Fluids, Electrolytes, Acid-Base Disorders, and Nutrition Support

Answer: D

Answer D, additional magnesium therapy should be

given daily for the next 4–5 days, is correct because it

takes 48 hours for magnesium to equilibrate after a short-

term infusion, making Answer A incorrect. Although

Answer B is common in clinical practice, failure to pro-

vide additional magnesium repletion in the setting of a

normal serum magnesium concentration the day after

a large intravenous dosage usually causes serum con-

centrations to decrease below the normal range again

over the next 1–2 days as magnesium equilibrates. Thus,

Answer B is not ideal management and is incorrect.

Answer C is incorrect because hypocalcemia should

autocorrect with magnesium supplementation within 48

hours of magnesium therapy; however, calcium therapy

can be given concurrently, if necessary (symptomatic or

ionized calcium concentration less than 1 mmol/L).

Answer: D

The current PN formula prescribed provides 3240 kcal/

day (42 kcal/kg/day with a glucose infusion rate of 5.8

mg/kg/minute), which is an excessive amount of energy

for this patient, and he has possible signs of overfeed-

ing in the form of hyperglycemia. Answer D is correct

because decreasing the dextrose dose to 315 g would

appropriately bring the patient’s energy down to 2101

kcal/day (27 kcal/kg/day with a glucose infusion rate

of 2.8 mg/kg/minute). An initial energy goal of 25–30

kcal/kg/day is appropriate for this patient, and by sig-

nificantly decreasing the dextrose and total energy load

provided in the PN, his hyperglycemia should improve.

Answer A is incorrect because the additional insulin

will not address the issue of overfeeding, and sliding-

scale insulin is unlikely to provide adequate glycemic

control for this patient. Answer B is incorrect because

temporarily adjusting the dextrose dose will not correct

the issue of overfeeding in the long term. Answer C is

incorrect because the total energy provided with these

changes would still provide 37 kcal/kg/day and exceed

the appropriate initial goal of 25–30 kcal/kg/day.

Answer: B

This patient’s pH is high at 7.46 mmHg so his primary

disorder is an alkalosis (Answer D is incorrect). His

serum HCO3 is 20 mEq/L (low) and Pco2 is 31 mmHg

(low). His high pH and low Pco2 indicate that his pri-

mary disorder is a respiratory alkalosis (Answer C is

incorrect). However, his laboratory values reveal an AG

of 19 (141 − 102 − 20 = 19), which indicates that a meta-

bolic acidosis is present, regardless of his pH or HCO3

values (Answer A is incorrect). His delta ratio is 1.25

([19−14] / [24−20]), which indicates that an AG meta-

bolic acidosis is present with no other hidden metabolic

process. Answer B is correct.