Trauma, surgery and infectious diseases trigger the production of cytokines which subsequently mediate different hormonal, metabolic, haemodynamic and immunological responses [1-4].
The pro-inflammatory cytokines are involved in the pathogenesis of the systemic inflammatory response syndrome, sepsis and multisystem organ dysfunction [5,6], while anti-inflammatory cytokines suppress the inflammatory response [7,8].
In adults, increased plasma concentrations of the pro-inflammatory cytokines interleukin-1β(IL-1β), IL-6, IL-8, tumour necrosis factor α (TNFα) and interferonγ (IFNγ) have been demonstrated after different types of surgery [1,2,9]. The IL-6 response seems to correlate with the extent of the surgical trauma and the development of post-operative infectious complications [1,9,10].
The haemodynamic, metabolic, endocrine and some of the immunological changes in children undergoing anaesthesia and surgery have previously been described [11-13]. However, little is known about their ability to mount a cytokine response to anaesthesia and surgery.
The aim of the present study was to describe the peri-operative cytokine response in young children undergoing major surgery.
Following local ethics committee approval and informed parental consent, 13 children less than 5 years of age scheduled to undergo elective abdominal or thoraco-abdominal surgery were studied (Table 1). Exclusion criteria were acute or chronic inflammatory diseases, and endocrine and neurological disorders.
Children <3 months of age did not receive any premedication. Children >3 months of age received a mixture of diazepam (0.5 mg kg−1) and morphine (0.15 mg kg−1) rectally.
All children received a standardized combined general and epidural anaesthetic technique. General anaesthesia was induced with thiopentone (4-7 mg kg−1), and vecuronium (0.1 mg kg−1) was used to facilitate endotracheal intubation. Anaesthetic maintenance comprised nitrous oxide and isoflurane in oxygen.
Following anaesthetic induction, an epidural catheter (lumbar or thoracic) was introduced in all children. Prior to surgery, all children received an initial dose of 0.25% plain bupivacaine 0.5 mL kg−1. Further increments of 0.25% bupivacaine were given as needed as were bolus doses of fentanyl (1-2 μg kg−1). All children were extubated at the end of surgery.
Post-operative pain management consisted of epidural infusion of 0.1% bupivacaine 0.2-0.3 mg kg−1 h−1 and fentanyl 0.4-0.6 μg kg−1 h−1, supplemented with rectal paracetamol 20-25 mg kg−1 every 4-6 h.
Blood samples for cytokine analysis obtained from a central venous line were as follows: sample 1 was obtained after induction of anaesthesia but before surgery; sample 2 was obtained at the end of surgery; and sample 3 was taken 24 h post-operatively. The last blood sample (4) was taken when the children were mobilized and had regained gastrointestinal function (i.e. were passing stools) at a median of 120 h post-operatively (range 48-168 h).
All blood samples were collected in heparinized tubes and immediately refrigerated on ice. Plasma was isolated by centrifugation at 1500 rpm for 10 min and subsequently stored at −80°C until assay.
A panel of seven cytokines was analysed: TNFα, IL-1α, IL-6, IL-10, IL-1Ra and IFNγ were measured by double-sandwich ELISAS . The inter- and intra-assay coefficients of variation for the concentration range between 30 pg mL−1 and 1 ng mL−1 were less than 12%. The sensitivity limits of these ELISAS were 8-30 pg mL−1. Cytokine IL-1β was measured by triple-sandwich ELISA . The inter- and intra-assay coefficient of variation for the concentration range between 30 pg mL−1 and 1 ng mL−1 was less than 15%. The sensitivity-limit of this ELISA was 15 pg mL−1
A median value at each of the four time points was calculated for each of the seven cytokines. Pre- and post-operative comparisons were made with Wilcoxon's paired signed rank test.
Thirteen children (seven females and six males) were included in the study. The type of surgery and demographic data are shown inTable 1. The median age was 19 months (range 1.5-54 months) and the median weight was 10.0 kg (range 4.8-17.8 kg). Overall, the plasma cytokine levels were highly variable. Cytokines TNFα and IL-1Ra were detectable in all children, whereas IL-1α was not detectable. The other cytokines were only sporadically detectable among a minority of the children. No significant changes were demonstrated in any of the cytokine levels pre- vs. post-operatively. The results are shown inTable 2.
In the present study, the peri-operative cytokine response was highly variable, with a pronounced inter- and intra-individual variation (Table 2). This contrasts with the findings in adult surgical patients, in whom a marked and transient pro-inflammatory cytokines response has been demonstrated [1,3,4,9,10,16,17]. However, the present findings are in accordance with another study, in which an early post-operative increase in IL-1Ra was demonstrated in 11 children undergoing Swenson's pull-through procedure for Hirschsprung's disease . In the present study, a trend towards a similar increase in IL-1Ra at the end of surgery was found (P = 0.1).
A marked IL-6 response has been reported in children with Hirschsprung's disease undergoing major colonic surgery . However, as in the present study, low and sporadic IL-6 levels have also been demonstrated in another paediatric study . These results contrast with several other studies showing that IL-6 is the dominating cytokine synthesized in response to surgery by both adults and children. Furthermore, IL-6 levels correlate with the extent of the surgical trauma [3,4,10,18,19].
The pre-operative TNFα concentrations found in this study were high compared with the undetectable or very low plasma levels reported in healthy adults and children[1,18,22,23]. Pre-operatively high TNFα plasma levels have not been demonstrated in other studies. However, several studies have shown a post-operative TNFα response, albeit not reporting levels as high as in the present study [1,10]. High levels of TNFα have also been reported during and after paediatric cardiac surgery [20,21], as well as in patients with sepsis or autoimmune diseases [2,4,6,8]. The children in the present study showed no clinical signs of infection or sepsis which could explain the high preoperative TNFα levels, nor did they develop any such complications post-operatively. However, the pre-operative blood sample was taken after the induction of anaesthesia. The impact of anaesthesia on the cytokine response has been investigated in few studies. A propofol/alfentanil- based anaesthetic technique attenuated the IL-6 response compared with an inhalational anaesthetic technique , while epidural analgesia did not modify the IL-6 response .
Several factors may contribute to the variability shown in the present study. Most importantly, cytokines are mainly paracrine molecules, i.e. they are produced and act locally. The amount of systemic spillover may be limited. Furthermore, having reached the circulation, cytokines are usually eliminated or rendered inactive very rapidly. Therefore, it would be more interesting to measure cytokines in the surgical field, i.e. in wounds or peritoneal fluid , rather than in peripheral blood.
This study comprised children undergoing different types of surgery, including colonic surgery. Surgery on the colon is frequently associated with bacteraemia and endotoxaemia, both known to be potent stimulators of cytokine cascades [20,26,27]. However, endotoxaemia and bacteraemia per se are not always accompanied by elevated cytokines in plasma .
Children with malignant tumours were also included in this study. Even though there were too few of these patients, it was our impression that the cytokine response in these children did not differ from that in children with non-malignant conditions. However, the influence of malignancy on the peri-operative cytokine response remains to be elucidated.
In conclusion, contrasting with the well-defined cytokine response in adults, this study demonstrated highly variable peri-operatve cytokine responses in infants and young children undergoing major surgery. Further studies comprising homogenous groups of patients, well-defined surgical trauma and standardized anaesthetic techniques are required.
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