Improvements to integrated blood pump/oxygenator having a rotating hollow fiber bundle assembly that both oxygenates and pumps blood are provided. An inner member arranged along a central axis of the device accelerates blood entering the fiber bundle to reduce microbubble generation and blood trauma. Shearing loads imposed on the fiber elements of the fiber bundle are reduced by the addition of a reinforcement structure, while the gas flow path is configured to reduce flooding and loss of oxygenation efficiency due to occasional rupture of fiber elements.