Cerebral protection during open-heart surgery

Cerebral blood flow and autoregulation during hypothermic cardiopulmonary bypass

Mean hemispheric cerebral blood flow (CBF) was studied following intravenous or intraarterial administration of xenon-133, in 10 men admitted for coronary artery bypass grafting. Repeated CBF measurements were performed to evaluate autoregulation before, during, and after cardiopulmonary bypass (CPB). During CPB mean CBF remained unchanged compared with the pre-CPB level, without evidence of cerebral hyperemia or impairment of autoregulation. A marked increase in CBF occurred after CPB and was followed by a time-dependent reduction toward the pre-CPB level. The data support the alpha-stat regulation theory but cannot explain the cerebral vasodilation observed after CPB.

Cerebral perfusion during major cardiac surgery in children

Six children undergoing major cardiac surgery had extensive cerebral monitoring during cardiopulmonary bypass (CPB). The monitoring included continuous recording of arterial blood pressure (BP), central venous pressure (CVP), cerebral electrical activity by a cerebral function monitor (CFM), and middle cerebral artery (MCA) flow velocity by the transcranial pulsed Doppler (TCD) technique. Introduction of the precooled blood containing priming solution resulted in rapid fall in BP as well as MCA velocities in these children at the start of CPB. During steady-state CPB at 20 degrees C, MCA flow velocities were reduced in five of six children, range 45%-105% of pre-bypass value. These flow velocity values were recorded at cerebral perfusion pressures (CPP = BP - CVP) in the range of 14-26 mmHg. This reduced cerebral perfusion during steady-state CPB appears to be more than sufficient to meet the cerebral metabolic demands at the particular temperature. The reduced cerebral perfusion is in contrast to the enhanced perfusion found in adults during moderately hypothermic (28 degrees-30 degrees C) low-flow, low-pressure CPB previously reported. It was presumably due to the reduced temperature, reduced perfusion pressure, and less hemodilution. During periods of constant temperature, hematocrit, and partial pressure of carbon dioxide (PaCO2), MCA flow velocities varied passively with changes in CPP, demonstrating that cerebral autoregulation was not operative. Transcranial Doppler appears to be a suitable tool for investigating CPB techniques optimal with respect to cerebral circulation.

Cerebral damage during open-heart surgery. Clinical, psychometric, biochemical and CT data

The incidence and extent of cerebral damage following open-heart surgery were prospectively investigated in 103 patients, using clinical assessment, psychometry, adenylate kinase analysis in cerebrospinal fluid (CSF-AK) and computed tomography (CT) of the brain. The surgical mortality was 1.9%. Clinically there was obvious cerebral dysfunction in four cases, subtle evidence of brain damage (mainly undue fatigue) in 16 and no evidence in 81 cases. In the 16 patients the mean CSF-AK was substantially increased (0.122 U/l) and the psychometric performance distinctly impaired (-12 points) postoperatively; in the 81 patients the figures were 0.55 U/l and -3.4. Psychometrically, 60% of the patients showed cerebral dysfunction, which was pronounced in 16%. CSF-AK analysis indicated cerebral damage as absent or trival in 45%, moderate in 33% and marked in 22%. CT revealed postoperative cerebral infarction in two cases. Results from the various methods showed reasonable correlation, but also considerable overlap. Open-heart surgery thus can cause brain damage additional to that neurologically discernible. Fatigue is an important sign in this context. In research on postoperative brain damage, the relative insensitivity of routine neurologic investigation calls for supplementary, refined methods.

Cerebral blood flow during cardiopulmonary bypass in man: effect of arterial filtration

Cerebral blood flow was recorded in 39 patients undergoing cardiac surgery by intraarterial injection of xenon 133. There were three subgroups of patients: 10 patients had a 20 micron arterial filter (Johnson) and 11 a 40 micron filter (Pall), and 18 had no arterial filtration. All patients had a 40 micron (Pall) filter in the coronary suction line. Significant changes in cerebral blood flow occurred during extracorporeal circulation (p less than 0.0001). For all patients cerebral blood flow increased from a resting prebypass level of 30 to 46 and 57 ml/100 g a minute during initial and stable hypothermic extracorporeal circulation respectively. Both measurements were obtained at 26 degrees C and the recordings were made on average 12 and 55 minutes after the extracorporeal circulation was started. During rewarming cerebral blood flow increased to 64, 53, 41, and 36 ml/g a minute at 31 degrees, 33 degrees, 35 degrees, and 37 degrees C respectively, and when measured four and 16 minutes on average after bypass it was 44 and 41 ml/100 g a minute. This general brain hyperperfusion was noticed in all patients with a high enough mean blood pressure to produce hyperaemia. Interposing 20 and 40 micron arterial filters reduced cerebral blood flow but did not prevent this hyperaemia. The cerebral autoregulation, which maintains a constant cerebral blood flow within wide limits of perfusion pressures, was not affected by arterial filtration. The lower limit of blood pressure at which a further reduction in blood pressure was followed by a reduction in cerebral blood flow was around 60 mm Hg in all three groups.

Central and spinal somatosensory conduction times during hypothermic cardiopulmonary bypass and some observations on the effects of fentanyl and isoflurane anesthesia

Somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded over Erb's point (N10), neck (N13) and scalp (N20) of 17 neurologically normal patients during hypothermic cardiopulmonary bypass. Anesthesia was induced with fentanyl and 100% oxygen, and supplemented with isoflurane as necessary. All 3 SEPs were recorded at esophageal temperatures (Te) of down to 19.5 degrees C. The central conduction time (CCT, defined as N20-N13 interpeak interval) increased exponentially with decreasing temperature (CCTTe = 1.066(37)-Te X CCT37; r = -0.96). The spinal conduction time (SCT, defined as N13-N10 interpeak interval) also increased exponentially but less steeply than the CCT (SCTTe = 1.047(37)-Te X SCT37; r = -0.89), and the N10 peak latency increased exponentially and least steeply (N10Te = 1.033(37)-Te. N10(37); r = -0.87). Anesthetic doses of fentanyl (75 micrograms/kg) did not affect the SEPs. Isoflurane (inspired concentration, 0.25-2.0%) produced dose-dependent increases in CCT of up to 13% and decreased N20 amplitude. All patients had normal CTs after rewarming and none suffered postoperative neurological deficits. Differences in slopes of the latency-temperature functions indicate that cooling produces more conduction slowing in central than in peripheral segments of the pathway and can be accounted for by estimates of the effects of cooling on synaptic delay and axonal conduction between wrist and cortex. The consistency of SEPs between patients both during stable hypothermia and when temperature was changing suggests their potential as a sensitive monitor of cerebral status during hypothermic cardiopulmonary bypass.

Early neurological complications of coronary artery bypass surgery

A prospective study of 312 patients undergoing elective coronary artery bypass surgery was undertaken to determine the incidence, severity, and functional impact of postoperative neurological complications. Detailed evaluation of the patients showed that neurological complications after surgery were common, occurring in 191 of the 312 patients (61%). Although such a high proportion of the total developed detectable changes, serious neurological morbidity was rare. Neurological disorders resulted in death in only one patient (0.3%) and severe disability in only four (1.3%). Forty eight patients were mildly disabled during the early postoperative period, and the remaining 138 with neurological signs had no serious functional disability. The postoperative neurological disorders detected included one death from cerebral hypoxic damage. Prolonged depression of conscious level was observed in 10 patients (3%) and definite stroke in 15 (5%); 78 (25%) developed ophthalmological abnormalities and 123 (39%) primitive reflexes; postoperative psychosis was observed in four (1%); and 37 (12%) developed disorders of the peripheral nervous system. The incidence of serious neurological problems such as fatal cerebral damage, stroke, and brachial plexopathy is in accordance with experience elsewhere. Lesser abnormalities, whose detection required detailed neurological examination, were much commoner than expected from previous reports.

Epileptic seizures due to thrombotic and embolic cerebrovascular disease in older patients

Thromboembolic vascular disease is a frequent precipitant of seizures, and is the most common etiology in older patients. The occurrence of seizures shortly after a stroke, however, does not necessarily indicate that the patient will continue to have seizures following initial recovery. This is true even when patients present in epileptic status. This may be because early and late seizures are produced by different pathophysiologic mechanisms.

Some observations on cerebral perfusion during cardiopulmonary bypass

Blood flow was recorded with an electromagnetic flow probe on one internal carotid artery (ICA) during cardiopulmonary bypass (CPB) in 5 patients. The ICA flow was monitored continuously along with arterial blood pressure, epidural intracranial pressure, and cerebral electrical activity using a cerebral function monitor (3 patients). The ICA flow increased by 50 to 100% at the inception of extracorporeal circulation. This rapid enhancement of flow occurred within a thirty-second period and was due to rapid arterial hemodilution caused by introduction of the priming solution. A transitory fall in ICA flow was observed during subsequent minutes when the well-recognized drop in blood pressure took place and the cerebral perfusion pressure (CPP = blood pressure - epidural intracranial pressure) was reduced to less than 30 mm Hg. In only one instance, however, when CPP fell to 15 mm Hg, was the fall in flow lower than the prebypass level. Throughout the rest of CPB, with steady-state hemodilution and CPP levels in the range of 30 to 50 mm Hg, ICA flow was markedly enhanced (50 to 100% above the prebypass level). The flow pattern, however, disclosed a pressure-passive system, indicating that cerebral autoregulation was impaired or that the CPP levels were lower than the individual lower limit of cerebral autoregulation during the period of steady-state hemodilution on CPB. A transient depression of cerebral electrical activity was seen in 2 patients shortly after the introduction of CPB. This phenomenon is suggestive of qualitatively insufficient perfusion and was observed even when ICA bulk flow was increased (hematocrit values, 13 to 17%).

Factors and their influence on regional cerebral blood flow during nonpulsatile cardiopulmonary bypass

In this study we examined the relationship of regional cerebral blood flow (CBF) to mean arterial pressure, systemic blood flow, partial pressure of arterial carbon dioxide (PaCO2), nasopharyngeal temperature, and hemoglobin during hypothermic nonpulsatile cardiopulmonary bypass (CPB). Regional CBF was determined by clearance of xenon 133 in 67 patients undergoing coronary bypass grafting procedures. There was a significant decrease in regional CBF (55% decrease) during CPB, with nasopharyngeal temperature and PaCO2 being the only two significant factors (p less than 0.05). In a subgroup of 10 patients, variation of pump flow between 1.0 and 2.0 L/min/m2 did not significantly affect regional CBF. We conclude that cerebral autoregulation is retained during hypothermic CPB. Under the usual conditions of CPB, variations in flow and pressure are not associated with important physiological or detrimental clinical affects.

Intensive care unit psychosis

Patients who become psychotic in intensive care units are usually suffering from delirium. Underlying causes of delirium such as anxiety, sleep deprivation, sensory deprivation and overload, immobilization, an unfamiliar environment and pain, are often preventable or correctable. Early detection, investigation and treatment may prevent significant mortality and morbidity. The patient/physician relationship is one of the keystones of therapy. More severe cases may require psychopharmacological measures. The psychotic episode is quite distressing to the patient and family; an educative and supportive approach by the family physician may be quite helpful in patient rehabilitation.

Intellectual function late after open-heart operation

Cerebral emboli are not uncommon complications after valve replacements. We investigated the hypothesis that there are emboli that are clinically unnoticeable but that may affect the intellectual function of the brain. One hundred sixty-five patients were studied with a battery of psychometric tests before and after operation, two months postoperatively, and 2 to 8 years after operation. Ten patients sustained late cerebral infarction or hemorrhage. Their late intellectual function was low, indicating an impairment in brain performance. The remaining 155 patients had had no cerebral complications postoperatively. Eighty-three had had valve replacement (Björk-Shiley valves); 51, aortocoronary bypass operations; and 21, closure of an atrial septal defect (all adult patients). Late intellectual function was significantly lower in the patients with a valve prosthesis than in the other two groups. However, this difference could be traced back to the operation. Thus, we have not been able to confirm our hypothesis that late intellectual function in patients with a heart valve prosthesis deteriorates as a result of clinically silent emboli. On the contrary, patients who have undergone aortocoronary bypass operation sustain more deterioration in late intellectual function than the other groups. Late intellectual function in this study population clearly was influenced by events during the operation. Because cerebral injury can be shown almost regularly after open-heart operation, this investigation provides an incentive for further efforts to improve the quality of open-heart surgery with the aim of keeping brain function as intact as possible.

The clinical significance of changes in cerebral perfusion pressure during open-heart surgery

In 34 high-risk patients, the intracranial epidural pressure (EDP) and the cerebral perfusion pressure (CPP) were monitored in connection with open-heart surgery. The findings were clinically evaluated, with special attention to affection of the central nervous system. Reduction of EDP to 10-30 mmHg for periods up to 10 min at the start of extracorporeal circulation and transient rise of EDP in the early postoperative period were relatively well tolerated. Late postoperative EDP rise, on the other hand, denoted an unfavourable trend, associated with permanent cerebral damage. Mannitol and/or barbiturates are indicated when an early rise in postoperative EDP persists or a late rise occurs. Covariation of EDP and arterial blood pressure (BP) should be regarded as a warning sign, especially if it is pronounced or appears during the postoperative course. In such conditions it seems important to stabilize the CPP by reducing a high EDP and by careful management of BP variations, i.e. with use of vasopressors. Postoperative epileptiform seizures seem to be prognostically unfavourable.

Total creatine kinase activity in cerebrospinal fluid as an indicator of brain damage during open-heart surgery

In a selected series of 33 patients undergoing open-heart surgery, the creatine kinase (CK) activity in cerebrospinal fluid (CSF) was compared with the clinical results in regard to the central nervous system. The level of CK activity in CSF showed correlation with the degree of irreversible neuronal damage. Determination of CK in CSF may thus be of prognostic value in these patients. Caution is essential, however, in the setting of strict limits above which return to normal or acceptable quality of life is not to be expected.

Prediction of cerebral outcome after extracorporeal circulation

50 open-heart patients were investigated using simultaneous clinical, electroencephalographical (EEG) and neuropsychological evaluation in order to assess the possibilities of predicting the postoperative outcome with preoperative measures. The presence of one or more of the following indices was prognostically unfavourable: a history of cerebrovascular diseases or syncope; delta or sharp wave EEG abnormalities or low quantitative EEG mean frequency; a poor performance score in one of the psychometric tests (colour naming). Using these measures, 28 cases with presumably high risks were indicated, and 24 (86%) sustained cerebral complications attributable to the operation. The observations contrast clearly with previous studies whose predictions, using only one single criterion, have proved invalid. A significant level of prediction seems to be obtainable, but only by the simultaneous consideration of several different cerebral functions. The prognostic approach may offer one way of achieving the necessarily needed improved cerebral safety in cardiac surgery.

Psychopatho-ophthalmology, gnostic disorders, and psychosis in cardiac surgery. Visual disturbances after open heart surgery

The visual disturbances of 45 patients following open heart surgery could be divided into disturbances of (1) visual acuity, (2) visual accuracy, and (3) visual reality testing. The non-hallucinatory phenomena consisted mainly of loss of colour vision, metamorphopsias, visual gnostic disorders and cortical blindness. The hallucinatory phenomena could be divided into the delirium type of hallucinations with clouding of consciousness and the spectator type of hallucinations with a clear sensorium. The causes of the visual symptomatology and cardiac psychoses are seen in microembolization and/or ischemic hypoxia. The basal ganglia and the occipital lobe are areas of predilection for embolic and hypoxic changes. Identical psychoses also occur in cerebral malaria and polycythemia vera which show the same embolic and anoxic neuropathological changes of vascular occlusion as do many patients who die following open heart surgery with extracorporal circulation.

Release of adenylate kinase into cerebrospinal fluid during open-heart surgery and its relation to postoperative intellectual function

In 33 of 36 patients having open-heart surgery, the levels of adenylate kinase in cerebrospinal fluid (CSF-AK) were raised. No such increase was seen in 8 patients who had had lung operations without cardiopulmonary bypass. A significant increase in CSF-AK was recorded in 18 patients whose CSF was examined both preoperatively and postoperatively, and this increase was correlated with change in an index of intellectual function. Since there was no evidence of damage to the blood-brain barrier, these findings point to a causal relation between brain-cell injury during cardiopulmonary bypass and release of AK into CSF. Measurement of CSF-AK may therefore prove useful in research to improve the quality of open-heart surgery.

The benefits of open-heart surgery as reflected in the EEG

A one-year electroencephalographic (EEG) follow-up study was carried out on 65 cardiac valvular replacement patients with the main aim of investigating the nature and determinants of EEG disturbances related to cardiac valvular disease and surgery. The pre-operative incidence of abnormal EEG was high (49%, indicating the impairing effects of prolonged circulatory inadequacy. The brain proved highly sensitive to operative strains, as is reflected in the observed EEG changes: marked increase in slow wave abnormalities; increase in bilateral and continuous disturbances; slowing of the dominant activity. Generally, the postoperative disturbances were rapidly reversible. The long-term EEG outcome was favourable: one year after operation the incidence of abnormal EEG had decreased to 25%. Of the operative factors, age, cardiologic diagnosis and technical difficulties during operation were found the most significant determinants of cerebral dysfunction.

Brain damage and neurological outcome after open-heart surgery

Cerebral damage remains a major hazard of open-heart surgery. A one-year follow-up investigation of 100 consecutive patients who underwent open-heart operation for valve replacement revealed an incidence of postoperative cerebral disorders of 37%. The occurrence of brain damage was clearly related to the presence of a history of previous neurological diseases, to operative hypoxia, and to unexpected events during operation, but long perfusion time proved to be the most significant risk factor. In contrast to previous findings, age and moderate operative hypotension proved unimportant. The abnormalities tended to resolve rapidly but, one year after operation seven patients still displayed residual signs. An interesting interhemispheric difference in susceptibility to damage was evident, the clinical signs indicating lesions of the right hemisphere in 71% of the damaged cases. The nature of both preoperative and postoperative signs and symptoms, the determinants of brain damage and the significance of the observed disparity between the hemispheres are discussed. The continuous occurrence of brain damage obliges us to develop preventive measures more efficient than those now available.

An ultrasonic analysis of the comparative efficiency of various cardiotomy reservoirs and micropore blood filters

The ability of 12 commercially available cardiotomy reservoirs to remove bubbles from aspirated blood was investigated by means of a simulated cardiopulmonary bypass circuit and an ultrasonic microbubble detector. Performance varied considerably. The number of gaseous microemboli remaining after passage of blood through the reservoir was reduced by (a) holding the blood in the reservoir, (b) reducing the volume of air mixed with the aspirated blood, and (c) using a reservoir that did not induce turbulence and that contained integral micropore filtration material. Further micropore filtration of the blood after passage through the cardiotomy reservoir was beneficial, and significantly more bubbles were extracted when the microfilter was sited below the reservoir than when it was placed in the arterial line.