A sealed ventilation circuit adapter that enables simultaneous patient ventilation and safe tracheal suctioning is embodied to accommodate any of a wide variety of commercially available suction catheters. The adapter comprises a manifold assembly, and a catheter carrier. The manifold assembly may be attached to a patient for an extended period, while the catheter carrier is advantageously constructed as a single procedural use disposable device. The carrier couples with the manifold assembly and functions to effect an introduction of a catheter through a normally closed valve structure carried by the manifold assembly.