Anesthesiology

Scoliosis

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What the Anesthesiologist Should Know before the Operative Procedure

Scoliosis is lateral and rotational deformity of the thoracolumbar spine. Idiopathic scoliosis is most common and most often seen in females, and patients usually present for surgery during adolescence. Congenital scoliosis is less common and is usually the result of a rib or vertebral anomaly; patients may present at a young age for surgery. Neuromuscular scoliosis is most often seen in patients with muscular dystrophies and cerebral palsy.

Scoliosis is corrected with spinal fusion, which involves implanting metal rods that are affixed to the spine. These rods correct the deformity and act as an internal splint. Most often, this procedure is performed through a posterior incision, with the patient in the prone position. In some cases, the patient must undergo both posterior and anterior fusion for correction.

Scoliosis is correctable from a posterior approach if the curve is still flexible; however, if the curve has minimal flexibility or if it is found in the lower thoracic or lumbar area, an anterior approach may be necessary to increase the child's flexibility. Which approach is chosen is the decision of the pediatric orthopedic surgeon. Questions surrounding the surgical approach should be addressed preoperatively with the surgeon.

1. What is the urgency of the surgery?

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

In general, surgical correction of scoliosis is an elective procedure. However, emergent surgery may be necessary for decompression of the spine in cases of peripheral nerve compression or loss of bladder or bowel function. For simplicity, we focus on the pediatric anesthesia issues surrounding elective spine fusion and reconstruction for scoliosis.

  • Emergent

- Rare, but may occur following elective spinal fusion procedure if there is loss of peripheral nerve motor or sensory function or even acute loss of bladder or bowel function. Bladder function loss may be masked because many of these patients have a Foley catheter in the postoperative period. Loss of bowel function can also be masked because patients routinely have delayed return of function in the perioperative period. In these cases, all patients should have an active type and cross with blood and blood products immediately available in the blood bank. Large bore IV access must be confirmed and arterial blood pressure monitoring is helpful. Motor and/or sensory potentials may be affected because of compression. We suggest either narcotic-based anesthesia with low dose volatile anesthetic or TIVA with narcotic and ketamine infusions.

  • Urgent

- Also rare, but may occur for reasons stated in the emergent section (above).

  • Elective

- Most scoliosis procedures are elective. The most common patient type is the adolescent female presenting with idiopathic scoliosis with a curve of more than 45 degrees. Patients with neuromuscular scoliosis usually have a more severe curve as well as other associated comorbidities. Congenital scoliosis is less common and patients may present at a very young age for correction. Issues related to elective scoliosis surgery include the need for large bore IV access, arterial blood pressure monitoring, urine output assessment with a Foley catheter and availability of blood products. Some patients choose to donate autologous blood prior to surgery.

2. Preoperative evaluation

The most common procedures are performed for idiopathic scoliosis in otherwise healthy adolescents. However, a fair number involve neuromuscular scoliosis, in which case, the patient may have cerebral palsy with or without underlying seizure disorders or severe developmental delay. Scoliosis is also common in patients with Marfan or Loeys-Dietz syndrome (LDS), who have underlying cardiac issues.

  • Medically unstable conditions warranting further evaluation include: poorly managed reactive airway disease, severe restrictive lung disease, gastroesphageal reflux disease (GERD), or seizure disorder. In addition, cardiac conditions without recent follow-up by a cardiologist may need further evaluation.

  • Delaying surgery may be indicated if the surgery is an elective procedure and medically unstable conditions exist.

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

The more common underlying diseases are restrictive lung disease, seizure disorders, GERD, airway abnormalities, or underlying cardiac diseases that may have an impact on induction, maintenance, and emergence from anesthesia.

  • Perioperative evaluation

- In addition to the usual history and physical exam, the degree of curve and the presence of kyphosis together with scoliosis should be part of the patient assessment. Patients with restrictive lung disease may need pulmonary function tests, usually patients with curves of more than 60 degrees. Female manarchal adolescents should have a preoperative pregnancy test.

  • Perioperative risk reduction strategies:

- Degree of curve: Children that may not be cooperative for certain preoperative evaluations, such as pulmonary function studies, so we suggest that the anesthesiologist know the degree of curvature in order to directly assess the risk of the procedure.

- Reactive airway disease: Patients should be optimized with bronchodilators and, if the patient has received steroid treatment in the past 6 months, should be treated with oral steroids (prednisone) for 3 days prior to surgery.

- Seizure disorders: Patients should be instructed to take usual medications on the day of surgery to prevent perioperative seizures. Patients on valproic acid may have an increased tendency to bleed intraoperatively.

- Gastroespohageal reflux disease (GERD): Patients should be instructed to take their antireflux medications on the day of surgery. Induction of anesthesia may require a rapid sequence induction if significant GERD exists.

- Cardiac disease: Patients should be seen by their cardiologist prior to surgery. Patients receiving either angiotensin-converting enzyme inhibitors or angiotensin receptor blockers may experience less hypotension with general anesthesia if these medications are held on the day of surgery.

- Recent upper respiratory infections: In general, patients presenting for elective surgery should be free of upper respiratory infection symptoms for 2 weeks prior to surgery.

b. Cardiovascular system

  • Acute/unstable conditions

- Dilated aortic root in patients with connective tissue disorders (e.g., Marfan syndrome, Loeys-Dietz) and patients with complex congenital heart disease who have undergone palliative procedures.

  • Baseline cardiac dysfunction

- Goals of management: Maintain baseline blood pressure and adequate preload.

c. Pulmonary

Reactive airway disease (asthma)

Many patients with neuromuscular scoliosis will have underlying reactive airway disease. They may be managed on the newer combination steroid inhalers. This therapy has to be optimized with the direct assistance of the primary physician or a pulmonologist. We usually instruct patients with milder reactive airway disease to take their usual bronchodilators and steroids for 3 days prior to surgery.

d. Renal-GI:

GERD

This can be a significant problem in patients with neuromuscular disease. Optimization should be assessed through historical cues, and we suggest continuing these therapies in the perioperative period.

e. Neurologic:

Many patients with neuromuscular scoliosis will have seizure disorders. We suggest optimization with the assistance of a pediatric neurologist as well as continuing these therapies in the perioperative period.

  • Acute issues are rare; however, postoperative seizures have been reported.

  • Chronic issues should be addressed prior to surgery.

f. Endocrine:

Rare.

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)

Many patients with neuromuscular scoliosis will have contractures. Positioning may be challenging, but meticulous padding of pressure points is highly recommended.

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

Otherwise healthy adolescents with idiopathic scoliosis and no cardiorespiratory disease are often on no medications preoperatively. The medications usually held the morning of surgery are angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, diuretics and nonsteroidal anti-inflammatory drugs. Aspirin-containing products should be held for 10 days prior to surgery if possible.

Patients on other anticoagulants or with coagulopathies or hemoglobinopathies should have a hematologist's recommendation for treatment in the perioperative period.

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

Patients with curves of more than 60 degrees or with neuromuscular disease may have associated respiratory symptoms that require bronchodilators and inhaled steroid therapy. These medications should be continued throughout the perioperative period. Marfan syndrome patients are usually on a beta-blocker, but they may also be on an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB). Preoperative ACEI and ARB have been associated with a higher incidence of hypotension in adult patients undergoing cardiac surgery, and there is anecdotal evidence of associated intraoperative hypotension in children.

Some centers advocate holding ACEI on the day of surgery, unless the patient is hypertensive. Patients on beta blocker therapy either for Marfan syndrome or for mitral valve prolapse, which is associated with 25% of patients with scoliosis, should have their beta blockers continued in the perioperative period.

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

  • Cardiac: Hold ACE and ARB the day of surgery. Discuss with Cardiology when taking care of patients with Marfan syndrome.

  • Pulmonary: Pretreat with steroids 3 days prior to surgery; take bronchodilators preoperatively the day of surgery.

  • Renal: Hold diuretics the day of surgery.

  • Neurologic: Take antiseizure medications the day of surgery.

  • Antiplatelet: Hold aspirin for 10 days prior to surgery.

j. How To modify care for patients with known allergies -

N/A

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.

Scoliosis patients with myelodysplastic syndrome are prone to latex allergy. Use only nonlatex-containing materials, paying particular attention to tourniquets and gloves. Pretreatment with corticosteroids and antihistamines is not a recommended therapy.

l. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

Prophylactic antibiotics are indicated for this procedure. Cefazolin is most commonly used. In cases of allergy to cephalosporins, the recommended alternative is vancomycin with or without gentamicin (usually at the discretion of the surgeon). Clindamycin has been associated with increased risk of surgical site infection in scoliosis surgery.

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

Malignant hyperthermia:

  • Documented: Avoid all trigger agents such as succinylcholine and inhalational agents:

  • - Proposed general anesthetic plan: Propofol and remifentanil or ketamine are frequently used in place of inhalational anesthetics for scoliosis surgery.

  • - Ensure that the MH drug tray is available and that MH protocol is followed in the event of a triggered episode.

  • - Patients with myopathy or Duchenne's muscular dystrophy should be treated as being susceptible to malignant hyperthermia.

Local anesthetics/ muscle relaxants

  • Patients who will undergo motor-evoked potential monitoring may be given a dose of a nondepolarizing muscle relaxant that allows for 2 out of 4 twitches. This can be given as bolus dose or as a continuous infusion.

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

Laboratory studies will be same for all procedures, with a difference by age and gender.

  • Hemoglobin levels: For all patients undergoing scoliosis surgery.

  • Electrolytes: For patients on preoperative cardiac medications, diuretics; patients with underlying renal or hepatic disease; and patients receiving steroid therapy.

  • Coagulation panel: Not recommended unless the patient has a history of easy bruising, nose bleeds, or is on anticoagulation therapy.

  • Imaging: MRI may occasionally be performed to look for occult neurological processes. Scoliosis series to define the extent of the curve is routinely performed.

  • Other tests:

- Pulmonary function tests in patients with respiratory impairment, who are able to cooperate with their testing in order to help to predict the risk of postoperative respiratory compromise.

- Pregnancy test for menarchal females.

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

Regional anesthesia

Neuraxial (for postoperative analgesia)

  • Benefits: Studies in the literature suggest the use of either intrathecal opioids or epidural analgesia for pain management after posterior spinal fusion. Epidural analgesia is comparable to PCA for pain relief and is associated with earlier advancement of diet and a 0.5 day shorter stay.

  • Drawbacks: High failure rate of epidural analgesia (37% failure rate in one report by Gaugher 2009).

General anesthesia

  • Benefits

- Scoliosis surgery is performed under general anesthesia. Use of intraoperative opioids assists in keeping the volatile anesthetic requirement low. Some providers use only TIVA with remifentanil or fentanyl with ketamine or propofol infusions. Bolus doses of fentanyl, hydromorphone, or morphine with a low dose of volatile anesthetic have all been used with good results. If a remifentanil infusion is used for general anesthesia, a longer-acting opioid must be given prior to the end of the case to ensure adequate pain relief. In addition, the potential for hyperalgesia secondary to remifentanil has been reported, following prolonged infusions with this drug.

  • Drawbacks

- Very high levels of volatile agents will affect motor and sensory-evoked potential monitoring. Prolonged propofol infusions can lead to acidosis. In addition to acidosis from propofol, there can be degradation of evoked potential signals from propofol as well. If a wake-up test is required due to loss of evoked potentials intraoperatively, it may take longer for propofol to wear off than a volatile agent would.

  • Other issues:

  • - Dexmedetomidine has been shown to attenuate the amplitude of motor-evoked potentials.

  • - Proper and meticulous positioning is a must for prone positioning. In our practice, we use the Jackson table.

  • - Proper perfusion to extremities should be confirmed after prone positioning. All pressure points must be padded.

  • - Eyes must be checked regularly while the patient is in the prone position to ensure that there is no pressure on the eyes.

  • - Ketamine can amplify evoked potentials.

  • Airway concerns

- Some patients may have recognized or even unrecognized difficult airways. If a difficult airway is not recognized until after induction, maintaining oxygenation while adhering to the difficult airway algorithm is highly recommended. For idiopathic scoliosis we usually place an arterial line in addition to two large bore intravenous catheters. Central venous access is most often utilized in children with poor venous access or underlying cardiac or pulmonary disease that require close monitoring of the patient's central venous pressures. There are many choices for arterial lines and central venous catheters. Each institution has its preferences. Generally, for idiopathic scoliosis, we transfuse for an hgb of around 7 to 8 mg/dL. However, for more complicated patients, the transfusion trigger may vary, depending on the child's comorbid diseases.

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

  • What prophylactic antibiotics should be administered? Cefazolin is the antibiotic of choice. If the patient is allergic to cefalosporins, then vancomycin with or without gentamicin is recommended.

  • What do I need to know about the surgical technique to optimize my anesthetic care? Most of the blood loss usually occurs during the period when the spinal muscles are stripped and when large areas of cancellous bone are exposed. Blood loss can vary from 15% to more than 100% of the patient's blood volume.

  • What can I do intraoperatively to assist the surgeon and optimize patient care? Maintain a mean arterial blood pressure of 60 mm Hg; useCell Saver to reduce need for red cell transfusions; use aminocaproic acid or tranxemic acid to reduce bleeding.

  • What are the most common intraoperative complications and how can they be avoided/treated?

  • - Loss of evoked potentials: TIVA may improve evoked potentials. Ketamine enhances evoked potentials but may not improve overall neurological outcome. A wake-up test may be necessary to test the integrity of the motor pathways if adjusting the anesthetic and optimizing hemodynamics does not result in improvement of evoked potentials. A wake-up test requires a decrease in anesthetic agents, reversal of muscle relaxants, and continuously talking to the patient and squeezing his or her hand and/or moving the legs. Once the patient has followed commands, immediately re-induce general anesthesia.

  • - Hypotension: Maintaining a blood pressure low enough to minimize bleeding but high enough to ensure good perfusion keeps the anesthesiologist busy during these procedures. Mean arterial pressure in the 60 to 70 mmHg range is preferred.

  • - Anemia: Ongoing blood loss is the primary cause of hypotension in these patients. Blood loss can be unrecognized and underestimated, especially in neuromuscular scoliosis. Hemodilution with crystalloid can reduce the hemoglobin to low levels very quickly. Frequent hemoglobin checks, in some cases every 30 minutes, may be required to prevent dangerously low hemoglobin levels.

  • - Metabolic acidosis: The primary cause of metabolic acidosis is hypovolemia. Large volumes of crystalloid are a rare cause of metabolic acidosis in these patients. Use only isotonic crystalloid solutions to reduce development of inappropriate ADH and hyponatremia postoperatively.

a. Neurologic:

Unique to procedure: Neurologic sequelae of spinal cord ischemia is a feared complication. Thus, it is important to document a neurologic exam prior to leaving the operating room.

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

Ensure that the patient is awake, following commands, has good strength, and can move lower extremities (or has baseline movement). If unable to move lower extremities, the patient may need to be reexplored, or may need imaging studies immediately post-op to determine cause.

c. Postoperative management

  • What analgesic modalities can I implement?

- Significant pain accompanies scoliosis surgery. If remifentanil is used as part of the anesthetic, the patient may develop hyperalgesia after the remifentanil is discontinued, resulting in an increased sensitivity to pain post-op. This can be counteracted by loading the patient with a longer-acting opioid prior to emergence. Postoperative pain is generally treated with patient-controlled analgesia (PCA,) with either a basal rate of morphine (0.02 mg/kg/hr) or hydromorphone (0.004 mg/kg/hr) combined with a low-dose naloxone infusion (0.25 micrograms/kg/hr) to control nausea and itching. The basal rate is supplemented by a bolus dose of morphine (0.02 mg/kg) or hydromorphone (0.004 mg/kg). Neuraxial techniques are also used with intraoperative intrathecal morphine, injected by the surgeon or a surgically placed epidural catheter prior to wound closure. In addition to opioids, acetaminophen and neurontin may be given as an adjunct, starting with the first doses in the immediate preoperative period.

  • What level bed acuity is appropriate?

- Usually, otherwise healthy patients with idiopathic scoliosis who have a routine, uncomplicated intraoperative course may be extubated at the end of surgery and monitored in a step-down unit. Patients with respiratory, cardiac, or neurologic comorbidities may require postoperative ventilation and ICU for one or more days, depending on the severity of disease. Patients with perioperative neurologic changes will require frequent neuro checks and ICU level monitoring.

  • What are common postoperative complications, and what are ways to prevent and treat them?

  • - Pulmonary insufficiency: Postoperative ventilation may be required in patients with significant baseline pulmonary disease, those with a long operative time in the prone position, and those who have had large volume replacement with crystalloid and/or blood products.

  • - Hypothermia: Patients with long operative times and inadequate warming methods during surgery.

  • - Neurologic sequelae: Immediate diagnosis and treatment of neurologic changes is the best hope for preventing long-term neurologic sequelae.

What's the Evidence?

Chan, G, Dormans, JP. "Update on congenital spinal deformities". Spine. vol. 34. 2009. pp. 1766-74.

(This is an orthopedic review of the preoperative assessment of patients with congenital vertebral anomalies.)

Boyer, J, Amin, N, Taddonio, R, Dozor, AJ. "Evidence of airway obstruction in children with idiopathic scoliosis". Chest. vol. 109. 1996. pp. 1532-5.

(A report of 44 children with idiopathic scoliois who underwent pulmonary function testing. These authors noted that 41% had restrictive lung disease and 46% had evidence for moderate to severe gas trapping that was responsive to bronchodilators.)

Kempton, LB, Nantau, We, Zaltz, I. "Successful monitoring of transcranial electrical motor evoked potentials with isoflurane and nitrous oxide in scoliosis surgeries". Spine. vol. 35. 2010. pp. E1627-9.

(A study of 247 consecutive patients undergoing spinal fusion with transdermal electrical motor-evoked potential monitoring. The authors noted that reliable monitoring can occur in the presence of inhaled anesthetic agents.)

Bernard, J, Pereon, Y, Fayet, G, Guiheneuc, P. "Effects of isoflurane and desflurane on neurogenic motor- and somatosensory-evoked potential monitoring for scoliosis surgery". Anesthesiology. vol. 85. 1996. pp. 1013-19.

(A study of 23 patients showed that neurogenic motor-evoked potentials can be preserved in the presence of IMAC desflurane or isoflurane.)

Eroglu, A, Solak, M, Ozen, I, Aynaci, O. "Stress hormones during the wake-up test in scoliosis surgery". J Clin Anesthesia. vol. 15. 2003. pp. 15-18.

(A study of 40 teenage patients undergoing scoliosis surgery demonstrated that propofol/remifentanil was similar to sevoflurane/remifentanil with respect to eye opening and movement for an intraoperative wake-up test. Of note was that a wake-up test was associated with an increase in neuroendocrine markers for stress, despite unchanged hemodynamic parameters.)

Brazel, PW, McPhee, IB. "Inappropriate secretion of antidiuretic hormone in postoperative scoliosis patients: the role of fluid management". Spine. vol. 21. 1996. pp. 724-7.

(This paper reports on the association of hypotonic fluid administration and syndrome of inappropriate ADH.)

Florentino-Pineda, I, Thompson, GH, Poe-Kochert, C, Huang, RP, Haber, L, Blakemore, LC. "The effect of amicar on perioperative blood loss in idiopathic scoliosis". Spine. vol. 29. 2004. pp. 233-8.

(Double-blind study of 36 patients randomized to amicar or placebo, who were undergoing idiopathic scoliosis repair. The use of amicar was associated with less blood loss and the need for autologous blood transfusion.)

Grant, JA, Howard, J, Luntley, J, Harder, J, Aleissa, S, Parsons, D. "Perioperative blood transfusion requirements in pediatric scoliosis surgery. The efficacy of tranexamic acid". J Pediatr Orthop. vol. 29. 2009. pp. 300-4.

(A retrospective study comparing low-dose tranexamic acid to high-dose tranexamic acid. The higher dose was associated with a 50% decrease in transfusion requirements.)

Van Boerum, DH, Smith, JT, Curtin, MJ. "A comparison of the effects of patient-controlled analgesia with intravenous opioids versus epidural analgesia on recovery after surgery for idiopathic scoliosis". Spine. vol. 25. 2000. pp. 2355-7.

(A retrospective study comparing epidural infusion to PCA for pain relief in 50 patients undergoing adolescent idiopathic scoliosis surgery. Epidural treatment was associated with earlier hospital discharge.)

Gauger, VT, Voepel-Lewis, TD, Burke, CN, Kostrzewa, AJ, Caird, MS, Wagner, DS, Farley, FA. "Epidural analgesia compared with intravenous analgesia after pediatric posterior spinal fusion". J Pediatr Orthop. vol. 29. 2009. pp. 588-93.

(Patient-controlled epidural analgesia was compared to intravenous PCA in 38 patients undergoing posterior spinal fusion. In this study, epidermal PCA was associated with a high failure rate.)
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