A plunger adapter and a detachable compression pad for piston driven chest compression devices optimizes the application of chest compressions to a fixed location on a patient's chest. The detachable compression pad may be removably secured to the patient above the patient's sternum to ensure that the compression pressure from the piston through the piston adapter is applied to a fixed location on the patient's chest. As the plunger and plunger adapter retract from the chest, the compression pad remains fixed to the patient's chest, and as the plunger and plunger adapter extend from the chest compression unit for subsequent compression strokes, the distal end of the plunger adapter reengages the compression pad to apply compression to a fixed location on the patient's chest.