Epidural

  The term epidural is often short for epidural anesthesia, a form of regional anesthesia involving injection of drugs through a catheter placed into the epidural space. The injection can cause both a loss of sensation (anaesthesia) and a loss of pain (analgesia), by blocking the transmission of pain signals through nerves in or near the spinal cord.

The epidural space (or extradural space or peridural space) is a part of the human spine inside the spinal canal separated from the spinal cord and its surrounding cerebrospinal fluid by the dura mater.

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Epidural anesthesia

Indications

Injecting medication into the epidural space is primarily performed for analgesia. This may be performed using a number of different techniques and for a variety of reasons. Additionally, some of the side-effects of epidural analgesia may be beneficial in some circumstances (e.g. vasodilation may be beneficial if the patient has peripheral vascular disease). When a catheter is placed into the epidural space (see below), the effects of the analgesia may be prolonged for several days, if required. Epidurals may be used:

• For analgesia alone, where surgery is not contemplated. An epidural for pain relief (e.g. in childbirth) is unlikely to cause loss of muscle power, but is not usually sufficient for surgery.
• As an adjunct to general anaesthesia. The anaesthetist may use epidural analgesia in addition to general anaesthesia. This may reduce the patient's requirement for opioid analgesics. This is suitable for a wide variety of surgery, for example gynaecological surgery (e.g. hysterectomy), orthopaedic surgery (e.g. hip replacement), general surgery (e.g. laparotomy) and vascular surgery (e.g. open aortic aneurysm repair). See also caudal epidural, below.
• As a sole technique for surgical anaesthesia. Some operations, most frequently Caesarean section, may be performed using an epidural anaesthetic as the sole technique. Typically the patient would remain awake during the operation. The dose required for anaesthesia is much higher than that required for analgesia.
• For post-operative analgesia, in either of the two situations above. Analgesics are given into the epidural space for a few days after surgery, provided a catheter has been inserted. Through the use of a patient-controlled analgesia (PCA) infusion pump, a patient may be given the ability to control post-surgical pain medications administered through the epidural.
• For the treatment of back pain. Injection of analgesics and steroids into the epidural space may improve some forms of back pain. See below.
• For the treatment of chronic pain or palliation of symptoms in terminal care, usually in the short or medium term.

A patient getting a modern epidural for pain relief generally receives a combination of local anesthetics and opioids. Common local anesthetics include lidocaine, bupivicaine, ropivicaine, and chloroprocaine. Common opioids are morphine (or hydromorphone), fentanyl, sufentanil, and pethidine (known as meperidine in the U.S.). These are then injected in relatively small doses. Occasionally other agents may be used, such as clonidine or ketamine.

Because of the nature of epidurals, they are most suitable for analgesia for the abdomen, pelvis or legs. They are much less suitable for analgesia for the chest, neck, or arms and are not possible for the head.

Technique

Epidural anaesthesia is performed by a trained anaesthetist with the patient either in the preferred sitting position or lying on the side.

• The patient is asked to arch his back, i.e. to push the small of his back out as if to assume the "posture of an angry cat".
• The anaesthetist palpates the patient's back and identifies suitable anatomical gaps between the bony spinous processes prior to the actual procedure.
• The level of the spine at which the catheter is best placed depends mainly on the site and type of an intended operation or the anatomical origin of pain, e.g. the pain during labor and childbirth.

The Procedure

• Using a strict aseptic technique a small volume of local anaesthetic, such as 1.0% lidocaine, is injected into the skin and interspinous ligament.
• A 16-, 17-, or 18-gauge Tuohy needle is then inserted to the interspinous ligament and a "loss of resistance to injection" technique is used to identify the epidural space. This technique works because the interspinous ligament is extremely dense, and injection into it is almost impossible. The anaesthetist advances the Tuohy needle slowly, attempting to inject through it every millimetre or so.
• Typically a "pop" is felt as the ligamentum flavum is breached. The epidural space contains only loose tissue and veins, which means that injection into it is very easy.
• The sensation of the "pop" followed by ease of injection is a strong indicator that the tip of the needle is in the epidural space.

Traditionally anaesthetists have used either air or saline for identifying the epidural space, depending on personal preference, however, evidence is accumulating that saline may result in more rapid and satisfactory quality of analgesia^[1].

• After placement of the tip of the Tuohy needle into the epidural space the catheter is threaded through the needle. The needle is then removed. Generally the catheter is then withdrawn slightly so that 4-6 cm remains in the epidural space. The catheter is a fine plastic tube, down which anaesthetics may be given into the epidural space.

Most commonly, the anaesthetist conducting an epidural places the catheter in the mid-lumbar, or lower back region of the spine, although occasionally a catheter is placed in the thoracic (chest) or cervical (neck) region. In adults, the spinal cord terminates at the first lumbar vertebra, below which lies a bundle of nerves known as the cauda equina ("horse's tail"). Hence lumbar epidurals carry a very low risk of injuring the spinal cord.

A common solution for epidural infusion in childbirth or for post-operative analgesia is 0.2 percent ropivicaine and 2 μg/mL of fentanyl. This solution is infused at a rate between 4 and 14 mL/hour, following a loading dose to initiate the nerve block.

Typically, the effects of the epidural are noted below a specific level on the body (dermatome). This level (the "block height") is chosen by the anaesthetist. The level is usually 3-4 dermatomes higher than the point of insertion. A very high insertion level may result in sparing of very low dermatomes. For example, a thoracic epidural may be performed for upper abdominal surgery, but may not have any effect on the perineum. However, giving very large volumes into the epidural space may spread the block both higher and lower. In some unusual instances, it may not be required to insert a catheter into the epidural space, e.g. for steroid injections; see below. The anesthesiologist may inject medication into the epidural space through the needle, then remove the needle.

Combined spinal-epidurals

For some procedures, the anaesthetist may choose to combine the rapid onset and reliable, dense block of a spinal anaesthetic with the post-operative analgesic effects of an epidural. This is called combined spinal and epidural anaesthesia (CSE).

The anaesthetist may insert the spinal anaesthetic at one level, and the epidural at an adjacent level. Alternatively, after locating the epidural space with the Tuohy needle, a spinal needle may be inserted through the Tuohy needle into the subarachnoid space. The spinal dose is then given, the spinal needle withdrawn, and the epidural catheter inserted as normal. This method, known as the "needle-through-needle" technique, may be associated with a slightly higher risk of placing the catheter into the subarachnoid space.

Caudal epidurals

The epidural space may be entered through the sacrococcygeal membrane, using a standard 21G needle. Injecting a volume of local anaesthetic here provides good analgesia of the perineum and genital areas. This is typically a single-injection technique and a catheter is not normally placed. This is known as a caudal epidural or "caudal".

The caudal epidural is an effective and safe analgesic technique in children undergoing pelvic or perineal surgery. It is usually combined with general anaesthesia.

Side effects

In addition to blocking the nerves which carry pain, local anaesthetic drugs in the epidural space will block other types of nerves as well, in a dose-dependent manner. Depending on the drug and dose used, the effects may last only a few minutes or up to several hours. This results in three main effects:

• Loss of other modalities of sensation (including touch, and proprioception)
• Loss of muscle power
• Loss of function of the sympathetic nervous system, which controls blood pressure

Pain nerves are most sensitive to the effects of the epidural. This means that a good epidural can provide analgesia without affecting muscle power or other types of sensation. The larger the dose used, the more likely it is that the side-effects will be problematic.

For example, a laboring woman may have an epidural running during labor which is providing good analgesia without impairing her ability to move around in bed. She requires a Caesarean section, and is given a large dose of epidural bupivacaine. After a few minutes, she can no longer move her legs, or feel her abdomen. Her blood pressure is noted to be lower and she is given an intravenous infusion of ephedrine or phenylephrine to compensate. During the operation, she feels no pain.

Very large doses of epidural anaesthetic can cause paralysis of the intercostal muscles and diaphragm (which are responsible for breathing), and loss of sympathetic function to the heart itself, causing a profound drop in heart rate and blood pressure. This requires emergency treatment, and in severe cases may require airway support. This happens because the epidural is blocking the heart's sympathetic nerves, as well as the phrenic nerves, which supply the diaphragm.

It is considered safe practice for all patients with epidurals to be confined to bed to prevent the risk of falls.

The loss of the sensation of needing to urinate may require the placement of a urinary catheter for the duration of the epidural.

Opioid drugs in the epidural space are very safe (as well as effective). However, very large doses may cause troublesome itch, and rarely, delayed respiratory depression.

Complications of epidural use

These include:

• Block failure (about 1 in 20). Partial failure may still give satisfactory pain relief. However, if pain relief is inadequate, another epidural may have to be performed.
• Bloody tap (about 1 in 30-50). It is easy to injure an epidural vein with the needle. In patients who have normal blood clotting, it is extremely rare (e.g. 1 in 100,000) for problems to develop. However, in a patient who has a coagulopathy, the patient may be at risk of epidural hematoma. If blood comes back down the needle, the anesthesiologist will normally site the epidural at another level.
• Accidental dural puncture (about 3 in 100 insertions^[2]) The epidural space in the adult lumbar spine is only 3-5mm deep, which means it is comparatively easy to cross it and accidentally puncture the dura (and arachnoid) with the needle. This may cause cerebrospinal fluid (CSF) to leak out into the epidural space, which may in turn cause the post dural puncture headache (PDPH). This can be severe and last several days, and in some cases weeks or months. It is caused by a reduction in CSF pressure and is characterised by postural exacerbation when the patient raises their head above the lying position. If severe it may be successfully treated with a "blood patch" (a small amount of the patient's own blood given into the epidural space via another epidural needle). Most cases resolve spontaneously with time.
• Catheter misplaced into a vein (uncommon, less than 1 in 300). Occasionally the catheter may be misplaced into an epidural vein, which results in all the anaesthetic being injected intravenously, where it can be toxic in large doses. This also results in block failure.
• High block, as described above (uncommon, less than 1 in 500).
• Catheter misplaced into the subarachnoid space (rare, less than 1 in 1000). If the catheter is accidentally misplaced into the subarachnoid space (e.g. after an unrecognised accidental dural puncture), normally cerebrospinal fluid can be freely aspirated from the catheter (which would usually prompt the anaesthetist to withdraw the catheter and resite it elsewhere). If, however, this is not recognised, large doses of anaesthetic may be delivered directly into the cerebrospinal fluid. This may result in a high block, or, more rarely, a total spinal, where anaesthetic is delivered directly to the brainstem, causing unconsciousness and sometimes seizures.
• Significant damage to a single nerve (very rare, less than 1:10,000).
• Epidural abscess formation (very rare, about 1 in 50,000-75,000). The risk increases greatly with catheters which are left in place longer than 72 hours.
• Paraplegia (extremely rare, less than 1:100,000).
• Arachnoiditis (extremely rare, fewer than 1000 cases in the past 50 years) ^[3]
• Death (extremely rare, less than 1:100,000).

Contraindications

These are circumstances in which epidurals should not be used:

• Patient refusal
• Bleeding disorder (coagulopathy) or anticoagulant medication (e.g. warfarin)
• Infection near the point of insertion
• Infection in the bloodstream which may "seed" onto the catheter
• Hypovolemia (low circulating blood volume)

Cautions

There are circumstances where the risks of an epidural are higher than normal. These circumstances include:

• Anatomical abnormalities, such as spina bifida, meningomyelocele or scoliosis
• Previous spinal surgery (which may cause an acquired tethered spinal cord)
• Certain problems of the central nervous system, including multiple sclerosis or syringomyelia
• Certain heart-valve problems (such as aortic stenosis)

Epidural analgesia in childbirth

Epidural analgesia is a relatively safe and effective method of relieving pain in labor. It provides immediate pain relief in most cases. Epidural analgesia is associated with longer labor. Some claim that it is correlated with an increased chance of operational intervention. The clinical research data on this topic is conflicting. For example, a study in Australia (Roberts, Tracy, Peat, 2000) concluded that having an epidural reduced the woman's chances of having a vaginal birth, without further interventions (such as episiotomy, forceps, ventouse or caesarean section) from 71.4% to 37.8%. Conversely, a 2001 study by researchers at the National Institute of Child Health and Human Development and a 2002 study by researchers at Cornell University and the University of Ontario demonstrated that epidurals do not increase the likelihood of a caesarean section. In 2005, a meta-analysis of 21 studies also showed that epidurals do not increase the likelihood of caesarean section, but they do increase the chance of a forceps or ventouse delivery by 40% (Anim-Somuah, Cochrane Review, 2005). The COMET Study, published in The Lancet in 2001 (vol358, No9275 p19-23) showed that a combined spinal epidural in labor may speed up the labor process by a few minutes, although those women receiving an epidural had a caesarean rate of 28% and only 35% had a normal birth without instrument assisted delivery.

What explains these differing outcomes? There are some data that demonstrate that the likelihood of increased intervention is directly related to the quality of the institution or practitioner providing the care: epidurals administered at top-rated institutions do not generally result in a clinically significant increase in caesarean rates, whereas the risk of caesarean delivery at poorly ranked facilities seems to increase with the use of epidural^[4] An alternative explanation is that women having difficult labors are more likely to request epidurals, and are also less likely to have an unassisted vaginal birth.

Some mothers worry that epidural analgesia may harm their newborn. Research puts this fear to rest: although epidural labor analgesia is associated with slower progress of labor, it has no adverse effect on perinatal outcome and perinatal complications.^[5]

One study concluded that women whose epidurals contain the drug fentanyl were less likely to fully breastfeed their infant in the few days after birth and more likely to stop breastfeeding in the first 24 weeks.^[6] However, this study has been criticised for several reasons, one of which is that the original patient records were not examined in this study, and so many of the epidurals were assumed to contain fentanyl when almost certainly they would not have.^[7] In addition, all patients who used epidurals in labor had also used systemic pethidine, which would be much more likely to be the cause of any effect on breastfeeding due to the higher amounts of medication used via that route. If that were the case, then early epidurals which avoided the need for pethidine may actually improve breastfeeding outcomes, not worsen them.

History

Prior to 1943, there was no practical way for the pain of childbirth to be diminished without risk of harm to the baby. Caesarian sections under general anesthesia were to be used only as an emergency measure. Three surgeons at the United States Marine Hospital at Stapleton, on Staten Island, New York -- Dr. Robert A. Hingson, Dr. Waldo B. Edwards, and Dr. James L. Southworth -- are credited with developing the technique of the continuous caudal anesthesia ^[8]. . In 1912, German physicians found that the injection of an anesthetic, at the base of the spinal cord, would prevent pain impulses from reaching the brain. Doctors in the United States developed the technique further. For expectant mothers, the injection "only reduced the pangs of childbirth; it did not eliminate them," wrote Dr. Morris Fishbein in the March 1943 issue of Hygeia, and a single nerve blocking injection was used only toward the end of labor ^[9].

Drs. Hingson and Southworth combined the concepts of caudal analgesia and the spinal injection in an operation to strip the varicose veins of a Scottish merchant seaman. The important leap forward came when the surgeons experimented with a continuous intravenous delivery of the local anesthetic, rather than removing the needle after the injection, to originate "continuous caudal analgesia". Dr. Hingson then collaborated with Dr. Edwards, the chief obstetrician at the Marine Hospital, to study the use of an anodyne in childbirth. The two studied the caudal region to determine where a needle could be placed to deliver anesthesia to the spinal nerves without placing the drugs into the the spinal fluid. Testing on a human being did not occur until January 6, 1942, when the wife of a Coast Guardsman was brought into the Marine Hospital for a delivery. Because the woman suffered from rheumatic heart disease, general anesthesia could not be used for an emergency Caesarian section, and it was believed that she would not survive the pains of labor. With the continuous use of a local anesthesia, the woman and her baby survived. According to Dr. Fishbein's article in Hygeia, a total of 589 women in more than twenty participating hospitals gave birth relatively painlessly in 1942. ^[10]. When the results were public in the January 23, 1943, issue of the Journal of the American Medical Association, the discovery of a safe and painless method of childbirth was reported worldwide ^[11].

Epidural steroid injection

An epidural injection, or epidural steroid injection, is used to help reduce the pain caused by a herniated disc, degenerative disc disease, or spinal stenosis. These spinal disorders often affect the cervical (neck) and lumbar (low back) levels of the spine. Pain may be accompanied either by numbness or tingling that radiates into the arms or legs. An epidural steroid injection (ESI) may be part of a patient’s multidisciplinary treatment plan including physical therapy. The effects of an epidural steroid injection may be either temporary or long-term. The injection works by reducing the inflammation or swelling, or both, of the nerves in the epidural space.

Epidural steroid injections are administered in a sterile setting such as an outpatient clinic or hospital. The medicine used in the injection is a combination of a local anesthetic (e.g. bupivacaine) and a steroid (e.g. triamcinolone). The procedure involves numbing the skin with a local anesthetic injection, allowing time for the anesthetic to work, and then inserting a needle to the epidural space. The procedure is performed using fluoroscopy (live x-ray) enabling the physician's viewing of the needle's placement. When the needle is properly positioned, the mixture is injected to the epidural space.

After the procedure, the patient is returned to the recovery area and monitored before being released to home. Patients might be asked to keep a pain diary to help them discuss their pain progress during a follow-up appointment. Some patients who have some residual pain after the first injection may receive a second or third epidural steroid injection. Patients who do not receive any relief from the first injection usually do not receive a second injection.

It is important that the patient scheduled for an epidural steroid injection follows the provided pre-procedure instructions. Instructions include ceasing certain medications such as blood thinning agents (e.g. aspirin, warfarin, clopidogrel) that increase the risk of bleeding and hence epidural hematoma formation. An epidural steroid injection, like other medical procedures, is not risk-free. There is a possibility of side effects and complications from the needle puncture and medications.

References

Other reading

• Roberts C, Tracy S, Peat B,Rates for obstetric intervention among private and public patients in Australia: population based descriptive study, British Medical Journal (BMJ), v321:p137, 15 July 2000

• Jun Zhang, Michael K. Yancey, Mark A. Klebanoff, Jenifer Schwarz and Dina Schweitzer, Does epidural analgesia prolong labor and increase risk of cesarean delivery? A natural experiment, American Journal of Obstetrics and Gynecology, Volume 185, Issue 1, July 2001, Pages 128-134.[1]

• Barbara L. Leighton and Stephen H. Halpern, The effects of epidural analgesia on labor, maternal, and neonatal outcomes: A systematic review, American Journal of Obstetrics and Gynecology, Volume 186, Issue 5, Part 2, May 2002, Pages S69-S77. Also available online.

• Boqing Chen and Patrick M. Foye, UMDNJ: New Jersey Medical School, Epidural Steroid Injections: Non-surgical Treatment of Spine Pain, eMedicine: Physical Medicine and Rehabilitation (PM&R), August 2005. Also available online.