De-airing of a cardiothoracic wound cavity model with carbon dioxide: theory and comparison of a gas diffuser with conventional tubes.

OBJECTIVES: To compare the efficiency of a new gas diffuser with conventional tubes for carbon dioxide (CO(2)) de-airing of a cardiothoracic wound cavity model, and to analyze how insufflation flow, outflow velocity, and diffusion affect de-airing.
DESIGN: Technical study in vitro.
SETTING: A nonventilated room at a University Hospital.
INTERVENTIONS: De-airing by CO(2) insufflation via 3 methods was studied in a symmetric cardiothoracic wound model.
MEASUREMENTS AND MAIN RESULTS: The studied insufflation devices were 2 open-ended tubes with an inner diameter of 2.5 mm and (1/4)-in (6.35 mm), respectively, and a gas diffuser (ie, a 2.5-mm tube with a diffuser at the end). CO(2) flows of 2.5, 5, 7.5, and 10 L/min were used. De-airing was assessed by measurement of remaining air content in a set of systematically distributed measuring points in the model. Three-, 2-, and 1-way analysis of variance all revealed significant interaction of device, flow, and depth on air content (p < 0.001). With tubes, the mean air content was 18% to 96% at the studied flows. With the gas diffuser, the mean air content in the cavity was below 0.2% at flows of 5 to 10 L/min. There was an exponential relation between calculated outflow velocity and air content. At a flow of 2.5 L/min, diffusion attenuated de-airing.
CONCLUSION: These data imply that de-airing of a cardiothoracic wound by CO(2) insufflation depends on flow and outflow velocity. To compensate for diffusion with ambient air, the CO(2) flow should be >/= 5 L/min, and the outflow velocity should be about 0.1 m/s or less to avoid turbulence in the wound. This is only attainable with a gas diffuser.