Patient characteristics, types of surgical repair, and intraoperative data for the entire cohort are summarized in and . Plasma samples from 48 consecutive children (median age 5.1 mos, IQR 1.7–34.2 mos) were obtained and analyzed. All of the children survived to hospital discharge. CPB resulted in a significant increase in expression of angpt-2, as shown in . These levels significantly increased by 6 h post-CPB when compared to baseline (4.62, IQR 1.16-6.93 ng mL-1
vs. 0.95, IQR 0.43-2.08 ng mL-1
, respectively; p<0.05) and remained significantly increased at 24h post-CPB (1.85, IQR 0.70–2.76 ng mL−1
; p<0.05). In contrast, CPB resulted in a decrease over time in angpt-1 levels, as shown in . Angpt-1 levels were significantly decreased at 24h after CPB when compared to immediately post-CPB (0.64, IQR 0.40–1.62 ng mL−1
vs. 1.99, IQR 1.23–2.63 ng mL−1
, respectively; p<0.05). Not surprisingly then, the ratio of angpt-2/-1, which may be a more important marker of endothelial injury, significantly increased by 6h post-CPB (0.59, IQR 0.34–1.52 vs. 0.20, 0.35–1.17, respectively; p<0.005) and remained significantly increased at 24h post-CPB (2.07, 0.44–3.52; p<0.05) (). We then measured the soluble Tie-2 receptor (sTie-2) and found a significant increase immediately post-CPB (6.40, IQR 4.35–8.86 pg mL−1
vs. 2.86, IQR 1.79–4.39 ng mL−1
; p<0.05) which returned to baseline by 24h post-CPB (3.28, IQR 2.09–4.38 ng mL−1
; p<0.05) (). Previous studies have suggested that CPB results in a transient increase in the expression of VEGF, an important marker of endothelial injury [9
]. However, VEGF levels in our cohort were unchanged from baseline ().
Patient Demographics, n=48 (CICU=cardiac intensive care unit; LOS=length of stay)
Procedures performed and corresponding complexity of surgery (VSD=ventricular septal defect; AVC=atrioventricular canal; ASD=atrial septal defect; TOF=tetralogy of Fallot; RACHS-1=Risk adjusted classification for congenital heart surgery)
Box-and-whisker plot of plasma angpt-2 levels following cardiopulmonary bypass.
Box-and-whisker plot of plasma angpt-1 levels following cardiopulmonary bypass.
Angiopoietin Expression Following Cardiopulmonary Bypass
Our practice is to routinely administer aprotinin to all children less than 2 months of age undergoing cardiopulmonary bypass. Thirteen children (28%) received aprotinin in the current cohort. Aprotinin may modulate the systemic inflammatory response to CPB [23
], and for this reason, we also analyzed our results excluding these children. Plasma angpt-2 levels remained significantly increased at 24 h post-CPB compared to baseline in these children (1.44, IQR 0.40–2.17 ng mL−1
vs. 0.32, IQR 0.04–0.60 ng mL−1
, p<0.05), though the increase at 6 h post-CPB (0.57, IQR 0.28–1.22 ng mL−1
) was no longer significant. Similarly, plasma angpt-1 levels remained significantly decreased at 6 h (0.76, IQR 0.44–1.34 ng mL−1
) and 24 h post-CPB (0.54, IQR 0.40–1.47 ng mL−1
) compared to immediately after CPB (1.89, IQR 1.28–2.50 ng mL−1
, p<0.05). There were no significant differences between plasma angpt-1 levels measured at baseline (1.12, IQR 0.52–2.36 ng mL−1
) compared to any of these other time-points.
There were significant correlations between angpt-2 levels measured at 6h following CPB and the duration of CPB (r=0.42, p=0.02), as well as the complexity of surgery, as noted by the RACHS-1 score (r=0.43, p=0.03). Importantly, there was a significant negative correlation between age and the 6h angpt-2 level (r=−0.58, p<0.001). Angpt-2 levels at 6h significantly correlated with the inotrope score at 24h (r=0.68, p<0.001), post-operative fluid balance (r=0.50, p=0.009), and CICU LOS (r=0.50, p=0.007). These associations remained significant at 24h angpt-2 levels for age (r=−0.48, p=0.008), inotrope score (r=0.47, p=0.009), duration of CPB (r=0.4, p=0.03), postoperative fluid balance (r=0.41, p=0.04), and CICU LOS (r=0.43, p=0.02).
In contrast, there were no significant correlations between plasma angpt-1 levels and any of these clinical indices. Consistent with our hypothesis that the ratio between the Tie-2 agonist/antagonist pair may be a more important marker of endothelial injury, there was a significant correlation between the angpt-2/-1 ratio at 6h and inotrope score (r=0.41, p=0.02), positive postoperative fluid balance (r=0.47, p=0.01), and CICU LOS (r=0.33, p=0.05). These correlations remained significant at 24h for inotrope score (r=0.40, p=0.02), positive postoperative fluid balance (r=0.44, p=0.02), and CICU LOS (r=0.48, p=0.004).
Finally, we performed univariate and multivariate regression analysis to determine factors which were independently associated with increased CICU LOS. We included all variables with a p≤0.20 on univariate regression () on subsequent multivariate regression analysis. Baseline angpt-2/-1 ratio (p=0.004), 24h post-CPB angpt-2/-1 ratio (p=0.05), 24h post-CPB angpt-2 (p=0.006), and positive postoperative fluid balance (p<0.001) remained significant independent predictors of prolonged CICU LOS.
Factors associated with increased CICU LOS by univariate analysis