Carbon dioxide is excreted by the lungs. Carbon dioxide production is based on metabolic rate and the substrates that are being utilized to drive the Kreb's cycle. Factors that influence pulmonary elimination of carbon dioxide include the volume of dead space, tidal volume, respiratory frequency and positive end-expiratory pressure (PEEP). The balance between arterial and venous carbon dioxide is based upon cardiac output. Hypocapnia can be controlled relatively through adjustment of ventilator settings to reduce minute ventilation in the sedated patient. The effects of hypercapnia and the associated acidaemia may be mitigated through the use of buffering agents. Traditionally, extracorporeal gas exchange (ECGE) has been utilized in patients only as a rescue therapy. In practice, clinicians adopt a technique somewhere between optimal carbon dioxide clearance and more liberal clearance targets, based on assessment of the severity of lung disease and the risks and benefits of ventilatory manipulations or associated interventions.