If the patient is obese, using the IBW
or ABW will give more accuracy than an actual weight.
Example
Question: Before surgery is to take place, what is
the estimated blood volume (EBV) of a female patient weighing
50 kg? Also, what is the allowable blood loss (ABL)
of this patient if her Hct is 45?
In the example above, EBV = 50kg x 65 (adult
woman's blood volume) = 3250
The initial Hct (Hi) = 45%, her current Hct
The final lowest acceptable Hct (Hf) = 30% (What ever
cut off is used clinically to decide how low the individual's
Hct will be allowed to drop. Thirty percent is used
in this calculator but in reality this will vary from case
to case.)
So the example would look like this:
3250 x (45 - 30) 45
= 1083
Using this rough estimate, the patient in
this example 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 and 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"
(Morgan & Mikhail, 1996).
Estimating
blood loss***
Dry sponges
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 blood with:
3 mL crystalloid (i.e. NS, Dextrose, LR)
1 mL colloid (i.e. albumin**, Hespan®, Dextran®)
1 mL whole blood
1 mL PRBC
