HYPOTENSION AND SHOCK
HYPOTENSION AND SHOCK: Excerpt from Differential Diagnosis in Primary Care
Many patients are told that 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 into the causes of “hypotension” would seem
unnecessary if the systolic pressure is above 80 mm Hg, especially when the
patient is asymptomatic.
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
from 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), by 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 that 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., TB]).
Other Useful Tests
-
Blood volume study (dehydration, hypovolemic shock)
- Electrolytes (Addison disease)
- 24-hour blood pressure monitoring
- ECG (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)
CASE PRESENTATION #53
A 52-year-old white man complained of generalized fatigue, weight loss,
and occasional diarrhea for the past year. His blood pressure was 75/50 mm
Hg. He was treated for pulmonary TB several years ago.
Pictures
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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