The invention concerns a manual resuscitation bag having a first PEP exhaust valve (4) arranged in a first conduit element (3) and fluidly communicating with the ambient atmosphere for venting gas to the atmosphere when the gas pressure, into the first conduit element (3), exceeds a given pressure threshold. The first PEP exhaust valve (4) has a valve body (5) and a calibration mechanism (6, 12； 7-10) for setting a desired pressure threshold. The calibration mechanism (6, 12； 7-10) is a rotatable member (6), actuatable by a user, arranged on the valve body (5) and cooperating with a pressure adjusting device (7-10) arranged into the valve body (5), and a support member (12) comprising several markings (11) corresponding to several settable pressure values, arranged between the rotatable member (6) and the valve body (5).
