Epidural anesthesia is a technique for perioperative pain management with multiple applications in anesthesiology. It is useful as a primary anesthetic, but most commonly it is used as pain management adjuvant. It can be a single shot or a continuous infusion for long term pain relief. Aside from the benefit of potentially providing excellent analgesia, its use reduces the exposure to other anesthetics and analgesics, decreasing side effects. It has also shown to decrease cortisol levels, expedite the return of bowel function, decrease the incidence of PE and DVT in the postoperative period, and shorten lengths of in-hospital stay.
The spinal cord is about 45 cm shorter than the spinal canal in the adult. It ends at L1 in 50% of the adults and L2 in about 40%. In the newborn, it goes down to L2-L3. Below this level, the lumbar and sacral nerves converge to form the cauda equine. The spinal cord is suspended in Cerebrospinal Fluid and surrounded by the arachnoid membrane. The arachnoid (and subarachnoid space) extends caudally in the adult to S2, to S3 in children and S4 in the newborn. The arachnoid is close to the dura mater. The dura is attached to the spine by its outer endosteal portion. It envelopes the brain intracranially, the spine and it also extends out through the foramina intervertebralia to the epineural connective tissues of the spinal nerves. The spinal epidural space contains fatty and connective tissues as well as vessels and lymph channels. These vessels may dilate with gravidity or ascites, which increase the likelihood of bloody puncture. The distance between the skin and the epidural space is variable depending on factors like age or weight. It may be 4 cm in normal-weight adults to 8 cm or more in obese patients. The epidural space has a dorsal limitation by the ligamentum flavum. More superficially, the remaining layers are the ligamentum interspinale (located between the spinous processes), ligamentum supraspinale (located on the surface of the spinous processes), subcutaneous tissue and skin.
Epidurals are useful for surgical anesthesia of thoracic surgery, major intra-abdominal surgery or spine surgery, granted that muscle relaxation is not needed. This technique may also be for intra-op or post-op pain management. It may decrease the surgical risk and morbidity of certain patient populations, for example, patients with ischemic cardiac disease. It also has shown to decrease post-op lung complications and increase the intestinal return of function after abdominal surgery.
Two approaches exist, medial (midline) and paramedian.
In the medial approach, the site of the insertion of the needle is between the spaces created by the vertebral spinous processes. Upon locating the desired spot, lidocaine 1% must be injected in the skin and underlying tissues to decrease the discomfort with the advancement of the epidural needle. Once achieving local anesthesia, the epidural needle must be advanced with its stylet in place and with its bevel point cephalad; this is ultimately going to contribute to the proper location of the epidural catheter. The epidural needle must be advanced through the skin, subcutaneous tissue, supraspinous, and interspinous ligaments. Once there, the stylet must be removed, and the Loss of Resistance syringe (filled up with saline, air or both) must be attached to the needle. The needle must be advanced while applying pressure to the plunger. Once the ligamentum flavum is pierced, a loss in resistance will be noted; this is the epidural space, and 5 to 10 cc of saline may be injected to expand the epidural space; this may decrease the risk of vascular injury.
In the paramedian approach, the insertion site of the needle is 1 cm lateral to the vertebral interspace. Local anesthetic must be administered as described for the medial approach. The epidural needle must then be advanced through the paraspinal tissues. Given this location, the needle will not transverse the supraspinous or interspinous ligaments. The advancement of the needle must stop upon feeling the engagement in the ligamentum flavum. The loss of resistance syringe must be then attached, and the epidural space must be located as described for the median approach.
Once either the midline or paramedian approach locate the epidural space, the epidural catheter must be advanced inside the needle after removing the loss of resistance syringe. The epidural catheter must be advanced to the 20 cm mark. The epidural needle is then removed, paying attention to the depth of the epidural space as indicated by the marks in the epidural needle. The epidural catheter is then withdrawn, aiming to leave its tip 5 to 6 cm into the epidural space; achieved by adding 5 to 6 to the depth of the epidural space. The resulting number is the mark at which the epidural catheter must be withdrawn.
Once the catheter is in its final position, a 3 cm syringe may be used to gently aspirate and rule out CSF leakage. If CSF is detected, the epidural catheter may be in the intrathecal space and must be relocated.
A test dose to rule out the intravascular position of the catheter is then performed, done by injecting 3 mL of 1.5% lidocaine with epinephrine (1 to 200000). An increase in HR of 20 to 30 bpm or 15 to 20 mmHg in systolic blood pressure, may indicate intravascular injection.
Caudal anesthesia is a variation of epidural anesthesia widely used in childhood. It is useful for interventions under the umbilicus line (circumcision, herniotomy, orchiopexy). The indications and contraindications match the ones described above.
The patient positioning is in lateral decubitus, and fetal position, the area sterile prepped and the hiatus sacralis located at the vertex of the sacrum, between the cornua sacra. The sacrococcygeal membrane must be pierced with a 22 to 25 G venous catheter in a 45-degree angle relative to the longitudinal axis of the body. The catheter must be advanced until the loss of resistance is felt. No additional advance must be attempted since the distance between the sacrococcygeal membrane, and the caudal end of the dural sac may be less than 10 mm. If CSF or blood is noted, the catheter must be repositioned. Once properly located, a test dose with Epinephrine 0.5 mcg/kg may be performed to rule out an intravascular injection.
The following complications can accompany epidural anesthesia:
The epidural technique is one of the earliest ones in the field of anesthesia. Properly performed, it is a safe technique that provides multiple benefits. It is usable as a sole anesthetic for surgical procedures, therefore decreasing the need for general anesthesia and airway management, with the risks that this implies. It also reduces the exposure to volatile anesthetics as well as it may potentially decrease the narcotics requirement, during or after a procedure. Hence lowering the incidence of the side effects associated with them; this is particularly relevant in the field of pediatric anesthesia since the controversy has been raised regarding the potential negative impact of certain anesthetic drugs in neurodevelopment. The epidural technique is also highly valuable for postoperative pain management as part of a multimodal approach.
There is a growing body of evidence that demonstrates the use of epidural anesthesia/analgesia techniques has positive effects like faster return in bowel function, a decrease of the hormonal stress response to pain, decrease in postoperative pulmonary complications, shortening in the length of in-hospital stay and patient satisfaction.
Close monitoring of the patient by nurses in the postoperative period is key to safety
Adequate consideration of risks and benefits is necessary on a case by case basis.
Safe and effective use of epidural anesthesia requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and pharmacists, all collaborating across disciplines to achieve optimal patient results. [Level V]
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