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NEW Added to close a syllabus gap — preoperative assessment and interpretation of investigations is the first item under Clinical Anaesthesiology.

Preoperative assessment

Risk scoring, functional capacity, airway assessment, and interpreting the investigations the syllabus names.

Scoring systems

ASA gradeDefinition
INormal healthy patient
IIMild systemic disease, no functional limitation
IIISevere systemic disease with functional limitation
IVSevere systemic disease that is a constant threat to life
VMoribund, not expected to survive 24 hours without the operation
VIBrain-dead organ donor
  • Add "E" for emergency. ASA describes physical status, not operative risk — though it correlates with outcome.
  • Functional capacity: 4 METs is the threshold — climbing a flight of stairs, walking uphill. Below that, risk rises. 1 MET = 3.5 ml/kg/min oxygen consumption.
  • CPET: an anaerobic threshold below about 11 ml/kg/min, or VO₂ peak below 15, predicts increased perioperative risk.
  • Revised Cardiac Risk Index (Lee): high-risk surgery · ischaemic heart disease · heart failure · cerebrovascular disease · insulin-treated diabetes · creatinine >177 µmol/L. Risk rises with the number of factors.
  • Others worth naming: NYHA for heart failure, Child-Pugh and MELD for liver disease, P-POSSUM for surgical outcome.

Airway assessment

TestConcerning value
MallampatiIII–IV. I = soft palate, fauces, uvula, pillars; II loses pillars; III soft palate and uvula base only; IV hard palate only
Thyromental distance< 6 cm (about 3 fingerbreadths)
Sternomental distance< 12.5 cm
Mouth opening (interincisor)< 3 cm
Neck extension< 90° · Wilson score · prominent incisors · receding mandible
  • No single test is adequate alone — all have poor sensitivity and specificity. Use them as a composite, and always plan for failure.
  • Ask about previous difficult intubation, review old charts, and look for: obesity, pregnancy, OSA, rheumatoid arthritis (atlanto-axial instability), ankylosing spondylitis, acromegaly, burns, radiotherapy, and neck masses.

Interpreting investigations

ECG

  • Rate 300/big squares · rhythm · axis (normal −30° to +90°; leads I and aVF both positive) · intervals: PR 120–200 ms, QRS <120 ms, QTc <440 ms.
  • Ischaemia: ST elevation (territory tells the artery — II/III/aVF inferior/RCA; V1–V4 anterior/LAD; I/aVL/V5–6 lateral/circumflex), ST depression, T inversion, Q waves.
  • Electrolytes: hyperkalaemia — peaked T, flat P, wide QRS, sine wave. Hypokalaemia — flat T, U waves, ST depression. Hypocalcaemia prolongs QT; hypercalcaemia shortens it.

Lung function tests

  • Obstructive: FEV₁/FVC <0.7, raised RV and TLC (gas trapping), reduced peak flow. Restrictive: ratio preserved or raised, all volumes reduced.
  • Flow-volume loops: a flattened inspiratory limb indicates extrathoracic obstruction; flattened expiratory limb indicates intrathoracic; both flattened indicates a fixed lesion.
  • Transfer factor (DLCO) assesses the alveolar-capillary membrane; reduced in emphysema, fibrosis and anaemia.

Cardiac catheterisation and echo

  • Normal pressures: RA 0–8 · RV 25/5 · PA 25/10 (mean 15) · PAWP 6–12 · LV 120/10 · aorta 120/80 mmHg.
  • Ejection fraction: normal 55–70%; below 40% is significant impairment.
  • Aortic stenosis — severe: valve area <1 cm², mean gradient >40 mmHg, peak velocity >4 m/s.

Fasting and premedication

  • 6 hours solids and formula · 4 hours breast milk · 2 hours clear fluids.
  • Routine preoperative investigations are guided by NICE NG45 — they are dictated by ASA grade and surgical severity, not ordered reflexively.