Ed Rivers, a 3rd year medicalstudent, was alone in the hospital ER one night. It was unusuallyquiet that night, and the resident was getting some much neededsleep. A patient, Mrs. X, was brought in showing signs of seriousdehydration. Ed tried to give here water, but she vomited this backup. Feeling he must try something, and not wanting to wake theresident, Ed administered 1 liter of sterile distilled water IV.Assume for simplicity that the red blood cells contain only solutesto which the rbc membrane is impermeable, and that the rbcs andplasma are in osmotic equilibrium when the patient is brought in.The osmolarity of the rbc is 300 mOsm/L.
2. The volume of Mrs. Xââ¬â¢s plasma was 3liters before Ed administered the IV. Assume that there was acomplete mixing of the administered water with her plasma but nomixing with her interstitial fluid. Calculate Mrs. Xââ¬â¢s plasmaosmolarity after the infusion mixed with her plasma but before anywater entered the rbcs.
Hint: What was the total # of mOsmin her plasma before the infusion? Once the plasma volume isincreased by 1 L, the total # of mOsm remains the same, but thevolume has changed. Now what is the new osmolarity (mOsm/L?) Doesthis fit your prediction, above?
Mrs. X got much worse after the Edââ¬â¢streatment, so the resident was called. She drew some blood from thepatient and centrifuged it. The supernatant above the packed rbcswas pink. The resident then decided to infuse a sucrose solutioninto the patient (the rbc membrane is impermeable to sucrose).
3. Why was the plasma pink?
4. Had Ed given Mrs. X a sucrose solutioninstead of water, he might have helped her. What concentration ofsucrose solution should he have administered to leave her rbcvolume unaffected?
Ed Rivers, a 3rd year medicalstudent, was alone in the hospital ER one night. It was unusuallyquiet that night, and the resident was getting some much neededsleep. A patient, Mrs. X, was brought in showing signs of seriousdehydration. Ed tried to give here water, but she vomited this backup. Feeling he must try something, and not wanting to wake theresident, Ed administered 1 liter of sterile distilled water IV.Assume for simplicity that the red blood cells contain only solutesto which the rbc membrane is impermeable, and that the rbcs andplasma are in osmotic equilibrium when the patient is brought in.The osmolarity of the rbc is 300 mOsm/L.
2. The volume of Mrs. Xââ¬â¢s plasma was 3liters before Ed administered the IV. Assume that there was acomplete mixing of the administered water with her plasma but nomixing with her interstitial fluid. Calculate Mrs. Xââ¬â¢s plasmaosmolarity after the infusion mixed with her plasma but before anywater entered the rbcs.
Hint: What was the total # of mOsmin her plasma before the infusion? Once the plasma volume isincreased by 1 L, the total # of mOsm remains the same, but thevolume has changed. Now what is the new osmolarity (mOsm/L?) Doesthis fit your prediction, above?
Mrs. X got much worse after the Edââ¬â¢streatment, so the resident was called. She drew some blood from thepatient and centrifuged it. The supernatant above the packed rbcswas pink. The resident then decided to infuse a sucrose solutioninto the patient (the rbc membrane is impermeable to sucrose).
3. Why was the plasma pink?
4. Had Ed given Mrs. X a sucrose solutioninstead of water, he might have helped her. What concentration ofsucrose solution should he have administered to leave her rbcvolume unaffected?
