What is moderate sedation, when is it employed, and what advantages does it offer?

What is moderate sedation, when is it employed, and what advantages does it offer?

Moderate sedation, previously known as conscious sedation, is a technique that strives to achieve a decreased level of consciousness during surgery whereby patients remain capable of independently maintaining the airway with reflexes intact, as well as responding appropriately to verbal instructions. When properly executed, moderate sedation provides anxiolysis, amnesia, and allows maxi-mum patient comfort and safety. Moderate sedation should be considered to be a valuable accompaniment and adjunct to a properly placed local anesthetic or regional anesthetic. Because interference with short-term memory occurs, the patient experiences a markedly distorted percep-tion of time. Therefore, the anesthesiologist can increase a patient’s tolerance and acceptance of the discomforts associated with an ongoing procedure by providing encouragement and a sense of well-being and security. The goal is to allow the patient, anesthesiologist, and surgeon to communicate throughout the operative procedure.

Moderate sedation is achieved by careful titration of intravenous agents administered by either intermittent bolus injection or continuous infusion. Since moderate sedation is part of a continuum, it is possible for moderate sedation to progress to deep sedation or even general anes-thesia. Propofol, midazolam, and remifentanil have ideal pharmacokinetic properties for the provision of moderate sedation. These characteristics include a rapid onset, easy titration, and a relatively short duration of action, which allow for an early recovery from their effects. It is useful to combine a benzodiazepine with an opioid. However, one must be vigilant for the insidious or sudden onset of respi-ratory depression including apnea. Hypoxemia or apneic episodes have been demonstrated to be more frequent when a combination of benzodiazepines and opioids is used, as compared with either drug used alone. Therefore, supplemental oxygen should be provided via mask or nasal cannula, and respiration should be carefully monitored.

Present standards of care require monitoring of heart rate, blood pressure, respirations and oxygen saturation, as well as the capability of measuring temperature and ECG. Nasal cannulae are now available with a separate tube that can be attached to the sampling probe from a capnograph, thereby allowing for end-tidal CO₂ monitoring. This is particularly useful during procedures where the anesthesi-ologist may be physically separated from the airway.

Though a patient may appear awake and fully recovered at the end of surgery using this technique, vigilance must be maintained throughout the postoperative period because delayed respiratory depression may occur. In the PACU, hypercarbia or even respiratory arrest may occur if the patient is left unstimulated.