Pre-anaesthetic Assessment & Premedication

The pre-anaesthetic evaluation is the single most important step in reducing peri-operative morbidity. It allows risk stratification (ASA grading), optimisation of co-morbidities, planning of anaesthetic technique, informed consent, and rational use of premedication to achieve a smooth, safe induction. This is a recurring, scoring topic in NEET PG — high on definitions, ASA classes, fasting guidelines, Mallampati grading, and the pharmacology of premedicants.

Goals of pre-anaesthetic assessment (PAC)

The Pre-Anaesthetic Check-up (PAC) is ideally done in a dedicated clinic days before elective surgery.

• Establish rapport, allay anxiety, obtain informed consent.
• Detect & optimise co-morbidities (HTN, diabetes, IHD, asthma, COPD).
• Predict and plan for the difficult airway.
• Decide anaesthetic technique (GA vs regional vs MAC).
• Order targeted investigations (not routine "battery" testing).
• Prescribe fasting orders and premedication.
• Risk-stratify using ASA grade and functional capacity.

High-yield: History is the most important component of PAC — it picks up more clinically relevant problems than examination or investigations combined.

Functional capacity — METs

Exercise tolerance is quantified in Metabolic Equivalents (METs). 4 METs is the key threshold.

METs	Activity	Significance
1 MET	Eating, dressing, using toilet	Poor reserve
4 METs	Climbing 1 flight of stairs, brisk walk, light housework	Cut-off — < 4 METs = poor capacity, higher risk
> 10 METs	Strenuous sport (swimming, singles tennis)	Excellent reserve

High-yield: A patient who cannot climb two flights of stairs (< 4 METs) is at increased peri-operative cardiac risk and warrants further evaluation.

ASA Physical Status Classification

Devised by the American Society of Anesthesiologists. It grades physical status, NOT operative risk directly, though the two correlate. The suffix "E" is added for emergency surgery.

ASA	Definition	Examples
I	Normal healthy patient	Healthy, non-smoker, no/minimal alcohol
II	Mild systemic disease, no functional limitation	Controlled HTN/DM, smoker, pregnancy, obesity (BMI 30–40), mild lung disease
III	Severe systemic disease, functional limitation	Poorly controlled DM/HTN, COPD, BMI ≥ 40, MI/CVA/stent > 3 months ago, ESRD on dialysis
IV	Severe disease that is a constant threat to life	Recent (< 3 mo) MI/CVA/stent, ongoing cardiac ischaemia, sepsis, severe valve dysfunction, ESRD not dialysed
V	Moribund, not expected to survive 24 h without surgery	Ruptured AAA, massive trauma, intracranial bleed with mass effect
VI	Brain-dead patient — organ harvesting for donation	—

High-yield: "E" denotes Emergency, not "extreme". A healthy patient for emergency appendicectomy is ASA I E.

Mnemonic for ASA: "Healthy, Mild, Severe, Threatening, Dying, Donor" (I → VI).

Airway assessment

The cornerstone of safe anaesthesia. The aim is to predict difficult mask ventilation, difficult intubation, and difficult front-of-neck access.

Mallampati classification (modified, Samsoon & Young)

Patient seated, mouth maximally open, tongue protruded, no phonation. Assesses oropharyngeal structures visible.

Class	Structures visible
I	Soft palate, uvula, fauces, pillars
II	Soft palate, uvula, fauces (pillars hidden)
III	Soft palate + base of uvula only
IV	Soft palate not visible (only hard palate)

High-yield: Class III and IV predict difficult laryngoscopy/intubation.

Other airway predictors

• Thyromental distance (Patil's test): tip of chin to thyroid notch with neck extended. < 6 cm (< 3 fingerbreadths) predicts difficult intubation.
• Sternomental distance: < 12.5 cm — difficult airway.
• Inter-incisor (mouth opening): < 3 cm (< 2 fingers) is concerning.
• Wilson score, upper lip bite test (Class III = lower teeth cannot reach upper lip = difficult).
• Atlanto-occipital extension: reduced movement predicts difficulty (e.g. ankylosing spondylitis, RA).

Difficult mask ventilation mnemonic — "BONES" / "OBESE": Beard, Obese (BMI > 26), No teeth (edentulous), Elderly (> 55), Snoring/Stiff lungs.

Difficult intubation mnemonic — "LEMON": Look externally, Evaluate 3-3-2 rule, Mallampati, Obstruction, Neck mobility.

High-yield: 3-3-2 rule → mouth opening = 3 fingers, hyoid-to-chin = 3 fingers, thyroid notch-to-floor of mouth = 2 fingers.

Pre-operative fasting (NPO) guidelines

Aimed at minimising gastric volume to reduce risk of pulmonary aspiration (Mendelson's syndrome). ASA "2-4-6-8" rule:

Intake	Minimum fasting time
Clear fluids (water, clear juice, black tea/coffee, carbohydrate drink)	2 h
Breast milk	4 h
Infant formula / non-human milk / light meal (toast)	6 h
Fatty/fried meal, meat	8 h

High-yield: Encouraging clear fluids up to 2 h before surgery is now recommended — prolonged fasting causes dehydration and hypoglycaemia without benefit.

Mendelson's syndrome: chemical aspiration pneumonitis. Classic risk if gastric volume > 25 mL (0.4 mL/kg) and pH < 2.5. Highest risk groups: pregnancy, obesity, diabetes (gastroparesis), hiatus hernia, emergency/full stomach. These warrant rapid sequence induction (RSI) with cricoid pressure (Sellick's manoeuvre).

Goals of premedication — "The 7 A's"

Premedication is the administration of drugs before anaesthesia to make the peri-operative course safer and smoother.

Mnemonic — Seven A's: Anxiolysis, Amnesia, Analgesia, Antisialagogue (↓ secretions), Anti-emesis, Anti-autonomic (blunt vagal reflexes), Antacid (↓ aspiration risk). Some add Attenuation of stress response and reduced Anaesthetic requirement.

Flow of a typical premedication plan: Anxiolytic (oral benzodiazepine night before/morning) → Aspiration prophylaxis (H2 blocker + PPI ± non-particulate antacid) → Antisialagogue if needed (glycopyrrolate) → Anti-emetic (ondansetron) → Analgesia/continue chronic meds.

Drug classes used in premedication

1. Anxiolytics / sedatives — Benzodiazepines

• Midazolam is the agent of choice — short-acting, water-soluble, produces excellent anterograde amnesia, anxiolysis. Oral/IV/IM/intranasal (useful in children).
• Diazepam, lorazepam — longer acting; lorazepam gives profound amnesia.
• Reversed by flumazenil.

High-yield: Midazolam is the most commonly used premedicant for anxiolysis and amnesia. Onset rapid; ideal context-sensitive profile.

2. Antisialagogues / anticholinergics

Block muscarinic receptors → ↓ secretions, ↓ vagal bradycardia. Important before ketamine, paediatric airway surgery, fibreoptic intubation.

Feature	Atropine	Glycopyrrolate	Hyoscine (Scopolamine)
Crosses BBB	Yes	No (quaternary)	Yes (most)
Antisialagogue effect	Moderate	Most potent	Strong
Tachycardia	Marked	Mild	Mild (can bradycardia)
CNS / sedation-amnesia	Central anticholinergic syndrome	None	Sedation + amnesia (best)
Anti-emetic	Weak	Weak	Good (anti-motion sickness)

High-yield: Glycopyrrolate is the best antisialagogue — twice as potent as atropine, does not cross the BBB (no central anticholinergic syndrome), and causes less tachycardia. Atropine is preferred when you want the heart rate to rise (e.g. bradycardia, with neostigmine reversal).

3. Aspiration prophylaxis

Three mechanisms — reduce volume, raise pH, neutralise acid:

• H2-receptor blockers — ranitidine: ↓ gastric acid secretion and volume; given evening before + morning of surgery.
• Proton pump inhibitors — omeprazole/pantoprazole: most effective at raising pH.
• Non-particulate antacid — sodium citrate (0.3 M): used in obstetrics immediately before emergency LSCS to neutralise existing acid. Particulate antacids (e.g. magnesium trisilicate) are avoided — they themselves cause pneumonitis if aspirated.
• Prokinetic — metoclopramide: ↑ gastric emptying, ↑ LES tone, anti-emetic.

High-yield: In the pregnant patient for emergency caesarean, the classic aspiration prophylaxis is ranitidine + metoclopramide + sodium citrate, plus RSI with cricoid pressure.

4. Anti-emetics (PONV prophylaxis)

• Ondansetron (5-HT3 antagonist) — first line.
• Dexamethasone, droperidol, metoclopramide, aprepitant, transdermal hyoscine.
• Apfel score predicts PONV risk: female sex, non-smoker, history of PONV/motion sickness, postoperative opioids (each = 1 point).

5. Analgesics

• Opioids (morphine, fentanyl) blunt the pressor response to laryngoscopy and provide pre-emptive analgesia.
• Multimodal: paracetamol, NSAIDs, gabapentinoids, alpha-2 agonists (clonidine, dexmedetomidine — also sedate and reduce anaesthetic requirement).

6. Special situations / aspiration-risk anti-aspiration

• Anti-allergic / steroid cover for patients on chronic steroids (stress dose).
• Bronchodilators continued in asthmatics/COPD.

Management of chronic medications

Drug	Peri-operative advice
Beta-blockers, statins	Continue (abrupt stop of β-blocker → rebound ischaemia)
ACE inhibitors / ARBs	Often withheld on morning of surgery (intra-op hypotension)
Oral hypoglycaemics / SGLT2i	Stop morning of surgery; metformin & SGLT2i (DKA risk) held; convert to insulin sliding scale
Warfarin	Stop ~5 days pre-op, bridge with LMWH if high thrombotic risk; check INR
Antiplatelets (clopidogrel)	Individualised — risk of stent thrombosis vs bleeding
OCPs / HRT	Stop 4–6 weeks pre-op for major surgery (VTE risk)

High-yield: Metformin is held peri-operatively because of risk of lactic acidosis (especially with contrast/renal impairment); β-blockers are continued.

Investigations — targeted, not routine

Modern practice: order tests guided by history, examination, age, and planned surgery — not a blanket battery.

• Hb/PCV — major surgery, anaemia symptoms, menstruating women.
• Coagulation — only if bleeding history, liver disease, anticoagulants.
• ECG — age, cardiac disease, major surgery.
• Blood sugar, renal function — diabetics, HTN, elderly.
• Chest X-ray — only if cardiopulmonary disease/symptoms (low yield routinely).
• Pregnancy test — women of childbearing age where relevant.

Complications & risks the PAC aims to prevent

• Pulmonary aspiration (Mendelson's syndrome) — full stomach, obstetric, obese, diabetic.
• Difficult/failed intubation — unanticipated difficult airway → hypoxia.
• Cardiac events — peri-operative MI in patients with poor reserve.
• Anaphylaxis — drug/latex allergy missed on history.
• Malignant hyperthermia — family/personal history is crucial (avoid suxamethonium + volatiles; have dantrolene ready).
• Awareness, PONV, hypothermia.

Key differentials / look-alike concepts

• ASA grade vs surgical risk score — ASA grades the patient; tools like the Revised Cardiac Risk Index (RCRI / Lee index) estimate cardiac event risk; Goldman index is the older version.
• Mallampati vs Cormack-Lehane — Mallampati is a pre-op bedside prediction; Cormack–Lehane (grades 1–4) is the actual laryngoscopic view at intubation.
• Atropine vs glycopyrrolate — distinguish by BBB crossing and chronotropy (see table).
• Non-particulate (sodium citrate) vs particulate antacid — only non-particulate used before anaesthesia.

Recently asked / exam angle

• ASA classification — match-the-following with examples; "ASA I E" trick for healthy emergency cases; recognising that uncontrolled DM = ASA III, recent MI (< 3 months) = ASA IV.
• Fasting guidelines — the 2-4-6-8 rule; clear fluids permitted up to 2 h; breast milk 4 h.
• Best antisialagogue = glycopyrrolate; "which does NOT cross BBB" = glycopyrrolate.
• Mallampati class III/IV predict difficult intubation; differentiate from Cormack-Lehane.
• Thyromental distance < 6 cm = difficult airway.
• Mendelson's syndrome definition + critical values (volume > 25 mL, pH < 2.5).
• Metformin withheld peri-operatively; β-blockers continued.
• Sodium citrate as the aspiration prophylaxis of choice in obstetric emergencies.
• METs < 4 = poor functional capacity, raised cardiac risk.
• Premedicant of choice for anxiolysis/amnesia = midazolam.

Rapid revision

1. History is the most valuable part of pre-anaesthetic assessment.
2. ASA I–VI; add "E" for emergency; ASA V = not expected to survive 24 h.
3. Functional capacity < 4 METs (can't climb 2 flights) → higher cardiac risk.
4. Fasting 2-4-6-8: clear fluids 2 h, breast milk 4 h, formula/light meal 6 h, fatty meal 8 h.
5. Mendelson's syndrome = aspiration pneumonitis; risk if gastric volume > 25 mL & pH < 2.5.
6. Mallampati III/IV & thyromental distance < 6 cm predict difficult intubation.
7. Cormack–Lehane = actual laryngoscopic view; Mallampati = bedside prediction.
8. Glycopyrrolate = best antisialagogue, no BBB crossing, least tachycardia.
9. Atropine chosen when you want ↑ heart rate (e.g. with neostigmine reversal).
10. Premedication goals = 7 A's (Anxiolysis, Amnesia, Analgesia, Antisialagogue, Anti-emesis, Anti-autonomic, Antacid).
11. Midazolam = premedicant of choice for anxiolysis + anterograde amnesia (reversed by flumazenil).
12. Obstetric aspiration prophylaxis = ranitidine + metoclopramide + sodium citrate + RSI with cricoid pressure; continue β-blockers, stop metformin.