What are the problems with epidurals?

The scope of the problem

It is probably reasonable to assume that at the basis of every woman’s consideration of epidural analgesia are two questions:

How is it likely to benefit me?

What risk does it present for myself and my child?

A ‘risk-benefit analysis’ of this kind is performed by an anaesthetist for every woman in labour who requests epidural analgesia. There are few procedures in medicine which do not have a large list of potential problems associated with them. Upon investigation, some of these will occur commonly and some will be extremely rare. If there was no benefit to be gained however, then there would be no justification in performing the procedure at all. If the benefit outweighs the risk, the procedure is more readily justified. Undergoing general anaesthesia in order to have an operation is a good example of this. On different occasions the balance will fall in one or the other direction.

It is imperative that safety standards are maintained to a level that ensures that serious complications associated with medical care are kept to a minimum. Australia has the best safety record for anaesthesia in the world. The death rate associated with anaesthesia overall is 1/20,000. Epidural analgesia carries the potential for many complications. Some of these are relatively common but not serious. Others are extremely rare and serious. Permanent paralysis, cardiac arrest and death are serious complications. These occur in a range between 1/20,000 to 1/1,000,000 in patients in labour. Epidural analgesia has been performed over a period of four decades. In hospitals with large obstetric units it is common for 50% of women to receive epidural analgesia for labour analgesia and 90% for caesarean section. It has a very good safety record. This is largely due to the high standard of training of anaesthetists who perform them. Anaesthetists are specialist doctors.

As a result of this, it is reasonable for a labouring woman, who is otherwise healthy, to consider pain relief for severe pain as a benefit of epidurals which might outweigh the risks. If pain can be adequately managed using simpler techniques, then the benefits associated with epidural analgesia may not outweigh the risks. Developing a birth plan in which these issues have been considered, but which is flexible, is a good approach to pain relief in labour. Many women employ a ‘wait and see’ approach and it works well.

The problems with epidurals can be divided into technical difficulty with inserting the epidural and with getting it to work well, problems due to the dose of local anaesthetic used and other complications.

TECHNICAL PROBLEMS

Headache - Post-Dural Puncture Headache

The epidural space is relatively empty and hence the distance across it is very small. If the epidural needle is pushed a little too far it may pierce the membrane (the dura) which forms the spinal sac. Recall that at the level at which epidurals are performed, the spinal sac contains spinal nerves travelling towards the pelvis and legs via the sacrum and cerebro-spinal fluid CSF. If there is a hole in the dura the fluid can leak out into the epidural space. This fluid leak can cause a ‘low pressure’ headache. Although CSF is formed continually (there is about 150mls of CSF, but 600mls is formed each day, so it is continually being absorbed), with a hole in the dura, the loss will be greater than usual and the pressure around the brain and spinal cord will be lower than usual. It is this low pressure which causes the headache associated with a dural puncture. This also explains the fact that the headache is better when you are lying down (there is less ‘drag’ pulling the brain down and stimulating pain sensitive structures).

The headache is typically felt in the front or back of the head and neck and gets worse upon sitting or standing up. It usually develops within 18 hours of the epidural and lasts for 4-5 days. Uncommonly, it lasts longer. Resolution indicates that the body has created a seal over the puncture and the CSF is no longer leaking. The severity varies. A dural puncture headache may be mild and go away by itself. Not uncommonly, it is severe enough to significantly impair the mother’s ability to nurse and care for the baby.

In itself, an accidental dural puncture is not a serious complication. It is in fact performed deliberately in a spinal anaesthetics or a combined-spinal-epidural technique. The calibre of spinal needles are significantly less than epidural needles which results in a smaller puncture and possibly an overall reduced severity of headache.

Dural puncture headaches can be treated. Things which can help improve the headache include bed rest, drinking plenty of fluid, caffeine and simple analgesics, such as paracetamol. If these fail then the most effective treatment is a ‘blood patch’. This is a simple procedure which involves another epidural, with some of your own blood injected through the needle to ‘patch up’ the hole. This completely and permanently resolves the headache in over 80% of women within a few hours. In the remainder the headache is either not relieved, or returns some time later. In these cases a second blood patch will resolve 95% of headaches.

Back pain

Back pain is very common after pregnancy and labour. You may have some local tenderness where the needle was put in which may last up to a week. 10% of women will develop lower back pain either during their pregnancy or around the time of the delivery. The likelihood of having continuing back pain after delivery are the same whether or not epidural analgesia was employed during labour.

Injury to nerves

About 1 in 3000 women having a baby will have some temporary damage to peripheral nerves. That is individual nerves outside of the spinal cord. This usually occurs during delivery, as a result of traction or direct pressure from the fetal head. Direct injury from instruments like forceps and epidurals is possible, however, the incidence is the same, whether or not an epidural has been employed.

Signs suggesting nerve injury include an area of numbness, weakness, or pain. It is usually experienced in the legs however, control of bladder and anal sphincters is another manifestation. Over 99% of these will recover spontaneously. One large study revealed that out of 50 cases reported, all had either completely or significantly resolved by 12 weeks.

Permanent injury to the spinal cord

Permanent paralysis resulting from epidural analgesia during labour is so rare that clear figures on its incidence are not available. A recent review of 500,000 cases performed in the United Kingdom did not reveal a single case. To the author’s knowledge one case has been reported in Australia. In this case, the patient had a rare malformation of blood vessels around the spinal cord. This was unknown to the patient and resulted in a blood clot which caused compression injury to the spinal cord.

Anaesthetists consider this to be an extremely serious, potential but very rare complication of epidural analgesia. Experience from the general surgical population reveals that this risk is increased in patients on blood thinning medications or who suffer from disorders of blood clotting. This may occur in association with severe hypertension during pregnancy. Anaesthetists employ conservative guidelines when advising labouring women about this risk. Blood tests can be performed which provide information on the state of the mother’s coagulation.

Permanent injury to the spinal cord could also occur as a result of infection. For this reason a sterile technique similar to surgical operations is enforced.

PROBLEMS RELATED TO DOSE OF LOCAL ANAESTHETIC

The local anaesthetic which is injected into the epidural space has the potential to blocks all the nerves it contacts, not only the ‘pain nerves’. This includes nerves that supply touch, muscle power and the ‘tone’ of blood vessels. The latter are involved in the control of blood pressure.

Hypotension ( Low blood pressure)  

A fall in blood pressure (hypotension) invariably occurs after receiving an epidural. There are two main reasons for this. First, the blood pressure is almost always raised before the epidural is inserted - for the simple reason that the patient is usually in pain. Once the pain is relieved, the blood pressure starts to fall (to 'normal') again. The second reason for a fall in blood pressure is that the epidural relaxes the muscles in the walls of blood vessels. This means that vessels which were previously constricted (secondary to pain) now become dilated. Consequently, the blood has to circulate through more blood vessels.

These circulatory effects are of little importance - provided, that is, you are not lying on your back. In this event ‘supine hypotension’ may occur. Understanding that hypotension is an expected effect of epidural analgesia, anaesthetists insert a cannula and commence intravenous therapy prior to the establishment of analgesia. Following this, they ensure that you are positioned on your side. As a result of this preventative management, it is unusual to experience low blood pressure when the epidural is used for labour analgesia. Nonetheless, the blood pressure is closely monitored and additional fluid or medication is readily available to keep it normal.

One of the earliest signs that an epidural is starting to take effect is that the feet begin to feel warm and dry. This is secondary to an increase in blood flow to the skin and blocking of the nerves which supply sweat glands. (Another early sign of success I have noticed is that feet lose their ticklishness! So, if you suffer from sweaty, cold and ticklish feet - an epidural provides an instant cure ). Hypotension sometimes causes people to feel faint or nauseated but these symptoms usually go away if you lie on your side and have a little extra fluid via the intravenous infusion. Some people have made a great deal of fuss about hypotension. But it is rarely of any importance and, in any case, is very easily remedied. It is blood flow, rather than blood pressure, which is important: a low pressure does not necessarily mean that flow is impaired. As we have seen with other epidural side effects, hypotension is also probably dose-dependent. It seems to occur more often following the stronger doses - needed for example during caesarean section.

If hypotension does not respond to change in posture and intravenous fluids, and is a cause of concern, then it is very easily treated by adding to the infusion a drug which causes the blood vessels to constrict (i.e. a vasopressor). The drug which is usually used (ephedrine) acts within a couple of minutes and is perfectly safe. (Having said this, I have had cause to give ephedrine in the labour ward on only two occasions during the last eighteen years: and even then there was no real urgency.)

Shivering

When local anaesthetics are used by themselves, shivering occurs very commonly following an epidural. In a study carried out some years ago we found that 50 per cent of women developed uncontrollable shivering soon after its insertion. Most of the women were not particularly concerned about this although 13 per cent described it as 'very irritating'. Strangely enough those who shivered did not usually feel cold. The cause for such shivering is obscure. Our study did demonstrate, however, that it could be very effectively controlled by giving a small dose of epidural pethidine. It is possible that other opioid drugs may be equally effective - although this has not been confirmed. Nowadays, shivering is witnessed only rarely in our own labour ward. The introduction of our epidural cocktail has practically abolished it.

Bladder distension

Muscle weakness associated with epidurals has the potential to cause the bladder to become overfull. This may lead to problems in the future with passing urine. This is compounded by loss of sensation of the discomfort caused by bladder distension.

The problem is reduced by the use of dilute solutions of local anaesthetic which preserve bladder sensation. In addition, bladder function is part of the normal care provided by midwives during labour. It may require a temporary catheter to ensure that the bladder drains.

There is limited clear data which describes the scope of the problem. Some loss of bladder function following a pregnancy is perceived to be a common occurrence. However, like temporary nerve injury and back pain it results from the normal processes of birth and there is no evidence that epidural analgesia increases it. Nonetheless, it has the potential to do so, and until clear data is available it is appropriate to incorporate guidelines on bladder care into the management of women who have epidural analgesia.

Leg numbness and weakness

Local anaesthetics have the potential to cause numbness and weakness in the legs. In this event, your legs will feel heavy, you will have decreased control over them, and you will not be able to get out of bed by yourself. The extent to which this happens depends largely on the strength of local anaesthetic given, as well as the amount given. The anaesthetist will vary the dose depending on the situation. For example, if you are going to have a caesarean section, the block needs to be very strong, so you will be given a dose of local anaesthetic which may mean you can’t feel or move your legs at all. If you are in early labour, however, we can give you a much weaker dose which means the contractions won’t hurt any more, but you may still be able to feel the tightening. Your legs will be much less affected too. In this event, you may be able to walk. Some centres allow women to walk with epidural analgesia in progress.

Lying flat on your back for any length of time during the last few weeks of pregnancy is harmful because it interferes with your circulation. This is caused by the weight of the baby compressing two large blood vessels (the aorta and vena cave) which lie in front of the spine and carry blood to and from the lower half of the body.

Compression of these vessels can severely restrict blood flow to the legs and to some of the internal abdominal organs - including the uterus. If this is prolonged for more than a few minutes it may interfere with the oxygen supply to your baby and lead to signs of stress (eg., slowing of the heart rate). Compression of the vena cave also interferes with the return of blood to the heart. Consequently the blood pressure falls and causes symptoms such as feeling faint, light-headed and nauseated. (Compression of these vessels in this way, incidentally, is peculiar to humans: no other mammal rests or sleeps lying on its back.)

For these reasons, you should avoid lying flat on your back during the last few weeks of pregnancy. It is much better to rest and sleep lying on your side. If you enjoy lying on your back hen place a pillow under one buttock so that you are well tilted to the side. This should be sufficient to take the weight of the baby off these important blood vessels. Many women in labour also find that their contractions are more painful when they lie on their backs. If you are asked to assume a reclining position on your back for the purpose of an internal examination the pain can sometimes feel overwhelming. Things are improved again by moving to a more upright position as soon as the internal is over. (So get someone to help you move once the examination is completed.)