Understanding Anesthesiology - The Global Regional Anesthesia ...

quences of the interstitial edema (which might occur
with crystalloid administration) are serious (e.g. cerebral
edema).
Blood products are administered for specific indications.
Red cell concentrates (RCC) are given to maintain
or restore oxygen carrying capacity. As hemoglobin
(Hb) concentration falls, oxygen delivery is preserved
by compensatory mechanisms: shifting the oxyhemoglobin
dissociation curve to the right and increasing
cardiac output (via an increase in heart rate and contractility).
When these compensations are inadequate
or detrimental, RCC should be transfused. General indications
for the transfusion of blood products are outlined
in Table 5.
A patient with Class 3 or 4 hemorrhagic shock (Table 3)
should be transfused immediately. For the slow but
steady blood loss which occurs during many types of
surgery, the lowest allowable hemoglobin, the “transfusion
trigger”, is determined on an individual basis.
Healthy patients can tolerate Hb levels that are approximately
½ of normal (60-70 g/L). Compensations
may be inadequate in patients with pulmonary, cardiac
or cerebrovascular disease. Compensation may be
harmful in patients with certain types of heart disease
such as severe coronary artery disease or aortic stenosis.
These patients should be transfused to relatively
higher Hb levels (80-100 g/L).
Once the lowest allowable hemoglobin has been determined,
then the allowable blood loss (ABL) can be calculated
as follows:
(Hb initial -Hb allowable) x EBV
Hb initial
Estimated blood volume (EBV) is approximately 60-70
mL/kg in the adult. When blood loss approaches estimated
ABL, the anesthesiologist confirms the current
Hb and considers transfusing.
Transfusion of plasma, platelets or cryoprecipitate is indicated
only for the correction of defective clotting and
is not indicated for volume resuscitation. Impaired clotting
may be observed or anticipated in a given clinical
scenario. For example, after one blood volume of RCC
has been transfused (6-12 units in an adult), coagulopathy
is likely on a dilutional basis and transfusion of
platelets and plasma will be required. Prolonged clotting
times or thrombocytopenia alone, without clinical
evidence of bleeding, are insufficient indications for
transfusion.
Risks and benefits of transfusion should be explained
to patients undergoing procedures likely to result in significant
blood loss. Consent for transfusion should be
obtained whenever possible.
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