17.1 Important Anaesthetic Techniques, Airway Management & Methods of Administration

Foundations of General Anaesthesia: The Balanced Anaesthetic Triad

General anaesthesia is a reversible, drug-induced state of unconsciousness, insensibility to pain, and amnesia that allows surgical interventions to be conducted safely. Modern anaesthetic practice relies upon the principle of balanced anaesthesia—combining smaller, targeted doses of multiple pharmacological agents to achieve three distinct clinical objectives while minimizing individual drug toxicities:

1. Hypnosis and Amnesia: Loss of consciousness and recall, achieved through intravenous hypnotic agents (propofol, etomidate, thiopental, ketamine) or volatile inhalational anaesthetics (sevoflurane, isoflurane).
2. Analgesia: Suppression of autonomic, hemodynamic, and neuroendocrine stress responses to noxious surgical stimuli, mediated primarily by opioid receptor agonists (fentanyl, morphine, remifentanil), NMDA receptor antagonists (ketamine), and regional nerve blocks.
3. Neuromuscular Blockade (Skeletal Muscle Relaxation): Facilitation of endotracheal intubation, optimal surgical field exposure (especially for abdominal, thoracic, and laparoscopic procedures), and prevention of patient movement, achieved via neuromuscular blocking drugs (NMBDs).

Preoperative Fasting: The Evidence-Based 2-4-6-8 Rule

Pulmonary aspiration of acidic gastric contents (Mendelson syndrome) represents a catastrophic perioperative complication characterized by chemical pneumonitis, severe hypoxemia, acute lung injury, and death. To minimize residual gastric volume while avoiding unnecessary dehydration, hypoglycemia, and patient distress, the ASA framework uses the 2-4-6-8 Fasting Rule for healthy elective patients. Follow local guidance: ESAIC paediatric guidance uses shorter intervals for some fluids and feeds.

Aspiration Risk Factors: The following conditions can increase risk despite fasting. Assess the individual patient and choose an airway/aspiration strategy, including RSI when indicated:

• Active labour and late pregnancy (>= 20 weeks; elevated progesterone slows gastric transit, enlarged gravid uterus displaces stomach and raises intragastric pressure).
• Acute trauma, severe systemic stress, or severe pain (sympathetic surge halts gastric motility).
• Bowel obstruction, ileus, acute peritonitis, or severe gastrointestinal bleeding.
• Diabetic gastroparesis (autonomic neuropathy), morbid obesity, symptomatic gastroesophageal reflux disease (GERD), or large hiatal hernia.
• Administration of parenteral opioids prior to fasting (opioids arrest gastric peristalsis).

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Intravenous Induction Agents: Comparative Pharmacology

Induction of general anaesthesia is most commonly achieved via rapid intravenous bolus administration. The choice of induction agent depends on the patient's hemodynamic stability, volume status, intracranial dynamics, and underlying comorbidities.

1. Propofol (2,6-diisopropylphenol)

• Mechanism of Action: Potentiates inhibitory gamma-aminobutyric acid (GABA-A) receptor currents by increasing chloride channel open duration, causing neuronal hyperpolarization and central nervous system depression.
• Pharmacokinetics: Ultra-rapid onset of hypnosis (30 to 45 seconds; one arm-brain circulation time). Rapid recovery (4 to 8 minutes) following a single bolus, driven primarily by rapid redistribution from the vessel-rich central compartment (brain, heart) to poorly perfused muscle and adipose tissues, rather than metabolic clearance. Hepatically glucuronidated and excreted renally.
• Hemodynamic & Respiratory Effects: Causes marked dose-dependent arterial vasodilation (systemic vascular resistance drops by 15-25%) and direct myocardial depression, precipitating significant hypotension and bradycardia. Inhibits hypoxic and hypercapnic ventilatory drives, frequently causing transient apnea following induction.
• Key Clinical Advantages: Potent direct antiemetic properties (antagonizes dopamine D2 and 5-HT3 receptors at sub-hypnotic doses); smooth emergence without hangover; blunts upper airway reflexes, facilitating laryngeal mask airway (LMA) insertion without neuromuscular blockade.
• Toxicity & Adverse Effects: Pain on injection (mitigated by IV lidocaine or large antecubital veins); lipid vehicle (10% soybean oil, 2.25% glycerol, 1.2% egg lecithin) supports rapid bacterial growth (vials must be discarded within 6-12 hours of opening); Propofol Infusion Syndrome (PRIS) occurs with prolonged, high-dose infusions (> 4-5 mg/kg/hr for > 48 hours), presenting with severe refractory metabolic acidosis, rhabdomyolysis, hyperkalemia, hepatomegaly, hyperlipidemia, and fatal cardiogenic shock/arrhythmias.

2. Etomidate (Carboxylated Imidazole)

• Mechanism of Action: Selective GABA-A receptor agonist, enhancing chloride conductance.
• Pharmacokinetics: Rapid onset (30-60 seconds) and short duration of action (3-5 minutes) due to redistribution. Hydrolyzed by hepatic and plasma esterases.
• Hemodynamic & Respiratory Effects: Exceptional cardiovascular stability. Etomidate causes negligible changes in myocardial contractility, heart rate, cardiac output, or systemic vascular resistance. Minimal respiratory depression compared to propofol.
• Key Clinical Indication: Induction agent of choice for patients with severe hemodynamic instability, hemorrhagic shock, cardiac tamponade, severe aortic stenosis, or severe cardiomyopathy.
• Major Adverse Effects & Limitations:
  • Adrenal Insufficiency: Potently and reversibly inhibits 11-beta-hydroxylase, the critical rate-limiting enzyme converting 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone in the adrenal cortex. A single induction dose can suppress adrenocortical steroidogenesis for 6 to 24 hours, associated with increased mortality in patients with septic shock.
  • High incidence of myoclonus (involuntary non-epileptic muscle twitches; seen in 50-80% of un-premedicated patients; attenuated by pre-treatment with opioids or benzodiazepines).
  • High rates of postoperative nausea and vomiting (PONV).

3. Ketamine (Phencyclidine Derivative)

• Mechanism of Action: Non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor phencyclidine-binding site, inhibiting excitatory glutamate transmission. Also interacts with opioid, cholinergic, and monoaminergic receptors.
• Dissociative Anaesthesia: Produces a unique neurophysiological state known as "dissociative anaesthesia"—a functional and electrophysiological dissociation between the limbic system and the neocortex. Patients appear awake, with eyes open, slow nystagmic gaze, maintained pupillary and corneal reflexes, and intact spontaneous respiration, while experiencing profound somatic analgesia and amnesia.
• Hemodynamic Effects: Indirect sympathomimetic. Stimulates central sympathetic outflow, inhibits neuronal reuptake of catecholamines, and releases endogenous epinephrine and norepinephrine. Causes significant increases in heart rate, mean arterial blood pressure, and cardiac output. (Caution: In critically ill patients who are catecholamine-exhausted, ketamine acts as an unmasked direct myocardial depressant).
• Respiratory & Airway Effects: Potent direct bronchodilator (relaxes bronchial smooth muscle via sympathomimetic beta-2 stimulation and direct spasmolytic action), making it the induction agent of choice in acute severe bronchospasm and status asthmaticus. Preserves protective airway reflexes (cough, gag) and maintain spontaneous minute ventilation.
• Cerebral Effects & Emergence Phenomena: Historically avoided in neurotrauma because it increases cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and intracranial pressure (ICP); modern data show this is mitigated by normocapnia and co-administered sedatives. Causes vivid hallucinations, nightmares, and emergence delirium in up to 30% of adults (dramatically reduced by co-administering IV benzodiazepines such as midazolam).

4. Thiopental Sodium (Ultra-Short-Acting Barbiturate)

• Mechanism of Action: Binds GABA-A receptors, prolonging GABA-mediated chloride channel opening and directly activating chloride channels at higher doses; depresses the reticular activating system.
• Pharmacokinetics: Rapid onset (20-30 seconds) and short duration of induction (5-10 minutes) due to rapid redistribution from brain to skeletal muscle. Highly alkaline solution (pH 10.5).
• Central Nervous System Effects: Potently decreases cerebral metabolic rate of oxygen consumption (CMRO2) and cerebral blood flow via cerebral vasoconstriction, causing a dramatic reduction in intracranial pressure (ICP) while preserving cerebral perfusion pressure (CPP = MAP - ICP). Drug of choice historically for neurosurgical induction and status epilepticus.
• Hemodynamic Effects: Direct negative inotrope and peripheral venodilator (reduces cardiac preload and stroke volume), precipitating marked hypotension in hypovolemic patients.
• Absolute Contraindications & Toxicities:
  • Acute Intermittent Porphyria (AIP): Absolutely contraindicated in patients with porphyria. Barbiturates strongly induce hepatic delta-aminolevulinic acid (ALA) synthase, precipitating catastrophic acute porphyric crises characterized by severe abdominal pain, peripheral motor polyneuropathy, psychosis, respiratory paralysis, and death.
  • Accidental Intra-Arterial Injection: Highly alkaline (pH 10.5); precipitates crystal formation, chemical endarteritis, severe intense arterial vasospasm, thrombosis, and distal extremity gangrene. Emergency protocol: Leave arterial cannula in situ; immediately inject heparin (anticoagulation), 1% procaine or lidocaine (vasodilation and pain relief), phentolamine or papaverine, and perform an emergency regional sympathetic block (stellate ganglion or brachial plexus block) to restore distal limb perfusion.
  • Releases histamine, precipitating severe bronchospasm in asthmatic patients.

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Inhalational Maintenance Agents & The MAC Concept

Inhalational anaesthetics are volatile liquids administered via calibrated vaporizers through the breathing circuit to maintain unconsciousness during surgery.

The Minimum Alveolar Concentration (MAC)

• Definition: The Minimum Alveolar Concentration (MAC) is the steady-state concentration of an inhalational anaesthetic in the alveoli (at 1 atmosphere of pressure) that prevents purposeful skeletal muscle movement in 50% of subjects exposed to a standardized supramaximal noxious stimulus (traditionally surgical skin incision).
• Potency Relationship: MAC is an objective index of inhalational anaesthetic potency: the lower the MAC value, the higher the potency of the agent. Potency closely correlates with lipid solubility, conforming to the Meyer-Overton hypothesis (anaesthetic potency is directly proportional to its oil:gas partition coefficient).
• Clinical MAC Multiples:
  • 1.0 × MAC: Prevents movement in 50% of patients.
  • 1.2 to 1.3 × MAC (MAC-incision): Prevents movement in 95% of patients (ED95).
  • 0.3 to 0.4 × MAC (MAC-awake): Concentration at which 50% of patients open their eyes to verbal command during recovery.
  • 1.5 to 2.0 × MAC (MAC-BAR): Concentration required to block autonomic responses (hypertension, tachycardia) to surgical incision.
• Factors Altering MAC:
  • Factors Increasing MAC (Decreasing Potency): Hyperthermia, young age (highest in infants 1-6 months), chronic alcohol abuse, hypernatremia, acute central sympathetic stimulation (ephedrine, amphetamines).
  • Factors Decreasing MAC (Increasing Potency): Hypothermia, advanced age (MAC decreases by ~6% per decade over 40 years), acute alcohol or sedative intoxication, pregnancy (elevated progesterone), systemic hypoxemia (PaO2 < 30 mmHg), severe hypotension (MAP < 40 mmHg), co-administered intravenous opioids, sedatives, or alpha-2 agonists (clonidine, dexmedetomidine).

Volatile Agents & Nitrous Oxide

1. Sevoflurane:
   • Physical Properties: Low blood:gas partition coefficient (0.65), enabling rapid uptake, rapid induction, and rapid alveolar wash-out for swift emergence. Non-pungent, sweet-smelling, and non-irritating to the tracheobronchial tree.
   • Clinical Role: Common inhalational induction agent in paediatric anaesthesia. In adults with anticipated difficult airway management, consider awake intubation; inhalation induction does not reliably preserve a manageable airway.
   • Toxicity: Degraded by dry alkaline carbon dioxide absorbents (barium hydroxide lime, soda lime) into Compound A (fluoromethyl-2,2-difluoro-1-[trifluoromethyl]vinyl ether), which causes dose-dependent proximal tubular necrosis in animal models. To prevent toxic Compound A accumulation, fresh gas flow should be maintained at >= 1-2 L/min.
2. Isoflurane:
   • Physical Properties: Blood:gas partition coefficient 1.4; MAC 1.15%. Highly pungent, pungent odor induces airway irritation, coughing, and laryngospasm during mask induction (unsuitable for inhalational induction; used strictly for maintenance).
   • Cardiovascular: Potent systemic vasodilator; preserves cardiac output well; historically implicated in coronary steal syndrome (dilation of normal arterioles diverting flow from stenotic beds), though of minimal clinical significance under normotensive conditions.
3. Nitrous Oxide (N2O):
   • Physical Properties: Inorganic gas; very low blood:gas partition coefficient (0.47); MAC is 104% (cannot achieve 1 MAC at atmospheric pressure alone without causing asphyxial hypoxia; administered in combination with volatile agents or opioids, typically 50-70% N2O in oxygen).
   • Analgesic Action: Potent NMDA-receptor blocking analgesic properties; produces minimal cardiac depression.
   • Closed Gas Space Expansion: Nitrous oxide is 34 times more soluble in blood than nitrogen. When N2O is administered, it diffuses into nitrogen-containing, air-filled closed body cavities far more rapidly than nitrogen can diffuse out. This causes a dramatic expansion of gas volume (in compliant structures) or an alarming increase in pressure (in non-compliant rigid structures).
   • Absolute Contraindications to N2O:
     • Pneumothorax (can rapidly expand into a fatal tension pneumothorax).
     • Bowel obstruction, ileus, or acute volvulus (causes massive intestinal distension and perforation).
     • Venous or arterial air embolism.
     • Middle ear surgery / tympanoplasty (causes graft dislodgement).
     • Pneumocephalus (after neurosurgery or skull base trauma; causes acute intracranial herniation).
     • Intraocular gas bubble injection (perfluoropropane or sulfur hexafluoride during retinal detachment repair; causes central retinal artery occlusion and permanent blindness).
   • Metabolic Toxicity: Irreversibly oxidizes the cobalt atom of vitamin B12 (cobalamin), inhibiting methionine synthase and thymidylate synthesis. Chronic or recreational exposure induces megaloblastic anemia, agranulocytosis, and subacute combined degeneration (SCD) of the spinal cord.

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Neuromuscular Blocking Drugs (NMBDs) & Reversal Strategies

Neuromuscular blocking drugs act at the post-junctional nicotinic acetylcholine receptors (nAChR) of the motor endplate, paralyzing skeletal muscle.

Depolarizing NMBD: Succinylcholine (Suxamethonium)

• Mechanism: Dimeric acetylcholine molecule that binds to post-junctional nAChR, causing sustained, continuous depolarization of the endplate. Initial uncoordinated depolarization presents clinically as visible muscle fasciculations. Because succinylcholine is not rapidly cleaved by junctional acetylcholinesterase, the endplate remains persistently depolarized and refractory to further action potentials, inducing flaccid skeletal muscle paralysis within 30 to 60 seconds (duration 5 to 10 minutes).
• Metabolism: Rapidly hydrolyzed in plasma by butyrylcholinesterase (pseudocholinesterase); only ~10% of injected dose reaches the neuromuscular junction.
• Life-Threatening Hyperkalemic Cardiac Arrest: In healthy individuals, succinylcholine causes a transient, benign rise in serum potassium of approximately 0.5 mEq/L. However, in conditions associated with muscle denervation, immobilization, or widespread trauma, skeletal muscle cells synthesize and express immature extrajunctional acetylcholine receptors (alpha-7 homopentamers and fetal alpha-2-beta-gamma-delta isoforms) across the entire sarcolemma outside the neuromuscular junction. When succinylcholine binds these widespread extrajunctional receptors, massive, uncontrolled systemic potassium efflux occurs, driving serum potassium to > 7-10 mEq/L within minutes, triggering refractory ventricular fibrillation and asystole.
• Absolute Contraindications to Succinylcholine:
  • Denervation injury: paraplegia, quadriplegia, stroke with hemiparesis (> 48-72 hours after onset until neurological recovery).
  • Major thermal burns (> 24-48 hours post-injury until full epithelialization, often > 1-2 years).
  • Massive crush injury, acute rhabdomyolysis, or severe abdominal sepsis.
  • Prolonged bedrest or immobility in the intensive care unit (> 1-2 weeks).
  • Muscular dystrophies (Duchenne, Becker muscular dystrophy) due to sarcolemmal fragility and fatal hyperkalemic rhabdomyolysis.
  • Personal or family history of Malignant Hyperthermia.
  • Pre-existing severe hyperkalemia (K+ > 5.5 mEq/L).
• Atypical Pseudocholinesterase & The Dibucaine Number: Genetic deficiency or structural mutation of plasma butyrylcholinesterase leads to failure of succinylcholine hydrolysis, resulting in prolonged apnea lasting 2 to 8 hours following a standard single dose. Diagnosed via the Dibucaine Test:
  • Normal Enzyme: Dibucaine (a local anaesthetic) inhibits normal pseudocholinesterase by ~80% (Dibucaine Number = 80).
  • Heterozygous Atypical: Dibucaine inhibits 50% to 60% (Dibucaine Number = 50-60; mild prolongation of apnea, ~20-30 min).
  • Homozygous Atypical: Dibucaine inhibits only ~20% of enzyme activity (Dibucaine Number = 20; severe prolonged paralysis for hours).
  • Management of Prolonged Apnea: Continued mechanical ventilation, full sedation to prevent awareness, and reassurance until spontaneous esterase metabolism or renal excretion clears the drug. Administration of fresh frozen plasma is possible but generally discouraged due to transfusion risks.

Malignant Hyperthermia (MH): Pathophysiology & Emergency Protocol

• Genetic Etiology: Autosomal dominant pharmacogenetic skeletal muscle channelopathy, caused in > 70% of cases by mutations in the RYR1 gene (ryanodine receptor type 1) or rarely the CACNA1S gene (alpha-1 subunit of the L-type voltage-dependent calcium channel / dihydropyridine receptor).
• Triggers: All volatile inhalational anaesthetics (sevoflurane, isoflurane, desflurane, halothane) and the depolarizing muscle relaxant succinylcholine.
• Pathophysiology: Uncontrolled, massive calcium release from the sarcoplasmic reticulum into the skeletal muscle sarcoplasm, overwhelms reuptake pumps. Continuous calcium presence drives sustained actomyosin cross-bridge cycling, producing relentless myofibrillar hypermetabolism, cellular ATP depletion, catastrophic lactic acidosis, cell membrane lysis, and rhabdomyolysis.
• Clinical Manifestations:
  • Earliest & Most Sensitive Sign: Unexplained, rapid, precipitous rise in end-tidal CO2 (EtCO2) that is completely refractory to marked increases in minute ventilation.
  • Masseter Muscle Rigidity (MMR) or generalized "lead-pipe" skeletal muscle rigidity following succinylcholine administration.
  • Tachycardia, tachypnea, unstable arrhythmias, and profound cyanosis/mottling.
  • Combined profound respiratory and metabolic (lactic) acidosis.
  • Hyperthermia: Temperature rises rapidly by 1°C every 5 minutes, frequently reaching 42-43°C (a late clinical sign; waiting for hyperthermia before treating results in high mortality!).
  • Rhabdomyolysis: Dark brown "tea-colored" urine (myoglobinuria), hyperkalemia, elevated serum creatine kinase (CK > 20,000-100,000 U/L), acute renal failure, and disseminated intravascular coagulation (DIC).
• Immediate Emergency Treatment Protocol (MHAUS Guidelines):
  1. Halt Triggers Immediately: Turn off all volatile vaporizers; discontinue succinylcholine. Do not waste time changing circuits—switch to 100% FiO2 at maximum fresh gas flow (>= 10-12 L/min) and insert activated charcoal filters into the breathing circuit if available. Maintain general anaesthesia with IV infusions (propofol, opioids).
  2. Call for Help & The MH Cart: Mobilize the clinical team.
  3. Administer Dantrolene Sodium:
     • Specific Ryanodine-1 receptor antagonist that blocks calcium release from the sarcoplasmic reticulum.
     • Initial Dose: 2.5 mg/kg rapid IV push.
     • Repeat boluses of 1 to 2.5 mg/kg every 5 to 10 minutes until hypermetabolism resolves (reversal of tachycardia, normalization of EtCO2, muscle flaccidity). Maximum cumulative dose is traditionally 10 mg/kg (can exceed if necessary).
  4. Active Patient Cooling: Cold IV isotonic crystalloids (30-40 mL/kg at 4°C); surface ice packs to the groins, axillae, and neck; avoid routine gastric or bladder lavage. Titrate chilled IV fluid to the volume that can safely be administered. Stop active cooling once core temperature drops below 38.5°C to prevent inadvertent hypothermic overshoot.
  5. Treat Life-Threatening Hyperkalemia: Intravenous calcium chloride (10 mL of 10%) or calcium gluconate (30 mL of 10%) for cardiac membrane stabilization; 10 units regular insulin with 50 mL of 50% dextrose; IV sodium bicarbonate (1-2 mEq/kg) to buffer severe metabolic acidosis.
  6. Maintain Urine Output: IV hydration and mannitol/furosemide to achieve urine output >= 1-2 mL/kg/hr, preventing obstructive myoglobin cast nephropathy.

Non-Depolarizing NMBDs: Classes & Pharmacokinetics

Non-depolarizing agents act as competitive antagonists at the post-junctional nAChR, preventing acetylcholine binding without inducing initial depolarization (no fasciculations). Characterized by "fade" on Train-of-Four (TOF) monitoring and post-tetanic potentiation.

1. Aminosteroid Compounds:
   • Rocuronium: Rapid onset (60 to 90 seconds at standard dose 0.6 mg/kg; 60 seconds at RSI dose 1.2 mg/kg, making it the primary non-depolarizing substitute for succinylcholine in rapid sequence intubation). Intermediate duration of action (30-60 minutes). Elimination is predominantly biliary/hepatic excretion (70%) with secondary renal clearance (30%).
   • Vecuronium: Intermediate onset (2-3 minutes) and duration (30-45 minutes). Deacetylated in liver, excreted via bile and kidneys.
2. Benzylisoquinolinium Compounds:
   • Cisatracurium: Intermediate onset and duration (35-45 minutes). Does not trigger histamine release (hemodynamically neutral).
   • The Hofmann Elimination: Spontaneously degrades in plasma and tissues via non-enzymatic Hofmann elimination (a pH- and temperature-dependent chemical cleavage) and non-specific plasma ester hydrolysis. Elimination is completely independent of hepatic and renal function. Cisatracurium is the absolute drug of choice for neuromuscular blockade in patients with acute kidney injury, end-stage renal disease, or severe hepatic failure.

Pharmacological Reversal: Neostigmine vs Sugammadex

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Airway Assessment & Rapid Sequence Intubation (RSI)

Unanticipated difficult airway management and pulmonary aspiration are leading causes of anaesthetic-related morbidity and brain injury.

Bedside Predictors of the Difficult Airway

• Mallampati Classification: Assessed with the patient sitting upright, head in neutral position, mouth opened maximally, and tongue protruded without phonation:
  • Class I: Soft palate, fauces, uvula, and bilateral tonsillar pillars fully visible (easy direct laryngoscopy anticipated).
  • Class II: Soft palate, fauces, and uvula visible; pillars hidden by tongue base.
  • Class III: Soft palate and base of the uvula visible; tonsillar pillars and posterior wall invisible.
  • Class IV: Only the hard palate is visible; soft palate completely obscured (high probability of difficult direct laryngoscopy).
• Thyromental Distance (Patil Test): Measured from the thyroid notch to the tip of the mental prominence with the neck fully extended. A distance < 6.0 cm (or < 3 ordinary fingerbreadths) indicates an anterior larynx and a sharp acute angle between the oral and pharyngeal axes, predicting difficult direct laryngoscopy.
• Inter-Incisor Gap (Mouth Opening): Normal is >= 4.0 cm (>= 2 to 3 fingerbreadths). An inter-incisor opening < 3.0 cm limits blade insertion and tube manipulation.
• Upper Lip Bite Test (ULBT): Evaluates mandibular range of motion. Class 1: lower incisors bite the upper lip above the vermilion border; Class 2: bite below the vermilion border; Class 3: cannot bite upper lip (predicts difficult laryngoscopy).

The 7 Ps of Rapid Sequence Intubation (RSI)

RSI is the gold-standard procedure designed to secure the trachea rapidly in patients at high risk of gastric aspiration:

1. Preparation (Zero Minus 10 Minutes):
   • Check and verify all equipment: two working suctions with rigid Yankauer tips under the mattress, functioning direct and video laryngoscopes (with alternate blade sizes), appropriately sized endotracheal tubes (ETTs with stylets or bougies pre-loaded; e.g., 7.0-7.5 mm for adult females, 8.0-8.5 mm for adult males), syringe for cuff inflation, rescue supraglottic airway (LMA), and emergency surgical cricothyroidotomy equipment.
   • Ensure reliable wide-bore intravenous access and verify functioning standard monitoring (ECG, pulse oximetry, non-invasive blood pressure, continuous quantitative capnography).
2. Preoxygenation / Denitrogenation (Zero Minus 5 Minutes):
   • Administer 100% FiO2 for 3 full minutes of tidal breathing (or 8 consecutive maximal vital capacity breaths) via a tight-fitting face mask with an airtight seal at high flow (>= 10-15 L/min).
   • Physiological Goal: Washes out nitrogen from the patient's Functional Residual Capacity (FRC; ~2,500 mL) and replaces it with pure oxygen, creating an intrapulmonary oxygen reservoir that extends the safe apnea time (time until SpO2 drops < 90%) from ~1-2 minutes up to 6-8 minutes in healthy adults.
3. Pre-treatment / Optimization (Zero Minus 3 Minutes):
   • Optional pharmacological adjuncts: Fentanyl (1-3 mcg/kg) to attenuate the sympathetic hypertensive surge in intracranial pathology; Lidocaine (1.5 mg/kg) to suppress reactive airway bronchospasm.
4. Paralysis with Induction (Zero Time):
   • Rapid, sequential intravenous administration of a predetermined, weight-adjusted hypnotic induction agent (e.g., Ketamine 1.5-2.0 mg/kg, Propofol 1.5-2.5 mg/kg, or Etomidate 0.3 mg/kg) followed immediately by a rapid-onset neuromuscular blocker (Succinylcholine 1.5 mg/kg or Rocuronium 1.2 mg/kg).
5. Protection & Positioning (Zero Plus 30 Seconds):
   • Cricoid Pressure (Sellick Maneuver): Application of posterior pressure (10 Newtons while awake, increasing to 30 Newtons upon loss of consciousness) to the complete, rigid signet ring of the cricoid cartilage, compressing the cervical esophagus against the anterior body of the sixth cervical vertebra (C6) to prevent passive regurgitation.
   • Controversial Rule: If cricoid pressure impairs laryngoscopic view, impedes ETT passage, or if the patient begins actively vomiting, cricoid pressure must be released immediately to avoid esophageal rupture.
   • Maintain oxygenation while limiting gastric insufflation: Classical RSI omits routine bag-mask ventilation, but gentle low-pressure ventilation may be needed to prevent hypoxaemia, especially in patients with limited reserve. Do not wait for severe desaturation; if intubation fails, promptly provide rescue facemask or supraglottic ventilation and follow the difficult-airway plan.
6. Placement of Tube (Zero Plus 60 Seconds):
   • As soon as muscle relaxation is established (cessation of fasciculations with succinylcholine, or at 60 seconds with 1.2 mg/kg rocuronium), perform gentle laryngoscopy, visualize the vocal cords, and pass the ETT with the cuff positioned 2-3 cm below the cords. Inflate the pilot cuff.
7. Post-Intubation Management & Tube Confirmation (Zero Plus 90 Seconds):
   • Waveform Capnography: The definitive gold standard for confirming tracheal placement is continuous quantitative waveform capnography, demonstrating sustained, rectangular exhaled CO2 waveforms for at least 5 to 6 consecutive breaths (ruling out transient CO2 cleared from the stomach). Auscultate bilateral mid-axillary lung fields and the epigastrium (silence over stomach). Release cricoid pressure only after confirmation.

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Regional & Local Anaesthesia: Neuraxial Techniques & LAST

Regional anaesthesia provides targeted surgical insensibility and superior postoperative analgesia while preserving spontaneous airway reflexes.

Neuraxial Anatomy & Clinical Performance: Spinal vs Epidural

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|                        SPINAL (SUBARACHNOID) VS EPIDURAL ANAESTHESIA                     |
+-----------------------------------------------------------------------------------------+
| SPINAL BLOCK (Subarachnoid Space)         | EPIDURAL BLOCK (Potential Epidural Space)   |
| - Punctures Dura & Arachnoid mater         | Does NOT puncture dura (potential space)    |
| - Injection into CSF below conus (L3-L4)  | Injection outside dura (loss-of-resistance) |
| - Needle: Thin, fine pencil-point (25-27G)| Needle: Large bore Tuohy needle (16-18G)    |
| - Volume: Small volume (1.5 - 3.5 mL)      | Volume: Large volume (10 - 20 mL)           |
| - Onset: Ultra-rapid (2 to 5 minutes)      | Onset: Slower, segmental (15 to 20 minutes) |
| - Dense sensory AND motor block            | Titratable; differential sensory block      |
| - Single shot (catheter rare)             | Indwelling catheter for continuous infusion |
+-----------------------------------------------------------------------------------------+

• Anatomical Landmarks & Safety: The adult spinal cord terminates as the conus medullaris at the lower border of L1 or upper border of L2 (in neonates and infants, it extends to L3). Therefore, lumbar puncture and spinal anaesthesia must always be performed below L2 (typically at the L3-L4 or L4-L5 interspace) to avoid traumatic needle impalement of the spinal cord. The intercristal line (Tuffier's line), connecting the superior margins of the iliac crests, crosses the spine at the L4 spinous process or L4-L5 interspace.
• Tissue Layers Traversed in Midline Approach:
  1. Skin
  2. Subcutaneous fat
  3. Supraspinous ligament
  4. Interspinous ligament
  5. Ligamentum flavum (dense, rubbery resistance; sudden pop/loss of resistance indicates entry into epidural space)
  6. Epidural space (epidural endpoint)
  7. Dura mater
  8. Arachnoid mater (pop indicates entry into subarachnoid space; withdrawal of stylet yields clear CSF; spinal endpoint)
  9. Subarachnoid space containing CSF and cauda equina.
• Physiological Consequences of High Sympathetic Blockade: Pre-ganglionic sympathetic fibers (T1 to L2) are small, thinly myelinated B fibers, and blocked at a level 2 to 4 dermatomes higher than sensory blockade. Sympathetic blockade causes arterial and prominent venous dilatation (venous pooling, drop in systemic vascular resistance and preload). If the block ascends to T1-T4, the cardiac accelerator sympathetic fibers are blocked, precipitating the clinical triad of profound hypotension, bradycardia, and decreased cardiac output. Management requires IV crystalloid volume loading and prompt administration of vasopressors: Phenylephrine (pure alpha-1 agonist; drug of choice in tachycardia) or Ephedrine (mixed alpha and beta agonist; drug of choice in concurrent bradycardia) or Epinephrine in severe collapse.
• Post-Dural Puncture Headache (PDPH): Caused by persistent CSF loss through a dural tear, causing intracranial hypotension, traction on pain-sensitive meninges and cranial nerves (CN V, IX, X), and compensatory cerebral vasodilation. Presents 12-48 hours post-procedure as a severe, fronto-occipital, throbbing postural headache (markedly aggravated by standing or sitting, completely relieved by lying flat) accompanied by neck stiffness, photophobia, and tinnitus. Conservative therapy: brief recumbency for symptom relief, adequate oral hydration (IV fluid if oral intake is inadequate), oral caffeine, and analgesics. The definitive curative treatment for persistent, debilitating PDPH is an Epidural Blood Patch (EBP): under sterile conditions, 15 to 20 mL of sterile autologous venous blood drawn from the patient's antecubital vein is injected into the epidural space at or adjacent to the original puncture site, immediately forming a fibrin gelatinous plug that seals the dural hole.

Local Anaesthetic Systemic Toxicity (LAST)

Local anaesthetic systemic toxicity (LAST) is a life-threatening emergency caused by inadvertent intravascular injection of local anaesthetics or rapid systemic absorption from highly vascular anatomical compartments (vascularity rank: intercostal > caudal > epidural > brachial plexus > femoral > subcutaneous).

• Cellular Mechanism: Local anaesthetics block voltage-gated sodium channels (Nav1.5 in myocardium, Nav1.1-1.3 in brain). Long-acting, highly lipophilic amide anaesthetics—particularly Bupivacaine—bind with high affinity to resting and inactivated sodium channels and dissociate exceptionally slowly during diastole. This leads to profound conduction block, prolonged PR and QRS intervals, re-entrant ventricular arrhythmias, negative inotropy, and sudden unheralded electromechanical dissociation.
• Clinical Progression & Warning Signs:
  • Central Nervous System Signs (Initial / Lower Concentrations): Circumoral numbness, metallic taste in the mouth, lightheadedness, auditory tinnitus, visual disturbances, slurred speech, shivering, involuntary muscle twitching, escalating rapidly into generalized tonic-clonic seizures, followed by CNS depression, unconsciousness, and apnea.
  • Cardiovascular Collapse Signs (Higher Concentrations): Sinus bradycardia, conduction heart blocks, broad complex ventricular tachycardia, torsades de pointes, ventricular fibrillation, severe refractory hypotension, and asystole.

The Emergency LAST Resuscitation Protocol: 20% Lipid Emulsion

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|                        LAST EMERGENCY RESUSCITATION BUNDLE                              |
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| 1. STOP INJECTION: Immediately halt local anaesthetic administration; call for help     |
| 2. AIRWAY & OXYGENATION: 100% FiO2; hyperventilate to prevent acidosis & hypercapnia   |
| 3. SEIZURE SUPPRESSION: IV Midazolam (1-2 mg); avoid large doses of propofol           |
| 4. ANTIDOTE: 20% LIPID EMULSION (INTRALIPID) PROTOCOL:                                  |
|    * Initial IV Bolus: 1.5 mL/kg over 2-3 minutes (~100 mL for a 70-kg adult)              |
|    * Continuous IV Infusion: 0.25 mL/kg/min (~18 mL/min; ~1,000 mL/hr)                  |
|    * Repeat bolus once or twice every 3-5 min if cardiac collapse persists             |
|    * Can double infusion rate to 0.5 mL/kg/min; max cumulative dose: 12 mL/kg in 30 min |
| 5. ACLS MODIFICATIONS: Small-dose Epinephrine (< 1 mcg/kg); AVOID vasopressin, lidocaine|
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• Mechanism of 20% Lipid Emulsion (The "Lipid Sink" Theory): Intralipid droplets form an intravascular lipid partition that extracts lipophilic local anaesthetic molecules from the aqueous plasma phase, pulling the drug away from high-affinity myocardial and cerebral binding sites. Additionally, lipid emulsion directly enhances myocardial fatty acid beta-oxidation, overrides mitochondrial toxicity, and activates calcium/potassium channel homeostasis.
• ACLS Protocol Modifications for LAST:
  • Epinephrine: Use reduced doses (< 1 mcg/kg boluses, e.g., 10 to 50 mcg IV in adults). Standard 1 mg ACLS doses exacerbate myocardial ischemia, hyperlactatemia, and trigger intractable arrhythmias in local-anaesthetic-poisoned hearts.
  • Absolute Drug Contraindications: NEVER administer Lidocaine or other local anaesthetics as antiarrhythmics. Avoid vasopressin (provokes pulmonary hemorrhage and worsens cardiac recovery), beta-blockers, and calcium channel blockers.
  • Prolonged cardiopulmonary resuscitation (CPR) for > 60 minutes is often required while lipid emulsion clears tissue levels; prepare for emergency veno-arterial Extracorporeal Membrane Oxygenation (VA-ECMO) or cardiopulmonary bypass if circulation fails to restore.