The investigators propose to examine the relationship between DO2 and VO2 in critically ill patients requiring an Extracorporeal Membrane Oxygenation (ECMO) machine. This machine can provide complete support of heart and lung function. In so doing, the investigators will be able to avoid physiologic coupling by increasing DO2 mechanically, by increasing blood flow through the ECMO circuit.

Null Hypothesis:

Increased oxygen delivery, by means of an increased rate of extracorporeal blood flow, is not associated with an increase in oxygen consumption.

Alternate Hypothesis:

Increased oxygen delivery, by means of an increased rate of extracorporeal blood flow, is associated with an increase in oxygen consumption.

Inclusion Criteria:

• Patients in the Critical Care Unit on veno-arterial ECMO.
• Hemodynamic stability established, as adjudged by the treating CCU staff physician.
• Informed consent by parent or legal guardian.
• Approval by treating CCU staff physician to approach parents/guardians for consent process at any given time.

Exclusion Criteria:

• Patients in the Critical Care Unit on veno-venous (VV) ECMO.
• Inability to tolerate study period without red cell transfusion.
• Presence of a large leak around the endotracheal tube (> 10% tidal volume).
• Patients requiring > 70 % FiO2 at the time of potential enrollment.
• Parent or legal guardian refuse consent.