It is important to distinguish three circumstances which may exist separately or together — see the Venn diagram (Figure 23.3)34 which emphasises the following:
34 J Venn (1834-1923) English logician who 'adopted the diagrammatic method of illustrating propositions by inclusive and exclusive circles' (Dictionary of National Biography). A medical pilgrimage to Cambridge, where Venn worked, should take in Gonville & Caius College (named after its founder, Dr Caius, physician to the Tudor Court and early president of the London College of Physicians in the 16th century); as well as stained glass windows celebrating Venn's circles, the visitor can see a portrait of the most famous medical Caian, William Harvey.
• Severe hypertension is not on its own an indication for urgent (or large) reductions in blood pressure.
• Blood pressure (BP) can occasionally require urgent (emergency) reduction even when the hypertension is not severe, especially where the BP has risen rapidly.
• Accelerated phase (malignant) hypertension rarely requires urgent reduction, and should instead be regarded as an indication for slow reduction in blood pressure during the first few days.
The indications for emergency reduction of blood pressure are rare. They are:
• Hypertensive encephalopathy (including eclampsia)
• Acute left ventricular failure (due to hypertension)
• Dissecting aneurysm.
In these conditions, blood pressure should be reduced over the course of an hour. In patients with a dissecting aneurysm, where the BP may have been completely normal prior to dissection, the target is a BP of 110/70 mmHg. Otherwise even small reductions will usually remove the emergency.
Accelerated phase hypertension was previously called 'malignant' hypertension because the lack of treatment heralded death within a year of diagnosis. It is characterised pathologically by fibrinoid necrosis of the small arteries. An important consequence is the loss of autoregulation of the cerebral and renal circulation, so that any reduction in blood pressure causes a proportional fall in perfusion of
these organs. It is therefore vital not to reduce diastolic BP by more than 20 mmHg on the first day of treatment. To ignore this is to risk cerebral infarction.
Treatment. Unless contraindicated, the best treatment for all circles in the Venn diagram is ¡3-blockade, e.g. atenolol 25 or 50 mg orally. In emergencies, a vasodilator should be given intravenously, in addition.
A theoretically preferable, but often impractical alternative is i.v. infusion of the vasodilator, nitro-prusside (see p. 470). In dissecting aneurysm, vasodilators should not be used unless patients are first p-blocked since any increase in the rate of rise of the pulse stroke is undesirable. Labetalol provides a convenient method of treating all patients within the three circles (except asthmatics), using either oral or parenteral therapy as appropriate. It is not the most effective, however, and should be combined with a long-acting formulation of nifedipine, orally, where further blood pressure reduction is required.
Low doses of all drugs should be used if antihypertensive drugs have recently been taken or if renal function is impaired.
Oral maintenance treatment for severe hypertension should be started at once if possible; parenteral therapy is seldom necessary for more than 48 h.
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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...