Question

As a third year medical, you find yourself the only “doctor” on duty in the Emergency Room (ER) when the residents, having been working for 36 hours, are trying to catch some sleep. A 62 year old male patient has been brought into the ER that is severely dehydrated. Not wanting to disturb the residents, you tried to administer water orally, but the patient vomited. Realizing the emergency and need to hydration, you grab the first sterile fluid available to you, sterile water, and administer 1 liter intravenously (IV).

The questions that follow are to determine the consequences of your actions. Assume that the patient weighs 160 lbs with a hematocrit of 54%. The osmolarity of the patient’s blood before the infusion is 300 mOsm/L.

Predict the direction of change (increase, decrease or not change) you expect the infusion to have on the following parameters:

Prediction
Patient’s plasma osmolarity after the infusion:

Patient’s hematocrit after the infusion equilibrates with the patient’s blood:

Based on the patient’s weight, calculate their plasma volume before you administered the IV. Average blood volume in a male is 75 mL per Kg. (show calculations)

Plasma volume (Liters) ____________
Use this number to calculate the osmolality of the patient’s blood after the IV. (show calculations)

Osmolality (mOsm/L)___________

After your treatment, the patient’s condition got much worse so a resident was called. The resident drew blood for routine lab tests, one of which is determining the hematocrit. The lab tech reports the hematocrit is lower than when the patient came in (only 45% down from 54%) and the plasma portion was pink. The resident immediately infused the patient with Lactated Ringers.
Why was the patient’s plasma pink?

If you had given the patient a sterile sucrose solution instead of sterile distilled water, what would the concentration of sucrose would need to be used to prevent the above condition?

The resident, figuring out what you had done, infused the patient with 1 L of 600 mM sucrose solution (600 mOsm/L). Based on the plasma volume and osmolarity after your infusion, predict the following parameters as to whether they will increase, decrease or show no change.

Prediction
Patient’s plasma osmolarity after the infusion:

Patient’s hematocrit after the infusion equilibrates with the patient’s blood:

Assuming that none of the 600 mOsm/L sucrose administered was absorbed or excreted, calculate the final plasma osmolality.

Final plasma osmolality ___________

Answer 1

Plasma volume (Liters) = Total blood volume (1-haematocrit)

Total blood volume = 75×72.6, this person is 72.6 kg

= 5445ml= 5.445L

Haematocrit = 54%

Put it in equation, Plasma volume= 5.445(1-0.54)

= 5.445×.46= 2.5 Literes

The sterile water used for infusion is hypotonic compared to the cytosol of the red blood cell, therefore, water will enter the red blood cell by osmosis causing the cell to expand and eventually lead to lyse. When his blood was centrifuged, the plasma appears pink because hemoglobin from the lysed red blood cells is released into the plasma.