High Yield Topics

Hyponatremia

By admin



Ovid: 5-Minute Sports Medicine Consult, The


Hyponatremia
Tod Sweeney
William W. Dexter
Basics
Description
  • Decrease in serum sodium concentration to <136 mmol/L
  • Serum sodium concentration and serum osmolarity normally are maintained under precise control by homeostatic mechanisms involving thirst, antidiuretic hormone (ADH), and renal handling of filtered sodium.
  • Increased serum osmolarity above normal (280–300 mOsmol/kg) stimulates hypothalamic osmoreceptors, which then cause increased thirst and circulating levels of ADH.
  • Can be associated with low, normal, or high tonicity
  • Effective osmolality or tonicity refers to the contribution to osmolality of solutes such as sodium and glucose that cannot move freely across cell membranes, thereby inducing transcellular shifts in water.
  • Most common form is hypotonic (dilutional) hyponatremia.
    • Excess of water in relation to existing sodium stores, which can be decreased, normal, or increased.
    • Retention of water most commonly reflects presence of conditions that impair renal excretion of water.
    • Less commonly caused by excessive water intake, with normal or near-normal excretory capacity.
  • Hypertonic hyponatremia results from a shift of water from cells to the extracellular fluid that is driven by solutes confined in the extracellular compartments (as occurs with hyperglycemia or retention of hypertonic mannitol).
  • Pseudohyponatremia is a form of iso-osmolar and isotonic hyponatremia identified when severe hypertriglyceridemia or paraproteinemia is present, which affects accurate laboratory measurement of sodium concentration.
Epidemiology
  • Occurs in 10–40% of ultraendurance athletes after a race
  • 7% of healthy elderly persons
  • Predominant gender: Male = Female.
  • More common in the very young and very old, who are less able to experience and express thirst and less able to autonomously regulate fluid intake.
Risk Factors
  • Elite endurance athletes who consume excessive fluids
  • In marathoners, more common in women, slower runners, and finishers who maintain or increase their body weight
  • Excess fluid losses (eg, excessive sweating, vomiting, diarrhea, GI fistulas or drainage tubes, pancreatitis, burns) that have been replaced primarily by hypotonic fluids
  • Infants given inappropriate amounts of free water
  • Thiazide diuretics, chlorpropamide, cyclophosphamide, clofibrate, carbamazepine, opiates, oxytocin, desmopressin, vincristine, selective serotonin reuptake inhibitors, or tolbutamide
  • Those with history of hepatic cirrhosis, congestive heart failure, or nephrotic syndrome, who are subject to increases in total body sodium and free water stores
  • Acute or chronic renal insufficiency in patients who may be unable to excrete adequate amounts of free water or those with salt-wasting nephropathy
  • Syndrome of inappropriate ADH secretion (SIADH)
  • Uncorrected hypothyroidism or cortisol deficiency
  • Consumption of large amounts of beer or use of the recreational drug methylenedioxy-methamphetamine (“ecstasy”)
  • NSAID use
Commonly Associated Conditions
  • Hyponatremic encephalopathy associated with noncardiogenic pulmonary edema in healthy marathon runners
  • Cerebral edema leading to brain stem herniation and death
  • Permanent CNS dysfunction
  • Central pontine myelinolysis characterized by weakness, muscle spasms, diplopia, confusion, delirium, or dysphagia
  • Seizures
  • Rhabdomyolysis
Diagnosis
History
Thorough past medical, past surgical, medication, and social history, with special attention to signs, symptoms, and differential diagnosis as listed above
Physical Exam
  • Signs and symptoms:
    • Varying range depending on the chronicity, cause, and the individual
    • Overhydration in athletes characterized by edema of the hands with swelling of the fingers
    • Anorexia
    • Headache
    • Muscle cramps
    • Nausea and vomiting
    • Difficulty concentrating
    • Confusion
    • Lethargy
    • Agitation
    • Obtundation
    • Coma
    • Status epilepticus
  • Physical examination:
    • Most abnormalities are neurologic in origin.
    • Assess level of alertness.
    • Assess degree of cognitive impairment.
    • Depressed deep tendon reflexes, ataxia, asterixis, pathologic reflexes, or pseudobulbar palsy (bilateral hemiplegia, dysarthria, dysphagia)
    • Look for signs of focal or generalized seizure activity.
    • In patients with acute severe hyponatremia, signs of brain stem herniation may be apparent, including coma; fixed, unilateral, dilated pupil; decorticate or decerebrate posturing; and respiratory arrest.
Diagnostic Tests & Interpretation
Imaging
  • Measure serum sodium level, and always consider possibility of laboratory error or improper sampling technique.
  • Measure blood urea nitrogen, creatinine, uric acid, urinary osmolality, and urinary sodium.
  • Measure serum osmolality (low <280 mOsmol).
    • If normal (280–285 mOsmol), measure blood sugar, lipid, and protein levels.
    • If elevated (>280 mOsmol), measure blood sugar.
  • If serum hyperglycemia is present, then serum sodium must be corrected by a factor of 1.6 mEq/L for each 100 mg/dL increase in serum glucose.
  • Consider chest x-ray, electrocardiogram, head CT scan, or other laboratory work based on history and physical examination.
Differential Diagnosis
  • Adrenal insufficiency and adrenal crisis
  • Congestive heart failure and pulmonary edema
  • Gastroenteritis
  • Hypothyroidism and myxedema coma
  • Renal failure, acute
  • Renal failure, chronic
  • SIADH
  • Cirrhosis
  • Nephrotic syndrome
  • Psychogenic polydipsia
  • Pseudohyponatremia
  • Iatrogenic
  • Medication related

P.317


Treatment
  • Long-term treatment
  • Acute treatment
  • Triathlete considerations:
    • Unconscious athlete should have bladder catheterized and should be moved promptly to a hospital for definitive management.
    • For severe hyponatremia (<126 mEq/L), patient should not receive fluids either orally or intravenously, except perhaps 3% saline solution (these athletes usually are volume overloaded).
    • For less severe hyponatremia (>130 mEq/L), watchful waiting is the cornerstone of therapy because most will self-correct.
  • Calculations:
    • Change in serum Na = (infusate Na – serum Na)/total body water + 1. Estimates effect of 1 L of any infusate on serum Na.
    • Total body water (in liters) is calculated as a fraction of body weight.
    • Fraction = 0.6 in children; 0.6 and 0.5 in nonelderly men and women, respectively; and 0.5 and 0.45 in elderly men and women, respectively.
    • Normally, extracellular and intracellular fluids account for 40% and 60% of total body water, respectively.
Additional Treatment
General Measures
  • Airway, breathing, and circulation (ABCs)
  • Establish IV access.
  • Determine cause by history, physical examination, and laboratory data, and direct treatment accordingly.
  • There is no consensus about the optimal treatment of symptomatic hyponatremia. Increase serum sodium rapidly by 1–2 mEq/L/hr over the 1st 1–2 hr for levels <120 mEq/L.
  • Patients with seizures or impending brain stem herniation should receive 3% saline (see “Calculations” above) to accomplish rapid correction, but only enough to arrest progression of symptoms; usually 4–6 mEq/L is sufficient. Be aware of cardiac status with aggressive IV therapy.
  • Patients with mild symptoms and serum sodium <125 mEq/L often have chronic hyponatremia and must be managed cautiously.
  • Rapid increase in serum sodium can lead to central pontine myelinolysis, but risk appears minimal if correction is at a rate <0.5 mEq/L/hr or 12 mEq/L/day. Isolated cases of osmotic demyelination after correction at 9–10 mEq/L/day have been reported; therefore, maximum correction of 8 mEq/L/day is a more conservative approach.
  • Hypovolemic hyponatremia with mild to moderate symptoms is treated with normal saline (see “Calculations” above), and frequent monitoring of serum sodium levels is important to assess rate of correction.
  • Hypervolemic hyponatremia treatment consists of sodium and water restriction and attention to the underlying cause.
  • Euvolemic hyponatremia treatment consists of free water restriction and correction of the underlying condition.
  • Patients with severe, symptomatic hyponatremia should be admitted to an ICU, with close monitoring of serum sodium levels.
  • Proper management of underlying cause with close clinical follow-up
  • Discontinue medications known to be associated with hyponatremia.
  • Clozapine appears to be effective in long-term treatment of schizophrenic patients with compulsive water drinking.
Ongoing Care
  • Although uncertainty about the diagnosis occasionally may justify a limited trial of isotonic saline, attentive follow-up is needed to confirm the diagnosis before substantial deterioration occurs.
  • Isotonic saline is unsuitable for correcting the hyponatremia of SIADH.
  • Great vigilance is required to recognize and diagnose hypothyroidism and adrenal insufficiency, which tend to masquerade as SIADH.
  • Presence of hyperkalemia always should alert the physician to the possibility of adrenal insufficiency.
  • Patients with persistent asymptomatic hyponatremia require slow-paced management, but those with symptomatic hyponatremia must receive rapid but controlled correction.
  • Education on fluid intake and appropriate placement of support stations was associated with a decreased incidence of symptomatic hyponatremia at ultraendurance sporting events.
  • Hypotonic fluids and excessive isotonic fluids should be avoided after surgery.
Additional Reading
Adrogue HJ, Madias N. Hyponatremia. N Engl J Med. 2000;342:1581–1589.
Ayus JC, Varon J, Arieff AI. Hyponatremia, cerebral edema, and noncardiogenic pulmonary edema in marathon runners. Ann Intern Med. 2000;132:711–714.
Craig S. http://www.emedicine.com/emerg/topic275.htm (hyponatremia). http://dynamicmedical.com Hyponatremia (hypotonic)
Kugler JP, Hustead T. Hyponatremia and hypernatremia in the elderly. Am Fam Physician. 2000;61:3623–3630.
Noakes TD, Mayers LB. A guide to treating ironman triathletes at the finish line. Physician Sportsmed. 2000;28.
Speedy DB, Rogers IR, Noakes TD, et al. Diagnosis and prevention of hyponatremia at an ultradistance triathlon. Clin J Sports Med. 2000;10:52–58.
Codes
ICD9
276.1 Hyposmolality and/or hyponatremia
Clinical Pearls
In ultraendurance athletes, IV should not be used unless there are signs of dehydration, including cardiovascular instability.


Continue Reading
You might also like More from author

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More