A 66-year-old man is brought to the emergency department with dyspnea, tachypnea, crampy pain, and paresthesias in his extremities. He arrived home a few hours after a long international flight. His temperature is 36.7 C (98.5 F), blood pressure is 120/80 mm Hg, pulse is 88/min, and respirations are 26/min. Physical examination is significant for carpopedal spasm and left calf swelling. CT scan reveals a segmental pulmonary embolus. Which of the following alterations in calcium metabolism is most likely present in this patient?

Question

A 66-year-old man is brought to the emergency department with dyspnea, tachypnea, crampy pain, and paresthesias in his extremities.  He arrived home a few hours after a long international flight.  His temperature is 36.7 C (98.5 F), blood pressure is 120/80 mm Hg, pulse is 88/min, and respirations are 26/min.  Physical examination is significant for carpopedal spasm and left calf swelling.  CT scan reveals a segmental pulmonary embolus.  Which of the following alterations in calcium metabolism is most likely present in this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d3bf_2934_bc81_a5bed066a753_MD0003_00 This patient with a pulmonary embolism likely resulting in hyperventilation and respiratory alkalosis also has signs and symptoms of hypocalcemia (eg, crampy pain, paresthesias, carpopedal spasm). Plasma calcium exists in 3 forms: Ionized calcium (45%) Albumin-bound calcium (40%) Calcium bound to inorganic and organic anions (15%) Homeostasis of these forms is significantly influenced by the extracellular pH level. An increased extracellular pH (due to respiratory alkalosis in this patient) causes hydrogen ions to dissociate from albumin molecules, thereby freeing up the albumin to bind with calcium. This increased affinity of albumin for calcium leads to decreased levels of ionized calcium. In contrast, acidosis (decreased extracellular pH) would cause increased levels of ionized calcium (Choice A). Because ionized calcium is the only physiologically active form, a decrease in ionized calcium can result in the clinical manifestations of hypocalcemia even though total calcium is unchanged (Choices C and F). (Choices B and E) The amount of calcium bound to organic and inorganic anions remains unaltered in patients with acute respiratory alkalosis. Educational objective: Increased extracellular pH (eg, respiratory alkalosis) causes dissociation of hydrogen ions from albumin, allowing increased binding of calcium and a drop in unbound (ionized) calcium. Ionized calcium is the physiologically active form, and decreased levels can result in clinical manifestations of hypocalcemia.

A 66-Year-Old Man Is Brought to the Emergency Department with Dyspnea