Posterior ischemic optic neuropathy related to profound shock after penetrating thoracoabdominal trauma.

ABSTRACT

Ischemic optic neuropathy is a rare cause of blindness reported most commonly in association with collagen-vascular diseases, infectious processes, and systemic hypotension related to massive exsanguinating hemorrhage. We report what we believe to be the first case of posterior ischemic optic neuropathy due to perioperative hypotension in a patient who had a penetrating thoracoabdominal injury with massive hemorrhage, severe hypotension, massive microcapillary circulatory leak, multiple system organ failure, and acute respiratory distress syndrome. Although the incidence of postoperative visual loss is low (-0.002%), awareness of this entity must be raised within the trauma surgical community.

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ISCHEMIC OPTIC NEUROPATHY is a rare cause of blindness that is usually associated with giant cell (temporal) arteritis, as well as with systemic hypertension, diabetes mellitus, hyperlipidemia, systemic lupus erythematosus, and herpes zoster ophthalmicus. (1-4) It has also been reported with systemic hypotension, most often in the context of massive hemorrhage during major surgery. (5-8) As the name implies, the common denominator of ischemic optic neuropathy is hypoperfusion of the optic nerve causing axonal injury and/or neuronal death, with consequent visual field defects and blindness.

Ischemic optic neuropathy is a diagnosis of exclusion, to be made only after eliminating other causes of optic nerve dysfunction such as inflammation, extrinsic compression, or demyelinating disease. Recovery of vision is rare, and no effective treatment has been described to date. Although systemic high-dose steroid therapy has been given, its use remains controversial. (2-9) It seems clear that the swift institution of measures to reverse hypotension offers the best opportunity for partial recovery of vision. (10)

We report what we believe to be the first case of posterior ischemic optic neuropathy (PION) due to perioperative hypotension in a patient who had a penetrating thoracoabdominal injury, with massive hemorrhage and severe hypotension, multiple system organ failure and acute respiratory distress syndrome.

CASE REPORT

A 38-year-old Hispanic man sustained a single stab wound to the left posterolateral chest at the level of the ninth thoracic vertebra (T9). In the field, his heart rate was 130/min, respiratory rate was 36/min, and blood pressure was unobtainable. The patient was transported on his side, and fluid resuscitation was initiated en route. On admission to the emergency department, his vital signs were heart rate 1 12/min, blood pressure 176/126 mm Hg, and respiratory rate 28/min, and his score on the Glasgow Coma Scale was 15. Initial hematocrit value was 43%, and Injury Severity Score was 32. Advanced trauma life support resuscitation protocols were initiated.

Physical examination revealed decreased breath sounds on the left hemithorax and diffuse abdominal tenderness. The knife remained in the patient's back and oscillated in synchrony with the patient's heart beat. The remainder of the physical examination was unremarkable. Despite an initial response to fluid resuscitation, the patient became hypotensive and was immediately transported to the operating room.

Upon arrival in the operating room, a left thoracostomy tube was inserted, yielding 700 mL of blood. Exploratory laparotomy was done with the patient positioned supine across two operating room tables and the knife dangling between the tables. Operative findings included a significant hemoperitoneum, a 10 cm diaphragmatic laceration, a splenic laceration through the hilum involving the vessels, and a through-and-through injury to the stomach with spillage of a large amount of gastric contents including undigested food containing large quantities of chili peppers into both the peritoneal and left pleural cavities.

Because of ongoing hemorrhage through the diaphragmatic laceration, a left anterolateral thoracotomy was done. The eighth and ninth intercostal arteries were found to be lacerated at their origins; their aortic ostia were closed and the distal arteries were ligated. A left lower lobe laceration was addressed with a stapled pulmonary tractotomy. (11) Splenectomy was done, both the diaphragmatic and gastric injuries were repaired, and the left upper quadrant was drained with Jackson Pratt drains. The patient required 13,000 mL of crystalloid, 16 units of packed red blood cells (5,120 mL), 8 units of fresh frozen plasma (2,560 mL), and 20 units of platelets (200 mL). Total fluid replacement was estimated at 20,880 mL, and estimated blood loss was 8 liters.

The lowest recorded intraoperative blood pressure was 80/40 mm Hg, and the worst arterial blood gas values were pH 7.12, P[CO.sub.2] 89 mm Hg, and Pa[O.sub.2] 46 mm Hg. During the procedure, the patient remained hypotensive and acidotic, damage control was undertaken, and he was transported to the surgical intensive care unit (SICU) in critical condition, on a ventilator, sedated and chemically paralyzed.

During the first postoperative day, an extremely severe microcapillary leak syndrome required resuscitation in excess of 30 liters of crystalloid, as well as increasing doses of vasopressors (including dopamine and dobutamine at 30 [micro]g/kg per minute, epinephrine at 30 [micro]g/min, and norepinephrine at 10 [micro]g/min) to maintain blood pressure. During this interval, increased airway pressures and progressively diminished cardiac and urinary output were noted. Bladder pressure was measured at 33 cm [H.sub.2]O, and physical examination was consistent with an abdominal compartment syndrome, which mandated immediate reintervention for abdominal decompression and the placement of an IV bag as a prosthetic closure of the abdomen. This was done in the SICU.

During the first postoperative week, multiple system organ failure became evidenced by poor oxygenation (necessitating high-frequency jet ventilation with increasing pressures), severe cardiovascular dysfunction, hepatic failure, and leukopenia. During the second and third postoperative weeks, the patient's oxygenation improved, vasopressors and high frequency jet ventilation were progressively discontinued, and he was able to mount a febrile response.

Cultures obtained from left upper quadrant abdominal drains grew Candida albicans. Percutaneous drainage of a loculated thoracic fluid collection detected by computed tomography (CT) grew multiple gram-negative organisms for which appropriate antibiotic and antifungal agents were instituted. The IV bag used to close the abdomen was removed, and the exposed bowel was covered with a meshed, cadaveric skin graft. A percutaneous tracheostomy was also clone in the SICU.

During the fourth postoperative week, the patient's mental status improved significantly. Despite the continued need for mechanical ventilation, he was able to indicate that his vision was poor, and ophthalmologic consultation was obtained. Funduscopic examination revealed bilateral optic nerve atrophy, which was confirmed by cranial CT. The patient was found to have bilateral PION due to perioperative hypotension caused by profound hypovolemia, severe capillary leak syndrome, and the lifesaving need for massive doses of vasopressors.

Treatment was believed to be fruitless 30 days after the presumed hypotensive ischemic insult, and prognosis was deemed to be poor. During the following week, the patient was decannulated, and a regular diet was instituted. He was subsequently transferred to a rehabilitation facility. He has been routinely followed up for 3 years after initial injury in anticipation for abdominal wall reconstruction, and he remains blind.

DISCUSSION

Loss of vision in the perioperative period is fortunately rare. By various reports, it may occur as rarely as once in 56,000 unselected anesthetic cases to as frequently as three occurrences per 100 patients having cardiopulmonary bypass. (12-15) Blindness may be caused by injury anywhere along the visual tract from cornea to occipital cortex. In the past, the most frequent cause of postoperative blindness was damage to the globe itself. (12) More common are cerebrovascular events causing infarction of the visual tracts. However, in some reviews, the most common cause of perioperative visual loss is ischemic injury to the optic nerve, accounting for about 24% of all cases. (15)

The optic nerve is anatomically divided into four distinct segments. The anterior or intraocular optic nerve consists of a short segment (about 1 mm) that passes through the lamina cribrosa of the sclera and includes the optic disk as visualized on ophthalmoscopy. The posterior or retrobulbar optic nerve is the long segment (23 to 30 mm) of nerve lying within the orbit. The next segment is the intracanalicular portion (about 8 to 10 mm) as the nerve exits the orbit to become the intracranial nerve (15 mm) before terminating in the optic chiasm. Whereas the intracanalicular and intracranial segments of the optic nerve possess a rich vascular supply, the anterior and posterior segments are significantly less well vascularized and hence far more commonly subject to injury from ischemic events. (1,16-18)

Ischemic insults can be classified into two categories, anterior ischemic optic neuropathy (AION) and PION, the latter being the rarer of the two. The optic nerve as it passes through the scleral canal is well supplied by multiple branches of the posterior ciliary arteries, which form an anastomotic ring of vessels. (19,20) In the presence of normal vessels, this ring guarantees a good blood supply. However, if the vessels are compromised by preexisting disease such as hypertension, the vascular anastomoses are tenuous, subjecting the anterior optic nerve to inadequate perfusion during periods of hypotension and resulting in AION. Diseases associated with AION include hypertension, diabetes mellitus, chronic renal failure, age >50, and systemic lupus erythematosus, all of which predispose to vascular wall hypertrophy and increased responsiveness to pressors. (1-4)

The majority of patients with AION present without a documented hypotensive event; AION is also known to be associated with hypotension, global hypoperfusion, massive crystalloid resuscitation of >20 L, with rapid intravascular volume expansion, massive blood transfusions, acute respiratory distress syndrome necessitating high positive end-expiratory pressure levels, and prone positioning in patients sustaining both blunt and penetrating thoracic and abdominal trauma. (21)

Ischemic injury to the anterior optic nerve can be broadly categorized as inflammatory or idiopathic in origin. (20,22) In giant cell or temporal arteritis, inflammation of the branches of the carotid artery results in ischemia to the supplied end organs. (1-4) This clinical syndrome is distinct, with symptoms including temporal headache, tenderness of the masseter muscles, and pain with mastication. Involvement of the optic nerve results in rapid and usually permanent blindness. This clinical syndrome is the only cause of optic nerve ischemia in which early and aggressive treatment with steroids has clearly proven utility and may result in reduction of the inflammation and partial salvage of vision.

The posterior portion of the optic nerve receives a peripheral vascular supply from the pial vessels derived from branches of the ophthalmic artery, whereas the central fibers are often supplied by branches of the central retinal artery. Although the ophthalmic artery has anastomotic connections with some branches of the external carotid arteries, this may be insufficient to protect the optic nerve from ischemia if severe hypovolemic shock occurs. (18) This is supported by the occurrence of PION after radical neck dissection (21,23-25) as compared with other surgical procedures causing PION, such as oral tumor resections, open heart surgery, (14) hip arthroplasty, or even partial gastrectomy. (5) Several predisposing factors for PION have been proposed, such as vascular disease, congenital anomalies, diabetes mellitus, or systemic hypertension. (25) None of these factors had been previously present in our patient.

The most typical clinical presentation of PION consists of acute visual loss, along with afferent pupillary defect, and the remarkable absence of ocular pain or headache. Some patients may have a prodromal transient blurring of vision. (24) Obviously, we were not able to notice these findings in our patient before noticing the development of complete blindness, since he was chemically paralyzed and sedated while on the ventilator.

The majority of patients with PION have immediate onset of visual loss, though in a small minority visual loss is delayed. This delay is hypothesized to be due to swelling of the ischemic neurons within the confines of the scleral canal. This swelling eventually impinges on the vascular supply and converts a reversible ischemic insult into irreversible axonal necrosis. (26-28) This delayed presentation may occur anywhere from several hours to 10 days after the hypotensive event. The severity of visual deficit ranges from small field defects and diminished acuity to complete loss of light perception. The classic finding consists of an altitudinal field defect, ie, loss of half of the visual field with retention of acuity in the other half. The afferent pupillary response corresponds to the degree of visual loss, with loss of pupillary response in severe injuries. On ophthalmoscopy, the optic disk is swollen. Over a period of 2 to 3 weeks, the swelling dissipates and is replaced by the pale, flat appearance of the atrophic optic disk. (29-31)

Although some series have cited an incidence of postoperative visual loss as approximately 0.1%, (32-34) some retrospective reviews found it to be no more than 0.002%. (35) Ischemic optic neuropathy seems to be the most common reported type of postoperative visual loss. Although AION is more common overall, PION is reported more frequently in postoperative patients. (36,37) We found no report of PION in penetrating trauma. Reported cases have established a firm link between severe hypotension and ischemic optic neuropathy. (8,38-10) The combination of hypotension and hemorrhage may result in PION, which basically consists of an infarct centered within the intraorbital portion of the optic nerve, precisely where the nerve is most vulnerable to ischemia if compared with the anterior, intracanalicular, and intracranial portions. (41,42)

Ophthalmoscopic examination does not reveal any change initially, but mild disk edema can be seen a few days later. Neuroimaging findings may include enlargement of the intraorbital portion of the optic nerve. (28) Fluorescent angiography reveals a delay in the onset of perfusion of the choroidal circulation in comparison with the retinal circulation. (9) In nonsurgical scenarios in which PION has occurred, magnetic resonance imaging (MRI) of the brain or carotid Doppler study might also be done to detect chronic small vessel ischernic disease.

In trauma patients, several vascular causes of postoperative loss of vision need to be excluded. Retinal artery occlusion due to emboli during the surgery will usually resolve within a few hours. Rarely, it may persist as postoperative blindness. Cortical blindness must also be excluded and has been reported after open heart surgery. (13,14,28-30) Severe hypotension may cause infarction or embolism of watershed areas in parietal or occipital lobes. Cortical blindness can be differentiated from PION by a normal pupillary response to light, as well as normal ophthalmoscopic findings. Computed tomography or MRI of the brain will confirm the diagnosis. (35)

Suspicion of ischemic optic neuropathy in a trauma patient after surgery or within the first 2 weeks after operation must prompt urgent ophthalmologic consultation, since the diagnosis of the exact location of the lesion will determine the prognosis. The treatment of PION remains unclear, but if initiated within the first 48 hours, high-dose steroids in combination with osmotic diuretics are known to decrease the optic nerve edema and assist the residual blood supply to the intraorbital portion of the optic nerve. (27) Systemic high-dose steroid therapy has been used successfully in the management of non-trauma patients. (9) However, other authors report no salvage of vision after steroid therapy, (2-4) and thus steroid therapy for PION remains controversial.

Avoiding perioperative drops in systemic blood pressure and sudden drops in hematocrit seem to be the optimal protection against postoperative loss of vision. Despite autoregulation in the retinal arteries, blood supply in choroidal or optic nerve circulation is directly related to the arterial pressure, suggesting a poor role for autoregulation on blood flow preservation. (25,26) Consequently, the maintenance of normotension is vital to prevent optic nerve ischemia. (15) Awareness of this entity must be raised within the trauma surgical community.

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RELATED ARTICLE: KEY POINTS

* Posterior ischemic optic neuropathy (PION) is a rare cause of blindness.

* The pathogenesis of PION is multifactorial.

* Ischemia and hypotension play a significant role

* Complete recovery is rare.

From the Division of Trauma and Critical Care, Department of Surgery, University of Southern California School of Medicine and the Los Angeles County/USC Medical Center.

Reprint requests to Juan A. Asensio, MD, University of Southern California School of Medicine, Los Angeles County/USC Medical Center, Division of Trauma and Critical Care, Department of Surgery, 1200 N State St, Room 10-750, Los Angeles, CA 90033-4525.