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MAC Sedation — ASA Continuum, Drug Selection, Rescue Plans
TEXTAnesthesia Care · 6 min read
MAC isn't a depth — it's a service. The patient may pass through every depth on the ASA continuum during a single case, and the safety net is the same as for general anesthesia.
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3 min read6 sectionsASA continuum of sedation
Minimal sedation (anxiolysis): normal response to verbal command, airway + ventilation + CV unaffected.
Moderate (conscious sedation): purposeful response to verbal/tactile, airway + ventilation adequate, CV usually maintained.
- purposeful response only to repeated or painful stimulus
- airway intervention may be needed
- ventilation may be inadequate
- CV usually maintained
- unarousable
- airway intervention often required
- ventilation frequently inadequate
- CV may be impaired
The depths are a continuum — patients drift between them depending on drug pharmacokinetics + stimulus intensity.
The provider must be qualified to RESCUE from one depth deeper than intended.
MAC defined — service not depth
Monitored anesthesia care is an anesthesia service in which an anesthesia provider monitors the patient + delivers sedation/analgesia/anxiolysis as needed + is prepared to convert to general anesthesia if required.
The depth during a MAC case may be anywhere from minimal to deep — and may transiently include unresponsiveness functionally indistinguishable from GA.
- IDENTICAL to GA: continuous ECG
- pulse oximetry
- NIBP q≤5 min
- capnography (ASA standard since 2011 for moderate + deep sedation)
- temperature when clinically significant
The provider stays in the room + does not leave.
Patient + procedure selection
- ASA I-III without predicted difficult airway
- cooperative (or sedatable to cooperation)
- procedure tolerable with local anesthesia + light-moderate sedation
- surgeon comfortable working on an awake or lightly sedated patient
- severe OSA (collapsible airway with sedation)
- morbid obesity
- predicted difficult mask + intubation
- GERD with aspiration risk
- anxiety requiring deep sedation
- long procedures
- prone positioning
- procedure type requiring deep planes (interventional pulm, complex GI endoscopy with stimulation)
MAC is NOT 'safer than GA' — the airway is unsecured + harder to access mid-procedure if it fails.
Drug selection + titration
1-2 mg IV titrated for anxiolysis + anterograde amnesia — synergistic respiratory depression with opioids.Fentanyl 25-50 mcg boluses for brief analgesic need; longer-acting hydromorphone 0.2-0.4 mg for longer cases.
Propofol 25-75 mcg/kg/min infusion — most titratable but easiest to oversedate; bolus loading is the highest-risk moment for apnea.
Remifentanil 0.05-0.1 mcg/kg/min for brief pain stimulation — predictable offset.
Dexmedetomidine 0.5-1 mcg/kg load over 10 min then 0.2-0.7 mcg/kg/hr — preserves airway + respiratory drive but causes hypotension + bradycardia + has slow offset.
Ketamine 0.25-0.5 mg/kg low-dose adjunct for analgesia without respiratory depression.
Combination approaches (dex + propofol, propofol + ketamine) reduce individual drug doses + airway risk.
Airway rescue ladder
Add oropharyngeal or nasopharyngeal airway.
Apply positive pressure via mask + bag with 100% O₂.
If ventilation inadequate or persistent apnea: LMA insertion as an intermediate rescue.
If LMA fails or aspiration risk: endotracheal intubation.
The DECISION to convert to GA must be made early — don't let oxygen saturation drift while you titrate down.
Equipment immediately available: full anesthesia machine or sedation cart, suction, oral + nasal airways of multiple sizes, LMA + ETTs of multiple sizes, laryngoscope or video laryngoscope, reversal agents (naloxone 0.04-0.4 mg titrated, flumazenil 0.2 mg q1min up to 1 mg — caution with chronic benzo users — seizure risk).
Common MAC failure modes + mitigation
Mitigate with infusion + small redoses + capnography.
Airway obstruction in obese/OSA: pre-position with chin-up + ramp; nasal trumpet at induction.
Hypotension from propofol + dex stacking: load slower, smaller boluses, fluid pre-load.
Patient movement at critical moment: communicate with surgeon, give propofol bolus 20-30 sec before known noxious step; remi infusion bridges movement during stimulus peaks.
Documentation: depth achieved, drugs + doses, any conversion to GA, any airway intervention — the medical record must distinguish 'MAC' from 'GA via supraglottic airway' for billing + medicolegal accuracy.
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