Lumbar Spine Fusion (Posterior Instrumented)
Patient phenotype
Spinal stenosis, spondylolisthesis, herniated disc with failed conservative management. Typically 50-75. Comorbidities common (DM, CAD, smoker). Chronic pain + opioid tolerance frequent.
Procedure
Prone position. Posterior incision over involved vertebrae. Pedicle screws + rods + interbody graft (TLIF/PLIF technique). Length varies wildly (single level ~3 hr, multi-level ± deformity ~8+ hr).
Anesthetic plan
GETA. A-line for long cases or comorbid. Two large PIVs. Multimodal analgesia (essential — opioid-tolerant population). Neuromonitoring (SSEPs/MEPs) common — adjust anesthetic accordingly.
Setup
- ·Standard ASA + temp + Foley
- ·A-line if anticipated > 3 hr or comorbid
- ·Two large PIVs
- ·Type & screen — multi-level can lose 1-2 L
- ·Jackson table or padded prone setup
- ·Eye protection + frequent face check (POVL risk)
- ·TIVA if MEP monitoring (volatiles blunt MEP)
- ·Neuromonitoring tech communication
Biggest concerns by phase
Opioid tolerance + pain management strategy
Many spine patients on chronic opioids — tolerance + hyperalgesia. Plan: continue baseline opioid, add multimodal (acetaminophen 1 g, ketorolac if surgeon agrees, gabapentin 300-600 mg pre-op, ketamine infusion 0.1-0.3 mg/kg/hr), regional (TLIP block), realistic postop expectations.
Prone positioning — the highest-risk part
Pre-position prep: face padding, eye check, breast/genitalia clear of pressure, arms < 90° abducted (brachial plexus). Move on count of 3, ETT secure. Recheck breath sounds + ETT depth after flip (can migrate). Verify peripheral access still patent.
Postoperative visual loss (POVL) — rare but devastating
Risk factors: long prone case, blood loss > 1 L, hypotension, head dependence, pre-existing vascular disease. Strategies: head neutral, eyes free of pressure (check q15 min), avoid sustained MAP < 65, avoid hemodilution to Hb < 8, head-up when possible. Document every check.
Neuromonitoring — anesthetic affects signals
SSEPs sensitive to volatiles (limit to ≤ 0.5 MAC), opioids OK. MEPs very sensitive — TIVA preferred (propofol + remifentanil). NMB: avoid completely if MEPs needed (or use TOF maintained at 1-2 twitches). Communicate with neuromonitoring tech.
Blood loss + autotransfusion
Multi-level fusion = significant ooze (300-1500+ mL). TXA 10 mg/kg + 1 mg/kg/hr infusion reduces loss. Cell saver useful for > 2 levels. Avoid hemodilution below Hb 9 in ASA 3+.
Wake-up testing + safe position change
Some surgeons request intraop wake-up test for motor function (rare with modern MEPs). At end: flip supine before wake-up, recheck ETT, suction, awake extubation if airway favorable. Check vision + neuro exam immediately on emergence.
Mock-defense scenarios
Practice answering these out loud. The probes show what an examiner is listening for.
Mid-case during a 4-level fusion, MEPs disappear suddenly bilaterally in lower extremities. BP is 95/55, MAP 68, anesthetic is propofol 100 mcg/kg/min + remi 0.15 mcg/kg/min, no NMB. Surgeon hasn't reported anything. What's happening and what do you do?
What an examiner probes for
- ▹Differentiate: surgical (cord/nerve injury), anesthetic (drug change, hypotension), positional, technical (electrode failure)
- ▹Immediate: tell surgeon, raise MAP > 80, call neuromonitoring tech to verify electrodes
- ▹If still absent: surgeon may pause, check positioning, consider CSF drainage, steroid
- ▹Communicate: document time, vitals, drug levels, surgical step
Sources
- Miller's Ch 57
- ASA POVL Practice Advisory
- SCA spine anesthesia consensus
Anatomy reference
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