Epidural catheters are widely used in the surgical, obstetric, and chronic pain settings as they serve as an excellent adjunct or alternative to general anesthesia. Through an epidural catheter, local anesthetic and other adjuvants can be continuously infused or given intermittently, inhibiting pain signals at the nerve root. This method of administration can potentially decrease adverse side effects and hospital length of stay while maintaining or improving optimal patient safety. This article will discuss the indications, contraindications, anatomy, equipment, and techniques of epidural catheter placement.
The spine consists of 33 bony vertebrae. This includes 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal. The spinal cord runs through the vertebral canal, extending from the foramen magnum to roughly the L1 level in most adults. It is surrounded by three meningeal layers: the pia, arachnoid, and dura. Nerve roots emerge bilaterally at each vertebral level to innervate their respective dermatomes.
Epidural catheters are placed within the epidural space. The epidural space exists circumferentially between the dura mater and the ligamentum flavum, extending from the foramen magnum to the sacral hiatus. Within the epidural space lies epidural veins, fat, lymphatics, and nerve roots.
Epidural catheter placement can be performed in a sitting or lying position at the cervical, thoracic, lumbar, or sacral levels. When approaching the epidural space from a posterior midline approach, three ligaments are traversed from superficial to deep; the supraspinous ligament, the interspinous ligament, and the ligamentum flavum. The supraspinous ligament anchors the tips of each spinous process while the interspinous ligament anchors the body of each spinous process. The ligamentum flavum anchors the laminae of each vertebra and serves as the posterior aspect of the epidural space. The ligamentum flavum is identified by its tough, gritty feeling as compared to the other layers. When approaching from a paramedian approach, only the ligamentum flavum is traversed.
Local anesthetic (LA) and adjuvants are injected into the epidural space to anesthetize the spinal nerve roots. This is believed to be the principal site of action of epidural anesthesia. Blockade of the posterior nerve root interrupts somatic and visceral sensation, while blockade of the anterior nerve root interrupts motor and autonomic function. Sympathetic outflow derives from nerve roots of the thoracolumbar region (T1-L2) levels. Interruption of this transmission from epidural anesthesia thus produces a sympathetic blockade or “sympathectomy,” possibly resulting in variable decreases of blood pressure and heart rate. Alteration to respiratory function is generally spared given the cervical innervation of the diaphragm.
Surface landmarks can be used to approximate spinal levels. The nipple line approximates T4, the inferior border of the scapula approximates T7, and the superior aspect of the iliac crests approximates L4.
Epidural anesthesia can be used as an adjunct or primary anesthetic. Epidural anesthesia can be advantageous in cases where a prolonged duration of analgesia is anticipated, or the need for titration is favorable. Epidural anesthesia can also be considered for patients with difficult airways or other concerns for respiratory compromise secondary to the effects of general anesthesia. Common uses of epidural anesthesia include obstetric, abdominal, urogenital, or lower extremity procedures. While upper abdominal procedures are feasible with epidural anesthesia, it is less common due to the difficulty in safely achieving anesthesia to the desired sensory level.
Absolute contraindications to epidural placement include:
Relative contraindications to epidural placement include:
* The American Society of Regional Anesthesia provides recommendations for providers regarding the use of anticoagulants or antiplatelet drugs. Providers should review up to date information about medications.
Necessary equipment for epidural placement includes:
Epidural catheters should only be placed by qualified experts in the field. This typically includes a board-certified anesthesiologist or certified registered nurse anesthetist. Physicians of other specialties such as physical medicine and rehabilitation or neurology may also perform the procedure if within their scope of practice and training. A supporting staff member is commonly present during the procedure to assist as needed.
Preparation for epidural anesthesia should initially include obtaining a medical history and physical exam. Patients should be asked about their medical conditions, prior anesthesia exposures, current medications, other drug and supplement use, family medical history, including reactions to anesthesia, and allergies. A thorough physical exam should be performed focusing on the patients’ airway, neurologic functioning, and the structure and function of the back and spine. Vitals and laboratory values should be reviewed, with an emphasis on coagulopathy indicators. Given a variety of anticoagulation medications, clinicians should stay up to date with the recommended parameters before administering any form of neuraxial anesthesia. For example, patients undergoing unfractionated heparin doses of 7,500 to 10,000 units twice daily, neuraxial anesthesia should be delayed four to twelve hours. Meanwhile, patients taking warfarin must be reversed or withheld from taking the medication for five days and have a documented international normalized ratio (INR) of less than or equal to 1.4. The procedure, indications, complications, potential risks, and alternatives should all be discussed with the patient, and an informed consent document completed upon patient comprehension and agreement.
A time-out confirming patient identity, allergies, the indicated procedure, consent, and coagulation status should be performed prior to proceeding. The patient can be positioned in either the sitting or lateral decubitus position subject to provider preference and procedure indication. A position of spinal flexion and neutral rotation should be achieved to establish a straight path for needle insertion between the spinous processes.
In the sitting position, the patient should have the back of their knees as close to the edge of the table as possible. The patient should then be instructed to touch their chin to their chest with their hands resting on their thighs, and then to slouch, pushing the belly button back towards the administering provider. A supporting staff member should be present to safely assist and stabilize the patient, preventing a forward lean, and possible fall from the table. Positional aids such as pillows and stands may also be used as needed if available.
In the lateral decubitus position, laterality is chosen based comfort of the patient and on having adequate room for support personnel and the proceduralist. Similar to when in the sitting position, the patient should be positioned with their back closest to the administering provider. The patient should be instructed to draw their thighs towards their mid-section while pushing their belly button out towards the administering provider, thus producing spinal flexion. With the help of a supporting staff member, a neutral rotational position should be maintained, and the patient stabilized once properly positioned.
Standard ASA monitoring equipment should be placed on the patient prior to positioning. This includes noninvasive blood pressure, pulse oximetry, and A-line, as indicated. Procedure equipment should be opened and prepared in a sterile fashion according to the Practice Advisory for the Prevention, Diagnosis, and Management of Infectious Complications Associated with Neuraxial Techniques, published by the ASA in 2017. The equipment tray should be positioned to administering provider preference for ease of access and maintenance of sterility.
Patient pre-medication can be titrated as needed for patient anxiety. Caution should be taken to achieve minimal sedation, given the need for patient positioning, cooperation, and feedback throughout the procedure.
As described in the Practice Advisory for the Prevention, Diagnosis, and Management of Infectious Complications Associated with Neuraxial Techniques, the administering provider should practice aseptic technique. This includes washing hands and removing all jewelry and wearing a cap, mask, and sterile gloves.
The first step after patient positioning is to identify the target level and spot for epidural placement. This is done by palpating the two spinous processes corresponding with the desired spinal level for placement. The target area for needle insertion will be between these two processes. Once identified, an antiseptic solution is used to cleanse the target area with wide margins. The solution should be given adequate time to dry, usually three minutes. Once dry, the area is draped.
A 25 gauge (g) needle is then used to establish a skin wheel with local anesthetic at the target area. The target area is midline for a median approach and roughly 1 cm to 2 cm lateral of the midline for a paramedian approach. The needle can be penetrated deeper along the anticipated path of the epidural needle to anesthetize the subcutaneous tissue. Next, the epidural needle is introduced along the anticipated projected path, penetrating through the supraspinous and into the interspinous ligament. Note that in a midline approach, the needle is directed straight anterior while in a paramedian approach, the introducer should be directed at a roughly 45-degree medial angle. The epidural needle is then introduced with the needle bevel pointed cephalad through the introducer needle, where it will pass through the ligamentum flavum before reaching the epidural space.
Prior to advancing the epidural needle, a glass syringe is applied. This syringe can be filled with air or normal saline pending administering provider preference. The purpose of this syringe is to identify a loss of resistance as the spinal needle advances from the ligamentum flavum into the epidural space. Depending on provider preference, an intermittent or continuous pressure technique can be utilized. As soon as a loss of pressure is realized, immediately stop needle advancement to avoid postdural needle puncture. If using air for loss of resistance, caution should be taken to avoid injecting more than 1 ml to 2 ml, as this may result in a patchy anesthetic and even possible air embolism.
Upon loss of resistance, remove the syringe and count the visible markings to determine the distance to the epidural space. Then thread the epidural catheter to where the 20 cm mark reaches the needle hub. Resistance upon advancement may be variable, though the catheter should advance with gentle continuous pressure. After catheter placement, the needle can be removed with careful attention taken towards preventing removing the catheter with the needle. The mark at which the catheter enters the skin should be withdrawn to leave roughly 4 cm to 6 cm in the epidural space. While the optimal length of catheter insertion into the epidural space is debated, length beyond 4 cm to 6 cm in the epidural space is not recommended as it increases the chance for inadequate function.
After placement of the catheter, administer the catheter connector to the end of the catheter to enable attachment of syringes or tubing. Aspirate the catheter with an empty and dry 3 ml syringe to ensure no return of cerebrospinal fluid (CSF). If negative, proceed to administer a test dose. If positive (CSF return), remove the catheter, and attempt re-insertion at a different level.
The test dose is aimed at identifying unintentional intrathecal or epidural vein catheterization. Intrathecal catheterization could result in a total or high spinal while that of a vein could result in local anesthetic toxicity. A 3 ml solution consisting of 1.5% lidocaine and 1:200,000 epinephrine is commonly used. A positive test dose is indicated by acute onset tachycardia (20 to 30 beats above baseline) within one minute of administration (intravascular placement) or a dense motor blockade within five minutes of administration (intrathecal placement). Clinicians should be aware of the potential for a blunted response in patients receiving beta-adrenergic blocker medications. An increase in systolic blood pressure (15 mmHg to 20 mmHg) without tachycardia may also be interpreted as a positive test dose. Chloroprocaine may be used as a single test dose alternative as small dose intravascular or intrathecal injection will cause noticeable but significantly blunted LA systemic toxicity effects. It is important to keep in mind that a negative test dose is not a definitive confirmation of proper placement. Once completed, a transparent sterile dressing should be placed over the catheter site, and the remaining catheter can be secured with tape.
There are a variety of potential complications from epidural catheter placement. Intrathecal injection or overdose in the epidural space, potentially resulting in a high or total spinal are among the most detrimental. In the case of severe hypotension and bradycardia from a high spinal, epinephrine is the recommended first-line treatment. Other complications include:
Epidural catheters with spinal anesthesia is an excellent mode of anesthesia in a number of clinical situations. It is safe and effective with minimal complications when used appropriately. It has the potential to provide long-term analgesia when needed in select patient groups as well.
Epidural catheter placement is a skill that can humble the most seasoned of providers. To enhance first attempt success, the provider should give clear instruction to both the patient and assisting staff to achieve optimal positioning. In the case of placement for a laboring patient, an early discussion should be had so that optimal timing of placement can be determined, as opposed to waiting until a time of extreme distress. Other considerations include having all necessary equipment accessible and ready for placement, optimize bed height and room lighting before beginning, utilizing sterile technique, and considering allowing an alternative provider to attempt after multiple failed attempts. When combined, such considerations may improve patient safety and efficacy of care, ultimately improving patient outcomes and satisfaction.
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