Chapter 94: Monitored Anesthesia Care and Sedation

INTRODUCTION

Monitored anesthesia care (MAC) is an anesthetic technique that achieves many of the similar goals as general anesthesia: sedation, amnesia, anxiolysis, and analgesia. Monitored anesthesia care carries the advantage of invoking less physiologic disturbance and allowing for a more rapid recovery and discharge rate than general anesthesia. While requiring patient acceptance and cooperation, it often leads to greater patient satisfaction. By using drugs with favorable pharmacokinetic profiles, many outpatient operations and satellite procedures are now performed under a MAC technique.

THE SEDATION CONTINUUM

Minimal Sedation

Also referred to as anxiolysis, the lowest level of the continuum is a drug-induced state of impaired cognition. Patients respond normally to verbal commands. The respiratory and cardiovascular systems are unaffected. Airway patency and reflexes are maintained. Typical drugs used include oral benzodiazepines. The Centers for Medicare and Medicaid Services (CMS) do not define minimal sedation as anesthesia.

Moderate Sedation/Analgesia

Previously known by the imprecise term “conscious sedation,” this level of sedation involves a slightly deeper depression of consciousness. Patients should still respond purposefully to verbal commands with or without light tactile stimulation. The respiratory and cardiovascular systems are unaffected. Airway patency and reflexes are maintained. Typical drugs used include intravenous benzodiazepines and opioids. CMS also does not define moderate sedation/analgesia as anesthesia.

Deep Sedation/Analgesia

In this deeper level of sedation, significant central nervous system depression occurs. Patients have lost consciousness and are not easily aroused. They should respond purposefully to painful stimulation. Respiratory depression and impairment of spontaneous ventilation occurs. Cardiovascular function may be depressed. Airway patency decreases, often necessitating assistance by hand (chin lift jaw thrust) or with a mechanical appliance (oral or nasal airway). Typical drugs used include benzodiazepines, opioids, propofol, ketamine, etomidate, and dexmedetomidine.

General Anesthesia

The final step in the continuum involves a complete loss of consciousness and lack of arousability to painful stimulation. Significant respiratory and cardiovascular depression occurs. Airway patency is lost, usually requiring insertion of a laryngeal mask airway or endotracheal tube. Positive pressure ventilation is often necessary due to hypoventilation and drug-induced depression of neuromuscular function. Typical drugs used include any of the intravenous or inhalation anesthetics.

These definitions utilize the term “purposeful response.” The reflex withdrawal from a painful stimulus is not considered such a response. Purposeful responses are movements of an extremity specifically to remove the source of pain. Nonpurposeful responses include movements of the extremities that are clearly not related to the avoidance of pain.

It is important to note that sedation falls on a continuum. When receiving MAC, each patient may respond differently. As such, every practitioner must be able to rescue a patient from the next level of sedation in the event of an exaggerated and unintended response. A ...