Every day approximately 90 million surgeries are performed worldwide. In 30 million cases, equipment is employed that uses breathing filters.

The primary purpose of breathing filters used between the patient and the respiratory circuit is prevention of cross infection between the patient and apparatus when performing endotracheal anesthesia or mechanical lung ventilation.

These procedures require that the upper airway be bypassed during respiration. The purpose of the upper airway is to remove particulates from the air to deactivate bacteria and viruses by means of biologically active substances having bactericidal and viricidal properties. These are secreted by the mucous membrane, and also to warm inspired air to 35°C-36°C and to humidify it to a relative humidity of 98%-100%

The recommendation that air filters should be used in medical devices is relatively recent.

From a list of 13 patients operated on in a private hospital in Sydney, 2 developed Hepatitis C post-surgery, and a further 3 became infected with HCV some weeks later. Investigation revealed that patient 5 on this list had been the source of the infection, supported by the fact that the virus from each patient was shown to have the same genotype. The conclusion was that viruses could penetrate and contaminate the reusable part of a breathing system, and the virus thereby be transmitted to subsequent patients. The result was that some form of barrier to blood/fluids and airborne contaminants emanating from the patient should be incorporated into medical devices.

There was a risk of anesthetic breathing systems becoming contaminated with organisms from the respiratory tract.

*An absorber in circle-systems might have a bactericidal effect on non-spore forming organism, but does not prevent the contamination of systems.

*Anesthetic and intensive therapy ventilators can cause cross infection.

*Of the filters currently available, only those using a pleated, hydrophobic media reliably prevent contamination of breathing systems.