Download Serum S-100 protein concentration after cardiac

European Journal of Cardio-thoracic Surgery 11 (1997) 645 – 649
Serum S-100 protein concentration after cardiac surgery: a randomized
trial of arterial line filtration
David P. Taggart a,*, Kausik Bhattacharya a, Niki Meston a, Susan J. Standing a,
Johnathon D.S. Kay a, Ravi Pillai a, Per Johnssson b, Stephen Westaby a
a
Oxford Heart Centre and Department of Clinical Biochemistry, John Radcliffe Hospital, Oxford OX3 9DU, UK
b
Department of Cardiothoracic Surgery, Uni6ersity Hospital of Lund, Lund, Sweden
Received 24 April 1996; received in revised form 7 August 1996; accepted 15 August 1996
Abstract
Introduction: Embolization of gaseous and particulate matter is incriminated in the neuropsychological morbidity of CPB and
can be reduced by membrane oxygenators and arterial line filtration. It is not known if the use of arterial line filtration in
conjunction with membrane oxygenators might have an additive effect in reducing cerebral injury. Methods: Forty patients
undergoing elective coronary artery surgery were prospectively randomized to a 43 mm heparin coated arterial line filter (Cobe
Sentry™) or to no filtration (control group). All operations were performed by one surgeon (DPT) using intermittent ischaemia
with nonpulsatile CPB, a COBE CML membrane oxygenator and alpha-stat paCO2 management. Flow rates were maintained
between 2.0 and 2.4 l − 1 m2 per min with a perfusion pressure of 50 – 80 mmHg and a systemic temperature of 34°C. Cerebral
injury was defined by careful neurological examination and serial measurement of the serum concentration of S-100 protein (a
highly specific astroglial cell derivative, elevated serum levels of which correlate with proven cerebral injury). Results: There was
no difference [mean (S.D.)] in the control and filter groups with respect to age [61(9) vs. 62(9) years], ejection fraction, number
of grafts [2.8(0.6) vs. 2.6(0.7)] or CPB times [55(19) vs. 57(18) min]. Preoperatively, no patient had detectable S-100. In the
postoperative period 23 of 40 patients (58%) showed elevated S-100 levels. At 1, 5 and 24 h the respective number of patients in
the control and filter groups with elevated S-100 was (14 vs. 9), (4 vs. 0), (4 vs. 0)) (P B0.05). No patient had overt cerebral injury.
Conclusions: This study suggests that (i) subclinical cerebral injury is common (58% of patients in this study) even after apparently
uncomplicated surgery with short CPB times; (ii) serum S-100 protein is a valuable marker for investigating potentially cerebral
protective innovations during CPB; and (iii) arterial line filtration significantly reduces but does not eliminate cerebral injury.
© 1997 Elsevier Science B.V.
Keywords: S-100; Cardiopulmonary bypass; Filter; Arterial line filtration; Cerebral injury
1. Introduction
Cardiopulmonary bypass (CPB) generates gas bubbles, biological aggregates, atheromatous debris and
inorganic matter [12] and microembolization of these
substances is incriminated as a major aetiological factor
in the neuropsychological morbidity of CPB [6,20].
* Corresponding author. Tel.: + 44 865 221121; fax: + 44 865
220244.
1010-7940/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved.
PII S 1 0 1 0 - 7 9 4 0 ( 9 6 ) 0 1 1 0 3 - 7
The potential for arterial line filtration to reduce
neuropsychological morbidity after CPB has been controversial and is dependent not only on the presence or
absence of a filter but on the type of oxygenator
employed. The efficacy of filtration in removing debris
from the extracorporeal perfusate was established more
than 20 years ago [4] but concerns were raised that
small pore filters might contribute to the generation of
embolic aggregates [7] and air trapping [23]. In a trial of
a 20 mm filter used in conjunction with a bubble
oxygenator, Aris and colleagues could find no differ-
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D.P. Taggart et al. / European Journal of Cardio-thoracic Surgery 11 (1997) 645–649
ence in neurological or neuropsychological morbidity
between the filtered and control groups [3].
Demonstration of cerebral microemboli using retinal
fluorescein angiography [6] and middle cerebral artery
Doppler ultrasonography [15] has, however, swung the
surgical pendulum in favour of membrane oxygenators
and arterial line filtration. Using transcranial Doppler
ultrasonography Padayachee and colleagues reported a
reduction in the cerebral embolic load with membrane
rather than bubble oxygenators and suggested that
much of the embolic load might be due to gas bubbles
[10,11]. Subsequently a number of studies have confirmed that membrane oxygenators reduce the neuropsychological morbidity of CPB [15,17,18]. Recently
Pugsley and colleagues reported a reduction in the
incidence of microemboli, detected by transcranial
Doppler ultrasonography, when a 40 mm arterial line
filter was used with a bubble oxygenator [16]. More
importantly, this strategy resulted in a reduction in
both neurologic and neuropsychological deficits following CPB [16].
To our knowledge there has been no trial of arterial
line filtration used in conjunction with membrane oxygenation on cerebral injury following CPB. Forty patients undergoing coronary artery bypass grafting
(CABG) with membrane oxygenators were randomized
to arterial line filtration or to no filtration. Cerebral
injury was defined by neurological examination and
serial measurement of the serum concentration of S-100
protein a specific astroglial cell protein [9] whose elevated serum concentration correlates with proven cerebral injury [13,14] and which has been reported to be
elevated after CPB [1,19,21,22].
2. Methods
2.1. Patients
Forty patients undergoing elective first time CABG
with membrane oxygenators were randomized to arterial line filtration or to no filtration. In the filtered
group a 43 mm heparin coated filter (Cobe Sentry™
Arterial Filter with PrimeGard™) was placed in the
arterial line of the CPB circuit. Patients with a previous
history of cerebrovascular accident, transient ischaemic
attacks or with marked renal impairment were excluded.
2.2. Surgery
All operations were performed by one surgeon (DPT)
using intermittent ischaemia and induced fibrillation.
CPB was performed with a roller pump and nonpulsatile flow between 2.0 and 2.4 l − 1 m2 per min at a
temperature of 34°C. A COBE CML membrane oxy-
genator and alpha-stat paCO2 management were employed and arterial pressure maintained at 50–80
mmHg.
2.3. Blood sampling
Blood samples for S-100 protein were collected before anaesthesia, at skin closure and at 5 and 24 h
postoperatively. Samples were centrifuged to separate
the serum which was frozen at − 20°C for batch analysis.
2.4. S-100 assay
Serum S-100 levels were measured by a monoclonal
two site immunoradiometric assay (Sangtec 100,
Sangtec Medical AB, Bromma, Sweden) which uses
three monoclonal antibodies SMST 12, SMSK 25, and
SMSK 28 to detect the S100bb and ab dimers which
are specific for astroglial cells. After dilution in a buffer
with bovine serum albumin the serum samples were
incubated for 1 h with a plastic bead coated with
monoclonal anti-S100 antibodies which binds the S100. After washing to remove remove any unbound
material the beads were incubated with I125 labelled
anti-S-100 antibody which binds to the S-100 bound by
the bead antibody. Following a further 2 h incubation
period and subsequent washing the amount of radioactive label bound to immobilized S-100 was measured by
gamma counter. Calibration of the assay involved rehydrating six lyophilized standards of S-100 concentration
with diluent as a zero standard to produce a standard
curve. High and low control samples were provided in
the kit. Samples were analyzed in duplicate to reject
those with more than 10% variation.
Any duplicate elevation in S-100 above 0.1 mg/l was
considered abnormal.
2.5. Postoperati6e examination
All neurologic examinations were performed by one
observor (KB) blinded as to whether the patient received arterial line filtration or not.
2.6. Statistical analysis
Results were analysed using SPSS. Clinical data is
presented as means and standard deviations. Biochemical results are presented as medians and inter-quartile
ranges and were compared between groups using a
Mann-Whitney test. The numbers of patients in each
group with elevated S-100 levels ( \ 0.1 mg/l) were
compared using a one tail Fisher Exact Test with the
probability that arterial line filtration reduces S-100
levels.
D.P. Taggart et al. / European Journal of Cardio-thoracic Surgery 11 (1997) 645–649
Table 1
Clinical data in the control and filter groups
4. Discussion
Non-filter
Filter
P Value
Number
Age (years)
Number of grafts
CPB time (min)
20
61 (9)
2.8 (0.6)
55 (19)
20
62 (9)
2.6 (0.7)
57 (18)
NS
NS
NS
Elevated S100b at:
Skin closure
5h
24 h
Number of deaths
Obvious cerebral
Injury
14
4
4
0
0
9
0
0
0
0
647
0.05
0.05
NS
NS
3. Results
Patient data is presented in Table 1. The groups were
very similar with regard to age, ventricular function,
ischaemic times, number of grafts and CPB times.
Serial changes in S-100 are presented in Fig. 1. S-100
was not detectable in any patient prior to operation but
was significantly elevated in both groups (P B0.001) at
skin closure [median and interquartile range for the non
filter group was 0.3 (0 – 0.55) mg/l compared to 0 (0–
0.39) mg/l in the filter group]. There was no elevation in
S-100 level in any patient in the filter group at 5 and 24
h, in contrast to persistently elevated levels in four
patients in the non-filter group at the same time points.
At skin closure, 5 and 24 h the respective number of
patients in the control and filter groups with elevated
S-100 was (14 vs. 9), (4 vs. 0), (4 vs. 0)) (P B 0.05).
In the non-filter group 6 patients had an S-100 level
greater than 0.5 mg/l at skin closure compared with 3 in
the filter group but no patient had overt evidence of
cerebral injury on clinical examination.
Fig. 1. S-100 levels in the control and filter groups before operation,
at skin closure and postoperatively at 5 and 24 h. Box plot and
whiskers indicate median, inter-quartile range and range. Black dots
represent out-liers which are values at least three times greater than
the respective inter-quartile range.
Morbidity from cerebral injury, both overt and subclinical, continues to limit the outcome after cardiac
surgery. A number of studies, reviewed by Smith [20],
have reported that 50–60% of patients have neuropsychological deficits 1 week after cardiac surgery and that
these abnormalities are still demonstrable in approximately one third of patients 6 months later. Whilst the
aetiology of neurological impairment is complex and
probably multifactorial, there is considerable circumstantial evidence to implicate microembolization of
gaseous and particulate matter [12]. Furthermore, current evidence suggests that methods to reduce the microembolic load generated by CPB may result in
improved cerebral outcomes. Such claims have been
made independently for arterial line filters [15] and
membrane oxygenators [5,16–18] but not in combination.
The need for a serum marker of cerebral injury
following cardiac surgery was highlighted more than a
decade ago when Aberg and colleagues reported a
correlation between elevated adenylate kinase levels in
the cerebrospinal fluid (CSF) and impairment of intellectual function in patients following CPB [2]. S-100 is
a dimeric protein consisting of two subunits (a and b)
with a molecular weight of around 21 kDa and a half
life in serum of approximately 2 h (9). S-100ao (aa) is
found predominantly in striated muscles, heart and
kidney while S-100a (ab) is found mainly in astroglial
cells and S-100b (bb) is present in high concentrations
in astroglial and Schwann cells. The assay used in our
study measures both the S-100a (ab) and S-100b (bb)
subunits, which are not normally detectable in the
circulation. Elevated S-100 protein levels have been
reported in the CSF and serum of patients with proven
cerebral injury including subarachnoid haemorrhage
and stroke [13,14]. Aberg’s group, comparing patients
undergoing cardiac surgery with control patients and a
mock perfusion circuit with donated blood, concluded
that elevated S-100 levels were not due to anaesthesia,
surgery or blood trauma but implied cerebral injury [1].
This group also reported that the maximum increase in
S-100 was reached at the termination of CPB with
return to normal levels shortly after [1]. This time
course of acute elevation in S-100 has also been confirmed by Westaby and colleagues [22] and may explain
Sellman and colleagues’ failure to detect elevated S-100
levels in CSF 24 h after surgery [19]. Westaby and
colleagues confirmed the elevation in serum levels of
S-100 after CPB but not in control patients and demonstrated a highly significant correlation with the duration
of perfusion [22]. Elevated serum levels of S-100 have
also been demonstrated to correlate with the duration
of total circulatory arrest despite the use of deep hypothermia and retrograde cerebral perfusion during
repair of the aortic arch [21].
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D.P. Taggart et al. / European Journal of Cardio-thoracic Surgery 11 (1997) 645–649
In total 23 of 40 patients (58%) in our study
showed an elevated S-100 level in the postoperative
period. This is similar to the percentage of patients
with demonstrable deficits on neuropsychological testing within 1 week of CPB [20]. Our randomized trial
showed a benefit of arterial line filtration in terms of
S-100 release and by implication cerebral protection,
when a heparin-coated arterial line filter was used in
conjunction with a membrane oxygenator. In the
filter group fewer patients demonstrated elevated S100 levels and both the magnitude and persistence of
the increase was less in the filter group. While previous studies have demonstrated improved cerebral outcome with membrane oxygenators compared to
bubble oxygenators and arterial line filtration compared to no filtration we are not aware of any other
study which has demonstrated a benefit of arterial
line filtration in conjunction with a membrane oxygenator.
The precise relationship of elevated S-100 levels to
subtle abnormalities in intellectual and neuropsychological function has not been clearly defined. In our
study because S-100 was not detectable in any patient
prior to surgery we considered any elevation of
S-100 above 0.1 mg/l, in duplicate samples, abnormal.
Furthermore, with reference to the assay the gradient
of counts per min against S-100 concentration is
very similar below 0.5 mg/l. In our study six patients
in the non-filter group and three in the filter group
had S-100 levels greater than 0.5 mg/l at skin closure but without overt evidence of cerebral injury.
This underlines the need to correlate elevated S100 levels with abnormalities demonstrable on neuropsychological testing and to define an appropriate ‘cut-off’ value for pathologically elevated S-100
levels.
It is interesting to speculate on the mechanisms of
S-100 release into the systemic circulation and
whether this reflects eventual drainage of CSF into
the venous circulation or alteration in the integrity of
the blood brain barrier. There is little direct evidence
of the effects of CPB on the function of the blood
brain barrier in man although one animal model
failed to demonstrate any disruption of the integrity
of the blood brain barrier after 2 h of moderately
hypothermic CPB [8].
In summary, our study confirms that S-100 appears
to be a valuable marker for the assessment and
investigation of subtle cerebral injury following CPB.
Our study suggests that subclinical cerebral injury
is common (58% of patients in this study) even after
apparently uncomplicated surgery with a short
period of CPB and that arterial line filtration significantly reduces but does not eliminate this cerebral
injury.
Acknowledgements
We wish to thank Dr Cortina-Borja PhD, Statistician, University of Oxford for expert statistical advice,
Anaesthetic and Nursing Staff for assistance in collection of blood samples, Cobe Cardiovascular Inc. for
providing the arterial line filters, Cambridge Life Sciences for technical support and Oxford Health Authority for financial support.
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