Fluid and electrolytes

What happens to total body water?

decreases

less muscle (muscle holds water)

more fat (fat contains less water)

decrease renal function (can’t retain water

💧 Hydrophilic (water-loving) drugs

• Examples: aminoglycosides, ethanol, lithium

➡ Older adults have less body water.
➡ These drugs dissolve in water, so with less water, they have less space to spread out.
➡ This makes blood levels higher, so the drug is stronger and more toxic.

what happens to ANP with age?

increased = marker of HF

Hyponatremia level

Serum sodium < 135 mEq/L

causes of hyponatremia

sodium deprevation (low sodium diets) and kidneys are slow to respond

diuretics

SIADH (some meds cause syndrome of inappropriate ADH)

ADH - antidiuretic hormone. too much of it = too much water in body = dilutes out sodium

Hypernatremia level

serum sodium > 145 mEq/L

Causes of hypernatremia

impaired thirst sensation or lack of access to water`

Hypokalemia level

K < 3.5

Hyperkalemia level

K > 5

Drugs that cause hypokalemia

Loops and thiazide diuretics

Drugs that cause hyperkalemia

potassium sparing diuretics (MRAs, triamterene)

• spironolactone is recommended to dose low because it can accumulate

ACE/ARB

Potassium

salt substitutes

bactrim

what usually happens to sodium with surgery?

usually hyponatremia because of large fluid loads or blood transfusion products

what usually happens to potassium with surgery?

hypokalemia more often due to fluid overload.

what usually happens to magnesium with surgery?

hypomagnesemia due to fluid overload

If this __ is low, is it hard to correct potassium or calcium.

magnesium

What should you check if your calcium level is low?

albumin

(40% of calcium is bounded to albumin)

the calcium not bounded to albumin is called ionized calcium, too much of it can cause shortened QT, kidney stones, bone pain, confusion, lethargy

If albumin is low (like in malnutrition, liver disease, or chronic illness):

• The total calcium lab drops (because there's less albumin-bound calcium).

• But ionized calcium (active calcium) is unchanged → no symptoms of hypocalcemia.

what happens to magnesium with surgery

usually hypo with fluid overload

what happens to phosphate with surgery?

hypo due to fluid overload

At what level should you treat hypophosphatemia?

< 2 mg/dL

<1 = critical

phosphate is used to make energy

A decrease of serum potassium of 0.3 mEq/L is how much in body stores?

100 mEq (= replace this much per day via oral)

(200-400 if chronic hypokalemia)

How much magnesium should you give for every decrease of 0.5 mg/dL?

1 g

what should you do if Mg < 1?

replace with 4-8 g over 12 - 24 hours

what is the corrected calcium equation?

Correct calcium = calcium + 0.8 x (4-albumin)

BUN/creatinine. At what ratio do we suspect dehydration?

higher than 10-20:1

what is in lactated ringers and when should you not use it?

Na, K, Cl, Ca, lactate

don’t use if in alkalosis (lactate becomes bicarb = worsen alkalosis), hypercalcemia or hyperkalemia

For electrolyte replacement, which route is preferred?

oral

IV puts them at risk of injuring veins