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Awareness during general anaesthesia
Awareness under anaesthesia is explicit recall of events during general anaesthesia; it usually comes from too little anaesthetic — by choice (an unstable patient) or by error (an empty vaporiser, a disconnected infusion) — and it is especially harmful when the patient is paralysed.
Why it matters in the exam
The exam asks who is at risk (intravenous anaesthesia with paralysis, caesarean section, cardiac surgery, hypotensive trauma, prolonged difficult intubation, previous awareness), why heart rate and blood pressure are not reliable signs, what reduces the risk (end-tidal agent monitoring, depth-of-anaesthesia monitoring), and what to do when a patient reports awareness.
In the UK audit NAP5 many cases happened at transition points — between induction and the start of the volatile agent, or at the end of surgery when the agent was stopped before paralysis had worn off. A paralysed patient who cannot move feels great fear, and some develop post-traumatic stress disorder. An end-tidal agent concentration of at least 0.7 MAC is an accepted target, and with intravenous anaesthesia plus paralysis depth-of-anaesthesia monitoring is recommended (such as BIS in the 40–60 range).
To detect a late case the patient is asked structured questions after surgery: what was the last thing remembered before sleep, the first thing on waking, and whether anything was remembered in between. When a patient reports awareness, they are believed, the account is documented in detail, what happened is explained with an apology, and the patient is referred for psychological support. Avoiding unnecessary paralysis reduces harm — a patient who can move will signal being awake.
Key points
- Awareness = explicit recall during general anaesthesia.
- Risk: intravenous anaesthesia with paralysis, caesarean, cardiac, trauma, difficult intubation.
- Prevention: end-tidal agent at least 0.7 MAC; depth monitoring with intravenous anaesthesia plus paralysis.
- Most cases occur at transition points.
- After an event: believe, document, explain, psychological support.
Summary table
| Issue | Details | Exam point |
|---|---|---|
| Risk factors | Intravenous anaesthesia with paralysis, caesarean, cardiac surgery, trauma, difficult intubation, previous awareness | Mainly at transition points |
| Technical causes | Empty vaporiser, disconnected infusion or wrong pump, drug error | Equipment checks and a visible infusion line |
| Prevention | End-tidal agent at least 0.7 MAC with an alarm; depth monitoring with intravenous anaesthesia plus paralysis | Heart rate and blood pressure are unreliable |
| Paralysis | Avoid unnecessary paralysis | Paralysis increases the distress |
| After an event | Believe, document, explain, apologise, psychological support | Risk of PTSD |
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Sources
- Royal College of Anaesthetists 5th National Audit Project (NAP5): Accidental Awareness during General Anaesthesia, 2014 — Causes, risk factors and prevention
- Miller's Anesthesia, 9th edition (2020) — Consciousness, Memory, and Anesthesia; Monitoring the State of the Brain
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.