Abstract: A gas processing unit in patient circuits for use in anaesthesia or respiratory care. The patient circuit comprises a gas source for creating gas mixture for patient breathing and circulating arrangement for delivering the gas mixture to the patient. The circulating arrangement comprises tubes through which gases flow to the patient and from the patient. The circulating arrangement has a proximal end connected to the gas source for creating gas mixture, and a distal end connected to the patient, and a processing unit. The processing unit comprising a housing and at least one processing element placed in the housing. The processing element is arranged to form an angle other than 90 degrees with respect to a direction of gas flow in the tubes.