For the following clinical scenario, predict the possible effect on a patient’s
ID: 51679 • Letter: F
Question
For the following clinical scenario, predict the possible effect on a patient’s erythrocytes. You need to memorize that the osmolarity of an erythrocyte (and the human body in general) is 300mOsm. Justify your answers by:
A. Calculating mM for ICF and ECF
B. Calculating mOsM for ICF and ECF
C. Determine the osmolarity of the solution
D. Determine the tonicity
E. Determine the permeability of the solute (permeable or impermeable)
F. Determine if diffusion is occurring and in what direction
G. Determine if osmosis is occurring and in what direction
SCENARIO:
A patient is administered an IV solution of 5% dextrose (dextrose is a synonym for glucose), which is approximately iso-osmotic to erythrocytes. Glucose does not dissociate, but it will transport across the erythrocyte membrane and be used in glycolysis (a reaction where glucose is broken down and used as an energy source to generate ATP, which is the energy molecule that directly powers cell activities).
Explanation / Answer
C. The 5% dextrose solution is isotonic to erythrocytes and it does not cause hemolysis. One liter of 5% dextrose solution contains 50 grams of glucose. One molar solution of dextrose contains 180 grams of glucose. So, 50 grams of dextrose in one litre solution equals to 0.278 molar solution. Thus, the osmolarity of 5% dextrose solution is 278 mosm/L.
D. The osmolarity of an erythrocyte (and the human body in general) is 300mOsm. So, 5% dextrose solution is almost isotonic or sligtly hypotonic to the erythrocytes when initially administered. As glucose is rapidly takenup by the cells, the solution becomes more hypotonic with respective to the surrounding plasma. Thus, fluid enters ICF from ECF.
E. Solute (dextrose or d- glucose) is permeable.
F. Glucose is rapidly takenup by the cells. So, diffusion of fluid to the intracellular and extracellular fluids occur. 2/3rd fluid reaches ICF and 1/3rd reaches ECF.
G. The osmolarity of plasma decreases. Infusion of 1 L of 5% dextrtose solution may result in a 2.5% decrease in osmolarity or 7 mOsm/L is observed.