Posterior spinal fusion

Posterior spinal fusion

Anesthesia type
Airway
Lines and access
Monitors
Primary anesthetic considerations
Preoperative
Intraoperative
Postoperative
Article quality
Editor rating	In development
User likes	0

Posterior spinal fusion is an orthopedic procedure performed to correct idiopathic scoliosis. It is the most common treatment for idiopathic scoliosis. Involved are the placement of implants (an array of hooks, screws, and wires) which are attached to affected segments of spine.

Overview

Indications

Generally indicated for severe scoliosis (Cobb angle >50 degrees).

Procedure

Patients are initially supine for intubation, line placement, and monitors. Once complete, they are flipping to the prone position. A large midline incision is made cutting through the back muscles to expose the spine. The surgeon will clear the tissue from the spine in order to create a surface for hardware placement. Controlled hypotension (MAPs no greater than the 70s, sometimes lower) limits bleeding during this part of the procedure.

Then, tightening of the wire implants stretches/distracts the spine, straightening it into midline position. It is important to maintain normotension once this begins in order to perfuse the spinal cord during distraction (which inevitably causes stretching of the nerves/nerve damage). Close neuromuscular monitoring by a technician allows surgeons to detect this early and stop manipulation. Steroids may be given if concern for nerve injury.

If the spine remains off center from the pelvis, a pelvic fixation may also be performed.

Other Interventions

Harrington rods were the original method but are no longer current as segmental implants allow surgeons more control and early mobilization without the need for bracing.

Anterior spinal fusion is another surgical method that comparatively has less blood loss and risk of neurologic injury. Advantages of posterior spinal fusion over anterior spinal fusion include avoidance of entering the thoracic cavity and potentially impairing pulmonary function.

Preoperative management

Patient evaluation

System	Considerations
Airway	ETT. Prone positioning.
Neurologic	Intra-op neuromonitoring. Avoid NMB. Steroids for protection against nerve injury.
Cardiovascular	Controlled hypotension
Pulmonary	Changes in compliance during surgical manipulation of spine
Gastrointestinal
Hematologic	Anywhere between 300 to 3000 mL of blood loss from the scraping of the epidural veins of the spine
Renal	AKI from hypovolemia or prolonged hypotension
Endocrine
Other

Labs and studies

ABG monitoring if observing significant blood loss. Should generally include lytes and iCa.

Operating room setup

1. A-line
2. 2 PIV, one large bore (16 gauge) for resuscitation and bolus of meds, one for infusions
3. Standard monitors/equipment including temperature probe/bear hugger (important given prolonged exposure
4. Ancillary equipment: Cell-saver, neuromuscular monitors

Patient preparation and premedication

Generally patients receive muscle relaxers (i.e. Valium) to help with muscle spasm that inevitably occurs with such a large surgery.

Intraoperative management

Monitoring and access

1. Evoked potentials (SSEV) are followed by a technologist.
2. Continuous arterial line blood pressure is monitored to ensure precise blood pressure control.
3. ABGs prn

Keeping track of the patient's hourly fluid goal is important to maintain intra-op euvolemia. Consider setting up the following table (example for 52 kg patient):

	Deficit	Maintenance	Insensible losses	EBL	Hourly total	Cumulative total
Hour 1	500	x (can skip while replacing fluid deficit)	x	x	500 mL	500 mL
Hour 2	500	x	375 mL	200 mL (multiply by 2 to get necessary volume to replace, in this case 400 mL)	1275 mL	1775 mL
Hour 3	x	92 mL	375 mL	x	467 mL	2242 mL

Calculating expected blood loss will help guide when to check ABG and consider transfusing blood (for a healthy patient, generally at a Hb of 7 or 8):

Example: 52 kg patient with starting Hb of 12.6

Estimated blood volume: 52 kg x 70 mL/kg = 3500 mL

Estimated cc per gram of Hb: 3500 mL divided by 12.6 g/dL = 277 mL per g Hb

To lose blood to go from Hb of 12.6 to 8.0: 12.6 - 8.0 = 4.6 g/dL Hb

Volume of blood to drop to reach transfusion threshold: 4.6 g/dL x 277 mL = 1274 mL

At an estimated blood loss of 1274 mL, the clinician can expect enough of a drop in Hb to transfuse blood.

Induction and airway management

Standard induction with the addition of large doses of opiate (in preparation for significant pain of the procedure) followed by placement of ETT. Avoid paralysis.

Positioning

Prone.

Maintenance and surgical considerations

A MAC of 0.5 for inhalational agents is used to prevent interference with intra-op neuro monitoring. Iso-nitrous is often used with these procedures but sevo and iso at low MAC is still appropriate. A mix of gas and an IV Propofol infusion can lower the MAC needed to maintain general anesthesia.

Ketamine may be considered to improve SSEV.

Emergence

Consider slowly starting to wean the Propofol infusion when surgeons begin throwing their deep dermal sutures which will help with faster emergence. Wean the gas when finished with skin and the patients is flipped back to supine positioning.

Consider extubating in the OR to perform a neuro exam prior to leaving for the PACU.

Postoperative management

Disposition

Admitted to inpatient

Pain management

Ketamine and opiate PCA. Valium prn.

Potential complications

Nerve injury. Significant blood loss.