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Thromb Haemost 1993; 70(06): 0937-0941
DOI: 10.1055/s-0038-1649703
Original Article
Clinical Studies
Schattauer GmbH Stuttgart

Heparin Therapy during Cardiopulmonary Bypass in Children Requires Ongoing Quality Control

Maureen Andrew
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Brian MacIntyre
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
James MacMillan
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
William G Williams
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Colleen Gruenwald
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Marilyn Johnston
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Fred Burrows
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Elaine Wang
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
,
Margaret Adams
The Department Pediatrics and Pathology, McMaster University, Hamilton, Ontario and The Hospital for Sick Children, Toronto, Ontario, Canada
› Author Affiliations
Further Information

Publication History

Received 24 September 1992

Accepted after revision 12 July 1993

Publication Date:
06 July 2018 (online)

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Summary

Heparin therapy for children undergoing cardiopulmonary bypass (CPB) is monitored in the operating room by automated whole blood activated clotting times (ACT). For many years our institution used Hemochron (HC) ACT machines but changed to HemoTec (HT) ACT machines because they required a smaller blood sample and provided results in duplicate. When HemoTec ACT machines were introduced at our institution, the surgical team was concerned that increased amounts of heparin were being administered to our patients during CPB. This study was conducted to investigate the potential mechanisms responsible for these clinical observations. First, we compared ACT values on ex vivo blood samples from 20 consecutive pediatric patients (6 samples each) during CPB. The HC ACT values were significantly and systematically increased over HT ACT values (HC: 750 ± 40 vs HT: 418 ± 26, Mean ± SEM, p <0.01). 94% of all HC ACT values were above 450 s compared to only 27% of HT ACT values. If HT ACT values had been used for patient monitoring, all patients would have received more heparin to achieve ACT values above 450 s. The two machines reported similar ACT values when heparin was added in vitro to whole blood (0.1-5.0 units/ml), (HC: Y = 98X + 104, r2 = 0.93 HT: Y = 82X + 109, r2 = 0.94). Heparin concentrations in our patients following a bolus of 300 U/kg of heparin, but prior to CPB were 3.2 ± 0.07 units/ml. Following the initiation of CPB, heparin concentrations decreased to 1.3 ± 0.05, reflecting, in part, hemodilution by the pump prime (1 U of heparin/ml). In contrast to the in vitro results, there was no relationship between ACT values measured by either machine and plasma heparin concentrations in ex vivo samples. Finally, plasma concentrations of 8 coagulation proteins measured prior to CPB and following CPB were decreased by 27-55%, predominantly reflecting the final dilution by CPB. In conclusion: 1) HT and HC machines cannot be used interchangeably in pediatric patients without risk of altering clinical practice in an uncontrolled fashion; and 2) ACT values from children on CPB correlate poorly with heparin concentrations, likely due to hemodilution. Optimal use of anticoagulant therapy during CPB in children requires further study in clinical trials and ongoing quality control.

 

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