A 38-year-old man is brought to the emergency department due to progressive nausea, confusion, and unsteady gait. Family members state that symptoms started 4 days ago after he went to the dentist due to a toothache, for which he was prescribed ibuprofen. He also takes lithium for bipolar disorder. On examination, he is drowsy and ataxic, having slurred speech and coarse tremors. His serum lithium level is 3.86 mEq/L (therapeutic range: 0.8-1.2 mEq/L), and serum creatinine and blood urea nitrogen are elevated. While in the emergency department, he develops a generalized tonic-clonic seizure. During emergent hemodialysis treatment, his blood is passed along a semipermeable membrane and allowed to equilibrate with a dialysate solution. Which of the following is most likely to increase the rate of drug removal?

Question

A 38-year-old man is brought to the emergency department due to progressive nausea, confusion, and unsteady gait.  Family members state that symptoms started 4 days ago after he went to the dentist due to a toothache, for which he was prescribed ibuprofen.  He also takes lithium for bipolar disorder.  On examination, he is drowsy and ataxic, having slurred speech and coarse tremors.  His serum lithium level is 3.86 mEq/L (therapeutic range: 0.8-1.2 mEq/L), and serum creatinine and blood urea nitrogen are elevated.  While in the emergency department, he develops a generalized tonic-clonic seizure.  During emergent hemodialysis treatment, his blood is passed along a semipermeable membrane and allowed to equilibrate with a dialysate solution.  Which of the following is most likely to increase the rate of drug removal?

Quizplus · Accepted Answer

11ec160b_3cfa_2382_9249_437be1fce28f_MD0001_00 This patient is presenting with severe lithium toxicity secondary to his recent NSAID use and requires urgent hemodialysis to lower his blood lithium levels. Multiple factors affect the rate of molecular diffusion across a semipermeable membrane separating 2 well-mixed compartments. The number of molecules that cross the membrane per second is proportional to the molecular concentration difference across the membrane, the surface area of the membrane, and the solubility of the substance. Diffusion is inversely proportional to the total membrane thickness and the molecular weight of the molecule. (Choice A) Adding lithium to the dialysate will decrease the concentration gradient between the dialysate and the patient's plasma. This would decrease the diffusion rate of lithium across the membrane. (Choice B) Diffusion rate generally increases with temperature due to increased molecular movement speed and increased macromolecule solubility. (Choices C and E) A decrease in membrane pore size would slow or prevent diffusion of larger molecules across the membrane. Increasing membrane thickness would also decrease diffusion rate. Educational objective: Diffusion speed across a semipermeable membrane increases with higher molecular concentration gradients, larger membrane surface areas, and increased solubility of the diffusing substance. Diffusion speed decreases with increased membrane thickness, smaller pore size, higher molecular weights, and lower temperatures.

A 38-Year-Old Man Is Brought to the Emergency Department Due