Intraocular Pressure During Abdominal Aortic Aneurysm Repair

The objective of this study will be to answer a clinical question that has not already been investigated; that is, what are the effects of aortic infrarenal clamping and unclamping on intraocular pressure during AAA repair? Depending on the results, this study may raise or alleviate concern that vascular surgery for abdominal aortic aneurysm could contribute to early perioperative exacerbation of pre-existing eye disease and increase a patient's vulnerability to developing a type of blindness known as ischemic optic neuropathy.

Perioperative blindness in nonocular surgery has gained significant clinical interest as an overwhelming complication with an increasing incidence. Initial published studies suggested a rare occurrence with an estimated postoperative visual loss of 0.002% and 0.0008% (1,2). However, retrospective reviews in spinal and cardiac surgery demonstrated higher rates of perioperative blindness; that is, between 0.2% and 0.06% respectively (3,4). The difference in published reports suggests that the true incidence is likely underestimated because of fears regarding litigation, ineffective means of reporting and extra work involved. Fortunately, numerous case reports and series in the middle to late 1990s were published; prompting the American Society of Anesthesiologists (ASA) Committee on Professional Liability to establish the ASA Postoperative Visual Loss Registry (POVL) in 1999 as a medium to collect confidential, comprehensive perioperative data on patients developing postoperative blindness.

The POVL registry, along with other case series, has demonstrated that the most common cause of visual loss is non-arteritic ischemic optic neuropathy (5,6,7). Perioperative non-arteritic ischemic optic neuropathy (ION) is a consequence of patient and surgery specific factors that results from hypoperfusion and infarction of the optic nerve head (8). Anatomical factors such as variation in the number of short posterior ciliary arteries (sPCA) supplying the optic nerve head, location of sPCA watershed zone, and small optic cup to disk ratio increase susceptibility to optic nerve ischemia (8,9). Surgery specific factors involve profound blood loss, anemia, hypotension, prone positioning and duration of surgery (5,6,7,10). The interaction of these surgical variables and patient specific anatomical factors can decrease ocular perfusion pressure (the difference between mean arterial pressure and intraocular pressure) and result in ION (11).

Based on the determinants of ocular perfusion pressure (OPP), low mean arterial pressure (MAP) and/or high intraocular pressure (IOP) can decrease OPP and lead to ION. Therefore, it is necessary to investigate changes in IOP incurred from different types of surgery that may increase vulnerability to developing ION. Normal IOP is between 12 - 20 mm Hg. Studies have been published assessing intraocular changes with prone positioning, laparoscopic surgery and cardiopulmonary bypass (12,13,14). However, there has been no literature evaluating intraocular pressure during abdominal aortic aneurysm (AAA) repair. AAA repair is a high-risk surgery associated with blood loss, hypotension and has been reported in a case series associated with ION (6). The surgery involves clamping and unclamping of the aorta to facilitate excision of the aneurysm and graft repair. Aortic cross clamping and unclamping is an intense physiologic insult affecting venous return, systemic vascular resistance, cardiac output, and acid base status. These physiologic changes are further pronounced with more proximal cross-clamping and longer duration. Because infrarenal abdominal aortic aneurysms are the most common type of AAA repair, we will be assessing IOP with patients undergoing elective infrarenal abdominal aortic reconstruction.

Infrarenal aortic cross clamping is associated with increases in venous return, central venous pressure and arterial blood pressure (15). The hemodynamic changes with infrarenal unclamping entail decreases in venous return, central venous pressure and arterial blood pressure (15). The determinants of intraocular pressure involve extraocular muscle tone, aqueous flow, choroidal blood volume and central venous pressure (16). The volume redistribution proximal to the aortic cross-clamp should cause a rise in venous pressure, increase resistance to aqueous drainage and increase choroidal blood volume thereby increasing intraocular pressure. However, after aortic unclamping, choroidal blood volume and IOP should decrease as venous return and central venous pressure decline. Therefore, our hypothesis is that IOP will be increased during aortic cross clamping and decreased following aortic unclamping.

• Perioperative Blindness
• Intraocular Pressure
• Ischemic Optic Neuropathy

• Roth S, Thisted RA, Erickson JP, Black S, Schreider BD. Eye injuries after nonocular surgery. A study of 60,965 anesthetics from 1988 to 1992. Anesthesiology. 1996 Nov;85(5):1020-7.
• Warner ME, Warner MA, Garrity JA, MacKenzie RA, Warner DO. The frequency of perioperative vision loss. Anesth Analg. 2001 Dec;93(6):1417-21, table of contents.
• Stevens WR, Glazer PA, Kelley SD, Lietman TM, Bradford DS. Ophthalmic complications after spinal surgery. Spine. 1997 Jun 15;22(12):1319-24.
• Nuttall GA, Garrity JA, Dearani JA, Abel MD, Schroeder DR, Mullany CJ. Risk factors for ischemic optic neuropathy after cardiopulmonary bypass: a matched case/control study. Anesth Analg. 2001 Dec;93(6):1410-6, table of contents.
• Lee LA, Roth S, Posner KL, Cheney FW, Caplan RA, Newman NJ, Domino KB. The American Society of Anesthesiologists Postoperative Visual Loss Registry: analysis of 93 spine surgery cases with postoperative visual loss. Anesthesiology. 2006 Oct;105(4):652-9; quiz 867-8.
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• Myers MA, Hamilton SR, Bogosian AJ, Smith CH, Wagner TA. Visual loss as a complication of spine surgery. A review of 37 cases. Spine. 1997 Jun 15;22(12):1325-9.
• Hayreh SS, Jonas JB. Optic disc morphology after arteritic anterior ischemic optic neuropathy. Ophthalmology. 2001 Sep;108(9):1586-94.
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• Williams EL, Hart WM Jr, Tempelhoff R. Postoperative ischemic optic neuropathy. Anesth Analg. 1995 May;80(5):1018-29. Review. No abstract available.
• 11 Hayreh SS. Anterior ischemic optic neuropathy. Clin Neurosci 1997;4:251-63.
• Cheng MA, Todorov A, Tempelhoff R, McHugh T, Crowder CM, Lauryssen C. The effect of prone positioning on intraocular pressure in anesthetized patients. Anesthesiology. 2001 Dec;95(6):1351-5.
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• Larkin DF, Connolly P, Magner JB, Wood AE, Eustace P. Intraocular pressure during cardiopulmonary bypass. Br J Ophthalmol. 1987 Mar;71(3):177-80.
• Gelman S. The pathophysiology of aortic cross-clamping and unclamping. Anesthesiology. 1995 Apr;82(4):1026-60. Review. No abstract available.
• Murphy DF. Anesthesia and intraocular pressure. Anesth Analg. 1985 May;64(5):520-30. No abstract available.

Inclusion Criteria:

• All patients presenting to St. Boniface General Hospital for elective AAA repair requiring an arterial line, central line and general anesthesia will be eligible for inclusion in this study.

Exclusion Criteria:

• . The exclusion criteria for this study are:

  1. Patients with a history of acute or chronic eye disease
  2. Allergy to topical ophthalmologic anesthesia
  3. Patients receiving nitrous oxide, ketamine or succinylcholine during anesthesia
  4. If the surgical procedure will require the aorta to be re-clamped following unclamping, those patients will also be excluded
  5. Patients that are VRE+ or MRSA+ will be excluded for infection control purposes