General Anaesthesia for Orthopaedic Surgery

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).

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.

Before any of this, the anaesthetist stratifies perioperative risk. The most widely used shorthand is the ASA physical status grade (I a normal healthy patient, II mild systemic disease, III severe systemic disease, IV a constant threat to life, V moribund, with an E suffix for emergencies) - a higher ASA grade predicts higher perioperative morbidity and mortality and frames how aggressively the patient is optimised before surgery. Many older orthopaedic trauma patients are ASA III or higher, which is exactly why pre-operative medical optimisation and orthogeriatric co-management matter so much.

Induction and maintenance agents

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.

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.

Malignant hyperthermia

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.

Positioning injuries

Three intraoperative crises are bound tightly to orthopaedic operations themselves rather than to anaesthesia in general. They are high-yield because the surgeon is at the table when they happen and is part of the response.

Bone cement implantation syndrome

Fat embolism syndrome

Fat embolism — the release of marrow fat into the circulation — occurs after long-bone and pelvic fractures and during intramedullary reaming and nailing. Most fat embolism is subclinical, but a minority develop fat embolism syndrome: the classic triad is respiratory distress (hypoxia), neurological dysfunction (confusion, drowsiness), and a petechial rash (typically over the chest, axillae and conjunctivae), developing 24 to 72 hours after the injury or surgery. It overlaps with BCIS mechanistically (both embolise marrow fat) but fat embolism syndrome is usually a postoperative ward diagnosis over hours to days, whereas BCIS is an immediate intraoperative collapse. Management is supportive — oxygen and respiratory support, careful fluid balance — and the most important lever is prevention through early fracture stabilisation.

Local anaesthetic systemic toxicity

Because regional anaesthesia and peripheral nerve blocks are central to orthopaedic care, every theatre team must recognise local anaesthetic systemic toxicity (LAST) — a toxic plasma level of local anaesthetic from inadvertent intravascular injection or overdose. It progresses from perioral tingling, tinnitus and agitation to seizures, and then to cardiovascular collapse and arrhythmia (bupivacaine is the most cardiotoxic agent). Treatment is to stop injecting, call for help, manage the airway and seizures, and give intravenous lipid emulsion (intralipid) alongside standard resuscitation. Prevention is meticulous technique: aspirate before injection, use ultrasound guidance, give incremental doses, and respect the maximum safe dose for the agent and the patient's weight.

This section deliberately stops short of tourniquet physiology (the metabolic, haemodynamic and reperfusion effects of limb exsanguination and inflation), which is covered in depth in the dedicated tourniquet use topic.

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.

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.

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.

• 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.