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J Thorac Cardiovasc Surg 2002;123:1092-1100
© 2002 The American Association for Thoracic Surgery
Cardiopulmonary Support and Physiology (CSP) |
From the Departments of Cardiac Surgery,a Cardiac Anaesthesiology,b and Cardiology,c Catholic University, Rome, and "Angela Valenti" Laboratory of Genetic and Enviromental Risk Factors for Thrombotic Disease,d Department of Vascular Medicine and Pharmacology, Consorzio Mario Negri Sud, Santa Maria Imbaro, Italy.
Received for publication April 26, 2001. Revisions requested June 13, 2001; revisions received Sept 26, 2001. Accepted for publication Oct 3, 2001. Address for reprints: Mario Gaudino, MD, Divisione di Cardiochirurgia, Policlinico Universitario A. Gemelli, Largo A. Gemelli 8, 00168 Rome, Italy (E-mail: mgaudino{at}tiscalinet.it).
| Abstract |
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| Introduction |
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This prospective randomized investigation was conceived to elucidate the effect of CPB temperature on the postoperative activation of the hemostatic and inflammatory systems in patients submitted to isolated coronary artery bypass procedures by using both clinical and hematic indexes.
| Patients and methods |
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From this date on, all patients scheduled to undergo isolated elective CABG at our center were screened. Rigorous exclusion criteria were adopted to maximize homogeneity and comparability between groups: Patients with associated cardiac or noncardiac surgical procedures, age greater than 80 years, single-vessel disease, emergency or urgent revascularization, left ventricular ejection fraction of less than 0.30, carotid artery disease, previous cerebrovascular accident, chronic dialysis, hepatic failure, respiratory or renal insufficiency, hemorrhagic conditions, active infection, and chronic anti-inflammatory therapy were all excluded from the study. Only patients operated on between 8 and 10 AM were considered to rule out possible confounding effects of circadian variability. After enrollment, patients were randomly assigned to be operated on with normothermic versus hypothermic CPB. (We adopted a 1:1 randomization according to a computer-generated random series of numbers.)
All patients gave their consent to participate in the protocol.
Data collection ended in May 1999, and a total of 113 patients were included.
Surgical technique
After median sternotomy, CPB was instituted in standard fashion by cannulating the right atrium and the ascending aorta. For anticoagulation, an intravenous bolus of heparin (300 IU/kg) was followed by boluses of 100 IU/kg to maintain activated clotting times of longer than 400 seconds.
During CPB, the nasopharyngeal temperature was kept at 37°C in the normothermic group (patients were actively rewarmed if their nasopharyngeal temperature fell below 34°C) and at 26°C in the hypothermic series. Myocardial protection was always accomplished by means of anterograde isothermic intermittent blood cardioplegia.
The left internal thoracic artery was used to graft the left anterior descending coronary artery, and other venous or arterial conduits were used for the remaining target coronary vessels. At the end of CPB, anticoagulation was reversed with protamine sulfate (1-1.5 mg per 100 IU of heparin).
Samples and assays
Blood samples were collected immediately before surgical intervention; 24, 48, and 72 hours thereafter; and at hospital discharge. The samples were collected in trisodium citrate (0.106 mol/L) and centrifuged without delay at 3000g and 4°C for 20 minutes. Plasma was stored at -80°C within 1 hour of sampling, and cellular pellets were kept at -20°C.
The plasma concentrations of the following factors were measured in a core laboratory blinded to the patients' status: C-reactive protein (CRP) was measured by using the nephelometric method (APS; Beckman, Palo Alto, Calif); plasma fibrinogen concentrations were assayed by using the modified Clauss functional method (Instrumentation Laboratory SpA, Milan, Italy); interleukin (IL) 6 levels were analyzed by using the IL-6 Human Biotrak Elisa System (Amersham Pharmacia Biotech, Monza, Italy).
Plasminogen activator inhibitor 1 (PAI-1) antigen levels were determined by means of double-antibody sandwich enzyme-linked immunosorbent assay (Instrumentation Laboratory SpA). This marker was chosen to assess the fibrinolytic capacity of plasma because it rapidly, irreversibly, and specifically inhibits both tissue-type and urokinase-type plasminogen activator.
2
Measurement of prothrombin time (expressed as international normalized ratio [INR]), activated partial thromboplastin time (PTT), and platelet, white blood cell (WBC), neutrophil, lymphocyte, and monocyte counts was performed in the hospital laboratory and was used also for clinical purposes in the management of patients after the intervention (see Appendix).
Statistical analysis
The
2 or Fisher exact test was used to compare discrete variables. Correlations were assessed by using the Pearson or Spearman methods. Continuous variables (presented as means ± SD) were compared by means of parametric or nonparametric (Kruskal-Wallis) analysis of variance. Repeated-measures multivariate analysis of variance (GLM procedure for SAS) was used to assess changes in levels of the different parameters over time in the overall population and according to the CPB temperature. Analyses were carried out with the SAS statistical package.
| Results |
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No significant differences in mortality and type and incidence of postoperative complications were found between patients operated on with normothermic CPB versus those operated on with hypothermic CPB (Table 3
). In the hypothermic series postoperative myocardial infarction and need for blood products occurred slightly more frequently (leading to a greater incidence of minor and hemorrhagic complications in this series), but these differences did not reach statistical significance. Mean blood loss did not significantly differ between the 2 subgroups.
Similarly, the mean stay in the ICU and in-hospital stay after the operation were similar between the 2 groups (although slightly superior among hypothermic patients).
Markers of hemostatic and inflammatory activity
Both hemostatic and inflammatory markers changed significantly in the postoperative period: IL-6 and WBC, neutrophil, monocyte, and lymphocyte counts peaked in the first hours after the operation. CRP levels peaked at 72 hours and remained elevated at discharge, whereas platelet levels were greatly reduced 48 hours after the operation and returned to normal values at the time of discharge. Mean fibrinogen concentrations declined slightly at 24 hours and then increased steadily until discharge (acting as an acute-phase protein), PTT showed only a trend toward prolongation at 24 hours, and INR values increased at 24 hours and returned to normal values 48 hours after the operation. Both PAI antigen and activity increased roughly 2-fold at 24 to 48 hours after the operation (acting as an acute-phase reactant) and tended to almost normalize by the time of discharge.
No significant difference in the postoperative level of any of the measured variables at any time point was evident between the patients undergoing normothermic and hypothermic CPB (Figures 1-4). The mean postoperative concentrations of fibrinogen, CRP, IL-6, and PAI-1, as well as the platelet and WBC counts and the PTT and INR, were similar between the 2 groups at all sampling intervals.
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| Discussion |
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On the other hand, major concerns about the safety of NSP (mainly with regard to central nervous system protection) have been expressed by several authors. Although the early report of a greater incidence of stroke in patients operated on with normothermic CPB has not been confirmed in successive studies,
6,7 we recently showed how normothermia is associated with a superior extension of brain damage and a worse neurologic outcome in patients who had an intraoperative stroke.
8,9
The lack of major clinical benefits and the possibility of deleterious effects suggests caution with regard to the widespread adoption of NSP and warrants further investigation into its limits and advantages.
One of the presumed theoretic benefits of normothermia is a better maintenance of the cellular and humoral homeostatic processes (less efficient in hypothermic conditions), with consequent reduction of the systemic reaction to CPB and of CPB-induced multisystem organ damage. However, this theoretic assumption (which constitutes one of the main conceptual arguments in favor of NSP) has found only partial confirmation on the basis of objective data.
Indeed, the major studies investigating the relationship between extracorporeal circulation temperature and degree of activation of the inflammatory system have reported conflicting results, supporting in turn a proinflammatory
10 or anti-inflammatory
11,12 effect of NSP or the lack of major differences.
13
Similar contradictions exist among the various investigations that have focused on postoperative indexes of activation of coagulation in patients operated on with hypothermic systemic perfusion versus NSP, with some series detecting a more pronounced alteration of the coagulation system after hypothermia
14,15 and others describing no significant differences between the 2 temperatures.
16,17
However, it must be stressed that the great majority of these studies were conducted on a limited number of patients and had a small number of sampling intervals and low statistical power. Moreover, most of them were not prospective randomized investigations and lacked rigorous criteria for the patients' inclusion and surgical management. In addition, the definition of both hypothermia and normothermia adopted by the different authors has been quite heterogeneous, thereby hindering an accurate comparison of the results from the various groups.
In our series CPB temperatures did not significantly affect in-hospital clinical results or laboratory evidence of activation of the inflammatory and hemostatic systems in patients undergoing primary isolated CABG. Mortality, morbidity, number, and type of postoperative complications; bleeding tendency; and ICU and in-hospital stay were comparable between the 2 groups (although a small tendency toward a greater incidence of postoperative complications was registered in the hypothermic series). More interestingly, no difference between hypothermic and normothermic CPB was found for any of the measured hematic markers of activation of the inflammatory and hemostatic system (CRP, IL-6, WBC and platelet counts, PAI-1, fibrinogen, INR, and PTT) at any time point.
Although these laboratory data are in contrast with those reported by most of the other trials on this subject, methodological and statistical issues seem the most probable explanation for this difference. In fact, in contrast with the described limitations of the previous reports, our study included a prospective randomized design, rigorous enrollment criteria, and a uniform surgical protocol. Although the absolute magnitude of our patient population is not wide, and the possibility of a type II statistical error can not be completely excluded, the high complexity and cost of sensible biochemical markers in patients undergoing cardiac surgery obviously limit the enrollment of a larger cohort of patients in this type of investigation, and in fact, our study has a sample size far larger than those of all published series on this issue.
These considerations provide strong arguments in favor of the reliability of our observations and are very likely to render the reasons for the discrepancies between our observations and those already published.
It is also noteworthy that those clinical trials on hypothermic versus normothermic CPB with sufficient statistical power and with a rigorous study design failed to demonstrate any significant difference in the postoperative course (including mortality, incidence, type of complications, and length of ICU stay) and blood loss between patients operated on with warm or cold bypass.
3,4 Even those clinical studies that specifically investigated the difference in the amount of postoperative blood loss between hypothermic and normothermic perfusion could not demonstrate any substantial reduction by using warm CPB.
15,18-20
Therefore, these sound clinical data seem to deny any measurable advantage of normothermia with regard to postoperative bleeding and provide a strong clinical correlate to our observations.
On this basis, it seems reasonable to assume that, in low-risk patients undergoing primary isolated CABG, NSP does not reduce (or increase) the extent of postoperative systemic inflammatory reaction or of activation of the hemostatic system. Although our study focused on highly selected cases and cannot definitely rule out possible differences in patients with organ dysfunction or those undergoing more complex cardiac operations, the almost identical magnitude of the systemic reaction to hypothermic and normothermic CPB (measured even using very sensible indexes) renders the hypothesis that these eventual differences are of any clinical relevance at least unlikely. These results, coupled with the reported concerns about neurologic safety with NSP, raise new doubts about the effective clinical advantages of normothermia in cardiac surgery and indicate the need for further careful investigation on the real pros and cons of normothermic CPB and on its specific effects on every organ and system.
| Appendix |
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Routine blood assay methods
Platelet, WBC, neutrophil, lymphocyte, and monocyte counts were measured automatically (Technnicon H3 RTX, Bayer, Germany). Measurements of prothrombin time (expressed as INR) and activated PTT were also carried out automatically (Elektra 1800, MLA).
| Acknowledgments |
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| References |
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