Page 141 Guide to Pain Management in Low-Resource Settings

Pharmacological Management of Pain in Obstetrics 129

Table 4
Characteristics of commonly used opioids in labor
Morphine Fentanyl Sufentanil Pethidine Diamorphine
Lipid solubility 816 1727 39 1.4 280
Normal epidural 50–100 μg 5–10 μg 25–50 mg 3–5 mg 2.5–5 mg
doses
Onset time (min) 5–10 5–10 5–10 30–60 9–15
Duration (h) 1–2 1–3 2–4 4–12 6–12

Epidural requirements diff er in pregnancy, and in- Midwives can be trained to give low-dose inter-
jection of a dose of local anesthetic results in a 35% mittent top-ups as the mother requires. Th e resulting
increase in segmental spread compared to the non- analgesia is excellent, and there is no need for expen-
pregnant state. Bupivacaine is the most popular local sive devices. Th e main benefi t of the intermittent tech-
anesthetic in use. Care has to be taken to avoid high nique—compared to continuous infusion—is the reduc-
blood levels by overdosing or accidental i.v. or intra- tion in the use of bupivacaine and fentanyl throughout
arterial injection (high blood concentrations may pro- labor, along with reduced side eff ects, especially motor
duce arrhythmias of the reentry type). Whether other block.
local anesthetics (e.g., levobupivacaine or ropivacaine) Patient-controlled analgesia is a choice for the
have less toxicity or less motor-fi ber-blocking poten- technically sophisticated obstetrics department. Th e pa-
tial, or both, is under discussion. tient can receive self-administered boluses by pressing a
Th e most commonly used epidural opioids are button. An electronic pump is required, and the patient
fentanyl and sufentanil. Th ey are sometimes eff ective in must be thoroughly educated about using the device.
early labor, but they usually need supplementation with For a background infusion, usually a dose of 10 mL/h
a local anesthetic as labor progresses. Th e main advan- is used, with a preset lockout interval of about 15–30
tage of epidural opioids is that they improve the qual- minutes. Mothers have welcomed the reduction in mo-
ity of analgesia and reduce the dose of local anesthetic tor block with this method and some of them decide to
needed. Th is reduction is considered an advantage, get up to use the toilet and to sit in a comfortable chair
since local anesthetics can produce unwanted motor by the bedside. Although not necessary in most cases,
block. Th erefore, most obstetric anesthesiologists com- someone should be at the patient’s side to support her
bine a diluted mixture of a local anesthetic with a small whenever she wants to get in case orthostatic hypoten-
opioid dose to achieve what is called a “walking epidu- sion develops. Mobilization is safe if the mother can
ral.” perform a bilateral straight leg raise while sitting in bed
Th e most commonly used combination is a low- and a deep knee bend while standing, provided she feels
dose mixture of fentanyl (2–2.5 μg/mL) and bupivacaine steady on her feet. Unfortunately, there is no evidence
(0.0625–0.1%). Continuous infusions or intermittent that active mobilization reduces the risk of assisted de-
boluses or both of these agents can be given throughout livery. Cardiotocography (CTG) (monitoring of fetal
labor, but the initial loading dose of 10–30 mL of the heartbeat and uterine contractions) can be performed
same mixture has to be given initially in divided doses. intermittently. If continuous monitoring is indicated for
Epidural solutions for labor may be continuous- obstetric reasons, the mother can be seated in a chair or
ly given for 12 hours or more. Drugs can be adminis- standing by the bedside.
tered via a catheter, and the analgesia can be maintained Complications of labor analgesia include hy-
by varying the infusion rate to provide an upper sensory potension (with much lower incidence nowadays with
level to T10. Low-dose local anesthetic/opioid mixtures low concentration of local anesthetic), accidental i.v.
are commonly started at 8–15 mL/h with the rate in- injection, unexpected high block (total spinal/subdural
creased or top-ups of 5–10 mL given for breakthrough blockade), urinary retention, pruritus, accidental dural
pain (minimum time between boluses: 45–60 min). Al- puncture (the more troublesome and common prob-
ternatively, a mixture of 0.0625% bupivacaine and sufen- lem), catheter migration, unilateral/partial blockade,
tanil 0.25 μg/mL can be used at the same dose. and shivering.