Obstetrical Analgesia and Anesthesia

Why do we care about labor anesthesia and analgesia? We’re obstetricians!

• Labor hurts!

  • Technically speaking, evolution of visceral pain to somatic pain in the second stage of labor when the fetus comes down to the perineum → pain through the pudendal nerve and S2-S4 distribution.

  • There is also a discrepancy with rating of pain and rating of satisfaction with pain relief in certain trials - possibly because there are varying expectations for pain control and labor experience 

What is available? 

• Parenteral or systemic analgesia 

  • IV opioids. Unfortunately, they have little effect on maternal pain scores, provide unreliable analgesia, and can have adverse effects, such as nausea or vomiting.

  • We usually use fentanyl, morphine or butorphanol (Stadol).

  • Cochrane review has not found the ideal parenteral opioid and though there is some pain relief with this, it’s poor overall.

  • Also, all opioids cross the placenta, and there can be some adverse effects on the fetus.

    • Drugs will take longer to eliminate in the newborn, and can cause respiratory depression if administered close to time of delivery. 

• Regional (Neuraxial) analgesia and anesthesia

  • More than 60% of women w/ singleton birth in the US get an epidural or a spinal 

    • Epidural - placement of a catheter into the epidural space; can have repeat or continuous administration of medication; usually a mixture of an opioid with a local anesthetic.

    • Spinal - single-injection of an opioid, local anesthetic, or both into the subarachnoid space; usually used for cesarean delivery and not for labor because it usually has a limited time frame.

    • Combined Spinal-Epidural Analgesia 

      • Inject into the subarachnoid space and also a placement of a catheter for ongoing analgesia 

      • This is usually used because of rapid onset of pain relief of spinal, combined with long-acting effect of epidural.

• Local anesthesetics 

  • Pudendal nerve blocks - local anesthesia that is injected transvaginally into the vicinity of the pudendal nerve below the ischial spines; usually just for second stage of labor or to help with lac repairs 

  • Local infiltration (usually for lac repair) 

• Inhaled agents 

  • Nitrous oxide - 50% of NO and 50% O2 with demand valve so only given when patients inhale using the mask.

  • Analgesia provided by NO is less effective than epidural when we look at pain scores; but NO is superior for mobility because patients can still move around, and also has quick termination of effect.

• General Anesthesia 

  • Exceptionally rare use for a vaginal delivery, and sometimes used for emergent cesarean sections.

  • The main issues is that these agents will transfer to the fetus → depression 

  • Also harder to manage airway of pregnant patient due to anatomic changes (increased airway edema).

Risks of Regional Analgesia and Anesthesia 

• Maternal 

  • Overall very low risk of maternal morbidity and mortality.

  • In a registry that was collected over 5 years (ended in 2009), in >300,000 recorded cases of anesthesia use, there were 157 complications.

    • There were 30 maternal deaths in this cohort, none of which were attributed to anesthesia.

    • There were 2 cardiac arrests attributable to anesthesia, 4 cases of epidural abscess or meningitis, 1 epidural hematoma, 10 failed intubations (no aspirations), 58 high neuraxial blocks

  • Minor complications can be things like pruritis, epidural headaches, hypotension, nausea/vomiting 

• Fetal 

  • Usually related to maternal effects of hypotension or transplacental passage of analgesic or anesthetic drugs 

  • Opioids can lead to neonatal depression (ie. respiratory depression, decreased muscle tone, decreased sucking) 

  • Alterations to FHT can also be seen; ie. minimal variability, bradycardia, prolonged deceleration in the first 15 minutes following spinal-epidural analgesia.

Who can’t get regional anesthesia? 

• Thrombocytopenia - relative contraindication, but safe lower limit for platelet count hasn’t been established.

  • One study stated that risk of epidural hematoma among obstetric patients was 0-0.6% when platelets were 70-100k, but stated that data was insufficient to assess risk when platelets were <70k.

  • So in most cases, epidurals/spinals can be considered same if platelets are 70K or above, as long as platelets are stable.

• Low dose aspirin - not a contraindication! 

• Anticoagulation 

  • Unfractionated heparin

    • Prophylactic dose (i.e., 5000u BID):

      • Not contraindication to neuraxial techniques

      • Place or remove catheter 4-6 hours after last dose.

    • Intermediate dose (7500-10000u BID):

      • Likely low risk to proceed with neuraxial anesthesia if > 12 hours after last dose 

    • High dose (>20,000u total daily):

      • Placement >24 hours after last dose and must have activated partial thromboplastin time within normal range or anti-factor Xa level undetected.

      • If taking unfractionated heparin >4 days, platelet count should be assessed for possible HIT.

    • Resume UF heparin >1 hour after catheter removal.

  • Low molecular weight heparin (ie. Lovenox)

    • Prophylactic dosing:

      • Stop medication at least 12 hours before placement or removal of epidural catheter 

    • Therapeutic dosing:

      • 24 hour delay in catheter placement.

    • Resume LMWH >4 hours after catheter removal 

• Space-occupying brain lesions - contraindication to neuraxial techniques because dural puncture can lead to increased intracranial pressure → hindbrain herniation.

  • However, not all space-occupying lesions result in increased ICP.

  • If imaging shows no mass effect, hydrocephalus, or other features suggestive of increased ICP, risk of herniation is minimal and epidural analgesia or anesthesia can be considered.