Monitor atlas: other perioperative and peripartum events
Stem
Monitors station, scenario 2 of 3. The card reads: a 36-year-old woman, 84 kg, at 39 weeks, is having a cesarean delivery under spinal anesthesia. She has an arterial line, and end-tidal CO2 is sampled from her nasal cannula. Two minutes after delivery of the placenta, the monitor shows:
Question
What is the most likely diagnosis, and what is your management?
Ideal answer
What the monitor showed: SpO2 fell from 99% to 82%, end-tidal CO2 from 32 to 14 mmHg with a preserved waveform, heart rate rose from 92 to 138, and arterial pressure fell from 118/70 to 62/34.
HeadlineAmniotic fluid embolism until proven otherwise: collapse minutes after placental delivery. I call for help, tell the obstetrician, and secure the airway with 100% oxygen.
- Read in order: oxygenation, ventilation, circulation, trend. End-tidal CO2 has dropped by more than half with hypotension: dead space from pulmonary vascular obstruction, or collapsed cardiac output.
- Name the differential. Venous air embolism, massive pulmonary thromboembolism, high spinal and anaphylaxis; AFE is a clinical diagnosis, and no laboratory test confirms or excludes it.1
- Norepinephrine or vasopressin; dobutamine or milrinone; no fluid loading. The first phase is right ventricular failure, and a dilated RV does not want volume.1 Pulseless: high-quality CPR.
- Coagulation studies now; 1:1:1 massive transfusion when bleeding. Coagulopathy often follows: plasma, platelets and red cells.1
Watch for: return of end-tidal CO2, the RV on TEE or TTE, and oozing from the wound.
Breaking down the answer
The outline's "other perioperative and peripartum events" category sits beside cardiac, respiratory and ventilator-mode scenarios, and the monitors include temperature and, from 2026, fetal heart rate.2 These events are recognized by a pattern across several monitors, not by one number.
| Event | Monitor pattern | First action |
|---|---|---|
| Amniotic fluid embolism | Peripartum; falling SpO2 and end-tidal CO2, hypotension, then bleeding | Oxygen, vasopressor and inotrope, CPR if pulseless, early coagulation screen1 |
| Venous air embolism | Sudden end-tidal CO2 drop, hypotension, tachycardia; site above the heart | Tell the surgeon to flood the field, stop nitrous oxide, 100% oxygen, support output3 |
| Anaphylaxis | Hypotension, tachycardia, rising peak pressure, falling or sloped capnogram; skin signs often absent | Stop triggers, adrenaline 50 mcg IV bolus in adults, fluid 500–1000 mL4 |
| Malignant hyperthermia | End-tidal CO2 rising despite more ventilation, tachycardia, then temperature | Stop volatile, dantrolene 2.5 mg/kg, 100% oxygen at 10 L/min5 |
| High spinal | Bradycardia, hypotension, falling tidal volume, then apnea | Airway, ventilation, ephedrine or epinephrine |
| Local anesthetic toxicity | Arrhythmia, wide QRS, hypotension after a block | Airway, seizure control, lipid emulsion |
- The direction of end-tidal CO2 sorts the list — a rise means more CO2 production (MH, thyroid storm, sepsis) or rebreathing; an abrupt fall with hypotension means embolism or low output. Saying this aloud shows organized reasoning.
- AFE is phased — after the RV comes left ventricular failure with pulmonary edema, then disseminated intravascular coagulation, present in up to 83%.1 Each phase changes the drug.
- Air is a surgical problem first — the fastest fix is stopping entrainment; the OpenAnesthesia review notes that air aspiration through a central line has no clear benefit and must not delay support.3
- Anaphylaxis hides its skin signs — in severe reactions the rash is often absent and wheeze may be absent, so unexplained hypotension after an antibiotic or relaxant earns adrenaline.4
Follow-up question
Second scenario: a 52-year-old man, 90 kg, receives cefazolin after induction for a hernia repair, and the monitor then shows:
There is no rash. What is happening, and what do you do?
Follow-up answer
What the monitor showed: arterial pressure fell to 64/30 with heart rate 132, peak airway pressure rose from 18 to 38 cmH2O, and the capnogram became a shark fin with end-tidal CO2 of 22.
HeadlineAnaphylaxis: hypotension, tachycardia and bronchospasm minutes after an antibiotic; the missing rash does not change that.4 I call for help.
Cefazolin and any other suspected trigger stopped, surgeon told to stop. 100% oxygen, adrenaline 50 mcg IV repeated, 500–1000 mL of crystalloid with more boluses as needed, and an adrenaline infusion if boluses do not hold the pressure.4 Inhaled salbutamol, with the volatile kept running if pressure allows. Systolic below 50 mmHg: CPR. Tryptase once stable, ideally 1–4 hours after onset, and a baseline at least 24 hours later; then the arterial trace, peak pressure and capnogram slope again.
Pitfalls that cost points
- Waiting for urticaria before giving adrenaline.
- Forgetting the fetus or the uterus in a peripartum scenario.
Rapid-fire
Q: Why does end-tidal CO2 fall in air embolism? A: Air blocks pulmonary blood flow, so ventilated alveoli are not perfused and dead space rises.3
Q: Is there a confirmatory test for AFE? A: No; it remains a clinical diagnosis, and no laboratory test should be used to confirm or refute it.1
Q: Arrest before delivery: when do you deliver? A: Prepare at the start of CPR; if there is no return of circulation, incise at about 4 minutes and aim for delivery by 5.1
Q: When do you stop cooling in MH? A: Below 38 °C, to avoid overshoot hypothermia.5
Numbers to know
| Item | Value |
|---|---|
| Adrenaline, anaphylaxis, adult | 50 mcg IV, repeat4 |
| Initial fluid, anaphylaxis | 500–1000 mL4 |
| Dantrolene | 2.5 mg/kg IV, repeat to effect5 |
| DIC in AFE | Up to 83%1 |
| Perimortem delivery | Fetus ≥23 weeks; incise ~4 min, deliver by 5 min of CPR1 |
| Lethal air volume | ~50–500 mL, depends on rate3 |
Links
- The monitors and echo station: format and timing, Monitor atlas: perioperative cardiac events, Monitor atlas: perioperative respiratory events, Malignant hyperthermia, anaphylaxis, Venous air embolism and the sitting position
- Atlas: Monitor atlas: ventilator modes and loops; Monitor atlas: quantitative NMB and fetal heart rate (2026)
- SMFM Clinical Guideline #9, Amniotic fluid embolism (2016); MHAUS treatment protocol
Sources
- 1.Society for Maternal-Fetal Medicine Clinical Guideline #9: Amniotic fluid embolism: diagnosis and management · SMFM, 2016 · assets.noviams.comAm J Obstet Gynecol 2016;215:B16-24.
- 2.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.org
- 3.Venous Air Embolism · OpenAnesthesia (IARS) · openanesthesia.org
- 4.Perioperative anaphylaxis treatment algorithm · Resuscitation Council UK, 2024 · resus.org.uk
- 5.Managing a Crisis (MH treatment protocol) · MHAUS · mhaus.org
Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.