SNACC-affiliated Centers Determine Risk Factors
For Ischemic Optic Neuropathy After Spinal Fusion Surgery
Postoperative visual loss (POVL) associated with spine surgery in adults is most often caused by ischemic
optic neuropathy (ION).1 The incidence of ION after spine surgery has been reported as high as 1 in 1000
spine operations.2 Because of this low incidence, determination of risk factors has been problematic.
Many suggested risk factors cited in the literature arose from case reports or case series, and may have
been surrogate markers of other perioperative events. In 1999, the American Society of
Anesthesiologists (ASA) Committee on Professional Liability established the ASA POVL Registry to collect
detailed perioperative data on cases of visual loss occurring after non-ocular surgery.3 The perioperative
profile of the ION cases associated with spine surgery were characterized by lengthy operative duration
(94% with an anesthetic duration of 6 or more hours) and large estimated blood loss (82% with an
estimated blood loss of one or more liters). Collection of cases by this voluntary national registry
allowed accumulation of the largest number of ION cases with detailed perioperative data to date.
Subsequently, the ION cases associated with prone spinal fusion surgery from the ASA POVL Registry
were utilized in a multicenter case control study to determine risk factors for this complication.4
Seventeen centers from across North America affiliated with SNACC who performed a large volume of
spinal fusion operations contributed controls for this study. Cases and controls were matched by year of
surgery from a database of over 43,000 control spinal fusion operations. After inclusion / exclusion
criteria were met, 80 ION cases were matched to 315 controls.4
Using stepwise multivariate logistic regression, independent risk factors for ION associated with spinal
fusion surgery were male sex, obesity, use of the Wilson surgical spine frame, increasing anesthetic
duration, increasing blood loss, and use of a decreased percentage of colloid in the nonblood volume
administration.7 Blood pressure less than 40% below baseline for a minimum of 30 minutes and lowest
hematocrit were not independent risk factors in the multivariate logistic regression, although they were
significant in the univariate analysis (p < 0.05). These results indicate that hypotension and anemia were
correlated with other risk factors with a stronger effect such as blood loss, duration, or fluid
administration.
Using published incidences of ION after spinal fusion surgery, a risk prediction table was created
demonstrating the absolute and relative risk for ION based on these six risk factors. Utilizing this table,
an obese male undergoing a ten hour prone spinal fusion operation on a Wilson frame with an
estimated blood loss of three liters and no use of colloid in the non-blood replacement would have a
632 fold increased risk of developing ION compared to a non-obese female undergoing spinal fusion
surgery on a non-Wilson frame for five hours with one liter of estimated blood loss and use of 10%
colloid in the non-blood administration. This risk prediction table may help guide decision making for
patients, surgeons and anesthesiologists in their management of patients with spine disease.
REFERENCES
1. Shen Y, Drum M, and Roth S. The prevalence of perioperative visual loss in the United States: A 10year study from 1996 to 2005 of spinal, orthopedic, cardiac, and general surgery. Anesth Analg.
2010; 109:1534-45.
2. Stevens WR, Glazer PA, Kelley SD, et al. Ophthalmic complications after spinal surgery. Spine. 1997;
22:1319-24.
3. Lee LA, Roth S, Posner KL, Cheney FW, et al. The American Society of Anesthesiologists Postoperative
Visual Loss Registry: analysis of 93 spine surgery cases with postoperative visual loss. Anesthesiology
2006; 105:652-59.
4. The Postoperative Visual Loss Study Group. Risk factors associated with ischemic optic neuropathy
after spinal fusion surgery. Anesthesiology. 2012; 116:15-24.