypertension is usually caused by vascular lesions of target organs (brain, heart, kidneys and eyes). This lesions lead to the serious uncontrolled neurological, ophthalmological, cardiac and nephrology problems. Specific antihypertensive drugs can significantly improve a vital function of the target organs and the long-term prognosis for these cats . There is a great range of possible antihypertensive drugs from different pharmacological groups. Today the main drugs to the treatment of feline hypertension are considered ACE inhibitors and calcium channel blockers from the dihydropyridine group (amlodipine). Use of combination antihypertensive therapy with ACE inhibitors and amlodipine is also very effective for the maximum angioprotection of the target organs.

Systemic hypertension (an abnormal increase in systemic blood pressure) as a circulatory pathology is often recorded in older cats. A high incidence of systemic hypertension is noted in cats with chronic renal failure (61%) and hyperthyroidism (87%) (Kobayashi et al, 1990). But at the same time, hypertension occurs in cats and in the absence of renal failure and euthyroidism (normal thyroid status). Because untreated cats with hypertension can lead to serious neurological, ophthalmic, cardiac, and nephrological disorders, treatment of these patients is strongly recommended. In addition, specific antihypertensive drugs can significantly affect end-organ vital function and long-term prognosis.

Systemic hypertension (SH) is usually presented as a complication of another systemic pathology and is therefore classified as secondary hypertension. However, in certain cases, when the cause of SH is not established in the process of a full examination, they speak of primary or idiopathic hypertension.

Epidemiology

Hypertension is more common in older cats, with a median age of 15 years ranging from 5 to 20 years ( Littman, 1994, Steele et al, 2002). It is not clear to what extent an increase in blood pressure with age can be a normal phenomenon in healthy older cats, or whether it should be regarded as an early subclinical stage in the development of the pathological process. Breed and sex predisposition to hypertension in cats has not been identified.

Pathophysiology

Although systemic hypertension is often found in cats with chronic kidney dysfunction, the link between elevated blood pressure and kidney damage as an underlying cause is not clear. Vascular and parenchymal diseases of the kidneys in humans are proven causes of hyperreninemic hypertension. At the same time, an increase in the volume of extracellular fluid is one of the mechanisms for the development of hypertension in patients in the late stages of kidney disease ( Pastan & Mitch, 1998). There is evidence that cats with naturally occurring hypertension and renal insufficiency do not show an increase in plasma renin levels and activity and an increase in plasma volume ( Hogan et al, 1999; Henik et al, 1996). This suggests that some cats have primary (essential) hypertension and kidney damage is secondary to chronic glomerular hypertension and hyperfiltration.

Similarly, the relationship between hyperthyroidism and hypertension in cats is not well defined, even though the prevalence of hypertension in cats with thyrotoxicosis is high. Hyperthyroidism leads to an increase in the number and sensitivity of myocardial β-adrenergic receptors and, as a result, an increase in sensitivity to catecholamines. In addition, L-thyroxine has a direct positive inotropic effect. Consequently, hyperthyroidism leads to an increase in heart rate, an increase in stroke volume and cardiac output, and, as a result, an increase in arterial blood pressure. However, no significant relationship has been found between serum thyroxine concentration and arterial blood pressure in cats ( Bodey & Sansom, 1998). In addition, in some cats, with proper and effective treatment of hyperthyroid status, arterial hypertension may persist. Thus, it is assumed that in a subset of cats with hyperthyroidism, hypertension is independent of hyperthyroid status. Other unlikely causes of hypertension in cats include hyperadrenocorticism, primary aldosteronism, pheochromocytoma, and anemia.

The fact that hypertension in cats can occur in the absence of kidney or thyroid disease suggests that in some cases, as in humans, systemic hypertension in cats can be considered a primary idiopathic process involving increased peripheral vascular resistance and endothelial dysfunction.

Clinical signs

Clinical signs are usually derived from target organ damage (brain, heart, kidneys, eyes). As blood pressure rises, autoregulatory vasoconstriction of arterioles occurs to protect the capillary bed of these highly vascularized organs from high pressure. Severe and prolonged vasoconstriction can eventually lead to ischemia, infarction, loss of capillary endothelial integrity with edema or hemorrhage. Hypertensive cats may present with symptoms such as blindness, polyuria/polydipsia, neurological signs including seizures, ataxia, nystagmus, hindlimb paresis or paralysis, dyspnea, epistaxis ( Littman, 1994). Rarer possible signs include "stopped eyes", vocalization ( Stewart, 1998). Many cats are asymptomatic and hypertension is diagnosed after murmurs, galloping, and electrocardiographic and echocardiographic abnormalities. In cats, systemic hypertension is often associated with left ventricular hypertrophy. Usually this is moderate hypertrophy and asymmetric septal hypertrophy of the left ventricle. Dilatation of the ascending aorta is detected radiographically or echocardiographically, but it is not clear whether this finding is due to hypertension or is a normal age-related change. Cats with systemic hypertension often have left ventricular diastolic dysfunction due to decreased wall relaxation.

The wide variability of electrocardiographic changes includes ventricular and supraventricular arrhythmias, expansion of the atrial or ventricular complex, and conduction disturbances. Tachyarrhythmias with proper treatment of hypertension are resolved.

Acute blindness is a common clinical manifestation of systemic hypertension in cats. Usually blindness occurs due to bilateral retinal detachment and/or hemorrhage. In one study, 80% of hypertensive cats had hypertensive retinopathy with retinal, vitreous, or anterior chamber hemorrhages, retinal detachment and atrophy, retinal edema, perivasculitis, retinal arterial tortuosity, and/or glaucoma ( Stiles et al, 1994). Retinal lesions usually regress with antihypertensive therapy and vision returns. Retinal detachment is a common cause of blindness in older cats and, much less frequently, dogs.

The cause of retinal detachment, in this case, is high blood pressure. Increased pressure changes the walls of the capillaries of the choroid and, over time, increases their permeability.

Clinical signs of retinal detachment are: dilated pupil, pupils of different sizes, impaired pupillary reactions, impaired chromatic pupillary reactions, intraocular hemorrhage, visual impairment. Retinal detachment is confirmed by ophthalmoscopy. In case of violation of the transparency of the light-conducting media, ultrasound of the eyeball can be used. Both of these methods allow simple and painless examination of the retina.

The stage of the disease depends on the change in the fundus picture. The assessment takes into account the condition of the optic nerve head, the presence of foci of retinal detachment, the condition of the retinal vessels, the presence of areas with signs of hemorrhage, the presence of hyperreflective areas.

Often, changes in the fundus are the first signs of a systemic disease. The animal may look healthy, have no problems with orientation in space, and at this time, early changes are already taking place in the fundus, which can be detected during ophthalmoscopy. Detection of early changes in the fundus allows the main diagnosis to be made in time and complications such as retinal detachment to be avoided.

The central nervous system is prone to damage from hypertension because it is replete with small vessels. In cats, these injuries can cause convulsions, head tilt, depression, paresis and paralysis, and vocalization.

Chronic hypertension can cause kidney damage as a result of changes in afferent arterioles. Focal and diffuse glomerular proliferation and glomerular sclerosis may also develop. (Kashgarian, 1990). After renal impairment, chronic systemic hypertension causes a sustained increase in glomerular filtration pressure, which plays a key role in the progression of deterioration in renal function. (Anderson & Brenner, 1987; Bidani et al, 1987). Proteinuria and hypostenuria are not common in hypertensive cats, but microalbuminuria is present. (Mathur et al, 2002).

Diagnosis of hypertension

The suspicion of hypertension in a cat may be based on the presence of characteristic retinal lesions. However, other causes of retinal detachment and/or hemorrhage cannot be ruled out. Arterial hypertension must certainly be confirmed by measuring blood pressure. Blood pressure measurements should be performed to confirm or refute the presence of hypertension in cats with left ventricular hypertrophy, renal dysfunction, or hyperthyroidism, and in cats over 7 years of age with murmurs, gallops. In addition, blood pressure measurements should be performed in cats with the above signs of brain damage.

Hypertension in cats was defined as an indirect systolic pressure greater than 160 mm Hg. (Littman, 1994; Stiles et al., 1994) or 170 mmHg Art. (Morgan, 1986) and diastolic blood pressure over 100 mm Hg. Art. (Littman, 1994; Stiles et al., 1994). However, blood pressure will increase with age in cats and may exceed 180 mmHg. systolic and 120 mm Hg. diastolic pressure in apparently healthy cats older than 14 years. (Bodey and Sansom, 1998). Thus, a diagnosis of hypertension can be made in a cat of any age whose systolic blood pressure is > 190 mmHg. rt. Art. and diastolic pressure > 120 mm. rt. Art. Cats with a clinical picture of the corresponding arterial hypertension and systolic pressure from 160 to 190 mm. rt. Art. also should be considered patients with arterial hypertension, especially if they are less than 14 years old. In the absence of clinical signs of hypertension and systolic blood pressure from 160 to 190 mm Hg. Art. and diastolic pressure between 100 and 120 mm Hg. Art., repeated measurements are necessary several times during the day or possibly several days.

Therapeutic strategy

Early diagnosis and treatment of cats with systemic arterial hypertension is important. Although not all cats show clinical signs, failure to promptly diagnose and treat can lead to extremely undesirable consequences. Drawing an analogy with arterial hypertension in humans, we can borrow the term "silent killer".

The main goal of treatment is to prevent further damage to the eyes, kidneys, heart, and brain. This is achieved not only by lowering blood pressure, but also by improving blood circulation in target organs.

Numerous pharmacological agents are available as antihypertensive drugs, including diuretics, β-blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, calcium channel antagonists, direct-acting arterial vasodilators, centrally acting α2-agonists, and α1-blockers.

Hypertensive cats tend to become refractorier to the antihypertensive effects of blockers such as prazosin as well as direct acting arterial vasodilators such as hydralazine. In addition, long-term use of direct-acting drugs often leads to undesirable stimulation of compensatory neurohumoral mechanisms. Diuretics, β-blockers, or a combination will effectively lower blood pressure in most hypertensive cats but will not reduce target organ damage (Houston, 1992).

In accordance with Poiseuille's law, blood pressure is determined by the product of systemic vascular resistance and cardiac output, and therefore, the decrease in blood pressure as a result of the use of diuretics and β-blockers occurs as a result of a decrease in cardiac output. These drugs lower blood pressure by a mechanism that reduces flow to target organs, thereby compromising myocardial, renal, and brain perfusion. At the same time, calcium channel antagonists, ACE inhibitors, angiotensin II receptor blockers reduce blood pressure by reducing vascular resistance. This mechanism is more efficient for improving target organ perfusion. Calcium channel antagonists, in particular, lack myocardiodepressant effects, and ACE inhibitors have shown beneficial effects on renal function, coronary perfusion, and cerebral perfusion in people with hypertension. (Houston, 1992; Anderson et al, 1986), centrally acting α-adrenergic agonists reduce blood pressure by reducing vascular resistance and have also been shown to maintain target organ function. Diuretics and β-blockers reduce cardiac output, stroke volume, coronary and renal blood flow, increasing renal vascular resistance. In addition, these drugs do not reduce left ventricular hypertrophy. On the other hand, calcium channel blockers, ACE inhibitors, angiotensin II receptor blockers, and centrally acting drugs have the opposite effect.

Amlodipine is a long-acting antihypertensive drug belonging to the calcium channel blockers. This drug relaxes vascular smooth muscle by blocking the influx of calcium. Its main vasodilating effect is a systemic decrease in vascular resistance. In addition, this action extends to the coronary arteries. This drug is safe and effective even in cats with kidney dysfunction when used orally at a dose of 0.2 mg/kg once daily. When taken daily, amlodipine lowers blood pressure within 24 hours (Snyder, 1998). In addition, cats do not develop refractoriness to amlodipine and have a persistent therapeutic effect with long-term therapy.

ACE inhibitors such as enalapril, ramipril, and benazepril are also good options for treating hypertension in cats. However, these drugs are often ineffective as monotherapy in cats. ACE inhibitors may be best used in combination with amlodipine.

In cats resistant to amlodipine or ACE inhibitors, only the combination of these drugs can safely provide adequate blood pressure control. When adding ACE inhibitors (enalapril or benazepril) to amlodipine therapy, doses of 1.25 to 2.5 mg/cat/day are used). Also, in some cats receiving this combination of drugs, there is an improvement in kidney function. Experimental data show that the combination of these two classes of antihypertensive drugs not only increases the effectiveness of lowering blood pressure, but also maximizes the protection of target organs. (Raij & Hayakawa, 1999). The angiotensin receptor blocker irbesartan in combination with amlodipine has been shown to be effective in some cats refractory to ACE inhibitors.

For cats with neurological disorders due to brain damage, aggressive treatment is needed to quickly lower blood pressure. Amlodipine and ACE inhibitors have a relatively slow hypotensive effect and require 2-3 days to reach the peak of the hypotensive effect. In such clinical situations, intravenous administration of sodium nitroprussid (Natrium nitroprussid) will be more effective for the rapid relief of a hypertensive crisis. However, safe use of this drug requires careful dose titration using an infusion pump (1.5-5 mg/kg/min) and continuous blood pressure monitoring. Hydralazine may be used as an alternative to sodium nitroprusside when rapid blood pressure reduction is not required. This drug is usually given orally every twelve hours, starting at a dose of 0.5 mg/kg and increasing if needed up to 2.0 mg/kg every 12 hours. Caution is advised when using fast-acting, potent antihypertensive drugs for the treatment of hypertensive crises. A rapid and abrupt drop in blood pressure can lead to acute cerebral ischemia and thus worsen the neurological deficit.

Target Organs in Hypertension

Organ/System

More often the manifestation of the effect of

Cats, like humans, suffer from hypertension quite often. The owner, seeing that his pet is not feeling well, may not suspect that he has high blood pressure. But this may indicate that the animal is seriously ill and needs urgent treatment. From this article you will learn what is the norm of pressure in a cat and how to measure it for your pet.

Hypertension is a persistent increase in blood pressure, leading to functional changes in the heart, organs of the central nervous system and kidneys. The physiology of animals is such that their cardiovascular system usually reacts with a rise in pressure to stressful situations or significant stress on the heart. But if, after a short rise, the indicator does not return to normal, but decreases only under the influence of antihypertensive drugs, they speak of the presence of a pathology.

Blood pressure is measured in millimeters of mercury and consists of two numbers:

the first digit (systolic) - indicates the amount of blood pressure on the walls of blood vessels at the time of maximum contraction of the heart muscle;
the second digit (diastolic) - indicates the force of the pressure of the blood flow on the walls of the vessels at the moment of maximum relaxation of the heart muscle.

The magnitude of blood pressure in the arteries depends on the frequency and strength of heart contractions, the tone of the vascular walls, and the volume of heart contractions.

Classification of types of hypertension

Depending on the causes, there are essential (primary) and symptomatic (secondary) hypertension. Primary hypertension develops as an independent disease. It is more common in older animals. In this case, the cause of pressure in cats is a worn out heart and weak vascular tone. The disease can also be hereditary.

Secondary hypertension, according to the definition, develops against the background of any underlying pathology. Most often, these are diseases of the organs involved in the regulation of blood pressure (kidneys, adrenal glands, heart, thyroid gland, and others). Secondary hypertension is more difficult to diagnose and treat.

Blood pressure measurement

In order to measure blood pressure in a pet, the clinic usually has a special feline tonometer, and at home an ordinary human device is suitable.

Measurement of blood pressure can be done by direct or indirect methods. The direct or invasive method is the most accurate. This is the so-called method of "peripheral artery catheterization". To measure the pressure, the animal is sedated, after which an arterial catheter is inserted into the artery, which is connected to a monitoring system. The method is called the "gold standard", but is rarely used because of its complexity.

Much more often used indirect methods, there are several of them:

Oscillographic (measurement is performed using an arterial oscilloscope);
Dopplerography (use a device that works on the principle of Doppler);
Photoplethysmographic (use the measurement of the attenuation of infrared radiation).

All these methods have a similar principle of action. A special cuff is put on the paw of the animal, into which air is injected. A change in tissue volume is recorded at the time of dosed compression and relaxation of blood vessels (impact of a pulse wave).

The most accurate of all is the oscilloscope method. It must be taken into account that the animal at the time of the procedure is most often under stress. This condition affects the results of the a/d measurement. In this regard, it is recommended to take measurements several times, taking the average value as the truth.

High pressure features

Secondary hypertension in cats can develop against the background of serious pathologies, such as:

diabetes;
heart failure;
endocrinological disorders (hyperthyroidism);
Cushing's disease (increased synthesis of the hormone of the adrenal cortex);
jade.

Pressure that lasts for a long time has a detrimental effect on the condition of the eyes. In addition, the walls of blood vessels suffer, the viscosity of the blood increases. A decrease in blood flow causes a decrease in the rate of metabolic processes in tissues. All this is fraught with serious consequences for the body. Therefore, during each scheduled preventive examination of a pet, it is necessary to measure the pressure.

It is also very important to periodically measure a / d for individuals who are already 5-7 years old. At this age, animals become susceptible to primary hypertension.

Symptoms of the disease

High blood pressure, first of all, worsens the condition of the eyes, cardiovascular and nervous systems. The main symptoms of hypertension appear from these organs. The signs and pathophysiology of arterial hypertension in cats are as follows:

Vision deteriorates sharply, dilated pupils, retinal hemorrhages are observed. In severe cases, retinal detachment, glaucoma, and even complete blindness can occur.
On the part of the nervous system, unsteadiness of gait is often observed due to poor coordination. Later appear lethargy, apathy, increased drowsiness.
On the part of the respiratory system - shortness of breath, oxygen starvation.
Increased swelling is also characteristic (paws swell especially strongly).
Sometimes nosebleeds occur.

Treatment of the disease

Normal a / d in cats averages 120 to 80 mm Hg. An animal needs medical attention in the following cases:

pressure above 150/100 mmHg - with these figures, constant monitoring is established;
pressure above 160/120 mmHg - start antihypertensive therapy.

Treatment of hypertension in cats is usually carried out in several stages:

Normalization of pressure with the help of antihypertensive drugs (Amlodipine, Benazepril, Lisinopril). In some cases, these drugs are prescribed to the animal for life.
Elimination of edema with diuretics (Diakarb).
Elimination of the cause of high blood pressure (in case of secondary symptomatic hypertension).
Constant monitoring of the condition of the kidneys and eyes.

At the time of treatment, it is necessary to provide the animal with constant peace, protect it from stressful situations.

Low pressure

Reduced a / d is of a secondary nature, that is, it reflects one or another physiological state in a cat. The main causes of hypotension are:

weakness of the heart muscle;
large blood loss;
shock states.

The main symptoms of hypotension are associated with the general condition of the animal:

feeling of weakness;
thready pulse;
fainting states;
drowsiness;
cold extremities.

Low blood pressure in most cases is episodic.

Carefully monitor blood pressure in cats before, during, and after surgery. Its sharp fall indicates a deterioration in the condition of the animal and the need to take urgent resuscitation measures.

In order for the pressure to stay within the normal range for as long as possible, you need to monitor the health of the cat, and especially the heart and blood vessels. To support them will help the correct diet, the adequacy of physical activity, annual preventive examinations, as well as adherence to the vaccination calendar.

It would seem that problems with blood pressure are characteristic exclusively for humans, but this is not so. Our pets can also suffer from this kind of pathology, even if it happens much less frequently. A good example is hypertension in cats.

Now veterinarians officially admit that high blood pressure in cats is an unpleasant reality. If this pathology is not dealt with in any way, it can even lead to the death of the animal. Hypertension is almost never an independent disease: more often it is caused by acute or chronic renal failure and / or. Statistics show that 60% of cats with renal insufficiency and approximately 90% of animals with hyperthyroidism have problems with blood pressure. Thus, the causes of hypertension in cats in most cases are serious functional disorders in the endocrine system and urinary organs.

Less commonly, pathology develops with inflammation of the adrenal glands, as well as with their tumors. There are also cases of idiopathic arterial hypertension, the causes of which remain a mystery. We must not forget that an increase in blood pressure can be a logical response to severe stress. For example, after a visit to the veterinarian, it is useless to measure the pressure of a cat, as it will be greatly increased.

Arterial hypertension severely injures four main systems: kidneys, eyes, central nervous system and cardiovascular system. In some cases, the pressure is so great that small capillaries begin to burst en masse. The lungs are particularly susceptible (pulmonary hypertension in cats). The result can be retinal detachment, pulmonary fibrosis, hemothorax, or stroke. Since hypertension hits the kidneys hard, a vicious circle is formed with kidney failure, when one pathology contributes to the development of the second. In most cases, this disease is diagnosed in older animals.

Symptoms of arterial hypertension

Unfortunately, the symptoms of hypertension in cats are very vague and uncharacteristic. Since this pathology is almost always secondary to diseases of the thyroid gland and kidneys, the clinical picture will largely correspond to the primary disease. The main signs are:

Loss of appetite.
Increased thirst and urination (polydipsia and).
Weight loss (may be rapid if the cat is severe).

Read also: Diarrhea in a kitten: a complete list of possible causes, treatment, nutrition, prevention

Sometimes heart murmurs or serious eye problems indicate pressure problems. These signs help to understand that the animal has serious functional disorders in the body. This is one of the reasons why it is extremely important to take your pet regularly for a complete preventive veterinary examination.

In the case when the pressure rises suddenly and sharply, a very characteristic symptom will be sudden onset blindness and disorientation in space. The blood vessels in the eye will rupture, the retina will detach. Vision is lost partially or completely. The cat's pupils are dilated. Cats panic, cannot move, and often bump into furniture, doors, and corners when trying to run.

Less commonly, chronic hypertension can cause cerebral hemorrhage. When walking, the cat leans heavily, falls sideways, it is disoriented, there may be sudden seizures that strongly resemble epilepsy. But much more often the animal simply falls into a coma and quickly dies.

Diagnostics

The most reliable method for detecting hypertension is ... a conventional blood pressure monitor, the cuff of which is put on the paw or the base of the tail. The procedure itself is absolutely painless, and in balanced animals, reliable results can be obtained already from the second or third time. But such "prudent" cats come across very rarely. Much more often you can observe a real hysteria, accompanied by attempts to scratch and bite both the veterinarian and his own owner.

If this is the case, you will have to try to calm your "palm tiger". Sit with the cat, stroke it. Some foreign forums even advise the use of aromatic oils and other homeopathy. These drugs do not reduce pressure, but they can help calm the cat. As a rule, to obtain reliable results, the pressure has to be measured several times.

How to treat this disease?

So how is hypertension in cats treated? It all depends on the primary disease that caused the increase in pressure. The sooner it is detected and the sooner effective treatment is prescribed, the greater the chance that hypertension will not develop at all.

Doctors call hypertension a "silent killer" because most people are asymptomatic, but statistics show that this pathology significantly increases the risk of diseases of the blood vessels of the brain, myocardial infarction and kidney failure. Unfortunately, the situation is quite different in veterinary medicine. In most animals, hypertension is diagnosed as a result of the onset of symptoms of severe KO lesions. This is largely because veterinarians neglect to measure blood pressure (BP) in their patients during routine diagnostic examinations: at present, BP is determined mainly in cases of clinical manifestations of systemic hypertension in animals.

MAIN PROVISIONS

> hypertension is usually diagnosed in cats when signs of end organ disease (TO) develop. The eyes are most often affected, which is accompanied by loss of vision in animals.
> Hypertension most often develops in aging cats; Animals with chronic renal failure are at the highest risk.
> Cats are easy to measure blood pressure (KD) non-invasive methods, but this can be difficult in animals in which hypertension develops from fear.
> Amlodipine, which blocks calcium channels, is currently the drug of choice for the treatment of hypertension in cats.

Clinical signs of hypertension

Hypertension-associated clinical signs that prompt cat owners to contact veterinarians are most often eye lesions, but there are cases when increased BP is accompanied by severe disorders of the brain, heart and kidneys, sometimes there are bleeding in the nasal cavity (epistaxis).

Visual impairment in hypertension

Unfortunately, owners of hypertensive cats most often begin to pay attention to the health of their pets when they suddenly go blind. Other visual disturbances that owners notice in cats with high blood pressure include bleeding into the anterior chamber of the eye (hyphema) and dilated pupils (mydriasis). An ophthalmological examination of cats blinded by hypertension reveals hemorrhages in the anterior chamber of the eyes, vitreous body, retina and underlying tissues, as well as serous retinal detachment. In typical cases, the lesions are bilateral, although the pathological changes in one eye may be stronger than the other. Examples of such violations are shown in Figs. one.

Figure 1. Lesions characteristic of hypertension in the eye of blinded cats,
but. Severe bumous retinal detachment.
b. Retinal detachment and numerous small retinal hemorrhages,
in. Hyphema.

Secondary changes that sometimes develop against the background of hypertension are glaucoma and retinal atrophy.

Mild changes are detected in cats only when examining the fundus before the loss of the cat's vision. At the same time, lesions such as small hemorrhages in the retina, its focal detachment and edema are detected. In addition, small, dark patches of focal degeneration may be seen in the retina. Such lesions are often found in the tapetum part of the fundus, near the optic disc. Examples of these changes are shown in fig. 2.

Figure 2. Eye changes that can develop in hypertensive cats with vision. Photos published with the kind permission of Rebecca Elks.
but. Foci of hemorrhage in the retina.
b. Small areas of bullous retinal detachment.
in. Small areas of bullous detachment and foci of retinal degeneration.

Although visual changes in hypertensive cats are usually described as "hypertensive retinopathy", in fact this pathological process mostly involves the vascular layer. For example, retinal detachment occurs when intraocular fluid is released from the terminal arterioles and capillaries of the iris and accumulates in the subretinal space. Degeneration of the retinal pigment epithelium occurs due to severe ischemia of the choroid. Optic nerve lesions are rarely reported in cats, possibly because such changes are masked by concomitant edema and hemorrhage. In addition, edema of the unmyelinated optic nerve, located in a secluded part of the eyeball, is quite difficult to detect in cats. The clinical features and pathophysiology of hypertension-associated pathological changes in the retina, iris, and optic nerve of cats are described in detail in a recently published review.

Neurological manifestations of hypertension

Hypertensive cats show the following neurological signs: weakness, ataxia, loss of the ability to navigate the environment. Signs of vestibular dysfunction, neck flexion, paraparesis, stupor, convulsions and death. In cats with hypertension, neurological symptoms develop less often than visual disturbances: nevertheless, this is noted in at least a third of all cases. Meanwhile, it is very likely that neurological disorders often remain unrecognized for a number of reasons. Because of the variability in symptoms seen in cats with hypertension, hypertension cannot be diagnosed based on the neurological nature of the pathology. Many cats in this situation are euthanized before a definitive diagnosis can be made. In addition, in cats with severe eye damage, some neurological impairment (eg depression) may be directly related to their blindness. The presence of mild neurological changes in hypertension may explain why many cat owners report an improvement in the clinical condition of their pets after starting their treatment with antihypertensive drugs, even if vision is not restored.

Cardiovascular manifestations of hypertension

Heart systolic murmurs and a gallop rhythm are often heard on auscultation of hypertensive cats. Diastolic heart murmurs and tachycardia are among other, less commonly recorded in this pathology, deviations from the cardiovascular system. arrhythmias and shortness of breath.

Meanwhile, heart murmurs and the other abnormalities mentioned are more frequently detected in aging cats, even those with normal KD. The latter circumstance does not allow us to assume hypertension based on the presence of such symptoms: in other words, to make such a diagnosis, it is necessary to measure BP.

Hypertensive cats rarely show signs of congestive heart failure. This happens when hypertension exacerbates some other existing cardiovascular disease in the animal, but is unlikely to be responsible for heart failure on its own. However, the suspicion of CVD in a cat does not eliminate the need to measure the animal's BP.

An x-ray examination in cats with hypertension establishes an increase in the heart, especially the left ventricle, and the presence of undulation of the thoracic aorta.
Echocardiographic changes most commonly seen in hypertensive cats include mild hypertrophy of the left ventricular wall and ventricular septum. However, it is noteworthy that heart sizes in many cats with systemic hypertension remain within the normal range. Differences in systemic echocardiographic parameters between normal and hypertensive cats of the same age are virtually minimal.

Diagnosis of hypertension

CD is determined by direct and indirect methods. Direct methods serve as the "gold standard". They are based on the puncture of an artery or the introduction of a catheter into an artery. Meanwhile, direct methods are unacceptable for routine measurement of BP in sick animals, which is due to difficulties in puncturing their arteries, increased BP as a result of pain reaction and stress in the animal during the procedure, and the risk of complications such as infection, vascular thrombosis, and hemorrhage. A method for measuring blood pressure with transponder sensors inserted into vessels for a long time is described, but so far it has found application only in experimental studies.

Indirect methods are more convenient for measuring BP in diseased animals. Of these, in working with cats, the Doppler method and oscillometric methods are most often used. Korotkoff's auscultatory method, widely used in medicine, cannot be used to determine BP in cats due to the low amplitude of arterial murmurs. The choice of an indirect method for measuring blood in cats is not easy - each of them has its own advantages and disadvantages.

Oscillometric method

Oscillometric equipment detects changes in blood pressure in an air-filled cuff surrounding a peripheral artery. The oscillation amplitude varies depending on the BP and cuff pressure. The advantage of the method is the ability to determine both systolic and diastolic blood pressure.

However, the values of KD. corresponding to high amplitude oscillations are usually more reliable than systolic and diastolic BP values. Studies conducted on cats in a state of general anesthesia have shown that the oscillometric method gives underestimated values of BP (especially systolic), while it is increased. A fairly high incidence of failed attempts to determine KD in cats has been reported; these data confirm the results of studies in conscious cats, in which the average duration of the procedure was found to be excessively long.

More importantly, there are reports of that the results of oscillometric measurements of BP do not correlate well with indications of direct methods for determining BP in conscious cats and do not make it possible to diagnose cases of hypertopic eye damage. A number of factors can negatively impact BP measurements in conscious animals, including locomotor activity and heart rate, which are higher than in cats under general anesthesia.

Doppler method

This method is based on the measurement of an ultrasonic signal reflected by moving blood cells with a transducer.

The value of the CD is determined using a sigmomanometer, the cuff of which covers the limb of the animal proximal to the sensor. In one publication comparing direct and indirect methods for determining KD in animals under general anesthesia, it was reported that. that the Doppler method is more accurate than the oscillometric method, but in another experiment opposite results were obtained.

Dopplerists, however, prefer this method because it is more reliable for measuring BP in conscious cats and can identify animals with hypertonic ocular disease. The use of this method is limited by the inability to determine diastolic KD.

However, the fluctuations of its consistently obtained readings are much smaller than those of other indirect methods for determining BP, these differences are most clearly manifested in the hypotensive state of animals.

Hypertension from fear

Whatever non-invasive method the veterinarian uses to measure BP, he should always take into account the existing phenomenon of hypertension from fright and take all possible measures to avoid this short-term increase in BP that occurs in animals during a visit to a veterinary clinic. The described phenomenon also manifests itself in people who are measured for BP, not only during an outpatient visit, but also during the provision of medical care. This can lead to an erroneous diagnosis of hypertension and subsequent treatment, which is not necessary. The possibility of developing the phenomenon of hypertension from fright in cats has been proven in experimental conditions. To measure blood pressure and heart rate, radio telemetry sensors were implanted in cats. Readings were taken under calm conditions and then during a visit to the veterinarian. It was found that the average systolic blood pressure in the latter case increased compared to the previous level, which was determined in a calm environment for 24 hours, by 18 mm Hg. Art. The nature and intensity of the manifestation of the phenomenon of hypertension from fright in different cats were not the same, and fluctuations in blood pressure during the period of short-term hypertension associated with it reached 75 mm Hg. Art. How pronounced the phenomenon of hypertension from fright would become could not be judged by changes in heart rate. The results of this and other studies have clearly shown the importance of giving cats the opportunity to adapt to the conditions in which they are supposed to be tested for KD.

Conditions for carrying out measurements of CD

KD can be measured on the front or hind limb, as well as on the tail. However, to obtain comparable results, this should always be done in the same place, since the results of determining the KD in different parts of the cat's body can vary significantly. The width of the cuff should be approximately 40% of the circumference of the animal's limb. The use of a cuff that is too wide will result in low readings, and a cuff that is too narrow will result in high readings; however, the differences between the two are usually quite small.

What are the criteria for hypertension?

There is no consensus as to what level of BP should be considered sufficient in cats to diagnose hypertension. Very few studies have been conducted to establish the normal values of this indicator. Although those values of KD. which were determined in healthy cats by different authors, differed significantly, however, the value of CD, determined in different experiments in young healthy animals using surgically implanted radiotelemetry sensors, turned out to be the same. This indicates that disagreements between different authors about the normal value of BP in cats are due to the unequal accuracy of their methods of indirect determination of BP or the phenomenon of hypertension from fright. A certain radiotelemetric level of CD in humans, cats and many other mammals turned out to be the same. Apparently, it corresponds to the value of BP, which achieves optimal blood supply to the brain and internal organs.

Mass surveys of people have shown that systolic and diastolic blood pressure has a pronounced long-term and etiological effect on the consequences of concomitant diseases. Therefore, knowledge of the value of "normal" and "hypertonic" blood pressure is unnecessary - it is only important to maintain blood pressure at an optimal level, at which undesirable consequences (for example, cardiovascular diseases) are prevented. The optimal BP for many people is much lower than what is commonly considered "normal". For example, according to statistics, in 25% of adults in the developing countries of the world, the KD exceeds the permissible norm, which dictates the need for their treatment with antihypertensive drugs. The situation is further complicated by that. what. as studies have shown, the optimal KD is not some kind of stable value, but depends on the clinical condition of the patient. For example, in people with kidney disease, the desired “optimal” BP should be significantly lower than for the world population as a whole (16). In cats, the only clinical complication of hypertension is ocular damage, as evidenced by the results of numerous retrospective observations made in uncontrolled conditions. We diagnose systemic hypertension in this animal species when the systolic blood pressure exceeds 175 mmHg. Art. and there are eye lesions. If no change in the organs of vision is detected, then such a diagnosis can only be made by re-establishing an increased systolic blood pressure in the animal during its re-examination at the next visit to the veterinary clinic. Once the diagnosis is made, treatment begins. Using these diagnostic criteria, it is possible to prevent the development of eye lesions in cats suffering from hypertension. However, it is not known if there is any further benefit from treating cats with lower BP. for example. 160-P5 mm Hg. Art.

Which cats are at increased risk for developing systemic hypertension?

In order to diagnose hypertension before the development of associated irreversible KO lesions and related symptoms, it is useful to have an understanding of Which cats are at the highest risk of systemic hypertension? Such patients should regularly measure BP as a preventive measure. Cats usually do not have primary hypertension - an increase in BP, as a rule, occurs against the background of other diseases (causing the development of hypertension or coexisting), most often - chronic renal failure and hyperthyroidism. These questions are discussed in detail below. In addition, there are a number of less frequently diagnosed diseases in cats that can lead to systemic hypertension.

Chronic renal failure

Chronic renal failure is the syndrome most commonly associated with severe hypertension in cats. In a mass screening of cats with hypertension accompanied by eye involvement, 44 out of 69 (64%) of the animals showed an elevated blood creatinine concentration.

HarrietM. Sim
Harriet M. Syme, BSc, BVetMed, PhD, MRCVS, Dipl ACVIM, Dipl ECVIM-CA
Lecturer in Domestic Animal Medicine, Royal Veterinary College, London, UK

Systemic hypertension (an abnormal increase in systemic blood pressure) as a circulatory pathology is often recorded in older cats. A high incidence of systemic hypertension has been noted in cats with chronic renal failure (61%) and hyperthyroidism (87%) (Kobayashi et al, 1990). But at the same time, hypertension also occurs in cats and in the absence of renal failure and euthyroidism (normal thyroid status). Because untreated cats with hypertension can lead to serious neurological, ophthalmic, cardiac, and nephrological disorders, treatment of these patients is strongly recommended. In addition, specific antihypertensive drugs can significantly affect end-organ vital function and long-term prognosis.

Systemic hypertension is usually presented as a complication of another systemic pathology and is therefore classified as secondary hypertension. However, in some cases where the cause of SH is not established, in the process of a full examination, they speak of primary or idiopathic hypertension.

Epidemiology

As mentioned above, hypertension is more common in older cats, with a median age of 15 years ranging from 5 to 20 years (Littman, 1994; Steele et al, 2002). It is not clear enough whether an increase in blood pressure is normal in healthy older cats or whether this should be regarded as an early subclinical stage in the development of the pathological process. Breed and sex predisposition to hypertension in cats has not been identified.

Pathophysiology

Although systemic hypertension is often found in cats with chronic kidney dysfunction, the link between elevated blood pressure and kidney damage as an underlying cause is not clear. Vascular and parenchymal diseases of the kidneys in humans are proven causes of hyperreninimic hypertension. At the same time, an increase in the volume of extracellular fluid is one of the mechanisms for the development of hypertension in patients in the late stages of kidney disease (Pastan & Mitch, 1998). There is evidence that cats with naturally occurring hypertension and renal insufficiency do not show increases in plasma renin levels and activity and plasma volume (Hogan et al, 1999; Henik et al, 1996). This suggests that some cats have primary (essential) hypertension and kidney damage is secondary to chronic glomerular hypertension and hyperfiltration.

Similarly, the relationship between hyperthyroidism and hypertension in cats is not well defined, even though the prevalence of hypertension in cats with thyrotoxicosis is high. Hyperthyroidism leads to an increase in the number and sensitivity of myocardial β-adrenergic receptors and, as a result, increased sensitivity to catecholamines. In addition, L-thyroxine has a direct positive inotropic effect. Consequently, hyperthyroidism leads to an increase in heart rate, an increase in stroke volume and cardiac output, and an increase in arterial blood pressure. However, no significant relationship has been found between serum thyroxine concentrations and changes in blood pressure in cats (Bodey & Sansom, 1998). In addition, in some cats, with proper and effective treatment of hyperthyroid status, arterial hypertension may persist. Thus, it is assumed that in a subset of cats with hyperthyroidism, hypertension is independent of hyperthyroid status. Other unlikely causes of hypertension in cats include hyperadrenocorticism, primary aldosteronism, pheochromocytoma, and anemia.

Hypertension in the absence of kidney or thyroid disease in cats suggests that in some cases, as in humans, systemic hypertension can be considered a primary idiopathic process involving increased peripheral vascular resistance and endothelial dysfunction.

Clinical signs

Clinical signs are usually derived from target organ damage (brain, heart, kidneys, eyes). As blood pressure rises, autoregulatory vasoconstriction of arterioles occurs to protect the capillary bed of these highly vascularized organs from high pressure. Severe and prolonged vasoconstriction can eventually lead to ischemia, infarction, loss of capillary endothelial integrity with edema or hemorrhage. Hypertensive cats may present with symptoms such as blindness, polyuria/polydipsia, neurological signs including seizures, ataxia, nystagmus, hind limb paresis or paralysis, dyspnea, and epistaxis (Littman, 1994). Rarer possible signs include "stopping eyes" and vocalizations (Stewart, 1998). Many cats show no clinical signs, and hypertension is diagnosed after murmurs, galloping, electrocardiographic, and echocardiographic abnormalities are identified. In cats, systemic hypertension is often associated with left ventricular hypertrophy. Usually it is moderate hypertrophy and asymmetric septal hypertrophy of the left ventricle. Dilatation of the ascending aorta is detected radiographically or echocardiographically, but it is not clear whether this finding is due to hypertension or a normal age-related change. Cats with systemic hypertension often have left ventricular diastolic dysfunction due to decreased wall relaxation.

Acute blindness is a common clinical manifestation of systemic hypertension in cats. Usually blindness occurs due to bilateral retinal detachment and/or hemorrhage. In one study, 80% of hypertensive cats had hypertensive retinopathy with retinal, vitreous, or anterior chamber hemorrhages; retinal detachment and atrophy; retinal edema, perivasculitis; tortuosity of the retinal arteries and/or glaucoma (Stiles et al, 1994). Retinal lesions usually regress with antihypertensive therapy and vision returns.

The central nervous system is prone to damage due to hypertension because it is replete with small vessels. In cats, these injuries can cause convulsions, head tilt, depression, paresis and paralysis, and vocalization.

Chronic hypertension can cause kidney damage as a result of changes in afferent arterioles. Focal and diffuse glomerular proliferation and glomerular sclerosis may also develop (Kashgarian, 1990). Following renal dysfunction, chronic systemic hypertension causes a sustained rise in glomerular filtration pressure, which plays a key role in the progression of renal deterioration (Anderson & Brenner, 1987; Bidani et al, 1987). Proteinuria and hypostenuria are uncommon in hypertensive cats, but microalbuminuria has been observed (Mathur et al, 2002).

Ophthalmological examination

Acute blindness is the most common cause of cat owners with hypertension. The owner notes that the cat has become less active in moving around the room, stopped jumping on furniture or misses in a jump. In some cases, the owner does not suspect that the cat's vision is sharply reduced or absent, since the cat, even completely blind, continues to navigate in a familiar room due to other senses. This is one of the reasons why the owner of the cat comes to the clinic late.

The main complaints of the owners are an enlarged "frozen" pupil, blood inside the eye, a change in the fundus reflex, loss of vision.

To identify pathology of the retina, it is necessary:

check pupillary reactions;
test reaction to bright light (dazzle reflex);
check the reaction to a threatening gesture;
conduct a "cotton ball" test to determine if a cat can track the movement of objects in its field of vision;
measure intraocular pressure;
examine the anterior segment of the eyeball with a slit lamp;
perform ophthalmoscopy;
if necessary, conduct an ultrasound of the eyeball.

The complex of these manipulations will help determine the degree of damage to the retina and, to some extent, give a prognosis for the restoration of vision.

The most valuable information about the state of the retina is obtained by the researcher thanks to ophthalmoscopy.

The picture of the fundus of the cat has a great variability. It is important to distinguish between norm and pathology. It must be remembered that the absence of tapetum or pigment may be in a completely healthy animal.

Signs of pathology are:

Rice. 6. Fig. 8.

In cases where ophthalmoscopy is not possible (with extensive hemorrhage into the vitreous body, with cataracts), it is necessary to conduct an ultrasound of the eyeball. The presence of a hyperechoic membrane that connects to the fundus in the region of the optic disc indicates retinal detachment (Fig. 8).

The suspicion of hypertension in a cat may be based on the presence of characteristic retinal lesions. However, other causes of retinal detachment and/or hemorrhage must be excluded. Arterial hypertension must certainly be confirmed by measuring blood pressure. Blood pressure measurements should be performed to confirm or refute the presence of hypertension in cats with left ventricular hypertrophy, renal dysfunction, or hyperthyroidism, and in cats over 7 years of age with murmurs, gallops. Also, blood pressure measurement should be performed in cats with the above signs of brain damage.

Hypertension in cats was defined as an indirect systolic pressure greater than 160 mmHg. Art. (Littman, 1994; Stiles et al., 1994) or 170 mmHg. Art. (Morgan, 1986) and diastolic blood pressure over 100 mm Hg. Art. (Littman, 1994; Stiles et al., 1994). However, blood pressure will increase with age in cats and may exceed 180 mmHg. Art. systolic and 120 mm Hg. Art. diastolic pressure in apparently healthy cats older than 14 years (Bodey and Sansom, 1998). Thus, a diagnosis of hypertension can be made in a cat of any age whose systolic blood pressure is 190 mmHg. Art. and diastolic pressure of 120 mm Hg. Art. Cats with a clinical picture consistent with arterial hypertension and a systolic pressure of 160 to 190 mm Hg. Art. also should be considered patients with arterial hypertension, especially if they are less than 14 years old. In the absence of clinical signs of hypertension, systolic blood pressure from 160 to 190 mm Hg. Art. and diastolic pressure between 100 and 120 mm Hg. Art. repeated measurements are needed several times during the day, or possibly several days.

Numerous pharmacological agents are available for use as antihypertensive drugs, including diuretics, β-blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, calcium channel antagonists, direct-acting arterial vasodilators, centrally acting α2-agonists, and α1-blockers. .

Hypertensive cats tend to become refractorier to the antihypertensive effects of blockers such as prazosin as well as direct acting arterial vasodilators such as hydralazine. In addition, long-term use of direct-acting drugs often leads to undesirable stimulation of compensatory neurohumoral mechanisms. Diuretics, β-blockers, or a combination of both, effectively lower blood pressure in most hypertensive cats but do not reduce end-organ damage (Houston, 1992).

According to Poiseuille's law, blood pressure is determined by the product of systemic vascular resistance and cardiac output, so the decrease in blood pressure as a result of the use of diuretics and β-blockers occurs as a result of a decrease in cardiac output. These drugs lower blood pressure by a mechanism that reduces flow to target organs, thereby compromising myocardial, renal, and brain perfusion. At the same time, calcium channel antagonists, ACE inhibitors, angiotensin II receptor blockers reduce blood pressure by reducing vascular resistance. This mechanism is more effective for improving the perfusion of target organs. Calcium channel antagonists, in particular, lack myocardiodepressant effects, and ACE inhibitors have, in fact, shown beneficial effects on renal function, coronary perfusion, and cerebral perfusion in people with hypertension (Houston, 1992; Anderson et al, 1986). Centrally acting α-adrenergic agonists also lower blood pressure by reducing vascular resistance and are indicated to maintain target organ function. Diuretics and β-blockers reduce cardiac output, stroke volume, coronary and renal blood flow, increasing renal vascular resistance. In addition, these drugs do not reduce left ventricular hypertrophy. On the other hand, calcium channel blockers, ACE inhibitors, angiotensin II receptor blockers, and centrally acting drugs have the opposite effect.

Amlodipine is a long-acting antihypertensive drug belonging to the calcium channel blockers. This drug relaxes vascular smooth muscle by blocking the influx of calcium. Its main vasodilating effect is a systemic decrease in vascular resistance. In addition, this action extends to the coronary arteries. This drug is safe and effective even in cats with kidney dysfunction when used orally at a dose of 0.2 mg/kg once daily. When taken daily, amlodipine lowers blood pressure within 24 hours (Snyder, 1998). In addition, cats do not develop refractoriness to amlodipine, and with long-term therapy, a persistent therapeutic effect occurs.

ACE inhibitors such as enalapril, ramipril, and benazepril are also good options for treating hypertension in cats. Vasotop®R (MSD Animal Health) is widely used in the Russian Federation. The active substance of the drug is ramipril. Ramipril has unique properties that distinguish it from other ACE inhibitors used in veterinary medicine.

However, these drugs are often ineffective as monotherapy in cats. ACE inhibitors may be best used in combination with amlodipine.

In cats resistant to amlodipine or ACE inhibitors, only the combination of these drugs can safely provide adequate blood pressure control. When adding ACE inhibitors (enalapril or benazepril) to amlodipine therapy, doses of 1.25 to 2.5 mg/cat/day are used). Also, some cats receiving this combination of drugs, there is an improvement in kidney function. Experimental data show that the combination of these two classes of antihypertensive drugs not only effectively lowers blood pressure, but also maximally protects target organs (Raij & Hayakawa, 1999). The angiotensin receptor blocker irbesartan in combination with amlodipine has been shown to be effective in some cats refractory to ACE inhibitors.

For cats with neurological disorders due to brain damage, aggressive treatment is needed to quickly lower blood pressure. Amlodipine and ACE inhibitors have a relatively slow hypotensive effect and require 2-3 days to reach the peak of the hypotensive effect. In such clinical situations, intravenous nitroprusside will be more effective for the rapid relief of a hypertensive crisis. However, safe use of this drug requires careful dose titration using an infusion pump (1.5-5 mg/kg/min) and continuous blood pressure monitoring. Hydralazine may be used as an alternative to nitroprusside when rapid blood pressure reduction is not required. This drug is usually given orally every twelve hours, starting at a dose of 0.5 mg/kg and increasing if necessary to 2.0 mg/kg every 12 hours. Caution is advised when using fast-acting, potent antihypertensive drugs for the treatment of hypertensive crises. A rapid and abrupt drop in blood pressure can lead to acute cerebral ischemia and thus worsen neurological deficits.