Louise Klinger

Microemboli and Cerebral Impairment During Cardiac Surgery

Arterial microemboli, which may be reduced by arterial line filtration, have been proposed as a factor con tributing to cardiopulmonary bypass (CPB)-related cerebral dysfunction. The authors report on a study investi gating the effects of arterial line fil tration on the incidence of microemboli and the neuropsycho > 50mmHg, flow 1.8-2.4L/m2/min) was standardized and continuously monitored. Transcranial Doppler measured middle cerebral artery blood velocity and the incidence of microembolic events (MEE). Forty patients (median age fifty-six years, range forty-three to seventy) have completed the protocol. MEE oc curred in all patients during aortic cannulation and at inception of by pass. During bypass, patients with filtered CPB had fewer MEE (0-10 per thirty minutes) than nonfiltered CPB patients (30- > 250 per thirty minutes) did. Seven of 20 nonfiltered CPB patients showed soft neurologic signs on the first postoperative day compared with 3/20 in the filtered CPB group (P = 0.27, Fishers). The filtered CPB patients performed bet ter on a verbal memory test (P < 0.01, Wilcoxon) at eight weeks than the nonfiltered CPB group did.

Subjective reports of cognition in relation to assessed cognitive performance following coronary artery bypass surgery.

Evidence has accumulated to indicate that a proportion of patients who undergo coronary artery bypass surgery (CABS) do develop significant cognitive deficits. This study examines whether those patients who report cognitive deterioration after CABS do show cognitive changes as assessed by neuropsychological testing. The patients who considered that aspects of their cognitive function had deteriorated, were not found to have reduced functions as assessed on appropriate neuropsychological tests. When mood state was examined, it was found that those who report a deterioration in a particular cognitive function, tended to have significantly higher levels of depression as assessed by the Beck Depression Inventory and, to a lesser extent, have higher levels of state anxiety. These findings emphasise that subjective reports of cognitive function following CABS do not reflect actual changes in cognition but rather appear to be sensitive to mood state.

Retinal microembolism and neuropsychological deficit following clinical cardiopulmonary bypass: comparison of a membrane and a bubble oxygenator. A preliminary communication.

To observe and quantify cerebrovascular microembolic events in the central nervous system during cardiopulmonary bypass, 40 patients having elective uncomplicated coronary surgery had retinal fluorescein angiograms 5 min before bypass was discontinued. Each patient also had 10 neuropsychological tests before and after surgery. A Harvey H1700 bubble oxygenator was used for 23 patients and a Cobe CML sheet membrane oxygenator was used for 17 patients. All 23 (100%) of patients in the bubble oxygenator group had retinal microvascular occlusions consistent with microembolism compared to 8/17 (47%) in the membrane oxygenator group (P less than 0.001). In those retinas with occlusions, the mean resultant area of non-perfusion was less in the membrane oxygenator group (0.11 mm2; n = 8) than in the bubble oxygenator group (0.29 mm2; P less than 0.01). Arterial PO2 levels during bypass were similar in both groups at moderate hypothermia, but the mean PaO2 during rewarming was higher in the bubble oxygenator group (27 kPa) than in the membrane group (13 kPa; P less than 0.001). Neuropsychological deficits were more common and more severe after bubble oxygenation than after membrane oxygenation, but in this small patient group, the difference was not statistically significant. We conclude that flat sheet membrane oxygenation during cardiopulmonary bypass may confer significant protection against cerebrovascular microembolism.

The Persistence of Neuropsychological Deficits Twelve Months After Coronary Artery Bypass Surgery

That some cardiac surgery results in brain damage has been known for some time and has been demonstrated in pathological findings [1, 2]. Much current attention has focused specifically on coronary artery bypass surgery (CABS) which has seen a dramatic increase in recent years. The techniques and time on extracorporeal circulation have, however, changed considerably over the years and studies performed some time ago may not provide an accurate picture of the frequency of deficits with current surgical practice [3].

Cerebral blood flow during cardiopulmonary bypass

In a study of the cerebral consequences of cardiopulmonary bypass (CPB), we have assessed cerebral blood flow (CBF) by intra-arterial Xenon 133 clearance, utilising a Novocerebrograph 10a, before, during and immediately following CPB. All patients (n = 51), under the care of a single surgical team underwent elective coronary revascularisation using a standardised anaesthetic and surgical protocol. CBF, measured as the initial slope index (ISI), fell significantly from before (median 22.5) to on bypass (median 20) (Wilcoxon P less than 0.005) and was significantly increased in the immediate post-bypass period (median 28) compared with pre-bypass (Wilcoxon P less than 0.001). Scattergrams reveal CBF to be independent of arterial pressure (BP) but show an important relationship between arterial PaCO2 and CBF. The correlations between PaCO2 and CBF prior to bypass (r = 0.46 P less than 0.005) and post-bypass (r = 0.46 P less than 0.001) are very similar, whilst on bypass, the correlation, although remaining significant, is reduced (r = 0.31 P less than 0.02). The median values for arterial PaCO2 are low throughout the study (pre-bypass median 33 mmHg, on bypass median 28 mm Hg and post-bypass median 36 mm Hg). The maintenance of PaCO2 within the normal range of 35-45 mm Hg may minimise the risk of low CBF due to hypocarbia which could theoretically be harmful in patients known to be at risk of both short term and long term cerebral dysfunction.

REPORTS OF COGNITIVE CHANGE, MOOD STATE AND ASSESSED COGNITION FOLLOWING CORONARY-ARTERY BYPASS-SURGERY

The impact of coronary artery bypass surgery (CABS) on the amelioration of angina and breathlessness has been dramatic with approximately 90% of patients reporting symptomatic improvement. In recent years this success has been clouded by studies which have indicated a deterioration in cognitive performance with formal neuropsychological testing performed preoperatively and postoperatively [1, 2]. Studies investigating neuropsychological changes have confirmed that approximately 35% of patients show deficits 8 weeks post surgery [31], still detectable in 33% at one year [4].

Arterial Line Filtration Reduces Microembolism and Significantly Improves Neuropsychological Outcome in Coronary Artery Surgery

From the earliest days of cardiac surgery there has been acute awareness of the possible damage that might be done to the brain. Henry Souttar was amongst the first to operate on the heart 1] in 1925. He saw the opportunity for surgical help and argued that valvular disease of the heart was “to a large extent mechanical, and as such should already be within the scope of surgery were it not for the extraordinary nature of the conditions under which the problems must be attacked.” It was thirty years before the development of the heart/lung machine so he had to operate on the heart while it was closed and beating “in view of the extreme danger to the brain from even the shortest check to its blood supply.” In a statement in that paper he showed remarkable foresight when he said: “We are, however, of the opinion that these conditions are mechanical, and that apart from them the heart is as amenable to surgical treatment as any other organ.”