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Monitored Anaesthesia Care (MAC) - Exam Questions with Viva-Ready Answers

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SECTION 1: DEFINITIONS AND TERMINOLOGY

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Q1. Define Monitored Anaesthesia Care (MAC).

• MAC does NOT describe a fixed depth of sedation - it can span the complete spectrum from minimal sedation to general anaesthesia
• The anesthesiologist's continuous attention is directed at optimizing patient comfort and safety
• Usually (but not always) involves drugs with anxiolytic, hypnotic, analgesic, and amnestic properties
• Provided as supplement to local or regional technique OR alone
• MAC implies potential for deeper sedation than moderate sedation/analgesia performed by nonanesthesiologists

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Q2. Distinguish MAC from Moderate Sedation/Analgesia (Conscious Sedation).

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SECTION 2: ASA CONTINUUM OF SEDATION

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Q3. Describe the ASA continuum of depth of sedation.

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SECTION 3: INDICATIONS AND CANDIDACY

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Q4. What are the indications for MAC?

1. Nature of the procedure - Minor surgical/diagnostic procedures (endoscopy, cataract surgery, colonoscopy, interventional radiology, cardiac catheterization, ophthalmic procedures, superficial biopsies)
2. Patient's clinical condition - Patients with significant comorbidities who might not tolerate GA
3. Need for deeper sedation than can be safely provided by moderate sedation alone
4. Patient preference - Anxious patient who wants to be sedated
5. Procedures requiring regional/local anaesthesia supplemented with sedation
6. ICD/Pacemaker insertion - deep sedation for defibrillation threshold testing

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Q5. What factors determine MAC candidacy in preoperative assessment?

• Full preanesthetic evaluation - same standards as GA
• Identify cardiopulmonary reserve
• Determine risk of conversion to GA
• Assess current medications and drug interactions

• Full airway assessment is mandatory - patient may become apnoeic or require conversion to GA
• History of snoring, sleep apnoea (OSA patients are at higher risk of airway obstruction during MAC)
• Neck mobility, mouth opening, Mallampati class
• Must be prepared to manage airway even during "sedation"

• Discuss level of awareness/amnesia expected
• Clarify that patient may remember parts of procedure
• Intraoperative awareness is actually acceptable in MAC (unlike GA where it is a complication)

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SECTION 4: MONITORING

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Q6. What monitoring is mandatory during MAC? (ASA Standards)

1. Pulse oximetry - continuous SpO2
2. Capnography (EtCO2) - monitoring of ventilation; useful for detecting early respiratory depression before hypoxia occurs
3. ECG - continuously displayed
4. Blood pressure - measured and recorded at least every 5 minutes
5. Temperature - when clinically significant changes are intended, anticipated, or suspected
6. Continuous presence of an anaesthesia care team member

• Arterial line, CVP if indicated by comorbidities

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Q7. How is depth of sedation monitored during MAC?

• Response to verbal stimuli
• Response to tactile/painful stimuli
• Respiratory pattern observation
• Direct observation - the anesthesiologist's continuous clinical assessment

• Ramsay Sedation Scale (RSS): 1-6 scale; RSS 2-3 targeted for MAC
• Richmond Agitation-Sedation Scale (RASS): -5 to +4
• Observer's Assessment of Alertness/Sedation (OAA/S) scale
• Bispectral Index (BIS): helpful but limitations in MAC

• EEG-derived parameter, 0-100
• 40-60: GA; 60-70: Deep sedation; 70-85: Moderate sedation; 85-100: Awake
• May help reduce drug use and improve recovery times during MAC
• Does not replace clinical assessment

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SECTION 5: PHARMACOLOGY

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Q8. What is the pharmacologic basis of MAC and what drugs are used?

• Analgesia, anxiolysis, amnesia, sedation
• Rapid onset and offset
• Minimal side effects, especially respiratory depression
• Easy titratability

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• Sedative-hypnotic; GABA-A agonist
• Advantages: Rapid onset, short context-sensitive half-time, antiemetic, pleasant recovery, highly titratable
• Disadvantages: No analgesic properties, respiratory depression, hypotension, pain on injection
• Doses for MAC: Induction 25-75 mcg/kg/min infusion; boluses 10-20 mg
• Preferred as infusion rather than boluses to avoid peaks of over-sedation

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• GABA-A agonist; anxiolysis, amnesia, sedation
• Advantages: Excellent anxiolysis and anterograde amnesia, reversal with flumazenil
• Disadvantages: Unpredictable sedation depth in elderly/obese/sick, paradoxical reactions, long context-sensitive half-time, no analgesia
• Midazolam dose: 0.5-2 mg IV; useful as premedication for MAC

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• Provide analgesia (lacking in propofol and benzodiazepines)
• Fentanyl: 25-100 mcg IV; rapid onset, short duration, respiratory depression
• Remifentanil: Ultra-short acting; ideal for procedures with brief intense pain; infusion required (no bolus due to chest wall rigidity risk)
• Risk: Synergistic respiratory depression with sedative-hypnotics - requires careful titration

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• NMDA antagonist; dissociative analgesia
• Advantages: Maintains airway reflexes, bronchodilator, preserves respiratory drive, excellent analgesia
• Disadvantages: Emergence phenomena (dysphoria, hallucinations), excessive secretions, increases ICP and IOP
• Dose in MAC: Sub-dissociative - 0.1-0.5 mg/kg IV
• Combine with midazolam to reduce emergence reactions

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• Combines propofol's sedation with ketamine's analgesia
• Propofol counteracts ketamine's emergence reactions and secretions
• Ketamine offsets propofol's respiratory depression and hypotension
• Common ratios: 1:1 or 1:4 (ketamine:propofol) by volume
• Increasingly popular for MAC in procedural settings

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• Selective alpha-2 adrenergic agonist; CNS and peripheral effects
• Unique advantage: "Cooperative sedation" - patients remain arousable/communicable while sedated (rousable but calm - "conscious sedation" without respiratory depression)
• Analgesic and anxiolytic properties
• Disadvantages: Bradycardia, hypotension, slow onset (loading dose required), expensive
• Loading dose: 0.5-1 mcg/kg over 10 min; Maintenance: 0.2-0.7 mcg/kg/hr
• Excellent for awake fiberoptic intubation, carotid endarterectomy (neurological monitoring preserved)

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Q9. What is context-sensitive half-time? Why is it important in MAC?

• Unlike elimination half-life (a fixed property), context-sensitive half-time increases with infusion duration for most drugs
• Drugs with short context-sensitive half-times are ideal for MAC (rapid recovery after procedure ends)
• Remifentanil: Context-sensitive half-time remains ~3-4 minutes regardless of infusion duration - ideal for MAC
• Fentanyl: Context-sensitive half-time increases significantly with infusion duration - less ideal for long cases
• Propofol: Relatively short context-sensitive half-time - one reason it is preferred for MAC infusions

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SECTION 6: COMPLICATIONS

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Q10. What are the complications of MAC? What is the leading cause of death?

Hypoxia due to suppression of spontaneous respiration by sedative-hypnotic drugs

• Most common serious complication
• Mechanisms: decreased respiratory drive, upper airway obstruction, loss of protective reflexes
• Sedatives + opioids = synergistic respiratory depression
• Risk factors: OSA, obesity, elderly, pre-existing lung disease
• Prevention: Oxygen supplementation, capnography monitoring, careful titration
• Treatment: Reduce or stop drugs; supplemental O2; jaw thrust/airway adjuncts; bag-mask ventilation; reversal agents (flumazenil, naloxone); convert to GA if needed

• Risk increases as sedation deepens (loss of protective airway reflexes)
• High-risk patients: full stomach, GORD, gastroparesis, obesity
• MAC patients should still follow NPO guidelines

• Can occur during deep sedation, particularly if airway is stimulated
• Treatment: Positive pressure ventilation, succinylcholine if severe

• Hypotension (propofol, dexmedetomidine)
• Bradycardia (dexmedetomidine, opioids)
• Myocardial ischemia in high-risk patients

• MAC often used with regional/local anaesthesia
• Anesthesiologist must be prepared to recognize and treat LAST
• Treatment: Stop LA injection; lipid emulsion 20% (Intralipid); airway management; seizure control

• Important and often exam-tested complication
• Combination of electrocautery + supplemental oxygen + alcohol-based prep + flammable drapes is dangerous
• Particularly during head/neck/facial procedures
• Prevention: Minimize O2 concentration, avoid pooling of alcohol prep, use fire-retardant drapes

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SECTION 7: SUPPLEMENTAL OXYGEN AND AIRWAY

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Q11. What are the considerations for oxygen supplementation during MAC?

1. Nasal cannula (most common) - 2-4 L/min; comfortable, easy to monitor EtCO2 with modified cannula
2. Simple face mask
3. Modified face mask with EtCO2 sampling port

• High-flow O2 under drapes around head/neck creates an oxygen-enriched environment
• Combined with electrocautery and alcohol-based skin preparation - significant fire hazard
• Clinical measures: Use minimum FiO2 needed, allow alcohol prep to dry completely, pack drapes to prevent O2 pooling, communicate with surgical team

• Supplemental oxygen can mask hypoventilation - SpO2 may remain normal despite significant hypercarbia
• This is why capnography is MORE important in oxygen-supplemented MAC patients

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SECTION 8: CLOSED CLAIMS AND MEDICOLEGAL

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Q12. What do closed claims data reveal about MAC?

1. MAC cases represent a significant proportion of anesthesia-related claims
2. Respiratory depression is the most common cause of severe injury/death
3. Over-sedation and inadequate monitoring are recurring themes
4. Many claims involved failure to recognize deteriorating respiratory status
5. MAC claims were more likely to involve:
   • Elderly patients
   • Procedures outside the operating room (OOR/NORA settings)
   • Inadequate monitoring equipment availability

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SECTION 9: SPECIAL TOPICS

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Q13. What is the difference between MAC and TIVA (Total Intravenous Anaesthesia)?

• MAC - Patient maintains consciousness, purposeful responses, and spontaneous ventilation. The anesthesiologist is prepared to convert to GA if needed.
• TIVA - Patient is rendered unconscious (general anaesthesia state) using only IV drugs, with airway management (LMA or ETT). No inhalational agents used.
• A MAC case that becomes a GA (loss of consciousness) is then essentially TIVA if IV agents are being used.

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Q14. What is patient-controlled sedation (PCS)?

• An emerging technique where the patient self-administers preset boluses of sedative (typically propofol, with or without opioid) via a PCA-like device
• Built-in lockout intervals and maximum dose limits prevent over-sedation
• Advantage: Patient titrates to their own comfort level; risk of over-sedation reduced; improved patient satisfaction
• Limitation: Requires patient cooperation; does not replace anesthesiologist monitoring
• Considered a future direction in MAC delivery

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Q15. What is Target-Controlled Infusion (TCI) in MAC?

• Computer-controlled drug delivery that targets a specific plasma or effect-site drug concentration using pharmacokinetic models
• The anesthesiologist sets a target concentration; the system calculates infusion rates based on patient's weight, age, height
• Advantage: More precise titration; reduces over/under-sedation; simplifies drug administration
• Common TCI models: Marsh and Schnider models for propofol; Minto model for remifentanil
• Limitation: Accuracy depends on how well the patient's pharmacokinetics match the model; inter-patient variability remains

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QUICK REVISION: HIGH-YIELD ONE-LINERS FOR VIVA

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COMMON EXAM MCQ TRAPS

1. "MAC means moderate sedation" - WRONG. MAC can encompass any depth, including GA.
2. "Dexmedetomidine has no analgesic properties" - WRONG. It has alpha-2 mediated analgesic effects.
3. "Capnography is not required during MAC" - WRONG. ASA mandates same monitoring as GA.
4. "Ketamine always causes respiratory depression" - WRONG. At sub-dissociative doses, it largely preserves respiratory drive - one reason it is valuable in MAC.
5. "The patient is awake and responsive, so it cannot be GA" - WRONG. If unresponsive to purposeful stimulation = GA regardless of whether intubated.
6. "Fentanyl is better than remifentanil for long MAC cases" - WRONG. Remifentanil's stable context-sensitive half-time makes it preferable for longer infusions.

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