Ed Rivers, a third-year medical student, was alone in the hospital emergency roo

ID: 32613 • Letter: E

Question

Ed Rivers, a third-year medical student, was alone in the hospital emergency room one night. It was unusually quiet in the ER, so the residents were getting some much-needed sleep. A patient, Ms. B., was brought in showing signs of serious dehydration. Ed tried to give her water but she vomited. Feeling that he must try something else and not wanting to wake the residents, he administered 1 liter (L) of sterile distilled water intravenously (IV).

The questions that follow are aimed at determining the consequences of Eds action. Assume for simplicity that red blood cells (RBC) contain only solutes to which the RBC membrane is impermeable. The osmolarity of the RBC, the concentration of solute particles, is 300 mOsm/L.

Predict the direction of change (Increase, Decrease, No Change) you would expect Eds infusion to have produced on and explain the reasoning for your answer

a)(2 points) Ms. Bs plasma osmolarity after the infusion ___________________________.

b)(2 points) Ms. Bs RBC volume after the infusion equilibrates with blood ____________________.

(In both cases be sure to explain your answer).

Ms. B. got much worse after Eds treatment so the head resident was called in. She drew blood from the patient and centrifuged it. The denser RBCs were forced to the bottom of the tube. The supernatant plasma was PINK!

a)(2 points) Why was the patients plasma pink?

b)(2 points) After seeing the supernatant the Head Resident gave the patient glucose. Why would this help?

Explanation / Answer

Ed Rivers took a wrong decision when he infused 1 liter (L) of sterile distilled water intravenously (IV) to the dehydrated patient Mrs. B.

Sterile water has little solute. Hence when this infusion equilibrates with Mrs. B's blood:

1a) Her osmolarity decreases as water enters into the RBCs to create balance between the high water level outside and low water level inside the RBC.

b) Mrs. B's RBC volume decreases as water rushes in and bursts the cell. This can be surmised due to the pink supernatant plasma which indicates a leak of the hemoglobin from the burst RBCs.

2 a) Mrs. B's plasma was pink which indicates a leak of the hemoglobin from the burst RBCs due to the hypotonic infusion of sterile distilled water unwisely administered by Ed.

b) When the Head Resident gave the patient glucose, it would help her as this would increase the solute concentration in her body which has reduced due to the distilled water infusion.

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Ed Rivers, a third-year medical student, was alone in the hospital emergency roo

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