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*Department of Clinical Anaesthesia, Royal Victoria Hospital; and
Department of Microbiology and Immunobiology, Queens University Belfast, Belfast, Ireland
Address correspondence and reprint requests to Helen Gilliland, FRCA, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, Ireland.
| Introduction |
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| Methods |
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Anesthesia was induced with IV ketamine (3 mg/kg) or inhaled halothane (0%3%). After the induction, patients received 25 µg/kg fentanyl IV. Maintenance was with 0.5% isoflurane in oxygen/air plus incremental fentanyl to a total dose of 50 µg/kg. During cardiopulmonary bypass (CPB), flow was maintained at 2.4 L · m-2 · min-1, reduced to 1.8 L · m-2 · min-1 if temperature was <28°C. A hollow-fiber, membrane oxygenator was used, and patients were cooled between 23° and 31°C.
Three leukocyte (L) adhesion molecules, L selectin, CD18, and CD11b were measured, as were systemic and lung levels of three cytokines: the neutrophil chemotactic factor interleukin-8 (IL-8), monocyte chemotactic protein-1 (MCP-1), and the antiinflammatory cytokine interleukin-10 (IL-10).
Arterial samples for adhesion molecule analysis were taken after the induction of anesthesia (Time 0), 10 min after fentanyl (Time 1), at the institution of CPB (Time 2), 10 min after aortic cross-clamp release (Time 3), and 2 h post-CPB (Time 4). Arterial and bronchoalveolar lavage (BAL) samples for cytokines were taken at Times 0, 1, 3, and 4.
BAL samples were obtained by advancing a fine suction catheter into the trachea until resistance was felt. One mg/kg of normal saline was then instilled, and after two breaths, BAL fluid was aspirated into a sputum trap. Direct microscopy of each sample confirmed that fluid instilled had reached the alveoli.
All samples were processed within 10 min of collection to minimize ex vivo stimulation. Samples for adhesion molecule expression were stained with fluorescent dye before cell lysis and analyzed using flow cytometry (4). Samples for cytokine analysis were centrifuged and stored at -70°C before enzyme-linked immunoassay (R&D Quantikine, Abingdon, Oxon, UK).
The ratio of the arterial partial pressure of oxygen to the fractional inspired oxygen concentration (PaO2/FIO2) was recorded 2 h after CPB.
Previous studies suggest that adhesion molecule data are normally distributed (4,5). In contrast, cytokine production may be genetically determined (6,7). Parametric tests were therefore applied to adhesion molecule data and nonparametric tests to cytokine data. Spearman and Pearson analyses were used to test for correlation between inflammatory mediators and perioperative events.
| Results |
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Granulocyte, but not monocyte or lymphocyte, CD18 expression was significantly higher than baseline 10 min after release of the aortic cross-clamp (Fig. 1). Both granulocyte and monocyte CD11b expression rose after cross-clamp release (P < 0.001, P < 0.05, respectively). In all cases, increased expression was transient (Fig. 1).
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| Discussion |
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L selectin is shed upon activation (11). Shedding of neutrophil L selectin has been reported during both simulated CPB and pediatric cardiac surgery (12,13) but did not occur in our study. This discrepancy may relate to the fact that cell separation techniques upregulate adhesion molecules (14,15). Staining blood before separation minimized such artefactual upregulation.
Although systemic levels of the chemokines IL-8 and MCP-1 increased during our study, their BAL levels did not change significantly. Despite this and the dilution inherent in lavage fluid, BAL IL-8 levels were consistently higher than systemic, a finding which points to the lung as an important source of this neutrophil-chemotactic cytokine.
Neither plasma nor BAL chemokine levels correlated with postoperative oxygenation. This supports authors who found no link between plasma IL-8 and respiratory dysfunction (16) but contradicts those who suggest using BAL IL-8 levels to predict the development of severe lung injury (17).
The two integrin molecules studied here, CD11b and CD18, belong to a group whose members share the CD18 component, bound to CD11a, -b, or -c. Expression of CD18, therefore, reflects changes across the group, whereas expression of CD11b gives information about the CD11b/CD18 heterodimer. Upregulation of integrins has been demonstrated during adult cardiac surgery (5) and, inconsistently, during pediatric cardiac surgery (13). Our study confirmed consistent, short-lived integrin activation and generated two additional findings: that CD11b upregulation was more marked than that of CD18 and that different cells were affected to different degrees. Granulocytes showed the greatest change, followed by monocytes, whereas lymphocyte integrin expression did not change at all. These results show that cardiac surgery preferentially affects expression of the CD11b/CD18 heterodimer on the granulocyte population.
Granulocyte integrin expression appeared to predict postoperative oxygenation, regardless of initial diagnosis. It is important to note, however, that postoperative PaO2/FIO2 ratio may have been influenced by residual shunt as well as lung injury. The exact stimulus for adhesion molecule upregulation remains unclear, as perioperative factors showed no correlation with this process. Perhaps upregulation of granulocyte integrins reflects the combined effect of many coexisting proinflammatory stimuli.
Systemic IL-10 production has been demonstrated after cardiac surgery and may represent an attempt to limit inflammatory side effects (18,16). In our study, the increase in plasma IL-10 two hours after CPB was not associated with better postoperative oxygenation. As this was the final sample time, later antiinflammatory effects remain a possibility.
In conclusion, this preliminary study suggests that granulocyte activation may predict postoperative oxygenation in pediatric patients undergoing heart surgery. This is an interesting finding that deserves further investigation.
| Acknowledgments |
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| References |
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