Urinary IRT. Although much lower, the urinary IRT profile was similar to the plasma profile (Fig. 2), namely, a sharp rise and fall between day 0 (13 h) and day 1 (AM), followed by a progressive and long-lasting increase starting on the second or third day. A statistically significant difference in the mean values was observed at each time point between PCI and no PCI patients.
Blood calcium. The mean values of total and free calcium increased from day 1 to day 0 (13 h). This increase was the consequence of the peroperative calcium administration (700 mg/L) within the Haemaccel solution used to prime CPB (Fig. 3). The values remained higher than the day 1 value afterward (P < 0.0001). The time course of total calcium differed according to the presence or absence of PCI. In the PCI group, calcium continued to increase up to day 0 (21 h), and slowly decreased afterward. In contrast, calcium decreased from day 0 (13 h) in the no PCI group and was lower than in the PCI group for each time point.
Plasma proteins. Despite a progressive increase in both groups, the time course of plasma proteins differed between the PCI and no PCI patients. Plasma protein concentration was already higher in the PCI than in the no PCI group preoperatively, and increased postoperatively more markedly in the PCI than in the no PCI group (Table 4).
In an attempt to determine the risk of developing a postoperative PCI from preoperative analyte levels, logistic regression was applied to determine critical cutoff points. It was found that any preoperative plasma value (day 1) of IRT ≥40 ng/mL (P < 0.0001 and percentage concordance 80%), total amylase ≥42 IU/L (P < 0.001 and percentage concordance 69%), and pancreatic isoamylase ≥20 IU/L (P < 0.005 and percentage concordance 66%) was associated with postsurgery PCI (Fig. 4, A-C). None of the other variables assessed were predictive of PCI.
From the separate analyses of the biological parameters, it seemed that the time courses of the 4 pancreatic enzymes (IRT, isoamylase, lipase, and total amylase) were highly interrelated. By regression analysis, the association between these 4 variables and potentially independent variables, including urinary IRT, MPO, α1-PI, α2-M, or total calcium, was assessed at each time point and in each group. It was found that the preoperative (day 1) values of the 4 enzymes were correlated with the urinary IRT concentration in both groups (P < 0.0001 for PCI, P < 0.05 for no PCI), total calcium in PCI group only (P < 0.05), MPO in no PCI group (P < 0.05), α2-M in PCI group (P < 0.0001), and creatinine in PCI group (P < 0.05). Postoperatively, the values of the 4 pancreatic enzymes were significantly correlated with urinary IRT and total calcium throughout the observation period in the PCI group, with MPO in the PCI group from day 2, with α1-PI in the PCI group from day 1 (AM), and with α2-M in the PCI group, up to day 0 (21 h) but no longer with creatinine from day 4.
In this study, we found systematic increases in the serum and urine levels of pancreatic enzymes after cardiac surgery with CPB with values higher than the reference ranges in 69% of the patients. The single-center design of this study can, of course, limit the generalizability of these findings. However, using our stringent definition, we found a higher number of PCI patients than by using as markers of pancreas injury total hyperamylasemia and/or hyperlipasemia. It thus seemed that the use of isoamylase and trypsin, both exclusively released from the pancreas, may increase the sensitivity for the detection of clinically silent pancreatic injury as compared with total amylase and lipase, which were used in previous studies (1, 3, 26, 28, 38-41). These 2 variables are not pancreas-specific because amylase can also be released by salivary glands and the activity of the pancreatic lipase cannot be distinguished from the activity of the liver, intestinal, subendothelial, and lipoprotein lipase (40-43). We used 2 variables, IRT and isoamylase, that cannot be released from any other tissue than the pancreas; and a simultaneous elevation of these 2 variables above the upper limit of normal in at least 3 consecutive samples was required to define PCI. For IRT, we used a stringent criterion, with the upper limit of normal being set at the mean value + 3 SD.
The time course study demonstrated that the release of the pancreatic enzymes was typically biphasic, similar for IRT (in blood and urine), isoamylase, total amylase, and lipase, with a first peak value directly after surgery and a second progressive increase starting 4 to 8 days after surgery. Interestingly, in the group of no PCI patients, we observed a similar biphasic profile for the 4 enzymes, but with mean values remaining within the reference range.
Without surprise, we observed that PCI was associated with male gender. Renal insufficiency could represent another theoretical explanation for the increase in IRT, but is unlikely because no significant difference was observed in the renal function evaluated by plasma creatinine and urine output between groups. Another argument against the involvement of renal failure in the increase in IRT is that the profile of IRT in urine was similar to that of plasma, but with much lower values. Inasmuch as kidneys only eliminate trypsinogen (44), this suggest that the IRT in plasma was mainly trypsin complexes with antiproteases, which are eliminated by macrophages (45).
An intriguing finding was the biphasic profile of the pancreatic enzyme release. The first peak could be attributed to ischemia or a peroperative inflammation reaction, and the second to inflammation. Indeed, a peroperative inflammation reaction with cellular acidosis and stimulation of neutrophils can be due to the surgical procedure (51, 52) and to the contact of blood with the material of the CPB circuit, increasing the adherence of phagocytes to the vessel walls. The CPB is accompanied by tissue hypoxia in splanchnic organs including pancreas (53), splanchnic hypoxia that is likely from a circulatory origin, even in the absence of significant decrease in hepatosplanchnic blood flow (54, 55), but could also originate from mechanical compression of the splanchnic area. In clinical practice, the presence of pancreatic ischemia is difficult to assess (56). Ischemia has been demonstrated to be linked to an increase in intracellular and intramitochondrial calcium concentrations (57). If ischemia of the splanchnic area contributed to the development of pancreatic injury, this ischemia has increased intra-acinar Ca2+ concentration, with a possible intracellular trypsinogen activation and neutrophil stimulation into the pancreatic circulation.
Another interesting and surprising point of our study was the demonstration by multivariate analysis of a positive predictive value for preoperative IRT, total amylase, and pancreatic isoamylase values. Hence, the systematic measurement of the preoperative value of IRT, the most sensitive predictor of postoperative PCI, could be an indication to follow the pancreatic function in these patients. Actually, the high IRT values that we measured could be related to a minimal preoperative pancreatic injury, as IRT reflects the leakage of unactivated proenzymes from injured acinar cells (60). The PCI observed after CPB could thus have been facilitated by a "primed" pancreas. The priming of pancreas could result from preoperative ischemia, although this was not assessed.
In conclusion, we confirmed that PCI was common in CPB patients; and with severe and highly specific criteria, we found a higher frequency of PCI than previously reported for AP. In agreement with previous studies, the PCI was linked to the serum concentrations of calcium and was not associated to clinical signs of pancreatitis. Therefore, the clinical relevance of the present findings is uncertain. We also demonstrated that the release of pancreatic enzymes was biphasic: a direct postoperative release that could be linked to peroperative ischemia and a late phase that could be attributed to postsurgery inflammation reaction. Interestingly, we determined that IRT, isoamylase, and total amylase preoperative values were predictive of a postoperative PCI, a phenomenon that could be taken into consideration for the clinical follow-up of the CPB patients.
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