What are the details of obstetrical analgesia and anesthesia?

Obstetrical Analgesia and Anesthesia: Comprehensive Overview

Fundamental Principles

Maternal request alone represents sufficient justification for pain relief during labor and delivery, and neuraxial techniques should be offered when resources are available. 1

The provision of obstetric analgesia and anesthesia requires balancing effective pain control with maternal and fetal safety, while understanding that not all women require anesthetic intervention during labor or delivery. 1

Neuraxial Analgesia for Labor and Vaginal Delivery

Timing and Indications

• Neuraxial analgesia should be offered on an individualized basis regardless of cervical dilation—there is no arbitrary threshold (such as 5 cm) that should delay its provision. 1, 2
• Patients can be reassured that neuraxial analgesia does not increase the incidence of cesarean delivery. 1, 2
• Maternal medical conditions (preeclampsia, cardiac disease) and obstetric conditions (twin gestation) may warrant neuraxial techniques to improve maternal and neonatal outcomes. 1

Technical Approach

• The primary goal is adequate maternal analgesia with minimal motor block, achieved by administering low concentrations of local anesthetics (0.25% or lower) with or without opioids. 1, 2
• Continuous infusion epidural (CIE) analgesia with local anesthetics and opioids provides superior pain relief compared to parenteral opioids. 1
• An intravenous infusion must be established before initiating neuraxial analgesia and maintained throughout the procedure. 1, 2

Medication Selection

• Bupivacaine at 0.25% and 0.5% concentrations is indicated for obstetrical anesthesia. 3
• The 0.75% concentration of bupivacaine is contraindicated for obstetrical use due to cardiac toxicity risk. 3
• Dilute local anesthetic solutions combined with opioids (fentanyl or sufentanil) optimize analgesia while minimizing motor block. 1, 2, 4

Safety Requirements

• Appropriate resources for treating complications must be immediately available, including equipment and medications for managing hypotension, systemic toxicity, and high spinal anesthesia. 1, 2
• When opioids are added, treatments for pruritus, nausea, and respiratory depression must be accessible. 1
• Continuous monitoring of maternal blood pressure and heart rate is required, as epidural anesthesia may cause hypotension. 2, 3
• Continuous electronic fetal heart rate monitoring should be maintained. 2, 3

Early Catheter Placement for High-Risk Patients

Early insertion of a spinal or epidural catheter should be considered for complicated parturients with obstetric indications (twin gestation, preeclampsia) or anesthetic indications (anticipated difficult airway, obesity) to reduce the need for general anesthesia if emergent procedures become necessary. 1

• In these cases, catheter insertion may precede the onset of labor or the patient's request for labor analgesia. 1

Anesthesia for Cesarean Delivery

Neuraxial Techniques

• Neuraxial anesthesia (epidural or spinal) is preferred over general anesthesia for cesarean delivery when not contraindicated. 1
• A sensory level to T4 is required for adequate anesthesia during cesarean section. 4
• Bupivacaine 0.5% and 0.75% (the latter only for non-obstetric procedures) can be used for surgical anesthesia. 3

Prevention of Aortocaval Compression

It is critical to avoid aortocaval compression by the gravid uterus during regional block administration—maintain the patient in left lateral decubitus position or displace the uterus to the left with a wedge under the right hip. 3

Maternal Hypotension Management

• Local anesthetics produce vasodilation by blocking sympathetic nerves, resulting in maternal hypotension. 3
• Elevating the patient's legs and left lateral positioning help prevent blood pressure decreases. 3
• The fetal heart rate must be monitored continuously, with electronic fetal monitoring highly advisable. 3

Aspiration Prophylaxis

Fasting Guidelines

• Clear liquids may be consumed during labor, but solid food intake should be avoided. 1
• For postpartum tubal ligation, fasting for solids should be 6-8 hours. 1

Pharmacologic Prophylaxis

• Nonparticulate antacids (sodium citrate, sodium bicarbonate) administered before operative procedures effectively decrease gastric acidity and reduce maternal complications. 1
• H2 receptor antagonists are effective in decreasing gastric acidity in obstetric patients. 1
• Metoclopramide reduces peripartum nausea and vomiting. 1

Alternative Analgesic Techniques

Systemic Analgesia

• Parenteral opioids (intravenous or intramuscular) provide less effective analgesia compared to neuraxial techniques but offer an alternative when neuraxial methods are contraindicated or unavailable. 1, 5
• Systemic analgesia carries greater risk of maternal sedation and neonatal respiratory depression compared to neuraxial techniques. 5

Non-Pharmacologic Methods

• Psychoprophylaxis and physical methods may provide adjunctive benefit but are often insufficient as sole analgesic modalities. 5

Special Considerations for Fetal Procedures

Fetal Analgesia During Invasive Procedures

Although the fetus cannot experience pain at gestational ages when most fetal procedures are performed (before 23-30 weeks), opioid analgesia should be administered to the fetus during invasive fetal surgical procedures to attenuate acute autonomic responses, prevent long-term consequences of nociception and physiological stress, and decrease fetal movement. 1

• Noxious stimuli can elicit neuroendocrine and hemodynamic responses by 18-20 weeks gestation, even though cortical pain perception is not yet developed. 1
• Elevations in fetal catecholamines and cortisol increase placental vascular resistance, decrease fetal blood flow, and may precipitate preterm labor. 1

Fetal Paralysis

• Fetal paralytic agents should be considered during intrauterine transfusion if needed to decrease fetal movement. 1

Common Complications and Management

Neuraxial Technique Complications

• Technical difficulties, dural puncture, bloody tap, hypotension, and insufficient block are the most frequent complications. 4
• Excessive motor block prolongs the second stage of labor and increases instrumental delivery rates. 4
• Every injection through an epidural catheter must be treated as a test dose with fractionated administration, as intravascular or subarachnoid migration can occur at any time. 4

Drug Interactions

Bupivacaine administration to patients receiving monoamine oxidase inhibitors or tricyclic antidepressants may produce severe, prolonged hypertension—concurrent use should generally be avoided. 3

• Concurrent vasopressor drugs and ergot-type oxytocic drugs may cause severe, persistent hypertension or cerebrovascular accidents. 3
• Phenothiazines and butyrophenones may reduce or reverse the pressor effect of epinephrine. 3

Contraindications

• Bupivacaine is absolutely contraindicated for obstetrical paracervical block anesthesia due to fetal bradycardia risk. 3
• Intravenous regional anesthesia (Bier Block) is not recommended with bupivacaine. 3

Effects on Labor Progress

• Epidural anesthesia may prolong the second stage of labor by removing the parturient's reflex urge to bear down or interfering with motor function. 3
• The use of obstetrical anesthesia may increase the need for forceps assistance. 3
• Meta-analysis shows an average increase of 24 minutes in the second stage duration and lower frequency of spontaneous vaginal delivery with continuous epidural local anesthetics. 1

Special Populations

Elderly Patients

• Patients over 65 years, particularly those with hypertension, are at increased risk for hypotension during anesthesia with bupivacaine. 3
• Elderly patients may require lower doses of bupivacaine. 3

Renal Impairment

• Bupivacaine is substantially excreted by the kidney—the risk of toxic reactions may be greater in patients with impaired renal function. 3