Neuraxial anesthesia or analgesia is the injection of the local anesthetic in the areas surrounding nerve roots from the central nervous system (CNS). Spinal anesthesia involves the injection of the local anesthetic in the cerebrospinal fluid (CSF) flowing in the subarachnoid space while epidural anesthesia or analgesia the local anesthetic (LA) is infiltrated in the fat tissue that surrounds the spinal nerve roots in the epidural space using a catheter inserted in the space through an epidural needle.
As a result, blockage of motor, sensory, or sympathetic impulse can occur in different combinations and degrees depending on variables such as dose, concentration, or volume of the LA. Epidural anesthesia can be performed at any level of the vertebral column, and the choice of placement depends on the desired anesthetic level. In contrast, spinal anesthesia is usually performed below L2 to avoid injury of the spinal cord.
During epidural anesthesia or analgesia, the epidural space is reached by inserting an epidural needle between two vertebrae in the cervical, thoracic or lumbar spine. The needle goes through different layers of tissues to reach the epidural space.
The boundaries of the epidural space are:
Epidural anesthesia can be used to supplement general anesthesia or as the main anesthesia method in certain surgical procedures involving thoracic, abdominal, pelvic, or lower extremities regions. However, spinal anesthesia is more commonly used in these instances.
Epidural analgesia is indicated for pain management during or after surgical procedures involving the regions previously mentioned, severe chronic pain in the context of malignancy, and for labor and delivery.
Epidural anesthesia is achievable using either the classic epidural, the combined spinal-epidural (CSE) technique, or dural puncture epidural (DPE). CSE and DPE include an additional step consisting of delivering a spinal dose of LA and coadjuvants (CSE) or only puncturing the dura mater (DPE) using a spinal needle. For this reason, it is essential to include a spinal needle as part of the equipment along with the epidural needle, empty syringe for loss of resistance testing, and epidural catheter.
Monitoring the patient hemodynamic status during the procedure is very important. The minimum monitors required are pulse oximeter for pulse and oxygen saturation as well as blood pressure cuff and continuous EKG to assess cardiovascular status.
Several drugs can be used in different combinations to achieve neuraxial anesthesia:
Local anesthetics: Llidocaine1% and 2%, bupivacaine 0.25%, 0.5% and 0.75%, tetracaine 0.5%, mepivacaine 1%, 1.5% and 2%, ropivacaine 0.75%, levobupivacaine 0.5%, chloroprocaine 2% and 3%.
Epidural Additives: Vasoconstrictors such as epinephrine and phenylephrine are used to decrease the vascular absorption of local anesthetics.
Opioids: fentanyl, morphine, hydromorphone, oxycodone, or sufentanil (augment analgesic effects of the LA).
Alpha-agonists: clonidine prolongs epidural analgesia.
Palpating the spine and recognizing the spinous processes can be challenging in obese and morbidly obese patients. The ultrasound helps to identify bony structures and the epidural space in these cases. Also, it has been associated with a decrease in procedure time and the number of attempts when compared to palpation alone. The identification of the midline is the most important use of the ultrasound for neuraxial anesthesia, which could be challenging in abnormal spine anatomy and fat accumulation in the area of the puncture.
Epidural anesthesia requires to be provided by a qualified and skilled professional. Most of the time, neuraxial anesthesia is provided by a board-certified anesthesiologist or an anesthesiology resident under supervision. Physicians specialized in pain management from neurology or emergency medicine and certified registered nurse anesthetists can also provide neuraxial anesthesia. A certified nurse presence is very important during and after the procedure to monitor the patient and baby (labor epidural analgesia) and to detect early signs of complications.
A comprehensive history, including allergies, must be taken from the patient with the primary purpose of anticipating complications and ruling out relative and absolute contraindications. A complete physical exam also contributes to this purpose. The physical exam focused on the spine is important to notice infection of the area and anatomical abnormalities or variations that can potentially affect the procedure. All the monitors must be placed and working, intravenous access placed, time out should take place before the procedure, and asepsis and antisepsis must be maintained. Risks must be discussed, and informed consent obtained.
Positioning: The patient's position plays a pivotal role in the procedure's success. Epidural placement can be performed more commonly in a lateral decubitus and sitting position or less frequently in the prone position. In the lateral decubitus position, the patient is completely resting on their side on the bed surface, and the spine is parallel to that surface as well. Thighs and neck are flexed forward, imitating fetal position. In the sitting positioning, the patient is sited on the bed or OR table, and the spine is perpendicular to the table's surface. The goal is to curve the spine forward in a letter "C" shape. Asking the patient to hug a pillow and placing a stool to rest their feet help to achieve correct positioning.
The epidural needle can be placed using the midline or paramedian approach. In both cases, lidocaine 1% is infiltrated in the epidural needle insertion area.
In the midline approach technique, the needle is placed in the midline between 2 spine processes. In the paramedian approach technique, the needle is inserted 1 cm lateral and 1 cm caudal to the lower border of the upper spinous process.
The epidural needle is advanced through ligaments and soft tissue. The epidural space is localized by using the loss of resistance (LOR) syringe. The syringe is filled with normal saline or air, and the resistance is tested by advancing the needle connected to the syringe and pushing its plunger until the resistance is lost once the epidural space is reached.
After reaching the epidural space, the syringe used for LOR is removed, and the epidural catheter inserted through the epidural needle. The catheter will be used to administer medications through bolus or infusion.
Maintenance of Analgesia Techniques
Intermittent injection of analgesics through the epidural catheter offers a better area of distribution and less LA consumption when compared to continuous infusion. On the other hand, intermittent boluses provide fluctuation between pain and analgesia with adequate pain management after bolus administration and increasing pain levels after analgesics start to wear off.
Continuous epidural infusion (CEI)
Continuous infusion of local anesthetics and opioids has been widely implemented after its first description because of its practicality and possibility to achieve stable analgesia. However, it has been associated with increased local anesthesia consumption and, therefore, profound and sustained motor blockade.
Patient-controlled epidural analgesia (PCEA)
This technique was described in 1988 by Gambling for the first time. The implementation of this method allows the patient to adjust the time of local anesthetic dosing to contractions and modify the intervals as labor progresses. One of the downsides of this method is the elevated cost of the equipment when compared to the CEP technique. Also, more training and staff education are involved. On the other hand, PCEA has shown lower total dose usage of bupivacaine and ropivacaine compared to CEI.
Neuraxial anesthesia allows the possibility of performing surgical procedures without putting the patient under general anesthesia. As a result, neuraxial anesthesia decreases the use of intravenous narcotics in the perioperative period and their effect on the patient, including respiratory depression, nausea, ileus, pruritus, etc. Also, it eliminated ventilator-associated complications and allows to evaluate the patient's neurological status.
Epidural anesthesia is routinely offered to laboring parturients to achieve pain management during labor, delivery, and the immediate postpartum period. Consequently, neuraxial analgesia can improve exhaustion and overall satisfaction in the obstetric population.
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