Allowable Blood Loss (ABL) Formula*
- E = Estimated Blood Volume (EBV)
- Hi = Initial hematocrit (Hct)
- Hf = Final lowest acceptable Hct
Estimated Blood Volume (EBV) Formula
W × B
- W = Weight in kilograms (kg)
- B = Average blood volume
|Premature neonates||95 mL/kg|
|Full term neonates||85 mL/kg|
|Adult men||75 mL/kg|
|Adult women||65 mL/kg|
Before surgery is to take place, what is the EBV of a female patient weighing 50 kg? Also, what is the ABL of this patient if her Hct is 45?
- EBV = 65 mL/kg
- Initial hematocrit Hct = 45%
- Final lowest acceptable Hct = 30%
The answer is 1083. Using this rough estimate, the patient could loose 1083 mL of blood without needing a transfusion.
†Replacing Blood Loss
Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion. At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level. For most patients, that point corresponds to a hemoglobin between 7–10 g/dL (or a hematocrit of 21–30%). Below a hemoglobin concentration of 7 g/dL, the resting cardiac output has to increase greatly to maintain normal oxygen delivery.
†Estimating Blood Loss
- 4x4 hold ˜ 10 mL blood
- Ray-techs ˜ 10–20 mL blood
- Lap sponges ˜ 100 mL blood
- **Pediatric cases should have sponges & gauze weighed for blood loss
†Blood Loss Replacement
Replace 1 mL of blood with:
- 3 mL crystalloid (e.g., NS, Dextrose, LR)
- 1 mL colloid (e.g., **albumin, Hespan®, Dextran®)
- 1 mL whole blood
- 1 mL PRBC
- Miller, R. D. (Ed.). (2000). Anesthesia. (5th ed.). Philadelphia: Churchill Livingstone.
- Morgan, G. E., Jr., & Mikhail, M., S. (1996). Clinical anesthesiology. (2nd ed.). New York: Lange Medical Books/McGraw-Hill
- Nagelhout, J. J., & Zaglaniczy, K., L. (2001). Nurse anesthesia (2nd ed.). Philadelphia: W.B. Saunders Co.