The Principal Investigator will obtain IRB approval under expedited review. No patient written informed consent will be required as this is a process improvement minimal risk study that does not necessitates use of patient Protected Health Information. Participants will not be actually enrolled. There will be no change to the standard of care resulting from data collection on CO2 absorbent use, and no patient identifiers will be exposed. The study will take place in three operating rooms, three rooms equipped with Drager Appollo® anesthesia workstations (Draeger Medical Inc., USA) requiring use of CLIC style absorbents. An unblinded member of the research team will have access to the randomization schedule and will be responsible to place Drägersorb® 800+, Drägersorb® Free, or Micropore SpiralithTM absorbents in the designated operating rooms with three Appollo® (CLIC style absorbent). The randomly selected absorbent will be loaded on the anesthesia workstation prior to the patient's arrival in the operating room and the date, time and randomization coding will be marked on the cassette as it appears on the randomization schedule. The anesthesia providers will use low flow anesthesia with or without Sevoflurane in the 3 selected operating rooms. The practice at this institution is to use a semi-closed breathing circuit and maintain a fresh gas flow rate of approximately 2L/min with a selected tidal volume of 6-8 mL/Kg during the maintenance phase of the procedure. Flow rate would be approximately 10 L/min during the induction of anesthesia. The investigators will document time that is required to achieve 90% of the sevoflurane target concentration. These guidelines will be clearly indicated on the anesthesia workstation to ensure consistency across the multiple providers. Data logger files will be saved at the end of each case using the same coding label as the marked cassette. When the absorbent is replaced, the date and time of removal should be clearly marked on the cassette. This same date and time information should also be recorded on the source document ensuring that operating room numbers and anesthesia workstations are clearly and accurately recorded. In order to maintain the anesthesia provider blinded to the type of absorbent used, a white sheet of paper will be taped around the outside of the cassette compartment. The time that the patient is connected and disconnected from the breathing circuit must be recorded on the source document. In addition the investigators will document The absorbent unit will be replaced when the inspiratory CO2 concentration (obtained from the inspiratory limb of the breathing circuit) reaches 4 mmHg. This is an acceptable maximal inspiratory CO2 concentration which leaves sufficient time to complete a case, thereby avoiding cassette replacement during anesthesia. The anesthesia workstation fresh gas flows will be turned off at the time that the patient is disconnected from the breathing circuit to avoid variability in absorbent water content.

The absorbing capacity of the cassettes will be determined by calculating the duration of absorbent use from the time of first use to the time of cassette removal. Each absorbent will be evaluated through a total of 5 rounds. We expect to have about 60 surgeries for each absorbent. Averaged duration of absorbent use will be compared between different types of absorbents (Drägersorb® 800+, Drägersorb® Free, Micropore SpiralithTM).