| Transcript |
Today, we're going to be talking about a coronary artery bypass graft, and not all the information that you need--just the neuron pieces. So we're going to talk about vision loss from having a coronary artery bypass. It is exactly what it says; we're trying to use a graft, using usually a saphenous vein graft that has been harvested from the leg, to bypass the obstruction in the coronary artery, and you don't need to know all the coronary arteries. You do need to know there's a right side and a left side, the right coronary, the left anterior descending, the circumflex. They have names--marginal, obtuse--you need to know a little bit about the coronary arteries. And that translates into how many of these arteries that they're going to bypass. So it might be x 1 x 2 x 3 x 4 depending on how many vessel disease you might have. And the reason you need to know it is, if you have a coronary artery bypass graft, you might have vision loss either right after surgery, or in the peri-or post-operative period, which usually is defined as less than 30 days. The main categories of vision loss, if you're unilateral or bilateral, is anterior ischemic optic neuropathy of the non-arteritic type. It can also be a normal appearing optic nerve initially and then turn pale; that is a posterior ischemic optic neuropathy. And you might have an embolic phenomenon, either a branch retinal artery occlusion or central retinal artery occlusion, that's way more likely to occur if you have the pump. And so you need to know whether this bypass graft is done on the pump or off the pump. So the off-pump coronary artery bypass graft is sometimes called the "beating heart CABG, "because they literally are operating and the heart has not been stopped because they're not on cardiopulmonary bypass. Obviously, that's a little more tricky to do the anastomosis on. If you're on the pump or if you're not on the pump, and you just have AFib post-operatively or you have embolus fly off in the perioperative period, you can get a central retinal artery occlusion or a branch retinal artery occlusion. And you could get cortical vision loss, either a homonymous hemianopsia from an intracranial stroke, or cortical visual impairment, cortically blind if it's both sides. So these are the main things we're looking for in post-operative vision loss, post-op POVL. Patients bring to the operating room their risk factors, including the ones you would expect for CABG--older patient, vasculopathic risk factors, hypertension, diabetes, high cholesterol, male, obesity, smoker, the usual things. And then you have intra-operative risk factors that occur from the CABG. The two most common surgeries that we see post-operative vision loss are spine surgery, which is the face down position, and coronary artery bypass graft because you're obviously working on the heart. The factors that we're going to be worried about are the blood pressure, including the use of vasoconstrictors; we're going to be worried about their blood volume, and whether they were replaced with crystalloid or colloid, colloid is going to hold the oncotic pressure and the intravascular volume better so crystalloid is not as good a choice; anemia, which is the blood counts, and whether they were transfused and how much blood loss they had; and then the positioning, and the positioning matters in spine surgery because they're in the facedown position because they're operating on their spine. In CABG the positioning matters because they might be using the Trendelenburg position, and if you're in the Trendelenburg position, the venous return might be compromised, and that will lead to facial edema, compromise of the venous return and could elevate the intraocular pressure. And so, the positioning can affect the intraocular pressure, they're normally not measuring the intraocular pressure so we really don't know what's going on during CABG for the IOP, and you need to know that the perfusion pressure of the optic nerve equals the mean arterial pressure minus the intraocular pressure. So anything that drops the MAP, including hemodynamic instability after CABG, or that raises the IOP, including the Trendelenburg position or the poor venous return created by the positioning, can lead to a perfusion pressure drop of the optic nerve and produce either non-arteritic anterior ischemic optic neuropathy or non arteritic posterior ischemic optic neuropathy. We're going to look in the eye for the emboli, and we're going to do a scan, MRI, to look for cortical visual loss if the eye exam is normal but they have vision loss. So you need to know a little bit about how a coronary artery bypass graft is done, and that post-operative vision loss can manifest to you in the eye(CRAO,BRAO,PION, AION),or in the brain(homonymous hemianopsia or cortical visual impairment). We're going to look at that op report, see how many vessels were operated on, whether it was on-pump or off-pump, and check the blood pressure, the blood volume, the blood counts, and what was the positioning of the patient |
