Monitor atlas: quantitative NMB and fetal heart rate (2026)
Stem
Monitors station. The card reads: a 30-year-old woman, 72 kg, at 25 weeks' gestation, is under general anesthesia with rocuronium for laparoscopic appendectomy, with continuous fetal heart rate monitoring. After insufflation her blood pressure falls to 80/42. The fetal monitor now shows:
Question
How do you interpret this fetal tracing, and what do you do?
Ideal answer
What the monitor showed: a 5-minute strip with a baseline of 145 bpm, minimal variability, no accelerations and no contractions; 90 seconds in, the rate falls abruptly to about 95 and stays down for the remaining 3.5 minutes without recovering.
HeadlineA prolonged deceleration with minimal variability, Category II, caused by maternal hypotension after insufflation. I treat the mother to treat the fetus.
- Read in order: baseline, variability, accelerations, decelerations, category. Baseline 145, inside normal 110 to 160; variability minimal; at least 15 beats below baseline for 2 minutes or more but less than 10, here about 3.5 minutes.1
- Category II, indeterminate, not yet Category III. That needs absent variability with recurrent decelerations or bradycardia, or a sinusoidal pattern.1
- Lower insufflation, left uterine displacement, phenylephrine and fluid. I tell the surgeon and obstetrics and restore her baseline pressure, because placental perfusion has fallen.
- Check her oxygenation and end-tidal CO2, because maternal hypoxemia or hypercarbia will also show on this trace.1
Watch for: Fetal rate back to baseline with moderate variability; if not, obstetrics decides next steps, at 25 weeks including a frank viability discussion.
Breaking down the answer
- New for 2026 — both monitors were added to the outline: neuromuscular blockade as qualitative and quantitative values, and fetal heart rate as waveform and value.2
| Finding | Definition | What it means |
|---|---|---|
| Baseline | 110–160 bpm1 | Outside this, look for maternal fever, drugs, hypoxemia |
| Variability | Absent; minimal ≤5; moderate 6–25; marked >25 bpm1 | Moderate variability predicts normal acid-base status |
| Early deceleration | Gradual, nadir with the contraction peak1 | Head compression; benign |
| Late deceleration | Gradual, nadir after the contraction peak1 | Uteroplacental insufficiency |
| Variable deceleration | Abrupt, onset to nadir <30 s1 | Cord compression |
| TOF count 0, PTC present | Deep block | Sugammadex 4 mg/kg at PTC 1–23 |
| TOF ratio 0.4 to <0.9 | Minimal block4 | Neostigmine is a reasonable alternative to sugammadex |
| TOF ratio ≥0.9 | Adequate recovery4 | Extubation threshold |
- Category drives action — Category I is likely normal acid-base status, Category III is associated with fetal acidemia, and Category II is everything between and needs evaluation and surveillance.1
- Intrauterine resuscitation is maternal physiology — lateral positioning, correcting hypotension, stopping oxytocin or uterine stimulants, and amnioinfusion for cord compression; maternal oxygen is reserved for documented maternal hypoxemia.1
- Quantitative, at the thumb — the 2023 ASA guideline recommends quantitative over qualitative monitoring, the adductor pollicis rather than eye muscles, and a train-of-four ratio of at least 0.9 before extubation.4
- Depth decides the drug — sugammadex is recommended over neostigmine at deep, moderate and shallow depths; neostigmine is reasonable only at minimal depth.4
Follow-up question
The fetal rate recovers. At closure, the acceleromyograph at her thumb shows:
The surgeon asks you to wake her up now. What do you do?
Follow-up answer
What the monitor showed: four twitches with a train-of-four ratio of 0.58; sinus rhythm at 82 and SpO2 99%.
HeadlineResidual minimal block, so she is not ready; I tell the surgeon I will extubate on a number, not a head lift.4
A ratio of 0.58 sits in the 0.4 to 0.9 band. Neostigmine is reasonable at this depth, and it sidesteps sugammadex, for which the label has no clinical trial data in pregnancy and notes binding to progestogen.3 With a second twitch present after rocuronium, the label dose is 0.03 mg/kg, about 2.2 mg, with glycopyrrolate first to blunt bradycardia;5 it generally reaches 0.9 within 10 to 20 minutes.5 Monitor running, normothermia, fetal monitor on through emergence; I extubate awake, on her left side, once the measured ratio reaches 0.9.
Pitfalls that cost points
- Treating the fetus with maternal oxygen while the mother stays hypotensive.
- Accepting a ratio of 0.7 or a sustained head lift as adequate reversal.
Rapid-fire
Q: When does a prolonged deceleration become a baseline change? A: When it lasts 10 minutes or more.1
Q: Describe a sinusoidal pattern. A: A smooth sine-wave undulation of the baseline, 3 to 5 cycles per minute, persisting 20 minutes or more; it is Category III.1
Q: What sugammadex dose at reappearance of the second twitch? A: 2 mg/kg for rocuronium or vecuronium.3
Q: Neostigmine maximum? A: 0.07 mg/kg or 5 mg total, whichever is less, with an anticholinergic.5
Numbers to know
| Item | Value |
|---|---|
| FHR baseline | 110–160 bpm1 |
| Moderate variability | 6–25 bpm1 |
| Prolonged deceleration | ≥15 bpm for ≥2 min and <10 min1 |
| Extubation threshold | TOF ratio ≥0.94 |
| Minimal block | TOF ratio 0.4 to <0.94 |
| Sugammadex | 2 mg/kg at T2; 4 mg/kg at PTC 1–23 |
| Neostigmine | 0.03–0.07 mg/kg, max 5 mg5 |
Links
- The monitors and echo station: format and timing, Neuromuscular blockade, monitoring and reversal, Fetal heart rate tracings and emergent delivery, Physiologic changes of pregnancy, laparoscopy
- Atlas: Monitor atlas: other perioperative and peripartum events; Monitor atlas: perioperative cardiac events
- ASA Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade (2023); NICHD three-tier FHR classification (2008)
Sources
- 1.Fetal Heart Rate Tracing: Assessment and Clinical Interpretation · StatPearls · ncbi.nlm.nih.govNICHD/ACOG three-tier definitions and intrauterine resuscitation.
- 2.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.orgNMB monitoring and fetal heart rate monitor marked 'testing to start in 2026'.
- 3.BRIDION (sugammadex) injection prescribing information · FDA / DailyMed · dailymed.nlm.nih.gov
- 4.New Practice Guidelines for Neuromuscular Blockade · APSF, 2023 · apsf.orgReproduces the recommendations of the 2023 ASA Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade.
- 5.BLOXIVERZ (neostigmine methylsulfate injection) prescribing information · FDA, 2015 · accessdata.fda.gov
Facts on this page were checked against these sources on Oct 15, 2026. Guidelines change; confirm doses against current institutional protocols.