Procedural sedation has allowed many painful procedures to be conducted outside the operating room. During such procedures, it is important to maintain an appropriate level of sedation to minimize the risk of respiratory depression (if the patients are over-sedated) or pain or anxiety (if under-sedated). However, there are no objective, data-driven means to measure a patient's evolving level of sedation during a procedure. Currently, clinicians use light physical or verbal stimulation to gauge the degree of the patient's responsiveness as a surrogate measure of sedation level. Furthermore, the current patient safety monitoring can detect but not predict adverse events. Therefore, despite the high level of surveillance offered by the standard monitoring systems in place today, adverse respiratory events, such as apnea and hypoxemia, frequently occur.