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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 (sometimes called the 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.

Contents 1 Epidural anesthesia 1.1 Indications 1.2 Technique 1.3 Combined spinal-epidurals 1.4 Caudal epidurals 1.5 Side effects 1.6 Complications of epidural use 1.7 Other concerns 1.8 Contraindications 1.9 Cautions 2 Epidural analgesia in childbirth 3 Epidural steroid injection 4 References 5 Other reading 6 External links

[edit] Epidural anesthesia

[edit] 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, 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.

[edit] Technique

Using a strict aseptic technique a small volume of local anaesthetic, such as 1% lignocaine (lidocaine in the U.S.), is injected into the skin and interspinous ligament. A 16, 17, or 18 gauge Tuohy needle is then inserted into 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<ref>Norman D. Epidural analgesia using loss of resistance with air versus saline: does it make a difference? Should we reevaluate our practice? AANA J 2003;71:449-53. PMID 15098532</ref>.

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.

[edit] 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.

[edit] 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.

[edit] 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 labouring woman may have an epidural running during labour 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 complete loss of sympathetic function, even to the heart itself, causing a profound drop in heart rate and blood pressure. This requires emergency treatment, and usually general anaesthesia. This happens because the block height is too high ("high block") and the epidural is blocking the heart's own 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.

[edit] 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 1 in 100 insertions). 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 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).
• Death (extremely rare, less than 1:100,000).

[edit] Other concerns

Back pain is occasionally reported after epidural insertion, and the epidural may be blamed. However, there is no good evidence linking epidural insertion to back pain. In women who have recently given birth, the incidence of back pain in those who had epidurals is not different from those who did not.

Occasionally, spurious studies appear which suggest that epidural analgesia during childbirth is responsible for behavioural problems in the baby, such as delay in establishment of breast feeding. The evidence for such conclusions is extremely poor.

[edit] 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

[edit] 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)
• Large lower back tattoos (unless sufficient ink-free space is available)<ref>Tattoo dilemma, a March 2006 Hamilton Spectator article</ref>

[edit] 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 recent study in Australia (Roberts, Tracy, Peat, 2000) demonstrated 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).

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<ref>Thorp JA, Breedlove G. Epidural analgesia in labor: an evaluation of risks and benefits. Birth. 1996 Jun;23(2):63-83. PMID 8826170.</ref> An alternative explanation is that women having difficult labours are more likely to request epidurals, and are also less likely to have an unassisted vaginal birth.

It is important that expectant mothers receive accurate information about the benefits and risks of the procedure, as well as about their other pain-relief options, in order that they may make an informed decision.

Less common in labor is spinal anaesthesia in which a much smaller needle (26G or 27G) is advanced slightly further to penetrate the dura (and arachnoid) and allow a rapid achievement of analgesia or anaesthesia depending on the dose given.

[edit] Epidural steroid injection

An epidural injection, or epidural steroid injection, is used to help reduce 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 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 that includes physical therapy. The effects of an epidural steroid injection may be temporary or long-term. The injection works by reducing the inflammation and/or swelling of nerves in the epidural space.

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

After the procedure, the patient is returned to the recovery area and monitored for a period of time before being released home. Patients may 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 patients scheduled for an epidural steroid injection follow the pre-procedure instructions provided. Instructions include stopping certain medications such as blood thinning agents (e.g. aspirin, warfarin, clopidogrel) which can 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 used.

[edit] References

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[edit] 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.

[edit] External links

• Epidurals for pain relief in labour Comprehensive information with women's stories - informedhealthonline.org
• Wendy Bellissimo: Willow's birth - The designer's story of her epidural during the birth of her third child
• Epidural and nerve root injections pain treatment explainedde:Periduralanästhesie

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