<p>Disclosed is an air circuit adapter comprising an outer pipe (1), an air collector (3) and an inner pipe (2). The outer pipe (1) has a first interface (4) and a second interface (5). A sampling interface is provided on the outer circumferential face (12) of the outer pipe (1). The inner pipe (2) is fixed within the outer pipe (1). At least part of the inner pipe (2) is located within the first interface (4). The air collector (3) is fixed within the inner pipe (2). The air collector (3) is in communication with the sampling interface (7) via an air sampling circuit (8). The air sampling circuit (8) passes through the inner pipe (2) and the outer pipe (1) radially. Adding the fixed inner pipe (2) within the outer pipe (1) reduces the amount of the expiratory air from a patient remaining within the air circuit adapter, such that the volume of dead space is reduced. The air collector (3) can prevent the condensed fluid within the air circuit from being sucked into the air sampling circuit (8), thereby preventing the air sampling circuit (8) from being blocked.</p>
