A reversible, drug-induced coma | Loss of consciousness, amnesia, immobility and blunted reflexes | The airway is the priority | Choice of general versus regional is shared with the anaesthetist
THE FOUR PHASES OF A GENERAL ANAESTHETIC
Critical Must-Knows
- General anaesthesia is a reversible, drug-induced state with four linked goals - unconsciousness (hypnosis), pain control (analgesia), lack of recall (amnesia) and stillness (muscle relaxation) - delivered as a balanced combination of drugs, not one agent
- Airway management is the single most important skill: a general anaesthetic abolishes airway reflexes, so the airway must be supported with a supraglottic device (laryngeal mask) or secured with a tracheal tube
- The difficult airway is the anaesthetist's nightmare and an exam favourite - assess it before every case (mouth opening, neck movement, Mallampati), and remember the cervical spine and trauma patient is high risk
- General versus regional anaesthesia for hip fracture shows broadly similar mortality and delirium in good trials, so the choice is individualised - regional avoids airway instrumentation but is not universally superior
- Postoperative delirium is the commonest serious complication after major orthopaedic surgery in older patients - prevent it with good analgesia, early mobilisation, and avoiding deliriogenic drugs
Clinical Pearls
- "The reason starvation (fasting) matters is aspiration of stomach contents at induction - a full stomach (trauma, pain, opioids) means a rapid sequence induction
- "A patient who cannot be intubated and cannot be oxygenated is a 'can't intubate, can't oxygenate' emergency - the end point is a surgical airway (front of neck access)
- "Suxamethonium can trigger hyperkalaemia and is a malignant hyperthermia trigger - know the at-risk groups
- "Always think about the cervical spine: manual in-line stabilisation during intubation in any patient with a possible unstable neck
Clinical Imaging
Airway management - the tools and views you must recognise
Critical General Anaesthesia Exam Points
The Goals (Triad Plus)
A balanced general anaesthetic delivers four things: unconsciousness (hypnosis), analgesia, amnesia, and muscle relaxation (immobility), while keeping the patient physiologically stable. No single drug does all four well, so a combination is used.
Airway is Everything
A general anaesthetic abolishes protective airway reflexes. The airway is supported with a supraglottic device (LMA) or secured with a cuffed tracheal tube. The feared scenario is can't intubate, can't oxygenate, which ends in a surgical front-of-neck airway.
Aspiration and Fasting
Loss of reflexes means gastric contents can be aspirated. Elective fasting reduces this risk; an unfasted or high-risk patient (trauma, pain, pregnancy) needs a rapid sequence induction with cricoid pressure and a fast-acting relaxant.
The Vulnerable Orthopaedic Patient
Many orthopaedic patients are elderly with hip fracture or have an unstable cervical spine. Think about postoperative delirium, cardiac risk, and manual in-line stabilisation of the neck during airway management.
Memory aids
HARMThe Goals of General Anaesthesia
| H | Hypnosis Unconsciousness - the patient is asleep and unaware |
| A | Analgesia Control of pain and the stress response |
| R | Relaxation Muscle relaxation / immobility for surgery and intubation |
| M | Memory loss (amnesia) No recall of the procedure |
| H | Hypnosis Unconsciousness - the patient is asleep and unaware | R | Relaxation Muscle relaxation / immobility for surgery and intubation |
| A | Analgesia Control of pain and the stress response | M | Memory loss (amnesia) No recall of the procedure |
Hook:A general anaesthetic must do no HARM - Hypnosis, Analgesia, Relaxation, Memory loss - the four goals delivered by a balanced technique.
LEMONPredicting the Difficult Airway
| L | Look externally Facial trauma, beard, small jaw, large tongue, obesity |
| E | Evaluate 3-3-2 Mouth opening, chin-to-hyoid and hyoid-to-thyroid distances |
| M | Mallampati How much of the pharynx is visible with the mouth open |
| O | Obstruction Tumour, abscess, swelling, foreign body, stridor |
| N | Neck mobility Reduced in arthritis, fusion, collar or unstable cervical spine |
| L | Look externally Facial trauma, beard, small jaw, large tongue, obesity | O | Obstruction Tumour, abscess, swelling, foreign body, stridor |
| E | Evaluate 3-3-2 Mouth opening, chin-to-hyoid and hyoid-to-thyroid distances | N | Neck mobility Reduced in arthritis, fusion, collar or unstable cervical spine |
| M | Mallampati How much of the pharynx is visible with the mouth open |
Hook:Squeeze the airway with LEMON - Look, Evaluate 3-3-2, Mallampati, Obstruction, Neck mobility - to predict who will be hard to intubate.
ORIENTPreventing Postoperative Delirium
| O | Optimise analgesia Treat pain - but limit deliriogenic opioids and sedatives |
| R | Reorient Clocks, glasses, hearing aids, family, daylight, sleep |
| I | Investigate causes Hypoxia, sepsis, electrolytes, urinary retention, constipation |
| E | Early mobilisation Get the patient up, fed and hydrated early |
| N | No tethers Remove catheters, lines and restraints as soon as possible |
| T | Trim risky drugs Avoid benzodiazepines and anticholinergics where possible |
| O | Optimise analgesia Treat pain - but limit deliriogenic opioids and sedatives | I | Investigate causes Hypoxia, sepsis, electrolytes, urinary retention, constipation | N | No tethers Remove catheters, lines and restraints as soon as possible |
| R | Reorient Clocks, glasses, hearing aids, family, daylight, sleep | E | Early mobilisation Get the patient up, fed and hydrated early | T | Trim risky drugs Avoid benzodiazepines and anticholinergics where possible |
Hook:Keep the patient ORIENTed to prevent delirium - Optimise analgesia, Reorient, Investigate, Early mobilise, No tethers, Trim risky drugs.
Overview
General anaesthesia is a reversible, drug-induced state in which the patient is unconscious, free of pain, has no memory of the procedure, and is still enough for surgery to proceed safely. It is best thought of as a controlled, temporary coma maintained by a balanced combination of drugs and undone at the end of the operation.
For an orthopaedic trainee, the point of understanding general anaesthesia is not to administer it yourself, but to be a safe and useful partner to the anaesthetist. You should know the phases of an anaesthetic (induction, airway and maintenance, emergence, recovery), the drugs and devices involved, the risks specific to your patients (the elderly hip fracture, the unstable cervical spine, the long bone fracture at risk of fat embolism), and the major complications you may be asked to recognise and help manage.
Three threads recur through this topic and the exam: the airway (how it is managed and what to do when it goes wrong), the general-versus-regional debate (what the evidence actually shows for hip fracture), and postoperative delirium (the commonest complication in your older patients, and largely preventable).
Principles: How a General Anaesthetic Works
The balanced anaesthetic
No single drug provides all four goals (hypnosis, analgesia, amnesia, relaxation) safely, so modern practice uses a balanced technique - several drugs each doing one job at a lower, safer dose. A typical sequence is an intravenous induction agent to put the patient to sleep, an opioid for analgesia, a muscle relaxant to allow intubation, and then a volatile gas or a propofol infusion to keep the patient asleep.
Induction and maintenance agents
Common Anaesthetic Agents
| Agent | Role | Key point for the exam |
|---|---|---|
| Propofol | Intravenous induction (and infusion for maintenance) | Smooth induction and fast recovery - causes vasodilation and a drop in blood pressure |
| Thiopentone | Intravenous induction | Fast acting; historically used in rapid sequence induction; can cause hypotension |
| Ketamine | Induction / analgesia | Maintains blood pressure and airway tone - useful in shock and trauma |
| Sevoflurane / volatile agents | Maintenance (and gas induction in children) | Inhaled; all volatiles are malignant hyperthermia triggers |
| Suxamethonium | Depolarising muscle relaxant | Very fast onset for rapid sequence; risks hyperkalaemia and malignant hyperthermia |
| Rocuronium / vecuronium | Non-depolarising muscle relaxants | Longer acting; rocuronium reversible with sugammadex |
Securing the airway
The airway sits at the centre of every general anaesthetic because the drugs abolish the reflexes that normally protect it. Three levels of airway support are used:
- Facemask / oral airway - for short cases or to oxygenate before intubation.
- Supraglottic airway (laryngeal mask) - sits over the laryngeal inlet (see the labelled image above). Quick, less stimulating, but offers only partial protection against aspiration.
- Tracheal (endotracheal) tube - a cuffed tube passed through the cords. It protects against aspiration and allows controlled ventilation, and is the choice for major surgery, the prone position, and the full or at-risk stomach.
The difficult airway
A difficult airway is one where mask ventilation, supraglottic placement or intubation is hard or fails. It is predicted before the case using assessments such as Mallampati grade, mouth opening, thyromental distance and neck movement (the LEMON aids in the memory section). When intubation fails, the anaesthetist follows a stepwise plan, escalating from optimised laryngoscopy and video laryngoscopy (images above) to a supraglottic device, and finally - in a can't intubate, can't oxygenate crisis - to a surgical front-of-neck airway.
Clinical Pearl
The orthopaedic relevance of the difficult airway is the cervical spine. Patients with rheumatoid arthritis, ankylosing spondylitis, a previous cervical fusion, or a suspected unstable injury are all difficult airways. The neck is kept still with manual in-line stabilisation during intubation, and an awake fibreoptic technique may be chosen.
Aspiration and the rapid sequence induction
Because anaesthesia removes the cough and gag reflexes, stomach contents can be regurgitated and aspirated into the lungs. Elective fasting reduces gastric volume, but many orthopaedic patients are not safely fasted - they have eaten before a trauma, or pain and opioids have delayed gastric emptying. In these patients a rapid sequence induction is used: pre-oxygenation, a fast-acting induction agent and relaxant given together, and immediate intubation to secure the airway before contents can be aspirated.
Clinical Relevance
General anaesthesia touches almost every orthopaedic operation and recurs throughout the exam. In trauma, you must understand the full-stomach patient, the rapid sequence induction, and the unstable cervical spine. In arthroplasty and major surgery, the questions are about positioning, blood loss, fat embolism, and the general-versus-regional choice. In the elderly, the dominant issues are cardiac risk, frailty and postoperative delirium. And in the basic-science viva, the mechanism of the agents, the airway plan, and the recognition of complications such as malignant hyperthermia and local anaesthetic systemic toxicity are classic asks.
Being a good orthopaedic surgeon means planning with the anaesthetist: optimising the patient before surgery, agreeing the anaesthetic technique, and sharing responsibility for a safe recovery.
General versus Regional Anaesthesia
The choice between general anaesthesia and regional anaesthesia (spinal, epidural or peripheral nerve block) is one of the most examined practical questions, especially for hip fracture in the elderly. The intuitive argument that regional must be safer - avoiding airway instrumentation and deep sedation - has not been borne out as a clear survival or cognitive advantage in good randomised trials.
General versus Regional - the trade-offs
| Issue | General anaesthesia | Regional anaesthesia |
|---|---|---|
| Airway | Requires airway support or a secured tube | Airway not instrumented (patient breathes spontaneously) |
| Mortality / major outcomes | Broadly similar in good trials | Broadly similar - no clear survival advantage |
| Delirium / cognition | No consistent difference from regional | No consistent difference from general |
| Postoperative analgesia | Needs separate analgesia plan | Nerve blocks give excellent early pain relief and less opioid |
| Practical limits | Useful when blocks fail, for long or prone cases, or anticoagulation | Limited by anticoagulation, patient refusal or inability to position |
The honest exam answer is that the two techniques give similar major outcomes, so the choice is individualised - guided by the patient's comorbidities, anticoagulation, the surgery planned, and patient preference - and that peripheral nerve blocks add value either way by improving early pain relief and reducing opioid use and confusion.
Evidence
Regional versus General Anaesthesia and Neurocognitive Outcomes in Hip Fracture
- Systematic review and meta-analysis of 8 randomised trials, 3555 patients over 65 undergoing hip fracture surgery
- No significant difference in postoperative delirium or cognitive dysfunction between regional and general anaesthesia at 24 hours, 3 days or 7 days
- No significant difference in other adverse events between the two techniques
- Authors conclude the anaesthetic choice should be based on individual patient characteristics, not on an expected outcome difference
Peripheral Nerve Blocks for Hip Fracture (Cochrane Review)
- 49 randomised trials, 3061 participants, comparing peripheral nerve blocks with no block (or sham)
- Nerve blocks reduce pain on movement within 30 minutes (high-certainty evidence)
- Nerve blocks reduce the risk of acute confusional state (delirium), number needed to treat about 12 (high-certainty evidence)
- Nerve blocks probably reduce chest infection and time to first mobilisation; permanent injury from blocks is rare
Depth of Sedation and Postoperative Delirium (STRIDE Randomised Trial)
- Double-blind RCT of 200 older patients having hip fracture repair under spinal anaesthesia with propofol sedation
- Lighter versus heavier sedation did not reduce overall delirium (34 versus 39 percent, not significant)
- In patients with no comorbidity, heavier sedation doubled the delirium risk (hazard ratio 2.3)
- Suggests sedation depth matters most in otherwise well patients, not those with multiple comorbidities
Complications
Complications of General Anaesthesia
| Complication | When it happens | Key point |
|---|---|---|
| Failed intubation / lost airway | Induction and emergence | Escalate through the difficult airway plan to a surgical airway if can't intubate, can't oxygenate |
| Aspiration of gastric contents | Induction in the unfasted or at-risk patient | Rapid sequence induction reduces the risk |
| Malignant hyperthermia | After a volatile agent or suxamethonium | Rising temperature, rigidity, rising end-tidal CO2 - treat with dantrolene |
| Anaphylaxis | Any time, often to relaxants or antibiotics | Hypotension, bronchospasm, rash - treat with adrenaline |
| Cardiovascular instability | Induction (hypotension) and surgery (blood loss) | Most agents drop blood pressure; the frail elderly tolerate it poorly |
| Postoperative delirium | Hours to days after surgery | Commonest complication in older orthopaedic patients - largely preventable |
| Nausea, sore throat, awareness | After emergence | Common and distressing; awareness is rare but a recognised harm |
Malignant hyperthermia
Malignant Hyperthermia is an Anaesthetic Emergency
Malignant hyperthermia is a rare inherited disorder of skeletal muscle calcium handling (often a ryanodine receptor / RYR1 defect). Exposure to a volatile anaesthetic or suxamethonium triggers uncontrolled muscle metabolism: a rising end-tidal carbon dioxide, muscle rigidity, tachycardia, and a late, rapid rise in temperature. Treatment is to stop the trigger, give 100 percent oxygen, cool the patient, and give intravenous dantrolene. It is a classic basic-science viva because it links genetics, muscle physiology and an emergency.
Postoperative delirium
Delirium is an acute, fluctuating disturbance of attention and awareness. It is the commonest serious complication after major surgery in older patients, it predicts longer stays, loss of independence and higher mortality, and it is largely preventable. Prevention is multi-component (the ORIENT aid above): treat pain but minimise deliriogenic drugs, restore glasses and hearing aids, mobilise and feed early, remove catheters and lines, normalise sleep, and actively look for treatable causes such as hypoxia, infection, electrolyte disturbance and urinary retention.
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Choosing the Anaesthetic for a Hip Fracture (~4 min)
"An 84-year-old woman with a displaced intracapsular hip fracture is listed for hemiarthroplasty. She has mild dementia and takes an anticoagulant for atrial fibrillation. The examiner asks how the anaesthetic technique is chosen and what you would contribute as the surgeon."
Shared decision: The choice between general and regional anaesthesia is made with the anaesthetist. I would explain that good randomised evidence shows the two techniques give broadly similar mortality and similar rates of delirium and cognitive dysfunction, so the choice is individualised rather than dogmatic.
This patient: Her anticoagulation is a key factor - a spinal or epidural may be contraindicated until the drug has cleared, which can favour a general anaesthetic or a delay. Her dementia raises her delirium risk whichever technique is used.
My contribution: I would push for a fascia iliaca or femoral nerve block early for pain relief, optimise her medically without delaying surgery unduly, plan to keep sedation light, and put a delirium-prevention bundle in place - good analgesia with minimal opioids and sedatives, early mobilisation, and her glasses and hearing aids.
The Difficult Airway in a Trauma Patient (~4 min)
"A 30-year-old man with a high-energy injury needs an urgent general anaesthetic for an open femoral fracture. He ate two hours ago, is in severe pain, has a hard cervical collar on, and has facial bruising. What are the anaesthetic concerns and how is the airway managed?"
Concerns: This is a high-risk airway. He is effectively a full stomach (recent food, pain and opioids delay gastric emptying), he may have an unstable cervical spine, and the facial injury may make laryngoscopy difficult and predict a difficult airway.
Plan: The anaesthetist would assess the airway (mouth opening, Mallampati, the LEMON criteria), pre-oxygenate fully, and perform a rapid sequence induction with cricoid pressure to reduce aspiration, using a fast-acting induction agent and relaxant and intubating immediately with a cuffed tube.
Cervical spine: The collar front is opened and manual in-line stabilisation is applied during laryngoscopy to keep the neck still. Video laryngoscopy improves the view with minimal neck movement, and a difficult airway trolley with a plan for a supraglottic device and front-of-neck access is ready.
If it fails: If intubation fails and the patient cannot be oxygenated, this is a can't intubate, can't oxygenate emergency requiring an immediate surgical front-of-neck airway.
GENERAL ANAESTHESIA FOR ORTHOPAEDICS
Clinical summary
The Essentials
- •Reversible drug-induced state: hypnosis, analgesia, amnesia, relaxation (HARM)
- •Balanced technique - several drugs, each at a safer dose
- •Four phases: induction, airway and maintenance, emergence, recovery
- •Induction and emergence are the highest-risk phases
Airway
- •Support with a laryngeal mask or secure with a cuffed tracheal tube
- •Tracheal tube protects against aspiration - use for major or at-risk cases
- •Predict the difficult airway (LEMON: Look, Evaluate 3-3-2, Mallampati, Obstruction, Neck)
- •Can't intubate, can't oxygenate ends in a surgical front-of-neck airway
Orthopaedic-Specific
- •Full stomach (trauma, pain, opioids) needs a rapid sequence induction
- •Unstable cervical spine - manual in-line stabilisation during intubation
- •GA versus regional for hip fracture: similar outcomes, individualise
- •Add a peripheral nerve block - less pain, less opioid, less delirium
Red Flags
- •Rising end-tidal CO2, rigidity and fever - malignant hyperthermia (dantrolene)
- •Hypotension, bronchospasm, rash - anaphylaxis (adrenaline)
- •New confusion after surgery - postoperative delirium (prevent with ORIENT)
- •Light, fluctuating depth - risk of awareness
Guidelines, Registries and Global Practice
- Difficult airway guidelines (for example the Difficult Airway Society in the UK and the American Society of Anesthesiologists difficult airway algorithm) share a common stepwise structure - optimise laryngoscopy and use video laryngoscopy, move to a supraglottic device, and proceed to front-of-neck access in a can't intubate, can't oxygenate emergency.
- Hip fracture pathways worldwide (for example NICE and the national hip fracture audit in the UK, and orthogeriatric co-management models internationally) emphasise early surgery, multidisciplinary care, peripheral nerve blocks for analgesia, and delirium prevention rather than mandating a single anaesthetic technique.
- The general-versus-regional question is answered consistently across major randomised trials and meta-analyses: comparable major outcomes, so the choice is individualised to the patient, the surgery and contraindications such as anticoagulation.
- Malignant hyperthermia registries and reference centres exist in many countries to support diagnosis, family screening and the supply of dantrolene, reflecting how a rare but lethal complication is managed at a system level.
- Fasting guidance is broadly harmonised (clear fluids until shortly before surgery, longer for solids), with the rapid sequence induction reserved for patients who are not safely fasted.