Intravenous Patient Controlled Analgesia for Labour and Delivery

In some circumstances, it is unwise to use an epidural to provide analgesia for labour. Your anaesthetist is the person who will make this assessment. Severe pre-eclampsia (high blood pressure during pregnancy) and bleeding disorders are examples of conditions in which the risks associated with the epidural may outweigh the benefits of the pain relief provided. Other methods of pain relief are available. One such method is intravenous patient controlled analgesia, or IV PCA.

PCA is a technique that allows the mother to administer her own pain relief. A solution of analgesic drug is loaded into a syringe or a bag and attached to a special delivery pump which is then connected with tubing to the intravenous drip. The delivery of the drug from the pump is controlled by the woman with a push button. As soon as she begins to feel another contraction coming on, she presses the button and a small amount of pain relieving medication is delivered into the drip. The button can be pressed as often as she wishes, but the pump will release the dose of drug only after a certain time has elapsed. This is called the lockout time and is usually five minutes. The lockout time ensures that the drug has had enough time to work before the next dose is given, because there is usually a lag of 3-5 minutes between delivery of drug into the drip and onset of effect. The lockout time protects the mother from giving herself too much drug. If she still feels discomfort from her contraction after the lockout period has elapsed, she may give herself another dose of medication from the pump by pressing the button. It is important that only the mother presses the button, as only she knows how much her contractions hurt and how much pain relief she needs. This also ensures that she does not get too much medication.

A typical modern PCA pump is shown in the photograph. The patient button can be seen in the bottom of the photograph.

A loading dose, usually given by the anaesthetist, is required in order for the woman to achieve a background level of analgesia before she commences self-administration. She is then instructed to press the button when she needs to. The amount of drug that is delivered with each demand, and the lockout time, can be adjusted to meet her needs as labour progresses. Labour is a dynamic situation and requirements for pain relief change frequently over time. PCA allows flexibility and individualisation of therapy. The changing blood levels of the opioid drug are shown graphically in the figure. The 'grayed' area of the trace representing the zone of satisfactory pain relief.

Despite the fact that opioids are the analgesic drugs most commonly given to ease labour pain, they have limited effectiveness when given via the intramuscular route and many women report that they were inadequate. PCA offers more effective pain relief than intramuscular injections. Pain relief is faster and more constant, and the dose can be easily adjusted to suit the mother’s changing requirements.

Although a variety of analgesic agents can be given via a patient controlled device, fentanyl is the one most commonly used for the woman in labour. Fentanyl is a synthetic opioid agent that has a very rapid onset of action, within 5 minutes of administration, and lasts for about 45 minutes. Its relatively short duration minimises the amount of drug accumulation in both mother and fetus.

It is important to remember that it is not possible to obtain complete analgesia with opioids. This also applies to PCA opioids. Increasing the dose is associated with a greater incidence of side effects in mother and foetus, for example, nausea and vomiting, delayed gastric emptying, respiratory depression, and disorientation. The extent of neonatal effects, primarily respiratory depression, depends on the total dose of opioid and the interval between dose and delivery of the neonate.

Nevertheless, IV PCA fentanyl, when correctly administered, can adequately blunt the pain of contractions, thus affording the mother some comfort during labour. The woman should be carefully instructed in the use of PCA. It should be explained to her that complete analgesia is not a realistic goal using a PCA technique, but it can still be used very effectively to provide her with pain relief.

Like all analgesic techniques, PCA requires high standards of safe nursing care. If you receive PCA you should expect that you will receive oxygen therapy via an oxygen mask and that the effectiveness of your breathing will be measured. The effectiveness of the pain relief, as well as side effects, will be evaluated by the anaesthetist and by the nursing staff. Opioids given with PCA can cross the placenta and cause respiratory depression in the infant. This is unusual. Moreover, respiratory depression is immediately reversible with an ‘antagonist’ drug called naloxone.