Anesthesiology

Anterior Lumbar Fusion

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What the Anesthesiologist Should Know before the Operative Procedure

Anterior lumbar fusions are becoming more common as interbody fusions alone and for the support of concomitant posterior fusions and for total disc replacements. Currently, there are several surgical approaches to achieve an anterior lumbar spinal fusion and all involve mobilization of vascular and visceral structures. Potential complications include hemorrhage from laceration of the iliac vessels, deep venous thrombosis (DVT), arterial thrombosis, bowel perforation, genitourinary injuries, adhesions, retrograde ejaculation, and infection. An open transperitoneal anterior lumbar interbody fusion (ALIF) is the most common approach to fusions of the anterior lumbar spine. This approach is commonly used in fusions involving L4-L5 and L5-S1.

However, there have been many modifications to this approach including retroperitoneal, mini-retroperitoneal, laparoscopic transperitoneal and endoscopic retroperitoneal approaches. Recently, endoscopic lateral transpsoas or extreme lateral approaches have been used for interbody fusions of L1-L4. This exposure is performed with the patient in the lateral decubitus position and avoids the need to mobilize the iliac blood vessels or sympathetic plexus. In most situations, surgeries for anterior lumbar fusions are elective procedures to correct degenerative conditions of the spine. Hence, only under unusual conditions should the surgery proceed in a patient who is not stable. Revision lumbar spinal procedures may, however, require emergency intervention when an implant has migrated into the spinal canal or on to a nerve root causing neurologic symptoms or the initial surgery has resulted in vascular compression or bleeding.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

This is generally elective.

Emergent: Revision lumbar spinal procedures may require emergency intervention when an implant has migrated into the spinal canal or on to a nerve root causing neurologic symptoms or the initial surgery has resulted in vascular compression or bleeding.

Urgent: Only under unusual conditions should the surgery proceed in a patient who is not stable.

Elective: This is generally an elective procedure.

2. Preoperative evaluation

Preoperative assessment of the patient for anterior spinal fusions should include an evaluation of the airway for tracheal intubation and general anesthesia, pulmonary status, cardiovascular risk assessment, risk for DVT, and preexisting coagulopathy.

Medically unstable conditions that warrant further evaluationinclude coronary artery disease. Delaying surgery may be indicated if:Some surgeons will delay the procedure until smoking cessation isachieved.

3. What are the implications of co-existing disease on perioperative care?

These procedures will require general anesthesia with endotracheal intubation. In this patient population with preexisting arthritic conditions, tracheal intubation often poses a challenge. Awake, sedated fiberoptic intubation of many of these patients is the safest approach to general anesthesia. Although the surgery will not involve entering the thoracic cavity, some of these patients will have scoliosis with restrictive lung disease. Cigarette smoking will not only affect the success of the spinal fusion but will also have an impact on the ability to mechanically ventilate the patient during the procedure and the successful extubation at the end of the procedure. Being morbidly obese in patients who are to undergo anterior spine procedures will have an impact on positioning, ventilation in certain positions, the length of surgery, and the incidence of complications.

Perioperative evaluation

In addition to the strategies presented next, smoking cessation is the single most important factor in promoting successful outcomes.

b. Cardiovascular system

For acute/unstable conditions, the American College of Cardiology (ACC)/American Heart Association (AHA) 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery proposed an algorithm for decisions regarding the need for further evaluation based on urgency of procedure, presence of active cardiac conditions (i.e., unstable coronary syndrome, decompensated heart failure, significant arrhythmias, or severe valvular disease), patient's clinical risk factors and functional capacity, and the predicted cardiac risk of the planned procedure. Anterior lumbar fusion is a nonemergent, intermediate-risk procedure that should proceed unless the patient presents with an active cardiac condition or if further noninvasive testing would change perioperative management.

c. Pulmonary

Chronic obstructive pulmonary disease (COPD): Pulmonary function should be assessed by exercise tolerance, and bronchodilator therapy maximized as needed.

Obstructive sleep apnea (OSA): Patients with sleep apnea should have the severity of the disease assessed, and appropriate strategies developed to reduce the potential for postoperative exacerbation of their disease by opioid-induced respiratory depression. They should continue the use of their CPAP therapy in the perioperative period.

Reactive airway disease (asthma): Bronchodilator therapy should be maximized as needed.

d. Renal-GI:

There are no specific renal or gastrointestinal concerns, although the presence of significant reflux disease (GERD) may impact airway management decisions.

e. Neurologic

The patient should be assessed for any neurologic deficits, particularly as related to cord compression.

f. Endocrine:

If the patient is diabetic, glucose control should be optimized and blood levels followed closely in the perioperative period.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

Again, smoking cessation is important in these patients.

4. What are the patient's medications and how should they be managed in the perioperative period?

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

There are usually no medications specific to diseases associated with this surgery, with the exception of opioid consumption. If the patient is consuming a significant amount of analgesics, a plan should be generated preoperatively to ensure adequate analgesia and avoid withdrawal symptoms. Narcotic requirements will typically be double or triple baseline use.

i. What should be recommended with regard to continuation of medications taken chronically?

All chronic medications should be continued with the exception of aspirin and NSAIDs, which might interfere with coagulation. If anticoagulation is present because of an intracoronary stent or valve replacement, consultation with a cardiologist is needed. Antiplatelet medications were discussed earlier.

j. How To modify care for patients with known allergies

Avoid drugs to which the patient is allergic.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Ensure all staff within the operative room are aware of the latex allergy and that all latex-containing products have been removed.

l. Does the patient have any antibiotic allergies? (common antibiotic allergies and alternative antibiotics)

N/A

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Documented: Avoid all trigger agents such as volatile agents and succinylcholine and ensure these are removed from the operating room prior to the patient's arrival. It is preferable in this instance to avoid general anesthesia. Regardless of the anesthetic technique used an MH cart should be immediately available.

Family history or risk factors for MH: A thorough history should elicit whether the patient is at risk for the condition. If MH is suspected, then the patient, ideally, should be tested preoperatively. If testing is not possible, it is safer to treat the patient as if he or she were MH positive, and a regional technique or local anesthetic technique may be the best anesthetic choice.

Local anesthetics/muscle relaxants

If the patient has an allergy to local anesthetics, it is important to determine in a history if this is an allergy to all local anesthetics and then determine the names of the local anesthetics to which the patient is allergic. If it is a true allergy, then avoidance of these agents is preferred. If the patient has no allergy to an alternative local anesthetic, this may be used if appropriate. If in doubt and the previous reaction has been severe, then general anesthetic is advised. If the patient has an allergy to muscle relaxants, these should be avoided. Ideally, a regional technique should be used.

5. What laboratory tests should be obtained and has everything been reviewed?

All patients who will undergo an anterior spinal fusion should be cross-matched for 2 units of blood prior to the procedure. Although in most cases the blood loss is minimal, these procedures (particularly the ALIF) have the potential for large blood losses if the iliac veins are lacerated. In addition, since there is retraction on the abdominal vessels, patients at risk for thrombus formation and a pulmonary embolism (PE) should receive aspirin and high-risk patients may require an inferior vena cava filter.

Hemoglobin levels should be assessed in view of potentialblood loss. A coagulation panel is appropriate in view of potentialblood loss and intraoperative coagulopathy.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

General anesthesia with endotracheal intubation will be required for all anterior lumbar fusion procedures. When the anterior fusion is not combined with a posterior procedure, an epidural catheter may be placed for postoperative analgesia. The general anesthetic must accommodate the neuromonitoring that is chosen and the surgical approach. In most cases, neuromonitoring will include somatosensory evoked potentials and electromyographic monitoring. For the ALIF, the patient is in the supine position with the lower and upper limbs abducted (da Vinci position). In this position using either the transperitoneal or retroperitoneal approach, neuromuscular relaxation will be required so that the surgeon can retract the muscular layers to achieve adequate visualization of the vertebral discs. Nitrous oxide should be avoided during this approach to the lumbar spine.

Because there is a real risk to iliac vein laceration, the patient should be monitored with an arterial catheter and large-bore venous access; if peripheral venous access is not accessible, then a central venous catheter should be inserted prior to incision. A pulse oximeter placed on one of the toes on the side on which the surgeon expects to be accessing the disc space will serve as a monitor for lower extremity ischemia during retraction of the iliac artery.

For the lateral transpsoas approach, the patient is positioned in the lateral decubitus position and flexed with Trendelenberg positioning to increase the distance from the rib cage to the iliac crest. In this position, attention must be paid to the padding of dependent parts of the body, including an axillary support, the ulnar nerve on the dependent arm, and pillows between both upper and lower extremities. Adequate ventilation may be a problem in the obese patient. The end plates of the disc space in the ALIF procedure are identified using a stimulus-evoked electromyogram (EMG)-producing instrument to avoid damaging the lumbosacral plexus. Hence, neuromuscular blocking medications cannot be administered during this procedure. In most cases this approach avoids major vascular injury. However, the incidence of genitofemoral nerve injury is 30%, usually presenting as temporary postoperative groin and thigh paresthesias and pain.

Total intravenous general anesthesia (TIVA) with an infusion of fentanyl, ketamine, and propofol will provide the best conditions for neuromonitoring during these procedures. The inclusion of ketamine will diminish the neurodepressant effects of propofol and as an NMDA inhibitor may reduce intraoperative and postoperative opioid requirements. Titration of an inhalational agent to 0.5 MAC will reduce the risk of intraoperative awareness without significantly affecting the spinal cord signals.

Regional anesthesia is not appropriate for intraoperative care but may be useful for postoperative analgesia (see later).

General anesthesia is discussed earlier. Monitored anesthesia care is not appropriate.

6. What is the author's preferred method of anesthesia technique and why?

See discussion above.

For prophylactic antibiotics, preincisional cefazolin is recommended. Vancomycin or clindamycin may be used for patients with severe allergies to penicillin or cephalosporin. Blood loss and associated coagulopathy are the major surgical issues. The most common intraoperative complications of hypotension and coagulopathy should be prioritized by urgency. If the patient is intubated, there are no special criteria for extubation.

a. Neurologic:

N/A

b. If the patient is intubated, are there any special criteria for extubation?

N/A

c. Postoperative management

For procedures involving only the ALIF, a transversus abdominus plane (TAP) block with a long-acting anesthetic (bupivacaine) will provide up to 24 hours of analgesia. When the patient has not had a posterior fusion, an epidural catheter placed prior to the procedure and then dosed during closure provides excellent postoperative analgesia. Both of these modalities are particularly effective in opioid-tolerant patients, although these patients will usually require additional systemic opioids. When neither of these options are available, intravenous PCA narcotics sometimes supplemented with a low-dose ketamine infusion are required.

With significant blood loss and coagulation problems, intensive observation is frequently required. Continued bleeding is a potential common postoperative complication.

What's the Evidence?

Benglis, DM, Elhammandy, MS, Levi, AD. "Minimally invasive anterolateral approaches for the treatment of back pain and adult degenerative deformity". Neurosurgery. vol. 63. 2008. pp. A191-A196.

Eck, JC, Hodges, S, Humphreys, SC. "Minimally invasive lumbar spinal fusion". J Am Orthop Surg. vol. 15. 2007. pp. 321-329.

Peng, CWB, Bendo, JA, Goldstein, JA, Nalbandian, MM. "Perioperative outcomes of anterior lumbar surgery in obese versus non-obese patients". Spine J. vol. 9. 2009. pp. 715-720.

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