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Drive 9 47 PM Mon Jan 21 30% Case Study Questions Dehydration is a serious and common condition. It changes body fluid volumes and can change body fluid composition and concentration. This can result in the redistribution of fluid between compartments. This problem deals with osmosis between red blood cells and ECF A patient was admitted to the ER late at night. The residents were asleep leaving a 3nd year medical student (Jim Stephens) on duty. The patient (Ms. Dry) was showing signs of severe dehydration. Jim tried to give her water by mouth but she immediately vomited. The ER had runout of premixed IV bags due to reduced production from facilities in Puerto Rico after Hurricane Maria. Not wanting to wake the residents and wanting to do something for the patient, Jim prepared a glass IV bottle and administered 1 liter of sterile distilled water by IV. The questions in the problem are aimed at determining the consequences of Jim's action. Assume for simplicity that red blood cells contain only solutes to which the RBC membrane is impermeable or Non Penetrating. The osmolarity of the RBC, the concentration of solute particles, is 300 mOsm/L.(hint: this is a starting condition) 1. Predict the change (increase, decrease, no change) you would expect Jim's infusion to have produced in the listed parameters. Explain your prediction a. Ms. Dry's plasma osmolarity after the infusion i. Prediction i. Explanation Ms. MB's RBC volume after the infusion equilibrates with blood. redci Explanationn C. The volume of Ms. Dry's plasma was 3L (hint: a starting condition) before Jim administered the IV. For simplicity of calculations, assume that there was complete mixing of the administered water with her plasma but no mixing with her interstifuid. Calculate Ms. Dry's plasma osmolarity after the infusion mixed with her plasma but before any water entered her RBC D.Assume that Ms. Dry's RBC volume (total) was 2L (hint: starting condiion) before the IV was given. Calculate her plasma and RBC osmolarity after the infused water equilibrated between her plasma and her RBC. How much would her RBC volume change? (again, assume that there was no mixing with her inte fuid.)

Answer 1

1.a) i. Prediction - After the infusion of one literacy sterile water by IV ,it will lead to decrease in the plasma osmolarity of the patient Mr. Dry.

a) ii. Explanation - when sterile water is infused it leads to transport of solute free water through tubular cells and back into blood ,it leads to decease in plasma osmolarity and increased urine osmolarity .

2. Mr. MB's RBC volume increases after infusion of sterile water. The infused sterile water expand the plasma volume and dilute the plasma osmolarity . The RBC osmolarity would decrease and plasma osmolarity would increase until the two solutions are equal

C. Total number of mOsm in the plasma = 300 mOsm

3liter is equal to 900 mOsm

After the infusion ,the plasma volume is 4L ( but still have 900mOsm ) . Therefore, the new plasma volume is 225 mOsm / L .

D. The osmolarity at equilibrium is = total mOsm / total volume

600 mOsm ( RBC ) + 900 mOsm ( plasma) = 1500mOsm

The total volume is 2L+ 3L+ 1L = 6L .

So, osmolarity is 1500 / 6 = 250 mOsm .

The new RBC volume is 600mOsm / 250mOsm = 2.4 L

and the plasma volume is 6L - 2.4 L = 3.6L