Certified Surgical Technologist (CST) Practice Exam

Which method of inhalation anesthesia allows complete rebreathing of expired gases?

1. Mask inhalation

2. Closed

3. Semi-closed

4. Open

The correct answer is: Closed

The method of inhalation anesthesia that permits complete rebreathing of expired gases is closed anesthesia. In closed systems, the breathing circuit is designed to recycle the exhaled gases, allowing the patient to re-inhale a mixture of fresh gas and the gases they have previously exhaled. This method helps maintain a stable anesthetic concentration and reduces the amount of anesthetic agent needed. In a closed system, the presence of unidirectional valves prevents the escape of gases from the circuit and allows for total rebreathing. This is beneficial for conserving anesthetic agents and can lead to a more efficient delivery of anesthesia. Additionally, it often requires precise management of the gas flow and monitoring of the patient to ensure adequate ventilation and gas concentrations. In contrast, the semi-closed system allows some rebreathing but also facilitates the escape of some expired gas, thus maintaining a level of freshness in the inhaled mixture. Open systems do not recycle expired gases at all, whereas mask inhalation could imply an open or semi-open method depending on the setup, leading to significant gas loss and less efficient rebreathing.