Also known as: Epidural Analgesia, Epidural Anesthesia, Thoracic Epidural, Lumbar Epidural, Regional Anesthesia
1. Description of the problem
What every clinician needs to know
Epidural anesthesia is used extensively in anesthesia practice because of the reduction of postop morbidity and mortality that it may confer. Many of these benefits may correspond to the ICU patient as well. Guidelines on contraindications to epidural analgesia are well established in anesthetic practice, but there seems to be little evidence or guideline use for epidurals in the ICU. Epidural analgesia has been shown to improve early return of ambulation, deep breathing, bowel function and coughing after abdominal surgery.
Several randomized studies support the use of epidurals in the postsurgical thoracic and abdominal patient when compared to intravenous opiates. Studies have also demonstrated reduced extubation times, decreased tachycardia, decreased myocardial ischemia, fewer MIs, and reduced ICU and hospital length of stay.
Placement of an epidural catheter enables local anesthesia and opiates to be administered close to the dermatomes of the surgical site. This allows maximum analgesia using relatively small doses at the site where pain fibers enter the spinal cord. Once in situ, the epidural will decrease the need for opiates, improving gut motility and decreasing respiratory problems, as well as causing less somnolence.
Indications for epidural anesthesia (EA) in the ICU include blunt trauma with or without rib fractures, thoracic, abdominal, orthopedic and vascular surgery, as well as nonsurgical problems such as intractable angina pectoris and acute pancreatitis.
Epidural analgesia is a pharmacologic approach to pain management that should be considered following an appropriate assessment of a patient’s pain. When combined with other pharmacologic agents and nonpharmacological interventions, patients can achieve better pain control, decreased suffering and anxiety, and improved physiologic outcomes. The implementation of comprehensive plans for pain management in this patient population may result in enhanced patient outcomes and reduced lengths of stay in both the ICU and, consequently, the hospital overall.
Key management points
When epidural analgesia is being considered, appropriate patient selection is important. Patients are selected based on an assessment inclusive of the overall patient status, risks, benefits, indications and contraindications of epidural analgesia.
Anticoagulation, once considered a relative contraindication to the use of epidural analgesia, has been a focus for the American Society of Regional Anesthesia and Pain Medicine (ASRA), which has published consensus statements concerning regional anesthesia and anticoagulation. These statements present the safety, efficacy, and risks of neuraxial anesthesia and analgesia based on the timing of needle insertion and catheter removal in relation to the time anticoagulants are administered. (See “Contraindications for epidural analgesia” below.)
For the patient selected for epidural analgesia administration, an appropriately placed and functioning epidural catheter can produce pain relief that is superior to other routes of analgesic administration. Placement of the epidural catheter requires technical skill on the part of the critical care provider, but nurses need to demonstrate a knowledge base regarding the anatomy of the epidural space, the surrounding structures, epidural catheter care, and patient care before and after catheter insertion. (See Figure 1)
The epidural space is a potential space occupied by fatty tissue, blood vessels and lymphatics. The posterolateral portion of the epidural space lies between the dura mater of the spinal cord and ligamentum flavum and laminae.
Epidural analgesia can be administered by three methods: single-injection and intermittent boluses, continuous infusion via an indwelling catheter or patient-controlled epidural analgesia (PCEA). Single-injection or intermittent epidural bolus requires the use of longer-acting opioids (e.g. preservative-free morphine) to achieve a realistic duration of analgesia.
The use of morphine for single-injection administration carries an increase in the risk of delayed-onset respiratory depression. Single-injection method or intermittent bolus of opioids results in a delay in the response to the patient’s complaints of continued pain because the anesthesia provider must be notified and respond to the request for pain management.
Continuous epidural infusion offers the distinct advantage of providing steady-state analgesia when compared with single-injection administration or intermittent boluses, especially when short-acting opioids are used for infusion.
Because it combines the benefits of continuous infusion with intermittent demand boluses, PCEA is gaining favor in many institutions. It affords patients control over their own pain management by allowing self-administration of boluses by way of a preset dose. Patients administer the dose on demand when their severity of pain increases.
Considering the severity of illness of patients in the ICU, continuous epidural infusions offer the most efficacious treatment for pain management. To initiate epidural analgesia, the anesthesia provider accesses the epidural space employing aseptic technique. The epidural catheter is inserted with the patient in the sitting or the side-lying position. If the patient is awake during catheter insertion, he or she will require assistance with positioning and reassurance throughout the procedure.
The catheter is placed using knowledge of dermatomes as they relate to a level appropriate to the anatomical site of pain. The catheter is secured with a bio-occlusive dressing to minimize catheter movement and to allow for inspection of the epidural catheter site for drainage, redness or inflammation. After the catheter is secured, it should be clearly identified as an epidural catheter, with a suitable label indicating “epidural catheter” to prevent inadvertent injection to the epidural space.
Continuous epidural infusion can usually provide analgesia for 5-7 consecutive dermatome areas. For patients with multiple sites of pain, other methods of analgesia may need to be implemented. An epidural catheter positioned within the dermatome region of the pain and catheter integrity promote the success of analgesia. For longevity of use (e.g. if a catheter is required for more than 48 hours) the catheter can be tunnelled so that the point of exit to the skin is away from the insertion point.
Contraindications for epidural analgesia
Infection at proposed catheter insertion site.
Acute, symptomatic hypovolemia (shock).
Allergy to local anesthetic agents and opioids.
Increased intracranial pressure.
Allergy to local anesthetic agents or opioids.
Complications of epidural analgesia
Hypotension and bradycardia
Hypotension and bradycardia are two very important potential hemodynamic consequences of epidural-induced sympatholysis. A recent prospective multicenter randomized trial found the incidence of hypotension after epidural or general anesthesia, defined as a greater than 30% reduction from baseline blood pressure, to be 41%, compared with 23% after general anesthesia alone (P = 0.049).
There were no significant differences in heart rate or episodes of bradycardia. Strategies employed to balance these untoward effects include preinduction fluid administration (500 ml of crystalloid or colloid before the block), avoidance of lidocaine and selected use of epidural fentanyl. Most important is the recognition of these problems. Early recognition and treatment lead to uneventful resolution of this problem.
Despite the known cardiovascular side effects of epidurals, recent analysis of POISE 2 trial subjects who received epidural analgesia did not demonstrate increased incidence of death nor nonfatal myocardial infarction.
Large surveys of patients receiving morphine through epidural catheters have found the incidence of respiratory depression to be less than 1%, which is comparable to parenteral and oral morphine. Additionally, the combination of epidural opioid and local anesthetic can reduce the amount of opioid needed. Epidural opiates have been shown to cause the same problems as via the parenteral route, with the exception of increased pruritus.
Twenty to eighty percent of patients receiving intrathecal opioids and 20%-93% of patients receiving epidural opioids get widespread pruritus. This can often be debilitating and has even led to the removal of epidural catheters. Large research studies have been undertaken to find agents that deal with this unpleasant sensation. One option is to take the opiate out of the epidural and just run a local anesthetic. Other strategies include adding pharmacological agents to decrease the pruritus. Effective agents include antihistamines, naltrexone, methylnaltrexone, ondansetron, propofol and naloxone.
Due to the lack of movement of the patient once the epidural is in place there is the potential for pressure sore formation in the dependent areas. To avoid this, one needs to pay meticulous attention to keeping the patient from remaining in one position for extended periods of time.
Under the influence of epidural analgesia, patients may not feel the urge to urinate, which may result in bladder over-distention and urinary retention.
Scott et al. monitored 505,000 epidural blocks in parturients, finding only 38 single root neuropathies (0.75/10,000). All deficits resolved by 3 months except for one. In a similar study involving 123,000 regional anesthetics in parturients, 46 cases of single nerve root neuropathy were reported (3.7/10,000), with complete recovery in all patients by 3 months.
Cardiac arrest occurred significantly more commonly following spinal anesthesia compared to epidural (6.4 vs. 1/10,000). While fatal cardiac arrest occurred in elderly patients undergoing hip arthroplasty (5/6), most recovered without sequelae. In obstetric patients, there were 3 cardiac arrests in 505,000 epidurals (0.06/10,000). Two patients recovered without sequelae and one had brain damage after severe hypotension following a “top-up.”
Intravascular administration of bupivacaine will result in cardiac arrest. Bupivacaine binds avidly to the sodium channel in a “fast in, slow out” manner. Thus, cardiac resuscitation is extremely difficult and often requires cardiopulmonary bypass until the bupivacaine dissociates from the sodium channel and is metabolized. Intravenous lipid emulsion is the standard treatment for local anesthetic systemic toxicity.
Post dural puncture headache
Headache is a frequent complication of dural puncture. Cerebrospinal fluid leakage from the subarachnoid space decreases the cushioning effect the fluid has on the brain, producing traction on nerves and blood vessels. The headache, worse when the patient’s head is elevated, and usually located in the frontal and occipital regions, is often associated with neck stiffness and nausea. The symptoms typically occur the day after dural puncture and are normally limited to 5 or 6 days.
The post-lumbar puncture headache’s incidence and severity are directly related to needle size. The mainstays of treatment are hydration and bedrest. Analgesics and tranquilizers can be used to relieve anxiety and muscle spasm. Severe symptoms unresponsive to conservative measures have been treated with an epidural blood patch. The success rate of this therapy is over 90%.
Epidural catheters may rarely break or shear. Catheters are never to be withdrawn through the needle. If part of a catheter is left in a patient, the patient should be informed. However, no surgery or attempts to retrieve the catheter are warranted unless there are persistent neurologic symptoms.
The epidural space is remarkably tolerant to chemical contamination, but the subarachnoid space is not. Drugs that have been accidentally injected into the epidural space without sequelae include thiopental, magnesium and TPN. Only undiluted KCl produced permanent paraplegia following epidural administration.
This is another feared but rarely seen complication of regional anesthesia (1/150,000-250,000) in healthy patients. Most epidural hematomas following regional anesthesia occurred in patients with hemostatic abnormalities, particularly those on anticoagulants. Low-molecular-weight heparins (LMWH) have been responsible for over 35 epidural hematomas following regional anesthesia and should be considered a strong, relative contraindication.
The symptoms of epidural hematoma are bilateral leg weakness, urinary incontinence and loss of rectal sphincter tone. These severe neurologic deficits may be preceded by sharp pain in the back or legs with progression over a few hours. Prolonged motor paralysis without regression of block should raise suspicion. Stat CT or MRI is indicated. CT should be reserved for when MRI is unavailable as there are reports of false negatives. Symptomatic epidural hematoma must be decompressed surgically within 6 hours for the best chance of full recovery.
Symptomatic epidural hematomas are usually associated with anticoagulation, catheter placement/removal during anticoagulation, and/or trauma during catheter placement. A review of 61 cases of symptomatic epidural hematomas found that 41 (68%) patients had coagulation defects. This association has led to one of the most controversial issues surrounding epidural anesthesia: the use of anticoagulation and risk of epidural hematoma formation.
The American Society of Regional Anesthesia and Pain Medicine (ASRA) has addressed the use of anticoagulation and epidural anesthesia. The ASRA reviewed several studies using therapeutic and/or subtherapeutic anticoagulation with epidural anesthesia. Therapeutic anticoagulation and epidural anesthesia had been used in 1,000 vascular surgery patients treated either with perioperative Coumadin (INR greater than 1.5) or with intravenous intraoperative heparin without the development of epidural hematomas. All of these patients had their epidural catheters safely removed after 48 hours.
Two other large studies of more than 650 orthopedic patients with epidural catheters receiving low-dose Coumadin postoperatively showed no evidence of epidural hematomas. The safe use of unfractionated subcutaneous heparin for deep venous thrombosis (DVT) prophylaxis and epidural anesthesia was supported in a review of more than 5,000 patients.
Thus, the safety of both therapeutic anticoagulation and DVT prophylaxis has been affirmed in multiple studies and by the ASRA. In addition, the other noted benefits of improved lower extremity blood flow, anticoagulant properties of local anesthetic and earlier mobility will likely augment the benefits of anticoagulation.
LMWH deserves particular attention because of the disparity in the literature regarding the risk of epidural hematoma. LMWH was first approved for use in Europe before its release in the United States in 1993. Review of the European experience with epidural anesthesia and LMWH in over 9,000 patients reported no bleeding complications associated with LMWH and regional anesthesia.
However, in the United States, there were several reports of hemorrhagic complications during LMWH use. Over a 5-year period between 1993 and 1998, 40 epidural hematomas were reported in association with LMWH, an incidence of approximately 1 in 10,000. The reason for the difference between the two continents was thought to be the dosing (higher doses in the USA), timing differences and the more frequent use of spinals in Europe, which carry a lower risk than epidurals.
In any case, the higher bleeding complications associated with LMWH and the inability to reverse its effects warrant caution, and the risk of epidural hematoma should be compared with the potential benefits of epidural anesthesia on an individual basis. The ASRA maintains an excellent informative website, http://www.asra.com/items_of_interest/consensus_statements/index.iphtml, which provides current recommendations regarding the application of regional anesthesia during various forms of anticoagulation.
As a last point it is important to mention that half of all hematomas occur at catheter removal rather than insertion. Practitioners need to be aware of the anticoagulation status of the patient.
Novel oral anticoagulants and platelet inhibitors
The past several years has seen the introduction of a new group of oral anticoagulants used for prevention of stroke in nonvalvular atrial fibrillation, venous thromboembolism (VTE) prophylaxis after total joint replacement, and treatment of VTE. These include the direct thrombin inhibitor dabigatran and factor Xa inhibitors rivaroxaban and apixaban. Elimination half-lives for dabigatran, rivaroxaban, and apixaban are 12-17 hours, 9-13 hours, and 15.2 hours, respectively. Half-life for all three drugs is prolonged in renal dysfunction. Eighty percent of dabigatran’s excretion is renal, and elimination half-life increases to 28 hours in end-stage renal disease. An interim update to ASRAs 3rd edition of guidelines for regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy suggested the following discontinuation interval for placement or removal of an epidural catheter in patients receiving these therapies: 5 days for dabigatran, 3 days for rivaroxaban, and 3 days for apixaban. For all three, anticoagulation therapy may be reinstituted 6 hours after catheter removal.
Antiplatelet medications including NSAIDs, thienopyridines, and glycoprotein IIb/IIIa inhibitors are used in primary and secondary prevention of thrombotic cardiovascular complications. Neuraxial techniques may be safely performed in patients on low dose aspirin (60-325 mg) and other NSAIDs. The thienopyridines, clopidogrel, ticlopidine, and prasugrel interfere with platelet-fibrinogen, and platelet-platelet interactions through ADP receptor antagonism. Current guidelines suggest awaiting return of platelet function prior to placement of an epidural catheter. This means waiting 5-7 days, 14 days, and 7-10 days for clopidogrel, ticlopidine, and prasugrel, respectively. Ticagrelor also works through ADP receptor antagonism. Recent guidelines suggest discontinuation for 5-7 days prior to initiating neuraxial anesthesia in patients receiving ticagrelor. Glycoprotein IIb/IIIa inhibitors, including tirofiban, eptifibatide, and abciximab, have a shorter duration of action. Return of normal platelet function can be expected in 8 hours for tirofiban and eptifibatide, and 24-48 hours for abciximab.
Epidural abscess is rare, accounting for 0.2-1.2/10,000 tertiary hospital admissions. Epidural abscess is usually due to infection in the body seeding the epidural space. Bacterial colonization of epidural catheters is not uncommon. A recent bacteriologic study involved culturing epidural catheters after removal; 8.8% of catheter tips had positive cultures, though no patient had superficial or deep infection. In one review, epidural anesthesia was associated with only in 1 in 39 epidural abscesses, while epidural anesthesia was unrelated to 35 abscesses in another review. Symptoms of epidural abscess usually develop a few days to a few weeks after delivery.
In a series of over 500,000 epidurals, only one patient (diabetic) developed an abscess, albeit 11 months after delivery! Symptoms include fever, malaise, headache and back pain at the level of the infection. Pain will be found on deep palpation over the site. White blood cell count will be elevated. Progression of symptoms to nerve root pain usually takes 1-3 days. Neurologic deficits will progress as the spinal cord is compressed, including lower extremity pain, weakness, bowel and bladder dysfunction and paraplegia. Surgical treatment is necessary.
Preparation of patients
Regardless of the indication for epidural analgesia, patients and their family members must be adequately prepared for this type of pain control. Prior to placement of the epidural catheter, patients/families should be allowed to voice any concerns they have regarding this technique. Explanations should be given in layperson’s terms about how epidural analgesia works and any side effects that may be experienced. Emphasize that these side effects are temporary during epidural administration and that they can be treated.
Patients may also require reassurance that they will not be asleep after the catheter is placed but that the epidural drugs will control their perception of pain. Lastly, patients should know how long the epidural is intended to be utilized, what analgesic regimen will be followed, and that the epidural drugs will not be stopped without provision for alternative pain control.
Sites for catheter placement
With the advent of epidural analgesia, many catheters were placed in the lower lumbar region, between L4 and L5. In this location, catheter placement is technically easier to perform as the spinal cord terminates above this area. However, with increased utilization of epidural analgesia, it has been shown that pain may be best relieved by placing the catheter at different sites depending on the location of the patient’s pain and/or surgical incision.
The actual site for catheter placement is determined by the dermatome innervating the area of pain. With thoracic procedures, the catheter is placed between T2 and T8, depending upon whether the upper or lower lobes of the lung are affected. Mund et al. reported that the majority of epidural catheters in lung transplant patients were inserted at the level of T9 (with a range from T4 to L4).
Similarly, with upper abdominal, orthopedic and peripheral vascular procedures, catheters are placed between T4 and L1, T10 and L3, and L4 and L5, respectively. In the case of trauma, the epidural catheter is placed directly at the site of injury. Selecting the proper dermatome level is even more important when the patient will receive epidural local anesthetics (compared to opioids) as these agents block both afferent and efferent nerve fibers.
Insertion of an epidural catheter is done by an anesthesiologist, physician in another specialty who has been granted clinical privileges by the institution, physician assistant or CRNA. Epidural catheters may be placed in the operating room or as a sterile procedure at the patient’s bedside. Strict aseptic technique must be used during the insertion, as well as with any contact with the solution, infusion, dressing or site, to prevent contamination. The lateral decubitus or sitting position is used for catheter insertion. These positions allow for maximal separation between the intervertebral spaces. The site is then prepared using topical antiseptic and sterile drapes.
A local anesthetic such as lidocaine is injected into the insertion site. A sterile syringe with air or preservative-free, sterile normal saline is attached to a blunt spinal needle, inserted into the selected interspace and advanced using gentle pressure. This technique, known as loss of resistance, is the most reliable placement technique, as the three tough ligaments that surround the spinal cord do not permit injection unless the needle has entered the epidural space. After the needle has entered the epidural space, normal saline or air may then be easily injected. The potential of intrathecal placement or nicking the dura is decreased by the fact that the flow from the needle pushes the dural layer away.
The hanging drop technique is another method for catheter placement. With this technique, it is believed that as the spinal needle enters the epidural space, negative pressure draws a drop of normal saline inward. As an additional measure, some centers place epidural catheters under fluoroscopy.
With either technique, a flexible catheter is threaded through the spinal/Touhy needle and advanced 2-3 cm into the epidural space. The spinal needle is then carefully removed and a slide-lock adapter is attached to the end of the catheter. This adapter permits attachment of the catheter to an injection port or infusion tubing. A filter can also be attached to the infusion tubing to ensure the injectate remains sterile and to prevent introduction of microparticles or bacteria into the epidural space. The filter may also be used with intermittent administration setups.
Catheter placement must be verified to avoid injection of the narcotic into the intrathecal space. The two techniques used to verify catheter placement are aspiration and the use of a test dose. However, the inability to aspirate or the presence of a negative test dose does not guarantee correct catheter placement.
The aspiration method involves attaching a syringe filled with 2 ml of preservative-free sterile normal saline to the end of the catheter and aspirating gently for 30 seconds. If no aspirate is obtained, the catheter should be in the epidural space. If more than 1 ml of clear fluid that tests positive for glucose is obtained, the catheter is most likely in the subarachnoid space. Bloody aspirate indicates that the catheter has punctured an epidural vein.
Additional verification of catheter placement may be performed by administering a test dose of a local anesthetic, such as bupivacaine or 1.5% lidocaine with 1:200,000 epinephrine. An increase in heart rate or blood pressure indicates that the tip of the catheter may be in an epidural vein. Loss of sensory or motor function in the lower extremities or lower abdomen with a decrease in blood pressure over 1-5 minutes indicates that the catheter tip may be in the intrathecal space. In the presence of these findings, the narcotic should be withheld until catheter placement can be fully assessed.
What's the Evidence?
Leslie, k, McIlroy, D, Kasza, J. “Neuraxial block and postoperative epidural analgesia: effects on outcomes in the POISE-2 trial”. Br J Anaesth. vol. 116. 2016. pp. 100-12.
Killoran, PV, Cattano, D. “From bedside to bench and back: perfecting lipid emulsion therapy for local anesthetic toxicity”. Anesthesiology. vol. 115. 2011. pp. 1151-2.
Benzon, HT, Avram, MJ, Green, D, Bonow, RO. “New oral anticoagulants and regional anaesthesia”. vol. 111. 2013. pp. i96-i113.
Horlocker, T, Wedel, D, Rowlingson, J. “Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: American Society of Regional Anesthesia and Pain Medicine Evidence-Based Guidelines (3rd Edition)”. Regional Anesthesia and Pain Medicine. vol. 35. 2010. pp. 64-101.
Horlocker, T. “Regional anaesthesia in the patient receiving antithrombotic and antiplatelet therapy”. British Journal of Anaesthesia. vol. 107. 2011. pp. i96-i106.
Stabille, DM, Diogo Filho, A, Mandim. “Frequency of colonization and isolated bacteria from the tip of epidural catheter implanted for postoperative analgesia”. Braz J Anesthesiol. vol. 65. 2015. pp. 200-6.
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