Ed Rivers, a 3rd year medical student, was alone in the hospital ER .pdf
Ed Rivers, a 3rd year medical student, was alone in the hospital ER one night. It was unusually quiet that night, and the resident was getting some much needed sleep. A patient, Mrs. X, was brought in showing signs of serious dehydration. Ed tried to give her water, but she vomited this back up. Feeling he must try something, and not wanting to wake the resident, Ed administered 1 liter of sterile distilled water IV. Assume for simplicity that the red blood cells contain only solutes to which the rbc membrane is impermeable, and that the rbcs and plasma are in osmotic equilibrium when the patient is brought in. The osmolarity of the rbc is 300 mOsm/L.The volume of Mrs. X’s plasma was 3 liters before Ed administered the IV. Had Ed given Mrs. X a sucrose solution instead of water, he might have helped her. What concentration of sucrose solution should he have administered to leave her rbc volume unaffected, and why? Solution 1L of sterile distilled water IV is added to the plasma but no mixing with her interstitial fluid and before any water entered her RBC’s. Therefore simple calculation, (3+1)L*X mOsm/L =3*300mOsm/L X=225, so her plasma osmolarity after the infusion mixed with her plasma would be 225mOsm/L Blood volume is RBC volume+Plasma volume. It says \"came to equilibrium\" so the RBC volume&Plasma volume would have the same osmolarity. Equilibrium osmolarity=300*2/(2+X)=225*4/(4-X). Therefore X=0.4 and the RBC volume change would be 0.4L. Her blood osmolarity was 300mOm/L so she should have been given a 300mOm/L sucrose solution Her total Blood volume is 6L now and the osmolarity is 250mOsm/L. Therefore we should alter this osmolarity back to 300mOsm/L which is the normal number. The equation would be (6*250+1*X)/(6+1)=300. X=600, so 1L of 600mOsm/L of sucrose solution should be administered..
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Ed Rivers, a 3rd year medical student, was alone in the hospital ER .pdf
- 1. Ed Rivers, a 3rd year medical student, was alone in the hospital ER one night. It was unusually quiet that night, and the resident was getting some much needed sleep. A patient, Mrs. X, was brought in showing signs of serious dehydration. Ed tried to give her water, but she vomited this back up. Feeling he must try something, and not wanting to wake the resident, Ed administered 1 liter of sterile distilled water IV. Assume for simplicity that the red blood cells contain only solutes to which the rbc membrane is impermeable, and that the rbcs and plasma are in osmotic equilibrium when the patient is brought in. The osmolarity of the rbc is 300 mOsm/L.The volume of Mrs. X’s plasma was 3 liters before Ed administered the IV. Had Ed given Mrs. X a sucrose solution instead of water, he might have helped her. What concentration of sucrose solution should he have administered to leave her rbc volume unaffected, and why? Solution 1L of sterile distilled water IV is added to the plasma but no mixing with her interstitial fluid and before any water entered her RBC’s. Therefore simple calculation, (3+1)L*X mOsm/L =3*300mOsm/L X=225, so her plasma osmolarity after the infusion mixed with her plasma would be 225mOsm/L Blood volume is RBC volume+Plasma volume. It says "came to equilibrium" so the RBC volume&Plasma volume would have the same osmolarity. Equilibrium osmolarity=300*2/(2+X)=225*4/(4-X). Therefore X=0.4 and the RBC volume change would be 0.4L. Her blood osmolarity was 300mOm/L so she should have been given a 300mOm/L sucrose solution Her total Blood volume is 6L now and the osmolarity is 250mOsm/L. Therefore we should alter this osmolarity back to 300mOsm/L which is the normal number. The equation would be (6*250+1*X)/(6+1)=300. X=600, so 1L of 600mOsm/L of sucrose solution should be administered.