Pain Relief In Labour – What’s Your Drug?

All drugs cross the placenta and will have an effect on the baby which will vary according to how much drug is used and how long it is in the mother’s system before the baby is born.

Before birth, the mother will metabolise and eliminate the drug from her own body as well as her baby’s. After birth, the baby must undertake these processes itself and this can take some time (days) due to its immature liver and kidneys.

It is impossible to predict how drugs will affect either the mother or her unborn baby. Everyone has their own tolerances to drugs, with some people finding that they are very sensitive while others are not. If you have not been exposed to the drugs given in labour before you will not know how they may affect you. It is impossible to know how your unborn baby will react to exposure to these drugs during labour.

There are alternative ways to ease the pain in labour without using drugs, and these should be explored fully before drugs are accepted.

Narcotic (Opiate) Drugs
Pethidine (demerol), Morphine, Heroin (diamorphine)
This group of drugs have similar properties and effects. They are usually given as a sedatives in labour. They are not pain killing drugs, but may ease the pain indirectly as the mother becomes sedated.

Pethidine (demerol) is the most widely used, so it will be used as an example. Less is known about the effects of the other opiates on women and newborns because less research has been conducted to test their efficacy and safety.

Dosage:
The drug is supplied in prepared doses and 100mg is the commonest size, although smaller doses may be available. It should be given according to body weight. Pethidine is usually prescribed by a doctor but given by the midwife, and if a smaller dose is requested by the mother, the midwife will have to consult the doctor before the dose can be varied. 75 mg would be required for an average man when being used for post-operative pain.

It may be possible to request a smaller dose to begin, on the basis that if this is not enough, more can be administered later. Once in the system it is impossible to remove the drug except by waiting for the woman’s body to eliminate the drug through her liver and kidneys (about 6 hours in a pregnant woman).

Time lag:
10-20 minutes

Duration:
2-3 hours

Route administered:
Usually by injection into the thigh or buttock. Sometimes via a drip, if one is in place.

When given:
During first stage, once labour is established. Should not be given if the birth is expected within 2 hours. Sometimes given for pain relief following Caesarean section.

Effects on the mother:
Advantages: 1. Sedates.
2. Has a secondary effect as a muscle relaxant, which ay lessen pain and reduce muscle tension, allowing faster dilatation.
3. May reduce pain.

Disadvantages: 1. Does not relieve the pain directly.
2. Creates a high’, with feelings of floating and light-headedness that makes concentration difficult.
3. Some people are so sedated that drowsiness makes it difficult to cope with contractions.
4. Nausea, vomiting and dizziness are all common side-effects. An additional drug to counteract these effects is usually mixed with the pethidine before injection.
5. Depresses the mother’s breathing rate, which can reduce oxygenation of the blood.
6. If the sedation results in a more rapid rate of dilatation than was expected, the baby may be born with more of the drug in its system than was intended.
7. Opiate drugs cause delayed emptying of the stomach, increasing the risks of aspiration syndrome, a serious complication, if a general anaesthetic becomes necessary.

Effects on the baby
Advantages: None.

Disadvantages: 1. Pethidine crosses the placental barrier and depresses the baby’s respiratory centre. This will cause breathing difficulties for the baby if it is born when the drug is at a maximum dosage in its system (between 1 and 3 hours after the injection).
2. An antidote to counteract the depressive effects on the baby can be given but this gives only temporary relief and the baby may still suffer breathing difficulties when the antidote wears off after a few hours.
3. Increased likelihood of jaundice as the baby’s immature system works to eliminate the drug (and its antidote, if given). It may take 4-5 days for the baby to eliminate most of this drug from its system.
4. Separation of mother and baby if these problems are severe.
5. Difficulties establishing breastfeeding due to a depressed suckling reflex.
6. Research has demonstrated a potential link between exposure of some babies to pethidine during labour and their later development of an addiction to opiate drugs as teenagers.

Other drugs sometimes mixed with pethidine

These drugs are sometimes given in the same injection with pethidine or may be given separately:

Sparine: to help enhance the action of pethidine and further reduce muscle tension.
Stematil: to help counter the side effects of nausea and dizziness caused by pethidine.
Maxilon: to reduce nausea and vomiting.

Nitrous oxide and oxygen (Entonox)
A combination of two gases, nitrous oxide and oxygen in provide pain relief. Many hospitals use a dispenser that allows the proportion of the gases to be varied within a given range.

Dosage:
The dosage is variable with the range from 30% nitrous oxide 70% oxygen to 70% nitrous oxide 30% oxygen. Entonox is a fixed proportion of 50% nitrous oxide and 50% oxygen.

Time lag:
15 seconds

Duration:
Only effective whilst being breathed, plus about 15 seconds longer.

Route administered:
Via a face mask, which the mother holds tightly over her mouth and nose. Deep breathing is required to activate the dispensing machine, which can then be heard making a gurgling noise. It is important to start using the mask as soon as a contraction is felt to obtain the maximum effect. The mask should be taken off the face between contractions.

A mouthpiece may be available as an alternative to the face mask.

When given:
Usually during the transition phase of labour.

Effects on the mother
Advantages: 1. An effective means of easing the pain, especially for the long and strong contractions of transition.
2. Extra oxygen can be beneficial.
3. Provides a distraction and a focus for attention during the turbulence of transition.

Disadvantages: 1. Nausea and vomiting can be side effects.
2. May make the mother drowsy and confused.
3. Some women find the face mask unpleasant, even claustrophobic.
4. Does not relieve the pain entirely.

Effects on the baby
Advantages: 1. Extra oxygen could be beneficial.

Disadvantages: 1. Research has shown a potential link between exposure of some babies to nitrous oxide during birth and their later development of an addiction to amphetamines as teenagers.

Anaesthetic injections

Drugs and anaesthetics

Before accepting any drugs their possible effects should be considered carefully.

Questions to ask

What to ask if you are offered drugs for easing pain in labour

Drugs and their effects

How drugs can effect you and your baby.

Addiction

The link between drugs for pain in labour and later drug addiction in the child.

Anaesthetic drugs can be given by injection to relieve pain during labour.

An anaesthetist is required to administer an epidural or spinal anaesthetic. Obstetricians and GPs can give pudendal blocks and doctors or midwives may give local anaesthetics.

Epidural anaesthetic
An injection of local anaesthetic into the epidural space around the spinal cord which numbs the body below the injection site and thus relieves the pain from contractions.

It is the preferred anaesthetic for a woman having a Caesarean section, in which case the anaesthetic is injected into the spine a little higher up to give more widespread numbness.

Route administered:
A procedure similar to an epidural except that the injection of the anaesthetic is made into the sac of cerebrospinal fluid that surrounds the end of the spinal cord.

Dosage:
If full strength anaesthetic is used then the numbness will be complete and the mother will be unable to move her limbs, as the nerves supplying the muscles to the legs will be completely anaesthetised.

Low dose epidurals use a half or quarter strength dose, and this will numb sensation and remove the pain of the contractions whilst not affecting the nerve supply to muscles. The mother will be able to move her legs and sit up, whilst not feeling any sensation.

Sometimes, the low dose of local anaesthetic is mixed with Pethidine or Fentanyl (a similar opiate) allowing less of each drug to be used, while still giving good pain relief. Greater mobility and fewer side effects are also reported.

Time lag:
Between 5 and 15 minutes from injection.

Duration:
About 3 hours for a full strength anaesthetic, proportionally less for low dose epidurals.

When given:

For pain relief, at any time in first stage, but usually once labour is fully established.
Prior to a Caesarean section.
To reduce high blood pressure during labour.
Effects on the mother
Advantages: 1. A usually reliable method of pain relief, with complete loss of sensation from the waist down.
2. Can help to control high blood pressure.
3. Facilitates a forceps delivery if complications are present.
4. Allows the mother to be conscious during a Caesarean section.
5. Relief from pain may allow greater relaxation and more rapid dilation.
6. Relieving the pain may increase the mother’s positive feelings about labour and birth.

Disadvantages: 1. The mother will be confined to bed, with resultant loss of mobility. If the dosage is half or quarter strength, she may be able to sit up, even move around, if well supported.
2. In 10-15% of cases, the anaesthetic may not take completely leaving some areas not fully anaesthetised.
3. Administration of an epidural slows the labour down so that oxytocic drugs may be needed to keep contractions going.
4. The mother’s blood pressure can fall dramatically following an epidural and this is sometimes used as a reason for using an epidural. A drip will always be inserted prior to epidural administration in case treatment for low blood pressure becomes necessary.
5. There is an increased likelihood that the mother’s temperature will rise the longer an epidural is in place. If this happens the baby’s temperature will also rise, increasing the risk of fetal distress.
6. It may be difficult to empty the bladder and a catheter is frequently necessary.
7. In inexperienced hands, the covering of the spinal cord may be punctured. This will result in a leaking of spinal fluid and the mother will have a severe headache (perhaps for several days) until the puncture wound heals and the leaking stops. It may be possible to repair the leak by injecting a small amount of the woman’s own blood into the epidural space. As this clots, it forms a patch over the hole, sealing it from further leaks. If successful, the headache will disappear almost immediately.
8. The muscles of the pelvic floor are relaxed by the anaesthetic and as a result the baby’s head is less likely to rotate, and a forceps delivery may be necessary.
9. With a full strength epidural, the mother will feel no urge to push unless it is allowed to wear off before second stage commences. Forceps may be needed to lift the baby out.
10. The mother will have a reduced sensation of giving birth to her baby.
11. Tenderness over the area where the needle was inserted is common in the days following birth.
12. There is an absence of tone in the muscles that support the lower vertebrae and sacroiliac joints especially with a full epidural in place. This causes lack of stability in the joints, and moving the mother may cause them to become misaligned, leading to chronic backache that may last weeks or months following the birth.
13. If the baby is affected by the drugs, the mother may perceive her baby as difficult and hard to settle, making breastfeeding and nurturing more difficult. This perception can persist for some months.
14. Paraplegia is a very, very rare but unpredictable complication.

Effects on the baby
Advantages: 1. The mother will be able to make immediate contact following a Caesarean section, and may be able to breastfeed.
2. Reduced risk of fetal distress if the mother’s high blood pressure can be reduced.
3. The mother may feel more positive about labour, birth and the baby if she is free of pain.

Disadvantages: 1. The baby will be affected by the drugs used, depending on the length of their exposure before birth. Common reactions include irritability, an inability to settle easily and a tendency to startle easily. These effects may last several weeks.
2. If any obstetric complications occur as a result of the epidural, these will have additional side effects on the baby.
3. Should further intervention become necessary, such as an oxytocin drip, forceps, vacuum extraction, episiotomy or Caesarean section, the baby will be affected by these procedures. See separate entries for summaries.
4. Any obstetric intervention or complication increases the likelihood of separation of mother and baby in the early post-natal period.

Spinal analgesia
A quick acting anaesthetic useful for emergency use for Caesarean section.

Route administered:
A procedure similar to an epidural, except that the injection of anaesthetic is into the spinal cord itself.

Dosage:
Only one tenth of the amount of anaesthetic (bupivacaine) is necessary compared to an epidural. Sometimes is it mixed with either pethidine or fentanyl. Is given as one-shot procedure (not topped up regularly).

Time lag:
Anaesthesia is usually achieved within 5 minutes.

Duration:
Lasts between 75 and 120 minutes.

When given:

For Caesarean section, especially in an emergency situation if an epidural is not already in place. Foe elective Caesarean sections. When the placenta needs to be removed manually.
Effects on the mother
Advantages 1. A quick acting anaesthetic in an emergency situation.
2. A very reliable form of anaesthetic, with very low failure rate in experienced hands.
3. Uses less anaesthetic, so reduces the risk of side effects.
4. Reduced risk of headache, as a very fine needle is used.

Disadvantages 1. Requires an experienced anaesthetist as it is a more technically difficult procedure.
2. Risk of a severe headache if several attempts are needed for successful placement.
3. Unable to be topped up if the anaesthesia proves inadequate. Other pain-killing drugs may have to be given in addition, or a general anaesthetic.
4. Too much anaesthetic may cause a profound drop in blood pressure which will require prompt treatment.
5. Nausea and vomiting may occur.

Effects on the baby
Advantages 1. May enable the baby to be born faster in an emergency.
2. Less exposure to drugs than for epidural anaesthetics.

Disadvantages 1. The baby may be affected by the drugs used.
2. A sudden drop in blood pressure may lead to fetal distress.
3. If any complication occurs as a result of the procedure (such as the need for a general anaesthetic), this may have effects on the baby.

Pudendal block
This is an injection of local anaesthetic into the perineal area to numb the outlet.

Route administered
The anaesthetic is injected through the walls of the vagina into the nerves on both sides of the vagina. This deadens the whole of the pelvic outlet.

Time lag:
The anaesthetic will take effect immediately.

Duration:
The area will stay numb long enough to enable any necessary stitching to be done after the birth.

When given:
At the beginning of second stage.

Effects on the mother
Advantages: 1. Numbs the perineum
2. Allows an early episiotomy
3. Allows a pain-free birth

Disadvantages: 1. Reduces the urge to push, which may delay second stage or require the use of forceps.
2. The mother cannot feel the baby being born
3. If an early episiotomy is done, then extensive bruising of tissues and blood loss will occur

Effects on the baby
Advantages: 1. The baby may be born faster if episiotomy is done

Disadvantages: 1. The baby may be affected by exposure to the anaesthetic