• Francis V. Salinas, MD

        INTRODUCTION

Since the first description of subarachnoid anesthesia by Bier, it has remained the simplest and most effective technique of regional anesthesia. The use of neuraxial techniques in outpatients has been a more recent development, awaiting ready availability of newer needles that reduced the side effect of postdural puncture headache to an acceptable level in the ambulatory setting. The last 10 years have seen a dramatic increase in the use of these techniques in outpatients, for several reasons.

        Simplicity and effectiveness should make central neuraxial techniques (either spinal or epidural) ideal in the outpatient setting. Both spinal and epidural anesthesia are more familiar to practitioners than peripheral nerve blocks and are easier to perform because they do not require nerve localization techniques. They can be performed rapidly and without assistance. Neuraxial techniques are effective for lower abdominal, perineal, and lower extremity surgery, and are among the best choices for practitioners who are just starting to incorporate regional anesthetic techniques in an outpatient practice. They also provide optimal outcomes in most of the important aspects of outpatient anesthesia. Patients with neuraxial blocks have lower pain scores on admission to PACU than patients receiving general anesthesia (GA).^1–5 Their frequency of postoperative nausea and vomiting (PONV) appears to be at most one-third of that after GA.⁶ Most importantly, the frequency of phase 1 PACU bypass is high,^1,6,7 and discharge times are comparable to even the fastest for GA techniques if appropriate local anesthetic agents and dosages are chosen.⁸ Modern small-gauge rounded point needles and short-acting drugs have reduced the side effects that were of concern in the past. With propofol infusions available to provide light but transient sedation, the objection to “being awake” during regional techniques has also disappeared, leaving neuraxial techniques as an excellent choice.

        This chapter will focus on the advantages, disadvantages, and practical points associated with spinal and epidural anesthesia in the outpatient setting.

        GENERAL CONSIDERATIONS

Advantages

Spinal Anesthesia

Spinal anesthesia (SA) is one of the simplest and most reliable of regional anesthesia techniques. The external anatomic landmarks are easily identified. The block can be performed with minimal discomfort, the end-point of cerebrospinal fluid flow is unmistakable, and the onset of anesthesia is more rapid than with any other regional technique. Because of the rapidity of onset, the block can be performed in the operating room without the requirement for additional personnel or a block room. The efficient performance of the block does not add substantially to operating room time any more than for the induction of GA. The onset of the sensory blockade is sufficiently rapid to attain surgical anesthesia by the time the positioning and preparation of the patient are completed. A variety of local anesthetic agents are available that can provide a wide range of duration of surgical anesthesia. The risk of nausea can be reduced if systemic opioids are avoided. Likewise, nausea and vomiting^2,9,10 and residual somnolence associated with general anesthetics or heavy premedication can be avoided, allowing a rapid return to full alertness in the PACU. SA is also a technique with a high degree of patient familiarity because of its use in obstetrics and thus is more likely to be accepted by many patient populations. In addition, it employs the lowest dose of local anesthetic of any major regional anesthetic technique and has minimal potential for systemic toxicity.

Epidural Anesthesia

Epidural anesthesia (EA) shares many of the advantages of SA, particularly clinician familiarity, simplicity of superficial landmarks, and ease of performance of the block. It has the additional advantage of allowing a continuous catheter to be placed in the epidural space, which creates the potential for tailoring both the segmental spread and duration of the block. Although it is a more flexible technique, this advantage is attained at the price of a slower onset of surgical anesthesia.

Combined Spinal-Epidural Anesthesia

Combined spinal-epidural anesthesia (CSEA) is also a useful technique in the outpatient setting. The procedure is technically more challenging: once the epidural space is identified, the spinal needle must be introduced through the epidural needle and advanced further into the subarachnoid space. After the local anesthetic is injected, the spinal needle is withdrawn and the epidural catheter is inserted into the epidural space and taped in place. This technique requires more time and technical skill, but CSEA provides the advantages of the rapid onset and dense block of SA along with the flexibility of an indwelling catheter to allow incremental and repeated injections to achieve the desired segmental spread and duration of surgical anesthesia. This technique has been used effectively for extracorporeal shock wave lithotripsy procedures, where the duration of treatment maybe unpredictable. Another advantage of the combined technique is the rapid onset of dense perineal anesthesia, which may not be provided by lumbar EA alone. It has also been used for knee arthroscopies when low doses of subarachnoid local anesthesia are used to provide a predictable short duration, but may be supplemented by epidural injection of local anesthetic if further spread or duration of blockade are needed.¹¹ Although the technique combines some of the disadvantages of both neuraxial procedures, it also maximizes the advantages and positive aspects of both SA and EA.

Drawbacks

Neuraxial anesthesia does have potential disadvantages. SA is typically a single-injection blockade, and thus careful attention must be paid to selection of the appropriate local anesthetic agent and dose. If the surgical duration was underestimated or becomes prolonged for unexpected reasons, supplemental GA may be needed. The “single-injection” aspect of SA frequently induces clinicians to give “just a little bit more” drug to ensure adequate distribution and duration; however, this tendency must be resisted, as the downside of this increased dosing pattern is a prolonged recovery and discharge time.⁶

        Postdural puncture headache (PDPH) remains a risk with SA. Newer pencil-point, smaller gauge needles have significantly reduced this frequency to less than 3%.¹² It is even less frequent in patients older than age 40. Although PDPH does not result in long-term neurologic damage and usually is not a prolonged inconvenience for the patient, it must be acknowledged in the discussion of SA with the outpatient. If it is inconvenient for a patient to return for an epidural blood patch or essential that the patient not have this debility, alternative anesthetic techniques should be considered.

        The most recent concerns about SA for outpatients have revolved around potential toxicity of local anesthetic drugs. A major concern was the reporting of permanent neurologic damage associated with very high doses of concentrated lidocaine injected through spinal microcatheters. This has not been a problem with standard doses of the local anesthetics used for single-injection spinal anesthetics, although all anesthetics injected in the subarachnoid space are potentially neurotoxic.¹³ A more common, relevant concern has been the symptoms of neurologic irritation associated primarily with lidocaine. This syndrome of “transient neurologic symptoms” (TNS) consists of a burning type of back pain radiating into the buttocks or legs that appears 6-24 h after the resolution of SA and can persist for 1 to 6 days.¹⁴ TNS occurs approximately 15-30% of the time, with the highest frequency following lidocaine SA.¹⁵ Obese outpatients are more susceptible, especially those having procedures performed in the lithotomy or knee arthroscopy positions.¹⁶ Although no sensory or motor deficits are associated with this syndrome,¹⁷ and to date no persistent neurologic deficits, it is nevertheless a significant source of morbidity in some patients. Many practitioners have sought alternatives to lidocaine to reduce the incidence of TNS (see section on Lidocaine).

        EA also has some potential drawbacks in the outpatient setting. Its slower onset of blockade compared with SA may cause a slight delay. However, if induction of EA is performed in a block room outside the operating room, the onset of anesthesia with drugs such as chloroprocaine (2-CP) or lidocaine is so rapid that there is little delay in the onset of surgery, and the use of EA may even promote operating room efficiency.¹⁸ Other drawbacks associated with EA include the greater risk for postdural headache if an unintentional durai puncture occurs. Since the potential for headache is directly related to the size of the needle, the use of the larger gauge epidural needles may represent a greater risk, although the incidence of PDPH from an unintentional durai puncture in experienced hands should be less than 0.5%. EA involves the use of larger doses of local anesthetic drugs, and thus represents a greater potential for systemic toxicity than occurs with SA. The careful use of safety steps is just as appropriate for the outpatient as for the inpatient.¹⁹

        Another limitation of both neuraxial techniques is the absence of residual analgesia. Multiple randomized comparisons of neuraxial techniques to GA show that early pain is significantly less with the regional techniques,^1–3,20,21 but once the block has resolved, some alternative mode of analgesia must be provided for the patient. This may be accomplished by the use of local anesthetic infiltrated into the wound, intraarticular injection of local anesthetic, or even a supplemental peripheral nerve block (eg, a femoral nerve or ankle block). The need for additional analgesia may not be an issue after relatively less painful procedures, such as diagnostic knee arthroscopy. Nevertheless, the possibility for breakthrough pain must be considered in the planning of the central neuraxial anesthesia for the outpatient.

        A common concern is the potential for difficulty with urination following neuraxial blockade. With higher doses of longer acting local anesthetics, the bladder is distended beyond its normal cystometric capacity during the prolonged duration of neural blockade and may be unable to return to normal function once the sensory blockade dissipates.²² Fortunately, with the short-duration central neuraxial blockades that are usually employed in the outpatient setting, bladder function returns promptly following complete resolution of the blockade. Patients can be successfully discharged home after short-duration spinal anesthetics with procaine, 2-CP, lidocaine, and even low doses of bupivacaine.²³ The use of certain additives, such as epinephrine, may impede this recovery.^24,25 The requirement for postoperative voiding is not essential with short-acting local anesthetics or low dose (< 6 mg) bupivacaine spinal anesthetic techniques.

        SPECIFIC OUTPATIENT SURGICAL PROCEDURES SUITABLE FOR NEURAXIAL ANESTHESIA

Hernia Repair

Inguinal herniorrhaphy is one of the most common procedures performed on an outpatient basis. Neuraxial anesthesia provides excellent anesthesia and motor relaxation for this operation.²⁶ SA with procaine or lidocaine in a hyperbaric solution (to give cephalad spread to the T4 through T6 level) is usually sufficient to provide high enough block with appropriate discharge times. The heavier solution (created by the addition of glucose to the local anesthetic) promotes spread to the “lowest” portion of the spinal canal, which is actually the midthoracic region when the patient is in the supine position. Using this technique creates higher spread of the dose, may allow a slightly lower dose to achieve anesthesia,²⁷’ and can provide a more rapid resolution of blockade compared with the same dose of local anesthetic injected as an isobaric solution. This more rapid resolution can be negated if higher doses of local anesthetic are used because of insecurity regarding adequate spread of anesthesia. Inappropriately high doses increase the risk of prolonged blockade and delayed discharge.

        Although postoperative voiding is not usually a problem after short-acting or low-dose bupivacaine, patients with hernia repairs frequently have urinary retention simply because of the postoperative pain that produces reflex inhibition of the voiding pathway. Generous use of local anesthetic infiltration during and after the procedure may help prevent this, but many centers still require hernia patients to void before discharge regardless of the anesthetic technique. EA offers an alternative for this surgical procedure because of the segmental band of anesthesia and the opportunity to use shorter acting drugs such as 2-CP or lidocaine, but with the ability to administer these agents via the indwelling epidural catheter to ensure an adequate distribution, depth, and duration of surgical anesthesia as dictated by the nature of the surgical procedure.

Anorectal Procedures

Whereas EA may have a delayed onset in the sacral fibers, intrathecal anesthesia limited to specific dermatomal fibers is an ideal application of SA. For lithotomy procedures, a traditional “saddle block” technique with hyperbaric 2-CP or procaine in small doses (20-30 mg) is appropriate. This may add some time to the procedure because of the need to keep the patient in the sitting position for at least 5 min to concentrate the local anesthetic in the sacral area. Because of the risk of TNS, lidocaine may not be an ideal choice. An excellent alternative is the use of the prone jackknife position, where procaine or 2-CP, as well as lidocaine can be made hypobaric.²⁸ This is easily accomplished by adding an equal volume of sterile water to the local anesthetic solution, usually 2 mL of each. This technique is efficient in the operating room because the block can be performed with the patient in the operating position, and onset is fast enough to allow surgery to begin as soon as the surgical preparation is complete. One hazard is that the level of anesthesia may rise if the patient is turned supine with the head elevated after a short procedure. Patients should be recovered form this technique in the full supine position for the first hour. Again, provision for adequate postoperative analgesia should be made by generous injection of local anesthetics during the procedure by the surgeon. The choice of an appropriate short-duration local anesthetic is important to provide competitive discharge times.²⁰

Laparoscopy

Although laparoscopic procedures of the upper abdomen are not tolerated well with regional techniques, pelvic laparoscopy appears to be suitable with neuraxial blockade in some hands. Vaghadia and colleagues have shown the successful use of low-dose SA for outpatient gynecologic laparoscopy. For this situation, lidocaine 25 mg combined with fentanyl 20 meg injected in the sitting position produces adequate sensory anesthesia with minimal motor blockade, which was well tolerated by their patients.²⁹ This is another example of the use of a hypobaric solution, this time providing upward spread of the solution by the dilution to a total volume of 3 mL with sterile water. In this case, the dilution also creates a lower dose of local anesthetic at each dermatome, and thus allows a less dense block and a more rapid resolution of the dilute anesthetic. The combination of low total dose and dilution provides rapid discharge and a high degree of patient satisfaction. This SA dosing strategy requires a gentle and skilled surgeon capable of performing the operation with less extensive distention of the peritoneum. If such a partnership can be arranged, patients appear to benefit from this technique.

Knee Surgeries

Knee surgeries are excellent situations for using neuraxial techniques, because they provide good surgical conditions and rapid recovery. Epidural blockade with a continuous technique is especially useful for providing a variable length of anesthesia for unpredictable or longer procedures, such as cruciate ligament repairs. With short- or intermediate- duration local anesthetics, timing of dosage can be managed to allow rapid and competitive discharge times.^3,4,8,30 The drawback is that larger initial doses are required to provide the lower lumbar spread to anesthetize the knee, especially the posterior portion. With the short-duration drugs, the onset time is usually rapid enough that surgical anesthesia is present by the time the surgical preparation and draping is completed.

        SA provides even more rapid onset, and has been used successfully, especially for the short predictable procedures such as diagnostic arthroscopy or partial menisectomy. The challenge here is choosing the correct drug and dose to provide adequate anesthesia but competitive recovery. Lidocaine had been the drug of choice before the TNS controversy and is still used in many institutions and provides competitive early discharge.⁵ Hodgson has used procaine as an alternative, with lower TNS but other side effects.³¹ Others have reported success with low-dose bupivacaine spinal block, with a low incidence of TNS.³² This technique requires addition of 20 to 25 meg of fentanyl to 5 mg bupivacaine to provide sufficient density of anesthesia with a low enough dose to permit rapid resolution. The high variability of spread and duration of bupivacaine, however, makes this a challenging technique.³³ Another approach to reduce TNS has been the use of very low dose lidocaine. Ben-David reported a 10-fold decrease in TNS (incidence comparable to bupivacaine) when he used 20 mg of lidocaine with 25 meg of fentanyl,³⁴ but others have not been able to confirm his results.³⁵ Most recently, the investigation of 2-CP as a spinal anesthetic has provided both rapid discharge and a suggestion of a low incidence of TNS;³⁶ it may therefore be a useful alternative in the future.

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. Preemptive Analgesia, Regional Anesthesia, & the Prevention of Chronic Postoperative Pain. Newer Amide Anesthetics & Sustained-Release Local Anesthetics1. Diagnosis & Management of Intraspinal, Epidural, & Peripheral Nerve Hematoma. Histology of Peripheral Nerves. Supraclavicular Brachial Plexus Block.