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Ann Thorac Surg 2003;75:1892-1897
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Serial measurement of serum S-100B protein as a marker of cerebral damage after cardiac surgery

^a Second Department of Surgery, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
^b Division of Intensive Care Medicine, Faculty of Medicine, Kagoshima University, Kagoshima, Japan
^c Department of Hospital Pharmacy, Faculty of Medicine, Kagoshima University, Kagoshima, Japan

Accepted for publication January 12, 2003.

^* Address reprint requests to Dr Ueno, Second Department of Surgery, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan.
e-mail: takayuki{at}m3.kufm.kagoshima-u.ac.jp

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
BACKGROUND: We used serial measurements of serum S-100B protein to evaluate the time course of serum S-100B protein concentration after cardiovascular surgery and to determine the clinical relevance of its concentration and cerebral damage.

METHODS: We assessed neurologic function in 149 patients undergoing cardiovascular surgery with cardiopulmonary bypass. The patients were classified into three groups according to their early postoperative outcome: those without complications (group A), those having unconsciousness or convulsion or both but no hemiplegia (group B), and those having unconsciousness and hemiplegia either with or without convulsion (group C). Serum S-100B protein concentrations were measured with a commercially available immunoluminometric assay, Sangtec 100 LIA, at seven time-points: before cardiopulmonary bypass, at the end of cardiopulmonary bypass, and at 5, 12, 24, 48, and 72 hours after cardiopulmonary bypass.

RESULTS: At 5 hours after cardiopulmonary bypass, the S-100B values in groups B and C were significantly higher than the value in group A. Although the S-100B level decreased in group C during the first 5 hours after cardiopulmonary bypass, it increased thereafter (12 through 24 hours) and continued at a high level until the final measurement at 72 hours. At 12 hours after cardiopulmonary bypass, S-100B was significantly higher in group C than in group B. This late increase in S-100B was associated with radiologically detected abnormalities and cerebral damage.

CONCLUSIONS: Serial measurement of serum S-100B protein in the initial 12 hours after cardiopulmonary bypass can be used to predict early postoperative brain injury.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Despite substantial methodologic improvements over the past decades, cardiovascular surgery with cardiopulmonary bypass (CPB) remains hazardous for the brain. Early postoperative neurologic assessment is difficult because of the influence of anesthesia, preoperative renal dysfunction, and postoperative acute renal failure. Early postoperative unconsciousness and convulsion are neurologic symptoms of possible cerebral damage in patients after cardiovascular surgery. But, it is difficult and risky to move newly operated patients in place for imaging with cranial computed tomography (CT) or magnetic resonance imaging (MRI) early postoperatively because of their unstable hemodynamics and respiration. Furthemore, imaging with cranial CT or MRI rarely reveals subtle changes early. Thus, there is a need to predict and manage cerebral damage early after operation. Elevation of serum S-100B protein levels has been shown to be a sensitive indicator of central nervous system damage [1]. S-100B protein leaks from structurally damaged nerve cells into cerebrospinal fluid and secondarily across the blood-brain barrier [2].

S-100 protein is an acidic calcium-binding protein with a molecular weight of 21 kDa and a biological half-life of approximately 2 hours [3]. The S-100 family consists of 17 monomers. Of these, S-100A1 (also known as S-100 ) and S-100B (also known as S-100 ß) are the most prominent. In the biologically active form, A1 and B form dimeric proteins, called S-100A1-A1, S-100A1-B, and S-100BB. S-100A1-A1 is found predominantly in the heart, kidney, and striated muscles, S-100A1-B in glial cells, melanocytes, adipocytes, chondrocytes, and epidermal Langerhans cells, and S-100BB in astrocytes and Schwann cells.

S-100B protein increases 50- to-100 fold after cardiac operation with CPB [4–6], a finding that supports association between CPB, microembolization, and brain damage. The postoperative serum concentration of S-100B increases with the duration of CPB and with the number of cerebral emboli detected by transcranial Doppler imaging [7]. However, several studies have suggested that in the absence of clear neurologic signs, transient elevations in serum S-100B protein reflect subclinical cerebral damage [8, 9]. To date, there has been no study of how serial measurement of serum S-100B protein levels can be used to predict early postoperative neurologic outcome. Since May 1999, we have used an immunoluminometric assay, Sangtec 100 LIA (Sangtec Medical, Bromma, Sweden), in our laboratory for serial measurement of serum S-100B protein. The aims of the present study were to evaluate the clinical relevance of changes in serum S-100B protein levels in relation to early postoperative neurologic outcome and to determine whether serial measurement of serum S-100B protein can be used to predict early postoperative cerebral damage in patients undergoing cardiovascular surgery with CPB.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
Patient population
Between May 1999 and March 2000 and between January 2001 and May 2002, 646 adults underwent elective and emergency cardiovascular surgery with CPB for valvular disease (n = 219), coronary disease (n = 260), thoracic aortic disease (n = 124), and other conditions (n = 43). Twenty-three percent of these patients (n = 149) provided approval from the hospital’s ethics committee and informed consent to participate in this study. Thus, the study patients comprised 90 men and 59 women, aged 66 ± 11 years (mean ± standard deviation), undergoing valvular surgery (n = 36), coronary surgery (n = 41), thoracic aortic surgery (n = 67), or another type of cardiovascular surgery (n = 5).

Clinical and neurologic assessment
All patients were assessed neurologically within 24 hours after surgery. The patients were classified into three groups according to their early postoperative outcome: those without complications (group A), those having unconsciousness or convulsion, or both but no hemiplegia (group B), and those having unconsciousness and hemiplegia either with or without convulsion (group C). Unconsciousness was defined as not waking up within 24 hours after surgery. Cranial CT was performed postoperatively in all group C patients and in selected group B patients. Patients in groups B and C were reassessed neurologically at and after discharge.

Blood sampling
Blood samples (5 mL) were collected from the central venous pressure line at the induction of anesthesia, after cessation of CPB, and at 5, 12, 24, 48, and 72 hours after CPB. The samples were allowed to clot for 20 minutes at room temperature and then were immediately centrifuged at 1,000 RPM for 10 minutes to separate the serum, which was then measured immediately.

S-100b protein assay
Serum S-100B protein was measured by a commercially available, monoclonal, two-site immunoluminometric assay (Sangtec S-100B LIA assay). The detection limit for S-100B protein is 0.02 µg/L. When the S-100B level was under the detection limit, the S-100B value was recorded as 0.02 µg,/L.

Surgical procedure
The valvular, coronary, and other surgeries were performed under mild hypothermic bypass (32°C to 34°C) with a membrane oxygenator (Dideco D 903 AVANT; Dideco, Mirandola, Italy), in which the tubing system included an arterial line filter (PALL Auto Vent-SV 40 µ; Pall Biomedical Product, Glencoe, NY). For thoracic aortic surgery, moderate hypothermic bypass (25°C to 28°C) was used for selective cerebral perfusion (SCP), intermediate hypothermic bypass (20°C to 23°C) was used for retrograde cerebral perfusion (RCP), and deep hypothermic bypass (16°C to 18°C) was used for circulatory arrest (CA). Bypass was performed with a membrane oxygenator (JMS LH-760 II; JMS, Hiroshima, Japan), in which the tubing system included an arterial line filter (PALL Auto Vent-SV 40 µ; Pall Biomedical Product). A nonpulsatile blood flow pump (MERA HAS-P150; Senko, Tokyo, Japan) was used. The flow rate throughout bypass was 2.0 to 2.4 L/m²/min. Myocardial protection was achieved by intermittent antegrade initial crystalloid cardioplegia and then by blood cardioplegia. In all patients of this study, cardiotomy suction with return of the aspiration to the perfusion system was used during CPB. However, the remnant blood in a cardiotomy reservoir at the end of CPB never was autotransfused to patients postoperatively.

Statistical analysis
Continuous data are expressed as means ± standard deviation, and categoric variables are expressed as percentages. Between-group differences in continuous clinical and operative data were analyzed by one-way analysis of variance (ANOVA) followed by Scheffé^’s test for multiple comparisons, and between-group differences in clinical categoric variables and hospital mortality were analyzed by -square test with m x n contingency table. Within-group changes in serum S-100B values were analyzed by repeated-measures ANOVA. Between-group differences in S-100B values at the different time points were analyzed by one-way ANOVA followed by Scheffé^’s test for multiple comparisons. StatView for Windows, version 5.0 (SAS Institute, Inc, Cary, NC) was used for descriptive statistics and inferential test. A probability value of less than 0.05 was considered significant.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Patient characteristics
Age, gender, disease type, preoperative complications, and the number of emergency operations performed in each group are shown in Table 1. Carotid disease was defined as unilateral or bilateral stenosis (>50%) and occlusion of the internal carotid artery by means of preoperative cervical ultrasonography or magnetic resonance angiography. One hundred twenty patients (81%) were included in group A, 21 (14%) in group B, and 8 (5%) in group C. Patients’ ages did not differ significantly between groups. All patients in groups B and C had ischemic heart disease or thoracic aortic disease (ie, atherosclerotic disease). Fourteen patients (12%) in group A, 5 (24%) in group B, and 2 (25%) in group C had carotid disease. Twelve patients had had a stroke (ischemic in 10 and hemorrhagic in 2) between 16 days and 13 years before surgery. The frequency of the past stroke was significantly higher in group C than in groups A and B. Emergency operations were performed in 26% of total cases. The frequency of emergency operations was significantly higher in groups B and C than in group A.

Follow-up
None of the survivors (15 patients) in group B had neurologic deficits at discharge. In a mean follow-up time of 19 months (range, 4 to 39 months), 2 patients died, 1 of pneumonia and 1 of acute myocardial infarction. None of the survivors (13 patients) had neurologic deficits at that time. At discharge, 5 group C survivors had mild (2 patients) to severe (3 patients) disturbance of consciousness with hemiplegia. In a mean follow-up time of 9 months (range, 3 to 17 months), 2 of these patients died of pneumonia, 1 at 5 months and 1 at 8 months postsurgery. All of the survivors (3 patients) had mild (2 patients) to severe (1 patient) disturbance of consciousness with hemiplegia at that time.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
Measurement of serum S-100B protein has been proposed as a useful method for detecting cerebral damage after cardiovascular surgery [4, 5, 8–11]. The presence of S-100B protein in serum after cardiac surgery with CPB may indicate cellular damage due to both macroembolization and microembolization [7, 12, 13], increased permeability of the blood-brain barrier [5, 8–11], or both. Damaged brain cells release S-100B into the cerebral spinal fluid, but cerebral S-100B will only appear in serum if there is a concomitant increase in blood-brain barrier permeability [14].

Moody and associates [15] showed the presence of small capillary and arterial dilatations (SCADs) in the brains of patients after cardiac operation with CPB but not after other types of surgical procedures. They considered the capillary dilatations to be the result of lipid microemboli. During histologic preparation, the embolized fat is dissolved and the resulting histologic finding is a SCAD. Evidence suggests that lipid microembolism is the cause of these diffuse cerebral changes [16]. In a recent study of CPB in dogs, Brooker and associates [17] detected 10 times more SCADs in the microvasculature of the brain when cardiotomy suction was used than when it was not. They argued that to a great extent, the dilatations were footprints of lipid microembolization from blood aspirated from the surgical field and reinfused through the aortic cannula. However, the clinical significance of these dilatations is not known. Although studies have supported the hypothesis that microemboli are the cause of the S-100B increase observed after CPB, in retrospect, many of the results can instead be attributed to the use of cardiotomy suction. Taggart and associates [18] found that the use of an arterial line filter in cardiac surgery with CPB in which cardiotomy suction is used can significantly reduce levels of S-100B. Anderson and associates [6] detected 10-fold greater S-100B levels in patients who underwent coronary artery bypass grafting with the use of CPB than in those who underwent the procedure without the use of CPB.

Studies on serum S-100B protein release during and after CPB have shown peak S-100B levels immediately after cessation of CPB, presumably resulting from a transient increase in permeability of the blood-brain barrier [5, 8–11]. Transient permeability of the blood-brain barrier to S-100B protein could be caused by the inflammatory response generated by CPB itself. Because the development of inflammation is time related, we might expect a positive correlation between perfusion time and S-100B protein release. However, no consistent correlation between perfusion time and S-100B levels has been documented [5, 8–11, 19, 20]. Jönsson and colleagues [8] showed that serum S-100B protein levels immediately after CPB did not correlate with cerebral outcome, although grossly elevated levels of serum S-100B protein at 48 hours after surgery were associated with clinically obvious stroke. The early release of S-100B protein after cardiovascular surgery with CPB may thus be a transient serum elevation without any relation to permanent neuronal damage. Magnetic resonance scanning has shown cerebral edema within an hour of CPB in patients undergoing routine coronary bypass [21]. The swelling is variable and may reflect transient change in permeability of the blood-brain barrier without injury to the brain itself. The transient increase in S-100B may then represent a reversible increase in permeability of the cellular and vascular membranes as opposed to structural neuronal damage.

The early S-100B studies in the above-mentioned past reports were interpreted without awareness that S-100B from extracerebral sources might confuse the issue by elevating overall levels. A recent study showed one of the factors causing the increase of serum S-100B protein after cardiac surgery to be extracerebral in origin [22–25]. Jönsson and associates [22] found that extracerebral S-100B was reduced by discarding cardiotomy blood and not retransfusing shed mediastinal blood, which have been shown to contain high levels of S-100B. Anderson and associates [23] compared the serum S-100B concentrations after conventional coronary artery bypass grafting with suction during CPB to a cardiotomy reservoir (CR) or to a cell-saving device (CS). At the end of CPB, serum S-100B in the CR group increased to approximately six times the level in the CS group. Furthermore, they measured S-100B concentration in the CS before processing and directly from the wound at sternotomy. The S-100B value was very high in both the CS and blood from the sternal wound. Consequently, they concluded that most serum S-100B just after CPB with cardiotomy suction may be of extracerebral origin and that the notion that an increase in S-100B during CPB in patients reflects cerebral injury is questionable.

The commercial immunoassay used in our present study has three different monoclonal antibodies directed against the ß-subunit of these dimeric proteins, and it will therefore detect any S-100 protein that contains at least one ß-subunit. The two dimers that are known to be analyzed together as S-100B consist of a protein containing only a single ß-subunit and one with two ß chains. As described previously, S-100A1-B is found not only in neuronal tissue but also in extraneuronal tissue. We showed here that there might be no significant relation between an increase of serum S-100B protein levels immediately after CPB and early postoperative organized cerebral injury. In fact, the serum S-100B levels transiently increased immediately after CPB in all patient groups and did not differ significantly between groups, although the serum S-100B levels in group C patients having organized cerebral injury tended to be higher than that in the patients in other two groups in our study. Distinguishing between permanent organized cerebral damage (as in our group C) and transient functional cerebral impairment (as in our group B) is important for predicting early postoperative organized cerebral damage. In the present study, the appearance of increased release of serum S-100B protein at 12 hours after CPB was associated with radiologic abnormalities and perioperative organized cerebral damage. We believe that the organized cerebral damage group may actually show an increase earlier than 12 hours after CPB, and that by measuring serum S-100B protein more often during the early hours after CPB (between 5 and 12 hours), the distinction between the groups could be detected sooner. Because so few patients in this study had organized cerebral damage after CPB, the actual predictive value of serum S-100B protein can not yet be determined. However, the pattern of initial decrease (1 to 5 hours after CPB), then late increase (12 hours after CPB) in release of the protein may be an important factor in distinguishing between permanent organized cerebral damage and transient functional cerebral impairment.

We conclude that serum levels of S-100B can be valid clinical predictors of adverse neurologic outcomes and that the serial measurement of serum S-100B protein can be used to predict early postoperative cerebral damage in patients undergoing cardiovascular surgery with CPB. We expect the serial measurement of serum S-100B protein to prove useful for planning and introducing neuroprotective treatment and assessing its effects.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ryuzo Sakata Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ueno, T. Articles by Nakamura, K. Search for Related Content PubMed PubMed Citation Articles by Ueno, T. Articles by Nakamura, K.