Significance of changes in cerebral electrical activity at onset of cardiopulmonary bypass.

Abstract

. (1977). Thorax, 32,[534][535][536][537][538] Significance of changes in cerebral electrical activity at onset of cardiopulmonary bypass. A study of 100 patients requiring open-heart surgery has been undertaken to ascertain whether prophylactic measures designed to minimise cerebral damage have influenced the incidence or severity of changes in cerebral electrical activity recorded at the onset of cardiopulmonary bypass. The incidence of change in cerebral electrical activity remains high but the severity of the disturbances has diminished as compared with a series investigated before prophylactic measures were introduced. Changes suggestive of cerebral depression were particularly notable in children under 10 years of age. The significance of these findings is discussed in the context of factors which might influence cerebral electrical activity at the onset of bypass.Changes in cerebral electrical activity are common at the onset of cardiopulmonary bypass and can be recorded easily using a heavily filtered electroencephalograph or cerebral function monitor (Maynard et al., 1969). In a previous survey from this unit (Branthwaite, 1973a) an alteration in the cerebral function monitor (CFM) record was noted during the first few minutes of bypass in 88 of 140 patients (62-9%), and these changes were classified into four arbitrary categories-no change; elevation, either abrupt or gradual; a biphasic response; immediate depression. Ten patients sustained cerebral damage and there was evidence which suggested that this had occurred at the onset of bypass in seven cases.In a separate study (Branthwaite, 1973b) it was shown that the arterial blood pressure during the first five minutes of perfusion is significantly lower when the pattern of change on the CFM suggests cerebral depression, and evidence was obtained subsequently (Branthwaite, 1974) to support the view that cerebral blood flow can fall at the onset of bypass if there is severe, sudden hypotension, even though the systemic flow rate is high. It was argued that this decrease in cerebral blood flow might be responsible for cerebral damage occurring at the onset of bypass, although microemboli from the perfusion apparatus could also contribute. After prophylactic measures had been introduced to control these two hazards, the incidence of neurological damage fell from 19-2% to 7 4% (Branthwaite, 1975). If it is indeed true that changes in cerebral electrical activity at the onset of bypass indicate some form of cerebral damage, and that excessive hypotension and microemboli are responsible, at least in part, the reduction in incidence of clinically apparent damage should have been accompanied by a comparable reduction in the incidence or severity of abnormal findings in the CFM records. A further study has been undertaken to explore this hypothesis. Material and methodsThe study was

Eeg Monitoring and Evoked Potentials in Brain Ischaemia

“…The severity of the EEG abnormality is related consistently to the degree of hypotension (Branthwaite, 1973b;Pronk, 1982) with minor and major abnormalities at MAP of 46 and 37 mm Hg, respectively. Kriticou and Branthwaite (1977) compared groups of patients before and after the introduction of measures designed to maintain adequate cerebral blood flow (by vasopressors) and prevent microemboli. Although EEG alterations remained frequent, they were usually trivial and neurological deficits decreased from 19.2% to 7.4% or less.…”

The Effect of Temperature, Mean Arterial Pressure, and Cardiopulmonary Bypass Flows on Somatosensory Evoked Potential Latency in Man

“…The lack of effect of byp ass initia tion on evoked potentials is surprising, particu larly in view of the marked electroencephalographic changes, albeit tempora ry, that have been associated with this event (16) . This may be related to the fact that the EEG changes are usually temporary.and these were therefore missed by a technique which samples over threequarter s of a minut e. Nevert heless, one would have expected more changes on the basis of temperature-reduction alone.…”

Prediction of cerebral outcome after extracorporeal circulation

“…There may occur embolization or air or particulate matter ( Brierley 1963, Branthwaite 1972, episodes of hypotension (Jawid et al. 1969, Branthwaite 1972, 1974, Kritikou & Branthwaite 1977, which cause disturbances in cerebral blood flow and oxygen metabolism (Brennan et al 1971, Henningsen 1973. However, the actual metabolic changes in man and, particularly their clinical significance, are not yet clearly understood.…”