Anesthesiology APPLIED Exam › Pharmacology, equipment and physics

Intraoperative awareness and depth monitoring

Pharmacology, equipment and physics·~4 min read· Physician-reviewed✓ Sourced · 3

Stem

A 27-year-old woman, 64 kg, arrives from the emergency department for an exploratory laparotomy after a motorcycle crash. She is pale, her blood pressure is 78/42 mmHg after two units of blood, and the heart rate is 132. She uses cannabis and takes no other drugs. The surgeons need her paralyzed for the abdomen, and the trauma bay has already placed a rapid infuser.

Question

She is at high risk of awareness. How will you prevent it while you resuscitate her?

Ideal answer

HeadlineI keep her alive without accepting awareness as the price: volatile from intubation, an alarmed agent floor, and processed EEG.

Check machine, vaporizer level and every intravenous connection, because a disconnected line or an empty vaporizer is an avoidable cause of awareness.¹
Reduced dose of a hemodynamically gentle induction agent, volatile as soon as the tube is in; small-dose midazolam once pressure allows, though it may delay emergence.¹
End-tidal agent alarm, floor about 0.7 MAC, the threshold used in the largest trial.²
Add processed EEG for when pressure forces me below it; the advisory leaves that case by case, and she is the case.¹
Twitch monitor, relaxant only to need, so movement can still warn me; as blood restores pressure, I deepen first.

Watch for: Recall: afterward I visit her and ask about it specifically.

Breaking down the answer

Name the risk factors, then act on each — she has trauma, emergency surgery, limited reserve forcing reduced doses, and paralysis. The advisory also lists substance use, prior awareness, difficult intubation, ASA 4–5, cardiac and cesarean surgery, TIVA and nitrous-opioid techniques.¹
Equipment checks prevent the avoidable cases — a machine checklist and confirmation of IV access, pumps and connections are explicit recommendations.¹ Changes if: TIVA, where the infusion line is the vaporizer.
ETAC alarm, not intuition — BAG-RECALL alarmed below 0.7 or above 1.3 MAC.² A volatile technique with an agent analyzer is the strongest everyday safeguard.
Processed EEG is selective — not routinely indicated.¹ In BAG-RECALL, a BIS protocol (alarm below 40 or above 60) was not superior to an ETAC protocol: definite awareness 0.24% versus 0.07%.² Changes if: TIVA, where no ETAC exists, so I use processed EEG.
Benzodiazepine is a judgment call — useful when doses must be small, at the cost of slower emergence.¹
Relaxant to need — paralysis masks movement, the most reliable clinical sign of light anesthesia.¹

Follow-up question

On the first postoperative day she tells the nurse she heard the surgeons talking about her spleen, felt the tube in her throat and could not move. She is tearful and frightened. What do you do?

Follow-up answer

HeadlineProbable awareness with recall. I go to her myself, the same day, sit down and believe her.

I take a detailed account: what she heard and felt, whether there was pain, and when. I explain plainly that her blood pressure forced us to give less anesthetic, acknowledge it and apologize for her experience, and tell her it is not a sign she is mentally unwell and that distressing memories can follow. I offer counseling and psychological support,¹ document the conversation, file an occurrence report for quality review,¹ and inform the surgeon and her primary team. I arrange follow-up before discharge and afterward, because post-traumatic symptoms can appear later, and note it in her record for future anesthesiologists.

Pitfalls that cost points

Saying a BIS monitor alone prevents awareness.
Lightening the anesthetic for hypotension without first giving volume or vasopressor.

Rapid-fire

Q: How common is awareness under general anesthesia? A: Rare: about 0.1–0.2%.¹

Q: What did BAG-RECALL show? A: In 6041 high-risk patients, a BIS protocol was not shown superior to an end-tidal agent protocol.²

Q: Should you warn high-risk patients beforehand? A: Yes, when circumstances permit, inform patients at substantially increased risk.¹

Q: What alarm does the monitoring standard require for inspired gas? A: An oxygen analyzer with a low-concentration alarm whenever a machine is used.³

Q: Why can a paralyzed patient be aware with a normal heart rate? A: Hemodynamic signs are unreliable, especially with beta-blockade or hypovolemia, and paralysis removes movement.

Numbers to know

Item	Value
Incidence	0.1–0.2%¹
BAG-RECALL size	6041 high-risk patients²
BIS alarm in trial	Below 40 or above 60²
ETAC alarm in trial	Below 0.7 or above 1.3 MAC²
Definite awareness	BIS 0.24% vs ETAC 0.07%²

Sources

1.Practice Advisory for Intraoperative Awareness and Brain Function Monitoring · ASA, 2006 · asahq.orgAnesthesiology 2006;104:847-64; approved October 2005.
2.Prevention of intraoperative awareness in a high-risk surgical population (BAG-RECALL) · New England Journal of Medicine (abstract via Washington University profiles), 2011 · profiles.wustl.edu
3.Standards for Basic Anesthetic Monitoring · ASA, 2025 · asahq.orgLast amended October 15, 2025.

Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.