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Carbon dioxide concentration under ophthalmic drapes increases during eye surgery under local anaesthesia. A new prototype has been designed which combines continuous suction of carbon dioxide enriched air and continuous oxygen insufflation under ophthalmic drapes to prevent carbon dioxide accumulation in spontaneously breathing patients undergoing cataract surgery.In a prospective randomised single blind study the effectiveness of this new prototype was examined in 50 unpremedicated elderly patients. In 25 patients suction was applied under ophthalmic drapes, whereas in the other 25 patients no suction was used. In all cases oxygen was insufflated under the drapes at a constant flow of 2 l/min. Carbon dioxide concentration in the ambient air surrounding the patient's head under ophthalmic drapes, transcutaneous partial pressure of carbon dioxide, respiratory rate, and oxygen saturation were measured.Carbon dioxide concentration under the drapes, transcutaneous partial pressure of carbon dioxide, and respiratory rate remained unchanged in the suction group, whereas in the non-suction group these values increased significantly. Oxygen saturation rose significantly in both groups without differences between the groups.Application of this new prototype for continuous aspiration of carbon dioxide enriched air prevents carbon dioxide rebreathing and subsequent hypercapnia associated with an elevated respiratory rate. This new equipment may therefore be useful in patients undergoing ophthalmic surgery under retrobulbar anaesthesia.