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Oral case 42

Created: 5/10/2004

Line isolation monitor

1. What is its purpose?

2. What should you do if the red light comes on, and the line isolation monitor alarm sounds?

Drug interactions

A 64-year old woman is taking nardil, a MAO inhibitor, for depression. She is to be anesthetized for electroconvulsive therapy.

1. What are her special anesthetic risks?

2. How will you proceed?

Hyponatremia during transurethral resection of the prostate

A 70-year old male undergoing transurethral resection of the prostate under subarachnoid block becomes disoriented and hypotensive.

1. What is your differential diagnosis?

The most likely cause is absorption of sodium-poor irrigant fluid and TURP syndrome. Other causes include administration of hypotonic fluids, inappropriate secretion of antidiuretic hormone, excess oxytocin, diuretics, adrenal insufficiency, nephrotic syndrome, and congestive heart failure.

2. What is your treatment?

If hyponatremia develops quickly as in this case, aggressive treatment is necessary so that hypertension, bradycardia, agitation, obtundation, or seizures are prevented. In simple, borderline hyponatremia, fluid restriction may be sufficient, but diuresis, or 3% hypertonic saline may be necessary. If seizures occur, airway protection, oxygenation, ventilation, and anticonvulsant therapy may be necessary. If a rapid sodium load is necessary, sodium bicarbonate may be given, as it has 1 mEq/ml sodium.

3. What is your differential diagnosis for hypernatremia?

Dehydration, diabetes insipidus, gastrointestinal loss, and renal failure.

4. How is antidiuretic hormone synthesized?

It is synthesized in the supraoptic and paraventricular nuclei in the hypothalamus, and transported along the axons of the pituitary stalk for storage until release into the capillaries.

5. How does antidiuretic hormone regulate body water?

Antidiuretic hormone, or ADH, is present in plasma, and increases cyclic adenosine monophosphate production in the distal tubules of the kidney. This increases water permeability, causing sodium and water retention with the urine being concentrated. It is stimulated by increased osmolarity, increased sodium, thirst, and angiotensin II.

6. What kind of urine results from antidiuretic hormone release?

Concentrated urine, with low urine output.

6. What stimulates release of antidiuretic hormone?

Physiological responses include the upright position, hyperosmolality, hypovolemia, beta-adrenergic or cholinergic stimulation, pain, and stress. Abnormal states include hyperthermia, increased intracranial pressure, hemorrhagic shock, head injury, and positive airway pressure. Medications include morphine, nicotine, barbiturates, tricyclic antidepressants, vincristine, cyclophosphamide and chlorpropamide.

7. What inhibits release of antidiuretic hormone?

Physiologic responses include hypervolemia, hypoosmolality, the supine position, alpha-adrenergic stimulation, excess water intake, and hypothermia. Medications include ethanol, atropine, phenytoin, reserpine, glucocorticoids, and chlorpromazine.

8. What kind of urine results from inhibition of antidiuretic hormone release?

Dilute urine, with high urine output.

9. What is diabetes insipidus?

It results from a defect in the synthesis, impaired release, or renal resistance to antidiuretic hormone. A large volume of dilute urine results, and can lead to dehydration.

10. What are causes of diabetes insipidus, and how do you treat it?

Neurogenic diabetes insipidus from vasopressin deficiency can be familial or acquired. Acquired causes include trauma from craniofacial or basilar skull fractures, tumors such as lymphoma, or craniopharyngioma, granulomas such as sarcoidosis or histiocytosis, infections like meningitis or encephalitis, vascular problems like Sheehan's syndrome, cerebral aneurysm, or cardiopulmonary bypass. Hypoxic brain damage is another cause.

Nephrogenic diabetes insipidus from vasopressin insensitivity by the kidney can also be familial or acquired. Acquired causes include infections like pyelonephritis, postrenal obstruction from the prostate or ureters, hematologic problems like sickle cell disease, infiltrative states like amyloidosis, polycystic kidney disease, hypokalemia, hypercalcemia, sarcoidosis, and medications like lithium, demeclocycline, and methoxyflurane.

Treatment is with exogenous replacement. Incomplete diabetes insipidus can respond to diuretics, chlorpropamide, carbamazepine, or clofibrate. Preparations to treat the syndrome include pitressin tannate in oil, aqueous pitressin, synthetic lysine vasopressin nasal spray, and intranasal 1-deamino-8-D-arginine vasopressin, or DDAVP.

11. What is the syndrome of inappropriate antidiuretic hormone release, and how is it properly diagnosed?

Antidiuretic hormone is abnormally released to nonosmotic stimuli, inhibiting renal water excretion. The patient must not be hypovolemic. The urine must be inappropriately concentrated, with the plasma being hypoosmolar and the urine being concentrated over 100 mOsm/kg. Normal function of the kidneys, heart, liver, adrenals and thyroid must be verified.

12. What is the normal treatment for this condition?

The postoperative condition is usually temporary and resolves spontaneously. Otherwise, water restriction is the primary treatment. For the chronic case, demeclocycline may be used. It blocks water resorption of antidiuretic hormone in the renal collecting ducts.

13. What are common causes of this condition?

Central nervous system and pulmonary causes are the most common. This includes conditions like intracranial hypertension, trauma, tumor, meningitis, subarachnoid hemorrhage, tuberculosis, pneumonia, asthma, bronchiectasis, hypoxemia, hypercarbia, and positive pressure ventilation. Malignancies also produce antidiuretic hormone-like products. Adrenal insufficiency and hypothyroidism are also implicated.

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