Table 1.

Summary of the studies on spine fusion and ION mentioned in this review.

References	Type	Study size	ION #	Findings
Buono and Foroozon (16)	Literature based review	83 (only ION) Lumbar spine	83	*Mean hemoglobin 9.5 g/dl *Mean blood loss 3.7 L *Mean operative duration 8.7 h *Mean lowest SBP 77 mm Hg
Lee (28)	ASA POVL Registry (anonymous case submissions)	93 Lumbar spine	83	*Lowest mean hematocrit 26% *Mean blood loss 2.0 L. *Operative duration mostly > 6 h *33%, lowest SBP was > 90 mm Hg *20%, lowest recorded SBP was ≤ 80 mm Hg. *57% had SBP or MAP 20–39% below baseline *25% SBP or MAP 40–49% below baseline. *Deliberate hypotension in 25%. *Median crystalloid fluid 10 L. *Surgical positioning: Wilson frame 30% and Jackson spinal table 27%. *Mean age 50. *Hypertension 41%, diabetes 16%, and coronary artery disease 10%.
Myers (23)	Case control single institution	37 Lumbar spine	22	*Age, lowest hematocrit and lowest blood pressure no different in cases vs. controls * < 50% hypertension, diabetes, vascular disease, and smoking history. * No known vascular risk factors in 42%.
Lee (18)	Case control multi-institutional	395 Lumbar spine	80	See Table 2 for main findings
Patil (29)	Case control using NIS	600,000 lumbar fusion (also studied cervical spine)	About 120	*Incidence about 0.02% *Increased odds ratio for ION with: Peripheral vascular disease, Diabetes, Hypertension, Obesity, Anemia, Blood transfusion, Hypotension
Rubin (7)	Case control using NIS	2.5M lumbar fusion	257	*Incidence about 0.01% *Increased odds ratio for ION with: age, transfusion, and obesity. Female sex was protective

ION, ischemic optic neuropathy; MAP, mean arterial blood pressure; SBP, systolic arterial blood pressure.