Heat labile instruments for use in surgical procedures can be best sterilized by:

Ethylene oxide gas is used in hospitals for the sterilization of heat-sensitive materials such as surgical instruments and plastics. It kills by alkylating both proteins and nucleic acids (i.e., the hydroxyethyl group attacks the reactive hydrogen atoms on essential amino and hydroxyl groups). Note - Ethylene oxide is an effective sterilizing agent for heat-labile devices such as aificial hea valves that cannot be treated at the temperature of the autoclave. Ref: Ray C.G., Ryan K.J. (2010). Chapter 3. Sterilization, Disinfection, and Infection Control. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e