End Tidal Carbon Dioxide Concentration and Depth of Anesthesia in Children
Carbon Dioxide (CO2) is a by-product of metabolism and is removed from the body when we breathe out. High levels of CO2 can affect the nervous system and cause us to be sleepy or sedated. Research suggests that high levels of CO2 may benefit patients who are asleep under anesthesia, such as by reducing infection rates, nausea, or recovery from anesthesia . CO2 may also reduce pain signals or the medication required to keep patients asleep during anesthesia; this has not been researched in children.

During general anesthesia, anesthesiologists keep patients asleep with anesthetic gases or by giving medications into a vein. These drugs can depress breathing; therefore, an anesthesiologist will control breathing (ventilation) with an artificial airway such as an endotracheal tube. Changes in ventilation can alter the amount of CO2 removed from the body. The anesthesiologist may also monitor a patient's level of consciousness using a 'Depth of Anesthesia Monitor' such as the Bispectral Index (BIS), which analyzes a patient's brain activity and generates a number to tell the anesthesiologist how asleep they are.

The investigator's study will test if different levels of CO2 during intravenous anesthesia are linked with different levels of sedation or sleepiness in children, as measured by BIS. If so, this could reduce the amount of anesthetic medication the child receives. Other benefits may be decreased medication costs, fewer side effects, and a positive environmental impact by using less disposable anesthesia equipment.
- EligibilityCriteria: Inclusion Criteria:  Children aged 3 - 11 years undergoing non- or minimally-stimulating elective procedures, defined as anesthesia without skin incision or painful manipulation (e.g., non-invasive imaging, auditory brainstem response testing), middle ear surgery, surgery with effective local or regional anesthesia before surgical incision (e.g dental procedures with local anesthetic infiltration, urology with regional block). American Society of Anesthesiologists (ASA) physical status I and II TIVA technique appropriate throughout induction and maintenance of anesthesia Controlled ventilation via endotracheal tube Anticipated surgical time ≥ 90 minutes: to allow time for anesthetic induction and subsequent testing and washout periods at all three EtCO2 levels.  Exclusion Criteria:  Need for inhalational induction of anesthesia Sedative premedication Use of ketamine intraoperatively Unable to place BIS electrodes due to surgical site or other contraindications (e.g., MRI) Allergy to study drugs (propofol, remifentanil, lidocaine) Depression of conscious level for any reason BMI <5th or >95th centile for age History of obstructive or central sleep apnea Known or suspected raised intracranial pressure Recent or historical traumatic brain injury - HealthyVolunteers: Accepts Healthy Volunteers - Gender: All - MinimumAge: 3 Years - MaximumAge: 11 Years - StdAgeList: Child