Intraocular Pressure During Abdominal Aortic Aneurysm (AAA) Repair

February 12, 2014 updated by: Amit Chopra, University of Manitoba

The Effect of Aortic Infrarenal Clamping and Unclamping On Intraocular Pressure During Abdominal Aortic Aneurysm (AAA) 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 infra-renal clamping and unclamping on intraocular pressure during Abdominal Aortic Aneurysm (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. The purpose of this observational study is to evaluate whether intraocular pressure measurements with a handheld tonometer will detect changes in intraocular pressure related to intraoperative events during aortic cross clamping and unclamping that may provide information on causes of perioperative blindness.

Study Overview

Status

Completed

Conditions

Detailed Description

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.

Study Type

Observational

Enrollment (Actual)

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

Canada
- Manitoba
  - Winnipeg, Manitoba, Canada, R2H 2A6
    - St. Boniface General Hospital

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

Genders Eligible for Study

All

Sampling Method

Non-Probability Sample

Study Population

All patients with known infrarenal abdominal aortic aneurysm for open repair will be screened through the preadmission anesthetic clinic. If they do not meet exclusion criteria and have signed informed consent for the the study, they will be enrolled to assess for changes in intraocular pressure during open abdominal aortic aneurysm repair.

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Time Perspectives: Prospective

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Right Intraocular Pressure During Various Event Intervals in Open Abdominal Aortic Aneurysm Surgery. Time Frame: Measurements made at baseline, post induction preincision, 1 min post clamp, 5 min post clamp, 1 min pre unclamp, 1 min post unclamp, 5 min post unclamp, skin closure	Intraocular pressure measurements were made with a tonometer. These measurements were recorded and kept blinded from the clinicians.	Measurements made at baseline, post induction preincision, 1 min post clamp, 5 min post clamp, 1 min pre unclamp, 1 min post unclamp, 5 min post unclamp, skin closure
Left Intraocular Pressure Time Frame: Measurements made at baseline, post induction preincision, 1 min post clamp, 5 min post clamp, 1 min pre unclamp, 1 min post unclamp, 5 min post unclamp, skin closure	Intraocular pressure measurements were made with a tonometer. These measurements were recorded and kept blinded from the clinicians.	Measurements made at baseline, post induction preincision, 1 min post clamp, 5 min post clamp, 1 min pre unclamp, 1 min post unclamp, 5 min post unclamp, skin closure

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Manitoba

Investigators

Principal Investigator: Amit Chopra, M.D., University of Manitoba, Department Of Anesthesiology, Faculty of Medicine

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

March 1, 2007

Study Completion (Actual)

August 1, 2007

Study Registration Dates

First Submitted

March 21, 2007

First Submitted That Met QC Criteria