Thurlow 2002.

Methods	Randomised, controlled trial. No statement on blinding. No statement on time of randomisation. The purpose of this trial was to compare the analgesic effect of remifentanil given as PCA with IM meperidine during labour. There are no details where or when the study was conducted. The authors’ origin is the UK. Trial Identifier: NA
Participants	Participant flow: Number assessed for eligibility: 36 Number randomised: 36 (18/18) Number receiving treatment: 36 (18/18) Number analysed: 36 (18/18) Inclusion criteria: Aged between 18 and 40 years, between 38 to 42 weeks of gestation in early labour Exclusion criteria: < 50 kg or >100 kg Baseline details: Remifentanil group (n = 18): Age (years, median (IQR)): 28 (22 ‐ 32) Weight (kg, median (IQR)): 66.5 (58 ‐ 78) ASA I/II (n/n): NA Type of delivery (n): spontaneous (11), ventouse (4), CS (3) Week of gestation (median (IQR)): 40.1 (39.25 ‐ 41) Singleton, twin, multiple pregnancy: NA Parity (n): 1 (13), 2 (0), 3 (3), 4 + (2) Duration of labour: ‐ First stage of labour (min, mean (SD)): NA ‐ Second stage of labour (min, mean (SD)): NA Meperidine group (n = 18): Age (years, median (IQR)): 29 (25 ‐ 30) Weight (kg, median (IQR)): 64 (58 ‐ 76) ASA I/II (n/n): NA Type of delivery (n/n): spontaneous (16/17), ventouse (1/17), CS (0/17) Week of gestation (median (IQR)): 39.6 (39 ‐ 40) Singleton, twin, multiple pregnancy: NA Parity (n): 1 (13), 2 (0), 3 (2), 4 + (0) Duration of labour: ‐ First stage of labour (min, mean (SD)): NA ‐ Second stage of labour (min, mean (SD)): NA
Interventions	Remifentanil group (n = 18): PCA: starting with a 5 µg bolus, an increasing dose of remifentanil was given at the beginning of each painful contraction until the contraction was pain‐free, and the next painful contraction was noted. Meperidine group (n = 18): IM Meperidine 100 mg
Outcomes	The primary endpoint of the study was not explicitly defined but power analysis was performed for pain score. Continuous: ‐ midwives' and mother's assessment of overall effective analgesia (VRS 1 to 5, within 2 h after delivery, individual patient data) ‐ pain intensity (VAS 0 to 100, at 0 and 1 h), max. pain score over 2 h (VAS 0 to 100) (median + IQR, respectively (asymmetric)) ‐ sedation score (unclear assessor, VAS 0 to 100, at baseline, median + IQR) Dichotomous: ‐ additional analgesia (Entonox, epidural) ‐ rate of CS, rate of assisted birth (ventouse) ‐ syntocinon use ‐ women: respiratory depression (< 8 breaths/min), oxygen desaturation (< 94%), nausea + vomiting
Notes	‐ Small trial sample size (< 200 participants) ‐ Power analysis performed (pain score, n = 30 in total) ‐ Abstract: fewer number of women ‐ The exact intervention in the remifentanil group remains unclear (“20 µg bolus over 20 s, 3 min lockout and no background infusion”) Concomitant medication: If the assigned analgesia was inadequate for the woman at any time, an alternative was offered (epidural analgesia) and further study recordings were discontinued. All women had access to Entonox at all times. Remifentanil group: No antiemetic was given unless indicated clinically. Meperidine group: antiemetic was given (promethazine 25 mg or prochlorperazine 12.5 mg) Funding: NA Intervention: Lockout time of 3 min seems too long for adequate analgesia (borderline).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “[…] women were assigned randomly to one of two groups by sequentially numbered, sealed opaque envelopes prepared by an independent practitioner.” The method used for randomisation was not described.
Allocation concealment (selection bias)	Low risk	Quote: “[…] sequentially numbered, sealed opaque envelopes…”
Blinding of participants and personnel (performance bias) All outcomes	High risk	The study did not address this issue. However, we assume that blinding of parturients and personnel did not occur due to technical reasons and at least the subjective1 outcomes or outcome measurements are likely to be influenced by lack of blinding.
Blinding of outcome assessment (detection bias) All outcomes	High risk	The study did not address this issue. However, we assume that blinding of outcome assessment did not occur due to technical reasons and at least the subjective1 outcomes or outcome measurements are likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	‐ Dropout rate: 0% ‐ There were no withdrawals. However, there are some outcome data (additional analgesia, mode of delivery) incomplete (missing from notes) without reasons. ‐ Rate of escape (Entonox): 55%/81% (may influence data on AE, satisfaction and pain) ‐ Rate of escape (epidural): 39%/17% ‐ Rate of cross‐over: NA ‐ Data‐analysis: Partial‐ITT
Selective reporting (reporting bias)	Unclear risk	There is no reference to a trial registry and no published study protocol.
Other bias	Low risk	The study appears to be free of other sources of bias.