Differences in Intraocular Pressure Changes During Cardiac Surgery Performed With or Without Cardiopulmonary Bypass

Abstract

Abstract: : Purpose: Anterior ischemic optic neuropathy (AION) is a well known and devastating cause of visual loss in patients who have conventional cardiac surgery with cardiopulmonary bypass (CPB). An increased intraocular pressure (IOP) during the procedure, as previously described, might contribute to the development of an AION. Currently, 10-15% of cardiac procedures are performed without CPB to reduce associated morbidity. However, off-pump (OP) heart surgery is associated with hemodynamic instability secondary to required positional changes of the patient and/or heart. Are these positional changes accompanied by significant changes in IOP? The following study was performed to compare changes in IOP during cardiac surgery with and without CPB. Methods: IOP was measured with a handheld tonometer before anesthesia induction and at several times during the surgical procedure. In addition blood pressure (BP), temperature, pCO2, pH, and hematocrit were recorded. For patients undergoing CPB (N= 27), measurements were taken just before CPB and at various times after induction of CPB. For patients having OP heart surgery (N= 7), measurements were recorded before and after repositioning of the heart and after vessel reperfusion. Results: None of the patients developed an ocular complication postoperatively. All patients showed a decrease in IOP after induction of anesthesia [P<0.0001]. In patients having CPB, a significant increase in IOP was evident within 15 minutes following initiation of CPB compared to pre-CPB levels. The average increase was 4.7±4.6 mm Hg [P<0.0001]. A pre-intubation IOP greater than 15 mm Hg was a statistically significant predictor of "maximal IOP change" [P= 0.008]. In OP patients, no IOP spikes above pre-intubation level were observed. Neither CPB nor OP patients showed a significant correlation between "maximal IOP change" and maximal change in: BP, temperature, pCO2, hematocrit or pH. Conclusions: To our knowledge, AION has not been reported in the literature in patients undergoing OP heart surgery, in contrast to cardiac surgery with CPB. The absence of IOP spikes above pre-anesthesia level in OP patients reported in this study may contribute to the absence of post-operative AION in these patients. Further studies are needed to confirm this hypothesis.

Keywords: intraocular pressure • clinical (human) or epidemiologic studies: out • neuro-ophthalmology: optic nerve