pRBC volume and infusion rates for an anemic dog
A 25 kg dog has a PCV of 15% from chronic IMHA. You decide to transfuse pRBC to a target PCV of 25%. Donor pRBC PCV is the default 80%. Calculate the total pRBC volume needed, the slow trial rate for the first 30 minutes, and the main rate to finish the transfusion over a 4-hour total window.
Hint
Volume needed depends on three things: the patient's total blood volume, how much PCV needs to rise, and how concentrated the donor product is. The math is one equation; the trick is knowing the species blood-volume constant.
Another hint
Blood volume = 90 mL/kg in dogs (60 mL/kg in cats). The slow trial is 0.5 mL/kg/hr for 30 minutes, designed to deliver 0.25 mL/kg total during the trial. The main rate finishes the remainder over 3.5 hours (4 hours total minus the 30-min trial).
Show worked answer
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Compute total blood volume. Dogs have ~90 mL/kg blood volume.
$$\text{blood volume} = 90 \,\tfrac{mL}{\cancel{kg}} \times 25\,\cancel{kg} = 2{,}250 \,mL$$ -
Compute the PCV rise needed.
$$\Delta\text{PCV} = 25\% - 15\% = 10 \text{ points}$$ -
Apply the transfusion volume formula: total pRBC volume = (PCV rise / donor PCV) × patient blood volume. The donor PCV in the denominator captures how concentrated each mL of product is.
$$\text{volume} = \frac{10}{80} \times 2{,}250 \,mL \approx 281 \,mL$$ -
Slow trial rate: 0.5 mL/kg/hr for the first 30 minutes. This delivers 0.25 mL/kg total during the trial, slow enough that acute reactions (anaphylaxis, hemolysis, febrile non-hemolytic) can be detected before a meaningful volume has gone in.
$$\text{slow trial} = 0.5 \,\tfrac{mL}{kg \cdot hr} \times 25 \,kg = 12.5 \,\tfrac{mL}{hr}$$ -
Volume given during the slow trial = 0.25 mL/kg × 25 kg = 6.25 mL. Remaining volume = 281 − 6.25 ≈ 275 mL.
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Main rate to finish in 3.5 more hours (4 hr total window):
$$\text{main rate} = \frac{275 \,mL}{3.5 \,hr} \approx 78.5 \,\tfrac{mL}{hr}$$ -
Monitor TPR every 15 min during the slow trial and every 30 min thereafter. Aim to complete the transfusion within 4 hours to limit bacterial contamination risk in an open product.
Total pRBC volume ≈ 281 mL. Slow trial at 12.5 mL/hr for 30 min, then main rate at ~78.5 mL/hr for 3.5 hr. Total infusion time 4 hr.