Which type of sterilization is appropriate for unwrapped instruments intended for immediate use?

The appropriate method of sterilization for unwrapped instruments intended for immediate use is steam under pressure, commonly known as autoclaving. This technique uses saturated steam at high temperatures, typically between 121°C to 134°C, along with increased pressure to effectively kill bacteria, viruses, fungi, and spores.

Steam sterilization is favored for immediate use because it achieves rapid sterilization in a relatively short time (usually around 3 to 30 minutes depending on the specific conditions and type of instrument) and is suitable for a wide variety of surgical instruments made from materials that can withstand moisture and high temperatures.

The other methods listed, such as ethylene oxide, are more suitable for items that cannot tolerate moisture or high heat and typically require long aeration times after sterilization. Dry heat sterilization is more time-consuming and is usually employed for items that might be damaged by moisture. Radiation is typically used for medical devices packaged for long-term storage and is not practical for immediate use scenarios.

Thus, steam under pressure is the optimal choice for ensuring prompt sterilization of unwrapped surgical instruments right before they are needed, ensuring that they are safe and effective for use in procedures.