Advantages, Disadvantages and Complications of Labour Analgesia

Psycho prophylaxis, environmental modifications and physical treatments are always helpful and complementary but usually inadequate as the only methods of labour analgesia. These methods are not fully utilised due to financial constraints and shortage of staff. 

TENS electrodes placed on either side of the spine at the level of T 11-L 1 nerve roots provide adequate pain relief to twenty percent of labouring women in the first stage (Robson JE, 1979) 

It is claimed that about twenty-five percent of selected labouring women can be hypnotised to a depth at which the appreciation of pain is abolished or greatly reduced (Moya F, James LS, 1960). Usually this requires the presence of a skilled hypnotist with the selected, previously trained labouring woman. Even then, the result may be only a partial success or even a total failure. 

Acupuncture may provide adequate analgesia to a small group of labouring women in the first stage of labour. Of these, only a fraction will get satisfactory pain relief in the second stage. Unfortunately, one cannot predict which patient will respond to this form of analgesia (Waldron BA, 1985). 

The methods discussed so far have no adverse effects for the mother or the baby. Only hypnosis and acupuncture need specific skilled providers. 

Self-administered Entonox, if used properly, provides good analgesia in the first stage, and is a good supplement in the second stage (Arthurs GJ, Rosen M, 1969). Forty-five seconds of continuous slow and deep inhalation is necessary for maximal analgesia. This should start at the initial painless phase of uterine contraction and should continue until the end of the contraction. The relatively insoluble nitrous oxide builds up a partial pressure rapidly providing analgesia and the gas is rapidly exhaled and excreted. This is a very safe form of analgesia as long as the Entonox cylinder is properly maintained at room temperature. At minus seven degrees Celsius, the nitrous oxide liquefies and remains at the bottom of the cylinder leaving the oxygen at the top. A patient inhaling from such a cylinder will receive pure oxygen first and then pure nitrous oxide making her drowsy. Even then, the demand valve in the Entonox apparatus provides safety. The drowsy patient, unable to hold the mask tight, cannot create the negative pressure required to release the gas. 

Systemic opiate, Demerol (and occasionally Nubain) is the most common analgesic used in labour. It provides adequate analgesia for fifty to sixty percent of labouring women. It causes nausea and vomiting, drowsiness, delay in gastric emptying and respiratory depression and hypotension (at higher doses) in the mother. It crosses the placenta rapidly and the foetal and maternal blood levels are almost equal within two minutes of an intravenous injection into the mother. Demerol accumulates in the baby and it takes three days for a baby to metabolise and excrete it. It takes even longer for a premature baby. Narcotic antagonist, Naloxone should be available to reverse the respiratory depression of Demerol in the baby. Since Demerol has a long half-life in the baby, respiratory depression, failure to suck and other neuro behavioural problems may arise several hours later. Bearing these in mind, one should seriously entertain a regional block if more than two doses of Demerol are required (Waldron BA, 1985).

Of the regional blocks, Para cervical block gives relief from pain of cervical dilatation. It is rarely used now, as it is associated with foetal bradycardia, and potential death (Rosen M, 1977). This is probably due to spasm of uterine vessels (Fishburne JI, 1979). Pudendal block is useful for vacuum or low forceps delivery. These are blocks used by the obstetrician. Injection of large amounts of the local anaesthetic or accidental injection into the vessels may cause serious central nervous system toxicity (light-headedness, dizziness, tinnitus, slurred speech and convulsions) or cardiac toxicity (hypertension and tachycardia to hypotension and arrhythmia). Severe foetal bradycardia may be associated with such complications. However, resuscitation of the foetus is best done in-utero by resuscitation of the mother. 

The technique of caudal block analgesia involves injecting a local anaesthetic into the extra dural space through the sacral hiatus. Although it may be useful for an instrumental delivery, it is rarely used now for fear of accidentally puncturing the foetal head. Further more, there is considerable variation in the anatomy of the bony sacrum, the capacity of the sacral canal and the extent of the dural sac (Trotter M, 1947). 

Lumbar epidural analgesia provides complete pain relief for eighty-five percent and partial relief in a further twelve percent of labouring women. Only three percent have no relief at all (Crawford JS, 1979). A continuous infusion maybe started early in the first stage and can be continued for anaesthesia if a caesarean section is required. 

A well-trained anaesthesiologist with an interest in obstetric analgesia is needed to provide an epidural analgesia service. Ideally, a twenty-four hour obstetric analgesia service should be in operation. The labouring woman should have had an informed discussion about the procedure, benefits and risks of epidural analgesia in the prenatal period. The epidural catheter should be inserted early in labour when the patient is more co-operative and the epidural veins are not dilated. 

The patient should be preloaded with intravenous fluids before the epidural insertion. The anaesthetic technique of the epidural catheter insertion is well described in the textbooks on obstetric anaesthesia (Glosten B, 1994). The anaesthesiologist who inserts the epidural catheter is obliged to stay with the patient until it is established that the epidural analgesia was working satisfactorily. The anaesthesiologist must also leave contemporaneous notes on the procedure, regimen for the infusion and emergency measures for possible complications and contact person in case of emergency. Occasionally, serious complications may result from an epidural analgesia. Central nervous system toxicity and cardio-respiratory arrest (from intravenous injection), total spinal blockade and hypotension may occur. The patients with epidural analgesia should have one-to-one nursing care by specially trained nurses. Monitoring devices, infusion pumps and resuscitation equipment must be readily available. In the absence of the above safety features, it would be malpractice to provide epidural analgesia. One has to sacrifice patients' comfort for their safety. 

Late in the first stage of labour or in the early second stage, where the patient is very distressed and unable to sit still for any length of time and the extra dural space is made smaller by the dilated epidural plexus, insertion of epidural catheter is more difficult and requires more time. Often times, the patient has delivered by the time an epidural is established. Spinal analgesia using a fine spinal needle, is quick, effective and most appropriate under these circumstances (Crawford JS, 1984) 

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