Obstetrics Simplified - Diaa M. EI-Mowafi

Relief of Pain in Labour

Pain Transmission

• During first stage: pain arises from the uterus, cervix and upper vagina passes through the Frankenhäuser’s ganglion to the hypogastric and then the pre-aortic plexuses to enter the spinal cord at T10-12 and L1. The pain is due to increased intrauterine pressure with each contraction to 25 mmHg or more and due to cervical dilatation. The highest degree of pain felt during the transitional period between the first and second stage.
• During second stage: pain arises from the vagina and perineum is transmitted through the pudendal nerves to enter the spinal cord at S2- 4.

Methods

Non-pharmacological methods

These are safe for the mother and foetus but it needs long time to be effective and of varying degrees.

• Breathing and relaxation exercises: increases the oxygen supply to the contracting myometium so ischaemia is reduced and pain is minimised.
• Acupuncture.

Pharmacological methods

Tranquillisers:

• Diazepam: 5-10 mg IM / 4 hours during the first stage. Complications: it may cause neonatal hypothermia, hypotonia and respiratory depression.
• Promazine HCL (Sparine): 50 mg IM potentiate the analgesic effect of pethidine and has a good antiemetic action.

Analgesics:

• Narcotic analgesics: given during the active phase of cervical dilatation and postpartum after caesarean section.
  • Pethidine: 50-150 mg IM. Maximum analgesic effect is achieved after 45 minutes and lasts for 3-4 hours. It has sedative, analgesic and antispasmodic effect. It should not be given 2 hours before delivery to avoid foetal respiratory depression.
  • Morphine. 10-15 mg IM. It has more potent analgesic effect but more depression to the foetal respiratory centre so it should not be given 4 hours before delivery.
  • The antidote of narcotic analgesics is Naloxone 5 mg/ kg body weight into the umbilical vein.
• Inhalational analgesics:
  • Inhaled during contractions by the mother herself so when she becomes drowsy her hand catching the inhaled analgesic falls away and she recovers immediately.
  • Nitrous oxide (50%) + Oxygen (50%) (Entonox).
  • Trichloroethylene (Trilene 0.5% in air): inhaled through Cyprane apparatus.
  • Methoxyflurane (Penthrane 0.35% in air): inhaled through Cardiff apparatus.

Anaesthetics:

• General anaesthesia:
  • Injectable agents:
    • Thiopentone (Intraval 0.5-1 gm): IV induces short acting general anaesthesia suitable for instrumental vaginal delivery and repair of episiotomy or perineal tear.
    • Ketamine (Ketalar): 2 mg/kg body weight IV. Its action lasts 5-10 minutes, indicated as thiopentone. Hallucination and unpleasant dreams may occur.
  • Inhalation agent:
    • Nitrous oxide (80%) + Oxygen (20%):
      • It is safe.
    • Ether:
      • It is of benefit in shocked patient as it does not lower the blood pressure but it is inflammable.
    • Halothane (Fluothane 0.5%):
      • It produces muscle relaxation suitable for intrauterine manipulations as internal podalic version but it may lead to atonic postpartum haemorrhage.
• Regional and Local Anaesthesia:
  • Epidural block:
    • Indications:
      • Relief of pain in the first stage.
      • Extension of analgesia to the lower birth canal during the second stage .
      • Caesarean section.
    • Lumbar block:
      • Using the Tuohy needle with catheter the lignocaine (Xylocaine) 1% or bupivacaine (Marcaine) 0.5% is injected into the extradural space between L3 and L4 vertebrae.
    • Sacral (caudal) block:
      • The anaesthetic agent is injected through the sacral hiatus. It abolishes the perineal reflex leading to prolonged second stage and hence increased incidence of instrumental delivery.
  • Spinal block:
    • Lignocaine 1% or bupivacaine 0.5% is injected into the subarachnoid space.
    • It is useful for vaginal operative procedures and caesarean section but never as a long term analgesia during labour.
    • Advantage over epidural anaesthesia is that procedure is easier and blockade can be rapidly achieved with a smaller dose of local anaesthetic.
  • Paracervical block:
    • Lignocaine 1% is injected into the paracervical tissues through the lateral vaginal fornices.
    • Its action lasts for about 2 hours.
    • It is effective in relieving pain during the first stage of labour but foetal bradycardia is a common complication.
  • Pudendal nerve block:
    • 10 ml of lignocaine 1% is injected in the region of the ischial spine on each side either from inside through the vaginal mucosa or from outside through the perineal skin with a guiding finger in the vagina in both procedures.
    • It may be supplemented by local infiltration anaesthesia into the fourchette, perineum and adjacent vagina.
    • It is safe, simple and can be used for spontaneous and instrumental delivery and repair of episiotomy.
  • Local (perineal) infiltration anaesthesia:
    • 10 ml of lignocaine 1% is injected into the episiotomy line including the lower vagina, fourchette, perineal muscles and skin.
    • It is suitable for episiotomy incision and repair as well as repair of perineal lacerations by injection around it.
    • It is the safest and simplest technique but time should be allowed to establish analgesia.

Complications of General Anaesthesia

• Foetal:
  • Depression of the respiratory centre and asphyxia.
• Maternal:
  • Uterine atony leading to postpartum haemorrhage.
  • Respiratory complications:
    • Pulmonary collapse.
    • Mendelson’s syndrome:
  • It is inhalation of the acidic gastric juice during anaesthesia.
  • Manifestations may appear immediately or after 1-3 hours in the form of:
    • initial bronchospasm,
    • dyspnoea,
    • cyanosis,  
    • tachycardia,
    • systemic hypotension,
    • pulmonary hypertension,
    • death supervenes within very short time.

Prophylaxis

• The patient should be fasting at least 6 hours before anaesthesia.
• Preoperative oral antacids e.g. magnesium trisilicate 15 ml / 3hours.
• Preoperative histamine-2 antagonist e.g. cimetidine or raniditine injection.
• During induction: occlude the oesophagus by cricoid pressure and guard the trachea by cuffed endotracheal tube.
• During recovery: remove the tube in lateral position with the head lower down and only when the patient is conscious.

Treatment

• Endotracheal intubation.
• Upper airway aspiration.
• Oxygen under positive pressure.
• Hydrocortisone 200 mg IV to minimise the inflammatory reaction.
• Antibiotics.
• Tracheostomy may be considered in severe cases.

Complications of Epidural Anaesthesia

• Hypotension: because block of the sympathetic nerve supply to the lower part of the body leads to peripheral vasodilatation.
• Accidental dural puncture: There is a 50% possibility of a low pressure headache which lasts for few days from leakage of cerebrospinal fluid into the epidural space.
  • Treatment
    • Ringer - lactate solution infused into the epidural space.
    • Bed rest for 4 days.
    • Analgesics.
    • Blood patch: if the previous methods failed, 10-20 ml from patient’s own blood is injected into her epidural space.
• Subarachnoid injection: The usual dose needed for spinal (subarachnoid) block is far less than that required for epidural block so if accidentally injected into the subarachnoid space it may result in paralysis of the respiratory muscles.
  • Treatment:
    • Endotracheal intubation + oxygen.
    • Rapid fluid infusion to combat hypotension.
    • Ephedrine hydrochloride 5-10 mg for hypotension.
    • Artificial ventilation is continued with nitrous oxide 50% + oxygen 50%.
• Increased incidence of forceps delivery: as the maternal perineal reflex and urge to push is blocked leading to prolonged second stage.
• Neurological complications:
  • Patches of numbness on the outer side of the thighs or legs for few days.
• Fracture of the catheter:
  • Fragments are left in situ as it causes no problems.

Links

• Obstetrical analgesia and anesthesia : Guidelines, reviews

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Edited by Aldo Campana,