MedWire News: Factors including obesity, Wilson frame use, long duration of anesthesia, and large estimated blood loss increase patients’ risk for ischemic optic neuropathy (ION) after spinal fusion surgery, report researchers.
Perioperative visual loss, usually caused by ION, is a very rare event, making it difficult to pinpoint risk factors. For the current study, the team led by Lorri Lee (University of Washington, Seattle, USA) identified 80 patients with ION from the American Society of Anesthesiologists Postoperative Visual Loss Registry and matched each one by the year of surgery to four patients who underwent spinal fusion surgery in 17 academic medical centers.
After accounting for multiple confounders, male gender, obesity, Wilson frame use, duration of anesthesia, and estimated blood loss were positively associated with risk for ION. Colloid as percent of total nonblood replacement was negatively associated with ION risk.
The number of fusions was also a risk factor in initial analyses, but proved to be a surrogate for duration of anesthesia and estimated blood loss.
Previous studies have reported ION to occur at rates of 0.017% and 0.1%. Based on an overall rate of 0.017%, the highest absolute risk for ION, of 48.11 per 10,000 procedures, occurred in men who were obese, were placed on a Wilson frame, had anesthesia lasting at least 10 hours, an estimated blood loss of at least 3 L, and no colloid in nonblood replacement. Their absolute risk based on an overall rate of 0.1% was 283.00 per 10,000 procedures.
Women with the above risk factors had absolute risks of 18.98 and 111.67 per 10,000 procedures if overall rates were 0.017% and 0.1%, respectively. Women with none of these factors represented the lowest-risk group, with corresponding absolute risks of 0.08 and 0.45 per 10,000 procedures.
The researchers note that most of the risk factors identified support the concept that venous congestion in the optical canal could underlie many cases of perioperative ION. They say that increased venous pressure in the head and neck could lead to “interstitial fluid accumulation from capillary leak, decreased venous outflow, and decreased perfusion of the optic nerve,” leading to damage. This is further supported by the fact that most cases involve the posterior optic nerve where there is poor collateral flow, they add.
But Lee et al observe that “the only preoperative factor that is practically modifiable” is avoiding surgical frames, such as the Wilson frame, that position patients’ heads lower than their hearts. Although the percent colloid in nonblood replacement was a statistically significant factor, the actual difference in percent colloid between cases and controls was just 4%, “making its clinical significance less certain.”
In an editorial accompanying the paper in Anesthesiology, Mark Warner (Mayo Clinic, Rochester, Minnesota, USA) says: “The lead authors and the many contributors to this study deserve our congratulations for creatively providing insights that finally allow us to move forward with additional studies.”
He adds: “Their work offers hope that we may one day reduce or eliminate perioperative blindness in spine surgery patients.”
The Postoperative Visual Loss Study Group. Risk Factors Associated with Ischemic Optic Neuropathy after Spinal Fusion Surgery.
