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Overview :
Karkouti et al developed a multivariate model for predicting
the need for blood transfusion in patients undergoing a first-time, elective
coronary artery bypass procedure. This can help identify patients who are more
likely to require blood replacement. The authors are from Toronto and Ottawa in
Ontario, Canada.
Populations: Elderly adults requiring first-time CABG
procedures at Toronto General Hospital between January 1, 1997 and September
30, 1998. Patients who were excluded: patients with autologous blood, patients
requiring re-exploration for bleeding, and patients who were transfused after
the first post-operative day (page 1195).
Parameters from multivariate analysis:
(1) age in years
(2) sex (male = 1, female = 0)
(3) body weight in kilograms
(4) preoperative hemoglobin in g/dL
X =
= (-0.7064 * (points for sex)) + (0.0366 * (age in years)) –
(0.0641 * (body weight in kilograms)) – (0.743 * (preoperative hemoglobin) +
12.3189
probability of requiring transfusion =
= 1 / (1 + EXP((-1) * X))
The authors selected a probability of 20% (0.20) as the
point for predicting the need for transfusion (sensitivity 82%, specificity
71%).
Based on this decision, they created tables for men (Table
8) and women (Table 9) with the pre-operative hemoglobin associated with the
need for transfusion using age and weight as axes.
However, if one reworks the equation (using probability =
0.2) , one can derive the following equation:
pre-op hemoglobin in g/dL below which transfusion is likely
=
= (1.3863 – (0.7064 *
(points for sex)) + (0.0366 * (age in years)) – (0.0641 * (body weight in
kilograms)) + 12.3189) / 0.743
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