Although spinal and epidural needles and catheters must, by virtue of their mode of action, pass close to nerve roots, the incidence of neurological damage appears to be very low. Surveys have suggested that around 1 in 2000 obstetric epidurals/spinals is complicated by numbness, paraesthesia or weakness in the distribution of a single nerve root that may take several days to a few months to resolve. The incidence of permanent symptoms is approximately 1 in 15, 000.
Problems and special considerations
Nerve root damage
A needle or catheter touching a nerve root is almost certain to cause paraesthesia in the awake patient, usually of a severe, lancinating quality and characteristically described as being like an electric shock in the distribution of the nerve root. Unless transient and mild, paraesthesia should always prompt the anaesthetist to remove the needle or catheter and to reorientate it. Presence or absence of paraesthesia should always be recorded. If damage has occurred, symptoms are usually experienced in the same distribution (Table 53.1).
Peripheral nerve damage
While it is perhaps natural to blame any lower limb neurological deficit on the neuraxial block that preceded it, nerve palsy is more likely to arise as a result of obstetric factors, as witnessed by patients with demonstrable permanent lesions despite not having had epidural or spinal procedures. The incidence of postpartum obstetric nerve palsies is around 1%, the causes and features of which are listed in Table 53.2. The potential for nerve damage during childbirth is apparent when one considers the anatomy of the nerves arising in the pelvis (seeFigure10.6), with possible mechanisms of injury including stretching or compression of the nerve.
Table 53.1 Neurologicaldeficit following nerve root trauma
|
Root |
Sensory loss |
Motor weakness |
|
L2 |
Upper anterior thigh |
Hip flexion |
|
L3 |
Lower anterior and medial thigh |
Thigh adduction |
|
L4 |
Lateral thigh, knee and medial leg |
Leg extension |
|
L5 |
Lateral leg and dorsum of foot |
Ankle dorsiflexion |
|
S1 |
Lateral foot |
Ankle plantar flexion |
Neuraxial analgesia may contribute indirectly to the development of nerve injury by eliminating the discomfort caused by prolonged nerve compression in certain positions, which would normally prompt the woman to re-position herself.
Central neurological lesions
Single nerve damage should be distinguished from the more serious central lesions that occur extremely rarely (see Chapter 54, Spinal cord lesions following regional anaesthesia; Chapter 55, Arachnoiditis; Chapter 56, Cauda equina syndrome).
Management options
Prevention is the most important aspect of management. Blocks should be performed with the patient awake (not normally an issue in obstetric practice), and care should be taken to ensure that the interspace chosen is below the level of termination of the spinal cord. Patients should be asked to indicate if they feel paraesthesia, and this should be a signal to the anaesthetist to remove the needle or catheter and start again. Spinal injections should only be given if there is free flow of cerebrospinal fluid, to ensure that the needle tip is not obstructed by nerve tissue. A note should always be made as to the presence or absence of paraesthesia during the procedure, as this information can be invaluable later.
Table 53.2 Nerve lesions with non-anaesthetic, obstetric causes
|
Lesion |
Presentation |
Cause |
|
Lateral cutaneous nerve of thigh |
Meralgia paraesthetica - altered sensation over anterolateral aspect of thigh |
Antenatal weight gain ± lumbar lordosis Prolonged pushing in lithotomy position |
|
Femoral nerve |
Loss of sensation front of thigh Quadriceps weakness Reduced kneejerk |
Hyperflexion of thighs, especially squatting or lithotomy position Instrumental delivery |
|
Peroneal nerve |
Foot drop |
Pressure from lithotomy poles or prolonged squatting |
|
Lumbosacral trunk |
Foot drop Loss of sensation especially L4-5, S1 |
Pressure in pelvis from fetal head or forceps |
|
Obturator nerve |
Weakness of thigh adductors Loss of sensation in an area in upper third of medial thigh Wide-based gait |
As for femoral nerve |
|
Conus of spinal cord |
Anterior spinal artery syndrome - cauda equina/paraplegia |
Obstruction of aberrant blood supply to conus by fetal head during prolonged labour Herniated disc |
Routine follow-up should be carried out assiduously, and midwives should be alerted to notify the anaesthetist if any mother shows signs of slow recovery of sensory or motor function. Careful mapping of the deficit should be carried out at the earliest opportunity to establish a baseline from which improvement can be measured. Other, non-anaesthetic, causes should be considered; the aetiology may be suggested by the distribution and nature of the deficit and by the presence of precipitating factors (see Table 53.2). The benign course of the vast majority of these lesions means that an explanation to the patient can include a reassuring prognosis. Generally, neuropraxias recover in 3-4 months, though occasionally chronic pain may ensue so postpartum follow-up should always be offered.
Except for minor and resolving lesions, further management should generally involve referral to a neurologist or neurophysiologist. Imaging of the thoracolumbar region should be considered in the presence of local or radicular back pain, associated sphincter incontinence, motor or sensory abnormalities in a root or cord pattern, signs of infection, and in patients with progressive symptoms or those with a history of immunosuppression. Nerve conduction studies are often invaluable, as they allow the site of the lesion to be identified and may help in estimating prognosis.
Key points
• Paraesthesia should always be documented and is a sign to withdraw the needle, reorientate it and start again.
• Delayed recovery needs assiduous follow-up to detect neuraxial haematoma or abscess.
• Nerve palsy is usually a result of pregnancy or childbirth and unrelated to regional anaesthesia.
Further reading
Cook TM, Counsell D, Wildsmith J; Royal College of Anaesthetists Third National Audit Project. Major complications of central neuraxial block: report on the 3rd National Audit Project of the Royal College of Anaesthetists. Br J Anaesth 2009; 102:179-90.
Moen V, Irestedt L. Neurological complications following central neuraxial blockades in obstetrics. Curr Opin Anaesthesiol 2008; 21: 275-80.
O’Neal MA, Chang LY, Salajegheh MK. Postpartum spinal cord, root, plexus and peripheral nerve injuries involving the lower extremities: a practical approach. Anesth Analg 2015; 120: 141-8.
Richards A, McLaren T, Paech MJ, et al. Immediate postpartum neurological deficits in the lower extremity: a prospective observational study. Int J Obstet Anesth 2017; 31: 5-12.
Wong CA. Nerve injuries after neuraxial anaesthesia and their medicolegal implications. Best Pract Res Clin Obstet Gynaecol 2010; 24: 367-81.