Impact of ION can be far-reaching

Ischemic optic neuropathy (ION) is a rare postoperative complication that can result in partial or complete loss of vision. ION results from an interruption of the blood supply to the optic nerve heads, which are supplied by the short posterior ciliary arteries, branches of the ophthalmic artery.

ION should be distinguished from embolic phenomenon of the central retinal artery, external compression and direct trauma to the eye, retinal detachment, and other visual cortex explanations for vision loss. Anterior ION, the subject of this article, is defined as taking place anterior to the cribriform plate (Fig. 1). The most commonly associated condition with posterior ION is giant cell arteritis.

Although most common immediately following surgery, ION can occur up to 72 hours following surgery. The visual loss associated with ION ranges from focal in one eye to bilateral no light perception (NLP). Spontaneous recovery may occur, but improvement from NLP is rare.

Occurrence
ION has been reported following otolaryngology, neurologic, general, and orthopaedic surgery in the prone, supine, and sitting positions. The greatest risk for ION is associated with surgeries, particularly scoliosis and other prolonged spine procedures, in the prone position. The occurrence rate is difficult to determine, but available statistics indicate that 0.087 percent of inpatient spine surgery patients had visual loss, and in 0.006 percent of these cases, the diagnosis was ION.

Causes
ION is most commonly associated with acute blood loss. Associated risk factors include hypotension, age, peripheral vascular disease, and diabetes, but these relationships are not clear and ION has been reported in patients with no clearly identified risk factors. Many cases of spine surgery-related ION occur following procedures that lasted more than 4 to 6 hours.

A theoretical predisposition to ION has been proposed, related to the ratio of optic nerve heads to capillary blood supply. Although this may be a factor, it is unconfirmed and has not resulted in a reliable method of risk stratification. The many contributing factors make it difficult to establish an exact correlation between any one factor and ION. No preoperative screening test can reliably stratify a patient’s risk for ION.

Treatment
No recognized therapy exists; hyperbaric oxygen, steroids, anticoagulants, vasodilators, and dextran have not been useful. A randomized trial of acute surgical decompression of the optic nerve demonstrated no effectiveness.

For this reason, recognizing and diagnosing postoperative vision disturbance is critical. Other etiologies of vision loss, such as embolic phenomena, may be treatable if diagnosed early. If the patient has documented normal vision immediately following surgery, later postoperative events, such as hypotensive episodes, may be important factors.

Prevention
Minimizing risk factors for ION—such as avoiding direct pressure to the orbit, hypotension, and anemia—is the best approach to take. Hypotension can be defined as a mean arterial pressure (MAP) of 20 mm Hg less than the patient’s base line or a MAP of less than 60 mm Hg. Anesthetic techniques for spine surgery have trended away from the use of controlled hypotension due to concerns regarding spinal cord profusion.

Facial edema can be reduced by using the reverse Trendelenberg position. Large amounts of crystalloid for fluid resuscitation can increase tissue edema and may increase periorbital edema in patients who are in the prone position for an extended time. This increased pressure may interfere with perfusion of the optic nerve heads, creating a compartment syndrome and contributing to ION. Colloid fluid resuscitation should be considered in this situation.

Informed consent and disclosure
Most institutions and states do not have clear guidelines regarding the essential elements of informed consent, especially for anesthesia. Orthopaedic surgeons and anesthesiologists, however, are generally held to a high standard of informed consent, and either can address the issue of visual loss following surgery during the consent process. A Practice Advisory from the American Society of Anesthesiologists Task Force on Perioperative Blindness recommends that the possibility of postoperative vision loss be part of the informed consent process.

The Texas Administrative Code Medical Disclosure Panel has published a list of procedures that require full disclosure of risks and hazards. It states that the possibility of permanent organ damage needs to be disclosed when general anesthesia is used.

In the case of Lindquist v. Ayerst Laboratories Inc., the court said “the anesthesia provider is not, especially for anesthesia, required to inform the patient of every conceivable risk, but only the significant risks.” In this statement, “significant” can be interpreted as either “important and serious” or “common” complications. Although the value of mentioning visual loss in the consent may be disputed due to its rarity, poorly understood etiology, unproven treatability, and unlikely impact on the decision to proceed, anesthesia closed claim analysis indicates that patients who sustained visual loss believe that they should have been informed of the risk of blindness.

Documentation of consent, however, does not relieve the provider of liability. Because communication is subjective, it is difficult to demonstrate a clear understanding of what has been communicated. Research has repeatedly demonstrated that patients not only desire full disclosure, but that their anxiety is not increased by having such information.

The poorly understood pathogenesis of visual loss is not a defense against a plaintiff’s strategy of “res ipsa loquitor.” Plaintiff attorneys focus on documentation of eye checks (even in cases of ION), hypotension, anemia, and informed consent. Closed claim analysis shows that payments are lower and less frequent in cases when consent is deemed adequate, even if lack of consent is not the primary issue of the complaint. Separate anesthesia consent documents are being developed, but many physicians simply document the communication in the notes.

Almost all ION-related medical liability suits raise the issue of informed consent. Both the surgeon and the anesthesiologist should agree on an approach to this issue before surgery. The discovery deposition is not the time to decide who is responsible for informed consent.

Litigation trends
The surgeon and anesthesiologist form an inseparable partnership during and immediately following a procedure, both legally and ethically. When singular intraoperative events such as hypotension, rapid blood loss, extended periods with a low hematocrit, facial edema, and the use of large amounts of colloid are followed by ION, there is often a search to identify a tort feasor (one who causes a civil injury for which damages are claimed). Those who may be held liable include surgeons who demand hypotension or fail to terminate an unnecessarily long surgery in favor of a staged procedure; anesthesiologists who allow prolonged hypotension, fail to appropriately administer fluid resuscitation or transfusions, or use large amounts of crystalloids for blood pressure maintenance; and operating room personnel who do not properly record and implement efforts to prevent pressure points.

Because court awards are often made on the basis of the severity of an injury and not individual culpability, the patient who had normal sight before surgery but enters a court room wearing dark glasses and using a white cane is a powerful argument against the defense.

Regardless of liability issues, ION is a tragic event. Sound surgical and anesthetic practice, a thoughtful informed consent policy, and prompt, well-documented investigation of complaints regarding postoperative visual disturbance are the best tools for the defense.

James W. Ogilvie, MD, is a member of the AAOS Medical Liability Committee; he can be reached at jwogilvie@msn.com

John Sanders, MBBS, FRCA, is an anesthesiologist.

Editor’s Note: Articles labeled Orthopaedic Risk Manager are presented by the Medical Liability Committee under the direction of contributing editor S. Jay Jayasankar, MD.

Articles are provided for general information and are not legal advice; for legal advice, consult a qualified professional.

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