Anaesthesia: Airway management and anaesthetic drugs

• The airway: Airway Anatomy for Anaesthesia | Airway Assessment | Basic Airway Management and Devices | Tracheal Intubation | Rapid Sequence Induction | The Difficult Airway — DAS Guidelines | Can't Intubate, Can't Oxygenate
• Anaesthetic drugs: IV Induction Agents | Inhalational Agents | Neuromuscular Blockers and Reversal | Opioids in Anaesthesia | Vasopressors, Antiemetics and Other Drugs | Drug Reactions and Pharmacogenetics | Oxygen Delivery and Ventilation Basics
• Revision: Airway and Anaesthetic Drugs at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🫁 Airway management and anaesthetic drugs. Keeping a patient oxygenated is the anaesthetist's first job. Most airways are straightforward, but difficulty is not always predictable, so every doctor who manages airways needs a plan A, B, C and D. The anaesthetic drugs — induction agents, volatiles, neuromuscular blockers and opioids — are powerful, have narrow safety margins and cause some of the classic exam reactions.
Your four questions for every airway and anaesthetic: Is this airway likely to be difficult — to mask, to intubate, or to rescue? What is my plan if the first attempt fails? Which drugs, at what doses, for this patient's physiology? What reactions or complications could occur — and am I ready for them?

Airway Anatomy for Anaesthesia

• Upper airway — nose and mouth → pharynx (nasopharynx, oropharynx, laryngopharynx) → larynx → trachea.
• Larynx — at C3–C6 in adults; epiglottis (covers the glottis on swallowing), vocal cords (the narrowest part in adults — the glottis), thyroid cartilage, cricoid cartilage (the only complete ring), cricothyroid membrane (between thyroid and cricoid — site for emergency front-of-neck access).
• Nerve supply — superior laryngeal nerve (internal branch — sensation above the cords; external — cricothyroid muscle), recurrent laryngeal nerve (sensation below the cords and all other intrinsic muscles — injury in thyroid surgery causes hoarseness; bilateral — stridor), glossopharyngeal (posterior third of the tongue).
• Laryngospasm — reflex closure of the cords from light anaesthesia with stimulation (secretions, blood, extubation) — jaw thrust (Larson's point), CPAP with 100% oxygen, deepen anaesthesia (propofol), suxamethonium if persistent.
• Trachea — C6 to the carina at T4/5 (angle of Louis), about 10–12 cm long; the right main bronchus is shorter, wider and more vertical — endobronchial intubation and inhaled objects go right.
• Upper airway obstruction when unconscious — the tongue and soft palate fall back — head tilt–chin lift, jaw thrust, adjuncts.
• Child vs adult airway — large occiput, large tongue, high anterior larynx (C3–4), floppy U-shaped epiglottis, narrow subglottis — see paediatric page.

Airway Assessment

• History — previous difficult airway (anaesthetic chart, airway alert letter), OSA, snoring, head and neck cancer or radiotherapy, trauma, burns, rheumatoid arthritis or ankylosing spondylitis (neck), acromegaly, obesity, pregnancy.
• Examination:
  • Mouth opening — inter-incisor distance under 3 cm (or 3 fingers) suggests difficulty.
  • Mallampati score (sitting, mouth open, tongue out):
    • Class I — soft palate, fauces, uvula and pillars visible.
    • Class II — soft palate, fauces and uvula.
    • Class III — soft palate and base of uvula.
    • Class IV — hard palate only (predicts difficulty).
  • Thyromental distance under 6 cm (3 finger-breadths).
  • Neck movement — limited extension; jaw protrusion (can't bite the upper lip).
  • Dentition — prominent upper incisors, loose teeth, crowns; beards (mask seal).
  • Neck circumference, BMI.
• Predicting difficult mask ventilation — "BOOTS" or "OBESE" — Beard, Obesity, Older age, Toothless, Snoring (OSA), restricted jaw protrusion.
• Cormack–Lehane grade (view at direct laryngoscopy) — 1 (full view of the cords), 2 (posterior part of the cords or arytenoids), 3 (epiglottis only), 4 (no epiglottis) — grade 3 and 4 are difficult.
• No single test is reliable — combine findings; plan for unexpected difficulty in every patient; nasendoscopy for head and neck pathology.

Basic Airway Management and Devices

• Manoeuvres — head tilt–chin lift, jaw thrust (suspected cervical spine injury), positioning ("sniffing the morning air" — neck flexed, head extended; ramped in obesity).
• Oropharyngeal (Guedel) airway — size from the incisors to the angle of the jaw; only in patients without a gag reflex (may cause vomiting or laryngospasm).
• Nasopharyngeal airway — tolerated in semi-conscious patients; avoid in suspected basal skull fracture (relative) and coagulopathy.
• Bag-valve-mask ventilation — a two-person technique (two hands on the mask, one squeezes) is more effective; airway adjunct helps.
• Supraglottic airway devices (SAD) — e.g. i-gel, LMA (laryngeal mask airway) — sit above the glottis; quick to insert; used for many elective GAs and as a rescue device in failed intubation and in cardiac arrest (second-generation devices have a gastric drain port).
  • Don't protect fully against aspiration — avoid in high aspiration risk (full stomach, pregnancy, obesity, reflux) for routine use.
• Tracheal tube — cuffed tube in the trachea — the "definitive airway" — protects against aspiration, allows controlled ventilation.
• Oxygen during apnoea — apnoeic oxygenation (nasal cannula at 15 L/min or high-flow nasal oxygen — THRIVE) extends safe apnoea time during intubation.

Tracheal Intubation

• Indications — airway protection (GCS 8 or less, burns, trauma, bleeding), respiratory failure, need for controlled ventilation, surgery (abdominal, prolonged, prone, head and neck), aspiration risk, transfer of a critically ill patient.
• Equipment — laryngoscopes (Macintosh curved blade — tip in the vallecula; videolaryngoscope — now recommended as first-line for many intubations — DAS/ICS), bougie, tubes (adult women 7.0–7.5 mm, men 8.0–8.5 mm), suction, 10 mL syringe, capnography, tube tie.
• Tube depth — about 21 cm at the teeth in adult women and 23 cm in men.
• Confirming tube placement:
  • Sustained waveform capnography — the gold standard ("no trace = wrong place").
  • Seeing the tube pass through the cords; chest movement; auscultation (both axillae and the epigastrium); misting; chest X-ray (tip 3–5 cm above the carina — position, not placement).
• Complications — oesophageal intubation (unrecognised — a never event), endobronchial intubation (right main bronchus — unilateral breath sounds, hypoxia), dental damage, sore throat, airway trauma, hypoxia, aspiration, hypotension (induction drugs and positive pressure), arrhythmias, laryngospasm and bronchospasm, cuff-related tracheal stenosis (prolonged).
• Hypoxia after intubation — "DOPES" — Displaced tube, Obstructed tube (secretions, kinking), Pneumothorax, Equipment failure (oxygen supply, ventilator), Stacked breaths (breath stacking — auto-PEEP in asthma and COPD).
• Awake tracheal intubation — flexible bronchoscope or videolaryngoscope with topical anaesthesia and light sedation — for predicted very difficult airways (DAS 2020).
• Extubation (DAS extubation guidelines) — plan; "low risk" vs "at risk" extubation; awake, sitting up, after suction, with 100% oxygen; reintubation plan.

Rapid Sequence Induction

• Purpose — secure the airway quickly in patients at risk of aspiration (emergency surgery, bowel obstruction, pregnancy, trauma, critically ill patients in ED and ICU) — minimise time from loss of airway reflexes to a cuffed tube.
• Preparation — checklist (e.g. NAP4 / DAS / RCEM / ICS), team roles, plan A–D verbalised, drugs drawn up, suction, two working IV lines, monitoring including capnography, optimise physiology ("resuscitate before you intubate" — fluids, vasopressor ready).
• Preoxygenation — 100% oxygen for 3 minutes (tight-fitting mask, head up, or NIV or high-flow nasal oxygen in hypoxic patients); apnoeic oxygenation with nasal cannulae.
• Drugs:
  • Induction — ketamine (1–2 mg/kg — haemodynamically safer in shock), propofol (1–2.5 mg/kg — reduced doses in unstable patients), thiopental (traditional for obstetric RSI), etomidate (adrenal suppression — not routinely in UK); often with fentanyl.
  • Neuromuscular blocker — rocuronium 1–1.2 mg/kg (onset about 60 seconds; reversible with sugammadex) or suxamethonium 1–1.5 mg/kg (onset 30–60 seconds, short-acting).
• Cricoid pressure (Sellick's manoeuvre — 30 N) — traditional; evidence weak; release if it hinders the view or ventilation; now optional in many UK guidelines.
• Gentle mask ventilation during the onset period is increasingly accepted (reduces hypoxia — PREVENT trial).
• Post-intubation — confirm with capnography, secure the tube, ongoing sedation (propofol, midazolam, opioid infusions), NG tube, chest X-ray, ventilator settings.
• Peri-intubation cardiac arrest — hypoxia, hypotension and acidosis ("the physiologically difficult airway") — optimise before induction, push-dose vasopressors ready.

The Difficult Airway — DAS Guidelines

• Difficult Airway Society (DAS) guidelines for unanticipated difficult intubation in adults (2015 — updated guidance 2025) — a stepwise plan with oxygenation as the priority:

  Plan	Aim	Actions
  Plan A	Facemask ventilation and tracheal intubation	Optimise position, preoxygenate, videolaryngoscopy, bougie, external laryngeal manipulation; maximum 3 attempts (plus 1 by a more experienced colleague) — declare failed intubation
  Plan B	Maintain oxygenation — supraglottic airway	Second-generation SAD (maximum 3 attempts); if oxygenation works — stop and think (wake the patient, intubate through the SAD with a fibreoptic scope, proceed with SAD or front-of-neck access)
  Plan C	Final attempt at facemask ventilation	Two-person technique with adjuncts; ensure full neuromuscular blockade; if successful — wake the patient (sugammadex if rocuronium)
  Plan D	Emergency front-of-neck access (FONA)	"Can't intubate, can't oxygenate" (CICO) — scalpel cricothyroidotomy

• Key principles — call for help early; limit attempts (repeated attempts cause swelling and bleeding); declare failure out loud; use the Vortex approach or similar cognitive aids; human factors (fixation error — NAP4).
• Predicted difficult airway — awake tracheal intubation, experienced operator, ENT surgeon present for possible tracheostomy under local anaesthetic.
• Airway alert — after a difficult airway, document fully, tell the patient (difficult airway alert letter) and GP.

Can't Intubate, Can't Oxygenate

• CICO — failure of tracheal intubation, SAD and facemask ventilation with falling oxygen saturation — a life-threatening emergency — declare "CICO — front-of-neck access".
• Scalpel cricothyroidotomy ("scalpel–bougie–tube" — DAS):
  • Ensure full neuromuscular blockade; extend the neck (pillow under shoulders).
  • Identify the cricothyroid membrane (laryngeal handshake); if it can't be felt — an 8–10 cm vertical midline skin incision then blunt dissection to find it.
  • Transverse stab incision through the membrane with a size 10 scalpel blade, rotate 90° (sharp edge towards the feet).
  • Slide a bougie along the blade into the trachea, then railroad a size 6.0 cuffed tube; inflate the cuff, ventilate, confirm with capnography, secure.
• Needle cricothyroidotomy — with jet ventilation — mainly children under about 8–10 years (scalpel technique in adults — needle techniques have high failure rates).
• Complications — bleeding, false passage, tracheal or oesophageal injury, subglottic stenosis; convert to formal tracheostomy later.
• Training — regular simulation; FONA kit in every airway trolley.

⚠️ Safety Pearl: Patients die from failure to oxygenate, not failure to intubate. Limit attempts, call it early — "this is a CICO situation" — and perform scalpel cricothyroidotomy before cardiac arrest, not after.

IV Induction Agents

• Reduce doses in older, frail, hypovolaemic and septic patients ("half the dose, twice the time").
• Dexmedetomidine — alpha-2 agonist — sedation without respiratory depression (ICU, awake procedures); bradycardia and hypotension.

Inhalational Agents

• Volatile anaesthetics — sevoflurane, desflurane, isoflurane — mechanism not fully understood (GABA-A potentiation and other ion channels).
• MAC (minimum alveolar concentration) — the alveolar concentration that prevents movement in 50% of patients in response to a surgical incision — a measure of potency (lower MAC = more potent); MAC falls with age, hypothermia, pregnancy, opioids and benzodiazepines; rises in children and with chronic alcohol use.
• Speed of onset and offset depends on the blood:gas partition coefficient — low solubility = fast (desflurane and nitrous oxide fastest, then sevoflurane, then isoflurane).
• Key features:

  Agent	Features
  Sevoflurane	Sweet-smelling, non-irritant — gas induction (children); bronchodilator; most widely used
  Desflurane	Fast offset (obesity, long cases); airway irritant (not for induction); needs a heated vaporiser; very high global warming potential — use is being phased out in the NHS
  Isoflurane	Cheap, pungent, slower
  Nitrous oxide (N2O)	Weak anaesthetic (MAC 105%), good analgesic (Entonox); expands gas-filled spaces (avoid in pneumothorax, bowel obstruction, middle ear surgery, intraocular gas); PONV; vitamin B12 inactivation (subacute combined degeneration with prolonged or recreational use); greenhouse gas

• Common effects of volatiles — dose-dependent hypotension (vasodilatation), respiratory depression, bronchodilatation, uterine relaxation (postpartum haemorrhage risk), raised ICP (cerebral vasodilatation at high concentrations), PONV, malignant hyperthermia trigger.
• Sustainability — anaesthetic gases contribute a large share of NHS anaesthetic carbon footprint — prefer sevoflurane or TIVA, low fresh gas flows; decommission nitrous oxide manifolds (waste).

Neuromuscular Blockers and Reversal

• Depolarising — suxamethonium:
  • Binds nicotinic acetylcholine receptors and depolarises the motor end plate → fasciculations then paralysis; dose 1–1.5 mg/kg; onset 30–60 seconds; duration about 5–10 minutes (metabolised by plasma butyrylcholinesterase).
  • Side effects — hyperkalaemia (rise of about 0.5 mmol/L; dangerous rises in burns after 24–48 hours, crush injury, denervation (spinal cord injury, stroke, Guillain–Barré), prolonged immobility, myopathies), bradycardia (especially repeated doses and children), myalgia, raised intraocular and intragastric pressure, malignant hyperthermia trigger, anaphylaxis, prolonged block (butyrylcholinesterase deficiency — "sux apnoea").
• Non-depolarising — competitive antagonists at the nicotinic receptor:
  • Rocuronium (aminosteroid) — fast onset at high dose (RSI), intermediate duration; reversed by sugammadex.
  • Atracurium and cisatracurium (benzylisoquinolinium) — Hofmann degradation (independent of liver and kidney — good in organ failure); atracurium releases histamine.
  • Vecuronium, mivacurium, pancuronium (older).
• Monitoring — peripheral nerve stimulator — train-of-four (TOF) (ulnar nerve — adductor pollicis); fade with non-depolarising block; TOF ratio over 0.9 before extubation (residual paralysis causes hypoxia and aspiration); quantitative monitoring now recommended.
• Reversal:
  • Neostigmine (anticholinesterase — raises acetylcholine) — given with glycopyrronium (or atropine) to block muscarinic effects (bradycardia, secretions, bronchospasm); only works when some recovery is present.
  • Sugammadex — a modified cyclodextrin that encapsulates rocuronium (and vecuronium) — can reverse even deep block (16 mg/kg for immediate reversal after RSI dose); reduces the effectiveness of hormonal contraception (extra precautions for 7 days); anaphylaxis (rare).
• Myasthenia gravis — very sensitive to non-depolarising blockers, resistant to suxamethonium; Lambert–Eaton — sensitive to both.
• Awareness — paralysis without adequate anaesthesia — the main risk factor for accidental awareness (NAP5).

Opioids in Anaesthesia

• Opioid side effects — respiratory depression (monitor sedation score — sedation precedes respiratory depression), nausea and vomiting, constipation, itch, urinary retention, hypotension, delirium, tolerance and opioid-induced hyperalgesia.
• Naloxone — 100–200 microgram IV increments (400 micrograms in arrest or overdose) — short half-life (about 1 hour) — repeat or infusion; watch for re-sedation.
• Opioid-sparing — regional anaesthesia, paracetamol, NSAIDs, dexamethasone, ketamine, lidocaine infusions, gabapentinoids (limited evidence; sedation).

Vasopressors, Antiemetics and Other Drugs

• Vasopressors in theatre:
  • Phenylephrine — pure alpha-1 agonist — raises BP with reflex bradycardia — first line for spinal hypotension in caesarean section (infusion).
  • Metaraminol — mainly alpha-1 (and some indirect) — bolus or infusion.
  • Ephedrine — indirect sympathomimetic (alpha and beta) — raises BP and heart rate — good when hypotension with bradycardia; tachyphylaxis.
  • Noradrenaline — infusion (central or peripheral short-term) — septic shock and major surgery.
  • Adrenaline — anaphylaxis, cardiac arrest, severe bronchospasm.
• Anticholinergics — glycopyrronium (doesn't cross the blood–brain barrier — less confusion) and atropine (crosses — central effects; faster for bradycardia) — bradycardia, antisialagogue, with neostigmine.
• Antiemetics (PONV prevention — see page 3):
  • Ondansetron (5-HT₃ antagonist) — QT prolongation, constipation.
  • Dexamethasone (4–8 mg at induction) — PONV, swelling, analgesia; raises glucose.
  • Cyclizine (H1 antagonist) — tachycardia, avoid in heart failure.
  • Droperidol, prochlorperazine, metoclopramide (dopamine antagonists — extrapyramidal effects; avoid in Parkinson's), aprepitant.
• Tranexamic acid — antifibrinolytic — reduces blood loss in orthopaedic, cardiac and trauma surgery and postpartum haemorrhage.
• Antibiotic prophylaxis — within 60 minutes before incision (re-dose in long operations or large blood loss) — e.g. cefuroxime ± metronidazole or co-amoxiclav per local policy.
• Dantrolene — for malignant hyperthermia (see next section).

Drug Reactions and Pharmacogenetics

• Perioperative anaphylaxis (NAP6 — about 1 in 10,000 anaesthetics):
  • Commonest causes — antibiotics (teicoplanin, co-amoxiclav), neuromuscular blockers (rocuronium, suxamethonium, atracurium), chlorhexidine, patent blue dye; latex is now rare.
  • Presentation — hypotension is the commonest first sign (often the only sign); bronchospasm, rising airway pressures, loss of capnography trace, rash may be absent or late.
  • Treatment — stop triggers, call for help, 100% oxygen, legs up, IV adrenaline 50 micrograms boluses (titrated) then infusion; IV fluids; CPR if systolic under 50 mmHg; mast cell tryptase at 0, 1–2 and 24 hours; refer to an allergy clinic; report (MHRA Yellow Card).
• Malignant hyperthermia (MH):
  • Autosomal dominant — RYR1 (ryanodine receptor) mutations (CACNA1S less often) — uncontrolled calcium release in skeletal muscle when exposed to volatile agents or suxamethonium.
  • Features — unexplained rise in end-tidal CO₂ (earliest), tachycardia, masseter spasm and generalised rigidity, hyperthermia (late), hyperkalaemia, metabolic and respiratory acidosis, rhabdomyolysis (high CK, myoglobinuria), arrhythmias, DIC.
  • Treatment (AAGBI MH guideline) — stop volatile agents (switch to TIVA), high-flow 100% oxygen, hyperventilate, call for help, IV dantrolene 2.5 mg/kg (repeat 1 mg/kg boluses up to 10 mg/kg), active cooling, treat hyperkalaemia and arrhythmias, ICU.
  • Follow-up — refer patient and family to the UK MH Investigation Unit (Leeds) — in vitro contracture test; genetic testing; "MH-safe" anaesthetics (TIVA, regional) in future.
• Butyrylcholinesterase (pseudocholinesterase) deficiency — inherited (autosomal recessive variants) or acquired (pregnancy, liver disease, malnutrition, some drugs) — prolonged paralysis after suxamethonium or mivacurium — keep sedated and ventilated until the block wears off (hours); test patient and family; alert card.
• Porphyria — acute porphyria triggered by thiopental, etomidate, some others — use propofol and check drug safety databases.
• CYP2D6 — codeine and tramadol ultra-rapid metabolisers (toxicity) and poor metabolisers (no effect).

💡 Clinical Pearl: An unexpected rise in end-tidal CO₂ that doesn't respond to increased ventilation is the earliest sign of malignant hyperthermia — high temperature comes late. Stop the volatile and give dantrolene.

Oxygen Delivery and Ventilation Basics

• Oxygen delivery devices:

  Device	Approximate FiO2	Use
  Nasal cannulae (1–4 L/min)	24–40%	Mild hypoxia; comfortable
  Simple face mask (5–10 L/min)	35–60%	Moderate hypoxia
  Venturi mask (fixed performance)	24%, 28%, 35%, 40%, 60%	COPD with CO2 retention — controlled oxygen (target 88–92%)
  Non-rebreather (reservoir) mask (15 L/min)	Up to about 80–90%	Critically ill, trauma, CO poisoning
  High-flow nasal oxygen (up to 60 L/min, heated, humidified)	Up to 100%, set precisely	Type 1 respiratory failure, preoxygenation and apnoeic oxygenation

• Oxygen targets (BTS 2017) — 94–98% for most; 88–92% if at risk of hypercapnic respiratory failure (COPD, obesity hypoventilation, neuromuscular disease, chest wall disease).
• Oxygen cascade — inspired PO₂ (about 21 kPa) falls through the alveoli (about 13 kPa — alveolar gas equation), arterial blood (about 12–13 kPa) to the mitochondria.
• Causes of hypoxaemia — low inspired oxygen, hypoventilation (opioids, neuromuscular weakness — high CO₂), V/Q mismatch (commonest — pneumonia, PE, COPD), shunt (doesn't correct with oxygen — ARDS, atelectasis, intracardiac), diffusion impairment.
• Intraoperative ventilation — volume or pressure control; lung-protective ventilation (tidal volume 6–8 mL/kg ideal body weight, PEEP 5 cmH₂O or more, recruitment) reduces postoperative pulmonary complications.
• Atelectasis — occurs in most patients under GA (high FiO₂, reduced FRC, supine position) — PEEP, recruitment manoeuvres, early mobilisation, physiotherapy.

Airway and Anaesthetic Drugs at a Glance

Spot the Diagnosis