Epidural administration (from Ancient Greek ἐπί, "on, upon" + dura mater) is a method of administration in which a drug is injected into the epidural space around the spinal cord. The epidural route is used by physicians and nurse anesthetists to administer local anesthetic agents, analgesics, diagnostic medicines such as radiocontrast agents, and other medicines such as glucocorticoids. Epidural administration is often accomplished through use of a catheter placed into the epidural space. The technique of epidural administration was first described in 1921 by Spanish military surgeon Fidel Pagés.
Epidural analgesia causes a loss of sensation, including pain, by blocking the transmission of signals through nerve fibres in or near the spinal cord. For this reason, epidurals are commonly used for pain control during childbirth and surgery. The technique is considered safe and effective for these purposes. When used during childbirth, there is no difference in adverse effects between earlier or later administration. An epidural injection may also be used to administer steroids for the treatment of inflammatory conditions of the spinal cord. An epidural is a complex procedure which must be administered by a trained person. It should not be used in some people with severe bleeding disorders or infections near the injection site.
Complications of epidural injections include problems resulting from improper administration, as well as side effects of the medicines administered. Side effects and complications of epidurals depend on the specific medication and dose being administered. Severe complications from epidural injections are rare. The most common complications of epidural injections include bleeding problems, headaches, and inadequate pain control. Epidural analgesia during childbirth may also impact the mother's ability to move during labor. Very large doses of anesthetics or analgesics may result in respiratory depression.
An epidural injection may be administered at any point of the spine - the specific administration site determines the specific nerves affected, and thus the area of the body from which pain will be blocked. There are multiple techniques to ensure proper placement and use of an epidural catheter. An epidural catheter may remain inserted for several days, but is usually removed when oral therapy becomes a viable alternative.
Pain relief during childbirthEdit
Epidural injections are commonly used to provide pain relief (analgesia) during childbirth. This usually involves epidural injection of opioids, commonly called an "epidural". This is more effective than oral or IV opioids and other common modalities of analgesia in childbirth. After an epidural is administered, a woman may not feel pain, but may still feel pressure. An epidural increases the ability of a woman to push with her contractions. Epidural clonidine is rarely used but has been extensively studied for management of analgesia during labor.
Epidural analgesia is considered a safer and more effective method of relieving pain in labor as compared to intravenous or oral analgesia. In a 2018 Cochrane review which included 52 randomized controlled studies involving more than 11,000 women, where most studies compared epidural analgesia with opiates, some advantages of epidural analgesia included better efficacy, fewer instances of naloxone use in newborns, and decreased risk of maternal hyperventilation. Some disadvantages of epidurals included an increase in the number of Caesarian sections required due to fetal distress, a longer labor, increased need for oxytocin to stimulate uterine contractions, an increased risk of hypotension and muscle weakness, as well as fever. However, the review found no difference in overall Caesarean delivery rates, and no evidence of negative effects to the baby soon after birth. Furthermore, the occurrence of long-term backache was unchanged after epidural use. Complications of epidural analgesia are rare, but may include headaches, dizziness, difficulty breathing and seizures for the mother. The child may experience a slow heartbeat, decreased ability to regulate temperature, and potential exposure to the drugs administered to the mother.
There is no overall difference in outcomes based on the time the epidural is administered to the mother, specifically no change in the rate of caesarean section, instrumental birth, and duration of labor. There is also no change in the Apgar score of the newborn, nor the cord blood pH, between early and late epidural administration. Epidurals other than low-dose ambulatory epidurals also impact the ability of the mother to move during labor. Movement such as walking or changing positions may help improve labor comfort and decrease the risk of complications.
Pain relief during other surgeryEdit
Epidural analgesia has been demonstrated to have several benefits after surgery, including decreasing the need for systemic opioid use, and reducing the risk of postoperative respiratory problems, chest infections, blood transfusion requirements, and myocardial infarctions. Use of epidural analgesia after surgery in place of systemic analgesia may also result in a reduced stress response,[clarification needed] as well as improve motility of the intestines through blockade of the sympathetic nervous system.
An epidural blood patch may be used to treat Post-dural-puncture headache, leakage of cerebrospinal fluid due to dural puncture occurring in approximately 1.5% of epidural neuraxial procedures. A small amount of a person's own blood is injected into the epidural space, clotting and closing the site of puncture. Another theory proposes that the injection of blood counteracts the decrease in cerebrospinal fluid from the puncture.[clarification needed]
The use of epidural analgesia and anesthetic is considered safe and effective in most situations. Epidural analgesia is contraindicated when an experienced person is not able to administer it, as well as in the case of infections such as cellulitis near the injection site and severe coagulopathy. In some cases, it may be contraindicated in people with low platelets, increased intracranial pressure, decreased cardiac output, and hypovolemia. Due to the risk of disease progression, it is also potentially contraindicated in people with preexisting progressive neurologic disease.
Risks and complicationsEdit
In addition to blocking nerves which carry pain, local anesthetics may block other types of nerve. Depending on the drug and dose, the effects may last only a few minutes or up to several hours. Sensory nerve fibers are more sensitive to the effects of the local anesthetics than motor nerve fibers. As such, an epidural can provide pain control without as much of an effect on muscle strength. For example, a woman in labor with a continuous epidural may not have impairment to her ability to move. A larger dose administered is more likely to result in side effects. Very large doses of epidural anesthetic can cause paralysis of the intercostal muscles and thoracic diaphragm, responsible for breathing. It may also result in loss of sympathetic nerve input to the heart, which may cause a significant decrease in heart rate and blood pressure.
If bupivacaine, commonly used for epidural pain control, is inadvertently administered into a vein, it can cause excitation, nervousness, tingling around the mouth, tinnitus, tremor, dizziness, blurred vision, or seizures as well as central nervous system depression, loss of consciousness, respiratory depression and apnea. Bupivacaine has been implicated in cardiac arrests resulting in death when accidentally administered into a vein instead of the epidural space. Large doses of epidural opioids may cause itching and respiratory depression.
The sensation of needing to urinate is often significantly diminished or completely absent after administration of epidural local anesthetics or opioids. Because of this, a urinary catheter is often placed for the duration of the epidural infusion. People with continuous epidural infusions of local anesthetic solutions typically ambulate only with assistance, if at all, in order to reduce the likelihood of injury due to a fall.
A potential complication of epidural analgesia is the failure to achieve adequate pain control. This can be caused by obesity, multiple prior births, history of opiate use, or cervical dilation of more than 7 cm at the time of administration.
If the dura is accidentally punctured, it may cause cerebrospinal fluid to leak into the epirudal space, causing a post dural puncture headache. This occurs in approximately 1 in 100 epidural procedures. Such a headache may be severe and last several days, and rarely weeks or months, and is caused by a reduction in CSF pressure. It is made worse when a person raises their head above a lying position. Mild post dural puncture headaches may be treated with caffeine and gabapentin, or if severe with an epidural blood patch. This consists of a small amount of a person's own blood administered into the epidural space to clot and seal the leak. Most cases resolve spontaneously with time. Less common but more severe complications include subdural hematoma and cerebral venous thrombosis.
In many women given epidural analgesia during labor oxytocin is also used to augment uterine contractions. In one study which examined the rate of breastfeeding two days following epidural anesthesia during childbirth, epidural analgesia used in combination with oxytocin resulted in lower maternal oxytocin and prolactin levels in response to breastfeeding on the second day following birth. This results in a decrease in the amount of milk produced.
Epidural administrations can also cause bleeding issues, including "bloody tap", which occurs in approximately 1 in 30–50 people. This occurs when epidural veins are inadvertently punctured with the needle during the insertion. It is a common occurrence and is not usually considered a problem in people who have normal blood clotting. Permanent neurological problems from bloody tap are extremely rare, estimated at less than 0.07% of occurrences. However, people who have a coagulopathy may have a risk of epidural hematoma. People with thrombocytopenia might also suffer from a bleed. A Cochrane review was conducted by comparing retrospective trials in 2018 to determine the effect of platelet transfusions prior to a lumbar puncture or epidural anesthesia for participants that suffer from thrombocytopenia. Evidence is unclear whether major surgery-related bleeding within 24 hours and the surgery-related complications up to 7 days after the procedure are affected by epidural use.
The epidural catheter may also rarely be inadvertently placed in the subarachnoid space (less than 1 in 1000 people). If this occurs, cerebrospinal fluid can be freely aspirated from the catheter. This is used to detect such occurrence, and the catheter will be withdrawn and replaced elsewhere, though occasionally no fluid is aspirated despite a dural puncture. If dural puncture is not recognized, large doses of anesthetic may be delivered directly into the cerebrospinal fluid. This may result in a high block, or, more rarely, a total spinal, where anesthetic is delivered directly to the brainstem, causing unconsciousness and sometimes seizures.
Rare complications of epidural administration include formation of an epidural abscess (1 in 145,000) or epidural haematoma (1 in 168,000), neurological injury lasting longer than 1 year (1 in 240,000), paraplegia (1 in 250,000), and arachnoiditis, Rarely, an epidural may cause death (1 in 100,000).
An epidural is injected into the epidural space, inside the bony spinal canal but just outside the dura mater ("dura"). In contact with the inner surface of the dura is another membrane called the arachnoid mater ("arachnoid"), which contains the cerebrospinal fluid. In adults, the spinal cord terminates around the level of the disc between L1 and L2 (in neonates it extends to L3 but can reach as low as L4), below which lies a bundle of nerves known as the cauda equina ("horse's tail"). Hence, lumbar epidural injections carry a low risk of injuring the spinal cord. Insertion of an epidural needle involves threading a needle between the bones, through the ligaments and into the epidural potential space without puncturing the layer immediately below containing CSF under pressure.
The person receiving the epidural may be seated, or lay lateral or prone. The level of the spine at which the catheter is placed depends mainly on the site of intended operation or the origin of the pain. The iliac crest is a commonly used anatomical landmark for lumbar epidural injections, as this level roughly corresponds with the fourth lumbar vertebra, which is usually well below the termination of the spinal cord. The Tuohy needle, designed with a 90-degree curved tip and side hole to redirect the inserted catheter vertically along the axis of the spine, may be inserted in the midline, between the spinous processes. When using a paramedian approach, the tip of the needle passes along a shelf of vertebral bone called the lamina until just before reaching the ligamentum flavum and the epidural space.
Along with a sudden loss of resistance to pressure on the plunger of the syringe, a slight clicking sensation may be felt by the operator as the tip of the needle breaches the ligamentum flavum and enters the epidural space. Saline or air may be used to identify placement in the epidural space. A systematic review from 2014 showed no difference in terms of safety or efficacy between the use of saline and air for this purpose. In addition to the loss of resistance technique, direct imaging of the placement may be used. This may be conducted with a portable ultrasound scanner or fluoroscopy (moving X-ray pictures).
After placement of the tip of the needle, a catheter or small tube is threaded through the needle into the epidural space. The needle is then withdrawn over the catheter. The catheter is generally inserted 4–6 cm into the epidural space, and is typically secured to the skin with adhesive tape, similar to an intravenous line.
Epidural administration is a procedure which requires the person performing the insertion to be technically proficient in order to avoid complications. Proficiency may be trained using bananas or other fruits as a model.
An epidural for pain relief may be used to administer a local anesthetic, an opioid, or both. Common local anesthetics used include lidocaine, mepivacaine, bupivacaine, ropivacaine, and chloroprocaine. Common opioids used include hydromorphone, morphine, fentanyl, sufentanil, and pethidine (meperidine). These are injected in smaller doses than required when administered intravenously. Other agents such as clonidine or ketamine are also sometimes administered through an epidural.
If a short duration of action is desired, a single dose of medication called a "bolus" may be administered. Thereafter, a bolus may be repeated if necessary provided the catheter remains undisturbed. For a prolonged effect, a continuous infusion of medication may be administered. There is some evidence that an automated intermittent bolus technique may provide better pain control than a continuous infusion technique even when the total doses administered are identical.
Typically, the effects of the epidural block are noted below a specific level or portion of the body, determined by the site of injection. A higher injection may result in sparing of nerve function in the lower spinal nerves. For example, a thoracic epidural performed for upper abdominal surgery may not have any effect on the area surrounding the genitals or pelvic organs. The intensity of the block is determined by the concentration of local anesthetic solution used.
The catheter is usually removed when it is possible to switch to oral administration. Catheters can safely remain in place for several days with little risk of bacterial infection, particularly if the skin is prepared with a chlorhexidine solution. Subcutaneously tunneled epidural catheters may be left in place for longer periods, with a low risk of infection or other complications.
The first record of an epidural injection is from 1885, when American neurologist James Corning of Acorn Hall in Morristown, NJ used the technique to perform a neuraxial blockade. Corning inadvertently injected 111 mg of cocaine into the epidural space of a healthy male volunteer, although at the time he believed he was injecting it into the subarachnoid space. Following this, in 1901 Fernand Cathelin first reported intentionally blocking the lowest sacral and coccygeal nerves through the epidural space by injecting local anesthetic through the sacral hiatus. The loss of resistance technique was first described by Achile Dogliotti in 1933, following which Alberto Gutiérrez described the hanging drop technique. Both techniques are now used to identify when the needle has correctly been placed in the epidural space.
In 1921 Fidel Pagés, a military surgeon from Spain, developed the technique of "single-shot" lumbar epidural anesthesia, which was later popularized by Italian surgeon Achille Mario Dogliotti. Later, in 1931 Eugen Aburel described using a continuous epidural catheter for pain relief during childbirth. In 1941, Robert Hingson and Waldo Edwards recorded the use of continuous caudal anesthesia using an indwelling needle, following which they described the use of a flexible catheter for continuous caudal anesthesia in a woman in labor in 1942. In 1947, Manuel Curbelo described placement of a lumbar epidural catheter, and in 1979, Behar reported the first use of an epidural to administer narcotics.
Society and cultureEdit
Some people have lasting concern, based on older observational studies, that women who have epidural analgesia during labor are more likely to require a cesarean delivery. However, evidence has shown that the use of epidural analgesia during labor does not have a significant effect on rates of cesarean delivery. A Cochrane review analysis of over 11,000 women confirmed there was no increase in the rate of Caesarean delivery when epidural analgesia was employed. Epidural analgesia does increase the duration of the second stage of labor by 15 to 30 minutes and may increase the rate of instrument-assisted vaginal deliveries as well as that of oxytocin administration.
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