Critical care practice has greatly changed over the last three decades. This is partly due to the advent of the pulmonary artery catheter and subsequent advances in technologies associated with it. The key determinants of cardiac performance, pressure, flow, and volume, are assessed either directly or indirectly. Parameters that were once only available on an intermittent basis can now be obtained continuously. Addition of mixed venous oxygen saturation to the cardiorespiratory profile and other derived parameters provides the bedside clinician with important variables to assess the cardiorespiratory status of the critically ill.