Cerebral microembolism during cardiopulmonary bypass. Retinal microvascular studies in vivo with fluorescein angiography.

To observe microembolic events in the central nervous system during cardiopulmonary bypass, we subjected 21 patients undergoing elective coronary operations to retinal fluorescein angiograms 5 minutes before cardiopulmonary bypass was discontinued. Patients with diabetes or clinically evident cerebrovascular disease were excluded. Bubble oxygenation and nonpulsatile perfusion were used for bypass. After 31 to 167 minutes of cardiopulmonary bypass, all 21 (100%) patients had retinal microvascular occlusions indicative of microembolism. Control fluorescein angiograms obtained preoperatively and in five patients immediately before bypass but after aortic cannulation showed retinal perfusion. During bypass there was a mean of 3.5 (range 1 to 7) blocked arterioles of less than 50 micron caliber and a mean of 6.3 (range 1 to 10) focal areas of capillary nonperfusion per 30-degree field of retina centered on the macula per patient. Repeat studies 30 minutes after discontinuation of bypass showed partial reperfusion with occlusions in four of the five (80%) patients and a decrease in the mean total microembolic count from 12.6 to 4.8 (38%). In later studies at a median of 8 days postoperatively, only two of 16 (12.5%) patients had persistently occluded retinal vessels. The total microembolic count did not correlate with bypass time (r = 0.14) and was not reduced by arterial line filtration with a Pall 40 micron filter (Ultipore) in a subgroup of 11 patients. Twenty patients completed four standardized psychometric tests. Retinal microvascular occlusions were more numerous in those patients with a psychometric deficit (n = 7) than in those with no deficit (n = 13; p = 0.075). In a dog model of cardiopulmonary bypass, eight of nine (88.9%) had retinal microvascular occlusions after 10 to 90 minutes of bypass. Retinal histologic studies revealed intravascular platelet-fibrin microaggregates 20 to 70 micron in diameter and focal ischemic changes in seven of the nine (77.8%) dogs. Six dogs undergoing sham bypass had normal retinal perfusion and histologic findings. This study demonstrates a very high incidence of microvascular occlusions in the territory of the internal carotid artery during bypass consistent with a microembolic origin. The clinical significance of these findings is uncertain.

Atheroembolism from the ascending aorta. An emerging problem in cardiac surgery.

As the ages of patients undergoing cardiac operations have increased, noncardiac causes of death have increased. To identify these causes of death, we analyzed the autopsy findings in 221 patients undergoing myocardial revascularization or valve operations between 1982 and 1989. Mean age was 65.6 +/- 9.5 years and the range was from 32 to 94 years; 130 patients (58.8%) were male. Autopsies were complete in 129 patients (58.4%) and limited to the chest and abdomen in the remainder. Embolic disease was identified in 69 patients (31.2%). Atheroemboli or abnormalities consistent with atheroemboli were identified in 48 patients (21.7%). Fourteen patients had thromboembolism and 7 had disseminated intravascular coagulation. The prevalence of atheroembolic disease increased dramatically from 4.5% in 1982 to 48.3% in 1989 (p = 0.001). Atheroembolic disease was found in the brain in 16.3% of patients, spleen in 10.9%, kidney in 10.4%, and pancreas in 6.8%. Thirty (62.5%) of the 48 patients had multiple atheroembolic sites. Atheroemboli were more common in patients undergoing coronary artery procedures (43/165; 26.1%) than in those undergoing valve procedures (5/56; 8.9%) (p = 0.008). There was a high correlation of atheroemboli with severe atherosclerosis of the ascending aorta. Atheroembolic events occurred in 46 of 123 patients (37.4%) with severe disease of the ascending aorta but in only 2 of 98 patients (2%) without significant ascending aortic disease (p less than 0.0001). Forty-six of 48 patients (95.8%) who had evidence of atheroemboli had severe atherosclerosis of the ascending aorta. There was a direct correlation between age, severe atherosclerosis of the ascending aorta, and atheroemboli. Incremental risk factors for atheroembolic are peripheral vascular disease and severe atherosclerosis of the ascending aorta.

Influence of oxygenator type on the prevalence and extent of microembolic retinal ischemia during cardiopulmonary bypass. Assessment by digital image analysis.

We have previously reported the occurrence of microembolic ischemia in the retina during cardiopulmonary bypass, as revealed by fluorescein angiography. This method has been extended by digital image analysis to include quantification of the extent of retinal ischemia and has been applied to a prospective comparative study of 64 patients undergoing elective coronary operations with either a bubble or a membrane oxygenator. Patients with diabetes or clinically evident cerebrovascular disease were excluded. Bypass procedures were standardized in all cases with pulsatile flow and a 40 microns arterial line filter (Pall EC Plus). Thirty patients had bypass with a bubble oxygenator (Harvey H1700) and 34 patients had bypass with a flat sheet membrane oxygenator (COBE CML). In each case retinal fluorescein angiograms were obtained preoperatively and 5 minutes before the end of bypass and were processed with a digital image analyzer (Context Vision GOP-302). Microembolic perfusion defects were identified by digital subtraction of preoperative and end-bypass angiograms and their total area was computed. Results. In the bubble oxygenator group retinal perfusion defects indicative of microembolism occurred in all 30 (100%) patients. In contrast, over half the patients in the membrane oxygenator group had normal retinal perfusion, and the prevalence of perfusion defects (44%; 70% confidence limits 34% to 54%) was significantly less than in the bubble group (p less than 0.001). In addition, those patients in the membrane group had significantly fewer lesions (median 0; 70% confidence limits 0 to 1) than patients in the bubble group (median 2; 70% confidence limits 2 to 2; p less than 0.001) and also had significantly smaller total areas of retinal ischemia (median 0 mm2; 70% confidence limits 0 to 0.16 mm2) than the bubble group (median 0.22 mm2; 70% confidence limits 0.21 to 0.27 mm2; p less than 0.001). There was no relationship between the extent of retinal ischemia and bypass time, arterial blood gas concentrations, volume of cardiotomy suction or donor blood returned to the pump, or recent medication with aspirin. Inferences. Digital image analysis of retinal fluorescein angiograms may provide a method of quantifying microembolic ischemia in the central nervous system during cardiopulmonary bypass. Flat sheet membrane oxygenation appears to provide significantly better protection against microembolic ischemia than bubble oxygenation.

Macroemboli and microemboli during cardiopulmonary bypass.

Macroscopic and microscopic emboli of gas, biologic aggregates, and inorganic debris can occur during cardiac operations with cardiopulmonary bypass and may result in end-organ ischemia. In the current era pump-generated embolism is a diminishing cause of perioperative neurologic injury, which now appears to be related mostly to atheroembolism from manipulation of the atherosclerotic ascending aorta, and presents a continuing technical challenge to the surgeon.

Homograft-autograft valve holder.

With the increasing use of homografts and pulmonary autografts for aortic valve grafting it is imperative that correct orientation of the tissue valve is maintained during the insertion procedure. To aid in this we have developed an easy-to-construct and use holder for valve conduits. The holder is made from materials easily available in any theater. We have used this holder in more than 50 patients and find it an essential aid to maintain orientation.

Interventional and surgical management of aortic stenosis and coarctation.

Two patients, aged 42 and 44 years old, presented with the combination of aortic valve stenosis and coarctation. To avoid potential problems associated with one stage repair, both patients underwent successful endovascular stent implantation for coarctation followed within 2 weeks by aortic valve replacement using pulmonary autografts (Ross operation). Spiral thoracic computed tomographic scans were performed within 1 week of stent implantation to ensure the absence of aneurysm formation related to the stent before cardiopulmonary bypass.

Intracardiac thrombus traversing a patent foramen ovale: impending paradoxical embolism demonstrated by transoesophageal echocardiography.

Paradoxical embolism is a rare but potentially catastrophic complication of deep venous thromboses and pulmonary embolism. We describe a patient in whom transoesophageal echocardiography demonstrated a large clot traversing the atrial septum which was successfully removed by surgery.

The hypoglycaemic action of somatostatin in the anaesthetized dog.

The hypoglycaemic action of somatostatin was investigated in fasted anaesthetized dogs. An isotopic turnover technique with radioactive D-[2-3H] glucose tracer was used to measure the rates of hepatic production and peripheral utilization of glucose before, during, and after a 60min infusion of 150 mug somatostatin. Plasma concentrations of insulin, glucagon, growth hormone, cortisol and free fatty acids were also measured. Somatostatin infusion caused a fall of plasma glucose demonstrable within 10 min. After 60 min plasma glucose had fallen to 75% of the pre-infusion concentration. Simultaneoulsy the specific activity of the D-[2-3H] glucose increased and calculation of the rates of production and utilization of glucose over 10 min intervals indicated that the mean hepatic production rate of glucose fell to 59% of the pre-infusion rate while the rate of peripheral utilization of glucose fell to 83% of the pre-infusion rate. These results show that the hypoglycaemic action of intravenous somatostatin depends exclusively upon the inhibition of hepatic glucose production. This effect may have been partly due to a fall of plasma glucagon concentration and occurred despite a fall of plasma insulin to less than 1 mu 1(-1).

Demonstration of cerebral microemboli occurring during coronary artery bypass graft surgery using fluorescein angiography.

Coronary artery bypass graft surgery is associated with an unacceptably high incidence of neurological and neuropsychological complications (Breur et al., 1981; Smith, 1988). The main cause of cerebral dysfunction following this type of surgery is probably cerebral microembolism (Dutton et al., 1974; Taylor, 1986). The eye is an outgrowth of the brain and therefore is uniquely suitable for the study of cerebral microcirculation. Retinal fluorescein angiography has been employed during this surgical procedure to demonstrate the changes which occur in the cerebral microcirculation during operation.

Automatic geometrical registration of fluorescein retinal angiograms.

Changes in retinal microvascular perfusion revealed by fluorescein angiography have been reported in patients undergoing coronary artery surgery. Quantification of these changes is important and current techniques depend on careful visual inspection of the angiograms by humans. Computer image processing methods can be used to identify and highlight differences, but geometrical registration of the images is a prerequisite to the comparisons. Automatic methods for locating and matching reference points have therefore been developed. In combination with an iterative process which used least-squares error to calculate the transformation coefficients, subsets of reference points were selected and used to register successfully 20 image pairs.