The difference between night & day: dealing with lytes in the hospital

J Rush Pierce Jr, MD, MPHDivision of Hospital Medicine, Univ of New Mexico

Resident's Thursday SchoolAugust 07, 2014

Roadmap

• Primarily common hospital-based cases – Sodium – Potassium– Phosphorus– Magnesium

• A touch of pathophysiology• Note evidence vs. expert opinion

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Sodium: start with etiology

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Case 1

• A 74 y/o woman with HTN admitted with N/V x 1 week. She takes HCTZ for HTN. BP = 120/60, P = 92, Wt = 60 kg, skin is thin. Na = 119, K = 2.9, Cl = 80, HCO3 = 30, BUN = 35, creat = 1.0.

• What do you order?

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Questions

1. What does serum Na tell us about her total body Na?

2. How are volume and Na related?3. How can hyponatremia hurt you?4. How can we get into trouble with Na

replacement?

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Hyponatremia – major causes

• Hyperosmolar and normo-osmolar states• Hypo-osmolar states

1. Hypervolemic states (CHF, renal failure, cirrhosis)

2. Euvolemic states (SIADH, hypothyroidism, beer potomania, psychogenic polydipsia)

3. Hypovolemic states (volume depletion with water drinking, adrenal insuff)

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Hyponatremia – basic evaluation

• Determine osmolar state– Serum Osm (can skip if hyponatremia corrects for

hyperglycemia – 1 mEq Na for each 62 mg% gluc)

• Determine if ADH is turned on or off– Urine osm < 50 if off (polydipsia)– Urine osm > 50 if on (all others)

• Determine volume status– Clinical exam– Urine Na (< 10 = volume depletion) or FENa

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Correcting hyponatremia

• Pseudohyponatremia – treat underlying condition

• Hypo-osmolar states– Hypervolemic – fluid restrict + loop diuretics– Euvolemic – fluid restrict – Hypovolemic – NS (be careful!)

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Correcting hypovolemic hyponatremia

• (Infusate [Na] - SNa) ÷ (TBW + 1) = Increase in SNa – So 1 liter of NS: (154 – 119) ÷ (30 + 1) = 1.12 mEq– Recommended rate of correction is 6 meQ/24 hr– 6 1.12 = 5.35 L/24 hr = 222 cc/hr

• Problems:– Correction of hypokalemia results in higher Na– Correction of volume depletion results in

excretion of free water08/07/2014 Electrolyte problems in the hospital 9

Hyponatremia helpful hints

1. Don’t use NS in hypervolemic hyponatremia2. Don’t use NS in SIADH3. Correcting hypokalemia will partially correct

hyponatremia4. When treating hypovolemic hyponatremia,

aim low and recheck serum sodium frequently

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Case 1

• A 74 y/o woman with HTN admitted with N/V x 1 week. She takes HCTZ for HTN. BP = 120/60, P = 92, Wt = 60 kg, skin is thin. Na = 119, K = 2.9, Cl = 80, HCO3 = 30, BUN = 35, creat = 1.0.

• What do you order? – Serum osm; Urinary Na, creat, osm– NS at 100 cc/hr– remeasure Na in 4 hrs

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Case 2

• A 64 year old man is transferred 3 days after a stroke with aphasic and dense R hemiparesis. BP = 120/60, P = 92, Wt = 70 kg, skin is thin. Na = 160, K = 3.8, BUN = 30, creat = 1.0.

• What do you order?

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Hypernatremia and thirst

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Approach to hypernatremia

• In adults usually water loss without drinking; occasionally DI

• If worried about DI, measure urinary osm• < 300 = DI• > 600 excludes DI

• Goal is to lower by 10 mEq/24 hrs• UpToDate formula is D5W at 1.35 ml/hr x wt

• 100 cc/hr for 70 kg

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Case 2

• A 64 year old man is transferred 3 days after a stroke with aphasic and dense R hemiparesis. BP = 120/60, P = 92, Wt = 70 kg, skin is thin. Na = 160, K = 3.8, BUN = 30, creat = 1.0.

• What do you order?– D5W at 100 cc/hr– Remeasure Na in 4 hrs

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Potassium – it’s mostly about choosing the right treatment

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Case 3• 22 y/o woman comes to the ED with several

hours of wheezing. She has had 3 previous ED visits in the past month for asthma. She takes no medications. She appears anxious and complains of tightness in the throat. On exam she has wheezes anteriorally. She is treated with oxygen and inhaled albuterol but does not improve. SaO2 = 98% on room air. Serum K = 2.9. Attending asks you why K is low.

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Hypokalemia

• Most common hospital electrolyte abnormality

• 20% hospitalized pts have it or develop it• Etiology in 95% of hospitalized patients is:

– Diuretics– Vomiting– Diarrhea

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Hypokalemia - etiology

1. Cellular shifts

2. Renal loss

3. Extra-renal loss

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Hypokalemia and cellular shifts

• Cellular shifts of K influenced by hydrogen– Alkalosis cause intracellular shift and may cause

hypokalemia on this basis alone– Magnitude of effect is ~0.4 mEq decrease K for

each 0.1 increase in pH (pH 7.4 ->7.6 = K 3.5 -> 2.7)

• Cellular shifts of K influenced also by beta-agonists, insulin, and thyroxin

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Renal causes of hypokalemia

• Diseases of kidney– RTA, salt-wasting nephropathies (incl Bartter’s)

• Delivery of non-reabsorbable anions (ketoacids, bicarb, toluene, PCN)

• Excess mineralocorticoid • Hypomagnesemia• Drugs

– diuretics, Amphotericin B, platinum

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Extra-renal causes of hypokalemia

• Sweat• Vomiting (5 – 10 mEQ/L)• Diarrhea (20 – 50 mEQ/L)• Dialysis, Plasmapheresis

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Case 3• 22 y/o woman comes to the ED with several hours

of wheezing. She has had 3 previous ED visits in the past month for asthma. She takes no medications. She appears anxious and complains of tightness in the throat. On exam she has wheezes anteriorally. She is treated with oxygen and inhaled albuterol but does not improve. SaO2 = 98% on room air. Serum K = 2.9. Attending asks you why K is low.

• Cellular shift

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Case 4

• 56 y/o man with cirrhosis and ascites is admitted with confusion. Meds include spironolactone and furosemide. BP 90/50, P = 102, T = 38.5. On exam is drowsy, has edema, shifting dullness, and asterixis. Na = 132, K = 3.4, BUN = 6, creat = 0.8.

• What do you order?

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Adverse effects of hypokalemia

• Effects:– Cardiac arrhythmias (acute MI < 3.5, cardiac surgery

< 3.7; CHF; in normal, rarely unless <3.0; Class I anesthesia <2.6) [observational data]

– Rhabdomyolysis < 2.5 [case reports]– Diaphragmatic muscle paralysis <2.0 [case reports]– Hepatic encephalopathy <3.5 [case reports]

• More likely with rapid decline of K• Arrhythmias more likely with CHF, IHD, digoxin08/07/2014 Electrolyte problems in the hospital 25

Adverse effects of hypokalemia in LV Failure

J Am Coll Cardiol 2004; 43:155–61

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Risks of treatment of hypokalemia

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Risks of treatment of hypokalemia

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JAMA 2012;307:156

Hypokalemia - Pierce opinion• Treat urgently (within a few mins)

– all pts with K < 2.5– sxtic pts with K <3.5 (serious vent ectopy, new

atrail fib, or new muscle weakness)– Pts with acute MI and K < 3.5

• Treat promptly (within an hour or so) pts with CHF, IHD, serious liver dz and K < 3.5

• Oral therapy is preferred• Use smaller doses and more freq monitoring in pts

with hematologic malignancy or if receiving Mg08/07/2014 Electrolyte problems in the hospital 29

Treatment – intravenous therapy (Brenner and Rector)

• Reserve for those unable to take orally, K ≤2.5 and true emergencies (significant arrhythmias, muscle weakness) – IV therapy only about 30 minutes faster than oral

• Use non-dextrose containing solutions• If > 10 mEq/hr, cardiac monitoring• KPO4 ≤ 50 mEq over 8 hours

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Treatment –oral therapy

• K-bicarb – if acidosis• KPO4 - if hypophosphatemic• KCl – all others

• Quantity – Studies in normal subjects– ↓ 0.3 mEq K →100 mEq total body K depletion– 75 mEq KCl → 1 – 1.5 mEq in 90 mins– 125 mEq → 2.5 – 3.5 mEq in 60 – 120 mins

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Case 4

• 56 y/o man with cirrhosis and ascites is admitted with confusion. Meds include spironolactone and furosemide. BP 90/50, P = 102, T = 38.5. On exam is drowsy, has edema, shifting dullness, and asterixis. Na = 132, K = 3.4, BUN = 6, creat = 0.8.

• What do you order? – KCl 40 mEq po

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Case 5

• A 64 year old diabetic woman is admitted for elective surgery. Lab: Na = 140, K = 6.1, Cl = 112, HCO3 = 20, creat = 2.1, glucose = 145

• What do you order?

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Hyperkalemia – adverse effects

• Muscle weakness - can lead to flaccid paralysis and hypoventilation.

• Altered electrical activity of heart, including ventricular fibrillation or asystole

• ECG changes in order of appearance– Tall peaked T waves, prolonged PR, AV conduction delay,

loss of P waves, sine wave, VF, asystole

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Algorithmic management of hyperkalemia.

Sood M M et al. Mayo Clin Proc. 2007;82:1553-1561

© 2007 Mayo Foundation for Medical Education and Research08/07/2014 Electrolyte problems in the hospital 36

Case 5

• A 64 year old diabetic woman is admitted for elective surgery. Lab: Na = 140, K = 6.1, Cl = 112, HCO3 = 20, creat = 2.1, glucose = 145.

• What do you order?– EKG

• Why is her K high?– Probably Type IV RTA

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Phosphorus

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Case 6

• A 54 year old woman is admitted with an osteoporotic vertebral fracture. Lab shows PO4 = 1.7. What do you order?

A. Order KPhos 30 Mmol IV x 2 dosesB. Order KPhos 30 Mmol IVC. Order KPhos 15 Mmol IVD. Order NeutraPhos 1 pkt QID

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Hypophosphatemia: common causes

• Internal redistribution– DKA, refeeding– respiratory alkalosis– Hungry bone syndrome

• Decreased intestinal absorption– Diarrhea– antacids

• Urinary loss– Hyperparathyroidism, Vit D def, Fanconi syndrome,

diuretics

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Hypophosphatemia: treatment principles

• Serious symptoms (muscle weakness, rhabdo) almost never occur until PO4 < 1.0

• Most pts will self-correct with treatment of underlying cause

• IV therapy can be associated serious complications (hypocalcemia, AKI, arrhythmias)

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Hypophosphatemia: Pierce treatment opinions

• PO4 < 1.25 – give 30 mmol IV over 6 hrs X 2 doses

• If PO4 = 1.25 – 1.5; give 15 - 30 mmol IV over 6 hrs

• If PO4 = 1.51 – 1.99; NeutraPhos 1 pkt QID; or 15 mmol IV over 4 hours

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Special considerations in patients on dialysis

• If patient is hypophosphatemic, don’t forget to stop phosphate binders

• Electrolytes checked within 3 hours of dialysis are not accurate and do not affect the baseline state.

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Case 6

• A 54 year old woman is admitted with an osteoporotic vertebral fracture. Lab shows PO4 = 1.7. What do you order?

A. Order KPhos 30 Mmol IV x 2 dosesB. Order KPhos 30 Mmol IVC. Order KPhos 15 Mmol IVD. Order NeutraPhos 1 pkt QID

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Magnesium – the orphan ion

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Case 7

• 45 y/o man adm with alcohol withdrawal. On exam is confused, agitated, tremulous, and refuses to swallow pills. BP = 170/100, P = 120, T = 37. K = 3.2, Mg = 1.1, BUN = 9, creat = 0.9

• What do you order?

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Magnesium homeostasis – principles

• No hormones regulate urinary magnesium excretion, and equilibration of circulating Mg with bone stores is slow (weeks)

• Plasma Mg is major regulator of urinary Mg excretion

• Diuretics, PO4 depletion and metabolic acidosis can alter urinary Mg transport

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Hypomagnesemia: common causes• Pancreatitis – saponification in necrotic fat• GI losses (upper GI losses > lower GI losses)– Diarrhea, malabsorption, small bowel bypass• Renal losses– Meds: diuretics, nephrotoxins, PPI– Alcohol– Uncontrolled diabetes– Hypercalcemia– Recovery from ATN, post-obstructive diuresis, after renal

transplant

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Hypomagnesemia: adverse effects

• Tetany, convulsions, delirium

• Hypocalcemia, hypokalemia

• Arrythymias

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Hypomagnesemia: Principles of treatment

• Guidelines vary and are not evidence-based; instructions often given in mEQ, but measurements and drugs in mg or mmol

• Abrupt elevation removes renal stimulus to magnesium reabsorption; cellular uptake is slow – up to 50% of IV dose is excreted

• IV Mg is safe in pts with functional kidneys• Urgency driven by clinical manifestations

– Sxs, Other electrolyte disturbances (K, Ca)08/07/2014 Electrolyte problems in the hospital 50

Hypomagnesemia: Pierce treatment opinions

• Caution if GFR < 30; very cautious if GFR < 15• If tetany or ventricular arrhythmias – give 1 - 2

gm IV over few mins, repeat every 6 hours until Mg > 1 mg/dL for 3 days

• For asxtic pts can give oral replacement– Mg = 1.0 - 1.2; Mg-Ox 400 mg daily– Mg = 0.5 – 0.9; Mg-Ox 400 mg BID– Mg < 0.5; Mg-Ox 400 mg TID

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Case 7

• 45 y/o man adm with alcohol withdrawal. On exam is confused, agitated, tremulous, and refuses to swallow pills. BP = 170/100, P = 120, T = 37. K = 3.2, Mg = 1.1, BUN = 9, creat = 0.9

• What do you order?• Mag sulfate 2 gr IV increment, repeat K and Mg

tomorrow

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