Background infusion versus no background infusion:
Seven RCTs (n=573 patients). Most studies used low infusion rates (<5mL/hour). Five studies used double-blinding, one study used single-blinding and the level of blinding was unclear in the seventh study.
Absence of background infusion was associated with a higher incidence of intense pain in one of five studies and more clinician interventions in two of five studies. There was no significant difference between treatment groups in significant motor block (five studies) or maternal satisfaction (five studies).
Ropivacaine versus bupivacaine:
Eleven studies (n=2,083 patients). Concentrations of agents ranged from 0.05% (with fentanyl) to 0.125% for bupivacaine and from 0.05% to 0.20% for ropivacaine. All studies used double or triple-blinding.
There was no significant difference between ropivacaine and bupivacaine in maternal analgesia (11 studies), maternal satisfaction (four studies) and clinician rescue bolus doses (six studies). Bupivacaine was associated with an increased incidence of motor block in five of 10 studies.
Bolus dose volume and lockout interval:
Six RCTs (n=588 patients). Studies evaluated bupivacaine (0.0625% to 0.125%) and ropivacaine (0.1% to 0.2%) with fentanyl or surfentanil. Bolus volumes ranged from 2mL to 20mL. Lock intervals ranged from five to 30 minutes. A background infusion was used in addition to PCEA in three studies. All six studies used double-blinding.
One study reported that increasing bolus volume and lockout interval improved maternal analgesia. One study reported that a shorter lockout interval was associated with improved PCEA success to demand ratio. There was no difference between treatment groups in unscheduled clinician interventions (six studies) and significant motor block (six studies). Larger bolus volumes were not associated with increased side effects of toxicity.
Drug concentration:
Six RCTs (n=789 patients). Studies evaluated bupivacaine (0.0625% to 0.25%) and ropivacaine (0.1% to 0.2%) with fentanyl or surfentanil. Four studies used double-blinding and one used single blinding; the other study did not mention blinding.
There was no difference between treatment groups in maternal analgesia (six studies).
High-concentration local anaesthetics were associated with: increased local anaesthetic use in four studies (local anaesthetic dose reduction with the more dilute solutions ranged from 35% to 75%), significantly greater motor block in three studies and higher PCEA success to demand ratios in two studies. Two studies found less pruritus with local anaesthetics without opioids.