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Labour Analgesia

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1. INTRODUCTION

• Provide effective, continuous analgesia for all stages of labour
• Not depress the mother or fetus
• Not interfere with the progress of labour
• Allow the mother to cooperate in delivery
• Be rapidly convertible to anaesthesia for operative delivery
• Be free of side effects

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2. PHYSIOLOGY OF LABOUR PAIN

First Stage of Labour (Latent Phase: T11-T12; Active Phase: T10-L1)

• Myometrial contractions against cervical and perineal resistance
• Progressive cervical dilation and distension of the lower uterine segment

• Latent phase: T11-T12 dermatomes
• Active phase: T10-L1 dermatomes

Second Stage of Labour (T10-S4)

• Morgan & Mikhail's Clinical Anesthesiology, 7e, p. 1607

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3. CLASSIFICATION OF METHODS OF LABOUR ANALGESIA

Labour Analgesia
├── A. Non-Pharmacological
├── B. Pharmacological (Systemic)
│   ├── Opioids (IV/IM)
│   ├── Inhalational agents
│   └── Sedatives/anxiolytics
└── C. Regional/Neuraxial
    ├── Epidural analgesia
    ├── Spinal (intrathecal) analgesia
    ├── Combined spinal-epidural (CSE)
    ├── Continuous spinal analgesia
    ├── Pudendal nerve block
    └── Paracervical block (largely abandoned)

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4. NON-PHARMACOLOGICAL TECHNIQUES

• Miller's Anesthesia, 10e, p. 8841

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5. SYSTEMIC (PHARMACOLOGICAL) TECHNIQUES

A. Opioids

• Dose-related neonatal respiratory depression
• Decreased FHR variability (both short-term and long-term)
• Decreased fetal movements (sedation)
• Lower Apgar scores with higher doses close to delivery
• Neonatal neurobehavioural depression

i. Meperidine (Pethidine)

• Once most commonly used opioid in obstetric practice - now rarely used
• IV: 10-25 mg; IM: 50-100 mg (max 100 mg total)
• Maternal half-life: 2.5-3 hours; active metabolite normeperidine half-life: 13-23 hours
• Both half-lives are 3x longer in the fetus/neonate
• Normeperidine accumulates with repeated doses and is neurotoxic
• Peak fetal depression: 10-20 min IV; 1-3 hours IM
• Given when delivery not expected for at least 4 hours

ii. Morphine

• Rarely used for labour pain
• Active metabolite morphine-6-glucuronide has longer half-life in neonates
• Causes significant maternal sedation and histamine release
• IM morphine used by obstetricians for latent labour (rest and analgesia)
• Onset: 10-20 minutes IM

iii. Fentanyl

• IV: 25-100 mcg/hour (PCA) or 25-100 mcg bolus doses
• Rapid onset: 3-10 min; lasts ~60 min (longer with repeated doses)
• Highly lipid-soluble; rapidly crosses placenta
• Lower doses: little or no neonatal respiratory depression; no effect on Apgar scores at low doses

iv. Remifentanil (PCA - increasingly popular)

• Ultra-short-acting opioid; rapidly metabolised by plasma esterases
• Popular PCA setting: 40 mcg bolus, 2-min lockout
• Equipotent or superior to other parenteral opioids
• Does not provide the degree of analgesia offered by neuraxial techniques
• Mandatory 1:1 nurse:patient monitoring required due to risk of maternal respiratory depression and apnoea
• Advantage: rapidly metabolised in fetus/neonate by plasma esterases

v. Mixed Agonist-Antagonist Opioids

• Nalbuphine: similar analgesic potency to morphine; IV/IM/SC 10-20 mg every 4-6 hours; ceiling effect on respiratory depression
• Butorphanol: 5x more potent than morphine; 1-2 mg IV or IM; ceiling on respiratory depression; may cause sedation
• Advantage: ceiling on respiratory depression reduces overdose risk

B. Inhalational Analgesia

• Most widely used inhalational agent for labour
• Administered via demand valve - patient-controlled, self-administered
• Onset: 30-45 seconds (best inhaled 30 seconds before next contraction begins)
• Provides 30-60% analgesia with good maternal satisfaction
• Does not cause respiratory depression at 50% concentration
• Occupational exposure risk to attendants - requires scavenging
• Can cause maternal nausea, light-headedness, and (rarely) loss of consciousness
• Does not affect labour progress or neonatal Apgar scores significantly

C. Sedatives and Anxiolytics

• Promethazine, hydroxyzine: antiemetics, adjuncts only; cross placenta
• Benzodiazepines: generally avoided; neonatal depression, hypotonia, hypothermia ("floppy infant syndrome")
• Ketamine (0.1-0.5 mg/kg IV): dissociative analgesic; preserves airway reflexes; useful when rapid analgesia needed and regional is contraindicated; can cause psychotomimetic effects; large doses may cause neonatal depression

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6. REGIONAL ANAESTHETIC TECHNIQUES

"Epidural or intrathecal techniques, alone or in combination, are currently the most popular methods of pain relief during labor and delivery." - Morgan & Mikhail, 7e, p. 1610

Contraindications to Neuraxial Labour Analgesia

Pre-procedure Assessment

• Focused preanesthetic evaluation: airway, back examination, vitals, obstetric history
• ASA recommends moderate amounts of clear liquids are allowed during neuraxial labour analgesia; solid foods should be avoided
• Laboratory testing not required in otherwise healthy patients

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A. EPIDURAL ANALGESIA

Advantages

• Titratable, continuous, adjustable analgesia
• Can be converted to surgical anaesthesia for cesarean delivery
• Reduces maternal catecholamines (improved uteroplacental blood flow)
• Improves maternal satisfaction
• Avoids systemic opioid side effects
• Allows "laboring down" in second stage

Timing

• Can be initiated at any point during the first stage of labour
• ASA guidelines: maternal request is sufficient justification - timing should not depend on arbitrary cervical dilation
• Early placement: easier positioning, functions as emergency backup catheter
• Meta-analysis of 15,399 parturients: early neuraxial analgesia (≤3 cm) does not increase cesarean delivery rate or prolong first stage

Level of Insertion

• L3-L4 or L4-L5 interspace (optimal for T10-S5 blockade)

Technique

• Lateral decubitus or sitting position (preferred in obese patients - easier midline identification; also promotes sacral spread for second stage)

• Loss of resistance (LOR) technique - using saline (preferred) or air
• If air used: limit to <2-3 mL (larger volumes cause patchy/unilateral block and headache)
• Average depth of epidural space in obstetric patients: ~6 cm from skin
• Ultrasound guidance: useful in obese patients with poor landmarks; estimates depth and needle angle

• 3 mL of 1.5% lidocaine with 1:200,000 epinephrine (standard test dose)
• Epinephrine 15-20 mcg: HR increase >20 bpm within 30-60 sec = intravascular placement
• Rapid motor block = intrathecal placement
• Wait 5 minutes before proceeding

Note: epinephrine test dose less reliable in parturients due to baseline HR variability with contractions. Monitor for CNS toxicity signs (tinnitus, dizziness, perioral numbness, metallic taste).

• Administer 10-15 mL of local anesthetic-opioid mixture at no faster than 5 mL per 1-2 minutes
• Position supine with left uterine displacement (>15° wedge under right hip)
• Monitor vitals every 1-2 min for first 15 min, then every 5 min

Drug Regimens

Maintenance Methods

Effects on Labour and Delivery

• First stage: Multiple RCTs and a 2018 Cochrane review (33 studies, n=10,350) found no difference in cesarean delivery rates between epidural and non-epidural analgesia
• Second stage: Modest prolongation by ~15 minutes (dense motor blockade may impede coordinated pushing)
• Assisted vaginal delivery: increased in older studies; post-2005 studies show no effect with modern dilute epidural solutions
• Early epidural does NOT prolong first stage or increase cesarean rates

• "Laboring down" technique: allows uterine contractions to lower fetal station before active pushing
• Protects perineum from tears by allowing controlled expulsion of fetus

• For forceps/vacuum delivery: supplement with 5-10 mL of 1-2% lidocaine or 2-3% 2-chloroprocaine
• For emergency cesarean: rapidly dose with concentrated LA (2% lidocaine, 0.5% bupivacaine, or 3% chloroprocaine)

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B. SPINAL (INTRATHECAL) ANALGESIA

Single-Injection Spinal

• Quick to perform; provides rapid analgesia
• Limited duration - best reserved for:
  • Multiparous women in advanced dilation
  • Second stage of labour
  • When epidural placement is technically difficult
• 14% of patients required additional analgesia in a retrospective study of 428 parturients
• Not ideal for nulliparous patients or those in early labour

Continuous Spinal Analgesia

• Considered in case of accidental dural puncture during epidural placement
• High incidence of PDPH (post-dural puncture headache) precludes elective use through standard epidural needles
• When used: requires clear labelling, documentation, and strict monitoring for excessive block
• Catheter dosing with small fractionated doses

• Miller's Anesthesia, 10e, p. 8852

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C. COMBINED SPINAL-EPIDURAL (CSE) ANALGESIA

Technique

1. Epidural needle advanced to epidural space (L3-L4 or L4-L5)
2. Long 27-gauge pencil-point spinal needle passed through epidural needle into subarachnoid space
3. Intrathecal drug injected
4. Spinal needle withdrawn; epidural catheter threaded and secured
5. Epidural catheter used for top-up doses as needed

Intrathecal doses for CSE initiation:

• Fentanyl 10-25 mcg + Bupivacaine 1.25-2.5 mg (most common)
• Sufentanil 5-7.5 mcg ± Bupivacaine 2.5 mg

Advantages of CSE over epidural alone:

• Faster onset of analgesia (intrathecal component)
• Lower total local anesthetic dose
• Preservation of motor function ("walking epidural")
• Better patient satisfaction scores in some studies
• Epidural catheter available for prolonged labour, top-ups, or emergency cesarean

Disadvantages / Concerns:

• Cannot immediately verify epidural catheter function until intrathecal dose wears off
• Higher incidence of fetal bradycardia (particularly with intrathecal sufentanil - possibly due to rapid decrease in circulating catecholamines altering uterine tone)
• Higher incidence of maternal pruritus (from intrathecal opioid)
• Maternal hypotension

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D. PUDENDAL NERVE BLOCK

• Blocks S2-S4 (pudendal nerve) - provides anesthesia for the perineum during the second stage
• Technique: Transvaginal approach using Koback needle or Iowa trumpet guide
  • Needle placed underneath ischial spine on each side
  • Advanced 1-1.5 cm through sacrospinous ligament
  • 10 mL of 1% lidocaine or 2% chloroprocaine injected after negative aspiration
  • Needle guide limits depth and protects fetus
• Often combined with perineal infiltration
• Effective for second stage but provides no first-stage analgesia
• Complications: intravascular injection, retroperitoneal hematoma, retropsoas or subgluteal abscess

E. Paracervical Block

• No longer used in standard practice
• High rate of fetal bradycardia due to proximity to uterine artery - causes uterine arterial vasoconstriction and uteroplacental insufficiency
• Local anesthetic rapidly absorbed into fetal circulation due to proximity

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7. MANAGEMENT OF COMPLICATIONS

A. Hypotension

• Most common complication of neuraxial anaesthesia
• Defined as: >20% decrease from baseline systolic BP, or systolic BP <100 mmHg
• Mechanism: sympathetic blockade → decreased SVR + aortocaval compression

• IV phenylephrine 40-120 mcg boluses (drug of choice - maintains uteroplacental flow)
• Supplemental oxygen
• Left uterine displacement (>15° wedge under right hip)
• IV fluid bolus
• If unresponsive: ephedrine 5-10 mg IV (has beta-adrenergic activity)

B. Dural Puncture and Post-Dural Puncture Headache (PDPH)

• Incidence of unintentional "wet tap" in obstetric patients: 0.25-9% depending on experience
• Incidence of intravascular catheter placement: 5-15%
• Incidence of intrathecal catheter placement: 0.5-2.5%

• Postural: worse upright, relieved lying flat
• Onset: 12-48 hours post-procedure
• Severe frontoparietal or occipital headache, may have visual/auditory symptoms
• Due to CSF leak through dural hole

• Conservative: bed rest, IV fluids, simple analgesics, caffeine
• Epidural blood patch (EBP): gold standard - 15-20 mL autologous blood injected into epidural space at same or adjacent interspace; ~85% success rate

C. High/Total Spinal

• Excessive cephalad spread of LA causing:
  • Respiratory paralysis (above C3-5)
  • Unconsciousness
  • Cardiovascular collapse

• Immediate airway management - intubation if necessary
• Vasopressors, IV fluids
• Left uterine displacement
• Prepare for emergency cesarean if fetal compromise

D. Local Anaesthetic Systemic Toxicity (LAST)

• Due to intravascular injection of LA
• CNS prodrome: perioral numbness, metallic taste, tinnitus, dizziness → seizures
• Cardiovascular: arrhythmias, cardiac arrest (especially bupivacaine - highly cardiotoxic)

• Stop LA immediately
• Airway, breathing, circulation
• 20% Intralipid emulsion: 1.5 mL/kg bolus IV, then infusion 0.25 mL/kg/min
• Avoid propofol as substitute for Intralipid
• BLS/ACLS (avoid vasopressin; reduce epinephrine dose)

E. Pruritus (Neuraxial Opioids)

• Most common side effect of intrathecal opioids (especially morphine/fentanyl)
• Mechanism: central (spinal cord µ-receptor activation) rather than histamine release
• Treatment: low-dose naloxone (0.1-0.2 mg/h IV), ondansetron, naltrexone, or propofol 10 mg IV

F. Neurological Complications

• Epidural hematoma: rare; spinal cord compression - immediate MRI + surgical decompression
• Epidural abscess: rare; back pain, fever, neurological deficit
• Transient neurological symptoms (TNS): with hyperbaric lidocaine (lidocaine increasingly avoided intrathecally)
• Direct needle or catheter trauma: rare

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8. EFFECTS ON THE FETUS AND NEONATE

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9. SPECIFIC SITUATIONS

Preeclampsia / PIH

• Neuraxial analgesia preferred (reduces BP spikes, prevents hypertensive crisis during painful contractions)
• Check platelet count (avoid if <80,000)
• Exaggerated hypotension response - careful fluid management

Coagulopathy / Anticoagulation

• Follow ASRA (American Society of Regional Anesthesia) guidelines for timing relative to anticoagulant dose

Cardiac Disease

• Pure intrathecal opioids (without LA) preferred for patients who cannot tolerate sympathectomy
• E.g., severe aortic stenosis, tetralogy of Fallot, Eisenmenger syndrome, severe pulmonary hypertension

Obesity

• Sitting position preferred for epidural placement
• Higher epidural failure rate; ultrasound guidance helpful
• Anticipate difficult airway if general anaesthesia needed

Previous Uterine Scar / VBAC

• Epidural analgesia safe and recommended for VBAC
• Does not mask pain of uterine rupture (epidural analgesia covers T10-L1, while uterine rupture pain often involves shoulder-tip pain, sudden abrupt pain change, or fetal heart rate abnormalities)

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10. SUMMARY TABLE: COMPARISON OF METHODS

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11. EXAM RECALL POINTS

1. Pain pathways: 1st stage T10-L1 (visceral); 2nd stage T10-S4 (somatic via pudendal S2-4)
2. Epidural space average depth in obstetric patients: 6 cm
3. Test dose: 3 mL 1.5% lidocaine + epinephrine 1:200,000; HR >20 bpm rise = intravascular
4. Meperidine normeperidine half-life 3x longer in fetus; avoid within 4 hours of delivery
5. Remifentanil PCA: 40 mcg bolus, 2-min lockout; mandates 1:1 monitoring
6. 2018 Cochrane review (33 studies, n=10,350): epidural does NOT increase cesarean rate
7. Second stage prolongation: ~15 minutes with neuraxial; no increase in CS rate
8. Early epidural (≤3 cm): does NOT prolong first stage or increase caesarean rate
9. CSE advantage: "walking epidural" - preserved motor function, rapid onset
10. Intralipid 20% 1.5 mL/kg for LAST
11. Phenylephrine is vasopressor of choice for neuraxial-induced hypotension in obstetrics
12. Paracervical block abandoned: fetal bradycardia from uterine artery vasoconstriction
13. Pudendal block: blocks S2-4; transvaginal, under ischial spine; 10 mL 1% lignocaine
14. PIEB (programmed intermittent epidural bolus) - superior to continuous infusion for labour
15. Maternal request is sufficient indication - no minimum cervical dilation needed for epidural

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• Morgan & Mikhail's Clinical Anesthesiology, 7e, pp. 1606-1621
• Miller's Anesthesia, 10e, pp. 8840-8865
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e
• 2018 Cochrane Review: Epidural versus non-epidural analgesia for pain management in labour (PMID: 29820014)