HYPONATREMIA - Approach to Patient
LEARNING OBJECTIVES:
KNOWLEDGE - The student will discuss:
- Define and describe the effect of hyponatremia on the brain and the
resultant presenting signs/symptoms.
- Define and describe the importance of total body water distribution and
its relationship to hyponatremia.
- Discuss the approach to a patient with hyponatremia including
pseudohyponatremia associated with hyperlipidemia or paraproteinemias.
- Discuss hyponatremia associated with hyperglycemia or mannitol
administration.
- Define and describe the concept of free water clearance by the kidney.
- Define and describe the differential diagnosis and treatment of
hyponatremia in the setting of volume depletion, euvolemia, and hypervolemia
associated with:
-
- Over-hydration - CHF, nephrotic syndrome or cirrhosis with ascites
- Dehydration:
- high urinary sodium - Addison's Disease, diuretic use, salt-losing nephropathies,
cerebral salt wasting
- low urinary sodium - extra-renal sodium and water loss
- Euhydration - SIADH, hypothyroidism, psychogenic water drinking, sick cell syndrome,
beer potomania, Teat and Toast syndrome, and exercise-induced
hyponatremia
- Define and describe the risks of too rapid or delayed therapy for
hyponatremia.
PATIENT CARE SKILLS:
- History taking - the student will illicit the symptoms of hyponatremia when relevant.
- 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
- 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
- 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 :
- DeFronzo, RA., Their, S. Pathophysiologic Approach to Hyponatremia . Arch Intern Med , July 1980. Vol 140 pp 897 – 902.
- Fraser, CL., Arieff, AI. Epidemiology, Pathophysiology, and Management of Hyponatremic Encephalopathy. The Science of Medical Care , Jan 1997;102:67-77.