Maintaining Epidural Analgesia for Labour and Delivery

After the epidural has been established ongoing analgesia during labour can be maintained by administering local anaesthetic (opioid) solutions by intermittent bolus top-up doses, continuous infusion or patient controlled epidural analgesia PCEA. All have been designed in an attempt to deliver satisfactory, continuous analgesia and minimise side effects such as muscle weakness. Despite the relative advantages and disadvantages of the various regimens, it has been difficult to prove the superiority of one over the other. Hospitals usually offer one of these.

I. Intermittent Bolus Top-Up Doses of Local Anaesthetic

A midwife or anaesthetist may administer intermittent bolus top-up doses of a local anaesthetic or a local anaesthetic-opioid mixture. The duration of pain relief obtained from any single top-up dose is different for each woman. The epidural remains in place throughout, and therefore, does not require reinsertion each time. Top-up regimens are usually employed in hospitals which offer ‘walking epidurals’. They have a good ‘track record’ of safety.

II. Continuous Infusion Epidural Analgesia

A continuous local anaesthetic epidural infusion technique works on the same principles as an intravenous opioid infusion with regard to maintaining constant levels of analgesia within the range required for pain relief. The difference is that these levels refer to those in the epidural space instead of the blood. Intravenous local anaesthetic infusions can be used in some circumstances associated with chronic pain but the degree of pain relief produced by this is unlikely to be reliable for labour pain. In labour, a certain dose is required within the epidural space in order to maintain the level of nerve block which is required for pain relief throughout the various stages.

With epidural infusions reliable analgesia can be achieved which is continuous. Moreover, the intensity and extent of sensory block can be carefully titrated to the constantly changing levels of pain relief required during childbirth. The potential risk associated with a top-up bolus of local anaesthetic being injected inadvertently into a blood vessel or the spinal sac is perceived to be reduced. In addition, continuous infusions may confer some stability to the maternal cardiovascular system, with decreased risk of hypotension. In some studies, a continuous infusion technique has been associated with fewer supplemental bolus injections, as compared to an intermittent top-up bolus injection technique, but in others, has resulted in the administration of a greater total dose of local anaesthetic. A continuous infusion provides good perineal analgesia, but over time, it can accumulate and result in significant motor block. Needless to say, this regimen requires a continuous infusion pump device and usually means that the mother-to-be is required to remain in bed.