The apparatus for immobilizing and treating a subject includes a suitable apparatus for performing mechanical CPR secured to an immobilization casing. The airtight flexible casing is secured to the apparatus for performing CPR, the casing having variable rigidity which varies as a function of the amount of air within the casing. Two or more slots through the casing permit passage of one or more elements of the CPR apparatus to pass through the casing. One or more incompressible windows may be included in the casing to optimize the performance of mechanical CPR by permitting one or more elements of the subject's skeleton to contact the CPR apparatus. A device for evacuating the air from within the flexible casing to control the rigidity of the casing is included within the CPR apparatus.