Anesthesiology

Neurologic Complications of Neuraxial Analgesia/Anesthesia: Needle/Catheter Related Nerve Injury

General Information

In the ASA Closed Claims Database, nerve injury was the most common cause of maternal injury in obstetric anesthesia claims from 1990 on.

1. Incidence

Intrinsic obstetric neuropathies related to labor and the mode of delivery are much more prevalent than those caused by direct trauma of needles and catheters used in neuraxial anesthesia.

The incidence of radiculopathy or peripheral neuropathy is difficult to assess due to rare occurrence. One review looking at 32 studies over 10 years estimated the incidence to be 3.78 in 10,000 for spinal anesthesia and 2.19 in 10,000 for epidural anesthesia.

Permanent neurologic injury after neuraxial anesthesia is rare, less than 1 in 100,000, including epidural hematoma and abscess, as well as direct nerve trauma.

2. Causes and Prevention

Paresthesias

Transient paresthesias are not uncommon when threading an epidural catheter or performing spinal anesthesia and are unlikely to cause nerve damage. However, painful or persistent paresthesias are much more concerning for nerve injury. The needle or catheter must be removed or repositioned immediately and the patient followed closely post partum. Likewise, any paresthesia or pain elicited by injection of local anesthetic down a needle or catheter should result in cessation of injection and close follow-up.

Spinal needles

Pencil-point needles have been shown to cause less tissue and nerve damage than beveled cutting needles. Despite this, trauma to the spinal cord or conus medullaris is probably more closely associated with the level of needle insertion than the type of needle. Studies have shown that clinicians are not good at accurately identifying the lumber intervertebral spaces, often inserting the needle one, two, or more spaces higher than intended.

Tuffier's line, drawn between the superior iliac crests, is commonly used as a starting point to identify lumber interspaces. It usually crosses at the level of the L4 spinous process, but not reliably so. Obesity, pregnancy, and the lateral position, often used for neuraxial block placement, all increase the inaccuracy of this method.

It is recommended that spinal needle insertion should ideally be below L3 to minimize the chance of spinal cord injury. It is also worth noting that the position of the orifice in pencil-point needles is further back from the tip of the needle compared to cutting needles (Whitacre more so than Sprotte needles), requiring the tip to be advanced farther to ensure the orifice is within the subarachnoid space. This increases the chance of damage to the spinal cord.

Epidural needles and catheters

Epidural placement is more likely to cause nerve root injury than is spinal needle insertion. Flexible catheters are less traumatizing than the more rigid variety, but can still wrap around nerve roots or become stuck in intervertebral foramina. Damage to the underlying spinal cord can occur, either as a consequence of incautious advancement of the epidural needle or secondary to abnormal anatomy, such as a tethered cord in patients with spina bifida. Signs and symptoms of this problem should alert the practitioner to the potential danger of epidural insertion prior to the procedure.

3. Diagnosis

History and physical

All paresthesias should be documented and followed-up post-partum. The absence of any paresthesia or pain during a neuraxial procedure makes any nerve injury much more likely to be obstetric in origin, but this does not absolve us of our responsibility to the patient if we were involved in their care.

If a patient complains of signs or symptoms of a nerve injury:

  1. Take a detailed history including:

    • Details of the symptoms

      • description: pain, numbness, weakness (including if unilateral or bilateral), sphincter dysfunction

      • onset relative to delivery and any neuraxial procedure

      • worsening or improving

        Most obstetric neuropathies are not painful, and symptoms are either unchanged or improving by the time patients complain of them. Neuropathies related to neuraxial anesthesia are frequently painful with worsening symptoms. Severe back pain and generalized lower extremity numbness and weakness with or without sphincter dysfunction are highly suggestive of a central lesion compromising the spinal cord.

    • Preexisting neurologic deficits (also part of the preprocedure assessment) secondary to:

      • diabetes

      • multiple sclerosis

      • skeletal abnormalities ± surgery

      • trauma

      • neuromuscular disorders

    • Obstetric course

      • mode of delivery

      • use of forceps

      • patient position when pushing

      • duration of second stage

      • orientation of fetal head

    • Neuraxial anesthesia:

      • epidural, CSE, or spinal for labor and delivery

      • occurrence of paresthesias or pain during procedure or on injection of local anesthetic

      • occurrence of a bloody tap

      • any unusual or unexpected sensory or motor blockade

2. Conduct a physical examination looking particularly for:

  • Fever. There are many causes of fever but combined with a raised white cell count it is suggestive of infection.

  • Sensory and motor deficits. Perform a full neurological examination to try and determine whether the injury is a peripheral or central lesion.

A basic knowledge of common obstetric neuropathies is useful in diagnosing the probable cause of the nerve injury. Mild sensory deficits can be diagnosed and managed by the obstetricians and/or anesthesiologists. More serious neuropathies with both sensory and motor involvement should be referred to a neurologist or neurosurgeon for further work-up and treatment.

Common Obstetric Peripheral Neuropathies (Table 1)

Table 1.

Nerve Nerve Roots Possible Mechanism Motor Deficit Sensory Deficit
Lateral femoral cutaneous nerve (most commonly injured) L2, 3 Excessive lithotomy position during pushingWide incision during cesarean delivery, stretching by retractor NONE Anterolateral thigh (meralgia paresthetica)
Femoral nerve L2-4 Excessive lithotomy during pushingStretching by retractor Quadriceps weakness affecting hip flexion and knee extensionWeak patellar reflex Anterior thigh, medial leg and foot
Obturator nerve L2-4 Fetal head forceps Weak thigh adduction Medial aspect of thigh
Lumbosacral trunk L1-S4 Fetal head forceps (macrosomia and malpresentation increase risk) FootdropQuadriceps and hip adduction weakness Lateral leg, dorsum of foot
Common peroneal nerve L4-S2 Poor positioning in stirrupsProlonged external compression on lateral knees by hands when flexing hips for pushing Footdrop Anterolateral leg and dorsum of foot

Investigations

i. MRI: Any indication of a central lesion requires an emergency MRI scan without delay. Laminectomy and decompression of an epidural hematoma or abscess within 6-12 hours of onset of symptoms are essential to avoid permanent injury.

ii. Electromyelography (EMG): Useful for diagnosing the site and severity of the peripheral nerve injury but may not show any abnormal activity for up to 3 weeks after injury. Abnormal results much sooner than this are suspicious for a preexisting injury.

4. Treatment

Most intrinsic obstetric peripheral nerve injuries are temporary and will spontaneously resolve within 6-8 weeks. Some may take longer. Treatment is supportive with physical therapy playing a major role to avoid muscle atrophy.

Recovery of nerve injury secondary to neuraxial procedures depends on the site and severity of the injury. Mild injuries will resolve in a similar time course to obstetric neuropathies, but severe injuries may have complete or partial loss of function.

Epidural hematoma or abscess require immediate decompression, as mentioned above, to avoid permanent injury.

What's the Evidence?

Lee, AJ, Ranasinghe, JS, Chehade, JM. "Ultrasound assessment of the vertebral level of the intercristal line in pregnancy". Anesth Analg . vol. 113. 2011. pp. 559-64.

(The authors found the intercristal line was at L3 or above in 6% of term pregnant patients using ultrasound.)

Wong, CA. "Nerve injuries after neuraxial anaesthesia and their medicolegal implications". Best Pract Res Clin Obstet Gynaecol. vol. 24. 2010. pp. 367-81.

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