Nothing terrifies an anaesthetist as much as the prospect of a patient waking up blind. It happens, but very infrequently. Who is at risk? What surgeries? What are the risk factors? Is there anything we can do to prevent and treat visual loss?
Perioperartive visual loss is associated with posterior ischemic optic neuropathy (ION), anterior ION, and central retinal artery occlusion (CRAO).
1. Preoperative Patient Evaluation and Preparation
- There are no clear preoperative patient characteristics that predispose patients to perioperative ION.
- However – prolonged procedures, particularly with the head elevated, with substantial blood loss (44.7%) appears to identify high risk patients. Spine surgery in the prone position that goes on for several hours (>6.5 hours) appears to be the highest risk operation.
- So Risks:
- Large volume blood loss
- Prolonged surgery
- Prolonged surgery with significant blood loss.
- There is no evidence that an ophthalmic or neuro-ophthalmic evaluation would be useful in identifying patients at risk for perioperative visual loss (PVL).
- Anaesthetists should consider informing patients in whom prolonged procedures, substantial blood loss, or both are anticipated that there is a small, unpredictable risk of perioperative visual loss.
- Because the frequency of visual loss after spine surgery of short duration is very low, it is probably unnecessary to inform all spine surgery patients of this risk.
- So Risks:
2. Intraoperative Management
Blood Pressure Management
- Systemic blood pressure should be monitored continually in high-risk patients.
- The use of deliberate hypotensive techniques during spine surgery has not been shown to be associated with the development of PVL (perioperative visual loss).
- The use of deliberate hypotension for these patients should be determined on a case-by-case basis.
- Blood pressure should be maintained within 24% of baseline, and the systolic blood pressure should not fall below 84mmHg. In addition, extreme care should be taken with patients that have chronic hypertension.
Management of Intraoperative Fluids
- Central venous pressure monitoring should be considered in high-risk patients (I disagree with this recommendation as I believe that there is no evidence that CVP is an accurate measure of blood volume or anything else for that matter).
- Colloids should be used along with crystalloids to maintain intravascular volume in patients who have substantial blood loss.
Management of Anemia
- Haemoglobin values should be monitored periodically during surgery in high-risk patients who experience substantial blood loss.
- However, there is no documented lower limit of hemoglobin concentration that has been associated with the development of perioperative visual loss. Experts suggest keeping HgB >9.4g/dL.
- Thus there is no clear transfusion threshold to prevent PVL.
Use of Vasopressors
- There is insufficient evidence to provide guidance for the use of α-adrenergic agonists in high-risk patients during spine surgery. There is concern that prolonged use of vasopressors may precipitate optic nerve ischaemia (although I don’t believe that there is any published evidence on this point).
- Prone positioned patients often emerge with significant facial oedema. There is no pathophysiologic mechanism by which facial oedema can cause perioperative ION.
- There is no evidence that ocular compression causes isolated perioperative anterior ION or posterior ION.
- Direct pressure on the eye should be avoided to prevent CRAO.
- The high-risk patient should be positioned so that the head is level with or higher than the heart when possible.
- The high-risk patient’s head should be maintained in a neutral forward position (e.g., without significant neck flexion, extension, lateral flexion, or rotation) when possible.
3. Staging of Surgical Procedures
- Staged spine surgery procedures may decrease the risk of PVL in some patients and should be considered.
4. Postoperative Management
- A high-risk patient’s vision should be assessed when the patient becomes alert (e.g., in the recovery room, intensive care unit, or ward).
- If there is concern regarding potential visual loss, an urgent ophthalmologic consultation should be obtained to determine its cause.
- Additional management may include optimizing blood pressure, haemoglobin and oxyhaemoglobin saturation.
- To rule out intracranial causes of visual loss, consider magnetic resonance imaging.
- There is no role for antiplatelet agents, steroids, or intraocular pressure-lowering agents in the treatment of perioperative PVL.