HYPONATREMIA - Approach to Patient

LEARNING OBJECTIVES:

KNOWLEDGE - The student will discuss:

1. The approach to a patient with hyponatremia including:
   • pseudohyponatremia associated with hyperlipidemia or paraproteinemias
   • hyponatremia associated with hyperglycemia or mannitol administration
   • hyponatremia associated with:
   • over-hydration - CHF, nephrotic syndrome or cirrhosis with ascites
   • dehydration:
     • high urinary sodium - Addison's Disease, diuretic use, salt-loosing nephropathies
     • low urinary sodium - extra-renal sodium and water loss
   • euhydration - SIADH, hypothyroidism, psychogenic water   drinking, sick cell syndrome
2. The deleterious effects of a rapid change in serum sodium concentration.
3. Treatment modalities for specific causes of hyponatremia based on pathophysiology and rapidity (or chronicity) of the development of the hyponatremia.
4. The concept of free water clearance by the kidney.

PATIENT CARE SKILLS:

1. History taking - the student will illicit the symptoms of hyponatremia when relevant.
2. Physical exam - the student will be able to determine the volume status of a patient using the physical exam including:
   • measuring jugular venus distention and estimating central venus pressure from that measurement
   • recognizing skin turgor including the pitfall of using only skin turgor to determine volume status
   • measuring for postural hypotension
   • detection of ascites, peripheral edema, pulmonary rales, and S 3
3. Laboratory tests - the student will:
   • know when and how to collect a spot urinary sodium
   • know how to calculate free water clearance
   • recognize states of hyperlipidemias and parprotinemias from routine laboratory testing
   • be able to calculate the estimated change in serum sodium for a given change in blood glucose
   • calculate serum osmolarity
4. Management
   • The student using history, physical and basic lab will be able to determine if specific treatment for hyponatremia is necessary, and if so, will be able to initiate treatment.
   • Be aware that not all states of hyponatremia need immediate or specific treatment and that too rapid correction of serum sodium can, in itself, be deleterious to the patient.

References :

1. DeFronzo, RA., Their, S.   Pathophysiologic Approach to Hyponatremia .   Arch Intern Med , July 1980.   Vol 140   pp 897 – 902.
2. Fraser, CL., Arieff, AI.   Epidemiology, Pathophysiology, and Management of Hyponatremic Encephalopathy.   The Science of Medical Care , Jan 1997;102:67-77.