Epidural Anesthesia and Analgesia

CHAPTER 3 Epidural Anesthesia and Analgesia



Peter W. Grigg


Epidural anesthesia (i.e., complete relief of pain and significant motor block) and analgesia (i.e., the relief of pain only, with as little motor block as possible) can be accomplished by injecting opiates, local anesthetics, or a combination of these medications into the epidural space. An epidural is an extremely versatile procedure; it may be used to enhance the birthing experience or to provide anesthesia or analgesia during or after surgical procedures. For prolonged analgesia, a catheter may be left in the epidural space for several days to allow additional medication to be injected by repeated bolus, patient-controlled epidural anesthesia (PCEA) pump, or controlled continuous infusion.


From an anesthetic perspective, the level of anesthesia refers to an anatomic level or segment of effect (e.g., up to the level of the umbilicus [T10] or the level of the xiphoid [T8]), whereas depth refers to the amount of sensation or motor activity remaining. Depth of blockade is determined by choice of drugs and concentrations. Segmental level of anesthesia or analgesia can be controlled by the level of the injection, the volume of solution injected, as well as other factors (see the note after the Technique section), and the depth can be increased or decreased as the clinical situation dictates. Such control is one of the advantages of epidural anesthesia over other forms of regional anesthesia.


Clinicians administering epidural anesthesia must have a good understanding of not only the relevant anatomy and needle placement techniques, but the pharmacology and physiology involved. The clinician must be familiar and experienced with the diagnosis and management of possible complications. A review of and familiarity with the updated American Society of Anesthesiologists (ASA) Practice Guidelines for Obstetric Anesthesia (2007) and the ASA Difficult Airway Algorithm are highly recommended for medical professionals providing epidural services to obstetric patients. Epidural anesthesia or analgesia should be performed only in a hospital, surgery center, or facility where equipment and adequately trained personnel are available to manage any and all possible complications. The equipment available should be comparable with that of a hospital operating room.


EDITOR’S NOTE: Although there is general agreement that epidural anesthesia is safe and is the most effective method of pain relief in labor, there has been some controversy regarding possible side effects. Meta-analyses attempting to determine whether epidurals increase the risk for cesarean section are conflicting, but the majority of current evidence suggests they do not. However, there is consensus among studies that epidurals prolong labor—the first stage of labor by 12 minutes and the second stage of labor by 42 minutes. There is also consensus that epidurals increase the need for assisted delivery and the likelihood of maternal fever. (The cause of epidural-associated maternal fever is unknown.) Fetal heart rate changes are also common with epidurals during labor. Although the cause of heart rate changes is not known, one theory suggests reduced uterine blood flow from maternal hypotension as the mechanism. Intravenous (IV) fluid preloading (volume expansion) may help reduce the risk of maternal hypotension. However, IV fluid preloading must be performed cautiously or slowly in patients with pregnancy-induced hypertension.



Anatomic Considerations


The spinal canal contains the spinal cord, its coverings (i.e., pia mater, arachnoid mater, dura mater), and cerebrospinal fluid. The pia mater is closely attached or adherent to the spinal cord. The dura mater is the separate, toughest, and outermost covering of the spinal cord. The arachnoid membrane is a delicate membrane interposed between the dura mater and the pia mater. It is separated from the pia mater by the subarachnoid space, which contains the cerebrospinal fluid.


The epidural space is a potential space, external to the dura mater and located between the dura mater and the ligamentum flavum (connective tissue covering the vertebrae; Fig. 3-1). Although the epidural space is a potential space, it is filled with spongy connective tissue, fat, and blood vessels. This allows for solutions injected into the space to flow freely in all directions and to bathe the nerve roots as they exit the spinal canal.


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Figure 3-1 Anatomy of the vertebral column and its contents in the lower lumbar and upper sacral regions.


(Redrawn from Moore DC: Regional Block, 4th ed. Springfield, Ill, Charles C Thomas, 1979.)



Physiologic Considerations


When an epidural is used in labor and delivery, it is important to remember that visceral pain from uterine contractions is partly conducted through the sympathetic nervous system. Impulses travel through the inferior, middle, and superior hypogastric plexuses to the sympathetic chain. This chain then connects to the spinal cord through the 10th, 11th, and 12th thoracic nerves. Any effective analgesic solution must spread cephalad enough to affect these levels.



Indications



• As an alternative to general or spinal anesthesia for selected surgical procedures

• Requested by patient or suggested by clinician (e.g., to avoid maternal fatigue) for labor and delivery

• Postoperative analgesia

NOTE: Epidural analgesia should not be withheld on the basis of achieving an arbitrary cervical dilation.


NOTE: Continuous epidural analgesia is being used more and more for obstetrics and postoperative analgesia; however, spinal anesthesia is still the most commonly used regional technique for surgical procedures.



Contraindications



• Patient declines

• Localized infection at the puncture site

• Severe, uncorrected hypovolemia

• Blood dyscrasias; coagulopathy; prolonged international normalized ratio (INR), prothrombin time (PT), or activated partial thromboplastin time (APTT); thrombocytopenia

• Anticoagulant therapy (e.g., heparin, warfarin, enoxaparin [Lovenox], fondaparinux [Arixtra], clopidogrel [Plavix])

• Allergy to specific epidural agents

• Spinal abnormalities, including scoliosis and other structural abnormalities

• Active systemic infection

• Lack of proper resuscitative equipment, skills, or trained staff

• Preexisting neurologic diseases (amyotrophic lateral sclerosis [ALS], other degenerative nerve diseases, polio)

• Preoperative headache (relative)

• Aortic stenosis

• Anemia


Equipment



• Disposable sterile gloves

• Equipment for the clinician to observe universal blood and body fluid precautions

• Disposable epidural tray containing the following:
1 Appropriate prep solutions, swabs, and sterile 4 × 4 gauze pads

2 Disposable drapes

3 Epidural catheter, threading assist guide, and syringe adapter attachment

4 Syringes
a Plastic Luer-Lok (3 mL) for local infiltration of lidocaine 1%

b Plastic syringe (20 mL) for administration of epidural agent

c Glass Luer-Lok procedural syringe (5 mL) filled with saline for loss-of-resistance technique (Fig. 3-2)

5 Needles
a Skin puncture needle (18 gauge)

b Tuohy epidural needle (18 gauge) or other epidural needle

c Filter needle (19 gauge) for drawing solutions into the syringes

d Skin wheal needle (25 or 27 gauge)

6 Filter (0.2 µm) and filter straw (4 inch)

7 Medications
a Lidocaine 1% (5-mL vial) for local infiltration

b Sodium chloride 0.9% injectable (10-mL ampule)

c Test dose lidocaine 1.5% injectable, with epinephrine 1 : 200,000 (5-mL vial)

d Epinephrine injectable 1 : 1000 (1-mL vial)

• Epidural medications (Table 3-1)

• Patient-monitoring equipment (e.g., automated blood pressure [BP] device, continuous electrocardiogram [ECG] monitor, pulse oximeter, fetal monitor [if used for obstetrics])

• Emergency and resuscitative equipment (e.g., suction, Ambu-bag, oxygen, defibrillator) as well as an anesthesia machine

• Emergency and other drugs not included in the epidural kit:
1 Ephedrine 5% (1 mL) for use if hypotension develops (usual dose to treat hypotension is 10 mg [0.2 mL] IV)

2 Phenylephrine (Neo-Synephrine)

3 Atropine

4 Diphenhydramine (Benadryl)

5 Metoclopramide (Reglan), ranitidine (Zantac), and Bicitra (a nonparticulate antacid; the generic is sodium citrate and citric acid solution 3 g/2 g per 30 mL)

6 Diazepam or midazolam

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Figure 3-2 Loss-of-resistance and hanging-drop methods of ascertaining when the point of the needle rests in the epidural space. A, Needle rests in interspinous ligament. B, Syringe plunger loses resistance when needle enters epidural space. C, Saline-filled syringe has been removed, leaving a hanging drop. D, Hanging drop disappears when needle enters epidural space.


(Redrawn from Moore DC: Regional Block, 4th ed. Springfield, Ill, Charles C Thomas, 1979.)



TABLE 3-1 Local Anesthetics Commonly Used for Epidural Anesthesia

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NOTE: A 1% solution equals 10 mg/mL.



Epidural Agents: Local Anesthetics


The two most commonly used local anesthetics for epidural anesthesia are lidocaine and bupivacaine (see Table 3-1). Lidocaine has a rapid onset (5–15 minutes) and lasts 1 to 2 hours, whereas bupivacaine has a slower onset of action (10–20 minutes) and a longer duration of action, lasting 2 to 4 hours. In general, increasing the concentration of the drug while maintaining the same volume decreases the latency (time to onset of anesthesia). The addition of epinephrine to lidocaine (available premixed 1 : 200,000 with lidocaine) or to 0.25% (or less) bupivacaine appears to increase the duration of action.


Bupivacaine is widely used for both obstetric and surgical epidural anesthesia and analgesia. Bupivacaine 0.25% provides adequate sensory analgesia with minimal motor blockade for 1 to 3 hours, and it is well suited for both obstetric and postoperative analgesia (Table 3-2). When used at 0.5% concentration, bupivacaine produces significant motor blockade. Because of toxicity at higher levels, bupivacaine 0.75% is not recommended for use in obstetrics.



TABLE 3-2 Local Anesthetics Commonly Used for Epidural Analgesia

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Epidural Anesthesia and Analgesia

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