HYPONATREMIA - Approach to Patient
KNOWLEDGE - The student will discuss:
- 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
- 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
- The deleterious effects of a rapid change in serum sodium concentration.
- Treatment modalities for specific causes of hyponatremia based on pathophysiology and rapidity (or chronicity) of the development of the hyponatremia.
- The concept of free water clearance by the kidney.
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
- 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.
- 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.