FRCA Notes

Remifentanil PCA for Labour Analgesia

The syllabus requires us to know about "other forms of pain relief when neuraxial analgesia is contraindicated" and "provide intravenous opiate analgesia including PCA for labour".

Remifentanil PCA was the subject of a CRQ in September 2020; the 29% pass rate reflected candidates with "little knowledge or experience of PCA Remifentanil"; knowledge of the dose, optimal timing of boluses, and protocols needed to deliver it safely was lacking.

A September 2024 CRQ on the parturient with thrombocytopenia asked for a remifentanil PCA prescription; this part was well answered and highlights that remifentanil PCA is the expected answer when neuraxial analgesia is contraindicated.

Resources

  • Neuraxial techniques remain the gold standard for labour analgesia
  • Remifentanil PCA is a useful alternative when neuraxial analgesia is contraindicated
  • NICE (2023) recommends that all labouring women are informed about remifentanil PCA as an option
  • Despite this, only around 50% of UK obstetric units offer it (NAP7), with wide variation in dosing, monitoring and staffing

  • Remifentanil is a short acting, synthetic μ-opioid receptor agonist
  • Its pharmacokinetics make it well suited to patient controlled use in labour:
    • Onset in 30 to 60s
    • Peak effect in 2 to 3mins
    • Rapid offset; context insensitive half time
    • Metabolised by non specific plasma and tissue esterases, so no accumulation

  • Readily crosses the placenta owing to its lipophilicity and high placental perfusion
  • However, it undergoes rapid metabolism and redistribution in the foetus, so neonatal effects are generally minimal and transient

  • The analgesic effect is most marked in early labour and may wane within 2-3hrs

Indications

  • Neuraxial analgesia contraindicated, e.g.:
    • Thrombocytopenia or coagulopathy
    • Therapeutic anticoagulation
    • Cardiac lesions where a sympathectomy is undesirable
  • Maternal preference
  • Failed or inadequate neuraxial analgesia

Contraindications and cautions

  • Patient refusal
  • Opioid allergy
  • Inability to provide continuous 1:1 presence
  • Birth outside an obstetric unit (midwifery led units and home births are not appropriate)

  • Systemic opioids within the preceding 4hrs
    • The 4hr opioid free window remains the starting point
    • Careful risk/benefit assessment may justify earlier use, e.g. a woman in severe pain after a failed epidural containing fentanyl

Higher risk groups

  • Almost all studies excluded high risk women, so data are sparse; the OAA has relaxed several of the traditional absolute contraindications
Group OAA position
Cardiac disease May be suitable in selected women; small series show stable haemodynamics, most managing on 20μg boluses
Pre-eclampsia May be suitable, excluding the most severe disease (e.g. eclampsia, pulmonary oedema)
Obesity May be suitable up to a BMI of 40kg/m2; individualised approach above this
IUFD May be used although other opioids may be superior
Avoid other opioids and ensure continuous midwife presence
Preterm labour
Multiple births
IUGR/SGA		 No strong evidence to contraindicate, but robust safety data are lacking



Parameter OAA recommendation
Mode PCA demand bolus only; no background infusion
Initial bolus 20 to 30μg
Titration Reduce to 10 to 20μg or increase to 30 to 40μg according to analgesia and side-effects
Lockout 2mins
Access Dedicated IV cannula with antireflux valve

  • Pumps must be capable of delivering a rapid bolus, and units should have enough pumps to meet demand
  • The only dose finding study found a median effective bolus of 0.4μg/kg (range 0.2 to 0.8μg/kg); ≈28μg for a 70kg woman
  • Side-effects increase with dose, but individual variability is marked; some women desaturate at very low doses

Timing of boluses

  • Peak effect (2 to 3mins) is similar in duration to the interval between contractions, so the bolus cannot be precisely matched to a single contraction
  • Women are therefore advised to press the button at the very first sign of a contraction (or as the previous one ends) so that effect builds into the peak of the contraction
  • The woman herself must be the only person to press the button

Background infusions

  • Not recommended: higher risk of sedation and respiratory depression
  • Escalating PCA boluses provide better analgesia than escalating infusions, with similar respiratory depression and less total drug

Single cannula

  • Acceptable only where unavoidable (e.g. very difficult venous access, needlephobia)
  • Remifentanil must be the infusion nearest the cannula, with an antireflux valve between it and all other infusions
  • This prevents a reservoir of drug building up in the line and being flushed in as an inadvertent bolus

Staffing and environment

  • Uninterrupted 1:1 care by a trained professional, observing for sedation, desaturation and apnoea
    • If continuous presence cannot be maintained, the PCA must be stopped for that period
    • Arrests reported in the literature occurred while the midwife was out of the room
  • Birth in an obstetric unit with 24hr access to medical staff, oxygen and resuscitation equipment
  • Clear unit criteria for when the anaesthetist should review and when the PCA should be stopped
  • Staff competent in BLS and formally trained in recognising and managing side effects, with regular updates and a departmental compliance log

Monitoring

  • Continuous SpO2
  • Regular respiratory rate and sedation score
  • Oxygen, naloxone and ventilation equipment immediately available

  • SpO2 alone is a poor monitor of apnoea; one study found it detected fewer than 15% of apnoeic episodes
  • Capnography has been trialled but is poorly tolerated, misses ≈25% of apnoeas and generates frequent false alarms
  • Direct observation of respiratory rate by the attending professional has the highest predictive value, reinforcing the need for 1:1 presence

  • In a stable parturient, continuous CTG is not required unless there is another indication

Supplemental oxygen

  • Apply when SpO2 falls below 94%; typically nasal cannulae at 2 to 3L/min
  • Routine oxygen from the outset is not recommended:
    • It does not prevent apnoea or hypoxic episodes
    • It may mask hypoventilation
    • Unnecessary hyperoxia may cause maternal and foetal oxidative stress

Entonox

  • May be used alongside remifentanil PCA with the same standards of monitoring
  • No significant increase in desaturation has been demonstrated

Respiratory depression and desaturation

  • The major safety concern with remifentanil PCA
  • Hypoxic episodes are common (up to 70% with 20μg boluses and a 1min lockout) but usually mild and brief (<16s)
  • Desaturation is more frequent than with epidural analgesia (odds ratio 2.8 to 7.0) or other systemic opioids
  • Apnoea is often not accompanied by desaturation
  • Respiratory and cardiac arrest have been reported, though with multiple contributing factors (concomitant opioids, absent midwife)

  • Management
    • Simple measures resolve most episodes:
      • Verbal or physical stimulation
      • Supplemental oxygen
      • Reduce the bolus dose

    • Stop the PCA and call a doctor if (typical protocol triggers):
      • RR less than 8-9/min or apnoea
      • SpO2 <92% on air, or <94 to 95% despite oxygen
      • Excessive sedation
    • Naloxone and airway support if required
    • Once physiology normalises the PCA may be restarted at a reduced bolus dose

Other maternal side effects

  • Sedation and drowsiness
  • Nausea and vomiting
  • Pruritus
  • Rates of nausea, vomiting and pruritus are similar to epidural analgesia

Neonatal effects

  • Reassuring data: no significant difference in Apgar scores, need for resuscitation or neonatal unit admission compared to epidural or other opioids
  • Neonatal resuscitation or ventilation in 1.4%; serious events possibly related to remifentanil in 0.3% (RemiPCA SAFE Network)
  • Fewer CTG abnormalities and interventions for foetal distress than with pethidine
  • Women should be told there is a small chance their baby may need brief respiratory support after birth

Stopping before delivery?

  • Some protocols advise stopping 5 to 10mins before cord clamping to reduce neonatal exposure
  • The OAA rejected this as a routine recommendation:
    • Timing of birth is very difficult to predict, risking a prolonged period without analgesia
    • It is ethically difficult to withdraw analgesia at the point it is most needed
    • The supporting evidence is not robust

Postnatal procedures

  • Remifentanil PCA should not be used as analgesia for postnatal procedures such as perineal repair
  • Once labour pain stops, the response to remifentanil cannot be assumed to remain within previously tolerated limits
  • It may be used to cover perineal infiltration of local anaesthetic, but must then be stopped
  • If already discontinued, it should not be restarted
  • Monitoring and 1:1 care must continue, and the operator cannot also supervise the patient


Advantages Disadvantages
No needle in the back; usable when neuraxial is contraindicated Inferior analgesia to epidural
Rapid onset and offset; patient controlled Analgesia may wane after 2-3hrs
Better analgesia than other systemic opioids or Entonox alone Higher rates of desaturation and apnoea
Maternal satisfaction comparable to epidural Requires continuous 1:1 presence and monitoring
Minimal, transient neonatal effects Cannot be extended for operative delivery

vs. epidural analgesia

  • Epidural provides superior analgesia across all stages of labour (high certainty)
    • The difference is apparent by 1hr and more pronounced by 2hrs
    • Conversion from PCA to epidural is far more common than the reverse
  • Maternal satisfaction is nonetheless comparable
  • Similar rates of spontaneous, instrumental and caesarean delivery
  • More maternal desaturation and apnoea with remifentanil
  • Similar neonatal Apgar scores

vs. pethidine

  • Compared to IM pethidine, remifentanil PCA provides better analgesia and halves the rate of conversion to epidural (RESPITE trial)
  • More maternal desaturation and use of supplemental oxygen with remifentanil
  • Fewer CTG abnormalities requiring intervention

vs. fentanyl PCA

  • Better analgesia in the first hour only; less conversion to epidural
  • More maternal sedation and desaturation, but less neonatal respiratory depression (no accumulation)

vs. Entonox

  • Better analgesia with remifentanil PCA, at the expense of greater sedation

Information for women

  • Relative benefits compared to other options, including that it is less effective than an epidural
  • Side effects: nausea, pruritus, sedation and respiratory depression which may need oxygen
  • The small chance of the baby needing brief respiratory support
  • The need for continuous monitoring and 1:1 care

Follow up and audit

  • No evidence of long term maternal or neonatal consequences
  • Postnatal follow up should assess satisfaction, effectiveness and side effects
  • Regular local audit of analgesic quality and adherence to safety standards