Hypotension -Types and Causes

Hypotension is diminished blood pressure. This could be acute or chronic.

Acute Recumbent Hypotension

Causes

1. Cardiovascular: Acute myocardial infarction, pulmonary embolism, dissecting aneurysm, ventricular tachycardia, cardiac rupture.
2. Intravascular volume contraction: Hemorrhage, vomiting, diarrhea, burns, intestinal obstruction, periotonitis, etc.
3. Anaphylaxis
4. Gram negative septicemia

Clinical Features

1. Due to shock: Tachycardia, vomiting, fainting
2. Due to causative disease
3. In vasovagal attacks, hypotension with brady-cardia
4. In postural hypotension, fall of BP occurs on suddenly assuming erect posture from supine posture.

Treatment

1. Of the cause
2. Posture: The patient should be in lying position with legs raised.
3. For vasovagal attacks: Atropine 0.6 mg IV
4. For anaphylaxis: Hydrocortisone hemisuccinate 100mg IV, repeated as required
5. For postural hypotension: This is best treated by advising the patients to assume the erect posture slowly and to wear elastic stockings and abdominal binder.
6. Vasoconstrictors: Dopamine, nor-epinephrine and ephedrine have been tried.
7. Salt: Adequate amount of salt (NaC1) in diet helps to expand the plasma volume.
8. Fludrocortisone Acetate: (0.1 – 0.2 mg) causes fluid retention and avoids postural fall of BP.

Chronic hypotension

A number of healthy subjects have a systolic BP of 80-100 mm which is compatible with long life expectancy. Only some patients complain of weakness, lethargy, easy fatiguability, dizziness and fainting on assuming erect posture or standing inactive for long periods.

This occurs due to interference with neural pathways between the vasomotor center and efferent sympathetic nerve endings in blood vessels and heart, so that the normal rise in cardiac output and vasoconstriction on assuming erects posture are abolished.

Causes

1. Cardiac

• Low output cardiac failure
• LV dysfunction
• Cardiac tamponade
• Constructive pericarditis
• Tight mitral stenosis
• Left atrial myxoma

2. Supine hypotension of pregnancy

3. Endocrine

• Addison’s disease
• Myxedema
• Hypopituitarism
• Serotonin secreting tumors

4. Neuogenic

• Diabetic neuropathy
• Extensive lumbosacral sympathectomy
• Peripheral neuropathy
• Tabes dorsalis
• Syringomyelia
• Multiple sclerosis

5. Chronic idiopathic orthostatic hyptension

Chronic idiopathic orthostatic hypotension

This occurs due to primary autonomic insufficient due to degeneration of central or peripheral autonomic nervous system. It is common in the elderly who may develop syncope, hypotension, convulsions but no tachycardia on standing. They may have associated anhydrosis, loss of hair, diminished lachrymal and salivary secretion, bladder atony and impotency.

Treatment

1. Mechanical: Elastic bandages over legs, head up position in bed etc.
2. Volume expansion with high fluid and salt intake
3. Fludrocortisone supplement
4. Drugs:

• Sympathomimetics-Ephedrine, amphetamine, L-dopa
• Prostaglandin synthesis inhibitors like indomethacin
• Alpha 2 receptor agonists

5. Atrial pacing

Shy-Dragger Syndrome

This is chronic orthostatic hypotension with degeneration of CNS, mainly involving extrapyrimidal tracts, basal ganglia and dorsal nucleus of Vagus. These patients have intact peripheral autonomic nervous system but are unable to activate it. (In primary autonomic insufficiency there is depletion of norepinephrine in the peripheral autonomic ganglia).

In both these, catecholamine blood levels do not rise on standing, although it may be normal at recumbency in chronic orthostatic hypotension but reduced in primary autonomic insufficiency.