Obstetric anesthesia

Question 1

Pain pathways innervating the uterus, vagina, and perineum

Answer 1

o T10 – L1 supply innervation to the uterus

o L1-L4 supply pain pathways to the vagina and deep pelvic structures

o S2 - S4 supply nerve fibers to the pudendal nerve

Question 2

Types of obstetric anesthesia

Answer 2

Regional

Local

General

Question 3

Types of regional anesthesia

Answer 3

Lumbar epidural injection:

• the most common type for vaginal delivery.
• for 1st and 2nd stages of labor
• Bupivicaine or similar local anesthetic is given to the epidural space.
• Possible hypotension and nausea from sympathetic nerve block, treat with ephedrine.

o Spinal injection:
- most common type for C-section.
- not used much for vaginal deliveries due to short duration of action
- patient must be constantly attended and vital signs must be checked every
5 min to detect and treat possible hypotension

Question 4

Contraindications to regional anesthesia

Answer 4

! Absolute: patient refusal, coagulopathy, infection at needle insertion site, severe
hypovolemia with ongoing blood loss

! Relative: prior back surgery, certain cardiac lesions (especially aortic stenosis),
increased intracranial pressure

Question 5

Types of local anesthesia

Answer 5

Pudendal block
- Been replaced by epidural injections
- Injections of a local anesthetic through the vaginal wall so that the anesthetic
bathes the pudendal nerve as it crosses the ischial spine
- It will anestheize the lower vagina, perineum, and posterior vulva
- It is a simple method for uncomplicated spontaneous vaginal deliveries

Paracervical block

• Rarely appropriate for delivery because incidence of fetal bradycardia is > 15%
• It is mainly used for 1st or 2nd trimester abortion
• 5-10ml of lidocaine is injected at the 3 and 9 o’clock positions

Question 6

General anesthesia, drugs used

Answer 6

o Nitrous oxide 40% with O2

• may be used for analgesia during vaginal delivery as long as verbal contact with the woman is maintained (inhalation with self-administration)
• Possible staff-toxicity and can only be used in well-ventilated rooms

o Thiopental (sedative-hypnotic) is commonly given IV with other drugs (e.g.
succinylcholine, N2O + O2) for induction of general anesthesia during c-section
- Induction is rapid and recovery is prompt
- It is mandatory during emergency c-section

o Opioids:
- All opioids readily cross the placental barrier and may cause neonatal
respiratory depression (antidote: naloxone)
- Fentanyl and nalbuphine are the most commonly used and have short neonatal
half-lives

o Potent and volatile inhalation drugs (e.g. isoflurane) can cause marked depression in mother and fetus and is therefore not recommended for routine delivery