Epidurals may not provide good pain relief during the actual delivery

 It is not uncommon to hear women lament that their epidural provided effective pain relief for much of their labour but wore off towards the end. This has until recent times been a reality for many women who have an epidural.

 On some occasions, this represents a real shortcoming of the epidural. This is unusual. On other occasions, this ‘failure’ represents a deliberate attempt by the midwife, anaesthetist or obstetrician to restore a degree of sensation to the lower birth canal so that the mother is better able to coordinate her pushing with the bearing down reflex. Inherent to this is the assumption that if the pain relieving effects of the epidural have worn off, then so too must any ‘motor’ effects which may be causing weakness of the pelvic floor muscles. That is, letting the epidural wear off is a sincere attempt to avoid the need for a forceps delivery.

 The mechanisms which underlie these apparent shortcomings of epidural analgesia are well understood.

 Epidurals may have difficulty in providing pain relief for the second stage of labour because the nerves which transmit pain during this stage are situated far away from the epidural catheter. The catheter is positioned in the epidural space near the nerves of first stage. The nerves of first stage cross the epidural space in the mid-back and join the spinal cord soon after entering the spinal sac. The procedure is more easily performed and safer when done this way. The pain of second stage is transmitted by the sacral nerves. These cross the epidural space in the sacral region, just above the coccyx. Thereafter, they travel for some distance within the sacral sac before they join the spinal cord not far from the nerves of first stage. As a result, the local anaesthetic solution delivered via the catheter is delivered in close proximity to the nerves of first stage but has to travel some distance to reach the sacral nerves.

 One can argue that it is more important to be able to deliver good pain relief during first stage as it is typically longer than second stage (11 hours versus 1.5 hours in a first pregnancy) and women usually request epidurals during this stage. It should be noted however, that epidurals usually function well enough to provide excellent pain relief during both stages of labour. Inadequate pain relief during second stage has been reported when very dilute solutions of local anaesthetic are used in the epidural as a means of preserving pelvic floor muscle strength. When this occurs, the addition of an epidural opioid may be all that is needed to improve pain relief. If this fails, using more highly concentrated local anaesthetic will in most cases achieve good conditions.

 Currently the weight of evidence suggests that the use of high concentration local anaesthetic during second stage will increase the likelihood of an instrumental delivery. At this point, it will be helpful to consider the circumstances in which added pain relief is desired. One woman may feel that she is able to deal with the pain and in anticipation of delivery in the near future, forego further pain relief. In contrast another woman may feel that the pain is so severe that she is unable to push effectively. In this circumstance a small ‘top-up’ may actually decrease the need for an instrumental delivery by providing just enough pain relief to allow more participation from the mother. In another scenario, the need for an assisted instrumental delivery may have already arisen as a result of factors unrelated to the epidural. This is usually the case. In this event, good pain relief or even dense anaesthesia may be required in the lower birth canal and perineum (vaginal opening). Often, higher concentration local anaesthetic will be needed to achieve these conditions.

 A much more common cause for ‘failure’ of an epidural during second stage is deliberate cessation of the epidural before delivery. As mentioned, this is generally done in good faith in the assumption that it will maximise muscle strength and hence decrease the likelihood of a need for an instrumental delivery. The practice dates from earlier times when the use of high concentration local anaesthetics was widespread. The trend toward a reduced forceps rate with the use of progressively more dilute solutions and combination epidural local anaesthetic-opioid solutions, suggests that the benefits to be gained from this practice should be falling. This has been supported by some studies. There is also evidence that demonstrates that women can have good analgesia and still be able to push effectively. Unfortunately, the effect of epidurals on the normal progress of labour is not clear-cut.

 The expectant mother trying to form her own opinion will need to know in advance how painful labour will be, if and when she will request epidural analgesia, how much ‘block’ will be present when she reaches the second stage and for how long her second stage will persist. These factors cannot be predicted in advance. Nonetheless, an awareness of this issue which surround second stage pain relief will enable the mother-to-be her to participate more fully in decisions which may need to be made during this stage of labour.