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Alpha-2 Agonists, Opioids & Mixed Agonist-Antagonists: MD Anaesthesia Flashcards

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🃏 CARD 1: Alpha-2 Agonists at a Glance

Mnemonic: "C is for Clumsy; D is for Dexterous"

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⚡ CLONIDINE vs DEXMEDETOMIDINE - Master Comparison Table

Mnemonic for Dexmed's advantages over Clonidine: "7 FARSIES"

• 7x more selective
• Fast acting IV
• Arousable sedation (cooperative patient)
• Respiratory drive preserved even at high doses
• Shorter t½ (titratable)
• ICU delirium reduction
• Effective in OSA/bariatric
• Shivering reduced

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🃏 CARD 2: Alpha-2 Receptor Locations - Mnemonic "Pre-Post-Periphery"

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🃏 CARD 3: Opioid Receptor Quick Reference

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⚡ MORPHINE vs FENTANYL - Master Comparison

Mnemonic: "MORPHINE = Makes Old Receptors Produce Histamine IN Everyone"

Mnemonic: "FENTANYL = Fast Entry, No Toxin ANd Yielding Lipophilics"

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🃏 CARD 4: Morphine Unique Points for MCQ

• Hysteresis: Plasma peak ≠ effect peak; peak effect lags by 1-2 hr after IV dose
• M6G (morphine-6-glucuronide): More potent than morphine itself; accumulates in renal failure → prolonged respiratory depression
• M3G (morphine-3-glucuronide): No analgesia; causes hyperalgesia, myoclonus, seizures
• Histamine: Urticaria, bronchospasm, hypotension - treat with antihistamines
• Neuraxial: Preservative-free only; intrathecal 0.1-0.3 mg gives 12-24 hr analgesia

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⚡ PENTAZOCINE vs BUTORPHANOL - Mixed Agonist-Antagonists

Mnemonic: "PENTA = Psycho, Elevates NorTensive Arteries"

Mnemonic: "BUTO = Better, nasal Use, Twice Or more potent"

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🃏 CARD 5: Mixed Agonist-Antagonist Class Rules (Applies to Both)

• Ceiling effect for analgesia (and respiratory depression)
• Avoid combining with full agonists (may precipitate withdrawal or ↓ analgesia)
• Withdrawal precipitated in opioid-dependent patients
• Dysphoria (especially pentazocine via σ)
• Safer respiratory profile than full agonists

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🃏 CARD 6: Big Picture - The "Receptor Fingerprint" of Each Drug

Drug         μ(analgesia/RD)   κ(sedation/spinal)   σ(dysphoria)
─────────────────────────────────────────────────────────────────
Morphine        +++                 +                   -
Fentanyl        ++++                -                   -
Pentazocine     antagonist         partial +            +++
Butorphanol     partial/antag      +++                  ±

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🃏 CARD 7: Clinical High-Yield One-Liners for Exam

1. Dexmed > clonidine for α2 selectivity: 1600:1 vs 200:1 (7x difference)
2. Only drug that causes arousable sedation = Dexmedetomidine
3. Fentanyl = intraoperative opioid of choice; Morphine = postoperative/neuraxial
4. M6G (active metabolite of morphine) accumulates in renal failure
5. Pentazocine raises BP/HR/PAP - contraindicated in MI
6. Butorphanol available intranasally; used in migraine/obstetrics
7. Both α2 agonists: no significant respiratory depression - safe in respiratory compromised patients
8. Wooden chest with high-dose fentanyl - treat with succinylcholine + intubation
9. Clonidine withdrawal = rebound HTN + tachycardia; do NOT use β-blocker alone
10. Context-sensitive half-life of fentanyl rises steeply with prolonged infusion (unlike remifentanil)

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Recent MI / IHD Patient for Emergency Laparotomy / Strangulated Hernia Repair

★★★★ Anaesthetic Management | MD Anaesthesia Exam

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THE CORE CONFLICT

Emergency surgery CANNOT wait (strangulated hernia / peritonitis = life-threatening). Yet recent MI carries highest reinfarction / mortality risk perioperatively. Your job = minimize cardiac morbidity while safely conducting a life-saving procedure.

Mnemonic: "LIFE vs LIMB = LIFE wins — but protect the HEART"

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🃏 CARD 1: Risk Stratification - Know BEFORE You Touch the Patient

Revised Cardiac Risk Index (RCRI) - 6 Predictors

• Score 0 = 0.4% risk | Score 1 = 0.9% | Score 2 = 6.6% | Score ≥3 = >11% major cardiac event

Key Timing Rule (ACC/AHA 2014):

• Elective surgery: defer 60 days after recent MI
• Emergency surgery: cannot defer - proceed with maximal precaution
• Risk of 30-day postop MI/death is highest when surgery within 60 days of MI

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🃏 CARD 2: Preoperative Assessment - "ABCDE" Framework

• Full stomach (emergency, bowel obstruction) → RSI mandatory
• Assess for difficult airway (obesity, short neck, reduced mouth opening)

• Baseline SpO₂, CXR - look for pulmonary oedema/LVF
• ABG if in distress

• Time since MI (hours/days/weeks?)
• Current antiplatelet status (aspirin, clopidogrel, DAPT for stents)
• Type of stent: BMS (bare metal stent) vs DES (drug-eluting stent)?
• Recent ECG: ST changes, Q waves, arrhythmia
• Echo/wall motion abnormality if available
• LV function (EF?) - severe LV dysfunction = very high risk
• Current medications (beta-blocker, statin, ACE inhibitor, nitrates)
• BP, HR, capillary refill, signs of cardiogenic shock / decompensated HF

• Continue: beta-blockers, statins, nitrates, aspirin
• Withhold/discuss: ACE inhibitors (may cause refractory hypotension), clopidogrel (bleeding risk vs stent thrombosis)

• K⁺ (hypokalaemia worsens arrhythmia risk), Na⁺, creatinine
• Level of haemodynamic compromise (is patient in shock?)

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🃏 CARD 3: Goals of Anaesthetic Management

Mnemonic: "MODS = Maintain O₂ Delivery, Stable Haemodynamics"

Maintain balance between Myocardial O₂ Supply and Demand

• HR: 60-80 bpm (avoid tachycardia above all else)
• MAP: 70-90 mmHg (keep within 20% of baseline)
• SpO₂: ≥ 98%
• Hb: ≥ 9-10 g/dL (in IHD, more generous transfusion threshold)
• Temperature: normothermia (hypothermia → catecholamine surge → ischaemia)

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🃏 CARD 4: Preoperative Preparation

Monitoring Setup (before induction):

• 5-lead ECG with ST-segment analysis (II + V5 detect >95% ischaemia)
• Pulse oximetry
• Invasive arterial line (radial) - beat-to-beat BP, ABG access
• Large-bore IV × 2
• Consider Central venous line - CVP, vasopressor access
• Urinary catheter - hourly urine output

Drugs to have ready:

• Vasopressors: Phenylephrine (pure α - raises BP without tachycardia), Noradrenaline, Metaraminol
• Chronotropes: Atropine, Isoprenaline (for bradycardia)
• Anti-ischaemics: IV Nitroglycerine (if ischaemia/HTN intraop)
• Beta-blocker (IV): Esmolol/Metoprolol (short-acting for tachycardia)
• Defibrillator/crash cart at bedside
• Blood cross-matched and available

Pre-induction:

• 100% O₂ preoxygenation × 3-5 min (desaturation during apnoea is catastrophic in IHD)
• IV access, fluid status (but avoid overload - risks LV strain)
• Continue beta-blocker if on it (abrupt cessation → rebound tachycardia/ischaemia)
• Consider IV fentanyl 1-2 μg/kg before induction (attenuates laryngoscopy response)

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🃏 CARD 5: Induction of Anaesthesia

RSI is MANDATORY (full stomach - emergency surgery)

But RSI in IHD = "Haemodynamically Gentle RSI"

• Laryngoscopy/intubation → massive sympathetic surge → tachycardia + HTN → ischaemia
• Induction agents can cause hypotension → coronary hypoperfusion

Induction Agents - Comparison:

1. Preoxygenation 100% O₂ × 5 min
2. IV fentanyl 2-3 μg/kg (blunts intubation response) - give 3-5 min before
3. Lignocaine 1.5 mg/kg IV (blunts laryngoscopy pressor response)
4. Etomidate 0.2-0.3 mg/kg OR titrated propofol + vasopressor ready
5. Succinylcholine 1.5 mg/kg (RSI - no Sellick's/cricoid pressure used routinely now, controversial)
6. Gentle, rapid laryngoscopy with best view - avoid prolonged attempts
7. Confirm ET tube with capnography

• Fentanyl (opioid blunting)
• Lignocaine (pressor response attenuation)
• induction agent (etomidate preferred)
• Succinylcholine RSI

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🃏 CARD 6: Maintenance of Anaesthesia

Volatile vs TIVA:

Muscle Relaxation:

• Atracurium (organ-independent metabolism) or Vecuronium (minimal CVS effects)
• Avoid Pancuronium (tachycardia) and Gallamine in IHD

Opioids:

• Fentanyl infusion intraoperatively (haemodynamically stable, no histamine)
• Morphine postoperatively (PCA for pain control)
• Avoid under-analgesia: pain → catecholamine surge → tachycardia → ischaemia

Adjuncts:

• Beta-blocker if tachycardia (esmolol 0.5 mg/kg bolus or infusion)
• GTN (Nitroglycerine) infusion if ST elevation or hypertension (0.5-2 μg/kg/min)
• Vasopressors if hypotension (phenylephrine preferred over ephedrine to avoid tachycardia)

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🃏 CARD 7: Intraoperative Monitoring for Ischaemia

ECG - The 95% Rule:

• Lead II = inferior ischaemia (RCA)
• Lead V5 = anterior/lateral ischaemia (LAD)
• II + V5 combined = detects >95% of ischaemic events
• II + V4 + V5 = detects >99%

Signs of Intraoperative Ischaemia:

• ST depression > 1 mm (subendocardial ischaemia - demand ↑)
• ST elevation > 2 mm (transmural = plaque rupture / vasospasm)
• New T-wave inversion
• Sudden ↑ in LVEDP (PAC if used)
• New wall motion abnormality on TOE

Treatment of Intraoperative Ischaemia:

• Step 1: Correct cause (Tachycardia → esmolol; Hypotension → vasopressor/fluid; Hypertension → deepen anaesthesia/GTN)
• Step 2: IV GTN 0.5-2 μg/kg/min (vasodilates coronaries)
• Step 3: Optimise Hb, oxygenation
• Step 4: If ongoing - call cardiac team, consider post-op IABP / ICU

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🃏 CARD 8: Special Considerations

Antiplatelet Management (Stent patients):

• BMS placed < 4-6 weeks = defer elective surgery; continue aspirin if emergency
• DES placed < 12 months = defer elective surgery; continue aspirin + clopidogrel in emergency (stent thrombosis > bleeding risk)
• ACC/AHA: If surgery cannot wait, continue DAPT; consult cardiology
• Heparin bridging may be considered

Stress Response:

• Emergency laparotomy = maximal surgical stress
• Catecholamine surge → tachycardia, hypertension, platelet activation, hypercoagulability → plaque rupture risk
• Counter with: adequate depth of anaesthesia, fentanyl, beta-blockers, alpha-2 agonists (dexmedetomidine infusion)

Dexmedetomidine:

• Ideal adjuvant in IHD: ↓ sympathetic tone, ↓ HR, ↓ catecholamines, no respiratory depression
• Infusion 0.2-0.7 μg/kg/hr intraoperatively / ICU sedation

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🃏 CARD 9: Regional Anaesthesia - Role?

Epidural Anaesthesia:

• Thoracic epidural (T6-T10) for laparotomy - excellent analgesia, reduces surgical stress response
• Benefits: ↓ sympathetic activation, ↓ pain, ↓ postop ileus, ↓ DVT
• BUT in emergency: antiplatelet drugs → epidural haematoma risk → CONTRAINDICATED if on DAPT
• Generally: not first choice for emergency in anticoagulated/antiplatelet patient

Conclusion for Route:

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🃏 CARD 10: Postoperative Management

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🃏 CARD 11: QUICK SUMMARY TABLE for Exam

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🃏 CARD 12: One-Liners the Examiner Wants to Hear

1. "Emergency surgery cannot be deferred despite MI; our goal is to minimise perioperative cardiac morbidity."
2. "RSI is mandatory due to full stomach, but we use a haemodynamically gentle technique."
3. "Etomidate is the induction agent of choice in haemodynamically compromised patients."
4. "Sevoflurane offers ischaemic preconditioning - this is a real biological benefit in IHD."
5. "Tachycardia is the most dangerous haemodynamic perturbation in IHD."
6. "II + V5 ECG leads detect > 95% of perioperative ischaemia."
7. "Beta-blockers must be continued; abrupt cessation causes rebound tachycardia and ischaemia."
8. "In DES stent < 12 months: continue DAPT for emergency surgery - stent thrombosis kills faster than bleeding."
9. "Phenylephrine preferred over ephedrine for hypotension - it raises BP without tachycardia."
10. "Post-op ICU, serial troponins, normothermia, and immediate resumption of cardiac medications are non-negotiable."

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