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Toronto Notes 2019
Electrolyte Disorders
Nephrology NP15
Table 9. Etiology of Hypophosphatemia
Inadequate Intake
Starvation Malabsorption (diarrhea, steatorrhea)
Antacid use
Alcoholism
Clinical Features
Renal Losses
Hyperparathyroidism Diuretics
X-linked or autosomal dominant hypophosphatemic rickets
Fanconi syndrome
Multiple myeloma
Early post-kidney transplant
Excessive Skeletal Mineralization
Osteoblastic metastases
Post parathyroidectomy (referred to as ‘hungry bone syndrome’)
Shift into Intracellular Fluid
Recovery from metabolic acidosis
Respiratory alkalosis Starvation refeeding (stimulated by insulin)
• instabilityofcellmembranesleadingtohemolyticanemiaorrhabdomyolysis
• MSK weakness, respiratory depression, low cardiac output/CHF from weakened cardiac muscles –
symptoms arise due to low ATP production
• neurological symptoms: irritability, encephalopathy, seizures, coma
• hematologic symptoms: hemolytic anemia, decreased release of oxygen from hemoglobin, impaired
leukocyte and platelet function (leading to worsening infections/defective clotting)
Treatment
• treatunderlyingcause
■ Oral PO43-: 2-4 g/d divided bid-qid (start at 1 g/d to minimize diarrhea)
■ IV PO43-: only for severely symptomatic patients or inability to tolerate oral therapy
Hypermagnesemia
Definition
• serummagnesium>1.05mmol/L
Etiology
• AKI/CRF
• Mg2+-containingantacidsorenemas
• IV administration of large doses of MgSO4 (e.g. for Preeclampsia; see Obstetrics, OB24)
Clinical Features
• rarelysymptomatic
• drowsiness,hyporeflexia,respiratorydepression,heartblock,cardiacarrest,hypotension
Treatment
• discontinueMg2+-containingproducts
• 10%calciumgluconate10-20mLIV(Mg2+-antagonist)foracutereversalofmagnesiumtoxicity • hemodialysisifrenalfailure,considerperitonealdialysisinsettingofhemodynamiccompromise
Hypomagnesemia
Definition
• serummagnesium<0.70mmol/L
Youwillbeunabletocorrecthypokalemiaor hypocalcemia without first supplementing magnesium if patient is hypomagnesemic
Etiology
GI losses
Starvation/malabsorption Vomiting/diarrhea Alcoholism
Acute pancreatitis
Clinical Features
Excess renal loss
2o hyperaldosteronism due to cirrhosis and CHF Hyperglycemia
Hypokalemia
Hypercalcemia
Loop and thiazide-type diuretics Nephrotoxic medications Proton-pump inhibitors
Early post-renal transplant
• tremors,nauseaandvomiting,lethargy/weakness,seizures,paresis,ChvostekandTrousseausigns,ECG changes (widened QRS, prolonged PR, T-wave abnormalities), and arrhythmias including Torsades de Pointes
Treatment
• treatunderlyingcause
• encourageincreaseddietaryintakee.g.fruits
• oral Mg2+ salts unless patient has seizures or other severe symptoms
• Mg2+ IM/IV; cellular uptake of Mg2+ is slow, therefore repletion requires sustained correction • discontinuediuretics
■ in patients requiring diuretics, use a K+-sparing diuretic to minimize magnesuria