Histamine release during cardiopulmonary bypass in neonates and infants

Plasma concentrations of inflammatory cytokines rise rapidly during ECMO-related SIRS due to the release of preformed stores in the intestine

Extracorporeal membrane oxygenation (ECMO) is a life-saving support system used in neonates and young children with severe cardiorespiratory failure. Although ECMO has reduced mortality in these critically ill patients, almost all patients treated with ECMO develop a systemic inflammatory response syndrome (SIRS) characterized by a 'cytokine storm', leukocyte activation, and multisystem organ dysfunction. We used a neonatal porcine model of ECMO to investigate whether rising plasma concentrations of inflammatory cytokines during ECMO reflect de novo synthesis of these mediators in inflamed tissues, and therefore, can be used to assess the severity of ECMO-related SIRS. Previously healthy piglets (3-week-old) were subjected to venoarterial ECMO for up to 8 h. SIRS was assessed by histopathological analysis, measurement of neutrophil activation (flow cytometry), plasma cytokine concentrations (enzyme immunoassays), and tissue expression of inflammatory genes (PCR/western blots). Mast cell degranulation was investigated by measurement of plasma tryptase activity. Porcine neonatal ECMO was associated with systemic inflammatory changes similar to those seen in human neonates. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-8 (IL-8) concentrations rose rapidly during the first 2 h of ECMO, faster than the tissue expression of these cytokines. ECMO was associated with increased plasma mast cell tryptase activity, indicating that increased plasma concentrations of inflammatory cytokines during ECMO may result from mast cell degranulation and associated release of preformed cytokines stored in mast cells. TNF-alpha and IL-8 concentrations rose faster in plasma than in the peripheral tissues during ECMO, indicating that rising plasma levels of these cytokines immediately after the initiation of ECMO may not reflect increasing tissue synthesis of these cytokines. Mobilization of preformed cellular stores of inflammatory cytokines such as in mucosal mast cells may have an important pathophysiological role in ECMO-related SIRS.

Histamine release during adult cardiopulmonary bypass

Histamine, an inflammatory mediator in its own right, may also be a marker for a more widespread systemic inflammatory process. In this study we have examined variations in plasma histamine concentrations produced during the course of cardiac surgery involving cardiopulmonary bypass, the relationship between these variations and intra-operative events. By assays of serum tryptase and CD-63 expression we have also attempted to identify the source of histamine. Histamine concentrations that were significantly raised from baseline level were demonstrated. These were elevated from the time of aortic cross-clamping and continued to be raised for 24 h postoperatively (p < 0.00625). This was associated with an increase in CD-63 expression (p < 0.025) (but not an increase in tryptase concentration) following aortic cross-clamping and protamine administration, suggesting that basophils are the source of histamine. 41% of patients had arrhythmias in the post bypass period. The rise in histamine levels was not related to the incidence of cardiac arrhythmias.

Dexamethasone: Benefit and Prejudice for Patients Undergoing On-Pump Coronary Artery Bypass Grafting

STUDY OBJECTIVES

Cardiac surgery with cardiopulmonary bypass (CPB) results in perioperative organ damage caused by the systemic inflammatory response syndrome (SIRS) and ischemia/reperfusion injury. Administration of corticosteroids before CPB has been demonstrated to inhibit the activation of the systemic inflammatory response. However, the clinical benefits of corticosteroid therapy are controversial. This study was designed to document the effects of dexamethasone on cytokine release and perioperative myocardial, pulmonary, renal, intestinal, and hepatic damage, as assessed by specific and sensitive biomarkers.

DESIGN AND PATIENTS

A prospective, double-blind, placebo-controlled, randomized trial for dexamethasone was conducted in 20 patients receiving either dexamethasone (1 mg/kg before anesthesia induction and 0.5 mg/kg after 8 h; n = 10) or placebo (n = 10). Different markers were used to assess the SIRS: interleukin (IL)-6, IL-8, IL-10, C-reactive protein (CRP), and tryptase; and organ damage: heart (plasma heart-type fatty acid binding protein, cardiac troponin I [cTnI], creatine kinase-MB), kidneys (N-acetyl-glucosaminidase [NAG], microalbuminuria), intestine (intestinal-type fatty acid binding protein [I-FABP]/liver-type fatty acid binding protein [L-FABP]), and liver (alpha-glutathione S-transferase).

RESULTS

Dexamethasone modulated the SIRS with lower proinflammatory (IL-6, IL-8) and higher antiinflammatory (IL-10) IL levels. CRP and tryptase were lower in the dexamethasone group. cTnI values were lower in the dexamethasone group at 6 h in the ICU (p = 0.009). Patients in the dexamethasone group had a longer time to tracheal extubation (18.86 +/- 1.13 h vs 15.01 +/- 0.99 h, p = 0.02 [mean +/- SEM]), with a lower oxygenation index at that time: Pa(O2)/fraction of inspired oxygen ratio, 37.17 +/- 1.8 kPa vs 29.95 +/- 2.1 kPa (p = 0.009). The postoperative glucose level (10.7 +/- 0.6 mmol/L vs 7.4 +/- 0.5 mmol/L, p = 0.005) was higher in the dexamethasone group. Serum glucose was independently associated with intestinal injury (urine I-FABP peak, R2 = 42.5%, beta = 114.4 +/- 31.4, significant at p = 0.002; urine L-FABP peak, R2 = 47.3%, beta = 7,714.1 +/- 1,920.9, significant at p = 0.001) and renal injury (urine NAG, R2 = 32.1%, beta = 0.21 +/- 0.07, significant at p = 0.009). Tryptase peaks correlated negatively with peaks of intestinal and renal injury biomarkers.

CONCLUSION

Even while inhibiting SIRS, dexamethasone treatment offered no protection against transient, subclinical, perioperative abdominal organ damage. Tryptase release could have a preconditioning effect, offering protection against perioperative intestinal and renal damage. Dexamethasone treatment resulted in more pronounced postoperative pulmonary dysfunction, prolonged time to tracheal extubation, and initiated postoperative hyperglycemia in patients undergoing elective on-pump coronary artery bypass graft surgery.

The isolated blood-perfused rat heart: an inappropriate model for the study of ischaemia- and infarction-related ventricular fibrillation

1. Well-characterized in vivo and in vitro models exist for the study of ischaemia- and infarction-related ventricular fibrillation (VF). In rats in vivo, VF appears to occur in distinct acute ischaemia- (early) and infarction-related (late) phases. Interestingly, isolated buffer-perfused rat hearts do not develop late VF. This raises the possibility that unidentified components of the blood may be responsible for late VF. We thus sought to characterize an isolated blood-perfused rat heart in order to investigate the possible influence of blood components on arrhythmias arising from ischaemia and infarction. 2. Hearts, excised from male Wistar rats, were perfused in the Langendorff mode with blood from support rats (male Wistar, 350-430 g) via an extracorporeal circuit. Perfused hearts underwent left coronary artery occlusion for 240 min or a sham procedure (n=10 group(-1)). 3. Only 10% of ischaemic hearts developed late VF (90-240 min). Tissue myeloperoxidase activity (an index of neutrophil accumulation) increased during ischaemia from 0.017+/-0.004 (six fresh hearts) to 0.056+/-0.005 units mg protein(-1) (P<0.05) at 240 min, but values were similar in sham hearts (0.083+/-0.013). Likewise, the decline (-1 vs 240 min of ischaemia shown) in circulating total white blood cells from 6.8+/-0.5 to 1.9+/-0.2 x 10(3) micro l(-1) and in platelets from 441+/-32 to 274+/-16 x 10(3) micro l(-1) (both P<0.05) was similar in time-matched sham hearts (data not shown). 4 Surprisingly, only 10% of ischaemic hearts developed early VF (0-90 min), although the incidence of early ventricular tachycardia was 100% in these hearts (P<0.05 vs sham hearts). Blood K+ values were normal (hyperkalaemia suppresses VF). 5 Although late VF was absent in blood-perfused hearts, it would be premature to conclude from this that late VF is not mediated by blood components. This is because the similar neutrophil accumulation in ischaemic and sham hearts, the decline in numbers of circulating blood components, and the unexpected paucity of early VF all question the validity of the model.

Is hyperglycemia seen in children during cardiopulmonary bypass a result of hyperoxia?

OBJECTIVE

We sought to identify whether elevated PaO (2) itself can directly cause hyperglycemia in newborns and to document any additional effects of cardiopulmonary bypass on this response.

METHODS

Piglets were exposed to either normoxia (88 +/- 6 mm Hg) or hyperoxia (470 +/- 28 mm Hg) in the following studies. Anesthetized 3-day-old neonatal pigs were either ventilated for 2 hours of normoxia (n = 5) or hyperoxia (n = 5) or placed on normothermic, normoxic cardiopulmonary bypass (n = 6) and then randomly assigned to either undergo a 2-hour normoxic period or a 1-hour hyperoxic episode, followed by a return to normoxia for an additional hour. Blood glucose levels were measured in all animals.

RESULTS

No significant changes were observed in blood glucose levels in neonatal pigs that underwent 2 hours of normoxic ventilation (5.0 +/- 0.6 mmol/L) or cardiopulmonary bypass (6.6 +/- 1.6 mmol/L). However, the ventilatory model showed a significant and sustained (P <.001) hyperglycemic response after both 1 hour (8.6 +/- 1.0 mmol/L) and 2 hours (9.8 +/- 1.6 mmol/L) of hyperoxia. In the cardiopulmonary bypass model, exposure to 1 hour of hyperoxia elicited a significant (P <.05) hyperglycemic response (10.3 +/- 1.2 mmol/L), followed by a return to normal blood glucose levels (6.6 +/- 1.6 mmol/L) with a return to normoxia. This hyperoxia-mediated hyperglycemic response was confirmed when data examined from children undergoing cardiopulmonary bypass for primary repair of their congenital defects also identified a significant positive correlation (r = 0.72, P =.02) between oxygen levels and blood glucose levels measured before and at the end of cardiopulmonary bypass.

CONCLUSIONS

Hyperoxia triggers a hyperglycemic response in both ventilatory and bypass models. Cardiopulmonary bypass does not exacerbate this response, as shown by the similar levels of hyperglycemia sustained for the duration of the hyperoxic exposure in both experimental models. Therefore, not only may hyperoxia play a crucial role in the hyperglycemic response seen during neonatal cardiopulmonary bypass, but its effect on glucose homeostasis should be considered whenever children are exposed to hyperoxia.