Obstetric anaesthesia and analgesia is always full of interest and challenge. As medically sicker patients becoming pregnant newer challenges have arisen. Some of these are discussed in the following article.
Pre-operative assessment
Early identification and planning of obstetric care by multidisciplinary teams was emphasised in the last CEMACH report1. To this end all maternity units should now have obstetric anaesthetic antenatal clinics dealing with relevant anaesthetic problems, and obstetric or medical illnesses that need anaesthetic input. The problems of the obese patient from both a regional and a general anaesthetic point of view need special consideration. Anaesthetists are suggested to review patients who are morbidly obese (BMI > 35). Apart from predicting problems these clinics allow planning for more complicated parturient management. All elective caesarean section patients should now be seen in pre-assessment clinics by anaesthetists.
Classification of caesarean section
The degree of urgency of caesarean section has long been a source of tribulation between obstetricians and anaesthetists. Communication about the need of immediacy of caesarean section by obstetricians has often been subjective with a variety of results. The terms ‘crash section,’ emergency, semi-emergency, semi-elective and elective were used but meant different things to different members of the team. A ’30 minute’ rule was used for emergency surgery but this is also subjective in terms of the potential emergency nature of the surgery. NICE guidelines and the Royal Colleges of both Obstetricians and Anaesthetists now recommend that classification2 be carried out on every case according to the following schedule:
Category 1: immediate threat to the life of the mother or fetus
Category 2: maternal or fetal compromise which is not immediately life threatening
Category 3: needing early delivery but no maternal or fetal compromise
Category 4: at a time to suit the woman and maternity team.
All maternity units should now have obstetric anaesthetic antenatal clinics dealing with relevant anaesthetic
problems, and obstetric or medical illnesses that need anaesthetic input
Equipment and staffing
Epidural equipment is standardised in the main with 16 or 18 gauge needles being in common practice. Newer refinements may occur soon with smaller and stronger epidural needles being manufactured. Newer advances in catheter material may allow for smaller atraumatic catheters to be manufactured. Safer loss of resistance devices which allow for two handed advancement of the needle and thus a potentially lower dural puncture rate have also been developed and the Epidrum® is one such example. This device has a small one ml priming pump attached to it which collapses once the epidural space is located.
Newer equipment that is often deemed necessary in the delivery suite include a thromboelastograph for instantaneous clotting profiles, haemoglobin measurement from oximetry, oesophageal Doppler cardiac output monitoring, a Level 1 tranfusor device to assist in major haemorrhage and major patient transfer equipment for the transfer of the critically ill patient to the Intensive Care Unit.
Maternity High Dependency Units of a Level 2 standard are now becoming an integral part of maternity units. Staffing of these areas is traditionally done by midwives. There are now several units with trained High Dependency Unit nurses assisting in the care of the ill parturient. Medical care can be delivered by these experienced staff and maternity care by midwives. More midwives are now trained in managing and understanding the sick mother.
Nerve injuries after neuraxial anaesthesia
Anaesthetists are often aware of obstetric palsies as regional anaesthesia is often blamed for them. However, the most common palsies are intrinsic and have a reported incidence of 0.6 to 92 per 10,000 deliveries. Stretch or compression injury to the lumbosacral plexus or lower extremity peripheral nerves in childhood is blamed for them but compression of the nerve vascular supply mechanism is another possibility. Nullparity, a prolonged second stage of labour, cephalo-pelvic disproportion, non-vertex presentation and forceps deliveries are associated with palsies. The most common is a lateral femoral neuropathy known as meralgia paresthetica. The nerve arises from the lateral border of the psoas muscle medial to the anterior superior iliac spine and then passes under or through the inguinal ligament and is vulnerable to compression. It is sensory to the lateral thigh and is also easily injured in caesarean section. Other nerves likely to be injured in childbirth include the femoral, obturator, sciatic and the common peroneal nerves3.
Anaesthetic related nerve damage does exist but is rare. Estimates in obstetric anaesthesia range from 1.2 – 0.3 per 100,000 procedures. Damage caused can include spinal haematoma, epidural abscess, traumatic spinal cord injury (from the needle), intracranial subdural haematoma, abducens nerve palsy and the development of Horner’s syndrome. Direct spinal cord trauma is most worrying as it can lead to permanent spinal cord injury and is most likely to arise from spinal or combined spinal epidural anaesthesia.
Recommendations for minimising this complication include choosing a lumbar puncture site below L3, halting needle advancement if the patient perceives pain or paraesthesia and injecting anaesthetic solutions only if all pain and paraesthesia has disappeared4.
Magnesium
Magnesium is a critical physiological cation and its deficiency in pregnant women may contribute to the development of pre-eclampsia, impaired neonatal development and to metabolic problems extending into adult life. Neurologically the inhibition of calcium channels and antagonism of the NMDA receptor raises the potential of neuronal protection and magnesium administration to prematurely labouring mothers may reduce the incidence of neonatal cerebral palsy. In the management of eclampsia magnesium has been shown to terminate convulsions and prevent further convulsions. It is also the agent of choice for the prevention of convulsions but the argument as to which pre-eclamptic mother should receive magnesium is unresolved. Magnesium therapy has potential complications in its own right and it is usually received for patients with severe disease5.
Effects of labour analgesia on the foetus
Labour pain and stress are associated with a progressiv