42 HYPONATREMIA General Discussion Hyponatremia generally is defined as a plasma sodium level of less than 135 mEq/L. Hyponatremia may lead to significant morbidity and mortality. Most patients with hyponatremia are asymptomatic, and symptoms usually do not appear until the plasma sodium level drops below 120 mEq/L. Symptoms of hyponatremia usually are nonspecific and include headache, nausea, and lethargy. However, neurologic and gastrointestinal symptoms may be present in cases of severe hyponatremia, with the risk of seizure and coma increasing as the sodium level decreases. If the sodium level decreases quickly, symptoms may be present at sodium levels above 120 mEq/L. The evaluation of hyponatremia begins with a targeted history to evaluate for causes of hyponatremia such as congestive heart failure, renal impairment, liver disease, malignancy, hypothyroidism, or Addison’s disease. Hyponatremia is then classified according to the volume status of the patient as hypovolemic, hypervolemic, or euvolemic. Hypervolemic hyponatremia results in increased total body water and the presence of edema. The three main causes of hypervolemic hyponatremia are congestive heart failure, liver cirrhosis, and renal impairment such as renal failure and nephrotic syndrome. Differentiating between hypovolemia and euvolemia may be difficult clinically. An elevated hematocrit or a blood urea nitrogen:creatinine ratio greater than 20 may suggest hypovolemia but are not always present. If the patient’s volume status is not clear, the measurements of plasma osmolality and urinary sodium concentration are useful for evaluating euvolemic or hypovolemic patients. Normal plasma osmolality (280–300 mOsm/kg of water) can be seen with pseudohyponatremia or after the absorption of large volumes of hypotonic irrigation fluid during transurethral resection of the prostate. Pseudohyponatremia may occur in the presence of severe hypertriglyceridemia and hyperproteinemia. Increased plasma osmolality (greater than 300 mOsm/kg of water) in a patient with hyponatremia is caused by severe hyperglycemia. Decreased plasma osmolality (less than 280 mOsm/kg of water) may occur in a patient who is hypovolemic or euvolemic. The urinary sodium excretion is used to further refine the differential diagnosis. A high urinary sodium concentration (greater than 30 mmol/L) may result from renal disorders, syndrome of inappropriate antidiuretic hormone secretion (SIADH), reset osmostat syndrome, endocrine deficiencies, medications, or drugs. A low urinary sodium concentration (less than 30 mmol per L) may result from vomiting, diarrhea, severe burns, acute water overload, or psychogenic polydipsia. SIADH occurs when antidiuretic hormone is secreted independently of the body’s need to conserve water. SIADH is a diagnosis of exclusion but should be suspected when hyponatremia is accompanied by a low serum osmolality with an inappropriately high urine osmolality. The diagnostic criteria for SIADH are: • Hypotonic hyponatremia • Urine osmolality greater than 100 mmol/kg • Absence of extracellular volume depletion • Normal thyroid and adrenal function • Normal cardiac, hepatic, and renal function. Medications Associated with Hyponatremia Amiodarone Carbamazepine Chlorpromazine Chlorpropamide Clofibrate Cyclophosphamide Haloperidol Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: ARTHRITIS AND ARTHRALGIA HAIR LOSS HYPOTHYROIDISM TRANSAMINASE ELEVATION Stay updated, free articles. Join our Telegram channel Join Tags: Instant Work-ups A Clinical Guide to Medicine Aug 17, 2016 | Posted by admin in PEDIATRICS | Comments Off on HYPONATREMIA Full access? Get Clinical Tree
42 HYPONATREMIA General Discussion Hyponatremia generally is defined as a plasma sodium level of less than 135 mEq/L. Hyponatremia may lead to significant morbidity and mortality. Most patients with hyponatremia are asymptomatic, and symptoms usually do not appear until the plasma sodium level drops below 120 mEq/L. Symptoms of hyponatremia usually are nonspecific and include headache, nausea, and lethargy. However, neurologic and gastrointestinal symptoms may be present in cases of severe hyponatremia, with the risk of seizure and coma increasing as the sodium level decreases. If the sodium level decreases quickly, symptoms may be present at sodium levels above 120 mEq/L. The evaluation of hyponatremia begins with a targeted history to evaluate for causes of hyponatremia such as congestive heart failure, renal impairment, liver disease, malignancy, hypothyroidism, or Addison’s disease. Hyponatremia is then classified according to the volume status of the patient as hypovolemic, hypervolemic, or euvolemic. Hypervolemic hyponatremia results in increased total body water and the presence of edema. The three main causes of hypervolemic hyponatremia are congestive heart failure, liver cirrhosis, and renal impairment such as renal failure and nephrotic syndrome. Differentiating between hypovolemia and euvolemia may be difficult clinically. An elevated hematocrit or a blood urea nitrogen:creatinine ratio greater than 20 may suggest hypovolemia but are not always present. If the patient’s volume status is not clear, the measurements of plasma osmolality and urinary sodium concentration are useful for evaluating euvolemic or hypovolemic patients. Normal plasma osmolality (280–300 mOsm/kg of water) can be seen with pseudohyponatremia or after the absorption of large volumes of hypotonic irrigation fluid during transurethral resection of the prostate. Pseudohyponatremia may occur in the presence of severe hypertriglyceridemia and hyperproteinemia. Increased plasma osmolality (greater than 300 mOsm/kg of water) in a patient with hyponatremia is caused by severe hyperglycemia. Decreased plasma osmolality (less than 280 mOsm/kg of water) may occur in a patient who is hypovolemic or euvolemic. The urinary sodium excretion is used to further refine the differential diagnosis. A high urinary sodium concentration (greater than 30 mmol/L) may result from renal disorders, syndrome of inappropriate antidiuretic hormone secretion (SIADH), reset osmostat syndrome, endocrine deficiencies, medications, or drugs. A low urinary sodium concentration (less than 30 mmol per L) may result from vomiting, diarrhea, severe burns, acute water overload, or psychogenic polydipsia. SIADH occurs when antidiuretic hormone is secreted independently of the body’s need to conserve water. SIADH is a diagnosis of exclusion but should be suspected when hyponatremia is accompanied by a low serum osmolality with an inappropriately high urine osmolality. The diagnostic criteria for SIADH are: • Hypotonic hyponatremia • Urine osmolality greater than 100 mmol/kg • Absence of extracellular volume depletion • Normal thyroid and adrenal function • Normal cardiac, hepatic, and renal function. Medications Associated with Hyponatremia Amiodarone Carbamazepine Chlorpromazine Chlorpropamide Clofibrate Cyclophosphamide Haloperidol Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: ARTHRITIS AND ARTHRALGIA HAIR LOSS HYPOTHYROIDISM TRANSAMINASE ELEVATION Stay updated, free articles. Join our Telegram channel Join Tags: Instant Work-ups A Clinical Guide to Medicine Aug 17, 2016 | Posted by admin in PEDIATRICS | Comments Off on HYPONATREMIA Full access? Get Clinical Tree
