Hypovolemia hyponatremia

Because Henle s loop is indirectly responsible for water reabsorption by the downstream collecting duct, loop diuretics can cause severe dehydration. Hyponatremia is less common than with the thiazides (see below), but patients who increase water intake in response to hypovolemia-induced thirst can become severely hyponatremic with loop agents. Loop agents are sometimes used for their calciuric effect, but hypercalcemia can occur in volume-depleted patients who have another—previously occult—cause for... 

Hyponatremia is an important adverse effect of thiazide diuretics. It is due to a combination of hypovolemia-induced elevation of ADH, reduction in the diluting capacity of the kidney, and increased thirst. It can be prevented by reducing the dose of the drug or limiting water intake. 

Treatment with thiazide diuretics is one of the most common causes of hyponatremia (92). Patients can present with variable hypovolemia or apparent euvolemia,... 

Depletional hyponatremia (excess loss of Na ) is almost always accompanied by a loss of ECF water, but to a lesser extent tlian the Na loss. Hypovolemia is apparent in the physical examination (orthostatic hypotension, tachycardia, decreased skin turgor). Loss of isosmotic or hypertonic fluid is the cause and this can occur through renal or extrarenal losses. If urine Na is low (generally <10 mmol/L), the loss is extrarenal (see Figure 46-2) because the kidneys are properly retaining filtered Na in response to increased aldosterone (stimulated by the hypovolemia and hyponatremia). Causes of extrarenal loss of Na" in excess of H2O include losses from the gastrointestinal tract or skin (see Figure 46-2). 

This includes patients with fluid losses caused by diarrhea, excessive sweating, and diuretics. This transient hypernatremic hyperosmolality results in osmotic release of ADH and stimulation of thirst. If sodium and water losses continue, more ADH is released as a result of hypovolemia. Patients who then drink water or who are given hypotonic fluids intravenously retain water and develop hyponatremia. Urine osmolality is generally greater than 450 mOsm/kg, reflecting the presence of ADH and formation of a concentrated urine. The urine sodium concentration is <20 mEq/L when sodium losses are extrarenal, as in patients with diarrhea, and >20 mEq/L in patients with renal sodium losses, as occurs in the setting of diuretic use or adrenal insufflciency. °... 

Renin A protease that is synthesized by the juxtaglomerular cells of the kidney and secreted into the bloodstream in response to conditions of hypovolemia and hyponatremia. It hydrolyzes circulating angiotensinogen to angiotensin 1. 

OTHER WATER-RETAINING STATES In patients with congestive heart failure, cirrhosis, or nephrotic syndrome, ejfective blood volume often is reduced, and hypovolemia frequently is exacerbated by the liberal use of diuretics. Since hypovolemia stimulates vasopressin release, patients may become hyponatremic owing to vasopressin-mediated retention of water. The development of potent orally active receptor antagonists and specific inhibitors of water chaimels in the collecting duct would provide an effective therapeutic strategy not only in patients with SIADH but also in the much more common setting of hyponatremia in patients with heart faftme, cirrhosis, or nephrotic syndrome. 

Furosemide (Lasix) Inhibits chloride reabsorption in thick ascending loop of Henie. High loss of K+ in urine. Preferred diuretic in patients with low GFR and in hypertensive emergencies. Also, edema, pulmonary edema, and to mobilize large volumes of fluid. Sometimes used to reduce serum potassium levels. Hyponatremia, hypokalemia, dehydration, hypotension, hyperglycemia, hyperuricemia, hypocalcemia, ototoxicity, sulfonamide allergy, hypomagnesemia, hypochloremic alkalosis, hypovolemia. 

The primary electrolyte imbalance associated with the hypovolemia, a loss of sodium (i.e., hyponatremia), may require sodium infusions until the underlying condition has been resolved. Since electrolytes may shift in response to sodium imbalances, other replacements may be indicated (see Chapter 5). 

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