HYPOTENSION AND SHOCK
HYPOTENSION AND SHOCK: Excerpt from Differential Diagnosis in Primary Care
Many patients are told they have a low blood pressure and are even treated for it when that blood pressure may be entirely normal for them. Asymptomatic hypotension may not be pathologic at all. At any rate, an expensive investigation for the causes of “hypotension” would seem unnecessary if the systolic pressure is above 80 mm, especially when the patient is asymptomatic.
HYPOTENSION AND SHOCK
The differential diagnosis of both hypotension and shock is best developed using physiology. There are three things that are necessary to sustain the blood pressure at the normal level: adequate blood volume, adequate cardiac output, and adequate tone in the arteries and arterioles. Alteration of any of these may produce hypotension.
Low blood volume may result from any of the following conditions:
- Hemorrhagic shock such as acute upper GI bleeding
- Chronic blood loss (e.g., peptic ulcer) or anemia of decreased production (such as aplastic anemia) or increased destruction (hemolytic anemias)
- Dehydration
- Decreased sodium chloride (NaCl) in blood from pituitary and adrenal insufficiency, diuretics, diarrhea or vomiting, chronic nephritis, or severe diaphoresis
- Decreased albumin in the blood from nephrosis, cirrhosis, and malnutrition or malabsorption syndrome.
Any one of the conditions listed above may be associated with hypotension.
Decreased cardiac output usually results from CHF of many causes and myocardial infarction. Many valvular lesions (e.g., mitral stenosis) may manifest hypotension without overt heart failure. Cor pulmonale may lead to hypotension from a decreased cardiac output.
Decreased arterial tone (e.g., vasomotor shock) occurs in the following conditions:
- When the sympathetic nerves are blocked by antihypertensive drugs (e.g., α-methyldopa, guanethidine, and pentolinium tartrate), diabetic neuropathy, or after a sympathectomy.
- When there is increased vagal stimulation, as in neurogenic shock (common faint) and late stages of increased intracranial pressure
- When toxins are introduced into the bloodstream from necrotic tissue, bacteria, or drugs that act directly on the arterioles.
Examples of the last type of hypotension are pulmonary infarction (necrotic tissue), toxins, septicemia (bacterial toxins), and hydralazine therapy.
Approach to the Diagnosis
The workup of shock must be vigorous with emergency CBC, blood cultures, blood gases, ECG, electrolytes, blood urea nitrogen (BUN), and type and cross-match of blood at the same time vigorous antishock measures are applied. Checking the GI tract for blood loss with a rectal and nasogastric tube can be both diagnostic and therapeutic. To work up chronic hypotension, one should not forget venous pressure and circulation times (to diagnose decreased cardiac output and CHF), serial electrolytes and cortisol levels (to rule out adrenal insufficiency), and sedimentation rate and cultures of various body fluids to exclude a chronic infectious disease (e.g., tuberculosis).
Other Useful Tests
- Blood volume study (dehydration, hypovolemic shock)
- Electrolytes (Addison disease)
- 24-hour blood pressure monitoring
- Echocardiogram (CHF, valvular heart disease)
- Visual field examination (pituitary tumor)
- Thyroid profile (hypothyroidism)
- CT scan of the brain (pituitary tumor)
- Drug screen (drug or alcohol abuse)
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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