Abstract: A demand-adapting and auto-regulatory ECMO system and method is disclosed that may be configured to provide complete cardiopulmonary replacement. The system and method employ a blood gas exchanger having a blood inlet, a blood outlet, a gas inlet, and a gas outlet, an oxygen sensor positioned to detect oxyhemoglobin saturation at the blood inlet, and a carbon dioxide sensor positioned to detect exhaust gas CO2 concentration at the gas outlet. A controller communicates with the oxygen sensor and the carbon dioxide sensor and controls blood flow and gas flow through the blood gas exchanger in response to a sensed oxygen level by the oxygen sensor and a sensed carbon dioxide level by the carbon dioxide sensor, in turn maintaining the sensed oxygen level and the sensed carbon dioxide level within a pre-designated range of values to maintain a patients metabolic requirements.