Dilutional hyponatremia

Several nonpeptidic, orally active vasopressin receptor antagonists have been developed. The dual V1A/V2R antagonist conivaptan is used in the treatment of hyponatraemia and could also become useful for diseases such as congestive heart failure, in which increased peripheral resistance and dilutional hyponatremia both are present [4]. Side effects of conivaptan include headache, injection site reactions, vomiting, diarrhoea, constipation and thirst. 

Higher vasopressin concentrations are linked to dilutional hyponatremia and a poor prognosis in HF. Vasopressin exerts its effects through vasopressin type la (Vla) and vasopressin type 2 (V2) receptors.5,7 Vasopressin type la stimulation leads to vasoconstriction, while actions on the V2 receptor cause free water retention through aquaporin channels in the collecting duct. Vasopressin increases preload, afterload, and myocardial oxygen demand in the failing heart. 

Hypotonic hyponatremia with an increase in ECF is also known as dilutional hyponatremia. In this scenario, patients have an excess of total body sodium and TBW however, the excess in TBW is greater than the excess in total body sodium. Common causes include CHF, hepatic cirrhosis, and nephrotic syndrome. Treatment includes sodium and fluid restriction in conjunction with treatment of the underlying disorder—for example, salt and water restrictions are used in the setting of CHF along with loop diuretics, angiotensin-converting enzyme inhibitors, and spironolactone.15... 

Loss of blood glucose control When a patient stabilized on any diabetic regimen is exposed to stress such as fever, trauma, infection, or surgery, a loss of control may occur. At such times, it may be necessary to discontinue the drug and give insulin. Disulfiram-like syncframe. A sulfonylurea-induced facial flushing or breathlessness reaction may occur when some sulfonylureas are administered with alcohol. Syndrome of inappropriate secretion of antidiuretic hormone (SIADH) Water retention and dilutional hyponatremia have occurred after administration of sulfonylureas to type 2 diabetes patients, especially those with CHF or hepatic cirrhosis. 

Vila, M.C., Coll, S., sola, R., Andren, M, Gana, J., Marquez, J. Total paracentesis in cirrhotic patients with tense ascites and dilutional hyponatremia. Amer. J. Gastroenterol. 1999 94 2219 -2223... 

The use of fixed combination of a thiazide and a potassium-sparing drug, often Moduretic (hydrochlorothiazide 50 mg with amiloride 5 mg), has been consistently implicated in diuretic-induced hyponatremia. Treatment with chlorpropamide (200-800 mg/day) along with Moduretic has precipitated hyponatremia in several cases (96). Simultaneous use of Moduretic with trimethoprim has also been reported to increase the risk (97). The mechanism appears to be impairment of the clearance of free water, resulting in dilutional hyponatremia. Whether... 

Four cases of acute renal insufficiency have been described in men aged 20-42 years who received mannitol 1172 (sd 439) g over 58 (sd 28) hours (7). The onset of acute renal insufficiency was detected 48 (sd 22) hours after the start of infusion. All the patients had dilutional hyponatremia (average 120 mmol/1) and serum hyper-osmolarity (osmolar gap 70 mosm/kg water). In the three anuric cases, in which hemodialysis was performed, there was immediate recovery of diuresis. This emphasizes the risk of renal insufficiency with mannitol and stresses the importance of early hemodialysis. Mannitol is dialysable and once its suppressive effect on renal perfusion is eliminated functional recovery is prompt. 

Typically when the plasma Na" concentration is low, the calculated or measured osmolality will also be low. This type of hyponatremia can be due to either excess loss of Na" deple-tional hyponatremia) or increased ECF volume dilutional hyponatremia). Differentiating these initially requires a clinical assessment of TBW and ECF volume by a history and physical examination. 

Dilutional hyponatremia is a result of excess H2O retention and can often be detected during the physical examination as the presence of weight gain or edema. In advanced renal failure, water is retained because of decreased filtration and H2O excretion. However, the remaining functional... 

The autonomous, sustained production of AVP in the absence of known stimuli for its release is called SIADH. In this syndrome, plasma AVP concentrations are inappropriately increased relative to a low plasma osmolality and to a normal or increased plasma volume. SIADH may be the result of one of several factors production of vasopressin by a malignancy (such as a small cell carcinoma of the lung), the presence of acute and chronic diseases of the central nervous system, pulmonary disorders, or a side effect of certain drug therapies. In addition, as many as 10% of patients undergoing pituitary surgery have a transient SIADH approximately 8 to 9 days after surgery (when the patient is at home), which responds to water restriction (2 to 3 days) and resolves without recurrence. In SIADH, a primary excess of AVP, coupled with unrestricted fluid intake, promotes increased reabsorption of free water by the kidney. The result is a decreased urine volume and an increased urine sodium concentration and urine osmolality. As a consequence of water retention, these patients become modestly volume expanded. The increase in intravascular volume causes hemodilution accompanied by dilutional hyponatremia and a low plasma osmolality. Volume expan-... 

The most common cause of hyponatremia in hospital patients is SIADH. However, other disorders can cause dilutional hyponatremia and must be differentiated from SIADH. These conditions include (1) congestive heart failure, (2) renal insufficiency, (3) nephrotic syndrome, (4) liver cirrhosis, and (5) hypothyroidism. Excessive administration of hypotonic fluids and treatment with drugs that stimulate AVP (e.g., chlorpropamide, vincristine, clofibrate, carbamazepine, nicotine, phenothiazines, and cyclophosphamide) can cause dilutional hyponatremia as well. Hyponatremia may also occur from renal or extrarenal sodium losses (depietional hyponatremia) as a result of vomiting, diarrhea, excessive sweating, diuretic abuse, saltlosing nephropathy, or mineralocorticoid deficiency. 

Alcohol inhibits the release of vasopressin (antidiuretic hormone see Chapter 29) from the posterior pituitary gland, resulting in enhanced diuresis. The volume loading that accompanies imbibing complements the diuresis that occurs as a result of reduced vasopressin secretion. Alcoholics have less urine output than do control subjects in response to a challenge dose with ethanol, suggesting that tolerance develops to the diuretic effects of ethanol. Alcoholics withdrawing from alcohol exhibit increased vasopressin release and a consequent retention of water, as well as dilutional hyponatremia. 

Patients with weakened hearts, including the elderly, who often have decreased cardiac capacity to adapt to volume changes, or pediatric patients, who have smaller hearts with less capacity to handle large volumes, are at particular risk for cardiac overload. 2 Increased fluid volume also could cause a dilutional hyponatremia. Thus symptoms of low sodium concentration with fluid shifts including cerebral edema could occur. 4... 

Avoid overhydration, which could result in dilutional hyponatremia. 

If hormone imbalance is present, treatment centers around restoring hormone status. For example, in hyperaldosteronism, the offending tumor or tissue is removed, and in Cushing syndrome (with corticosteroids that behave like aldosterone causing absorption of sodium), treatment centers on decreasing the excess aldosterone or corticosteroids. If the level of aldosterone or corticosteroids is severely limited in the body, a deficiency of either hormone could occur, resulting in hyponatremia. 6 In diabetes insipidus (i.e., decreased ADH secretion), supplemental ADH is provided. Care must be taken during treatment with supplement to avoid excess ADH intake, which will cause retention of water and potential for dilutional hyponatremia. 6... 

The sodium level is unchanged, but the water level is increased, causing a dilution of sodium (i.e., dilutional hyponatremia). 

Relatedly, malfunction of one of the sodium-water control mechanisms, such as a kidney that normally excretes excess water, can result in fluid retention and dilutional hyponatremia. The pituitary gland and hypothalamus function to release ADH (which controls water reabsorption), and the cortex of the adrenal gland seaetes aldosterone (which controls sodium reabsorption). An alteration in the function of either of these hormone systems will alter the body s regulation of sodium or water and can result in hyponatremia. 2 For example, in the syndrome of inappropriate antidiuretic hormone (SIADH), excessive ADH is produced (usually by a tumor or some pulmonary diseases such as tuberculosis or bacterial pneumonia), and the kidneys reabsorb excessive fluids, resulting in dilutional hyponatremia. Conditions causing decreased aldosterone secretion include... 

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