Hemochron vs. Hemotec Kaolin ACT Comparison with Aprotinin Use in Congenital Heart Surgery

Between July 1994 and January 1995, ten patients underwent reoperative cardiac surgery with cardiopulmonary bypass for correction of various congenital anomalies. The patients' ages ranged from 0.17 to 34 years. Aprotinin was used according to surgeon protocol (200 mg/m2 body surface area initial loading dose and in pump prime, and 50 mg/m2 hourly infusion). The purpose of this study was to compare the simultaneous ACT values obtained from the Hemotec cartridge and the Hemochron kaolin tube. A 3 ml blood sample was drawn and duplicate ACTs run at four time periods during the procedure: 2 ml in a prewarmed kaolin Hemochron tube and 0.4 ml in each well of a pre-warmed Hemotec cartridge. Information recorded at each time period included: event [pre-CPB, onCPB hypothermia, on-CPB rewarming, post-CPB], temperature, and ACT values from each machine. A total of 74 paired samples were analyzed. Two-way ANOV A was used to compare the values. Multiple comparison tests using the Bonferonni method were performed to maintain the Type I error rate at 0.05. Regression, correlation, and residual analyses were performed. Cohen's kappa statistic was used to assess the degree of agreement between the two devices. There was a statistically significant difference between the ACT values obtained between the two devices (p<.01); however, the correlation between the values was high and significant (r=0.841, p<.01). The Hemotec was an average of 86 seconds lower than the Hemochron. The kappa statistic was 0.688, which indicates good agreement. The differences between these two devices have been previously reported using the celite Hemochron tubes, and it appears that there is still a difference when both tubes contain kaolin. Differences in the method of clot detection, differences in sample volume, and differences in the adsorption of aprotinin may explain the differences observed in this study. The Hemochron kaolin ACT is an acceptable alternative to the Hemotec ACT for monitoring heparinization when aprotinin is in use in congenital heart surgery.