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.
Definition & Importance
Hypoxia (inadequate oxygen delivery to the tissues) and hypoxaemia (low arterial oxygen) are among the most dangerous events in anaesthesia, because a few minutes of severe hypoxia cause irreversible brain injury or death. Prevention, early detection (pulse oximetry, capnography, clinical signs) and rapid correction are fundamental to anaesthetic safety.
Category Examples Low inspired oxygen Hypoxic gas mixture, disconnection, empty cylinder Hypoventilation Respiratory depression, obstruction, apnoea, high block Diffusion / shunt Atelectasis, aspiration, pneumothorax, oedema Airway problems Obstruction, laryngospasm, oesophageal/endobronchial tube Circulatory Low cardiac output, anaemia, severe hypotension Causes
Causes span the oxygen pathway: a low inspired oxygen (hypoxic mixture, disconnection, equipment failure); hypoventilation (drug-induced respiratory depression, airway obstruction, a high spinal); airway/tube problems (obstruction, laryngospasm, oesophageal or endobronchial intubation); pulmonary problems (atelectasis, aspiration, bronchospasm, pneumothorax, oedema); and circulatory causes (low cardiac output, severe anaemia).
Management
Management is immediate and systematic: give 100% oxygen, check the airway and ventilation (chest movement, capnograph, breath sounds — exclude obstruction, disconnection, oesophageal/endobronchial tube), ventilate manually to assess compliance, and check the circulation. Then treat the specific cause (e.g. relieve obstruction, suction, treat bronchospasm/pneumothorax, deepen anaesthesia for laryngospasm). Call for help early.
⚠️Hypoxia kills within minutes — respond immediately with 100% oxygen and a systematic check of airway, breathing and circulation, and call for help. Never delay to find the cause before oxygenating.💡For a falling saturation, act first (100% O₂) then reason through the oxygen pathway: inspired oxygen → ventilation → airway/tube → lungs → circulation. The commonest theatre causes are airway obstruction, hypoventilation and tube malposition.Timing — Induction, Maintenance & Recovery
Hypoxia can strike at any stage of the anaesthetic, and the likely causes differ with the phase. At induction the dangers are a difficult or failed airway, oesophageal intubation and apnoea before the airway is secured, which is why preoxygenation builds a reserve; during maintenance the concerns are disconnection, tube displacement or obstruction, hypoventilation and developing lung problems such as atelectasis or bronchospasm; and in recovery the risks are residual anaesthetic and relaxant effects causing hypoventilation, airway obstruction from a depressed conscious level, and laryngospasm. Recognising the phase-specific pattern helps the anaesthetist anticipate and rapidly identify the cause when the saturation falls, and it explains why monitoring and oxygen are continued right through into the recovery room.
Preventing Hypoxia
Prevention is as important as treatment, and it rests on a set of well-established safeguards built into every anaesthetic: careful preoxygenation before induction to create an oxygen reserve, an oxygen analyser and hypoxic-guard on the anaesthetic machine to prevent delivery of a hypoxic mixture, disconnection and airway-pressure alarms on the ventilator, continuous pulse oximetry and capnography, and confirmation of tube placement. Together these detect the great majority of problems before they cause harm, which is why anaesthesia is far safer than it once was; the anaesthetist’s role is to keep these defences in place, respond to their alarms, and maintain the clinical vigilance that ties them together.
💡For any falling saturation the discipline is oxygenate before you diagnose: give 100% oxygen and work down the oxygen pathway — inspired oxygen, ventilation, airway and tube, lungs, then circulation — while calling for help, because a few minutes of severe hypoxia cause irreversible harm.Always check the circuit and tube position first. 🔑KEY POINTS TO REMEMBER- Hypoxia/hypoxaemia is rapidly fatal — prevention, monitoring & fast correction are essential.
- Causes: low inspired O₂ (disconnection/hypoxic mix), hypoventilation, airway/tube problems, lung disease, circulatory.
- Manage: 100% O₂ first, then systematic airway–breathing–circulation check.
- Exclude disconnection, obstruction, oesophageal/endobronchial tube; ventilate manually to assess.
- Treat the specific cause; call for help early; oxygenate before diagnosing.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Trigger
Malignant hyperthermia (MH) is a rare, inherited (autosomal dominant) life-threatening hypermetabolic crisis of skeletal muscle, triggered by exposure to potent volatile anaesthetic agents and/or suxamethonium. A defect (commonly in the ryanodine receptor) leads to uncontrolled release of calcium in muscle, causing sustained contraction and a massive rise in metabolism.
Clinical Features
The earliest and most sensitive sign is an unexplained rise in end-tidal CO₂ (from increased production), with tachycardia, and often masseter/generalised muscle rigidity. Later: a rapidly rising temperature (a late sign), metabolic and respiratory acidosis, hyperkalaemia, arrhythmias, and rhabdomyolysis (myoglobinuria, high creatine kinase) leading to renal failure. It is fatal if untreated.
Management
Management is urgent: stop the trigger (discontinue volatile/suxamethonium), call for help and hyperventilate with 100% oxygen; give dantrolene (the specific treatment — it reduces calcium release) in repeated doses; and provide active cooling and supportive treatment of hyperkalaemia, acidosis, arrhythmias and myoglobinuria (fluids to protect the kidneys). Continue monitoring in intensive care.
⚠️A rising end-tidal CO₂ with tachycardia, rigidity and a climbing temperature during a volatile/suxamethonium anaesthetic is malignant hyperthermia until proven otherwise — stop the trigger, call for help, and give dantrolene without delay. Temperature rise is a late sign; do not wait for it.Susceptible Patients
Patients with a personal or family history of MH (or of an unexplained anaesthetic death) must have a trigger-free anaesthetic — total intravenous anaesthesia with a vapour-free machine, avoiding all volatiles and suxamethonium — with dantrolene available. Susceptibility is confirmed by specialist muscle (in-vitro contracture) testing.
💡MH = inherited hypermetabolic crisis triggered by volatiles and suxamethonium; earliest sign is rising ETCO₂. Treatment is stop trigger, 100% O₂, dantrolene, cool, correct hyperkalaemia/acidosis. Susceptible patients need a trigger-free (TIVA) anaesthetic. Nitrous oxide and IV agents are safe.Pathophysiology in Detail
The crisis of malignant hyperthermia arises from an inherited abnormality — most often of the ryanodine receptor that controls calcium release from the sarcoplasmic reticulum of skeletal muscle. When a susceptible patient is exposed to a triggering agent, this channel releases calcium in an uncontrolled way, so the muscle cannot relax and enters a state of sustained contraction; the enormous, futile consumption of oxygen and ATP that follows generates heat and carbon dioxide, depletes energy stores and, as membranes fail, releases potassium and myoglobin into the circulation. This single underlying defect therefore explains the whole clinical picture — the rising carbon dioxide and temperature, the rigidity, the acidosis and hyperkalaemia, and the rhabdomyolysis that threatens the kidneys — and it explains why dantrolene, which reduces this calcium release, is the specific antidote.
Distinguishing MH from Mimics
Not every rise in temperature or carbon dioxide under anaesthesia is malignant hyperthermia, and part of the skill is distinguishing it from conditions that mimic it: inadequate ventilation or exhausted soda lime raise carbon dioxide without hypermetabolism, sepsis and a warm environment raise temperature, thyroid storm and certain drug reactions produce hypermetabolic pictures, and light anaesthesia produces tachycardia and hypertension. What points to malignant hyperthermia is the combination — an unexplained, progressive rise in end-tidal carbon dioxide that outstrips ventilation, with tachycardia, rigidity and a later temperature rise, in the context of a triggering agent — and because the condition is rapidly fatal if missed, it is treated on suspicion while these alternatives are considered.
Rising EtCO₂ with masseter spasm is the earliest sign. Feature Detail Trigger All volatile agents, suxamethonium Genetics Autosomal dominant, RYR1 mutation Earliest sign Rising end-tidal CO₂, masseter spasm Later signs Tachycardia, rigidity, hyperthermia, acidosis Specific drug Dantrolene 2.5 mg/kg, repeated Confirmation Caffeine-halothane contracture test 🔑KEY POINTS TO REMEMBER- MH: inherited (ryanodine receptor) hypermetabolic muscle crisis; triggers = volatile agents & suxamethonium.
- Earliest sign: unexplained rising ETCO₂ + tachycardia; rigidity; late → hyperthermia, acidosis, hyperkalaemia, rhabdomyolysis.
- Treat: stop trigger, 100% O₂/hyperventilate, DANTROLENE, active cooling, correct K⁺/acidosis, protect kidneys.
- Susceptible patients: trigger-free TIVA, vapour-free machine, dantrolene available.
- Nitrous oxide & IV agents do NOT trigger MH.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Triggers
Anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction. Under anaesthesia it is usually caused by drugs given intravenously — most commonly neuromuscular blocking agents (especially suxamethonium), antibiotics, chlorhexidine and latex — and, because the patient is draped and unconscious, it may present atypically and be recognised late.
Immediate management of anaesthetic anaphylaxis: stop the trigger and call for help, secure the airway with 100% oxygen, give adrenaline, give large-volume IV fluids, and add adjuncts (with a later tryptase). Clinical Features
Features under anaesthesia include cardiovascular collapse (severe hypotension, tachycardia — often the first and most prominent sign), bronchospasm (high airway pressures, difficult ventilation, wheeze), cutaneous signs (flushing, urticaria, angioedema — may be hidden by drapes), and desaturation. Cardiovascular collapse and bronchospasm may dominate.
Management
Management is immediate: stop the likely trigger and call for help; secure the airway and give 100% oxygen; give adrenaline (the key drug — IM, or titrated IV boluses under monitoring for severe reactions); give large volumes of IV fluid (for the profound vasodilatation/capillary leak); and add adjuncts (antihistamine, corticosteroid). Later, take serial tryptase samples to confirm the reaction and refer for allergy testing to identify the culprit.
⚠️Adrenaline is the first-line, life-saving drug in anaphylaxis — do not delay it for antihistamines or steroids (which are adjuncts). Sudden unexplained hypotension, bronchospasm or high airway pressures under anaesthesia should prompt consideration of anaphylaxis.💡Anaesthetic anaphylaxis: commonest triggers are muscle relaxants, antibiotics, chlorhexidine, latex; it often shows as cardiovascular collapse and bronchospasm. Treat with adrenaline + oxygen + fluids (adrenaline first), then tryptase and allergy referral.Grading & the Central Role of Adrenaline
Anaphylactic reactions vary in severity from mild cutaneous signs to life-threatening cardiovascular collapse and bronchospasm, and under anaesthesia the milder cutaneous features are often hidden by the drapes, so the reaction may first announce itself as sudden, profound hypotension or as unexpectedly high airway pressures. Whatever the presentation, adrenaline is the single most important treatment, because it simultaneously reverses the key problems — it constricts blood vessels to counter the vasodilatation, supports the heart, relieves bronchospasm and reduces further mediator release. Antihistamines and corticosteroids have only an adjunctive, later role, and the common, dangerous error is to reach for them first; the correct instinct is early adrenaline, oxygen and large volumes of intravenous fluid while the trigger is removed and help summoned.
🔑KEY POINTS TO REMEMBER- Anaphylaxis: severe systemic hypersensitivity; anaesthetic triggers — muscle relaxants (esp. suxamethonium), antibiotics, chlorhexidine, latex.
- Features: cardiovascular collapse (often first), bronchospasm/high airway pressures, flushing/urticaria (may be hidden), desaturation.
- Manage: stop trigger, call help, airway + 100% O₂, ADRENALINE (first-line), large-volume IV fluids, adjuncts.
- Antihistamine/steroid are adjuncts — don’t delay adrenaline.
- Later: serial tryptase to confirm + allergy referral to identify the culprit.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Importance
Postoperative nausea and vomiting (PONV) is one of the commonest and most distressing complications of anaesthesia and surgery. Besides patient discomfort, it can cause dehydration, electrolyte disturbance, wound strain, aspiration and delayed discharge, so it is actively predicted, prevented and treated.
Risk factor category Examples Patient Female, non-smoker, previous PONV/motion sickness, younger Anaesthetic Volatile agents, nitrous oxide, opioids, longer anaesthesia Surgical Gynaecological, ENT/middle-ear, laparoscopic, squint Risk Factors
Well-recognised patient risk factors (the Apfel score) are female sex, non-smoker, a history of PONV or motion sickness, and postoperative opioid use. Anaesthetic factors include volatile agents, nitrous oxide and opioids; surgical factors include gynaecological, laparoscopic, ENT/middle-ear and squint surgery.
Prevention & Treatment
Management combines reducing risk and anti-emetic drugs. Risk is reduced by using propofol/TIVA (propofol is anti-emetic), avoiding nitrous oxide and minimising opioids (multimodal, opioid-sparing analgesia), and ensuring good hydration. Anti-emetics from different classes are combined for prophylaxis in at-risk patients: ondansetron (5-HT₃ antagonist), dexamethasone, and a dopamine antagonist (e.g. metoclopramide/droperidol), with additional agents to treat established PONV.
💡Predict PONV with the Apfel factors (female, non-smoker, previous PONV/motion sickness, opioids). Reduce risk with TIVA (propofol), no nitrous oxide, opioid-sparing analgesia, and give multiple anti-emetics from different classes (ondansetron + dexamethasone ± a dopamine antagonist).⚠️PONV is not merely unpleasant — it can cause dehydration, electrolyte disturbance, aspiration, wound dehiscence and delayed discharge. In high-risk patients, use combined prophylaxis and a low-PONV technique rather than waiting to treat.A Multimodal, Risk-Stratified Approach
Modern management of postoperative nausea and vomiting is risk-stratified and multimodal: the patient’s risk is estimated from factors such as the Apfel score, and the number of preventive measures is matched to that risk. For the low-risk patient little or no prophylaxis may be needed, whereas the high-risk patient receives a combination of strategies — a propofol-based technique avoiding nitrous oxide and minimising opioids, adequate hydration, and two or more anti-emetics acting at different receptors given prophylactically. This layered approach, attacking the problem at several points rather than relying on a single drug, is far more effective than waiting for nausea to develop and then treating it, and it has become central to enhanced-recovery programmes because nausea and vomiting are major causes of patient distress and delayed discharge.
Anti-emetic Drug Classes
The anti-emetics used against postoperative nausea and vomiting act at different receptors, which is why they are combined for additive effect: the 5-HT₃ antagonists such as ondansetron block serotonin receptors and are a mainstay; corticosteroids such as dexamethasone, given at induction, provide prolonged prophylaxis by an incompletely understood mechanism; dopamine antagonists such as metoclopramide, droperidol and prochlorperazine block the chemoreceptor trigger zone; and antihistamines and anticholinergics (for example cyclizine and hyoscine) act on the vomiting pathways and vestibular input. Choosing agents from different classes for a high-risk patient attacks the problem at several points and is more effective than increasing the dose of any single drug.
💡Sum PONV up as predict, prevent, treat: score the risk (Apfel), lower it with a propofol-based, nitrous-free, opioid-sparing technique, and give combined anti-emetics from different classes to the at-risk patient rather than waiting to treat established vomiting.Female, non-smoker, past PONV, opioid use — the four Apfel factors. 🔑KEY POINTS TO REMEMBER- PONV: very common; causes dehydration, electrolyte disturbance, aspiration, wound strain, delayed discharge.
- Apfel risk factors: female, non-smoker, previous PONV/motion sickness, postoperative opioids.
- Anaesthetic/surgical factors: volatiles, nitrous oxide, opioids; gynae/ENT/laparoscopic/squint surgery.
- Reduce risk: TIVA (propofol), avoid nitrous oxide, opioid-sparing analgesia, hydration.
- Prophylaxis: combine anti-emetic classes (ondansetron + dexamethasone ± dopamine antagonist).
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition
Accidental awareness under general anaesthesia is the unintended consciousness of a patient during general anaesthesia, with subsequent explicit recall of events. Though rare, it can be highly distressing and cause long-term psychological harm (including post-traumatic stress), so its prevention is an important safety goal.
Causes & Risk Factors
Awareness occurs when the delivered anaesthetic is inadequate for the patient’s needs. Risk is higher with muscle relaxants (which abolish the movement that would otherwise signal light anaesthesia), with total intravenous anaesthesia (a failed or disconnected infusion delivers no drug), during deliberately light anaesthesia (haemodynamically unstable patients, caesarean section, cardiac and major trauma surgery), and with equipment problems (vaporiser empty, infusion failure).
Prevention
Prevention combines adequate dosing, monitoring and vigilance: monitor end-tidal anaesthetic agent (keep an adequate MAC) for volatile anaesthesia, use depth-of-anaesthesia (processed-EEG/BIS) monitoring especially during TIVA with relaxants, ensure a secure, visible drug-delivery system, check equipment, and remain alert to clinical signs (sweating, lacrimation, hypertension, tachycardia). Suspected awareness is discussed with the patient and support offered.
⚠️Awareness is most likely under muscle relaxants and TIVA, when movement is abolished and an infusion may fail unseen. Guard against it with end-tidal agent and/or depth-of-anaesthesia monitoring and a secure, visible IV line — and take reports of awareness seriously.💡Awareness = explicit recall during GA, worst under relaxants + TIVA. Prevent by adequate dosing + end-tidal agent/BIS monitoring + a secure visible infusion, and by watching autonomic signs. Take any report seriously and offer support.Consequences & the Human Impact
Although accidental awareness is rare, its consequences can be severe and lasting, which is why it receives attention out of proportion to its frequency. Patients may recall sounds, sensations of paralysis or, worst of all, pain, and the experience of being conscious yet unable to move or signal distress can be profoundly frightening and lead to long-term psychological harm, including post-traumatic stress disorder. This human impact means that a report of awareness must never be dismissed but taken seriously, with an honest explanation, acknowledgement, and the offer of psychological support and follow-up; and it is the reason prevention — through adequate dosing, monitoring of end-tidal agent or processed EEG, and a secure drug-delivery system — is regarded as an important quality-and-safety priority rather than a merely technical concern.
Balanced Anaesthesia & the Role of Relaxants
A central reason awareness is bound up with muscle relaxants is that balanced anaesthesia separates the components of the anaesthetic — hypnosis, analgesia and relaxation — into different drugs, so that a patient can be fully paralysed while the hypnotic component is, unintentionally, inadequate. Without relaxants a lightly-anaesthetised patient would move, giving warning, but paralysis removes this sign, so the anaesthetist must rely on other indicators: the delivered dose and end-tidal concentration of the anaesthetic, processed-EEG depth monitoring, and the autonomic signs of sweating, lacrimation, hypertension and tachycardia. This is why the combination of relaxants with total intravenous anaesthesia, in which a delivery failure is silent, represents the highest-risk situation and warrants the most careful monitoring.
💡Awareness is the price of separating paralysis from hypnosis: because relaxants remove the warning sign of movement, prevent it with adequate dosing, end-tidal agent or BIS monitoring and a secure, visible infusion — and always take a patient’s report of awareness seriously, with honest explanation and support.⚠️Do not rely on any single safeguard against awareness: an end-tidal agent value can be normal yet a vaporiser run dry between breaths, and a depth monitor can be misled, so awareness is best prevented by combining adequate dosing, agent or depth monitoring, a checked and visible delivery system, and attention to autonomic signs.Highest risk in cardiac, obstetric and trauma anaesthesia. 🔑KEY POINTS TO REMEMBER- Accidental awareness: unintended consciousness with explicit recall under GA — rare but psychologically harmful.
- Risk: muscle relaxants (mask movement), TIVA (infusion may fail), deliberately light anaesthesia, equipment failure.
- High-risk surgery: caesarean, cardiac, major trauma.
- Prevent: adequate dosing, end-tidal agent monitoring, depth (BIS) monitoring in TIVA, secure visible line, watch autonomic signs.
- Take reports seriously; offer psychological support.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Risk
Pulmonary aspiration is the entry of gastric contents into the lungs when the airway is unprotected under anaesthesia — causing a chemical pneumonitis (Mendelson’s syndrome) and/or airway obstruction. It is a risk in the ‘full stomach’ patient: emergencies, trauma, pregnancy, reflux, obstruction, diabetes and obesity.
Prevention & Management
Prevention: fasting, identifying at-risk patients, aspiration prophylaxis (H₂ blocker/PPI, sodium citrate, prokinetic), and a rapid sequence induction with cricoid pressure and a cuffed tube. If aspiration occurs: head-down/lateral tilt, suction the airway, secure the airway (intubate) and give 100% oxygen, with respiratory support (ventilation/PEEP as needed). Antibiotics only for secondary infection; steroids are not recommended.
⚠️Prevention outweighs treatment: identify the full-stomach patient and use a rapid sequence induction with cricoid pressure. If aspiration occurs, tilt head-down, suction, intubate and give oxygen; do not give routine steroids.💡Aspiration risk = full stomach (emergency, pregnancy, reflux, obstruction). Prevent with fasting, prophylaxis and RSI + cricoid pressure; treat with tilt, suction, intubate, oxygenate — antibiotics only for infection, no routine steroids.Recognition & Consequences
Aspiration may be witnessed — gastric contents seen in the pharynx or the tube — or suspected when a patient develops wheeze, falling oxygen saturation and difficulty with ventilation during or after anaesthesia, sometimes with signs appearing on a chest radiograph. Its severity depends on the volume and acidity of the aspirate and on whether solid material causes obstruction, ranging from a mild, self-limiting pneumonitis to severe respiratory failure and secondary pneumonia. Because established aspiration is difficult to treat and potentially fatal, the emphasis remains firmly on prevention through fasting, identification of the at-risk patient and a rapid sequence induction, with prompt supportive treatment if it nonetheless occurs.
Prevention by fasting, RSI and cricoid pressure. 🔑KEY POINTS TO REMEMBER- Aspiration: gastric contents into lungs when airway unprotected → Mendelson’s pneumonitis/obstruction.
- At risk: emergency, trauma, pregnancy, reflux, obstruction, diabetes, obesity (full stomach).
- Prevent: fasting, prophylaxis (H₂/PPI, sodium citrate, prokinetic), RSI + cricoid pressure + cuffed tube.
- Treat: head-down/lateral, suction, intubate, 100% O₂, support; antibiotics only if infected; no routine steroids.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Use
Dantrolene is the specific drug treatment for malignant hyperthermia (MH). It is a skeletal muscle relaxant that acts directly on muscle by reducing calcium release from the sarcoplasmic reticulum (via the ryanodine receptor), thereby switching off the sustained muscle contraction and hypermetabolism that drive the MH crisis.
Administration & Points
In an MH crisis, dantrolene is given intravenously in repeated doses until the hypermetabolic signs (rising CO₂, tachycardia, rigidity, temperature) settle, alongside stopping the trigger, cooling, and correcting acidosis and hyperkalaemia. Because a crisis needs many vials rapidly, dantrolene must be immediately available wherever triggering agents are used, and staff must know where it is and how to reconstitute it.
💡Dantrolene treats MH by reducing calcium release from the sarcoplasmic reticulum (ryanodine receptor), stopping the hypermetabolism. It must be immediately available wherever volatiles/suxamethonium are used, and given in repeated IV doses.Availability & Storage
A practical point that examinations often test is that dantrolene must be stocked and immediately accessible in every location where triggering anaesthetic agents are used, because a malignant hyperthermia crisis requires a large number of vials to be given quickly and the drug is slow to reconstitute. Departments therefore keep a dedicated supply, ensure staff know its location and how to prepare it, and rehearse the emergency, since any delay in giving dantrolene worsens the outcome; alongside the drug itself, the response depends on immediately stopping the trigger, calling for help and beginning cooling and the correction of the metabolic disturbances.
💡Dantrolene works by shutting off the runaway calcium release from the sarcoplasmic reticulum that drives malignant hyperthermia, and the two things examiners want are its mechanism and the fact that it must be immediately available and given in repeated IV doses in a crisis.In Brief
In short, know its mechanism and that a department must be able to lay hands on it — and enough of it — within moments.
Specific treatment for malignant hyperthermia — must be immediately available. 🔑KEY POINTS TO REMEMBER- Dantrolene: specific treatment for malignant hyperthermia.
- Acts directly on muscle — reduces sarcoplasmic-reticulum calcium release (ryanodine receptor).
- Given IV in repeated doses until hypermetabolic signs settle (with stop trigger, cool, correct K⁺/acidosis).
- Must be immediately available where triggering agents are used.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Causes
Postoperative shivering is involuntary muscular activity after anaesthesia. It is most often a thermoregulatory response to perioperative hypothermia (heat lost through anaesthetic-induced vasodilatation and a cold theatre), but it can also be non-thermoregulatory (related to certain anaesthetic agents, pain).
Consequences & Management
Shivering is uncomfortable and — importantly — markedly increases oxygen consumption and cardiac work, which can be harmful in patients with limited cardiorespiratory reserve. Management: active warming (forced-air blanket, warmed fluids), supplemental oxygen, and drug treatment if needed — pethidine (meperidine) is classically effective, and other agents may be used. Prevention is by maintaining normothermia intra-operatively.
💡Postoperative shivering is usually due to hypothermia and matters because it raises oxygen demand and cardiac work. Prevent with normothermia; treat with warming, oxygen and — classically — pethidine.Significance in the Cardiac Patient
The clinical importance of postoperative shivering lies chiefly in its metabolic cost: the vigorous involuntary muscle activity can increase oxygen consumption several-fold, and this surge in demand, together with the associated rise in cardiac output and catecholamines, can precipitate myocardial ischaemia in a patient with limited coronary reserve. For this reason shivering is not dismissed as a trivial nuisance but actively prevented by maintaining normothermia and treated promptly when it occurs, with warming, supplemental oxygen to meet the increased demand, and drug treatment such as pethidine, which is particularly effective at suppressing the shivering response.
💡Treat postoperative shivering as more than discomfort: it can double or triple oxygen consumption and stress the heart, so prevent it with normothermia and treat it with warming, oxygen and — classically — pethidine, which suppresses the shivering reflex.In Brief
In short, warm the patient and, where reserve is limited, remember that the shivering itself is a cardiac stressor worth suppressing.
Raises oxygen demand sharply — hazardous in cardiac disease. 🔑KEY POINTS TO REMEMBER- Postoperative shivering: usually thermoregulatory (hypothermia); sometimes drug-related/pain.
- Raises oxygen consumption & cardiac work — risky in limited reserve.
- Manage: active warming, supplemental oxygen, pethidine (classically) if needed.
- Prevent by maintaining normothermia intra-operatively.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Causes
Delayed recovery is failure to regain consciousness or adequate function within the expected time after anaesthesia. The causes are usefully grouped: drug effects (residual anaesthetic/opioid/sedative, residual neuromuscular block, relative overdose, slow metabolism), metabolic (hypoglycaemia, hypothermia, electrolyte or acid–base disturbance, hypercapnia), hypoxia/hypoperfusion, and neurological events (intra-operative stroke).
Assessment
Assessment is systematic: ensure oxygenation and ventilation (exclude hypoxia and hypercapnia), check blood glucose and temperature, review the drugs given (consider reversal — naloxone for opioids, flumazenil for benzodiazepines, ensure neuromuscular block is reversed), check electrolytes, and consider a neurological cause if no other explanation is found. Treat the cause and support the patient meanwhile.
💡For delayed recovery, work through drugs, metabolic, oxygenation and neurological causes: exclude residual anaesthetic/relaxant, hypoglycaemia, hypothermia, hypoxia/hypercapnia, and — if unexplained — a neurological event.A Structured Approach
Because the causes of delayed recovery are so varied, a structured approach prevents important reversible problems from being missed: the first priority is always to confirm adequate oxygenation and ventilation, since hypoxia and carbon dioxide retention are both dangerous and treatable; attention then turns to simple metabolic causes such as hypoglycaemia and hypothermia, which are quickly checked and corrected; the drugs given are reviewed and reversal agents considered; and only when these have been excluded is an uncommon but serious neurological cause, such as an intra-operative stroke, actively investigated. Throughout, the patient’s airway, breathing and circulation are supported while the cause is sought.
💡Approach delayed recovery through four buckets — drugs, metabolic, oxygenation and neurological — checking oxygenation, glucose and temperature first because they are common, dangerous and quickly corrected.Check glucose and neuromuscular block before assuming drug effect. Category Causes Drug related Residual anaesthetic, opioid, muscle relaxant, premedication Metabolic Hypoglycaemia, hypothermia, electrolyte disturbance, hypercapnia Respiratory Hypoxia, hypercarbia Neurological Stroke, raised intracranial pressure, seizure 🔑KEY POINTS TO REMEMBER- Delayed recovery: not waking/functioning in the expected time after anaesthesia.
- Causes: drug effects (residual anaesthetic/opioid/relaxant), metabolic (hypoglycaemia, hypothermia, electrolytes, hypercapnia), hypoxia, neurological (stroke).
- Assess: oxygenation/ventilation, glucose, temperature, drugs (reversal), electrolytes; consider neuro cause.
- Treat the cause; support the patient meanwhile.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Risk
Venous air embolism (VAE) is the entrainment of air (or other gas) into the venous circulation, which can obstruct the right heart/pulmonary circulation. It occurs when the operative site is above the level of the heart and a vein is open — classically neurosurgery in the sitting position, but also head/neck surgery, and from central venous access.
Features & Management
A significant VAE causes a sudden fall in end-tidal CO₂ (obstructed pulmonary blood flow), hypotension, hypoxia and arrhythmias, and a classic ‘mill-wheel’ murmur. Management: stop further air entry (flood the field with saline, lower the site below the heart, compress neck veins), give 100% oxygen (stop any nitrous oxide, which expands the bubble), aspirate air from a central line if present, position head-down/left lateral, and support the circulation.
⚠️Suspect venous air embolism with a sudden fall in end-tidal CO₂ and hypotension during surgery above heart level — stop air entry, give 100% oxygen and stop nitrous oxide (it expands the embolus), and aspirate from a central line if present.💡VAE (surgery above the heart, e.g. sitting neurosurgery): sudden fall in ETCO₂, hypotension, mill-wheel murmur. Treat by stopping air entry, 100% O₂, stopping N₂O, head-down/left-lateral, and aspirating a central line.Prevention & Monitoring
In operations that carry a significant risk of venous air embolism, particularly neurosurgery in the sitting position, specific measures are taken to prevent and detect it: the patient is kept well hydrated to maintain venous pressure, nitrous oxide is often avoided because it would enlarge any entrained bubble, and sensitive monitors — capnography for a fall in end-tidal carbon dioxide, and in high-risk cases precordial Doppler or echocardiography — are used to catch small emboli early. A central venous catheter may be positioned so that entrained air can be aspirated. These precautions reflect the principle that early recognition, before the embolus becomes large enough to cause collapse, is the key to a good outcome.
Flood the field, left lateral head-down position, 100% oxygen. 🔑KEY POINTS TO REMEMBER- VAE: air entrained into veins when operative site is above the heart (sitting neurosurgery, head/neck, central lines).
- Features: sudden fall in ETCO₂, hypotension, hypoxia, arrhythmia, mill-wheel murmur.
- Manage: stop air entry (flood field, lower site), 100% O₂, STOP nitrous oxide (expands bubble), aspirate central line, head-down/left lateral.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Definition & Mechanism
Peripheral nerve and positioning injuries are complications of the anaesthetised, immobile patient, who cannot feel or respond to a harmful position. Nerves are damaged by stretch, compression or ischaemia when limbs are poorly positioned or padded, and pressure areas and the eyes are also vulnerable.
Common Injuries & Prevention
The commonest is ulnar nerve injury (at the elbow), followed by the brachial plexus (arm abduction/head position) and the common peroneal nerve (lithotomy). Prevention: careful positioning and padding of pressure points, avoiding excessive limb abduction/extension, protecting the eyes (taping/lubrication to prevent corneal abrasion), and attention to pressure areas in long cases. Most nerve injuries recover, but some are permanent.
💡The anaesthetised patient can’t protect themselves — position and pad carefully. The classic nerve injuries are ulnar (elbow), brachial plexus (arm abduction), and common peroneal (lithotomy); protect the eyes against corneal abrasion.Consent & Documentation
Because positioning and nerve injuries can occur despite reasonable care, and because a small proportion are permanent, they are an important part of the consent discussion for procedures in which the risk is appreciable, such as prolonged surgery or the lithotomy position. When an injury is suspected postoperatively it is documented and assessed, the mechanism considered, and — for a significant or non-resolving deficit — neurological advice and nerve-conduction studies sought, since most compression injuries recover over weeks to months but some require longer follow-up. Careful attention to positioning and padding at the time remains the single most effective way of avoiding these often-overlooked complications.
💡The message is that the paralysed, insensible patient cannot protect their own nerves, so meticulous positioning and padding — sparing the ulnar nerve, the brachial plexus, the common peroneal nerve and the eyes — is the anaesthetist’s responsibility.Careful padding and neutral positioning prevent most injuries. 🔑KEY POINTS TO REMEMBER- Positioning/nerve injuries occur because the anaesthetised patient can’t feel/respond; nerves hurt by stretch/compression/ischaemia.
- Common: ulnar (elbow), brachial plexus (arm abduction/head), common peroneal (lithotomy).
- Prevent: careful positioning & padding, avoid excessive abduction/extension, protect eyes (corneal abrasion), care in long cases.
- Most recover; some permanent.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.Why Investigate
After a suspected perioperative anaphylaxis, it is essential to confirm the reaction and identify the culprit, because the patient will need future anaesthetics and must avoid the trigger — an unidentified allergen risks a fatal repeat reaction.
Tryptase & Referral
Mast-cell tryptase is released in anaphylaxis, so serial (timed) tryptase samples are taken — during/soon after the reaction, a few hours later, and a baseline — and a rise and fall confirms an anaphylactic (mast-cell) reaction. The patient is then referred to a specialist allergy/immunology clinic for skin testing (and other tests) against the drugs given, to identify the culprit and safe alternatives. The event, drugs and results are clearly documented and the patient warned/given an alert.
💡After anaesthetic anaphylaxis: take serial tryptase (a rise then fall confirms it) and refer for allergy skin testing to identify the culprit drug and safe alternatives — then document and warn the patient. Muscle relaxants, antibiotics, chlorhexidine and latex are the usual suspects.Practical Timing & Communication
The value of tryptase depends on timing the samples correctly, because the level rises soon after the reaction and then falls back towards the patient’s baseline over hours, so a sample taken during or shortly after the event, a further sample a few hours later and a baseline sample taken later or from records together demonstrate the characteristic rise and fall. Equally important is clear communication: the suspected reaction, the drugs given and the results are documented, the patient is informed and, once the culprit is identified by allergy testing, given written information and an alert to carry, so that every future anaesthetist can avoid the trigger and choose a safe alternative.
💡Two actions define the follow-up of anaesthetic anaphylaxis: serial tryptase to prove it was a mast-cell reaction, and allergy referral for skin testing to name the culprit and a safe alternative — then document and warn the patient.In Brief
In short, prove it with timed tryptase and name the culprit with skin testing, then make sure the patient carries that warning forward.
Neuromuscular blockers are the commonest trigger under anaesthesia. 🔑KEY POINTS TO REMEMBER- Investigate perioperative anaphylaxis to confirm it & identify the culprit (future safety).
- Serial timed tryptase samples — a rise and fall confirms a mast-cell (anaphylactic) reaction.
- Refer to allergy/immunology for skin testing against the drugs given (culprit + safe alternatives).
- Document the event/drugs/results; warn the patient / give an alert.
📚SOURCES: Morgan & Mikhail’s Clinical Anesthesiology; Miller’s Anesthesia; Ajay Yadav’s Short Textbook of Anaesthesia.