There are a minimum number of hours specified by Federal Aviation Regulations (FARs) Part 61. I don't know the average now, but the national average used to be about 20 hours over the minimum. Those students who took less than the national average were those who took 3 to 5 lessons a week (some went 7 days).
A rare but very serious risk associated with blood transfusions is transfusion-related acute lung injury (TRALI). It occurs more often with platelets and plasma than with red cells. TRALI is a poorly understood condition, in which a personâs lungs suddenly become very inflamed within six hours of the transfusion.
However, early transfusions were risky and many resulted in the death of the patient. By the late 19th century, blood transfusion was regarded as a risky and dubious procedure, and was largely shunned by the medical establishment.