Epidural anesthesia for common surgical procedures

Epidural anesthesia for common surgical procedures

Epidural Anesthesia for Common Surgical Procedures D a n J. K o p a c z , M D Many common surgical techniques can be conducted with lumbar epidural a...

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Epidural Anesthesia for Common Surgical Procedures D a n J. K o p a c z , M D

Many common surgical techniques can be conducted with lumbar epidural anesthesia as the sole anesthetic. Many factors influence whether it should be chosen over general anesthesia or another type of regional anesthesia. The less frequently used paramedian approach to the central neuraxis offers several advantages, particularly in patients without palpable landmarks, and/or in patients who are unable to flex because of arthritic or painful comorbid conditions. Specific details of using lumbar epidural anesthesia as the sole anesthetic is illustrated in three common clinical conditions: total abdominal hysterectomy, lumbar laminectomy, and femoral-popliteal bypass. Copyright 9 1999 by W.B. Saunders Company

he decision to employ epidural anesthesia for many

T common surgical procedures is often a complex process.

Many factors influence whether a regional anesthetic is appropriate for a given planned procedure, which regional anesthetic technique is most appropriate, and whether a regional anesthetic should be combined with a light plane of general anesthesia. Factors influencing these decisions include patient age and comorbid disease, the anesthesiologist's experience and general level of comfort with epidural anesthesia, specifically in the particular surgical situation, and the surgeon's level of skill and cooperation. A thorough discussion of the interaction of these elements would be too extensive so I have, instead, chosen three common surgical techniques (total abdominal hysterectomy [YAH], lumbar laminotomy, and femoral-popliteal bypass grafting) as examples of the use of epidural anesthesia for common surgical procedures. I will explain my idiosyncrasy about the technique of lumbar epidural placement (the paramedian approach), and discuss the rationale for the intraoperative conduct of the epidural anesthetic in each of these scenarios.

The Paramedian Approach I primarily place neuraxial blocks with the patient in the lateral decubitus position. This is a matter of personal preference and the sitting position is quite acceptable. The main advantage of the lateral decubitus position is the ability to administer increased amounts of sedation, when needed. However, it does require a three-dimensional visualization of the spine, which anesthesia practitioners possess to varying degrees. The paramedian approach to the epidural space has always made sense to me. Like most anesthesiologists, I originally From the Department of Anesthesiology, Virginia Mason Medical Center, Seattle,WA. Address reprint requests to Dan J. Kopacz, MD, Staff Anesthesiologist, Virginia Mason Medical Center, Departmentof Anesthesiology, 1100 Ninth Ave, Mailstop: B2-AN, Seattle,WA 98111. Copyright 9 1999 by W.B. Saunders Company

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learned the midline approach first and was taught to use the paramedian approach "if you can't get in through the midline," perhaps after trying several interspaces. [t was something you could try just before you gave up altogether. Does this make sense? The difficult situations cannot always be predicted; why not use the paramedian approach first if it is eventually going to be the only successful route. The main reason, in my mind, that the midline approach is more popular is that it is more practiced. If we had all learned to use the paramedian approach first, and only tried the midline approach when the paramedian approach fails, we would obviously be much more comfortable with the paramedian approach. This is analogous to the use of a Macintosh or Miller blade for endotracheal intubation. Perhaps the only legitimate reason that I have heard, although not substantiated by the literature, for not attempting the paramedian approach first is "they hurt more than midlines." But after watching attempts to reach the midline epidural space through several interspaces, with a redirection of the needle several times (and contacting sensitive periosteum) at each level, it is hard to imagine how the paramedian approach could "hurt more." We have all observed it; we have all performed it. There are anatomic reasons for the paramedian approach being easier and more successful. A quick, straight-on inspection of the lumbar spine (Fig 1, left) shows that the midline region (arrow, A) offers the narrowest aperture for passage of a needle. The region just lateral to the midline (paraspinous region, arrow, B) offers greater dimensions, as the opening between the laminae and spinous processes open up into much broader butterfly wings. One has to wonder how often our needle actually deviates off the midline to enter the spinal canal through these paraspinous zones. Granted the spine in Fig 1 is not flexed and the midline will open up more with flexion. However, many patients in whom neuraxial blockade is indicated cannot flex very well (eg, osteoarthritis, pregnancy, scoliosis, etc) or will be hurt when attempting to maximize the flexion of their spines (eg, hip or lower extremity fractures). The slight rightward rotation of the spine (Fig l, right) shows what a needle advancing toward the spinal canal from the paramedian approach would see. The target area (arrow, C) for the needle to hit is much larger than even the paraspinous zone previously talked about. In those cases in which epidural placement is anticipated to be difficult (usually grossly obese patients in which landmarks can be imagined, but not actually palpated) the needle can be used as a surrogate finger to define the bony landmarks. When difficulty arises in these patients, usually one of two scenarios is present: (1) no bone is encountered even at what seems to be adequate/excessive depths, and when bone is found, the

Techniquesin RegionalAnesthesiaand Pain Management,Vol 3, No 4 (October), 1999: pp 230-232

A

AB Fig 1. (A) Midline approach (coronal view). (B) Paramedian approach (oblique view).

operator has no idea what part of the vertebra is being contacted, or (2) bone is encountered everywhere. The routine I use to perform a paramedian epidural is to first locate a lamina (in the decubitus position, the dependant side), just adjacent to the cephalad end of the lumbar spinous process (Fig 2A). This can often be located with a 1.5-inch infiltration (finder) needle, at which point a small amount of 1% lidocaine is deposited to anesthetize the periosteum. In large patients, it may be necessary to use the Tuohy needle (9 cm) to define the landmarks. The needle is then withdrawn slightly and redi-

Fig 2. (A) A needle placed appropriately will quickly contact the side of the spinous process when 'walked' directly medial (A-white line). When redirected medial and cephalad (from the original point 'A'), the needle will be felt to slip off the lamina to engage the ligamentum flavum (A-black line). (B) A needle placed too far lateral will not reach the spinous process within a few medial 'steppings' of the needle (Bwhite line). This needle should be removed and replaced at a point approximately 5 mm more medial, for if instead an attempt is made to walk medial and cephalad, the needle may remain in contact with bone as it progresses up the articular process and/or onto the vertebra above without successfully reaching the interspace. EPIDURAL ANESTHESIA FOR COMMON SURGERY

rected directly medial (Fig 2, left white dotted arrow) until it is obvious that the needle is walking up the side of the spinous process. This simple move affirms that your needle is, in fact, on the side of the spine you think you it is on. The needle is returned to the original location on the lamina, and then walked medial and cephalad (Fig 2, left black dotted arrow) until contact with the lamina is lost. At this point, the needle tip is usually within 1 to 3 mm of entering the ligamentum flavum, so the syringe can be switched to perform a loss-ofresistance using whichever method (air or saline; 1 prefer saline) is most comfortable to you. This method of performing a paramedian epidural has several advantages. First, as the depth of lamina is intentionally located, excessive plunging of the needle to unknown depths (which could cause dural perforation) is avoided. If ligament flavum is not encountered within 3 to 4 mm after walking off the lamina, the needle should be withdrawn, its position on the lamina reestablished, and the process repeated. Secondly, the step of determining the proximity of the spinous process may not be necessary in patients with easily palpable surface landmarks. However, in the large patient in whom absolutely no landmarks can he felt, it cannot be emphasized enough. The simple step of confirming the location of the midline with your needle prevents you from later wasting time by redirecting the needle in the wrong direction (away from the midline), in which only the bone of the transverse and articular processes will be contacted. It is also possible to have your starting point too far lateral (Fig 2B). When the needle is redirected cephalad and medial from a point too far lateral (Fig 2, right black dotted line), it may not be possible to "walk off" of the lamina. The needle will instead march up the superior articular process of the vertebra, or onto the lamina of the vertebra above. If an initial direct medial walking of the needle does not locate the spinous process within 5 to 6 mm (Fig 2, right white dotted line), the entrance point should be shifted more medially, Although this approach initially feels quite foreign, my suggestion would be to take a 1- or 2-month period and use

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nothing but the paramedian approach for the first attempt at locating the epidural space.

TAH Once the epidural space is located, with the exception of epidural catheters placed for labor, I inject the initial local anesthetic dose through the needle. One can never be entirely sure that a catheter will not deflect to a side, or that the needle may be moved in the process of passing the catheter. Regardless of the agent selected, injecting the first dose of local anesthetic through the needle also allows it to start working that much sooner, and in these days of minimizing turnover times, this is increasingly important. Many failures of epidural anesthesia are due to insufficient dosing of local anesthetic and a resultant low block height. Just as for Cesarean section, the optimal block height for TAH (or any other intraperitoneal procedure) is above T6. To obtain this in 95% of patients, my starting dose is usually 20 mL or more (the first 3 mL containing epinephrine as a test dose). For an uncomplicated TAH, I would choose 2% lidocaine with 1:200,000 epinephrine to provide maximum relaxation of the abdominal musculature, and would start the postoperative analgesia in the operating room with either epidural morphine (3 to 5 rag) or an infusion of bupivacaine (0.05%) and fentanyl (4pg/mL). I[ the surgical duration is anticipated to be longer (node dissection, etc), I would choose 0.75% bupivacaine with epinephrine instead of lidocaine. The intraoperative redosing of an epidural catheter is a skill that improves with experience, and is a function of the impact of initial dose (peak block height, hemodynamic response, and degree of abdominal muscle relaxation), the amount of surgery remaining, and the acceptability of sedation as a substitute for a waning block. Generally, redosing on a strict time schedule is unwarranted, and the amount injected (volume and concentration) can be reduced by approximately 50% (eg, 8 to l0 mL of 1.5% lidocaine or 0.25% to 0.5% bupivacaine).

Lumbar Laminotomy The performance of lumbar laminotomy/laminectomy with epidural anesthesia has several benefits. Foremost are the patient's ability to cooperate in the awkward positioning, as the epidural block is gradually setting up, and the avoidance of placing excessive pressure on contact points or vital organs throughout the procedure. The absence of ventilator-induced positive intrathoracic pressure minimizes epidural venous distension, creating a relatively bloodless surgical field. The uncertainty of inducing general anesthesia in the prone position makes many practitioners shy away from using epidural anesthesia for back surgery. However, if one adheres to three checkpoints, this is very rarely required (less than 1 in 1,000 at my institution). First, make sure the epidural is setting

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up solidly before surgery is allowed to start. If absolutely no signs of blockade have developed after a reasonable period of time (15 minutes), indicating the local anesthetic most likely was not deposited in the epidural space, induce general anesthesia while the patient is still in the supine position. Second, and like TAH above, aim for a high (T4) block. Although the surgical stimulus does not go above the T10 dermatome, the awkward positioning becomes unpleasant with time. This discomfort can be avoided by inducing a high block. For these reasons, I would choose 0.5% bupivacaine with epinephrine (15 to 20 mL starting dose), with shorter duration agents reserved for only the most efficient, reliable, and cooperative surgeons. I avoid epidural opiates so that the possibility of urinary retention does not create confusion later. It is prudent to place an epidural catheter for the short period of time between block placement and positioning. Once positioned, the block can again be checked, a sense for its ultimate block height obtained, and additional local anesthetic administered, if necessary. The catheter can be removed immediately before preparation and draping. Finally, be sure your surgeon will cooperate should the procedure go longer than the estimated time. The surgeon can easily "top up" the block with an intrathecal injection of 0.5% bupivacaine (1 mU isobaric) through the surgical site with a 30-gauge needle.

Femoral-Popliteal Bypass Unlike the two previous case scenarios, femoral-popliteal bypass grafting does not require a high dermatomal level of blockade. Furthermore, the patient population tends to be less healthy, is known to have cardiovascular disease, and may not tolerate a dense sympathectomy. I would initiate the epidural with 10 mL of solution. The chosen agent is variable, most of these procedures require more than 3 hours to complete, so bupivacaine would be appropriate. However, with the possibility of needing to add anticoagulation intra- or postoperatively, it is also reasonable to start with a shorter-duration local anesthetic so that the block will wear off rapidly and the patient's neurological status can be monitored soon after surge W. Dense muscle relaxation is not necessary, so 0.5% bupivacaine or 1.5% lidocaine is sufficient. The vasodilation and increased blood flow produced by continuance of the epidural into the postoperative period as an infusion of low concentration bupivacaine (0.05 % to 0.1%) will improve graft patency.

Conclusion Lumbar epidural anesthesia can easily be used as the sole anesthetic for many common surgical procedures. The paramedian approach offers several advantages, particularly in patients with difficult anatomy.

DAN J. KOPACZ