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

Patient Case

Questions 4 and 5 pertain to the following case.

A 65-year-old man (weight 87 kg) is admitted to the hospital with severe acute pancreatitis. A computed tomog-

raphy (CT) scan of the abdomen reveals a pancreatic pseudocyst. He is to remain NPO (nothing by mouth)

because of marked abdominal pain on a low-fat diet and during a trial of EN; therefore, he is given PN. He is a 2

pack/day tobacco smoker and has a history of frequent alcohol consumption. His serum laboratory values are as

follows: sodium (Na) 139 mEq/L, potassium (K) 3.3 mEq/L, Cl 102 mEq/L, total CO2 content 25 mEq/L, BUN

14 mg/dL, SCr 0.8 mg/dL, calcium 7.6 mg/dL, phosphorus 2.2 mg/dL, magnesium 1.5 mg/dL, and albumin 2.5

g/dL.

Which potassium-phosphorus dosing regimen would be most appropriate for this patient?

tube x 2 doses.

venously x 1 dose.

doses.

In addition to potassium and phosphorus supplementation, the patient is given magnesium sulfate 6 g intra-

venously for 6 hours. His repeat serum magnesium the next day is 2.0 mg/dL. Which therapeutic option

would be best for this patient?

Calcium homeostasis overview

Most prevalent intracellular cation in body; 99% of body’s calcium is in bone; highly protein bound

in plasma

Total body stores: About 1–1.2 kg of calcium

Normal serum concentration: 8.5–10.5 mg/dL; normal serum ionized concentration 1.12–1.32

mmol/L

Changes in plasma albumin concentration – For every 1 g/dL in serum albumin below 4 g/

dL, serum calcium will decrease by around 0.8 mg/dL (Clin Chim Acta 1971;35:483-9). This

estimation of serum calcium concentrations is inaccurate in critically ill patients and should

not be used (JPEN J Parenter Enteral Nutr 2004;28:133-41). Ionized calcium concentrations

should be used for assessing calcium in critically ill patients. However, most critically ill

patients (85%) with a total serum calcium concentration less than 7 mg/dL are hypocalcemic

ii.

Changes in pH (for every 0.1-unit increase in arterial pH, serum ionized calcium will decrease

by about 0.05 mmol/L) (Arch Pathol Lab Med 2002;126:947-50) because of increased protein

binding