Introduction

Blood pressure management is a vital aspect of veterinary care, especially for our canine and feline companions. Just like in humans, hypertension can lead to severe health issues in pets if left unmanaged. This article delves into the intricacies of managing blood pressure in cats and dogs, highlighting the importance of early diagnosis, understanding the types and causes of hypertension, and implementing effective treatment strategies.

What is Hypertension?

Hypertension, or high blood pressure, refers to a condition where the force of blood against the walls of the arteries remains consistently elevated. In veterinary medicine, hypertension is often categorised as either systemic or pulmonary, with systemic hypertension being more commonly encountered in clinical practice, and pulmonary hypertension being more common in dogs (1) . 

Different Types of Hypertension

Hypertension in dogs and cats can be classified into three main types:

1. Situational Hypertension: This occurs when normotensive animals display an increase in blood pressure only in a clinical setting, potentially due to anxiety, stress or excitement. Hypertension can often be misclassified as situational, leading to failure to diagnose (1, 2).
2. Primary (Idiopathic) Hypertension: This type is relatively rare in animals and is diagnosed when no underlying cause is identified. It is more commonly observed in older animals (2).
3. Secondary Hypertension: This is the most common form in companion animals and is usually associated with underlying diseases such as chronic kidney disease (CKD), hyperthyroidism (especially in cats), diabetes mellitus, or hyperadrenocorticism (Cushing's disease) (2, 3, 4, 5)

Causes and What It Leads to (Target Organ Damage)

The causes of hypertension in pets are often linked to the underlying conditions mentioned above. Persistent hypertension can lead to significant damage to tissues, collectively known as target organ damage (TOD) (2). The organs most commonly affected include the kidneys, eyes, heart, and brain (2). In cats, hypertension often manifests as retinal detachment, leading to sudden and often permanent blindness (1, 2, 4) . In dogs, it may result in congestive heart failure or chronic kidney failure if left untreated (1, 2). Therefore, all preventative measures and antihypertensive treatment are aimed to reduce the risk of target organ damage.

What is the Normal, Moderate, and High Blood Pressure Range?

According to the American College of Veterinary Internal Medicine (ACVIM), blood pressure values and their associated risk of TOD are categorised as follows:

Table 1. Classification of hypertension based on risk of TOD in dogs and cats. Adapted from table 6. of the ACVIM consensus statement (2).

Values above 180 mmHg are considered severe and result in hypertensive emergencies  therefore warranting immediate medical intervention, especially if the following TOD manifestations are evident:

• Acute onset seizures
• Altered mentation
• Lateral recumbency
• Blindness (2)

Diagnosis

Direct Blood Pressure (DABP) Measurement

Direct measurement is the gold standard for accuracy, involving the placement of an arterial catheter to measure systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) (2). However, this is invasive, therefore is impractical in common clinical settings (for screening and treatment) (2). This technique is typically reserved only for critically ill patients or those undergoing anaesthesia, where precise blood pressure monitoring is crucial.

A normal blood pressure systolic (SAP), diastolic (DAP), and mean arterial pressure (MAP) for dogs and cats are as outlined below:

Table 2. Normal ranges of systolic, diastolic and mean arterial pressure for dogs and cats. From table 10.1 from Williamson and Leone (6).

Indirect Blood Pressure (IABP) Measuring Devices

Indirect methods are most commonly used in clinical settings and typically in conscious animals due to their non-invasive nature (2, 7, 8). This involves using devices to indirectly estimate BP, thus due to their indirect nature, ACVIM recommended that all devices must be validated for use in species of interest and circumstances (2). The key techniques include:

• Doppler Ultrasonography: Often preferred for small animals like cats and small dogs, Doppler ultrasonography provides reliable systolic blood pressure readings by detecting blood flow via ultrasonic waves. While it requires manual operation, it is valued for its accuracy in detecting SBP.
• High definition oscillometric: This method is more user-friendly and suitable for larger dogs. Oscillometric devices measure systolic, diastolic, and mean arterial pressure by fluctuations in pressure from arterial pulsation but can be less reliable in animals of all sizes due its sensitivity to movement and positioning.

Table 3. Advantages and disadvantages of key indirect BP measuring devices.

ACVIM Protocol

The American College of Veterinary Internal Medicine (ACVIM) has provided a standard protocol for an accurate and reliable blood pressure measurement using indirect BP devices. ACVIM recommended that this protocol should be undertaken by clinics or relevant person(s) for all measurements using doppler or oscillometric devices to once again ensure reliability and accuracy, and subsequently better diagnosis (2).

The summary of this protocol is as follows:

Table 4. Summary of the ACVIM protocol. Adapted from Table 1. from the ACVIM consensus statement.

When Should/Who Should Be Screened for Hypertension?

The ACVIM do not recommend a routine health screening (BP measurements) of all dogs and cats for systemic hypertension, as this can lead to high likelihood of a false diagnosis from false readings (2). Instead, screening is only recommended for dogs and cats that are 9 years old or older, as most conditions leading to secondary hypertension are associated with age. BP measurements should be done if the animals has but not limited to the following clinical abnormalities:

• Chronic Kidney Disease (CKD)

• hypertensive choroidopathy

• Retinopathy

• Hyphema

• Seizures, proteinuria

• Hyperthyroidism (in cats)
• Diabetes Mellitus
• Hyperadrenocorticism (Cushing's Disease) (2)

These can be assessed by conducting a thorough physical examination, consisting of funduscopic evaluation, cardiac auscultation, assessment of renal function including proteinuria, and neurologic examination (2).

Early detection through regular monitoring is essential for managing hypertension and preventing TOD in at-risk animals. Therefore, in absence of any clinical signs, the ACVIM recommended that a high index of suspicion must be maintained to avoid misdiagnosis and misclassification as situational hypertension. BP measurements can be undertaken in animals with early signs of hypertension such as morning headaches, facial flushing and anxiety (2).

Treatment

Antihypertensive Medications

Treatment of hypertension in pets typically involves antihypertensive medications tailored to the individual animal, considering species, underlying conditions, and the severity of hypertension.

• Angiotensin-Converting Enzyme Inhibitors (ACEIs): Commonly used in dogs, especially those with concurrent CKD or heart disease, ACEIs like enalapril and benazepril reduce the production of angiotensin II, leading to vasodilation and lower blood pressure (2, 4). 
• Angiotensin II Receptor Blockers (ARBs): Telmisartan, an ARB, is increasingly used in cats to manage hypertension by blocking the angiotensin II receptor, offering an alternative to ACEIs, especially for cats that do not tolerate ACEIs well.
• Amlodipine: A calcium channel blocker, amlodipine is the first-line treatment for hypertension in cats due to its effectiveness in reducing SBP. In dogs, it is often used in combination with ACEIs or ARBs for more comprehensive blood pressure control (5).

Specifically for Cats

As mentioned above, in cats, amlodipine is the preferred treatment for managing hypertension due to its efficacy and tolerability. For cases of secondary hypertension, such as those related to CKD or hyperthyroidism, treating the underlying condition is also critical. When monotherapy with amlodipine is insufficient, ACEIs or ARBs may be added to the treatment regimen (2, 5). 

The recommended starting dose of amlodipine to treat hypertension is 0.625 mg every 24 hours. If the SBP is 200 or higher, a dose of 1.25mg every 24 hours can be considered. If this is insufficient or causes inadequate response, dose can be doubled/increased in a 7 day interval up to a maximum of 2.5mg every 24 hours (5).

Specifically for Dogs

As mentioned above, in dogs, hypertension management often involves ACEIs and ARBs as a first-line of treatment, however it can be combined with amlodipine, particularly in cases where secondary hypertension is due to CKD or Cushing’s disease. The choice of medication and dosage should be tailored to the individual dog’s needs, considering any concurrent conditions that may influence treatment (2, 5).

The ACVIM recommends a starting dose of ACEIs or ARBs in dogs at 0.5 mg/kg every 12‐24 and 1 mg/kg every 24 hours (2). Decisions to increase dose due to inadequate responses can be considered but using ACEI or ARBs drugs such as telmisartan in combination with amlodipine has resulted in a high efficacy (5).

Emergency Management

In cases of severe hypertension (SBP > 180 mmHg) accompanied by signs of acute TOD, emergency intervention is essential. There are currently no medications that have been clinically studied for veterinary use, however the ACVIM has recommended the most feasible intravenous antihypertensive agents such as fenoldopam or labetolol in dogs may be administered to rapidly lower blood pressure (2). Furthermore, patients must be continuously monitored 24-hour in a hospital setting until blood pressure stabilizes. Once BP has stabilised for 12-24 hours, and for high BP animals accompanied by no sign of acute TOD, oral antihypertensive medications such as amlodipine in cats or hydralazine can be used (2).

Conclusion

Blood pressure management in dogs and cats is a critical component of veterinary care, particularly for animals with chronic conditions. Early, accurate diagnosis and intervention, facilitated by monitoring of high-risk animals and appropriate use of antihypertensive medications, are vital in preventing serious complications associated with hypertension such as damages to vital organs. By staying informed about the latest diagnostic and treatment protocols (e.g. ACVIM), veterinarians can provide the best possible care, ensuring improved health outcomes and quality of life for their patients.

References:

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