FLUIDS AND ELECTROLYTES

Question 1

Low urinary fractional excretion of sodium, high
urine osmolality, high serum osmolality

Answer 1

Dehydration

Question 2

Low urine osmolality, high serum sodium, and
serum osmolality (urine osmolality < serum
osmolality)

Answer 2

Diabetes insipidus

Question 2

High urinary fractional excretion of sodium, low
serum sodium, low serum osmolality,
inappropriately high urine osmolality

Answer 2

Syndrome of inappropriate ADH secretion
(SIADH)

Question 3

Low serum and urine osmolality

Answer 3

Primary polydipsia

Question 4

Child with mild to moderate dehydration because of diarrhea, able to drink with no emesis. What is the best treatment?

Answer 4

Oral rehydration solution (ORS)

Question 5

What is the mechanism of action of ORS?

Answer 5

Sodium-glucose transporter in the gut
(co-transports one sodium with one glucose)

Question 6

Child with moderate dehydration, no emesis, and low serum potassium (K) level 2.6 mEq/L. No other symptoms. What is the best treatment?

Answer 6

ORS and oral K chloride supplementation (oral
replacement is better than IV if tolerating oral
intake)

Question 7

Child with vomiting, weakness, lethargy,
moderate-severe dehydration, and low serum
potassium (K) level 2.6 mEq/L. What is the best
treatment?

Answer 7

IV bolus 20 ml/kg normal saline, then IV fluids
and electrolyte replacement

Question 8

Based on the Holliday-Segar method, what is the maintenance fluid rate for 45 kg child?

Answer 8

First 10 kg × 4 = 40
2nd 10 Kg × 2 = 20
25 kg × 1 = 25
40 + 20 + 25 = 85 ml/h

Question 9

A 12-month-old girl with 4 days of frequent
watery stool; she is listless. O/E: dry mucous
membrane, skin is tenting, HR 150, BP
85/45 mmHg. Weight 8.5 kg. Weight before illness 10 kg, serum Na 136 mEq/dL. 200 mL of NS given IV. What is the most appropriate IV fluid and rate for this child?

Answer 9

D5 ½ NS +KCl 40 meq/L to run at 95 mL/h
(15% dehydration; fluid deficit is 1500 + 1000
(maintenance—200 (bolus) = 2300/24 h = 95 ml/h)

Question 10

A 12-month-old girl with 4 days of frequent watery stool, she is listless. O/E: dry mucous
membrane, skin is tenting, HR 170, BP 80/40 mmHg. Weight 8 kg. Weight before illness 10 kg, serum Na 136 mEq/dL. 200 mL of NS given IV. What is the most appropriate IV fluid and rate for this child?

Answer 10

D5 ½ NS + KCl 40 meq/L to run at 116 mL/h
(20% dehydration; fluid deficit is 2000 + 1000
(maintenance—200 (bolus) = 2800/24 h =
116 ml/h)

Question 11

A quick calculation in the previous case?

Answer 11

The maintenance rate for a 10 kg child = 40 ml/h
→ triple the maintenance rate in 20% dehydration → 120 ml/h (close to 116)

Question 12

A quick calculation of IV fluid rate in 5%
dehydration

Answer 12

1½ times the maintenance rate

Question 13

A quick calculation of IV fluid rate in 10%
dehydration

Answer 13

Double the maintenance

Question 14

A quick calculation of IV fluid rate in 15%
dehydration

Answer 14

2 ½ times the maintenance rate

Question 15

What is the advantage of ORS over other fluid
options?

Answer 15

Low carbohydrate, high sodium and potassium
(minimizing osmotic loads that drive more
diarrhea)

Question 16

What is a normal anion gap?

Answer 16

Na+ – (Cl– + HCO3 –) = 10–12 mEq/L

Question 17

What are the causes of anion gap metabolic
acidosis?

Answer 17

Methanol poisoning, Uremia, DKA, Paraldehyde, Iron toxicity, INH, Lactic acidosis, Ethylene glycol, Salicylate poisoning (MUD PILES)

Question 18

What are the causes of non-anion gap metabolic acidosis?

Answer 18

Renal tubular acidosis Diarrhea Chronic total parenteral nutrition (TPN) Acetazolamide (carbonic anhydrase inhibitor)

Question 19

A 3-week-old boy with projectile vomiting after
each feed, dehydration, metabolic alkalosis,
hypochloremia, hypokalemia, oliguria, and low
urinary chloride (< 20 mEq/L)

Answer 19

Pyloric stenosis (metabolic alkalosis and low
urine chloride)

Question 20

Child with bloody diarrhea, high fever, weakness, edema, oliguria, BUN 80 mg/dL, creatinine 5 mg/ dL, K level is 7.5 mg/dL. EKG shows a widening of QRS complexes and an increased PR interval. What is the best management?

Answer 20

Intravenous calcium gluconate, glucose, and
insulin, beta agonists, cation exchange resins
(sodium polystyrene sulfonate), until dialysis
can be initiated

Question 21

What is the earliest EKG manifestations in cases of mild hyperkalemia?

Answer 21

Tall and peaked T waves

Question 22

What is the EKG manifestation in cases of
moderate hyperkalemia?

Answer 22

Widening of QRS complexes and an increased
PR interval

Question 23

What is the EKG manifestation in cases of severe hyperkalemia?

Answer 23

Broad and low amplitude P waves, a prolonged
QT interval, and ST-segment changes (elevation
or depression)

Question 24

What is the EKG manifestation in cases of severe hyperkalemia?

Answer 24

Broad and low amplitude P waves, a prolonged
QT interval, and ST-segment changes (elevation
or depression

Question 25

What is the EKG manifestation of hyperkalemia
> 8 mEq/L?

Answer 25

Gradually widening QRS complexes and absent
P waves → ventricular fibrillation or asystole