A method and system for improving gas exchange properties of oxygenators which utilize hollow fiber membranes for removing carbon dioxide or adding oxygen to a patient's blood via extracorporeal circulation by removing moisture accumulating in the fibers are disclosed. The system utilizes a vacuum source for drawing sweep gas into the oxygenator, a moisture collection unit for storing moisture removed from the oxygenator, the moisture collecting unit being in communication with the oxygenator and the vacuum source and a flow control mechanism having an open position which allows sweep gas exiting the oxygenator to flow to the moisture collecting unit and a closed position which stops the flow of sweep gas from the oxygenator to the moisture collecting unit. The vacuum source draws sweep gas through the oxygenator and moisture collecting unit when the flow control mechanism is in the open position and the vacuum source creates a vacuum buildup in the moisture collecting unit when the flow control mechanism is in the closed position. The vacuum in the moisture collecting unit provides a sudden increase to the flow rate of the sweep gas to draw moisture with the sweep gas exiting the oxygenator when the flow control mechanism is returned to the open position.
