Lumbar disc disease.
This group comprises the majority of patients with a neurological disorder presenting to the obstetric anaesthetist, yet little appears in anaesthetic textbooks. Exacerbation of disc disease is common in pregnancy, with mothers limping into antenatal clinics and complaining of sciatic pain, partly as a result of the postural changes of pregnancy. These patients are often denied the choice of an epidural or subarachnoid block at the insistence of their attending neurosurgeon who fears a deterioration in their condition. There appears to be little scientific evidence to support this view. In fact, epidural injections of local anaesthetics, with or without steroids, have been used successfully in the treatment of disc prolapse for many years.
Post-laminectomy and spinal fusion patients are sometimes referred to the obstetric anaesthetist in early pregnancy and often carry a letter from their neurosurgeon counselling against regional block in labour (Chapter 115). Except in rare and specific cases, this prohibition of regional anaesthesia would appear to be unjustified. Nevertheless, epidural block in patients with disc disease, including post-surgical cases, may be technically difficult, time-consuming and require a paramedian approach or special technique (Chapter 48). The resulting block may initially be patchy but perseverance usually results in satisfactory analgesia without neurological sequelae (1, 2). The avoidance of adrenaline-containing solutions may be wise if it is considered that there might be an ischaemic element in the symptomatology of disc prolapse.
Many patients with marked disc disease are now managed with elective caesarean section in order to avoid back strain in labour. It seems unreasonable not to allow most, if not all, of these women the option of regional techniques (Chapter 84).
Multiple Sclerosis (MS).
This disease of uncertain aetiology is characterized by plaques of nerve demyelination which can produce widespread symptoms including visual disturbances, muscle weakness, paraplegia, neurogenic bladder and emotional lability. It is classically a relapsing and remitting condition. Infection, fatigue, emotional trauma, pregancy and labour may all precipitate a relapse. In general, pregnancy is usually well tolerated and, if relapses develop, they tend to occur in the first 3 months postpartum.
Theoretical concerns about the use of regional techniques in MS include the possibility that:
1. exacerbation of symptoms may, coincidentally, follow a satisfactory block and blame may be wrongly attributed to the technique; and
2. local anaesthetics may be toxic to demyelinated nerves. For this reason, subarachnoid block (Chapter 63) is not recommended in this condition.
Epidural analgesia is said not to be contraindicated in MS, but adrenaline-containing solutions should be avoided because local ischaemia may be deleterious in this situation. In practice, there have been several individual case reports and one series describing the safe use of epidural block for labour analgesia and caesarean section (3). In this review, of the 14 patients who received epidural block, 5 (36%) relapsed in the first 12 weeks postpartum, as compared to 4 (22%) of 18 patients who received general or local infiltration anaesthesia. High concentrations of local anaesthetics may be associated with a greater relapse rate and the use of a low as concentration as necessary seems wise.
A discussion with the patient regarding the choice of technique for labour, delivery and/or caesarean section should, preferably, occur early in the pregnancy.
Myasthenia gravis.
In this condition, auto-antibodies to acetylcholine (ACh) receptors produce a diminution in the number and size of post-synaptic ACh receptor sites and motor end-plates. The symptoms include weakness and easy fatiguability of voluntary muscles.
Epidural block may be used for labour or caesarean section provided that high levels of block are avoided. Excessively high blocks have the potential to further impair ventilatory function. For vaginal delivery, low spinal block may also be suitable.
Dosage levels of anticholinesterases may have to be adjusted.
Paraplegia.
On the surface, it would seem that an obstetric patient who is paraplegic (or quadriplegic) with a sensory level above T10 should not require analgesia for labour. However, because autonomic hyperreflexia can be life-threatening to these patients, some form of neuraxial block is mandatory. Autonomic dysreflexia occurs in the majority of patients with lesions above T7 and occurs when the skin or viscera below the lesion are stimulated. The autonomic dysfunction may range from sweating and facial flushing to bradycardia with severe hypertension (10% of patients) and headache. The hypertension may be severe enough to produce convulsions or subarachnoid or cerebral haemorrhage (4).
Other conditions.
Epileptic patients may benefit from a tranquil labour under continuous epidural blockade.
Epidural analgesia would also benefit patients with most neuromuscular disorders in the absence of any marked cardiomyopathy or respiratory embarrassment.
In myotonic conditions, the addition of fentanyl to the epidural solution may have the added benefit of reducing "epidural shivering" which may precipitate the characteristic attacks.
Opinions differ as to the advisability of attempting epidural blockade in patients with an intracranial tumour or raised intracranial pressure. Provided the considerable risk of cerebral herniation and sudden death associated with dural puncture in these patients is realized, and the utmost care is taken by an experienced anaesthetist, epidural blockade may be invaluable in the management of labour.
Benign intracranial hypertension (pseudo-tumour cerebri) is a different proposition, as there is generalized, not localized, cerebral oedema. Epidural or subarachnoid blocks may be safely undertaken.
Cases of peripheral neuropathy are usually suitable for regional techniques, following detailed discussion with the patient. Prolonged motor and sensory blocks, lasting up to 12 hours following epidural bupivacaine 0.5%, have been observed in patients with diabetic neuropathy.
With poliomyelitis on the wane, it is increasingly unusual to encounter women with residual paralysis in labour. However, those with polio affecting a lower limb should be warned that, occasionally, motor block may be prolonged in the affected leg.
References:
1. Daley MD, Morningstar BA, Rolbin SH et al. Epidural anesthesia for obstetrics after spinal surgery. Regional Anesthesia 1990 15:280-284.
2. Crosby ET, Halpern SH. Obstetric epidural anesthesia in patients with Harrington instrumentation. Canadian J Anaesth 1989 36:696.
3. Bader AM, Hunt CO, Datta S et al Anesthesia for the obstetric patient with multiple sclerosis. J. Clin Anesth 1988; 1:21-28
4. Stirt JA, Marco A, Conklin KA. Obstetric anesthesia for a quadriplegic patient with autonomic hyperreflexia. Anesthesiology 1979;51:560-562.