What is the difference between Monitored Anesthesia Care (MAC) awake and MAC aware in anesthesia practice, and when is each preferred?

MAC Awake vs MAC Aware in Anesthesia Practice

MAC "awake" and MAC "aware" are not formally distinct anesthetic categories, but represent critically different levels of consciousness: MAC awake maintains patient responsiveness to verbal commands and communication with the surgical team, while MAC aware achieves deep sedation with unresponsiveness to noxious stimuli (essentially general anesthesia) while preserving spontaneous breathing. 1

Defining the Spectrum

MAC Awake

• Patient maintains ability to follow commands and communicate effectively with the surgical team throughout the procedure 1
• Represents conscious sedation where patients can respond appropriately to verbal stimulation and maintain protective airway reflexes 2
• The three fundamental elements are safe sedation, anxiety control, and pain management while preserving patient cooperation 2, 3

MAC Aware

• Achieves a state of unresponsiveness to noxious stimuli (functionally equivalent to general anesthesia) while maintaining spontaneous breathing through the patient's own airway 4, 1
• Responsiveness is significantly obtunded, and patients cannot reliably respond to verbal commands 1
• The requirement for spontaneous breathing serves as a constraint that helps prevent excessively deep anesthesia, but does not preclude complete unresponsiveness 4

Critical Monitoring Differences

MAC Awake Monitoring Requirements

• Standard monitoring includes ECG, SpO₂, and NIBP with continuous presence of appropriately trained personnel 1
• Capnography should be added whenever there is loss or likelihood of loss of normal response to verbal contact 4

MAC Aware Monitoring Requirements

• Requires identical monitoring to general anesthesia, including mandatory capnography throughout the procedure due to loss of verbal responsiveness 1
• An anesthetist must remain present at all times during the episode of care 4
• Monitoring must begin before sedation is initiated and continue throughout the procedure and recovery 1
• Documentation of vital signs (heart rate, blood pressure, SpO₂, ETCO₂) should be recorded at least every 5 minutes 1

Safety Profile Comparison

Respiratory Considerations

• MAC, particularly when achieving deep sedation/aware state, is associated with more adverse respiratory events than general anesthesia 4, 1
• During MAC aware, hypotension, oxyhemoglobin desaturation, apnea, and airway obstruction can occur, especially following rapid bolus administration 5
• Propofol-based MAC aware frequently causes apnea: in adults receiving 2-2.5 mg/kg, apnea lasted >60 seconds in 12% of patients 5

Hemodynamic Considerations

• MAC demonstrates a lower incidence of hypotension (14%) compared to general anesthesia (59%) 4, 1
• Vasopressor requirements are significantly reduced with MAC (7% vs 44% with general anesthesia) 4, 1
• When hypotension occurs with MAC, the duration is brief (1 minute with MAC vs 4 minutes with general anesthesia) 4, 1

Clinical Decision Algorithm

When to Choose MAC Awake

• Procedures requiring patient cooperation and intraoperative communication (e.g., awake craniotomy for brain mapping) 6
• Patients who can comprehend the procedure and provide cooperation throughout 3
• When minimizing sedative depth is prioritized to maintain verbal responsiveness 2

When to Choose MAC Aware

• Complex procedures requiring complete patient immobility and unresponsiveness to noxious stimuli, but where spontaneous breathing is desired 1
• Patients with significant comorbidities where avoiding intubation is beneficial but deep sedation is necessary 1
• Procedures where the constraint of spontaneous breathing helps prevent excessively deep anesthesia 4

Administration Techniques

Initiation Principles

• During initiation of MAC aware, slow infusion or slow injection techniques are mandatory over rapid bolus administration 5
• For propofol-based MAC aware, infusion at 100-150 mcg/kg/min for 3-5 minutes while closely monitoring respiratory function 5
• Alternatively, approximately 0.5 mg/kg administered over 3-5 minutes and titrated to clinical response 5

Maintenance Strategies

• A variable rate infusion is preferable over intermittent bolus administration to minimize undesirable cardiorespiratory effects 5
• For MAC aware maintenance, rates typically range from 25-75 mcg/kg/min, with most patients requiring 25-50 mcg/kg/min after the first 10-15 minutes 5
• Allow approximately 2 minutes for onset of peak drug effect when titrating 5

Common Pitfalls and How to Avoid Them

Critical Errors to Avoid

• Never assume MAC always means the patient is communicative—deep sedation under MAC aware can render patients completely unresponsive 1
• Do not reduce monitoring intensity for MAC aware compared to general anesthesia; the risk profile demands equivalent vigilance 1
• In elderly, debilitated, or ASA-PS III-IV patients, rapid (single or repeated) bolus dose administration must never be used for MAC sedation 5

Terminology Confusion

• The term "sedation" is imprecise and means different things to different practitioners—always clarify the intended depth of sedation before proceeding 4, 1
• In the context of procedures like ERCP, MAC aware really refers to unresponsiveness to noxious stimuli (general anesthesia) in a spontaneously breathing patient, not light sedation 4

Special Population Considerations

• In elderly, debilitated, or ASA-PS III-IV patients, reduce propofol dosage to approximately 80% of usual adult dosage and administer over 3-5 minutes 5
• Elderly patients require reduced doses of sedatives due to altered pharmacokinetics and pharmacodynamics 1

Depth Monitoring

• Processed EEG monitoring should be used when TIVA is administered for MAC aware, particularly when neuromuscular blockade is involved 4
• Clinical signs alone are inadequate to assess depth of sedation in MAC aware 1