Keywords
perioperative visual loss - spine surgery - prone position - ischemic optic neuropathy
- informed consent - perioperative visual deficit
Introduction
Perioperative vision loss (POVL) after nonocular surgery is a worrisome complication
as it has significant impact on the patient's quality of life. The reported incidence
of POVL varies from 0.05 to 1.3%.[1] Cardiac surgeries (incidence 0.09%) and spine surgeries (incidence as high as 0.2%)[2] pose the highest risk of POVL. Other nonocular surgeries associated with POVL reports
include orthopedic joint surgeries,[3] endoscopic sinus/nasal surgeries,[4] obstetrics/gynecologic, and urologic surgeries.[5] Etiologies of POVL[6] include ischemic optic neuropathy (ION) that can be anterior (AION) or posterior
(PION), and retinal ischemia, which may be due to central retinal artery occlusion
(CRAO) or branch retinal artery occlusion (BRAO), cortical blindness (CB), and corneal
abrasion (CA). In 2012, the American Society of Anesthesiologists’ (ASA) Task Force
on Perioperative Visual Loss, in its advisory, defined POVL as permanent or total
loss of vision during spine surgery under general anesthesia (GA).[7]
We describe a patient who developed permanent postoperative visual impairment after
spine surgery in prone position. Postoperative visual impairment was unanticipated,
as known risk factors during preanesthetic workup were absent. Surgical risk factors,
such as prolonged duration and extent of blood loss, were not anticipated.
Case Report
A 71-year-old female patient, 160 cm in height, weighing 65 kg, was posted for dorsolumbar
spinal decompression and fixation for D12–L1 fracture/collapse with kyphosis due to
suspected Pott's spine. She had no other comorbidities and had no ophthalmologic complaints
prior to surgery. On preoperative evaluation, she was accepted for GA in ASA physical
status II. Preoperative laboratory values were essentially normal, with hemoglobin
(Hb) level being 11.20 g/dL. She was administered injections of propofol, atracurium,
and nalbuphine at induction, in standard doses, prior to intubation. Anesthesia was
maintained with O2, air, and isoflurane. Routine ASA monitoring was done, with additional invasive blood
pressure monitoring. She was positioned prone on Allen's frame, taking due precautions.
Intraoperatively, her eyes were examined every 30 minutes via reflector mirror of
Allen's frame. Total duration of anesthesia was 6.5 hours, and the patient remained
prone for 6 hours. Estimated blood loss was 3,500 to 3,800 mL, which was managed with
adequate crystalloids, colloids (500 mL volulyte), blood (2 units packed red blood
cells), and blood products (4 units fresh frozen plasma). Hypotension, with systolic
blood pressure of 50 to 70 mm Hg, necessitated the use of noradrenaline infusion.
On completion of surgery, the patient was shifted to the neurosurgical intensive care
unit (ICU) on mechanical ventilatory support, on noradrenaline infusion. Postoperative
Hb was 6.5 g/dL, for which 2 more units of packed red cells were transfused, following
which noradrenaline infusion was tapered. The patient was extubated the following
day, around 24 hours after completion of surgery. On the second postoperative day,
she complained of diminished vision in her left eye, without any associated pain.
The loss of vision was partial, but progressive. Ophthalmologic opinion was obtained.
On confrontation, left temporal hemianopia was present, and on funduscopy, changes
suggestive of disc edema were seen. The patient was given a trial of intravenous methylprednisolone,
125 mg twice daily for 48 hours. Three months after discharge, she still has visual
impairment.
Discussion
Vision loss or deficit after surgery is a rare complication, with poor prognosis.
In AION, it typically occurs 24 to 48 hours after surgery.[8] The pressure in the central retinal artery is around 50 to 60 mm Hg, whereas intraocular
pressure (IOP) in upright position is between 10 and 15 mm Hg, providing a perfusion
pressure of approximately 50 mm Hg.[9] IOP doubles when an anesthetized patient is made prone from supine, and then continues
to rise with time, reaching 40 mm Hg after 320 minutes.[9] At an IOP of 60 mm Hg, blood flow to the optic nerve at the disc ceases. Risk factors
for ION after spinal fusion surgery are:
-
Male sex
-
Obesity
-
Use of Wilson's frame
-
Prolonged duration of surgery and anesthesia: ≥ 6.5 hours[7]
-
Significant intraoperative blood loss: ≥ 40% of estimated blood volume[7]
-
Excessive crystalloid use for blood loss replacement
This case, presumed to have developed AION, highlights that postoperative visual deficit
can occur following spine surgery in prone position, even if the patient does not
have comorbidities that increase the risk of POVL. In our case, the prolonged duration
and extent of blood loss could not be anticipated preoperatively, and consent for
possible POVL was not obtained. During retrospective analysis, it was obvious that
adequate units of blood and blood products had not been arranged. If more packed red
blood cells had been arranged and transfused intraoperatively, it is possible that
the risk of this complication could have been reduced. POVL can occur due to multiple
etiologies, and there are no proven effective treatment modalities. Therefore, disclosure
of the information and risks regarding POVL to the patient and his/her relatives preoperatively,
and obtaining the consent for the same, seems appropriate. The dilemma that arises
from this case is whether one should obtain informed consent for POVL in all spine
surgeries in prone position, including cases presumed to be at low risk preoperatively.
The second issue relates to whether the surgeon, the anesthesiologist, or both should
obtain the consent.
Depending on the suspected etiology, the investigations advised can include computed
tomography (CT) of the head, funduscopy, and fluorescein angiography. It is important
to differentiate between AION and PION, as prognosis is better in AION. AION presents
as painless loss of vision, with the lesion in or adjacent to the optic disc, whereas
PION is seen in the posterior portion of the optic nerve. Disc edema is noted in AION
but not in PION.
Other mechanisms of POVL include retinal ischemia, due to CRAO/BRAO, resulting from
external compression of the eye during surgery, and thrombotic or ischemic events
within occipital lobes during surgery, which can result in cortical blindness. The
prognosis of these types of POVL is usually not good, due to absence of any specific
therapy.
Conclusion
Perioperative visual deficit or loss can occur in patients presumed to be at low risk
on routine preoperative evaluation. There are unresolved issues on whether to obtain
consent for POVL in all cases undergoing spine surgery in prone position, even if
anticipated blood loss is not expected to be high and duration of surgery is expected
to be less than 6.5 hours. If POVL is mentioned in the consent, would it be reasonable
for both the surgeon and anesthesiologist to obtain the same? Thorough preoperative
evaluation and preparation, intraoperative positioning of patients with head neutral
or above heart level, aggressive correction of anemia, maintenance of hemodynamics,
management of intravenous fluids, and optimization of duration of surgery are the
steps that can be taken to decrease the incidence of this dreaded complication.
