Dexamethasone

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 [+ or -] 1.13 h vs 15.01 [+ or -] 0.99 h, p = 0.02 [mean [+ or -] SEM]), with a lower oxygenation index at that time: Pa[O.sub.2]/fraction of inspired oxygen ratio, 37.17 [+ or -] 1.8 kPa vs 29.95 [+ or -] 2.1 kPa (p = 0.009). The postoperative glucose level (10.7 [+ or -] 0.6 mmol/L vs 7.4 [+ or -] 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, [R.sup.2] = 42.5%, 13 = 114.4 [+ or -] 31.4, significant at p = 0.002; urine L-FABP peak, [R.sup.2] = 47.3%, [beta] = 7,714.1 [+ or -] 1,920.9, significant at p = 0.001) and renal injury (urine NAG, [R.sup.2]= 32.1%, [beta] = 0.21 [+ or -] 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.

Key words: cardiac surgery; cardiopulmonary bypass; coronary artery bypass grafting; dexamethasone; fatty acid binding proteins; mast cell tryptase

Abbreviations: [alpha]-GST = [alpha]-glutathione S-transferase; AUC = area under the curve; CABG = coronary artery bypass graft surgery; CI = confidence interval; CK-MB = creatine kinase MB; CPB = cardiopulmonary bypass; CRP = C-reactive protein; cTnI = cardiac troponin I; ELISA = enzyme-linked immunosorbent assay. FI[O.sub.2] = fraction of inspired oxygen; H-FABP = heart-type fatty acid binding protein; I-FABP = intestinal-type fatty acid binding protein; IL = interleukin; L-FABP = liver-type fatty acid binding protein; MAP = mean arterial pressure; NAG = N-acetyl-glucosaminidase; NO = nitric oxide; SIRS = systemic inflammatory response syndrome

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Organ damage after cardiac surgery with cardiopulmonary bypass (CPB) is caused by two related pathophysiologic mechanisms: the systemic inflammatory response syndrome (SIRS) and ischemia/reperfusion injury. SIRS is triggered by the exposure of blood to large areas of synthetic materials of the extracorporeal circuit. It causes a complex inflammatory reaction involving activation of complement, platelets, neutrophils, monocytes, and macrophages with increased blood concentrations of cytokines and leukotrienes. Additionally, SIRS initiates activation of the coagulation, fibrinolytic, and kallikrein cascades. A subsequent increase in endothelial cell permeability allows transvascular migration of activated leukocytes into the tissues with additional vascular and parenchymal damage). (1,2)

Ischemia/reperfusion injury is triggered mainly in the heart and lungs secondary to aortic cross-clamping and cardioplegic arrest. (3,4) During aortic crossclamping, the heart is excluded from the circulation, being protected by cardioplegia and hypothermia. The lungs are deprived as well of pulmonary blood flow. Ischemia/reperfusion injury has been documented also in other organs such as kidneys and intestine, probably due to alterations in blood flow at the microcirculatory level. (5,6)

Preoperative administration of corticosteroids to patients undergoing cardiac surgery with CPB has been demonstrated to inhibit the activation of the plasmatic and cellular inflammatory response, (7) decrease the proinflammatory to antiinflammatory interleukin (IL) ratio, (8) and minimize tissue edema. (9) Based on these findings, corticosteroids are routinely used in a considerable number of institutions. The studies on the clinical benefits, however, show conflicting results when referring to changes in hemodynamic, pulmonary function, and glucose metabolism. (10-13) Clinical investigations by Chancy et al (12,13) indicate that methylprednisolone offers no clinical benefit, and may in fact be detrimental by initiating postoperative hyperglycemia and delaying postoperative tracheal extubation for undetermined reasons.

As a contribution to the issue of CPB-related SIRS and organ injury, we document the effect of dexamethasone on perioperative myocardial, pulmonary, renal, intestinal, and hepatic damage, as assessed by newly available specific and sensitive biomarkers. Furthermore, to describe the effects of corticosteroids on the systemic inflammatory response, we measured cytokine response and systemic tryptase release as a marker of mast-cell activation. (14) Finally, a new hypothesis relating tryptase to the attenuation of perioperative organ injury will be discussed.

MATERIALS AND METHODS

Patients

The study was designed as a prospective, double-blind, placebo-controlled, randomized trial for dexamethasone. After approval by the hospital ethics committee and written informed consent, patients scheduled for first-time coronary artery revascularization were studied. All patients included in the study had coronary artery disease with normal renal function (as assessed by a serum creatinine level < 120 [micro]mo]/L and normal urinalysis results) and normal hepatic, cerebral, and cardiac function (ejection fraction > 45%). Patients with diabetes, recent myocardial infarction, unstable angina, or recent use of radiocontrast agents or corticosteroids were excluded, as these conditions might be associated with increased baseline levels of the markers used in this study.

Anesthetic Management

The patients (n = 20) were randomized in a double-blinded fashion to receive either dexamethasone or placebo. A baseline serum glucose sample was obtained after overnight fasting. In the treatment group, patients received dexamethasone, 1 mg/kg, at induction of anesthesia and 0.5 mg/kg 8 h later. Patients in the control group received a placebo at the same time points.

Anesthesia was provided according to a fixed protocol. (15) Premedication consisted of oral diazepam, 10 to 15 mg 2 h preoperatively. After insertion of peripheral venous and radial cannulae under local analgesia, general anesthesia was induced with sufentanil, 2.5 [micro]g/kg, and midazolam, 0.1 mg/kg. Tracheal intubation was achieved with pancuronium, 0.1 mg/kg, and the lungs were ventilated with air and oxygen (fraction of inspired oxygen [FI[O.sub.2]] = 0.4). A flow-directed pulmonary artery catheter was inserted into the right internal jugular vein, and an indwelling bladder catheter was used for urine collection. Anesthesia was maintained with sufentanil, midazolam, and pancuronium. Cefuroxim, 1,500 mg, was administered after induction. Hydroxyethyl starch, 200/0.5 6% solution, and lactated Ringer solution were used to obtain a mean arterial pressure (MAP) > 60 mm Hg, to maintain filling pressures and cardiac output. Transfusion of packed RBCs was administered at a hemoglobin level < 4.5 mmol/L. According to standard care in our clinic, 1V insulin was started at a serum glucose level > 10 mmol/L. Inotropic support with dopamine was started at a cardiac index < 2.2 L/min/[m.sup.2].

Diuretics, mannitol, or aprotinin were not administered during the entire study period. Patient characteristics and perioperative variables were recorded prospectively.

CPB

Nonpulsatile CPB was performed using a roller pump (CAPS HLM; Stockert Instruments; Munich, Germany) and a membrane oxygenator (Cobe Optima; Cobe Laboratories; Lakewood, CO). The extracorporeal circuit was primed with 500 mL of hydroxyethyl starch 6% and 1,000 mL of lactated Ringer solution. During CPB, the flow was maintained at 2.4 L/min/[m.sup.2] with moderate hypothermia (32[degrees]C) and [alpha]-stat regulation of blood pH. Cold St. Thomas solution was infused into the aortic root to maintain cardioplegia during aortic cross-clamping. During CPB, the MAP was allowed to vary from 60 to 90 mm Hg. Deviations were corrected with phenylephrine or nitroglycerine.

The urine collection was divided in six intervals: (1) preoperative (baseline: during 12 h prior to surgery); (2) preheparinization (from skin incision to systemic heparinization); (3) sternum closure (from heparinization to sternum closure); (4) 2-h ICU during postoperative 2 h); (5) 6-h ICU (postoperative 2 to 6 h); (6) 24-h ICU (postoperative 6 to 24 h). Urinary excretion of the measured biomarkers was calculated as ratio to urine creatinine concentration and adjusted to time interval in order to correct for changes in urinary flow: urinary production = measured urine concentration/(time interval for urine collection x urine creatinine concentration). Blood sampling was performed before induction of anesthesia (preinduction), 5 min after aortic crossclamp release (aortic clamp release), 6 h after operation (6-h ICU), and 24 h after operation (24-h ICU). Urine and plasma were stored at - 20[degrees]C until assay.

Biomarkers

Inflammatory Biomarkers: Inflammatory markers include the following: (1) IL-6, IL-8, IL-10: solid-phase, enzyme-labeled, chemiluminescent sequential immunometric assay (Immulite; Euro/DPC; Los Angeles, CA); (2) C-reactive protein (CRP): high sensitive enzyme-linked immunosorbent assay (ELISA) [HemoScan; Groningen, the Netherlands]; and (3) tryptase (proteolytic trypsin-like enzyme released from activated mast cells): enzymatic assay (HemoScan). Serum glucose concentration was determined using an analyzer (Vitros; Ortho Clinical Diagnostics; Beerse, Belgium).

Myocardial Injury Biomarkers: Myocardial injury biomarkers include the following: (1) plasma heart-type fatty acid binding protein (H-FABP; cytosolic protein released from injured myocytes) ELISA kit (HyCult Biotechnology B.V; Uden, the Netherlands); (2) cardiac troponin I (cTnI; myofibrillar protein released from injured myocytes): microparticle enzyme immunoassay (AxSYM; Abbott Laboratories; Abbott Park, IL); (3) creatine kinase MB (CK-MB) activity: Vitros analyzer (Ortho Clinical Diagnostics).

Kidney Injury Biomarker: Urine N-acetyl-glucosaminidase (NAG; enzyme released from injured proximal renal tubules): modified enzyme assay according to Lockwood and Bosmann (16) at pH 4.5 and corrected for nonspecific conversion (HemoScan).

Intestinal Injury Biomarkers: Intestinal-type fatty acid binding protein (I-FABP)/liver-type batty acid binding protein (L-FABP)/ H-FABP: cytosolic proteins in the enterocytes released into the blood stream and excreted by kidney early in the course of intestinal ischemia (17): ELISA kit (HyCult Biotechnology BV).

Hepatic Injury Biomarkers: [alpha]-Glutathione S-transferase ([alpha]-GST; enzyme released from centrilobular and periportal damaged hepatocytes reported as having uniform hepatic distribution, high cytosol concentration, and short half-life (18)): ELISA kit (Biotrin International Ltd.; Dublin, Ireland).

Statistical Analysis

The statistical analysis was performed using statistical software (Statistical Package for the Social Sciences, version 12.0; SPSS; Chicago, IL). A power analysis based on previous studies of IL-6 and IL-8 plasma levels in this population suggested that at least 20 patients have to be studied in order to detect a 1-SD difference between the two groups, with a reliability of 5% and a power of 80%.

Before analysis, the data were tested for distribution according to Kolmogorov-Smirnov goodness-of-fit test. The variation of the urinary and plasma markers over the study period, and the differences between groups were investigated using repeated-measures analysis of variance. A total area under the curve (AUC) was calculated for all plasma biomarkers. Continuous variables were compared by means of parametric (Student t test) or nonparametric tests (Mann-Whitney U test). Fisher Exact Test was used to compare discrete variables. Correlation analysis between variables was tested using Spearman correlation test. Regression analysis was used to detect predictors for organ injury. Statistical significance was accepted at p < 0.05. Results are presented as mean [+ or -] SEM unless stated otherwise.

RESULTS

All 20 patients included completed the study and survived the hospital stay. The following complications were observed: revision for bleeding (n = 2), perioperative myocardial infarction (n = 1), atrial fibrillation (n = 1), and nosocomial pneumonia (n = 1). Seven patients in the dexamethasone group and two patients in the placebo group (Fisher Exact Test, p = 0.025) received dopamine < 5 [micro]g/kg/min because of low cardiac index. Six patients in the dexamethasone group and one patient in the placebo group received insulin to regulate serum glucose in the postoperative period (Fisher Exact Test, p = 0.057). Fever (highest measured rectal temperature) was more prominent in the placebo group during the first 24 h postoperatively (Table 1), Additional patient characteristics and operative data are shown in Table 1. The patients in the dexamethasone group were slightly older than patients in the placebo group. However, age did not prove to be a predictor for any of the biomarkers tested. Marked blood loss occurred in one patient in the dexamethasone group, who received 13 U of blood > 6 h after bypass. As this would affect only the last time point of the study, this patient was included in the analysis.

Inflammatory Biomarkers

Plasma levels of proinflammatory cytokines IL-6 and IL-8 increased significantly (significant at p < 0.001 [repeated measures Wilks [lambda]]) in both groups, with a lower response in the dexamethasone group (lower total AUC in dexamethasone group for both IL-6 and IL-8, p < 0.001). The peak values were measured at 6-h ICU for IL-6 and during sternum closure for IL-8 (Fig 1, top, left, and top, right). The IL-6 values were significantly lower in the dexamethasone group at 6-h ICU and 24-h ICU (p < 0.001). IL-8 was significantly lower in the dexamethasone group after aortic clamp release (p = 0.023), during sternum closure (p < 0.001), at 6-h ICU (p = 0.003), and total AUC (p < 0.001). IL 6 values at 24-h ICU were higher than baseline values in both groups (p < 0.001). IL-8 values returned to baseline values after 24 h in both groups.

[FIGURE 1 OMITTED]

Plasma IL-10 increased significantly (significant at p < 0.001 [repeated measures Wilks [lambda]]) in both groups. In the dexamethasone group, plasma IL-10 had an approximate fourfold higher peak at sternum closure. The differences between groups were statistically significant after aortic damp release and sternum closure (p < 0.001), 6-h ICU (p = 0.029), and total AUC (p < 0.001) [Fig 1, bottom, left]. The IL-10 values returned to baseline values after 6-h ICU in both groups.

Plasma levels of CRP did not increase during the operation. The differences between groups on their overall plasma CRP were statistically significant (p = 0.048). The dexamethasone group had lower total AUC (p = 0.028) and lower CRP levels at 6-h ICU (4.9 [+ or -] 1 [micro]g/mL in dexamethasone group vs 39.5 [+ or -] 24.9 [micro]g/mL in the placebo group, p = 0.043) and at 24-h ICU (842.7 [+ or -] 524 p[micro]g/mL in dexamethasone group vs 2,463.5 [+ or -] 968 [micro]g/mL in the placebo group, p = 0.028).

Tryptase increased significantly during operation in both groups (Wilks test, significant at p = 0.018) [Fig 1, bottom, right]. In the dexamethasone group, tryptase concentrations increased only moderately with peak values at sternum closure. In the placebo group, the values rose abruptly reaching peak values immediately after releasing the aortic cross-clamp, and decreased after sternum closure. The tryptase values were significantly lower in the dexamethasone group after aortic clamp release (p = 0.015), during sternum closure (p =0.009), and total AUC (p = 0.05). Tryptase values returned to baseline values after 6-h ICU in both groups.

Myocardial Injury Biomarkers

The release patterns of the myocardial damage markers had a different time course. Plasma H-FABP (Fig 2, top) started to rise directly after aortic clamp release, reaching peak values after 1.23 h (95% confidence interval [CI], 0 to 2.66 h), which was significantly earlier (p < 0.001) than the peak values of cTnI and CK-MB (cTnI: mean, 14.1 h; 95% CI, 6.36 to 21.84 h; CK-MB: mean, 16.35; 95% CI, 9.23 to 23.47 h). The only difference between the treatment groups was observed at 6-h ICU, with a lower value of cTnI in the dexamethasone group (p = 0.009) [Fig 2, bottom].

[FIGURE 2 OMITTED]

Renal Injury Biomarkers

Glomerular and tubular function in this very group of patients has been recently described elsewhere. (19) Briefly, urinary NAG increased significantly in time (p = 0.009 [repeated measures Wilks [lambda]), reaching peak values at 2-h ICU, with no significant effect for the dexamethasone treatment (Fig 3). Microalbuminuria increased during CPB, with peak values in urine collected during CPB for both groups (mean, 7.9 mg/mmol creatinine; 95% CI, 4.8 to 10.9 mg/ mmol creatinine).

[FIGURE 3 OMITTED]

Intestinal Injury Biomarkers

Urinary I-FABP and L-FABP (Fig 4) increased significantly during CPB (p = 0.02 [repeated measures Wilks [lambda]], I-FABP; and p = 0.013, L-FABP) in both groups, reaching peak values in urine collected during the first postoperative 2 h and 6 h, respectively. The change in mean urinary L-FABP production was significantly dependent on dexamethasone treatment (p = 0.026 [repeated measures Wilks [lambda]]), with higher values in the dexamethasone group. When analyzing each individual time point, no statistical significant differences between groups were detected for I-FABP and L-FABP.

[FIGURE 4 OMITTED]

Hepatic Injury Biomarkers

[alpha]-GST increased promptly after initiation of CPB in both groups, with peak values during sternum closure (p < 0.001 [repeated measures Wilks [lambda]]) [Fig 5]. There were no differences between the groups (time points and total AUC). Alanine aminotransferase remained constant for the duration of the investigation. Aspartate aminotransferase increased moderately in both groups with maximum values at 24-h ICU (58.9 [+ or -] 10.8 U/L).

[FIGURE 5 OMITTED]

Dexamethasone treatment increased significantly the serum glucose levels (p = 0.009) [Fig 6]. During sternum closure, the values reached peak values of 10.7 [+ or -] 0.6 mmol/L in the dexamethasone group and 7.4 [+ or -] 0.5 mmol/L in the placebo group. The glucose values in the dexamethasone group were significantly higher than in the placebo group during sternum closure (p = 0.005), at 6-h ICU (p = 0.007), and at 24-h ICU (p = 0.023).

[FIGURE 6 OMITTED]

Predictors of Organ Injury

Peak serum glucose values were significant independent predictors for urine I-FABP peak values ([R.sup.2] = 42.5%, regression coefficient [beta] = 114.4 [+ or -] 31.4 mmol/L, significant at p = 0.002), urine L-FABP peak values ([R.sup.2] = 47.3%, regression coefficient [beta] = 7,714.1 [+ or -] 1,920.9 mmol/L, significant at p = 0.001), urine H-FABP peak values ([R.sup.2] = 48%, regression coefficient [beta] = 2,829.5 [+ or -] 694.5 mmol/L, significant at p = 0.001) and urine NAG peak values ([R.sup.2] = 32.1%, regression coefficient [beta] = 0.21 [+ or -] 0.07, significant at p = 0.009). Perfusion duration was a significant independent predictor for urine I-FABP peak values ([R.sup.2] = 22%, regression coefficient [beta] = 6.7 [+ or -] 3 min, significant at p = 0.03), urine L-FABP peak values ([R.sup.2] = 6.6%, regression coefficient [beta] = 476 [+ or -] 186.4 min, significant at p = 0.02), and urine H-FABP ([R.sup.2] = 37.7%, regression coefficient [beta] = 206.3 [+ or -] 62.5 min, significant at p = 0.004).

Correlations

Inflammatory Biomarkers: Statistical correlations found between the inflammatory markers are shown in Table 2. CRP at 6-h ICU correlated positively with peak cTnI concentrations (correlation, 0.49, p = 0.02). Tryptase peak values correlated negatively with peak plasma I-FABP (correlation, -0.445, p = 0.04), peak urinary I-FABP (- 0.474, p = 0.03), peak urinary L-FABP (-0.647, p = 0.002), peak urinary H-FABP (- 0.60, p = 0.005), peak urinary NAG (- 0.609, p = 0.004), and peak microalbuminuria (- 0.559, p = 0.01).

Myocardial Biomarkers: cTnI AUC correlated significantly with plasma H-FABP (AUC correlation, 0.469, p = 0.03; peak correlation, 0.444, p = 0.05) and CK-MB (AUC correlation, 0.80, p < 0.001; peak correlation, 0.77, p < 0.001).

Intestinal Biomarkers: Urine I-FABP correlated significantly with urine L-FABP (peak correlation, 0.81, p < 0.001).

Renal Biomarkers: The urinary peak of H-FABP correlated strongly and significantly with the urinary peak of NAG (correlation, 0.65, p = 0.002) and peak microalbuminuria (correlation, 0.66, p = 0.001). In addition, the peaks of intestinal damage markers correlated significantly with the peak values of renal damage markers (I-FABP to NAG: correlation, 0.55, p = 0.01; I-FABP to H-FABP: correlation, 0.77, p < 0.001; L-FABP to microalbuminuria: correlation, 0.57, p = 0.009).

DISCUSSION

In the present study, we found that administration of dexamethasone inhibited the SIRS in patients undergoing elective on-pump CABG. However, administration of dexamethasone did not offer protection against pulmonary, renal, and intestinal perioperative damage. Even more, dexamethasone-induced hyperglycemia was found to be a strong independent predictor of intestinal and renal perioperative damage. Postoperative pulmonary function was adversely affected by dexamethasone, with decreased Pa[O.sub.2]/FI[O.sub.2] ratio and prolonged time to tracheal extubation in the dexamethasone group of patients.

Myocardial Injury

Dexamethasone seemed to offer, to a small extent, myocardial protection during the first 6 h of reperfusion as shown by lower concentration of cTnI, but with no further protection after 24 h of reperfusion. Additionally, the protective effect was not noticeable when estimating the myocardial damage by the plasma concentration of H-FABP. The recently introduced marker H-FABP is a cytosolic protein abundant in the myocardium, with a 10-fold lower expression in the skeletal muscles, kidney (distal tubules), lung, brain, and endothelial cells. (20,21) H-FABP has been introduced as a plasma marker for an early assessment of myocardial tissue injury with a peak as early as 3 h after acute myocardial infarction and 2 h after reperfusion after CABG. (22,23) The early plasma peak also present in our study promotes H-FABP as a valuable myocardial injury marker, since peak levels of troponin T and I occur only much later, at approximately 18 h after reperfusion. (24)

Pulmonary Injury

Dexamethasone treatment resulted in more pronounced postoperative pulmonary dysfunction and prolonged time to tracheal extubation The detrimental consequence of dexamethasone on lung function was clinically relevant in terms of a significantly lower Pa[O.sub.2]/FI[O.sub.2] ratio immediately after extubation, and the significantly prolonged time to tracheal extubation in the patients in the dexamethasone group. These adverse effects of dexamethasone treatment on pulmonary function confirm the findings of Chaney et al (12,13) after treatment with methylprednisolone in a similar group of patients.

Renal Injury

Urinary NAG (enzyme released from injured proximal renal tubules) and microalbuminuria increased significantly during CPB, with no effect of dexamethasone. Measurements of urinary H-FABP proved to be a better indication of kidney damage than of myocardial damage, since the urinary peak of H-FABP did not correlate with the others cardiac markers but correlated strongly and significantly with the urinary peak of NAG (proximal tubules injury) and peak microalbuminuria (glomerular injury). This measurement might be explained by a urinary release of H-FABP from the damaged distal renal tubules. H-FABP has been associated previously with early release following injury of the distal renal tubules (25,26)

Intestinal Injury

I-FABP and L-FABP are cytosolic proteins readily released into the circulation following enterocyte damage, with a 40-fold higher content of L-FABP, reported as useful urine markers for the detection of intestinal injury. (27-29) Elevated I-FABP in relation to GI complications following CPB was described earlier. (29) The increased values of I-FABP and L-FABP during CPB reported in our study confirm the indirect line of evidence suggesting mucosal integrity loss during CPB, reported previously as a reduction in intramucosal pH, increase in gut permeability, and endogenous endotoxemia. (30-32) Significantly elevated I-FABP urine levels in critical ill patients correlated with clinical development of the SIRS. (33) In our study, 20% in the variation of intestinal injury markers and 30% in the variation of renal injury markers were explained by the CPB duration.

Hepatic Injury

[alpha]-GST increased promptly after initiation of CPB in both groups, with peak values during sternum closure, without effect for the dexamethasone treatment. Increased levels of [alpha]-GST as indication of hepatocyte injury were reported before in patients undergoing CPB. (34)

Inflammatory Response

The release of proinflammatory IL was inhibited by dexamethasone, while the antiinflammatory interleukin IL-10 was increased. The acute-phase protein CRP was found in lower concentration during the first postoperative day in the plasma of the patients receiving dexamethasone. These data confirmed that the administered dose of dexamethasone (1 mg/kg before induction of anesthesia and 0.5 mg/kg after 8 h) was therapeutically effective. In the first 24 postoperative hours, rectal temperature was moderately but significant higher in the placebo group. In a recent study, (35) postoperative temperature was controlled by active surface cooling to prevent cerebral damage. The present study demonstrates that temperature can be controlled as effectively with medication. The modulation of the humoral inflammatory response and lower postoperative rectal temperatures as a result of dexamethasone treatment observed in this study are in agreement with previous studies (7,8) published on the subject. Glucocorticoid administration prior to CPB was shown to attenuated inflammatory response, as based on biochemical analysis of serum inflammatory mediators, to reduce the incidence of postoperative febrile episodes in pediatric cardiac surgery (36) and to decrease incidence of postoperative hyperthermia in adult surgery. (11)

Only a limited amount of data characterizing mast-cell activation with subsequent tryptase release during CPB are available in the literature. (37,38) This study reports an important mast-cell degranulation (activation), with a peak in the systemic release of tryptase as early as the release of the aortic clamp. Dexamethasone was effective in inhibiting tryptase release.

Tryptase is a serine proteinase with trypsin-like properties, being released in peripheral blood subsequent to mast-cell activation in lungs, heart, stomach, spleen, skin, colon, and kidneys. (39,40) Extracellular release of tryptase is known to recruit inflammatory cells, induce IL-8 secretion from airway epithelial cells, and promote airway inflammation. (41) In our study, tryptase correlated positively and significantly with IL-6 and IL-8 (Table 2).

Surprisingly, we also found a negative correlation between tryptase and organ damage markers. Lower levels of tryptase correlate significantly with higher levels of intestinal injury (plasma I-FABP, urinary I-FABP, urinary L-FABP) and high levels of proximal (urine NAG), distal (urine H-FABP), and glomerular (microalbuminuria) renal damage during the first 2 h of reperfusion after CPB.

These data support the hypothesis of a preconditioning effect of tryptase: the early release of tryptase might offer protection against perioperative intestinal and renal damage. By amplifying the signal for histamine release, (42) and thus inducing an endothelial-nitric oxide (NO)-dependent vasodilator effect, tryptase might counteract the vasoconstriction induced by the hyperglycemia and ischemia/reperfusion injury. This hypothesis is supported by data showing that histamine-induced vasodilatation mediated by endothelial-derived NO was attenuated under hyperglycemic conditions. (43) In our study, we found high serum glucose levels in patients undergoing CPB while receiving dexamethasone. Serum glucose levels had strong positive predictive value for postoperative intestinal and renal damage. The variation in serum glucose concentration explained > 40% in the variation of intestinal damage biomarkers (I-FABP and L-FABP) and > 30% in the variation of renal tubule damage markers (NAG and urine H-FABP). In addition, the patients in the dexamethasone-treated group tended to require more insulin treatment.

To explain our results on the effect of acute hyperglycemia on organ injury, we refer to the recent published results of Vanhorebeek et al, (44) showing in a study of critically ill patients that hyperglycemia was associated with organ injury, as demonstrated by mitochondrial ultrastructural abnormalities with increased production of reactive oxygen species in the hepatocyte of hyperglycemic patients (10 to 11.1 mmol/L). Using animal experiments, Bohlen and Lash (45) and Jin and Bohlen (46) demonstrated that oxygen radicals formed during acute hyperglycemia affect flow-mediated endothelium regulation in the intestinal vasculature due to depression of NO, resulting in reduced blood flow.

Our data quantify for the first time the effect of hyperglycemia on organ injury. These results might provide an explanation for the increased morbidity and mortality among critically ill patients in the surgical ICU when the blood glucose level is > 6.1 mmol/L. (47)

A limitation of this study is that, despite randomization, patient characteristics were slightly different. In the dexamethasone group, patients were slightly older and therefore the possibility of confounding exists. However, this influence seems limited, since age did not prove to be a predictor for any of the biomarkers tested. Moreover, baseline values of a large number of sensitive markers were similar in both groups, and there was no correlation between age and the baseline levels of the markers tested. The patients in this study had little comorbidity and thus belong to the "healthy" CABG group. Dexamethasone in patients of a higher risk profile could have different effects on inflammatory response and organ injury. Finally, this study was not powered to analyze effects on mortality, or possible differences in wound healing and postoperative infections.

CONCLUSIONS

Dexamethasone, as administered in this study, offered no protection against transient, perioperative renal, intestinal, and hepatic injury in patients undergoing on-pump CABG. Dexamethasone treatment resulted in more pronounced postoperative pulmonary dysfunction, prolonged time to tracheal extubation, and initiated postoperative hyperglycemia. Given the strong positive predictive value of hyperglycemia for renal and intestinal tissue injury, a stricter management of serum glucose may offer beneficial effects.

As a contribution to the efforts made for understanding the complex pathophysiologic mechanism of the "post-CPB" syndrome, this study verified theories existent in the literature and also brought to attention new essential aspects: (1) higher glycemic values as strong predictors for higher intestinal and renal damage, and (2) preconditioning effect of mast-cell activation and tryptase release for subsequent postoperative intestinal and renal injury.

ACKNOWLEDGMENT: We thank J.G.M. Burgerhof, MSc, Department of Epidemiology and Statistics, University Medical Center Groningen, for assistance with statistical analysis.

This study was presented in part at the Third EACTS/ESTS Joint Meeting, Leipzig, Germany, September, 12-15, 2004; and CHEST 2004-Seventieth Annual International Scientific Assembly of the American College of Chest Physicians, Seattle, WA, October 23-27, 2004.

Support was provided by DPC Immulite (Los Angeles, CA), HemoScan (Groningen, the Netherlands), HyCult Biotechnology (Uden, the Netherlands), and Biotrin International (Dublin, Ireland).

Manuscript received March 17, 2005; revision accepted April 13, 2005.

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Aurora M. Morariu, MD; Berthus G. Loef, MD; Leon P. H. J. Aarts, MD, PhD; Gerrit W. Rietman, MD; Gerhard Rakhorst, DVM, PhD; Wim van Oeveren, PhD; and Anne H. Epema, MD, PhD

* From the Department of Biomedical Engineering/Artificial Organs (Drs. Morariu, Rakhorst, and Oeveren), Cardiothoracic Intensive Care Unit (Dr. Loef), and Department of Cardiothoracic Anesthesiology (Drs. Aarts, Rietman, and Epema), University Medical Center Groningen, Groningen, the Netherlands.

Correspondence to: Aurora M. Morariu, MD, Department of BioMedical Engineering/Artificial Organs, University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, the Netherlands

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