Bypass circuits as the source of thromboemboli during extracorporeal membrane oxygenation.

To determine the presence and extent of thrombus formation in the apparatus used for extracorporeal membrane oxygenation we studied various portions of the polyvinylchloride circuit from five infants who received extracorporeal membrane oxygenation for 70 to 330 hours. All infants had right-sided cannulation. Sections were cut from the circuit at the time of decannulation and subjected to light and scanning electron microscopy. The site that contained the most thrombus formation was the membrane oxygenator bypass circuit, which is subjected to repeated periods of unclamping and clamping to direct blood flow through the membrane oxygenator. Autopsy results from nonsurvivors showed evidence of pulmonary and renal infarcts, a left frontal lobe infarct, a thromboembolus of the left external and internal carotid arteries, and thrombi in the lungs, kidney, brain, and coronary arteries. One survivor had computed tomographic evidence of infarction of the left middle cerebral artery distribution. We suggest that the areas of the extracorporeal membrane oxygenation circuit subjected to repeated changes in flow dynamics may be the source of microemboli.