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Most healthy adults have enough cardiovascular reserve to tolerate mild anaemia or polycythaemia. But in older people who need major surgery, even slight deviations in haematocrit values are associated with a higher risk of death, say researchers from the US.
They mined a national quality improvement database for more than 300000 patients over 65 (mostly men) who had their haematocrit value measured shortly before major surgery. They found a clear link between 30 day mortality and haematocrit values that were higher or lower than normal. Each percentage point deviation either way was associated with an increase of 1.6% (95% CI 1.1% to 2.2%) in the risk of death compared with a normal haematocrit of 39.0-53.9%. A combined outcome of death, cardiac arrest, or heart attack was also more common in patients with an abnormal haematocrit result.
The researchers did their best to adjust for multiple confounding factors, but their observations still don't prove that abnormal haematocrit measurements cause postoperative deaths directly. A linked editorial (pp 2525-6) warns doctors not to correct abnormalities before surgery, because treatments such as transfusions and synthetic erythropoietins may do more harm than good.