The goal of this study is monitor anesthetic depth of children undergoing propofol anesthesia using electroencephalography (EEG). The main questions it aims to answer are:

1. EEG spectral edge frequency (SEF95) readings where 50% of patients do not respond to three stimuli.
2. The propofol blood concentration that corresponds to each of the three EEG SEF95 readings Participants will undergo EEG monitoring, stimuli (placement of oral pacifier, electrical stimulation, and laryngoscopy), and blood collection.

Sevoflurane inhalation and propofol intravenous anesthesia are the mainstays of delivering general anesthesia in children. Propofol anesthesia in children is gaining popularity due to fewer respiratory complications, less post-operative nausea vomiting and emergence delirium, compared to sevoflurane. However, unlike sevoflurane, the pharmacodynamics of propofol is less studied in infants and toddlers, particularly the biomarker for propofol brain effect site concentration (Ce), indicative of anesthetic depth. The lack of a real-time biomarker often results in over- or under-dosing of propofol in clinical practice. The goal of this study is to utilize electroencephalography (EEG) as the biomarker of propofol effect site concentration and clinical anesthetic depth, thereby improving the safety and efficacy of propofol anesthesia in this population. In infants and toddlers receiving propofol anesthesia, EEG will be recorded while the patient undergoes three stimuli used to assess anesthetic depth (placement of oral pacifier, electrical stimulation, and laryngoscopy). The EEG index (spectral edge frequency-SEF95) where 50% of patients (ED50) do not respond to each of the three stimuli will be determined as the biomarker of propofol clinical anesthetic depth. In the same cohort, the regression between EEG SEF95 and plasma propofol levels will be determined to assess relationship between EEG SEF95 and propofol Ce.

Inclusion Criteria:

1. Children 3 to 24 month old undergoing surgery.
2. Planned laryngoscopy and endotracheal intubation or laryngeal mask airway (LMA) placement for clinical care.
3. Planned propofol anesthesia for anesthesia maintenance.
4. American Society of Anesthesiologists (ASA ) < III.
5. Muscle relaxant not indicated per planned clinical care for laryngoscopy/intubation or LMA.
6. Anticipated surgery duration approximately < 2h40min

Exclusion Criteria:

1. Patients undergoing emergency surgery.
2. Known severe neurological disease which might result in abnormal EEG SEF.
3. Deformities of forehead (difficult EEG sensor placement).
4. Known difficult airway.
5. Allergy to propofol.
6. Attending anesthesiologist on record caring for patient plans to administer additional IV medication besides propofol during study phase.
7. Currently on anti-seizure medication (might alter propofol pharmacodynamics).