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Let’s start our USMLE Review with Hypothyroidism and Hyperthyroidism from the Gold Standard USMLE Foundations of Medicine Audio Review program.
Play USMLE Audio MP3 10 13 Pathophysiology of Myxedema Coma Below
Begin 10 13 Pathophysiology of Myxedema Coma Transcription
The pathophysiology of myxedema coma involves three major aspects.
First, CO2 retention and which condition of decreased oxygen flow?
- CO2 retention and hypoxia.
Second, imbalances of which two things?
- Fluid and electrolyte imbalances.
And Third, a condition of decreased body temperature?
Student doctor please pause the tape and repeat three major aspects of the pathophysiology of myxedema coma.
- Major aspects of the pathophysiology of myxedema coma are CO2 retention and hypoxia, fluid and electrolyte imbalances, and hypothermia. CO2 retention and hypoxia are probably due in large part to a marked depression in ventilatory responses.
Please pause the tape and list seven or eight other factors which contribute.
- Factors which contribute to the CO2 retention and hypoxia at the root of myxedema coma include CNS depression, heart failure, ileus, immobilization, pleural or peritoneal effusions, pneumonia, and weak chest muscles. The failure of the myxedema patient to respond to hypoxia or hypercapnia may be due to hypothermia.
Impairment of ventilatory drive is often severe in the myxedema coma patient, usually requiring what type of assistance?
- Assisted respiration.
Why does hypothermia often escape detection and recognition?
- Hypothermia can often escape detection because ordinary clinical thermometers only go down to about ninety-three degrees Fahrenheit. A lab thermometer with a broader scale must be used to correctly indentify hypothermia.
And why is it not a good idea to actively rewarm a myxedema coma patient suffering from hypothermia?
- Active rewarming of the body is contraindicated because it could induce vasodilation and vascular collapse.
What type of therapy will correct hypothermia and greatly improve ventilatory response to hypoxia in the myxedema coma patient?
- Thyroid hormone therapy.
The major fluid and electrolyte disturbance is water intoxication due to which syndrome involving the inappropriate secretion of vasopressin?
- SIADH (The Syndrome of Inappropriate Antidiuretic Hormone Secretion).
What is the principle action of the hormone vasopressin in pharmacological doses?
- Vasopressin causes contraction of smooth muscles, especially all blood vessels. Larger doses can cause cerebral or coronary arterial spasm.
How does SIADH usually present?
- SIADH usually presents as hyponatremia and is managed by water restriction.
Student doctor please pause the tape and summarize the salient points about hypothermia and fluid or electrolyte imbalance in the pathophysiology of myxedema coma. Please include impairment of ventilatory drive, detection and recognition of hypothermia, thyroid hormone therapy, water intoxication, and SIADH.
- The failure of the myxedema coma patient to respond to hypoxia or hypercapnia may be due to hypothermia. Impairment ventilatory drive is often severe, requiring assisted respiration. Hypothermia often goes undetected due to the inadequacy of standard clinical thermometers. Active rewarming of the body is countraindicated as this could induce vasodilation and lead to vascular collapse. Thyroid hormone therapy corrects hypothermia in the myxedema coma patient and greatly improves ventilatory response to hypoxia. The major fluid and electrolyte disturbance in myxedema coma is water intoxication due to SIADH, a Syndrome of Inappropriate Antidiuretic Hormone secretion. SIADH normally presents as hyponatremia and is managed with water restriction.
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