Hypertensive emergencies

What is a hypertensive emergency?

Hypertensive emergency describes a situation where elevated blood pressure values are present, plus acute hypertension-mediated organ damage. If untreated, it may lead to life-threatening end-organ damage over the course of hours.¹

Examples of hypertensive emergencies include:²

• Hypertensive encephalopathy.

• Acute pulmonary oedema.

• Acute renal failure.

• Aortic dissection.

• Acute coronary syndrome.

• Severe pre-eclampsia, or eclampsia.

• Phaeochromocytoma crisis.

• Intracerebral haemorrhage.

• Hypertensive thrombotic microangiopathy.

• Malignant hypertension (see below).

In the 2020 International Society of Hypertension guidelines, there is no specific blood pressure threshold used to define a hypertensive emergency.³ Other guidelines have proposed a cutoff; for example, the 2017 American College of Cardiology and American Heart Association guidelines used a blood pressure threshold of ≥180 mm Hg systolic and ≥120 mm Hg diastolic as part of their definition of a hypertensive emergency.⁴

Hypertensive emergencies are generally associated with severely raised blood pressure values (eg, ≥180 mm Hg systolic or ≥120 mm Hg diastolic), but not always; a moderate elevation of blood pressure, particularly if it occurs rapidly, may be potentially life-threatening in some situations.¹ Conversely, severely raised blood pressure values alone - without evidence of acute end-organ damage - are not hypertensive emergencies.

Malignant hypertension is a related concept. It is often used interchangeably with the term 'accelerated hypertension'. It describes a form of severe hypertension characterised by vascular damage resulting from failure of autoregulation of blood flow. It is diagnosed clinically based on the presence of:¹⁵

• Blood pressure readings of 180mmHg systolic or higher, or 120mmHg diastolic or higher, and;

• Evidence of grade 3 hypertensive retinopathy (flame or dot-shaped haemorrhages, cotton -wool spots, hard exudates and microaneurysms), or grade 4 hypertensive retinopathy (bilateral papilloedema).

Untreated malignant hypertension can lead to hypertensive encephalopathy, thrombotic microangiopathy, and acute renal failure (termed complicated malignant hypertension). Some guidelines consider malignant hypertension to be a type of hypertensive emergency,³ whereas other authors consider uncomplicated malignant hypertension (malignant hypertension with retinal changes or papilloedema only) to be a type of uncontrolled severe hypertension (albeit one with a poor prognosis), rather than a 'true' hypertensive emergency.¹

Hypertensive emergencies should be distinguished from severe hypertension without acute end-organ damage. This is usually defined as a blood pressure of 180mmHg systolic or higher, or 120mmHg diastolic or higher, with no signs or symptoms of acute end-organ damage.

Severe hypertension without acute end-organ damage has also been termed "hypertensive urgency",² "severe asymptomatic hypertension",⁶ and "severe hypertension without life-threatening end organ damage".¹

Hypertensive emergencies require emergency treatment in hospital, often with aggressive blood pressure-lowering treatment. In contrast, severe hypertension without end-organ damage does not require same-day hospital referral,⁵ and should be managed with oral antihypertensives, with the aim of reducing blood pressure over days to weeks.¹

How common are hypertensive emergencies? (epidemiology)

Determining the prevalence of hypertensive emergencies is challenging, not least due to differing definitions and diagnostic criteria. Severe hypertension without acute end-organ damage is common in both primary care and Emergency Departments (being present in 4.6% of outpatient visits in one large US study,⁷ and in 18% of Emergency Department patients in another).⁸ Hypertensive emergencies are much less common, with one estimate being that they account for 0.3% of all attendances to Emergency Departments.⁹

Causes of hypertensive emergencies (aetiology).

Most patients with hypertensive emergencies have underlying uncontrolled or unrecognised essential (primary) hypertension.² Hypertensive emergencies may also be associated with any cause of secondary hypertension, such as:¹⁰

• Unilateral renovascular hypertension - eg, renal artery stenosis.

• Renin-secreting neoplasms.

• Trauma to the kidneys.

• Renal vasculitis - eg, scleroderma, polyarteritis and systemic lupus erythematosus.

• Phaeochromocytoma.

• Cocaine abuse.

• Drugs such as monoamine-oxidase inhibitors, combined oral contraceptives or the withdrawal of alcohol, alpha-stimulants such as clonidine, or beta-blockers.

• Sodium-volume overload and low renin levels - eg, acute glomerulonephritis, primary aldosteronism.

• Pre-eclampsia/eclampsia.

• Hyperthyroidism or hypothyroidism.

Symptoms of a hypertensive emergency (presentation)

The symptoms of a hypertensive emergency depend on which organ is affected by end-organ damage. They might include:

• Headache.

• Seizures.

• Drowsiness.

• Nausea and vomiting.

• Visual disturbance.

• Chest pain.

• Shortness of breath.

• Decreased urine output.

• A focal neurological deficit.

• Bleeding due to disseminated intravascular coagulopathy (DIC).

Assessment

The assessment will depend on the presenting symptoms, but, in general terms, initial assessment of someone with severe hypertension should aim to determine whether they have severe hypertension without end-organ damage, malignant hypertension, or a hypertensive emergency.¹

In primary care, same-day referral to hospital is required if a person has a blood pressure of 180mmHg systolic or higher, or 120mmHg diastolic or higher, and:⁵

• Signs of retinal haemorrhage or papilloedema (indicating malignant hypertension), or;

• Symptoms or signs of life-threatening acute end-organ dysfunction (indicating a hypertensive emergency), such as chest pain, new-onset confusion, signs or symptoms of heart failure, or acute kidney injury, or;

• Suspected phaeochromocytoma.

Pregnant women with suspected pre-eclampsia (or eclampsia) should also be referred immediately for emergency secondary care assessment.¹¹

Otherwise, people with severe hypertension without evidence of acute end-organ damage can be investigated and managed in primary care.⁵

The assessment of someone with suspected malignant hypertension or a hypertensive emergency should include:¹

• Full history - including:
  

  • Past medical history.

  • Full systems review.

  • Drug history including recreational drugs and over-the-counter herbal remedies.

• Full examination - including:
  

  • Blood pressure measurements: lying, standing and in both arms (looking for coarctation or aortic dissection).

  • Fundoscopy - retinopathy: eg, grade III (flame haemorrhages, dot and blot haemorrhages, hard and soft exudates) to grade IV (papilloedema).

  • Cardiovascular examination: lying and standing blood pressure; look for signs of cardiac failure or pulmonary oedema, carotid or renal bruits, left ventricular heave, cardiac murmurs, third or fourth heart sounds. Check for radio-femoral delay.

  • Neurological examination.

• Blood tests:
  

  • FBC ± clotting screen.

  • U&Es, creatinine, bicarbonate.

  • Liver and TFTs.

  • Blood glucose measurement and HbA1c.

  • Troponin measurements, if cardiac ischaemia is suspected.

  • NT-proBNP, if heart failure is suspected.

• Urine dip testing for protein and blood.

• Urine albumin-creatinine ratio.

• Plasma metanephrines ± urinary metanephrines, if a phaeochromocytoma is suspected.

• Testing for Cushing's syndrome, if suspected.

• Aldosterone and renin measurement, if primary hyperaldosteronism is suspected (these tests may be affected by the subsequent initiation of certain antihypertensives).

• ECG: left ventricular hypertrophy, left atrial enlargement, or signs of cardiac ischaemia.

• Imaging - the choice depends on the clinical picture, but may include:

  • CXR, to look for cardiomegaly and signs of pulmonary oedema.

  • Neuroimaging (CT or MRI), if there are neurological signs or symptoms (including papilloedema), to investigate for a stroke or space-occupying lesion.

  • A CT angiogram of the aorta, if an aortic dissection is suspected.

  • Renal imaging to look for renovascular lesions, eg, CT or MR angiography, or renal artery Doppler ultrasound.

Managing hypertensive emergencies¹⁵

General measures

The overall aim is blood pressure reduction, but the choice of treatment, blood pressure target, and speed of reduction differ depending on the type of hypertensive emergency, and the underlying aetiology.

Rapid and excessive blood pressure reduction can be harmful. Blood flow to organs is controlled by autoregulation, which maintains nearly-constant blood flow across a range of arterial pressures. In people with normotension, this autoregulation operates across a mean arterial pressure range from about 50mmHg to 150mmHg. In people with chronic hypertension, the autoregulatory range increases; thus, rapidly reducing blood pressure to 'normal' or 'low' levels may lead to organ hypoperfusion.¹ There are numerous case reports of watershed cerebral infarcts,¹² myocardial infarctions, severe hypotension, and death¹³ following very rapid reduction of blood pressure with IV medications or instant-release nifedipine.

Malignant hypertension

Uncomplicated malignant hypertension (with retinal changes only) can be managed with oral antihypertensives, with the goal of reducing blood pressure over days. Some patients may require inpatient admission for monitoring, although others can be closely monitored on an ambulatory basis.¹

Malignant hypertension that co-exists with other hypertensive emergencies (ie other acute end-organ hypertensive damage) should be managed as per the hypertensive emergency (see below).¹

Hypertensive emergencies

Hypertensive emergencies generally require intravenous blood pressure-lowering medications, and close haemodynamic monitoring in a high-dependency unit or intensive care unit.^{1 3}Continuous blood pressure monitoring, using an arterial line, is helpful.¹⁴

Treatment differs depending on the exact type of hypertensive emergency. In most situations, the evidence base is relatively weak, and recommendations are made based on observational evidence or expert opinion. In general, most guidelines recommend a controlled, partial blood pressure reduction over the first few hours, aiming to reduce the mean arterial pressure by no more than 25%, except in aortic dissection, where rapid and aggressive blood pressure reduction is indicated.³

Severe hypertension may cause volume depletion due to pressure natriuresis; volume expansion with isotonic sodium chloride solution may be required, alongside blood pressure-lowering therapy.

Specific advice on the speed of blood pressure reduction, blood pressure targets, and medication choice is given in the 2022 British and Irish Hypertension Society (BIHS) Position Document, covering recommendations for hypertensive encephalopathy, intracerebral haemorrhage, ischaemic stroke, subarachnoid haemorrhage, acute aortic syndromes, acute coronary syndrome, pulmonary oedema, and severe pre-eclampsia and eclampsia.¹

Drugs

As above, uncomplicated malignant hypertension may be treated with oral antihypertensives, such as amlodipine, long-acting nifedipine, or low-dose atenolol. Angiotensin receptor blockers and ACE inhibitors should be avoided initially, as they may produce a too-rapid reduction in blood pressure.¹

Intravenous blood pressure-lowering agents, for use in hypertensive emergencies, include:

• Labetalol.

• Nircardipine.

• Nitroprusside.

• Glyceryl trinitrite (GTN).

• Esmolol.

• Phentolamine.

See the BIHS position statement¹ and the ESC Council position statement² for more detail on these options.

Phentolamine is the drug of choice for a phaeochromocytoma crisis.¹

Prognosis

Without treatment, malignant hypertension may result in death within a year in over 90% of patients, as a result of end-organ damage - eg, myocardial infarction, CVE or renal failure.¹⁵ The prognosis has improved dramatically over the period of a few decades and with optimal treatment the five-year survival rate is >90%.¹⁶