The relationship between transfusion and hypoxemia in combat casualties

The relationship between transfusion and subsequent hypoxemia was examined retrospectively in the records of combat casualties studied by the first three U.S. Army Surgical Research Teams in Vietnam. There was no evident relationship in 425 casualties studied before anesthesia and operation. In 199 casualties studied preoperatively and on at least two of the first three postoperative days, there was no evident relationship in those with injuries not involving the chest or abdomen. Eighteen such casualties received over ten units of blood each (average 24.5) and exhibited subsequent changes in arterial oxygen tension (PaO2) which were indistinguishable from those transfused lesser amounts or not all. Similar observations were made in casualties with injuries to the abdomen, although there was a tendency to lower PaO2 two days after injury in those heavily transfused. In those with thoracic injury, there was statistically significantly lower PaO2 on the first two postoperative days in those heavily transfused. Two possible interpretations are considered, one that blood transfusion contributed to hypoxemia, and alternatively, that a greater magnitude of the injuries accounted for both the worsened hypoxemia and the need for more transfusions. The latter was thought more likely. The differences in PaO2 related to the type of injury exceeded the differences associated with transfusion.