Anaesthesia
Final Professional MBBS — Anaesthesiology. Explanation-first answers covering the principles and conduct of anaesthesia, the anaesthesia machine, airway, drugs, regional techniques, monitoring, fluids, complications and resuscitation, with classifications, comparison tables, drug doses, clinical pearls and key-point recaps from Morgan & Mikhail and Miller's Anesthesia.
Purpose
Preoperative assessment is the evaluation of a patient before anaesthesia and surgery. Its aims are to assess fitness for the proposed procedure, identify and optimise co-existing disease, predict and plan for difficulties (airway, cardiovascular, aspiration), plan the anaesthetic technique and postoperative care, obtain informed consent, and allay anxiety. Good assessment reduces perioperative morbidity, cancellations and delays.
History
The history covers the presenting surgical problem; co-existing medical conditions (especially cardiovascular, respiratory, diabetes, renal, hepatic and neurological disease); previous anaesthetics and any problems (nausea, difficult intubation, prolonged recovery) and a family history of anaesthetic problems (e.g. malignant hyperthermia, suxamethonium apnoea); a full drug history and allergies; and functional capacity (exercise tolerance). Smoking, alcohol, and, in women, pregnancy are recorded.
Examination
Examination focuses on the airway (mouth opening, Mallampati class, neck movement, thyromental distance, dentition — to predict difficult intubation), the cardiovascular and respiratory systems, and any relevant systems suggested by the history. Baseline vital signs, weight and height (BMI), and venous access are noted.
Investigations
Investigations are guided by the history, examination, the patient and the surgery — not ordered routinely. Common tests where indicated: full blood count (anaemia, infection), urea & electrolytes (renal disease, diuretics), blood glucose/HbA1c (diabetes), coagulation (liver disease, anticoagulants), ECG (cardiac disease, older patients), chest X-ray and echocardiography/pulmonary function in selected cases, and group and save/cross-match for procedures with blood-loss risk.
💡Investigations should be indicated, not routine: order a test only if the result could change management. Blanket ‘routine’ bloods and X-rays in fit patients for minor surgery add cost and false positives without benefit.Risk Assessment & Optimisation
The assessment concludes with an estimate of perioperative risk (using the ASA physical status, functional capacity and the magnitude of surgery) and a plan to optimise modifiable problems (e.g. controlling blood pressure or glycaemia, treating anaemia or infection, adjusting medications). High-risk patients are identified for enhanced monitoring, critical-care planning and senior involvement.
Airway Assessment
A structured airway assessment is a defining part of the anaesthetic pre-visit, because an unanticipated difficult airway is a major cause of anaesthetic harm. Alongside the Mallampati view, the anaesthetist assesses mouth opening (inter-incisor distance), thyromental distance, neck flexion and extension, jaw protrusion and the state of the dentition, and asks about previous difficult intubation, snoring or obstructive sleep apnoea, and conditions that distort the airway (rheumatoid arthritis, prior surgery or radiotherapy, tumours). No single test is reliable, so a combination is used to build an overall impression and, where difficulty is predicted, to plan an appropriate technique and equipment in advance.
Timing & the Pre-Assessment Clinic
Ideally the assessment happens far enough ahead of surgery that problems can be corrected — in a pre-assessment clinic for elective cases — rather than being discovered on the day when cancellation is the only option. Early assessment allows anaemia to be treated, blood pressure or diabetes to be brought under control, medications to be adjusted, further tests or specialist opinions to be obtained, and the patient to be given clear fasting and medication instructions, all of which reduce last-minute cancellations and improve safety and efficiency.
💡The pre-anaesthetic visit does three things at once: it gathers the information needed to plan a safe anaesthetic, it identifies and allows time to optimise problems before elective surgery, and it builds rapport and reduces anxiety — which is itself a form of premedication and improves the patient’s experience and recovery.Optimisation before surgery reduces perioperative morbidity most. 🔑KEY POINTS TO REMEMBER- Preop assessment: assess fitness, optimise disease, predict difficulty, plan technique, consent, reassure.
- History: co-existing disease, previous anaesthetics/family problems, drugs/allergies, functional capacity.
- Examination: airway (Mallampati, mouth opening, neck), CVS/RS, vitals, BMI, access.
- Investigations are indicated (by patient & surgery), not routine.
- Conclude with risk (ASA + functional capacity + surgery) and optimisation of modifiable problems.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition
The American Society of Anesthesiologists (ASA) physical status classification is a simple, widely used system that grades a patient’s overall pre-anaesthetic physical fitness. It provides a common language for describing how a patient’s general health may affect anaesthetic risk, and correlates broadly with perioperative morbidity and mortality — though it is not by itself a complete risk score.
Class Description Example ASA I Normal healthy patient Fit, non-smoker, no disease ASA II Mild systemic disease Well-controlled hypertension/diabetes, smoker, pregnancy ASA III Severe systemic disease (not incapacitating) Poorly controlled diabetes, stable angina, COPD ASA IV Severe disease that is a constant threat to life Recent MI, severe cardiac/respiratory failure ASA V Moribund; not expected to survive without operation Ruptured aneurysm, massive trauma ASA VI Brain-dead; organs for donation Organ retrieval Use of the ‘E’ Suffix & Interpretation
The suffix ‘E’ is added for an emergency operation (e.g. ASA IIIE), because emergency surgery independently increases risk. The ASA class captures only the patient’s physiological status — it does not account for the difficulty of the airway or the magnitude of surgery — so it is combined with functional capacity and the nature of the operation to estimate overall perioperative risk.
💡A quick anchor: ASA I = healthy; II = mild, well-controlled disease; III = severe but not immediately life-threatening; IV = severe and a constant threat to life; V = moribund; VI = brain-dead donor. Add ‘E’ for emergencies.⚠️ASA status is a description of physical fitness, not a stand-alone predictor of a specific patient’s outcome, and it does not measure airway difficulty. Use it alongside airway assessment, functional capacity and surgical risk rather than in isolation.Clinical Importance
Despite its simplicity, ASA status is valuable: it standardises communication, flags patients needing optimisation, higher monitoring or critical-care planning, and is used in audit and research. A higher ASA class prompts more thorough assessment, senior involvement and consideration of the risk–benefit balance of surgery.
Origins & Limitations of the System
The ASA classification was introduced to provide a simple, reproducible description of a patient’s pre-anaesthetic physical status, and its great strengths are its simplicity and universal familiarity. Its weaknesses are equally important to understand: assignment can be subjective, with inter-observer variation especially around classes II and III; it deliberately says nothing about the airway, the type or urgency of surgery, or the skill of the team; and it is a description of status, not a validated individual risk calculator. For these reasons it is used as one input into an overall clinical judgement of risk, complemented by functional capacity, disease-specific assessment and, where appropriate, formal risk indices.
💡A practical way to use ASA well is to treat it as shorthand for ‘how much systemic disease, how well controlled’, and then always append the two things it omits — the airway and the surgery — plus the patient’s functional capacity, to reach an overall risk picture.⚠️Do not let a comfortable-looking ASA class breed complacency: a patient may be ASA II on paper yet have an unrecognised difficult airway, or face high-risk emergency surgery that the physical-status grade does not capture. The class is a starting point for risk assessment, and the airway examination, urgency and surgical magnitude must always be considered alongside it.Grades physical status, not operative risk directly; E suffix for emergency. 🔑KEY POINTS TO REMEMBER- ASA I–VI grades pre-anaesthetic physical fitness; correlates broadly with perioperative risk.
- I healthy → II mild disease → III severe (not incapacitating) → IV constant threat to life → V moribund → VI brain-dead.
- ‘E’ suffix = emergency (independently raises risk).
- Reflects physiology only — not airway difficulty or surgical magnitude.
- Standardises communication; flags need for optimisation/critical care; used in audit.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Rationale
Anaesthesia abolishes the protective airway reflexes, so any gastric contents that regurgitate may be aspirated into the lungs, causing a chemical pneumonitis (Mendelson’s syndrome) or airway obstruction. Preoperative fasting aims to ensure an empty stomach at induction, reducing the volume and acidity of gastric contents and hence the risk and severity of aspiration.
Intake Minimum fast before anaesthesia Clear fluids (water, clear juice, black tea/coffee) 2 hours Breast milk 4 hours Formula / non-human milk / light meal 6 hours Fatty/fried food, large meal 8 hours or more The ‘2–4–6 (–8)’ Rule
Standard elective fasting follows the ‘2–4–6’ rule: 2 hours for clear fluids, 4 hours for breast milk, and 6 hours for solids/formula/non-human milk (with 8 hours for fatty meals). Importantly, encouraging clear fluids up to 2 hours before surgery keeps patients comfortable and does not increase risk.
Patients at Increased Risk
Some patients have a ‘full stomach’ despite fasting or delayed gastric emptying: emergencies/trauma (pain, opioids), pregnancy (from the second trimester), gastro-oesophageal reflux/hiatus hernia, diabetes (gastroparesis), bowel obstruction, and raised intra-abdominal pressure/obesity. These patients need aspiration precautions.
Aspiration Prophylaxis
In at-risk patients, prophylaxis reduces the volume and acidity of gastric contents and secures the airway: pharmacological — an H₂-receptor antagonist (ranitidine) or proton-pump inhibitor the night before/morning of surgery, a prokinetic (metoclopramide), and a non-particulate antacid (sodium citrate) immediately before induction; and technique — a rapid sequence induction with cricoid pressure and a cuffed tracheal tube to protect the airway.
⚠️Fasting does not guarantee an empty stomach in emergencies, pregnancy, diabetes or obstruction — treat these as a ‘full stomach’ and use a rapid sequence induction with aspiration prophylaxis rather than relying on nil-by-mouth alone.Physiology of Gastric Emptying & the ‘Full Stomach’
Fasting works because the healthy stomach empties clear fluids within about two hours, whereas solids and fatty meals take much longer, so a timed fast leaves the stomach reliably empty for elective surgery. That assumption breaks down whenever gastric emptying is delayed or gastric volume is increased — by pain and opioids after trauma, by the mechanical and hormonal effects of pregnancy, by the autonomic neuropathy of diabetes, by bowel obstruction, or by raised intra-abdominal pressure — which is why such patients are managed as having a ‘full stomach’ regardless of how long they have fasted, and why fasting alone is never regarded as a guarantee of an empty stomach.
Balancing Fasting Against Its Harms
While fasting reduces aspiration risk, excessive or poorly-managed fasting has its own harms — thirst, hunger, headache, irritability, dehydration and, in children and the frail elderly, hypoglycaemia and haemodynamic instability — and prolonged ‘nil by mouth’ from cancelled or delayed lists is a common, avoidable problem. Modern practice therefore actively encourages clear fluids up to two hours preoperatively and, in some settings, carbohydrate drinks, because these empty rapidly and improve patient comfort and metabolic state without increasing gastric volume at induction. The goal is a stomach that is empty of solids and low in residual fluid, not a needlessly dehydrated, miserable patient.
⚠️Two fasting errors recur: relying on the fasting time in a patient who actually has a full stomach (emergency, pregnancy, diabetes, obstruction), and, at the other extreme, subjecting patients to needlessly prolonged nil-by-mouth from repeatedly delayed lists. The safe course is to identify true aspiration risk and use RSI for it, while otherwise encouraging clear fluids up to two hours to keep patients hydrated and comfortable.The 2-4-6-8 rule balances aspiration risk against dehydration. 🔑KEY POINTS TO REMEMBER- Anaesthesia abolishes airway reflexes → aspiration risk (Mendelson’s syndrome).
- Elective fasting ‘2–4–6’: clear fluids 2 h, breast milk 4 h, solids/formula 6 h (fatty 8 h).
- Clear fluids up to 2 h are encouraged — comfort without added risk.
- ‘Full stomach’: emergency, pregnancy, reflux, diabetes, obstruction, obesity.
- Prophylaxis: H₂ blocker/PPI + prokinetic + sodium citrate; RSI with cricoid pressure + cuffed tube.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Aims
Premedication is the administration of drugs before anaesthesia to prepare the patient. Its aims are classically remembered as the ‘several As’: Anxiolysis (relieve anxiety), Amnesia, Analgesia, Antisialagogue (reduce secretions), Anti-emesis, Antacid/Aspiration prophylaxis, and Attenuation of autonomic (vagal) responses — plus continuation of essential regular medication.
Purpose Drug examples Anxiolysis / amnesia / sedation Benzodiazepines (midazolam, diazepam) Analgesia Opioids (morphine), NSAIDs, paracetamol Antisialagogue / antivagal Anticholinergics (atropine, glycopyrrolate) Anti-emesis Ondansetron, metoclopramide, dexamethasone Aspiration prophylaxis H₂ blocker/PPI, sodium citrate, metoclopramide Choosing Premedication
Premedication is tailored to the patient and procedure, not routine. A benzodiazepine (e.g. oral midazolam) relieves anxiety and provides amnesia; anticholinergics reduce secretions and blunt the vagal bradycardia caused by some drugs and airway manipulation; anti-emetics reduce postoperative nausea and vomiting; and analgesics contribute to multimodal pain control. Children may receive oral or intranasal sedation, and topical local anaesthetic cream for cannulation.
Continuation & Omission of Regular Drugs
Most regular medications are continued through surgery (e.g. antihypertensives — though ACE inhibitors/ARBs are sometimes withheld on the day; anti-anginals; inhalers; steroids). Some are adjusted or withheld: anticoagulants/antiplatelets (balancing bleeding and thrombosis), oral hypoglycaemics/insulin (adjusted for fasting), and certain others. This medication review is a key part of premedication.
💡Remember the aims of premedication as the ‘A’s: Anxiolysis, Amnesia, Analgesia, Antisialagogue, Anti-emesis, Antacid (aspiration prophylaxis) and Attenuation of vagal reflexes. Premedication is selective, chosen for the individual, not given to everyone.⚠️Sedative premedication must be used cautiously in the elderly, those with respiratory compromise or obstructive sleep apnoea, and in emergencies/full-stomach patients, where it can cause respiratory depression or obtund airway reflexes — and it should not delay urgent surgery.Timing & Routes
Premedication is timed and routed to suit its purpose: oral drugs are given with a sip of water an hour or so before surgery, while drugs needed rapidly (or in a patient who cannot swallow) are given intravenously in the anaesthetic room. In children, palatable oral or intranasal sedatives and topical local-anaesthetic cream for cannulation are particularly valuable in reducing distress. The choice always balances the benefit of a calm, comfortable, protected patient against the risks of over-sedation, and increasingly there is a move away from routine heavy sedative premedication towards a targeted approach and good preoperative explanation and reassurance, which itself reduces anxiety and the need for drugs.
💡Two ideas capture premedication: it is a menu, not a fixed prescription — you pick the ‘A’s the individual patient needs — and the most important single decision it contains is often the review of regular medications, deciding what to continue, adjust or stop around surgery.⚠️Sedative premedication is not free of hazard: in the elderly, in respiratory disease or obstructive sleep apnoea, and in the unfasted emergency patient it can cause respiratory depression, airway obstruction or blunted protective reflexes, and it must never be allowed to delay urgent surgery. It is prescribed selectively, in reduced doses in the vulnerable, and with monitoring where appropriate.Reduces anaesthetic requirement and smooths induction. 🔑KEY POINTS TO REMEMBER- Premedication = drugs before anaesthesia; aims = the ‘A’s (anxiolysis, amnesia, analgesia, antisialagogue, anti-emesis, antacid, attenuate vagal).
- Benzodiazepines (anxiolysis/amnesia), anticholinergics (secretions/vagal), anti-emetics, analgesics.
- Tailored to patient & procedure — not routine.
- Continue most regular drugs; adjust anticoagulants, antiplatelets, diabetic drugs; care with ACE-I/ARB.
- Cautious sedation in elderly, respiratory disease/OSA, and full-stomach patients.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Principle
Patients frequently have co-existing medical disease that increases anaesthetic risk. The principle is to assess control, optimise before elective surgery, continue key medication, and plan an anaesthetic that minimises the stress on the affected system. A selection of common conditions illustrates the approach.
Condition Key anaesthetic concern & plan Hypertension Optimise control; continue most antihypertensives; avoid wide BP swings Ischaemic heart disease Defer elective surgery after recent MI; continue anti-anginals; maintain O₂ supply/demand Diabetes mellitus Control glucose; adjust insulin/OHAs for fasting; first on the list; monitor glucose Asthma / COPD Optimise; continue inhalers/steroids; avoid triggers; regional where possible Chronic kidney disease Fluids/electrolytes; avoid nephrotoxins & renally-excreted drugs; timing of dialysis Cardiovascular Disease
Hypertension should be reasonably controlled before elective surgery to avoid exaggerated swings in blood pressure; most agents are continued. In ischaemic heart disease, elective surgery is deferred after a recent myocardial infarction, anti-anginal therapy is continued, and anaesthesia is conducted to maintain the balance of myocardial oxygen supply and demand (avoiding tachycardia, hypotension and hypertension).
Diabetes & Respiratory Disease
Diabetes: assess control (HbA1c) and end-organ disease; adjust insulin/oral hypoglycaemics for the fasting period, place the patient first on the operating list, and monitor blood glucose closely (a glucose–insulin–potassium or variable-rate insulin regimen for major surgery). Asthma/COPD: optimise and continue inhalers/steroids, avoid triggers of bronchospasm, and favour regional techniques where suitable.
💡Two high-yield rules: defer elective surgery after a recent MI (risk of re-infarction is highest early), and put the diabetic patient first on the list with glucose monitoring to minimise the fasting disturbance.⚠️Never cancel or proceed with elective surgery in a poorly controlled patient without weighing the risk–benefit and, where time allows, optimising first — but do not inappropriately delay emergency surgery for optimisation that can be done concurrently.A General Framework for Any Coexisting Disease
Faced with any chronic condition, the same framework applies: assess how severe and how well controlled the disease is and whether it has caused end-organ damage; optimise what can reasonably be improved before elective surgery; decide which medications to continue, adjust or withhold; anticipate how the disease and its drugs will interact with anaesthesia; and plan monitoring and postoperative care accordingly, involving relevant specialists and critical care where needed. This structured approach matters because the perioperative period imposes major physiological stress, and it is the interaction between that stress, the disease and the anaesthetic that determines outcome.
Steroids & Other Special Cases
A few specific situations recur in exams: patients on long-term corticosteroids may have a suppressed hypothalamic–pituitary–adrenal axis and need perioperative steroid supplementation to cover the stress of surgery and avoid an Addisonian crisis; patients with thyroid disease should be rendered euthyroid before elective surgery; and those on anticoagulants and antiplatelet agents require a careful plan that weighs the thrombotic reason for the drug against the bleeding risk of surgery and any planned regional technique. Recognising these special cases and planning for them in advance prevents avoidable perioperative crises.
💡Carry two exam-favourite rules into any coexisting-disease question: defer elective surgery after a recent myocardial infarction, when the risk of re-infarction is highest, and give stress-dose steroid cover to patients on long-term corticosteroids to prevent an Addisonian crisis under the stress of surgery.Elective surgery is deferred until comorbidity is optimised. 🔑KEY POINTS TO REMEMBER- Assess control, optimise before elective surgery, continue key drugs, plan to protect the affected system.
- Hypertension: control BP, continue agents, avoid swings; IHD: defer after recent MI, balance O₂ supply/demand.
- Diabetes: adjust insulin/OHAs, first on list, monitor glucose.
- Asthma/COPD: continue inhalers/steroids, avoid triggers, favour regional.
- Weigh risk–benefit for elective surgery; don’t delay emergencies for optimisation that can run concurrently.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition
The Mallampati classification is a bedside test used in airway assessment to predict the ease of laryngoscopy and intubation. With the patient sitting, mouth opened maximally and tongue protruded (without phonating), the visibility of the oropharyngeal structures is graded I–IV.
Mallampati classes I–IV: progressively less of the faucial pillars, uvula and soft palate is visible as the tongue obscures the view. Grades & Significance
Class I: soft palate, uvula and pillars visible. Class II: soft palate and uvula. Class III: soft palate and base of uvula only. Class IV: only the hard palate is seen. Higher classes (III–IV) predict a more difficult laryngoscopy/intubation. The test is one predictor among several — used with mouth opening, thyromental distance, neck movement and jaw protrusion — as no single test is reliable alone.
💡Higher Mallampati (III–IV) suggests a potentially difficult airway, but the test has limited sensitivity/specificity on its own; combine it with other predictors and always have a difficult-airway plan ready.Class Structures visible (mouth open, tongue out) I Soft palate, uvula, fauces, both pillars II Soft palate, uvula, fauces III Soft palate and base of uvula only IV Hard palate only — soft palate not seen Significance III and IV predict difficult intubation 🔑KEY POINTS TO REMEMBER- Mallampati: sitting, mouth open, tongue out — grades oropharyngeal view I–IV.
- I: palate+uvula+pillars; II: palate+uvula; III: base of uvula; IV: hard palate only.
- Higher class (III–IV) predicts more difficult laryngoscopy/intubation.
- One predictor among several — combine with mouth opening, thyromental distance, neck movement.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Indication
Rapid sequence induction (RSI) is a technique of inducing anaesthesia and rapidly securing the airway with a cuffed tracheal tube in patients at risk of aspiration (‘full stomach’ — emergencies, trauma, pregnancy, reflux, obstruction), minimising the time the airway is unprotected.
Technique
The classic steps: thorough preoxygenation; a predetermined dose of a rapidly acting induction agent (e.g. propofol/thiopentone) immediately followed by a rapidly-acting muscle relaxant (suxamethonium, or rocuronium); cricoid pressure (Sellick’s manoeuvre) applied as consciousness is lost; no manual ventilation (to avoid gastric insufflation) until the airway is secured; and prompt intubation with a cuffed tube, confirming placement before releasing cricoid pressure.
💡The essence of RSI is to move from awake to a protected airway as fast as possible — preoxygenate, give induction agent and fast-acting relaxant together, apply cricoid pressure, avoid bag-mask ventilation, intubate and confirm, then release cricoid.⚠️RSI patients are, by definition, at high aspiration risk and may desaturate quickly — have suction, a range of tubes, a bougie and a difficult-airway plan ready, and do not release cricoid pressure until the cuffed tube is confirmed in the trachea.Cricoid Pressure & Controversy
Cricoid pressure (Sellick’s manoeuvre) applies backward pressure on the cricoid cartilage to occlude the oesophagus against the vertebral body, aiming to prevent passive regurgitation reaching the pharynx during induction. It is applied as consciousness is lost and maintained until the cuffed tube is confirmed, but it is released if it impairs the view at laryngoscopy or if active vomiting occurs (to avoid oesophageal rupture). Its effectiveness is debated and it can distort the airway, so it is now regarded as a helpful but not infallible component of the technique rather than an absolute guarantee against aspiration.
💡The whole point of RSI is to minimise the unprotected interval: preoxygenate well, give the induction agent and a fast relaxant together, apply cricoid pressure, avoid bag-mask ventilation, and intubate — confirming the tube before releasing cricoid pressure.Used where aspiration risk is high — full stomach, pregnancy. 🔑KEY POINTS TO REMEMBER- RSI rapidly secures the airway in aspiration-risk (full-stomach) patients.
- Preoxygenate → induction agent + fast relaxant (suxamethonium/rocuronium) → cricoid pressure.
- Avoid manual ventilation; intubate with cuffed tube; confirm before releasing cricoid.
- Have suction, tubes, bougie & a difficult-airway plan ready.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition
Mendelson’s syndrome is the chemical (aspiration) pneumonitis that results from aspiration of acidic gastric contents into the lungs during anaesthesia. It was originally described in obstetric patients and is a feared complication of a ‘full stomach’ under anaesthesia.
Pathophysiology & Features
Aspiration of gastric acid (classically a pH < 2.5 and volume > 25 mL is considered high-risk) causes a chemical burn of the airways and alveoli, with bronchospasm, pulmonary oedema and hypoxaemia. Features include wheeze, cyanosis, tachypnoea, tachycardia and falling oxygen saturation, sometimes progressing to acute respiratory distress and secondary infection (aspiration pneumonia).
Prevention & Management
Prevention is paramount: fasting, identifying full-stomach patients, aspiration prophylaxis, and rapid sequence induction with cricoid pressure. If aspiration occurs: head-down/lateral position, suction the airway, secure it (intubate) and give 100% oxygen, with supportive respiratory care (ventilation/PEEP as needed). Antibiotics are given for secondary infection (not routinely), and steroids are not recommended.
💡The dangerous combination is acidic (pH < 2.5) and voluminous (> 25 mL) gastric aspirate. Prevention (fasting, prophylaxis, RSI with cricoid pressure) matters far more than any treatment after the event.Why Obstetric Patients Are High Risk
Mendelson described the syndrome in obstetric anaesthesia, and pregnant women remain a paradigm of aspiration risk: from mid-pregnancy the gravid uterus raises intra-abdominal pressure and displaces the stomach, progesterone relaxes the lower oesophageal sphincter, and labour and opioids delay gastric emptying, so a labouring woman is treated as having a full stomach. This is why obstetric general anaesthesia classically combines antacid prophylaxis with a rapid sequence induction, and why regional anaesthesia — which avoids instrumenting the airway of an unfasted patient — is generally preferred for caesarean section.
💡Fear the aspirate that is acidic and voluminous (pH < 2.5, > 25 mL): prevention through fasting, prophylaxis and RSI with cricoid pressure matters far more than anything you can do once pneumonitis has occurred — and steroids are not part of the treatment.Prevention by fasting and prophylaxis is far better than treatment. 🔑KEY POINTS TO REMEMBER- Mendelson’s syndrome = chemical pneumonitis from aspiration of acidic gastric contents.
- High-risk aspirate: pH < 2.5, volume > 25 mL → airway burn, bronchospasm, hypoxaemia.
- Features: wheeze, cyanosis, tachypnoea, desaturation ± later infection.
- Prevent (fasting, prophylaxis, RSI + cricoid); treat with suction, intubation, O₂, support; no routine steroids.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Uses
Anticholinergic (antimuscarinic) drugs — chiefly atropine and glycopyrrolate (and hyoscine) — are used in anaesthesia to reduce airway secretions (antisialagogue), block vagally-mediated bradycardia (from drugs such as suxamethonium or from airway/surgical stimulation), and as an adjunct with neostigmine during reversal of neuromuscular blockade (to prevent its muscarinic bradycardia).
Feature Atropine Glycopyrrolate Onset/heart rate Fast; marked tachycardia Slower; less tachycardia CNS (crosses BBB) Yes (can cause delirium) No (quaternary) — no central effects Antisialagogue Good More potent, longer Placenta Crosses Minimal crossing 💡Glycopyrrolate is a quaternary amine that does not cross the blood–brain barrier or placenta well, so it lacks central (delirium) effects and is preferred as an antisialagogue and with neostigmine; atropine acts faster on the heart and is the drug for acute bradycardia.Cautions
Anticholinergics cause tachycardia (caution in ischaemic heart disease), dry mouth, blurred vision, urinary retention, and — with atropine/hyoscine — central anticholinergic effects (confusion, especially in the elderly). They are used cautiously in glaucoma and the elderly.
Physostigmine & Central Anticholinergic Syndrome
Because atropine and hyoscine cross the blood–brain barrier, they can occasionally cause a central anticholinergic syndrome — confusion, restlessness or excessive sedation, particularly in the elderly — which can be reversed by physostigmine, a tertiary anticholinesterase that also crosses into the brain. Glycopyrrolate, being a quaternary compound that does not cross the barrier, avoids this problem, which is one of the reasons it is often preferred when an antisialagogue or an antimuscarinic partner for neostigmine is required.
💡Choose by the job: atropine for acute vagal bradycardia (fast, but crosses into the brain), glycopyrrolate as the antisialagogue and neostigmine partner (potent, longer, no central or placental effects).Glycopyrrolate does not cross the blood-brain barrier. 🔑KEY POINTS TO REMEMBER- Antimuscarinics (atropine, glycopyrrolate): reduce secretions, block vagal bradycardia, adjunct to neostigmine.
- Atropine: fast, marked tachycardia, crosses BBB (delirium) — drug for acute bradycardia.
- Glycopyrrolate: quaternary — no central effects, potent antisialagogue, minimal placental transfer.
- Cautions: tachycardia (IHD), dry mouth, retention, confusion (elderly), glaucoma.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Purpose
Pharmacological aspiration prophylaxis aims to reduce the volume and acidity of gastric contents (and promote emptying) in patients at risk of aspiration, so that if regurgitation occurs the aspirate is less harmful. It complements — but does not replace — fasting and a rapid sequence induction.
Drug Groups
H₂-receptor antagonists (e.g. ranitidine) and proton-pump inhibitors (e.g. omeprazole) reduce gastric acid secretion, raising the pH of contents (given the night before and/or morning of surgery). Prokinetics (metoclopramide) promote gastric emptying and increase lower-oesophageal sphincter tone. A non-particulate antacid (sodium citrate) given immediately before induction neutralises acid already present — particulate antacids are avoided as they themselves damage the lung if aspirated.
💡Use a non-particulate antacid (sodium citrate), not a particulate one, before induction — it neutralises residual acid without the risk of particulate matter causing its own pneumonitis. A classic combination is an H₂ blocker/PPI + metoclopramide + sodium citrate (e.g. in obstetrics).Putting the Regimen Together
In practice the drug groups are combined according to risk: for a high-risk elective patient an acid-suppressing agent is given the night before and morning of surgery to reduce the acidity of newly-secreted juice, a prokinetic encourages emptying, and, for the highest-risk situations such as obstetric general anaesthesia, a dose of non-particulate sodium citrate is given immediately before induction to neutralise the acid already in the stomach. The regimen never stands alone — it is always coupled with appropriate fasting, a rapid sequence induction and airway protection.
💡Reach for a non-particulate antacid: sodium citrate neutralises the acid already present without the lung-damaging particles of older antacids — and it works alongside, never instead of, fasting and a rapid sequence induction.⚠️Never regard pharmacological prophylaxis as a substitute for the mechanical protection of the airway: in a genuinely full-stomach patient the drugs reduce the harm of an aspirate but do not prevent regurgitation, so a rapid sequence induction with a cuffed tracheal tube remains essential.Non-particulate antacid is used — particulate antacids themselves damage lung. 🔑KEY POINTS TO REMEMBER- Reduce volume/acidity of gastric contents in aspiration-risk patients (adjunct to fasting + RSI).
- H₂ blockers/PPIs reduce acid secretion (raise pH).
- Prokinetics (metoclopramide) speed emptying & raise LOS tone.
- Sodium citrate (non-particulate antacid) neutralises residual acid — avoid particulate antacids.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition
Functional capacity — a patient’s ability to perform physical activity — is a valuable, simple predictor of perioperative (especially cardiac) risk. It is expressed in metabolic equivalents (METs), where 1 MET is the oxygen consumption at rest (~3.5 mL/kg/min). The more a patient can do, the greater their cardiorespiratory reserve.
METs Activity 1 MET Eating, dressing, using the toilet 4 METs Climbing a flight of stairs, walking on level ground briskly > 10 METs Strenuous sport (swimming, running) Clinical Use
A functional capacity of ≥ 4 METs (e.g. able to climb a flight of stairs without stopping) suggests adequate reserve and is reassuring before non-cardiac surgery, often allowing surgery to proceed without further cardiac testing. Patients unable to reach 4 METs, or whose capacity is unknown/limited by non-cardiac factors, may need further evaluation before major surgery.
💡A practical rule of thumb: a patient who can climb a flight of stairs (≥ 4 METs) without stopping usually has enough reserve for most surgery — poor or unknown functional capacity is a flag for closer assessment.Objective Measurement
When the history of functional capacity is unclear or the surgery is major, more objective assessment can be used, the most sophisticated being cardiopulmonary exercise testing (CPET), which measures oxygen uptake during graded exercise and yields values such as the anaerobic threshold that predict the ability to meet the increased oxygen demand of the perioperative period. Simpler surrogates such as the ability to climb stairs remain useful at the bedside, but CPET provides a quantified estimate of reserve that helps guide the level of postoperative care in high-risk major surgery.
💡Let the stairs be your bedside test: a patient who can climb a flight without stopping has roughly 4 METs of reserve and usually tolerates surgery well, whereas poor or unknown capacity is the signal to look harder before a major operation.⚠️Beware the patient whose functional capacity is unknown or limited by non-cardiac factors (arthritis, claudication, general debility): their inability to climb stairs may mask, rather than exclude, cardiac disease, so poor or indeterminate capacity before major surgery is a prompt for objective assessment rather than false reassurance.Climbing two flights of stairs is roughly 4 METs. 🔑KEY POINTS TO REMEMBER- Functional capacity predicts perioperative (cardiac) risk; measured in METs (1 MET = resting O₂ use).
- 4 METs = climbing a flight of stairs / brisk level walking.
- ≥ 4 METs is reassuring — often allows surgery without further cardiac testing.
- Poor/unknown capacity flags the need for further evaluation before major surgery.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Importance
Informed consent for anaesthesia is the process by which a patient (or, where they lack capacity, an appropriate substitute decision-maker) voluntarily agrees to the proposed anaesthetic after being adequately informed. It is both an ethical and legal requirement, respecting patient autonomy.
Requirements
Valid consent requires that the patient has the capacity to decide, is given sufficient information — the nature of the anaesthetic, its benefits, significant risks and alternatives (e.g. general vs regional) — in understandable terms, and consents voluntarily without coercion. The discussion (and, where used, the written form) is documented. In an emergency where the patient cannot consent, treatment proceeds in their best interests.
💡The three pillars of valid consent are capacity, information and voluntariness. Anaesthetic consent should specifically cover the technique and its material risks and alternatives — not be assumed to be covered by the surgical consent alone.Consent for the Patient Lacking Capacity
Special situations test the principles of consent: a patient who lacks capacity (through unconsciousness, cognitive impairment or the effects of illness) cannot give valid consent, so emergency treatment proceeds in their best interests, ideally informed by any advance directive and by discussion with those close to the patient. Children’s consent is given by a person with parental responsibility, with the child’s own wishes increasingly weighted as they mature, and throughout, the anaesthetist’s duty is to inform honestly, respect autonomy where it exists, and document the process carefully.
💡Anchor consent on its three pillars — capacity, information and voluntariness — and remember that the anaesthetic, with its own risks and alternatives (general versus regional), needs its own discussion rather than being folded silently into the surgical consent.⚠️Consent is a process, not a signature: a signed form without genuine understanding is not valid consent, and information should be tailored to what a reasonable patient in that situation would want to know about the anaesthetic’s material risks and alternatives.Consent is a process of communication, not merely a signature. 🔑KEY POINTS TO REMEMBER- Informed consent = voluntary agreement after adequate information; ethical & legal requirement.
- Requires capacity, sufficient information (nature, benefits, significant risks, alternatives), voluntariness.
- Document the discussion; cover the anaesthetic technique specifically.
- Emergency without capacity → act in the patient’s best interests.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.