electrolyte disorders Flashcards
↑↑ ADH → reabsorb H20 in collecting tubules→ concentrate urine:
low serum osmolality, low serum Na
syndrome of inappropriate ADH (SIADH)
causes of SIADH
1) ectopic ADH from small cell lung cancer (paraneoplastic syndrome)
2) pulm disease: COPD, pneumonia
3) head trauma, stroke, CNS infection
4) drugs: cyclophosphamide (immunosuppresant)
5) idiopathic
common cause of low serum Na (hyponatremia)
SIADH
complication of correcting low serum Na+ too quickly
central pontine myelinolysis: lysis of myelin in pons
causes LOCKED IN SYNDROME (conscious, can’t move, can’t communicate)
↓ ADH → ↓ H20 absorption in collecting tubules →↑ urine volume = dilute urine:
high serum osmolarity
low urine specific gravity
diabetes insipidus
abnormal ADH production by hypothalamus
if no ADH = complete central DI
insufficient ADH = partial central DI
central diabetes insipidus
kidneys unresponsive to ADH
nephrogenic diabetes insipidus
causes of nephrogenic diabetes insipidus (kidneys don’t respond to ADH)
1) lithium: interferes with aquaporin channel insertion due to ADH
2) demeclocycline: interferes with ADH function in kidney (use: SIADH)
3) hypercalcemia
4) ADH receptor gene mutation (hereditary)
evaluation of excessive thirst, polyuria
1) DM: urine glucose, serum glucose (if normal):
2) DI: urine + serum osmolarity (if low urine osmolarity, high serum osmolarity):
3) confirm dx of DI: water deprivation test: restrict drinking water → recheck urine osmolality
(normal response: secrete ADH and ↑ urine osmolality, abnormal response: no ADH and urine osmolarity stays low)
4) differentiate type DI: desmopressin (ADH analog) challenge: if improve = ↑ urine osmolarity = central DI, if no change = nephrogenic DI
central DI treatment
intranasal desmopressin (ADH analog)
nephrogenic DI treatment
1) hydrochlorothiazide - DOC: thiazide makes dehydrated → PT will reabsorb more H20 → concentrated urine by time in distal tubule
2) indomethacin(can use in combo with thiazide): inhibit PG synthesis, ↓ RBF →↓ UO
3) amiloride for lithium-induced (can stay on lithium): block Na channel lithium uses to enter PC
presentation of hyponatremia
alters resting membrane potential of neurons → CNS problems confusion AMS (esp elderly) seizures stupor coma
presentation of hypercalcemia
“stones, bones, ab groans, psychiatric overtones (confusion, delerium)”
may not have calciuria
presentation of hypocalcemia
tetany: Trousseau sign (Tighten cuff - carpopedal spasm) Chvostek sign (tap cheek - facial nerve spasm)
presentation of hypomagnesemia
tetany
EKG changes: wide QRS, torsades de pointes (type of vtach with variable amp)
