2-29-08 Water Balance
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Water Balance
Diabetes Insipidus
• Diabetes Insipidus - results from an ADH deficiency
• Etiology - can be from trauma/iatrogenic, also neoplasm, idiopathic, familial, & other lesions
• Pathophysiology - unable to concentrate urine ( water deprivation ( polydipsia & polyuria
• Water Deprivation Test - assess for diabetes inspidus:
o Unable to concentrate urine (diabetes insipidus) ( ↑ plasma Osm, but urine Osm unchanged
o ADH Administration:
▪ Pituitary DI - ADH not being made; ( ADH added = urine Osm ↑
▪ Nephrogenic DI - kidney doesn’t respond ( ADH added = urine Osm unchanged
• Causes - familial, renal disease, hypercalcemia, hyperkalemia, Li toxicity
o Non-DI 1o Polydipsia - urine Osm increases normally as water restricted
• ADH Deficiency Tx - give DdAVP bid, urination will return to normal
o Hyponatremia - risk if too much DdAVP, thus once a week hold dose until thirsty
Diabetes Insipidus Presentation
• Presentation - 25 yo man, sudden onset polyuria/polydipsia, insomnia from constant urination
• Labs - patient has high urine volume
• Test - give water deprivation test ( urine Osm ↑;DdAVP added, urine Osm returns to normal
SIADH
• Syndrome of Inappropriate ADH - ADH secretion despite hypoosmolar & hyponatremia
• Etiology - arise from CNS disorder, malignant ADH tumor, pulmonary disease, drugs
• Pathophysiology - too much ADH ( drink water even though don’t need it ( volume expansion
o Steady State - usually reach a new steady state, but at very expanded hyponatremic state
• Sx - has neural symptoms based on severity
o Na > 120 - patients usually ASx
o Na 110-120 - patients usually confused & lethargic
o Na < 110 - convulsions, coma, death
• QUIZ: Rate of Na fall - is more important than the absolute Na level, indicates SIADH
• Dx - made by a hypotonic plasma and inappropriately hypertonic urine
o Exclude - make sure other causes of hyponatremia exluded: hyperglycemia, hyperlipidemia
o Appropriate ADH - during vol. depletion, HF, cirrhosis, nephrotic, hypothyroid, cortisol def.
• Tx - need to manage acute & chronic Sx
o Acute - give hypertonic saline; can add furosemide in order to promote water excretion
▪ Tolvaptan - ADH V2 receptor antagonist ( blocks, promotes water excretion
▪ Too rapid correction - bad! Can cause brain damage, need to gradually correct
o Chronic - treat underlying disorder & regulater water:
▪ Underlying disorder - best approach, disease will then resolve…
▪ Water restriction - lower water intake despite patient being thirsty
▪ Demeclocycline - induces nephrogenic DI ( combats SIADH, but risk of renal failure
▪ Oral ADH Antagonist - under research…
SIADH Presentation
• Presentation - 61 yo man, convulsions & confusion; 3 mo anorexia/nausea/weight loss
• Labs - present with decreased plasma Osm ( hyponatremia and abnormally high ADH
• Imaging - has 3 cm right hilar mass ( malignant tumor secreting ADH
Heart Failure & Na/H2O Restriction
• HF & Na Excess Only - if salt restrict, then water should follow, and water returns to appropriate level
• HF, Na Excess & Water Retention Problem - if salt restrict ( hyponatremia, since water not following
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