Lytes

Question 1

How do you calculate percentage of total body water?

Answer 1

• males: BW x 0.6
• females: weight x 0.5

Question 2

What percentage of total body water is intracellular, extracellular, and intravascular?

Answer 2

• ⅔ is intracellular
• ⅓ is extracellular (¼ of this is intravascular)

Question 3

What is an individuals total blood volume?

Answer 3

• pediatric: 80cc/kg
• adult 70cc/kg

Question 4

What maintenance fluid is preferred for neonates and why?

Answer 4

D5 ¼ NS + 20mEq K due to their decreased ability to concentrate urine

Question 5

What are the contents of lactated ringers?

Answer 5

• 130 mEq Na
• 4 mEq K
• 2.7 mEq Ca
• 109 mEq Cl
• 28 mEq HCO3

Question 6

What are the contents of normal saline?

Answer 6

154mEq Na and 154mEq Cl

Question 7

How much sodium does an average person need a day? Potassium?

Answer 7

• sodium is 1-2 mEq/kg
• potassium is 0.5-1 mEq/kg

Question 8

How is FENa calculated?

Answer 8

(UNa/SNa) / (UCr/SCr)

Question 9

How is serum osmolality calculated?

Answer 9

• 2Na + glucose/18 + BUN/2.8
• simplies to 2Na + 10

Question 10

How is sodium deficit calculated?

Answer 10

(140 - actual) x TBW

Question 11

How is free water deficit calculated?

Answer 11

TBW x {(actual Na - 140)/140}

Question 12

What do labs look like for diabetes inspidus?

Answer 12

• high serum osmolality
• low urine osmolality
• high serum Na

Question 13

How can you distinguish central from peripheral DI?

Answer 13

give DDAVP, central patients will respond

Question 14

How are neurogenic and nephrogenic diabetes insipidous managed?

Answer 14

• neurogenic: vasopressin, DDAVP
• nephrogenic: free water supplementation, thiazide diuretic

Question 15

What EKG abnormality is seen with hypoCa?

Answer 15

prolonged QT interval

Question 16

What are common symptoms associated with hypocalcemia?

Answer 16

• weakness
• paresthesia
• anxiety
• cramping
• seizures
• chovstek’s sign (perineal twitching with facial nerve tapping)
• trosseau’s sign (carpal-pedal spasm with BP cuff inflation)
• heart block, torsades

Question 17

What is the most common cause of hypercalcemia?

Answer 17

• outpatient: hyperparathyroidism
• inpatient: malignancy

Question 18

What are the symptoms and management of hypercalcemia?

Answer 18

• “stones, bones, groans, thrones, and psych overtones”
• renal stones, bone pain, abdominal pain, constipation, psychosis
• create with NS volume expansion, loop diuretics, bisphosphonates, calcitonin, glucocorticoids, and dialysis

Question 19

Hypomagnesemia most commonly causes what EKG abnormality?

Answer 19

• prolonged QT is most common
• can progress to torsades

Question 20

How is anion gap calculated? What’s normal?

Answer 20

• gap = Na + K - Cl - HCO3
• normal < 12

Question 21

Vomiting leads to what electrolytes abnormalities?

Answer 21

hypokalemic, hypochloremic, metabolic alkalosis

Question 22

What cation primarily determines serum osmolality?

Answer 22

sodium

Question 23

What is the primary intracellular cation?

Answer 23

potassium

Question 24

What are the three most common electrolyte abnormalities seen in those with re-feeding syndrome?

Answer 24

• hypophosphatemia
• hypokalemia
• hypomagnesemia

Question 25

A baby with pyloric stenosis will present with what electrolyte abnormalities?

Answer 25

- hypochloremic - hypokalemia - metabolic alkalosis (paradoxical aciduria where Na reabsorption and K secretion leads to proton secretion in urine)

Question 26

Acidosis does what to the oxygen dissociation curve?

Answer 26

shifts it to the right, allowing easier unloading of O2

Question 27

Diarrhea causes what electrolyte abnormality?

Answer 27

hypokalemic metabolic acidosis (non-gap)