Review Note
Last Update: 03/02/2025 07:56 PM
Current Deck: ACG Part 2::Obstetrics
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Commit #293140
SS_OB 1.22 Evaluate the analgesic options for labour and delivery
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Commit #293140Pain through stages of labour/delivery:
- First stage:
- Visceral, poorly localised, dull ache - lumbrosacral, iliac crests, gluteal region
- Due to cervical dilation, lower uterine segment dilation, uterine contraction
- Visceral afferent C sympathetic fibres from lower uterus and cervix → hypogastric nerves → dorsal root ganglia of levels T10 to L1
- Cervical pain also via S2-3 parasympathetic pelvic splanchnic nerves
- Second stage:
- Somatic pain: Stretching/tearing of perineum, distension and pulling of pelvic structures
- Pain is due to a combination of visceral pain (uterine contractions and cervical stretching) and somatic pain (distention and tearing of vaginal and perineal tissues)
- Pudendal nerve carries somatic afferent pain signals (Aδ) from vaginal canal and perineum → dorsal root ganglia of S2 to S4
- Third stage:
- Same as stage 2 but usually less severe
Three most commonly used options:
- Inhaled N2O
- Opioids
- Neuraxial techniques
- Non-pharmacologic may also be used e.g.: massage, acupuncture, TENS, warm water bath (poor evidence that these reduce pain scores but may be helpful)
Pharmacological techniques:
- Nitrous oxide
- Inhaled entonox 50% N2O, 50% O2
- Analgesia onset seconds after inhalation, peak effect 45 seconds, short duration of effect (good for contractions)
- Side effects: nausea, presyncope, drowsiness, disorientation, adverse haematological and immunological effects with prolonged exposure
- Contraindications: Pneumothorax, severe sinus disease, recent retinal detachment
- N2O is a greenhouse gas
- Opioids
- Orals:
- Worldwide pethidine commonly used but has a long half life in the fetus (18-23hrs), reduced FHR variability, can affect breastfeeding and associated with changes in fetal neurobehavioral scores, contraindicated in epilepsy
- Morphine more effective than pethidine
- IM/IV:
- Morphine
- Pethidine
- Fentanyl
- Each has pros and cons
- PCA:
- Fentanyl or remifentanil PCA commonly used in those with contraindications to neuraxial block
- Remifentanil has best profile for labour pain/contractions but significant morbidity associated with poor monitoring from respiratory depression
- If using needs: dedicated IVL, midwife in room AT ALL TIMES, more frequent observations, continuous sats, anaesthetist titrates dose and stays in room for 30mins post any changes. At national womens: dose range is 0.2 to 0.8 microgram/kg with a fixed lockout time of three minutes based on lean body weight
- Regional: Epidural
- Most effective form of analgesia in labour, especially if prolonged or augmented
- Indications:
- Maternal request, high risk of operative delivery
- Conditions that would make GA difficult or life threatening: difficult airway, morbid obesity
- Maternal co-morbidities, especially those from which sympathetic stimulation might cause material or fetal deterioration e.g.
- CVS disease (regurgitant lesions, PHTN, AS)
- Respiratory disease (cystic fibrosis, restrictive lung disease)
- Specific neurological disease (intracranial AVM’s, spinal cord injury)
- Obstetric disease (PET with coagulopathy/HELLP)
- Contraindications:
- Absolute:
- Maternal refusal
- Local sepsis or severe systemic sepsis
- Raised ICP
- LA allergy
- Uncorrected hypovolaemia, haemorrhage
- Coagulopathy: Variation into which numbers to use, risk/benefit, spinal safer than epidural. Generally:
- Platelets >75 with normal coags
- Can consider lower platelets if GA very high risk
- Plts and Coags within 6 hours of procedure, consider rate at which platelets are falling (and when to remove epidural)
- Relative:
- Expectation of significant haemorrhage
- Untreated systemic infection
- Specific cardiac disease (severe valvular stenosis, eisenmenger's syndrome, peripartum cardiomyopathy)
- Previous back surgery with scarring of epidural space
- Risks:
- Hypotension, failure, PDPH, prolonged second stage, nerve injury, paraplegia (and more)
- Before inserting epidural:
- Midwife available
- Established IV access
- Sterile technique: gloves, gown, hat, mask
- Position: Full lateral or sitting
- Fetal HR monitoring before and during (as able)
- Skin sterilization 0.5% chlorhexidine, allowed to dry, away from tray
- Insertion:
- Tuohy needle 16ga or 18ga
- LOR with saline reduces incidence of accidental dural puncture and ‘missed segments’ compared to LOR with air
- Decreased chance of puncturing vessel if 10mls of saline in epidural space prior to inserting catheter
- Leave 3.5–5cm of catheter in the epidural space; longer increases risk of unilateral block and shorter increases risk of catheter pulling out of the epidural space
- Aspirate catheter for blood or CSF.
- If blood: Withdraw catheter, if still present remove and start again
- Test dose: Should be able to produce block (but not a high block) within 5 mins if catheter is in CSF
- Can test for IV placement with 1:200000 adrenaline but has high false positive and negative rates
- After 5 mins, load with remaining dose
- Monitoring:
- BP every 5 mins for 20 mins
- Usually FHR
- Maintaining epidural:
- PCEA: larger volume, low concentration + fentanyl usually msot effective
- Continuous infusion
- Intermittent top ups by midwife
- PIEB - decreased risk of breakthrough pain compared with continuous infusions
- CSE for labour
- Rapid onset of analgesia with minimal motor block if low doses used
- Good to re-establish analgesia in those with a failed epidural or those that cannot sit still for an epidural
- Some evidence of improved epidural analgesia after spinal wears off
- Can be needle through needle or separate injections
- Spinal dose example 0.5-1ml 0.25% bupivacaine + 5-25 mcg fentanyl
- After 15 mins check sensory/motor block, then top up epidural (test then top up)
- Dural puncture epidural
- Modification of CSE
- Dural puncture with 25G pencil point (not 27G)
- No intrathecal agents injected, then epidural catheter inserted
- Analgesia onset is slightly quicker adn of slightly better quality
- Likely due to epidural bolus leaking into CSF
- Lower rates of maternal hypotension, pruritus and uterine hyperstimulation compared with CSE