Hypo/hypernatremia and K homeostasis Flashcards
Causes of hypovolemic hyponatremia
Renal loss –> UNa > 20, Uosm iso
- acute diuretic use
- salt wasting nephropathy
- adrenal insufficiency
- osmotic diuresis
Non-renal –> UNa < 20, Uosm high (concentrated urine)
- GI loss –> vomiting, diarrhea, fistulas
- skin loss
- remote diuretic use
Causes of hypovolemic hyponatremia
Renal loss –> UNa > 20, Uosm iso
- acute diuretic use
- salt wasting nephropathy
- adrenal insufficiency
- osmotic diuresis
Non-renal –> UNa < 20, Uosm high (concentrated urine)
- GI loss –> vomiting, diarrhea, fistulas
- skin loss
- remote diuretic use
Cause of euvolemic hyponatremia
UNa > 20, Uosm > 300 (concentrated urine) –> elminating Na; does not appear volume depleted to kidneys bc eliminating Na = inappropriate secretion of ADH –> no osmotic or volume stimulus
- SIADH
- psychogenic H2O ingestion
- Hypothyroidism
- Drugs
Causes of hypervolemic hyponatremia
UNa 300 (concentrated urine)
- CHF
- cirrhosis
- nephrosis
- oligurinc renal failure
Signs/symptoms of hyponatremia
Signs
- abnormal sensorium
- depressed deep tendon reflexes
- cheyne-stokes respirations
- hypothermia
- pathological reflexes
- pseudobulbar palsy
- seizures
Symptoms
- lethargy, apathy
- disorientation
- muscle cramps
- anorexia
- nausea
- agitation
Management of hyponatremia
Raise serum Na by less than 10 mEq/L in the first 24 hours and less than 18 mEq/L in the first 48 hours
Acute hyponatremia –> correct rapidly
- usually produces symptoms due to cerebral edema –> more water enters cells = swelling –> brain has not had time to decrease solutes
- usually an iatrogenic cause
- treat with hypertonic saline –> alone if volume depleted, with furosemide if euvolemic
Chronic hyponatremia –> correct slowly
- usually asymptomatic –> brain has adapted to hyponatremia by decreasing solutes
- H2O restriction, treat volume depletion/CHF/other underlying causes
If patient is symptomatic and you are uncertain as to the chronicity of the hyponatremia –> rapidly raise serum Na by 10% then correct slowly
Causes of hypovolemic hypernatremia
Loss of H2O in excess of Na –> dehydrated and intravascular volume depleted
UNa < 20 = extra-renal losses
- Excessive sweating
- Burns
- Fevers
- Diarrhea
UNa > 20 = renal losses
- diuretics (osmotic or loop)
- intrinsic renal disease
Causes of euvolemic hypernatremia
Loss of H20 with normal body Na –> dehydrated but not intravascular volume depleted
- variable UNa
Extrarenal losses
- insensible losses –> lung or skin
- hypodypsia
Renal losses
- DI –> central or nephrogenic
Causes of hypervolemic hyponatremia
Gain of Na in excess of H20–> neither dehydrated or intravascular volume depleted
All iatrogenically driven, UNa > 20
- hypertonic infusion
- hypertonic dialysis
- NaCl tablets
Clinical manifestations of hypernatremia
- muscle rigidity –> inconsistent finding
- change in mentation –> slight confusion to overt coma
- –> metabolic encephalopathy = global derangement of mental function
Renal causes of hypokalemia
- Obligate renal loss –> kidneys cannot render the urine K free; depletion may occur if intake is severely decreased (anorexia + alcoholic)
- Renal losses
- mineralocorticoid excess –> primary/secondary hyperaldosteronism, glucocorticoid excess, licorice abuse
- renal tubular acidosis (types 1 and 2)
- ostmotic diuresis
- chronic interstitial nephritis
- diuretic therapy
Gi causes of hypokalemia
Vomiting, NG tube suctioning, diarrhea –> cause alkalosis –> results in hypokalemia in 3 ways:
- alkalosis causes of shift of K into cells in exchange for H
- acute rise of plasma HCO3 conce exceeds capacity for PCT to reabsorb it = K is secreted as obligate cation partner to the bicarb
- metabolic alkalosis is often present in states of vol depletion = increased aldo = increased K secretion
Drug induced changes in K levels
- Altered affects of aldosterone = decreased K secretion (ACE inhibitors, ARBs, spirinolactone)
- Alter lumen potential = decreased K secretion (Amiloride, TMP-SMX)
- Change flow rate = diuretics –> increased flow = increased K secretion
Physiological consequences of hypokalemia
- neuromuscular effects –> ileus, muscle weakness, tetany, encephalopathy
- renal effects –> attempts at K conservation
- –> polyuria + polydypsia (loss of concentrating ability)
- –> alkalosis + Na retention (increased PCT Na + HCO3 reabsorption)
- –> hypokalemia nephropathy - metabolic effects –> abnormal carbohydrate metabolism, negative nitrogen balance
- vasoconstriction
- rhabdomyolysis
- cardiac –> ECG changes = T wave flattening, U wave appears
Causes of hyperkalemia
Confirm that its true and not pseudohyperkalemia
Causes of true hyperkalemia:
- Redistribution
- –> acidemia = H is taken up by cells in exchange for K = hyperkalemia
- –> hyperkalemic periodic paralysis - Decreased excretion –> most common cause
- –> acute/chronic kidney disease
- –> K sparing diuretics
- –> adrenal insufficiency = Addison’s or Type IV RTA (hyporeninemic hypoaldosteronism) - Increased input
- –> endogenous = intravascular hemolysis, rhabdomyolysis
- –> exogenous = salt substitutes, K+ penicillin
