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

concentration of less than or equal to 1.5 mg/dL is more

likely to contribute to the pathogenesis of hypocalce-

mia. Answer B is incorrect because a urine output of 0.5

mL/kg/hr is not excessive.

Answer: B

A short-term intravenous infusion of 4 g of calcium glu-

conate (1 g = 4.6 mEq) for 4 hours has been shown to

be a safe and effective therapeutic regimen for moder-

ate to severe hypocalcemia (ionized calcium less than 1

mmol/L) (Answer B is correct). Answer A is incorrect

because it is an insufficient dosage of elemental calcium.

A bolus/push dose of calcium chloride (1 g = 13.6 mEq),

as given in answer C, would be an effective means for

treating symptomatic severe hyperkalemia, but it would

be unnecessarily aggressive for treating hypocalcemia

in this patient scenario. Answer D is incorrect because

the moderate to severe hypocalcemia should be cor-

rected in this post-operative trauma patient who is

anemic and at high risk for bleeding complications.

Answer: A

Examination of the pH indicates that the patient has an

acidemia because it is lower than 7.35. Looking at Pco2

and serum bicarbonate would indicate that the primary

etiology is metabolic because both are low. Calculation

of the AG (145 − 118 − 18 =9) shows that no AG is present

(Answers B and C are incorrect). A correction for serum

albumin concentration is not needed because it is nor-

mal. The serum lactate is near the high end of the normal

range but still within the normal range. This would indi-

cate that the patient’s dehydration has not become so

extreme that a significant decrease in tissue perfusion

was not evident (yet). Respiratory compensation appears

to be intact ([1.5 x 17] + 8 = 33 vs. 34 mm Hg) on the

blood gas, and it appears that the patient’s history of

smoking did not compromise her ability to mount a rea-

sonable respiratory response to the acidosis. The serum

chloride of 118 mEq/L indicates hyperchloremia. A

non-AG hyperchloremic metabolic acidosis is common

for patients with severe diarrhea. The low serum potas-

sium and magnesium would also strongly suggest that

the patient has significant diarrhea (Answer A is correct).

Answer D is incorrect because the decreased Pco2 is in

response to the metabolic acidosis and the patient does

not have a metabolic alkalosis but rather an acidosis.

Answer: C

Initial therapy with lactated Ringer solution would

be the ideal choice (Answer C is correct). Treatment

with 0.9% sodium chloride (Answer B) is incorrect

because it would worsen the hyperchloremic acidosis.

A 5% dextrose solution (Answer D) would be a poor

choice because sodium/isotonic fluids are necessary

to restore intravascular volume. Because the severity

of the patient’s acidemia is mild (pH 7.29), aggressive

therapy with sodium bicarbonate is not indicated.

After the first day of lactated Ringer solution to restore

intravascular volume and improve pH, it would be rea-

sonable to change to 0.45% sodium chloride to continue

to restore volume depletion, depending on the patient’s

response to the lactated Ringer solution (e.g., restora-

tion of normal pH, adequate urine output, resolution

of tachycardia). Thus, answer A would be incorrect as

the question asked for the most appropriate initial treat-

ment. Of course, aggressive potassium and magnesium

repletion is indicated as well. This could be done with

infusions as previously discussed, and it would be rea-

sonable to add 20 mEq of potassium chloride per liter to

the 0.45% sodium chloride upon discontinuation of the

lactated Ringer solution.

The current PN regimen provides 61 kcal/kg/day total

(glucose 6.1 mg/kg/minute and lipid emulsion 1.5 g/

kg/day) and protein 4 g/kg/day. The PN regimen rep-

resents gross overfeeding of this small woman and can

explain her hyperglycemia and hypercapnia. Cutting

all macronutrients by about one-half would result in a

more reasonable regimen for this patient: 30 kcal/kg/

day (glucose 3 mg/kg/minute and lipid emulsion 0.8 g/

kg/day) and protein 2 g/kg/day. Because she is so small

(weight 40 kg), it would be important to double-check

the weight-based calculation to see whether this new

regimen is appropriate to meet her caloric needs without

overfeeding by calculating the BEE using the Harris-

Benedict equation for women (caloric intake should not

exceed 1.3–1.5 x BEE for a critically ill patient with

traumatic injuries) (Answer C is correct). Although

answer A reduces the respiratory quotient of the nutri-

ent admixture, this will not solve the primary problem

of overfeeding the patient because excessive calories

are being provided. Answers B and D may help with

the consequences of overfeeding (e.g., hyperglycemia

and respiratory acidosis) but do not address the primary