It is well established that the combination of anaesthesia and major surgery including cardiac surgery with cardiopulmonary bypass (CPB) is associated with a temporary perioperative immunological alteration. Recently, considerable interest has been focused on the systemic inflammatory response syndrome (SIRS) and the involvement of cytokines during and after CPB [1-5]. Cytokines are a large and rapidly expanding group of polypeptides produced by many different cell types and necessary for optimal function of the immune system.
The pro-inflammatory cytokine response to cardiac surgery is dominated by TNF-α, interleukin 6 (IL-6) and interleukin 8 (IL-8). Recent studies have shown the myocardium to be a major source of these cytokines [6,7]. The release of the pro-inflammatory cytokines has been associated with the development of complications after CPB [8-11]. They can significantly alter myocardial contractility [11-13] and reduce vascular tone, thus resulting in postoperative low systemic vascular resistance . Cytokines also exert direct damaging effects to other organs and contribute to the development of multiorgan failure . Finally, the release of cytokines due to CPB may be involved in immunological alterations that can develop in the postoperative period [15,16].
Although the nature of peroperative cytokine response seems to be especially determined by direct surgical trauma, anaesthesia as well may exert a modifying effect [17-20]. Up to date, there are no confirmed data about the effect of different anaesthetic techniques on cytokine response during cardiac surgery. After acceptance of volatile induction and maintenance of anaesthesia (VIMA) with sevoflurane as an alternative technique to total intravenous anaesthesia (TIVA) in cardiac surgery [21,22], we have designed the present study to test the hypothesis that the choice of anaesthesia either VIMA or TIVA may influence the pro-inflammatory cytokine response during CABG surgery. The aim was to evaluate the effect of VIMA with sevoflurane versus two different TIVA techniques on the cytokine response to cardiopulmonary bypass.
After approval by the local Hospital Ethics Committee, written informed consent was obtained from 30 patients with angina pectoris NYHA class II-IV and ejection fraction >40%, undergoing elective CABG surgery. Patients with unstable angina pectoris, severely impaired left ventricular function (ejection fraction <40%), severe systemic non-cardiac disease, renal or liver impairment, insulin-dependent diabetes, recent myocardial infarction (<6 weeks), or under immunosupressive treatment were excluded. On the morning of surgery, the patients were randomly allocated to receive VIMA with sevoflurane (Group 1) or TIVA with propofol (Group 2) or moderate dose sufentanil-midazolam (Group 3). Usual cardiac medications, including β-adrenergic blocking agents, calcium-channel blocking agents and nitrates, were continued up to the morning of surgery. All patients were premedicated with lorazepam 40 μg kg−1 orally the night of the operation and morphine sulphate 70 μg kg−1 and scopolamine 8 μg kg−1 intramuscularly 1 h before the operation.
In Group 1 (n = 10), anaesthesia was induced by tidal breathing of high concentration sevoflurane using a semi-closed anaesthetic breathing system, primed with 5-8% sevoflurane in oxygen supplemented by sufentanil 0.7 μg kg−1, and maintained by 0.5-2% end-tidal sevoflurane supplemented with low dose of continuous sufentanil infusion 0.2 μg kg−1 h−1.
In Group 2 (n = 10) anaesthesia was induced with propofol 2 mg kg−1 and sufentanil 0.7 μg kg−1, and maintained with propofol at a plasma concentration of 0.5-2 μg mL−1.
In Group 3 (n = 10), anaesthesia was induced with sufentanil 2 μg kg−1 and midazolam 0.15 mg kg−1, and maintained with sufentanil 1.0 μg kg−1 h−1 and midazolam 0.12 mg kg−1 h−1.
In the three groups, tracheal intubation was facilitated with pancuronium bromide 0.1 mg kg−1. A bolus dose sufentanil 0.5 μg kg−1 was given before skin incision. No acute normovolaemic haemodilution was allowed, and no corticosteroids were given.
Patients' lungs were ventilated with oxygen/air (FiO2 = 0.5) with tidal volumes of 5 mL kg−1 aiming at normocapnia.
Cardiopulmonary bypass was standardized for the priming method (modified gelatine), degree of hypothermia (28-32°C), type of oxygenator (membrane) and flow characteristics. Cardiac arrest was induced by a modified St Thomas' Hospital cardioplegia solution.
After completion of surgery, patients were transferred to the intensive care unit (ICU) and weaned from mechanical ventilation as soon as they were haemodynamically stable, responded to verbal stimulation, were completely rewarmed and blood loss did not exceed 100 mL h−1. Postoperative pain management was achieved with piritramide (pirinitramide).
Blood sampling for determination of TNF-α, IL-6 and IL-8 was performed at the following time points:
- Time 0: before induction of anaesthesia
- Time 1: immediately before skin incision
- Time 2: immediately before cardiopulmonary bypass (CBP)
- Time 3: after aortic declamping
- Time 4: end of CBP
- Time 5: 2 h after skin closure
- Time 6: 24 h after skin closure.
Samples were collected in tubes containing lithium heparin (Venoject®; Terumo, Europe NV, Leuven, Belgium). The samples were immediately centrifuged at 1000g, and the plasma was stored at −70°C until assay of plasma could be determined. Enzyme-linked immunosorbent assays (ELISA) for TNF-α, IL-6 and IL-8 were performed according to the manufacturer's instructions (Immulite®; DPC, Los Angeles, CA, USA). The analytical sensitivity of IL-6 and IL-8 assays was 5 pg mL−1, and the analytical sensitivity of the TNF-α assay was 4 pg mL−1. Concentrations less than the limit of detection were taken as 0 pg mL−1.
Data were expressed as means ± SD. The sample size of the studied group was such that a standardized difference of 1.2 between anaesthetic techniques would be detected with 80% power at a two-sided significance level of 5%. Comparability of patient data was checked using a one-way ANOVA test for numerical variables and χ2-test for nominal variables. Logarithmic transformation of the absolute measures of serum cytokine concentration was applied to reduce skewness. The ANOVA test tested the difference between groups. Then the change between two time points within the same group was tested with paired t-tests. Pearson's test was used to test the bivariate correlation between variables. In all cases, P < 0.05 was considered as significant.
No significant difference between groups was noticed with regard to demographic data, duration of aortic cross-clamping, duration of cardiopulmonary bypass, duration of anaesthesia, duration of intubation, intraoperative fluid or blood intake (Table 1). The peroperative course was uneventful for all patients. Postoperatively, three cases of myocardial infarction were recorded, one in each group.
Plasma concentrations of IL-6, IL-8 and TNF-α were zero or just reached the detection level until the time of aortic declamping in the three groups. The concentrations of TNF-α and IL-8 were comparable in the three groups during all measurement (Figs 1 and 2).
After skin incision and before starting the CPB, the IL-6 concentration was significantly higher in Group 1 compared with Group 2 (P = 0.009) and Group 3 (P = 0.030). After CPB and when the patients were in the ICU, no further differences were detected between the groups (Fig. 3). Concentrations of IL-6 and IL-8 started to increase significantly after aortic declamping and peaked 2 h after the skin closure without differences between groups (Figs 2 and 3). There was significant correlation between the concentrations of these two cytokines and the duration of aortic cross-clamping (r = 0.54 for IL-6; r = 0.62 for IL-8) (Figs 4 and 5). There was also a significant correlation between concentrations of TNF-α and the length of ICU stay (r = 0.78) (Fig. 6).
The possible effects of anaesthesia on the immune system have been discussed from as early as 1916 . General anaesthesia may influence the host defence system. Although the exact cellular mechanisms involved are not yet clear, anaesthetics may either modulate the host defence indirectly by affecting the afferent neuronal input from the operative site, thus affecting the neurohumoral response to injury, or directly act on immune cells [17,24]. In the studies of Pirttikangas and colleagues, propofol anaesthesia increased the percentage of T-helper cells (CD4+lymphocytes) in the circulation, but conventional balanced anaesthesia or combined isoflurane anaesthesia had no such effect [25-27]. T-helper cells play a critical role in immune responses, with their effects largely depending on their cytokine production . Similarly, inhibition of the release of cytokines by cultured mononuclear cells has been reported after exposure to opioids and various anaesthetics, including volatile anaesthetics and intravenous anaesthetics, e.g. ketamine [29,30].
The present study found that the pro-inflammatory cytokine response to coronary artery bypass grafting surgery was characterized by an increase in TNF-α, IL-6 and IL-8 starting immediately after release of the aorta cross-clamp to reach a peak 2 h after the end of the operation. Traditionally, this pro-inflammatory cytokine response has been attributed to the stress response of surgery or the response to CPB. In contrast, Lahat and colleagues observed significant elevation in TNF-α immediately after induction of anaesthesia with high-dose fentanyl even before surgery commenced . In addition to TNF-α, McBride and colleagues found a significant rise in IL-8 after induction of anaesthesia with high-dose fentanyl even before intubation and commencement of surgery .
In the present study, it was noticed that in Groups 2 and 3, the IL-6 concentrations were significantly lower before the beginning of CPB compared with Group 1. This may be explained by the effect of propofol, midazolam and sufentanil on the monocytes, which are the main source of IL-6 production. In an in vitro study, Heller and colleagues reported that propofol and midazolam affect neutrophil and monocyte oxidative burst and phagocytosis only in high concentrations . In the same study, the polymorphonuclear phagocytosis also was impaired with propofol even in clinically used concentrations. Sufentanil may decrease IL-6 production by binding the opioid receptors on the monocyte cell surface resulting in a decrease in intracellular concentrations of cAMP, which is one of the signalling mechanisms for IL-6 secretion [34,35]. Compared with the present results, Crozier and colleagues showed that propofol-alfentanil anaesthesia delays the onset and reduces the magnitude of the IL-6 response during major abdominal surgery as compared with isoflurane anaesthesia . They attributed this to the effect of alfentanil on opioid receptors of the monocytes. However, Brix-Christensen and colleagues found that a high- or a low-dose opioid has the same effect on the perioperative cytokine response to CABG surgery . This may imply that the lower levels of IL-6 in Groups 2 and 3 that was noticed in the present study may be due to the effect of propofol or midazolam and not due to the effect of the different doses of sufentanil.
The present study confirms the results of Brix-Christensen and colleagues that showed that the anaesthetic drug or technique does not modify the cytokine response to CPB, which implies that the pro-inflammatory cytokine responses during cardiac surgery seems to be largely determined by an ischaemia-reperfusion phenomenon or the effect of CPB itself. The lower concentrations of IL-6 that were noticed in the present study before the beginning of CPB in the two TIVA groups compared with the VIMA may indicate that anaesthetic drugs are capable of exerting a modifying effect on the cytokine response to surgical stimulation [18-20].
The correlation between the ischaemia time and high concentrations of IL-6 and IL-8 that were noticed in the present study has also been previously reported [11,37]. Although direct haemodynamic effects of IL-6 are doubtful , increased concentrations of this interleukin have been associated with cardiac dysfunction after CPB . IL-8 is a potent chemo-attractant for neutrophils and may play a role in lung injury associated with pulmonary leukocyte sequestration . Increased concentrations of TNF-α during and after CBP have been shown by many studies and are confirmed in the present study. It has been previously suggested that TNF-α may contribute to myocardial dysfunction and haemodynamic instability following CPB, which may explain the correlation between this cytokine and the length of stay in the intensive care unit noticed here. From the present results, it is concluded that the choice of anaesthetic technique - either VIMA with sevoflurane or TIVA with propofol or midazolam - may affect the pro-inflammatory cytokine response to surgery. However, neither technique could modify the cytokine response to the effect of the ischaemia-reperfusion phenomenon or CPB itself.
The authors thank Mr Corne Endschot and Mr Jan van Velthoven for excellent laboratory assistance. The study was entirely conducted in the Thoraxcentre in Breda with financial support from the Egyptian government. S. R. E. A. has been affiliated to The Netherlands for the duration of the study by the Egyptian Ministry of Higher Education and Scientific Research.
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