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.