Pocket ObGyn – Neuraxial Anesthesia in Obstetrics
See Abbreviations
- Most effective method for labor pain
- Also std for C/S, postpartum tubal ligations, urgent postpartum procedures whenever poss
| Mechanisms of pain in labor | |||
| Pain | Mech | Pathways | Neuraxial anesthesia |
| Visceral 1st stage 2nd stage 3rd stage | a. Contractions ® ischemia ® release of pain mediators
b. Stretch/distention |
Sensory nerves follow symp nerve pathways, enter spinal cord at T10–L1 | Block T10–L1 afferents |
| Somatic 2nd stage 3rd stage | Fetal head distends vagina/perineum
Pain from lacerations |
Pudendal nerves enter spinal cord at S2–4 | Extend block to S4 Or: Pudendal block, local infiltration |
- Indications for spinal/epidural anesthesia in labor Maternal request
Anticipation of operative vaginal deliv or shoulder dystocia; breech extraction; high risk of C/S; Risk of hemorrhage; difficult intubation
Maternal condition where signif pain or stress would create medical risk (eg, sev respiratory or cardiac dz)
Maternal condition which could worsen & potentially limit use of neuraxial anes- thesia later in labor course (eg, worsening thrombocytopenia or coagulopathy)
- Contraindications to spinal/epidural anesthesia in labor
Absolute: Maternal refusal, uncooperative pt; soft tissue infxn of site; uncorrected hypovolemia; uncorrected therapeutic anticoagulation; Lovenox w/i 24 h; certain spinal conditions (eg, ependymoma); sev thrombocytopenia (<50 K)
Relative: Certain spinal conditions (eg, discectomy, rod fusion); mod thrombocy- topenia (<75 K); LP shunt, some neurologic dzs (ie, multiple sclerosis); fixed cardiac output conditions (ie, AS)
- Types of neuraxial blocks: Spinal, epidural, & CSE
Spinal:
Anesthetic/opioid delivered directly into spinal fluid w/ needle through dural puncture
Benefits: Rapid onset (2 min); 1/20 epidural dose used so less risk tox
Disadvantages: Limited duration (1–1.5 h)
Epidural:
Anesthetic/opioid delivered into epidural space via continuous infusion through catheter
Benefits: Ability to continuously infuse & adjust dosage as needed; pt controlled
Disadvantages: Slower onset (20 min), larger doses used (20´ spinal doses)
CSE:
Meds delivered directly into spinal fluid, then catheter placed in epidural space Benefit: Combination of rapid onset & ability to continuously infuse Disadvantages: More technically challenging than epidural or spinal alone;
increased risk of PDPH compared to spinal alone
Figure 4.1 Epidural block
Reprinted with permission from Mulroy MF. Regional Anesthesia: An Illustrated Procedural Guide. Boston, MA: Little, Brown and Company; 1996:109.
| Complications of neuraxial anesthesia | |||
| Complication | Incid | Mech | Treatment |
| HoTN | 28–31%
Prehydration = slightly less |
Local anesthetic causes vasodilation via parasympathetics | Prehydration decreases incid to some degree
Epi/phenylephrine |
| Fever >100.4°F (incid above that in women w/ parenteral opioids) | 15–33% nullips
1–5% multiples |
Not well understood; noninfectious, inflamm resp, altered thermoregulation | Conservative measures
Acetaminophen does not reliably treat epidural fever |
| Fetal HR
decelerations (transient) |
8% | HoTN, decreased uterine perfusion | Maternal positioning, hydration, oxygen, epi |
| Complication | Incid | Mech | Treatment |
| PDPH (“spinal HA”) | 1.5–3% spinal
1–2% epidural overall; 80% w/ epidural “wet tap” |
Leakage of CSF through dural puncture | Supine position, analgesics, caffeine
Bld patch if lasts 24+ hours |
| Pruritus (w/ opioid in spinals/ epidurals) | 1.3–26% epidural
41–85% spinal |
Periph morphine agonist effects | Nalbuphine |
| Inadq blockade | 9–15% epidural | ||
| Rare complications: Epidural hematoma, abscess, total spinal blockade, local anesthetic tox | |||
| From Obstet Gynecol 2002:100:177. | |||
| Neuraxial anesthetics | ||
| Combination of local anesthetic & opioid typical. The local anesthetic provides the best anesthetic effect, but also causes motor blockade & potential tox (0.02% after epidural) (Int J Obstet Anesth 2004;14:37; Am J Obstet Gynecol 2001;185:128) The opioid has a synergistic effect w/
the local anesthetic, allowing for lower dose (20–30% less local anesthetic) & has no intrin- sic motor blockade. |
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| Local anesthetic | Advantages | Disadvantages |
| Bupivacaine
Most common choice |
Good motor/sensory differentiation
Long duration Overall good safety, no tachyphylaxis (acute ¯ in resp to drug after its administration) |
Cardiotoxicity, prolonged Na+ channel block
Slower onset: 20 min |
| Lidocaine | Rapid onset: Used for test dose, rapid bolus for perineal repairs, instrumental deliv | Poor sensory–motor differentiation
More tachyphylaxis |
| Chloroprocaine | Very rapid onset: Used for test dose, rapid bolus for perineal repairs, instrumental deliv | Poor sensory–motor differentiation
Very short duration |
| Opioid | Advantages | Disadvantages |
| Fentanyl
Most common choice Sufentanil: Similar SE profile, more potent |
Less side effects than morphine
More rapid onset |
Pruritus (occurs w/ all opioids) |
| Morphine | Pruritus, N/V Slower onset | |
| Hydromorphone | Superior analgesia to fentanyl in some studies; similar crossing of bld– brain barrier as fentanyl but longer half-life | Similar SE profile to morphine limits use |
| Effect of neuraxial anesthesia on labor course and outcome | |
| 1st stage of labor | Statistically but not clinically signif lengthening; may be slower to reach 4–5 cm |
| 2nd stage of labor | Avg 15–30 min longer due to decreased sensation/urge to push |
| Labor augmentation | Increased rates of labor augmentation (Lancet 2001;359:19) |
| Operative vaginal deliveries | Slightly increased rates of operative vaginal deliveries (BMJ 2004;328:1410) |
| C/S rate | Not a/w in Cesarean rate (Cochrane Database Syst Rev 2005;CD 000331) |