Depth of sedation exists as a continuum from minimal sedation where the patient is able to interact during the sedation to deep sedation which is just short of general anesthesia.
Patient-controlled sedation is an extension of patient-controlled analgesia, where the patient is able to control the depth of sedation that is comfortable for them during an invasive procedure.
Primary focus on the use of patient-controlled sedation is in the setting of ambulatory procedures that are typically performed under local or regional anesthesia.
The highly titratable nature of sedation requires the use of medications that are highly potent with rapid onsets of action.
The use of target-controlled infusion allows for more stable plasma concentrations of the sedative medication during the procedure.
Patient-maintained sedation utilizing target-controlled infusions is produces more stable plasma concentrations; however, the time to reach adequate sedation is relatively slower as compared to patient-controlled sedation.
Most common adverse event encountered during sedation is respiratory depression, manifested as hypoxemia and decreased respiratory rate.
Sedation is an induced altered state of consciousness following the administration of a sedative agent. According to the American Society of Anesthesiologists, depth of sedation exists as a continuum1 ranging from minimal sedation to deep sedation, just prior to achieving general anesthesia (Table 64–1). With minimal sedation, patients are in a state of anxiolysis and may have impaired cognitive function, but retain protective airway reflexes and the ability to respond normally to verbal commands. Moderate sedation, previously referred to as conscious sedation, refers to a state of depressed consciousness with a purposeful response to verbal commands and light tactile stimulation, such as glabellar tap. In a state of deep sedation, patients are not easily arousable but are able to purposefully respond to repeated or painful stimuli. In cases where the level of sedation becomes deeper than initially intended, interventions in airway management or hemodynamic support may become necessary. Other similar measures of sedation such as the Observer Assessment of Alertness and Sedation Scale2 are also commonly used (Table 64–2).
Table 64–1Continuum of depth of sedation. ||Download (.pdf) Table 64–1Continuum of depth of sedation.
| ||Minimal Sedation ||Moderate Sedation ||Deep Sedation ||General Anesthesia |
|Responsiveness ||Normal response to verbal stimulation ||Purposeful response to verbal and tactile stimulation ||Purposeful response following repeated or painful stimulation ||Unarousable to painful stimulation |
|Spontaneous Ventilation and Airway ||Unaffected ||Adequate, no intervention required ||May be inadequate, may require intervention ||Frequently inadequate, intervention required |
|Cardiovascular Function ||Unaffected ||Usually maintained ||Usually maintained ||May be impaired |
Table 64–2Observer assessment of alertness and sedation scale.