Thoracic Approach to Spine Procedures

Introduction

Thoracic spine surgery can be performed from anterior, posterior, or combined approaches. Selection of the appropriate surgical approach depends on the optimal surgical procedure for the patient, the complexity of intervention to be performed, the location and extent of the pathology, and the surgeon’s comfort with each technique. Thoracic spine surgery has historically been performed from a posterior approach. Recently, the anterior approach has come in and out of favor for its ability to decrease fusion levels and avoid the posterior musculature of the spine versus its higher reoperation rates and surgical complications. There has been a resurgence in the performance of anterior surgery for various pathologies, including the novel anterior vertebral body tethering (AVBT) nonfusion scoliosis correction or anterior scoliosis correction, specifically for adolescent idiopathic scoliosis (AIS). The anterior approach is predominantly used for the correction of scoliosis but is also used in the management of thoracic disc disease, vertebral fractures, malignancy (70% of spine metastases occur in the thoracic region), and vertebral infections.

U.S. Food and Drug Administration (FDA)-approved indications for AVBT include skeletally immature patients with a scoliosis angle between 30 and 65 degrees, although slight deviations from these indications is common. Patients diagnosed with AIS typically suffer from diminished health, poor quality of life, body image disturbance, and other psychosocial effects. ^, In addition, asymptomatic adolescent patients who decline early surgical intervention undergo the natural history of the disease, which may result in progressive deformity, pain, and disability. Postponing the surgical intervention in the adult often requires a greater number of levels fused and is associated with higher complication rates, longer operative times, and greater blood loss than their adolescent counterparts.

To plan and perform a safe and appropriate anesthetic for anterior thoracic spine surgery, the anesthesiologist must discuss the case with the surgical and neuromonitoring teams, as well as the patient and/or guardian. The anterior approach to thoracic spine surgery has special perioperative important considerations for the anesthesiologist, including utilization of one-lung ventilation (OLV), blood conservation strategies, intraoperative neuromonitoring, and a multimodal approach to managing postoperative pain. This chapter will focus on management of scoliosis, as that is the most common indication for the anterior approach to thoracic spine surgery.

Case Presentation

The patient was a 12-year-old, 68-inch, 45-kg girl with double major idiopathic adolescent scoliosis defined as a typical double “S” shaped spinal curvature ( Fig. 46.1 ). She did not experience pain but had progressive worsening of her spine curvatures and significant spinal deformity with expected continued worsening of the curvatures. Because of the natural history of curvatures of the size seen in this patient that will later result in back pain, as well as the potential impact on pulmonary function, surgery was recommended.

Preoperatively, the patient was seen by her pediatrician and found to be in her usual state of good health. Laboratory findings, including a basic metabolic panel, a complete blood count, and coagulation studies were all within normal limits.

The patient and her family also met with the surgeon and extensively discussed the options for treatment. Surgical options included the standard of care posterior instrumented fusion versus the more novel AVBT procedure via a thoracic approach. It was noted that the AVBT is growth and motion sparing. The surgeon had a detailed discussion with the family regarding the risks and benefits of the AVBT procedure compared with the standard of care spinal fusion. This technique places a compressive force over the convex side of the spine (slowing down growth) to permit the concave side of the spine to relatively grow more and create a straighter spine. The goals of these procedures, as opposed to spine fusion, are to correct the spinal deformity and maintain the spine motion, particularly in the low back.

The surgeon explained that because the patient had a complex double major scoliosis, she required surgical correction of the deformity through both right-sided and left-sided incisions. The planned surgical approach on the right side consisted of a 5-cm minithoracotomy between the seventh and eighth ribs at the mid-axillary line, a second mid-axillary line portal four intercostal spaces more cephalad, and an anterior axillary line portal placed in the eighth or ninth intercostal space for introduction of the scope ( Fig. 46.2 ). After completion of the right-sided thoracic tether from T5 through T10, the surgical team would correct the left-sided curvature. The surgical team would then perform a left-sided correction from T10 to L3 through a limited thoracotomy between the 10th and 11th ribs and a portal proximal to the thoracotomy incision in the mid-axillary line to permit access to the distal thoracic spine ( Fig. 46.3 ).

The surgeon instructed the patient to take gabapentin 100 mg 3 times a day for 1 week before surgery.

Case Management

The patient presented for surgery in her usual state of good health. A confirmatory type and screen was drawn and 2 units of packed red blood cells were placed on hold in the blood bank. The anesthesiologist assessed the patient, discussed the anesthetic plan, including its risks, benefits, and alternatives, and answered all questions of the patient and her family. An intravenous catheter was then placed.

Before induction of anesthesia, the patient was administered three nonopioid analgesics to mitigate postoperative pain: gabapentin 300 mg by mouth (PO), acetaminophen 650 mg PO, and celecoxib 200 mg PO. She then received midazolam 4 mg for anxiolysis and anterograde amnesia and was transported to the operating room. The perioperative team assisted her into a sitting position in which a thoracic epidural was placed via a paramedian approach one to two rib spaces above the planned site of the postoperative chest tubes and above the major scoliotic curvature for ease of placement, at the T6–T7 interspace.

The patient was then positioned supine on a Jackson table with a flat-bed insert. After placement of standard American Society of Anesthesiologists monitors and preoxygenation, general anesthesia was induced with weight-appropriate dosages of lidocaine (1.5 mg/kg), propofol (2 mg/kg), fentanyl (4 mcg/kg), ketamine (0.5 mg/kg), and succinylcholine (2 mg/kg). The patient was orally intubated with a 7.5 mm single-lumen standard cuffed endotracheal tube (ETT). After successful endotracheal intubation, the tube was secured using adhesive and umbilical tape.

Total intravenous anesthesia (TIVA) was initiated for maintenance of anesthesia. This consisted of propofol (100–150 mcg/kg/min), fentanyl (1–3 mcg/kg/h), dexmedetomidine (0.2 mcg/kg/h) and a ketamine infusion (for a total of 1.5–2.5 mg/kg during the case). A phenylephrine infusion (0.05–0.5 mcg/kg/min) was needed intermittently to maintain mean arterial pressure over 85 mm Hg at critical portions of the procedure to optimize spinal cord perfusion, particularly during placement of implants and vertebral correction. A total of 8.83 mg of phenylephrine was used during the case.

A 9-Fr bronchial blocker (BB) was placed in the lumen of the right mainstem bronchus with the aid of a 4.0 mm flexible fiberoptic bronchoscope in anticipation of the right-sided procedure. A second large-bore 18-gauge intravenous (IV) line was placed for the administration of intravenous anesthetics, fluids, and potential blood products. In addition, a radial arterial line was secured for close hemodynamic monitoring and laboratory ­assessment of oxygenation, hematocrit, and serum electrolytes. A neuromonitoring team placed electrodes on the patient for monitoring somatosensory evoked potentials (SSEPs), transcranial motor evoked potentials (TcMEPs), and electromyography (EMG) to continually assess spinal cord ­integrity for the duration of the case. A bite block was placed to protect the tongue from injury during the performance of TcMEPs.

The patient was positioned in the left lateral decubitus position and an axillary roll was placed to relieve pressure on the neurovascular plexus of the dependent arm. All pressure points on the upper and lower extremities were well-padded. Care was taken to ensure that there was no excessive pressure on the eyes and ears. A final positioning check was performed before surgical preparation and draping.

Dexamethasone 10 mg IV was administered for antiinflammatory and antiemetic effects. Cefazolin and gentamicin were dosed by weight for antimicrobial prophylaxis.

A preincisional bronchoscopy was performed to ensure proper placement of the BB in the right mainstem bronchus. Subsequently, the cuff on the BB was inflated, initiating OLV, and the lumen of the BB was placed on gentle suction to facilitate lung deflation to optimize surgical exposure. To improve oxygenation during the early stages of OLV, the patient was placed on an fraction of inspired oxygen (FiO2) of 100% for 15 to 30 minutes and then maintained on an FiO2 of 80% to 100% for the duration of the procedure with a target oxygen saturation (SpO2) over 94%.

Vertebral body screws were placed and connected with a tethering cable to correct the scoliosis. Next, the incision was closed and a chest tube was placed in the seventh intercostal space. The BB was then deflated to reinitiate two-lung ventilation. Next, the patient was returned to the supine position and the placement of the BB in the left mainstem bronchus was facilitated by the use of fiberotic bronchoscopy. The patient was placed in the right lateral decubitus position for left-sided scoliosis correction. Once completed, a chest tube was inserted in the 10th intercostal space on the left side.

Approximately 1 hour prior to the conclusion of the procedure, the dexmedetomidine, fentanyl, and ketamine infusions were discontinued. After closure of the diaphragm and chest wall, the propofol infusion was slowly titrated down to allow for timely anesthesia emergence and extubation. At the end of the surgery, the patient was returned to the supine position and extubated. Total operative time was 300 minutes and estimated blood loss was 500 mL. In the operating room, a neurologic examination was performed by the surgical team to assess spinal cord and nerve root integrity. Subsequently, the patient was transferred to the pediatric intensive care unit (PICU) for postoperative care and observation. Note that a pediatric stepdown unit may also be appropriate depending on the institution.

Once in the PICU, the patient-controlled epidural analgesia (PCEA) infusion of hydromorphone (5 mcg/mL) at a rate of 20 mcg/h with three demand doses of 10 mcg available per hour was initiated. In addition to PCEA, the postoperative pain regimen consisted of acetaminophen (15 mg/kg IV every 6 hours; maximum 1 g/dose), ketorolac (0.5 mg/kg IV every 6 hours for 3 days) and gabapentin (100 mg PO three times daily). The acute pain service assessed the patient’s pain regimen each morning and further tailored it as appropriate. Hydromorphone (0.3–0.6 mg IV q2h) for pain and diazepam (2–4 mg IV q8h) for spinal muscle spasms were administered as needed. The chest tubes were removed on postoperative day 3, after which the epidural infusion was stopped, and the catheter was removed. Once the patient’s pain was well controlled on oral medications and she was able to ambulate, she was discharged home from the hospital.

The postoperative, postdischarge analgesic regimen consisted of several medications. The patient was prescribed a 10-day supply of oxycodone 5 mg PO every 4 hours (plus additional tablets for breakthrough pain as needed), diazepam 2 mg PO every 8 hours as needed for muscle spasms, ibuprofen 400 mg PO three times daily, acetaminophen 15 mg/kg PO every 6 hours, and gabapentin 100 mg PO three times daily. The patient was instructed to take polyethylene glycol 17 g PO twice a day and docusate 100 mg PO three times daily to mitigate the side effect of constipation. As an aside, note that if the patient does not tolerate oxycodone because of nausea or it does not provide adequate analgesia, the surgical team can provide an equivalent dosage of oral morphine or hydromorphone.

Risks, Benefits, and Alternatives