If the process is not stopped, homeostatic failure begins, leading to loss of cerebral and local autoregulation, organ system ischemia and dysfunction, and myocardial infarction. Single-organ involvement is found in approximately 83% of hypertensive emergency patients, two-organ involvement in about 14% of patients, and multi-organ failure (failure of at least 3 organ systems) in about 3% of patients.In the brain, hypertensive encephalopathy - characterized by hypertension, altered mental status, and swelling of the optic disc - is a manifestation of the dysfunction of cerebral autoregulation. Cerebral autoregulation is the ability of the blood vessels in the brain to maintain a constant blood flow. People with chronic hypertension can tolerate higher arterial pressure before their autoregulation system is disrupted. Hypertensives also have an increased cerebrovascular resistance which puts them at greater risk of developing cerebral ischemia if the blood flow decreases into a normotensive range. On the other hand, sudden or rapid rises in blood pressure may cause hyperperfusion and increased cerebral blood flow, causing increased intracranial pressure and cerebral edema, with increased risk of intracranial bleeding.In the heart, increased arterial stiffness, increased systolic blood pressure, and widened pulse pressures, all resulting from chronic hypertension, can cause significant damage. Coronary perfusion pressures are decreased by these factors, which also increase myocardial oxygen consumption, possibly leading to left ventricular hypertrophy.
A hypertensive emergency is very high blood pressure with potentially life-threatening symptoms and signs of acute damage to one or more organ systems (especially brain, eyes, heart, aorta, or kidneys). It is different from a hypertensive urgency by this additional evidence for impending irreversible hypertension-mediated organ damage (HMOD). Blood pressure is often above 200/120 mmHg, however there are no universally accepted cutoff values. Signs of organ damage will be discussed below. Signs and symptoms
Symptoms may include headache, nausea, or vomiting. Chest pain may occur due to increased workload on the heart resulting in inadequate delivery of oxygen to meet the heart muscles metabolic needs. The kidneys may be affected, resulting in blood or protein in the urine, and acute kidney failure. People can have decreased urine production, fluid retention, and confusion.Other signs and symptoms can include:
Chest pain
Abnormal heart rhythms
Headache
Nosebleeds that are difficult to stop
Dyspnea
Fainting or the sensation of the world spinning around them (vertigo)
Severe anxiety
Agitation
Altered mental status
Abnormal sensationsThe most common presentations of hypertensive emergencies are cerebral infarction (24.5%), pulmonary edema (22.5%), hypertensive encephalopathy (16.3%), and congestive heart failure (12%). Less common presentations include intracranial bleeding, aortic dissection, and  pre-eclampsia or eclampsia.Massive, rapid elevations in blood pressure can trigger any of these symptoms, and warrant further work-up by physicians. Physical exam would include measurement of blood pressure in both arms.