Cauda Equina Syndrome - complication of epidural or spinal anesthesia

Cauda Equina Syndrome

Cauda Equina Syndrome is rare but devastating complication of epidural or spinal anesthesia. It is most commonly associated with the use of high concentration of Lignocaine and continuous spinal block, both of which are not currently recommended in obstetric practice.

A 31-year-old woman at 36th week of pregnancy came to the hospital because of sudden onset of pain in the buttock. The pain radiated down the leg. The woman also had slight urinary incontinence – a leaky bladder. She had two caesarean sections in the past without problems. She also had a known back problem that was diagnosed by MRI after her second caesarean: the small disc bulge the level of L5/S1, without the compression of nearby nerves roots. She was treated conservatively and had no pain throughout pregnancy. Her other health problems were hypertension and type 2 diabetes. She used to be obese, but managed to lose considerable amount of weight after she had gastric bypass surgery three years earlier.

The woman was examined and was found to have mild weakness and decreased reflexes in the ankle and paresthesia – “pins and needles” in both ankles and feet. As pregnancy progresses the back pain may become worse. Because of that and the fact that it was difficult to control her diabetes it was decided to proceed with early delivery via caesarean section. She received combined spinal-epidural anesthetic which went smoothly and without problems. About 17 hours after the baby was born the epidural catheter was removed, the patient began moving around and was passing urine at will after the urinary catheter – obligatory attribute of every caesarean – was removed.

Approximately 36 hours after the operation the woman had a sudden episode of fecal incontinence, or loss of control of bowel movement. She was immediately examined and it was found that her gait was unaffected, but the sensation in the perineum – also called saddle region – was decreased. Urgently performed MRI revealed a large disc bulge at the level of L5/S1. The bulge was large and compressed cauda equine – the nerves extending in the spinal canal below the spinal cord. The patient was taken to the operating theatre where an urgent spinal decompression was performed. Straight away after the operation the patient was able to walk, but could not control the urination. She was later referred for rehabilitation and after three weeks had only sporadic episodes of fecal incontinence. She however needed to catheterize her bladder in order to urinate.

This is the case report of Cauda Equina Syndrome (CES), a very rare but potentially devastating complication of spinal and epidural anesthesia. The incidence of this complication in obstetric patients is low.

Cauda Equina Syndrome results from the dysfunction of multiple sacral and lumbar nerve roots in the lumbar vertebral canal. As explained in the chapter on spinal anatomy, spinal cord extends to the level of L1 or L2. Below this level spinal canal is filled with nerve roots that are bundled together and at first glance resemble the tail of a horse, which is the literal translation of Cauda Equina from Latin. These nerve roots exit the spinal canal at lumbo-sacral level and eventually extend as the nerves supplying the perineum – the saddle area – and lower limbs. The dysfunction of these roots can cause various symptoms, the term Cauda Equina Syndrome is used only when they include impairment of bladder, bowel, or sexual function, and perianal or “saddle” numbness. Impairment of bladder function can manifest either as urinary incontinence – the inability to hold urine – or difficulty of passing it. Bowel dysfunction manifests as fecal incontinence, or involuntary defecation. The symptoms of impaired sensory or motor function in the lower limbs may or may not accompany CES.

The most common cause of the CES in the general population is herniation, or bulging, of the intervertebral discs at the level of L4/5 or L5/S1. Some clinicians suggested that the blood supply to the neural tissue at this level is low relative to other areas, and that is why cauda equina is more sensitive to mechanical compression than other areas. According to data from Slovenia cauda equina syndrome as the result of intervertebral disc herniation happens on the average in 1.8 people per million of population. Estimated data from the US suggests that each year 0.12% of herniated discs are likely to cause cauda equina syndrome. There are many other, rarer causes of CES, such as spinal injury, tuberculosis, tumors or infections. There is also an additional group of causes called iatrogenic, meaning “brought forth by a healer” (iatros means healer in Greek), or in other words the result of the actions of doctors or other medical personnel. In the early nineties serious concern was caused by the series of case reports of iatrogenic CES.

The vast majority of these cases were observed when a new technique, continuous spinal anesthesia was used. Spinal block is usually utilized when a quick block of limited duration is required, such as in caesarean section which lasts less than an hour in most cases. Epidural allows placement of catheter and keep administering local anesthetic mixture for as long as needed, hours, days and even months, as for pain control in cancer patients.

In the late eighties-early nineties there were experiments with continuous spinal anesthesia, where a catheter of very thin diameter (microcatheter) was inserted through the spinal needle into the subarachnoid space. The advantages of this technique were easier placement technique, higher success rate and the use of lower doses of drugs. Spinal is generally more reliable because of the clearer end point, the appearance of CSF in the needle, which is a definite sign that the tip of the needle is in subarachnoid space. Epidural block relies on less reliable sign, loss of resistance.

Continuous spinal gained popularity. However, soon series of case reports of devastating CES appeared in the literature. It appeared that in most cases 5% Lignocaine was used for the block. Using short acting local anesthetic as an infusion makes perfect sense as it gives better control of the situation: switch the infusion off and the block wears off within half an hour or so. The problem with the continuous subarachnoid infusion though is that it allows for the collection of larger than usual dose of the drug to accumulate in one space. This increases toxic effect of local anesthetic, and in the case of Lignocaine this toxicity is sufficient to cause nerve damage. At the direction of the Food and Drug Administration (FDA) spinal microcatheters were removed from clinical practice.

The treatment of CES depends on the cause. If the cause is mechanical, such as herniated disc or a tumor, surgery is necessary to remove them. If it is caused by infection, the course of antibiotics is given. In the case of CES as the result of local anesthetic toxicity the prognosis is poor, and the patient is likely to suffer permanent damage. That is why prevention of this devastating complication is of paramount importance.

Spinal microcatheters do offer advantages, and recently they have been re-introduced into practice, though very carefully and under strict monitoring conditions. Lignocaine is contraindicated in contimuous spinals.

There is a situation when intrathecal catheters are used in labor analgesia. During placement of epidural inadvertent dural tap can occur. This is indicated by free flow of CSF through the epidural needle and almost invariably results in post-dural puncture headache. If this occurs it is recommended to insert the epidural catheter into the subarachnoid space and continue using it for labor analgesia. It is thought that the presence of plastic in the dura causes low grade inflammation in the area, which, after the removal of the catheter helps the healing of the defect, thus preventing the headache. The dose of local anesthetic has to be considerably reduced in this situation. Needless to say, Lignocaine is contra-indicated in this situation.

With drugs and techniques currently in use modern clinical use CES is rare. Recent review from Sweden analyzed severe neurologic complications following neuraxial anesthesia from 1990 to 1999. During that period an estimated 1,250,000 spinals and 450,000 epidural blocks were performed, including about 200,000 epidurals in labor. Cauda equina syndrome was reported in 32 cases: 18 of them after spinal block and 2 after continuous spinal. Sadly, all patients had permanent neurologic damage. CES occurred in patients undergoing orthopedic or general surgery. No cases of this complication were reported in obstetric patients.

The case presented at the beginning of this chapter is an example of difficulties encountered by clinicians in obstetric practice. Epidurals are often blamed for various complications and unfavorable side-effects. The woman in the report already had a problem with her intervertebral disc and the decision to proceed with caesarean section was by a large degree dictated by her worsening condition. Even though it is theoretically possible that CES was the complication of spinal block, it is not likely. Most probable cause is the progression of the spinal disease which would probably occur without neuraxial block.

References:

1. Chow J, Chen K, Sen R, Stanford R, Lowe S. Cauda equina syndrome post-caesarean section. Australian and New Zealand Journal of Obstetrics and Gynaecology 2008; 48: 218–224.

2. Lavy C, James A, Wilson-MacDonald J, Fairbank J. Cauda equina syndrome. BMJ 2009; 338: 881-884.

3. Moen V, Dahlgren N, Irestedt L. Severe Neurological Complications after Central Neuraxial Blockades in Sweden 1990–1999 Anesthesiology 2004; 101:950–9.

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Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural