Principles of Hypertensive Emergencies

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Hello Hivers!
In today's article, we'll talk about Hypertensive Emergencies. Acute or severe increases in blood pressure are serious medical concerns that require prompt therapy which may be lifesaving.
Let's go.



Automatic brachial sphygmomanometer. By Steven Fruitsmaak - Own work, CC BY 3.0.


Clinically, these situations can be classified either as hypertensive urgencies or as hypertensive emergencies (crisis). We'll understand the difference between these two terms soon.

There are no specific blood pressure values in defining a hypertensive emergency. Rather, the term "hypertensive crisis" is generally applied when there is an acute elevation of blood pressure, with a systolic blood pressure of greater than 180mmHg or diastolic blood pressure of greater than 110mmHg.


Hypertensive emergency

It defined as severe hypertension or a sudden increase in blood pressure with evidence of acute injury to target organs like the brain, heart, kidney, vasculature, and the retina. A hypertensive emergency usually warrants parenteral drug therapy and hospitalization.

Examples of hypertensive emergencies include cerebral infarction, flash pulmonary oedema, hypertensive encephalopathy, acute left ventricular failure, aortic dissection, intracranial haemorrhage, malignant hypertension (when intravenous therapy is indicated), adrenergic crisis (cocaine toxicity/pheochromocytoma), eclampsia, myocardial infarction, unstable angina, etc.


Hypertensive urgency

It is defined as severe hypertension without evidence of acute target organ injury but occurring in a setting in which it is important to decrease blood pressure to safer levels over a 24 to 48-hour period. Such cases usually do not require hospitalization. It is required to gradually lower blood pressure with oral therapy.

Some examples of hypertensive urgency include severe hypertension in a person with known coronary artery disease, an aneurysm of the aorta (or other sites), or a history of congestive heart failure OR severe hypertension immediately following major surgery.


Causes

Causes of Hypertensive Emergencies include neglected essential hypertension, discontinuation of antihypertensive therapy especially clonidine and β-blockers, renovascular disease, scleroderma, pheochromocytoma, stroke and monoamine oxidase inhibitors and tyramine - containing foods.

Approximately 50% of hypertensive crises occur in persons with pre-existing hypertension.


Pathophysiology

Hypertensive crises are thought to be initiated by humoral vasoconstrictors causing an abrupt increase in systemic vascular resistance. This ultimately overwhelms the body's auto-regulatory mechanisms.

Failure of these mechanisms begins a physiological cascade. The elevated pressures in proximal capillary beds accompany arteriolar dilation and ultimately smaller arterioles may rupture or leak, resulting in fibrin deposition into their walls.

This fibrinoid necrosis of the vessel walls is responsible for end-organ damage, resulting in ischemia and further release of vasoactive mediators, effectively activating a cycle of progressively worsening blood pressure elevation and subsequent organ injury.



Malignant Hypertension

Malignant hypertension is a clinical syndrome associated with abrupt severe elevation of blood pressure in a patient with underlying hypertension or related to the sudden onset of hypertension in a previously normotensive individual. Any form of hypertension can progress to the malignant phase. The absolute level of blood pressure is not as important as its rate of rise.

It is characterized by a marked increase in peripheral vascular resistance due to systemic (angiotensin II) or locally generated (endothelin) vasoconstrictor substances.

Pathologically, the syndrome is associated with a diffuse necrotizing vasculitis, arteriolar thrombi, and fibrin deposition in arteriolar walls. Fibrinoid necrosis of arterioles is the characteristic vascular lesion of malignant hypertension and is found in arterioles of the kidney, brain, retina, and other organs.

Arteriolar injury worsens ischemia and promotes the further release of vasoactive substances, setting up a vicious cycle. Microangiopathic hemolysis with the fragmentation of erythrocytes and intravascular coagulation may occur with fibrinoid necrosis.

Clinical features of Malignant Hypertension.

These include severe hypertension with a diastolic blood pressure of greater than 130mmHg, progressive retinopathy, deteriorating renal function with proteinuria, microangiopathic hemolytic anaemia and encephalopathy.

There might be associated use of monoamine oxidase inhibitors and recreational drugs like cocaine and amphetamines in affected persons.

Encephalopathy is another clinical feature commonly associated with malignant hypertension. Under normal conditions, cerebral blood flow is kept constant by cerebral vasoconstriction in response to increases in blood pressure. In patients without hypertension, flow is kept constant over a mean pressure of 60 to 120mmHg.
In patients with hypertension, the flow is constant over a mean pressure of 110 to 180mmHg because of arteriolar thickening. When blood pressure is raised above the upper limit of autoregulation, the arterioles dilate resulting in hyperperfusion and cerebral oedema causing severe headache, nausea and vomiting, focal neurologic signs, and alterations in mental status.

Others features include papilledema, visual loss, coma, seizures and death within hours.


An intra parenchymal bleed with surrounding edema. By James Heilman, MD - File:Parachemableedwithedema.png, CC BY-SA 4.0



Hypertensive retinopathy, evidence of nerve fiber infarcts due to ischemia (cotton-wool spots). By BruceBlaus. Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0.


Kidney Biopsy showing thrombotic microangiopathy. By Nephron - Own work, CC BY-SA 3.0.



Differentials of Hypertensive Emergencies include cerebral ischemia, hemorrhagic or thrombotic stroke, seizure disorder, mass lesions, pseudotumor cerebri, meningitis, acute intermittent porphyria, traumatic or chemical injury to the brain, uremic encephalopathy, etc.

Management of hypertensive emergencies

The general goals of management are rapid but controlled blood pressure reduction, which is the reduction of the mean arterial blood pressure by no more than 25% within minutes to 1 hour then, if stable, to 160/100-110mmHg within the next 2 to 6 hours.

Investigations that may be carried out include full blood count to check for evidence of microangiopathic hemolytic anaemia, electrolyte, urea and creatinine levels, serum calcium, fasting blood glucose/random blood glucose, coagulation profile, a urinalysis to check for proteinuria, microscopic hematuria, and red blood cell or hyaline casts and cardiac enzymes assay to check for heart function.

A urinary catecholamines test or a 24-hour urine collection for vanillylmandelic acid (VMA) and catecholamines can also be helpful. Others include thyroid-stimulating hormone assay, chest radiograph to assess cardiac enlargement, pulmonary oedema or involvement of other thoracic structures, electrocardiography, echocardiography, and a brain CT scan.

Hospitalization in an intensive care unit is necessary. An arterial catheter is also required to monitor blood pressure continuously.



Arterial catheter. By Privatarchiv Foto von MrArifnajafov - Own work, CC BY 3.0.


As soon as possible, regular oral treatment should be initiated and intravenous treatment tapered down. After blood pressure has been controlled, the cause of the hypertensive crisis must be managed and secondary causes especially renovascular disease, pheochromocytoma, and primary aldosteronism must be considered.


Do you have any questions, concerns or anything to add? Tell me what you think below.

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Resources

  • Thomas L (October 2011). "Managing hypertensive emergencies in the ED"
  • "Management of severe asymptomatic hypertension (hypertensive urgencies) in adults". www.uptodate.com. Retrieved 2020-08-25.
  • Pak, Kirk J.; Hu, Tian; Fee, Colin; Wang, Richard; Smith, Morgan; Bazzano, Lydia A. (2014). "Acute hypertension: a systematic review and appraisal of guidelines". The Ochsner Journal.
  • Nicol, Maggie; Bavin, Carol; Cronin, Patricia; Rawlings-Anderson, Karen; Cole, Elaine; Hunter, Janet (2012). Essential Nursing Skills E-Book. Elsevier Health Sciences.




Written by @gamsam - a Medical Student
All images used are copyright free
Vancouver Style was used for References.




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