Obstetric Anesthesia — The Basics

Pregnancy changes nearly every system relevant to anesthesia:

• Neuro: MAC is decreased. Engorged epidural veins shrink the epidural space and CSF volume → local anesthetic spreads more near term (use less).
• Respiratory: the airway is friable and edematous (often needs a smaller cuffed ETT); FRC falls while O₂ consumption rises → rapid desaturation on induction; tidal volume and minute ventilation rise.
• Cardiovascular: ↑ blood volume, ↑ cardiac output (can jump ~80% right after delivery), ↓ SVR.
• Aortocaval compression: supine, the gravid uterus compresses the IVC and aorta → put a bump under the right hip (~15 cm) for left-uterine displacement.
• GI: increased reflux and a full stomach (slow motility) → aspiration risk. Treat every pregnant patient as a full stomach.

The anesthesia team places and manages the labor epidural — typically a dilute local anesthetic ± opioid infusion, seated or in the left lateral position. Check the level periodically (ice or a pin) for the dermatome of analgesia.

Complications: - Hypotension (the most common) — sympathetic blockade → ↓SVR/BP. Nausea is often the first sign. Pre-treat with IV fluid; treat with left-uterine displacement, fluids, and a vasopressor (phenylephrine or ephedrine). - High spinal / high epidural — block higher than intended → trouble breathing, unconsciousness, CV collapse. Turn the infusion down, communicate; a total spinal means intubate and support the patient while monitoring fetal tones. - Slowed labor — you may be asked to turn the rate down for the second stage.

Don't be fooled — a C-section is full abdominal surgery, usually under regional (dose up a working epidural, or place a spinal/combined spinal-epidural). Be ready to convert to general if the patient becomes unstable or the block fails — run a full machine/room check so the equipment is ready.

• Aspiration prophylaxis: metoclopramide (motility), an H₂ blocker like cimetidine (acid), sodium citrate PO (neutralize acid).
• After delivery: oxytocin (after the placenta); methylergonovine IM for uterine atony if asked; deepen volatile if the surgeon needs uterine relaxation.
• If general is needed: the OB airway is difficult until proven otherwise — thorough airway exam, smaller ETT, your most experienced intubator, RSI with cricoid, left-uterine displacement, pre-oxygenate well, surgeons scrubbed/draped before induction, and a failed-airway backup plan. Because she's a full stomach, wake her up before extubating.