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Anticoagulation of Children Undergoing Cardiopulmonary Bypass Is Overestimated by Current Monitoring Techniques

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Anticoagulation of Children Undergoing Cardiopulmonary Bypass Is Overestimated by Current Monitoring Techniques PAPER Anticoagulation of Children Undergoing Cardiopulmonary Bypass Is Overestimated by Current Monitoring Techniques John T. Owings, MD; Marc E. Pollock, MD; Robert C. Gosselin, MT; Kevin Ireland, RN, CCP; Jonathan S. Jahr, MD; Edward C. Larkin, MD Hypothesis: Children who undergo cardiopulmonary reserve, fibrinogen; the natural antithrombotic, anti- bypass (CPB) are proportionally more hemodiluted than thrombin; and heparin concentration. adults who undergo CPB. Current methods of monitor- ing high-dose heparin sulfate anticoagulation are depen- Results: Ten children and 10 adults completed the study. dent on fibrinogen level. Because of the decreased fi- Children had lower fibrinogen levels than adults through- brinogen levels in children, current methods of monitoring out CPB (P,.05). All adults had both therapeutic ACT and heparin anticoagulation overestimate their level of anti- Heparin Management Test levels measured throughout coagulation. CPB. Although children had therapeutic ACT levels, their Heparin Management Test levels were subtherapeutic while Design: Prospective controlled trial. undergoing CPB. The children had significantly higher thrombin-antithrombin complexes and prothrombin Main Outcome Measure: Production of thrombin (ad- fragment F1.2 than adults, indicating ongoing thrombin equacy of anticoagulation). production (P,.01). The increases in thrombin- antithrombin complexes and prothrombin fragment F1.2 Methods: Children and adults undergoing cardiac sur- in children were inversely proportional to their weight. gery who received CPB were anticoagulated in the stan- dard fashion as directed by activated clotting time Conclusions: Children undergoing CPB with heparin (ACT) results. Each subject had blood sampled at base- dosing adjusted to optimize the ACT manifest inad- line; heparinization; start of the CPB; CPB at 30, 60, equate anticoagulation (ongoing thrombin formation). and 90 minutes; and at termination of CPB. Samples High-dose heparin anticoagulation therapy in children were used to assess anticoagulation with the Heparin undergoing CPB should be directed by tests (like the Hep- Management Test (less dependent on fibrinogen level arin Management Test) that are less dependent on fi- than ACT). We also assessed 2 subclinical markers of brinogen level than ACT. thrombosis, thrombin-antithrombin complexes and prothrombin fragment F1.2; a marker of procoagulant Arch Surg. 2000;135:1042-1047 NE OF the most impor- rin therapy. They found that patients’ tant advances facilitat- anticoagulant responses varied from 3-fold ing cardiopulmonary to 4-fold as a result of changes in body tem- bypass (CPB) and thus perature and dosage-interval duration. cardiac surgery has been Based on these findings, a method of hep- Othe ability to provide adequate anticoagu- arin titration to individual patient effect was lation. Early in the development of CPB recommended rather than either fixed dose From the Departments of it was recognized that failure to achieve or titration to plasma heparin levels. Surgery (Drs Owings and adequate anticoagulation would result in A critical factor in attaining the goal Pollock and Mr Ireland), both postoperative bleeding due to the of adequate anticoagulation has been the Pathology (Mr Gosselin and consumption of procoagulant factors and ability to assess an individual patient’s level Dr Larkin), and Anesthesiology end-organ dysfunction (eg, acute respira- of anticoagulation (heparin effect). In 1966 (Dr Jahr), University of tory distress syndrome due to deposition Hattersley,4 from our institution, intro- California–Davis Health of the consumed factors in the lungs).1 duced the whole blood activated clotting System, Sacramento, Calif. During the early stages of CPB, large time (ACT) as a means of assessing anti- The authors have no 2,3 commercial, proprietary, fixed doses of heparin sulfate were used coagulation or heparin effect. Bull et al or financial interests in the in attempts to achieve adequate antico- incorporated the ACT as the primary tool products or companies agulation. In 1975 Bull et al2,3 demon- used to assess the degree of heparin anti- described in this article. strated a wide patient response to hepa- coagulation during CPB. The ACT was (REPRINTED) ARCH SURG/ VOL 135, SEP 2000 WWW.ARCHSURG.COM 1042 ©2000 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 PATIENTS AND METHODS Medtronics Inc, Minneapolis, Minn) that uses a kaolin ac- tivator. Whole blood sample is added to a double–test well inserted into the device. Once the blood is added, plung- Our study was reviewed and approved by our institu- ers move in an upward and downward motion mixing the tional review board on human experimentation. The ex- reagent and blood. As the clot forms, the increase in resis- periment was conducted for a 4-month period at the Uni- tance to plunger movement is optically detected and the versity of California–Davis Medical Center in Sacramento. resultant time displayed. We studied 2 patient groups—10 children and 10 adults. The HMT uses a celite activator. Citrated whole blood Patients were enrolled in each group as a consecutive case was added to the test cartridge and inserted into the throm- series. The primary inclusion criterion for patients in both bolytic assessment system analyzer. The sample moved by groups was that they were to undergo cardiac surgery re- capillary action, mixing with reagent and paramagnetic iron quiring CPB. The single distinguishing inclusion criterion oxide particles, simultaneously starting a pulsating mag- for children was that they were prepubescent. Patients re- netic field that caused the paramagnetic iron oxide par- ceiving aprotinin therapy were excluded, as this drug is ticles to move. As the sample clotted, the decrease in para- known to interfere with the ACT method used in this study.5 magnetic iron oxide particle movement was detected and All patients were treated following our standard CPB the resultant time displayed. In a previous study of pa- protocol using unfractionated porcine heparin. Children and tients undergoing CPB, we validated the therapeutic range adults were treated with standard prepackaged roller pump for the HMT to be shorter than 350 seconds.6 (Sanrs, Ann Arbor, Mich) and membrane oxygenator cir- Frozen plasma was tested for markers of thrombosis. cuit (Cobe, Arvada, Colo). The routine prime pump solu- Before analysis, the plasma was quick thawed in a 37°C wa- tion for adults was a 2-L albumin saline mixture; whereas, ter bath for 5 minutes and vortexed before use. Each plasma for children it ranged from 1.1 to 2 L. Therapy was started sample was tested for the following 6 assays: (1) heparin for both patient groups by hypothermic bypass using the levels based on anti-Xa activity (Stago Asserachrome, Par- membrane oxygenator and roller pump circuit. Ultrafiltra- sippany, NJ) on the medical laboratory automation re- tion was not used during the pump runs. The recorded hy- sults (MLA model 900C; Medical Laboratory Automation, pothermic temperature was measured by core body tem- Pleasantville, NY); (2) prothrombin fragment F1.2 using perature. Just before bypass, heparin sulfate was given at a an enzyme immunoassay method (Dade-Behring Diagnos- dose of 300 U/kg. The degree of anticoagulation was then tics Inc, Deerfield, Ill); (3) thrombin-antithrombin com- monitored by ACT with a target of longer than 400 sec- plexes (TAT) using enzyme-linked sandwich immunoas- onds. The ACT was routinely measured at 30-minute inter- say (Dade-Berhing Diagnostics Inc); (4) fibrinogen (FBG) vals during CPB. Additional heparin was given in cases where using a modified Clauss technique (Dade International Inc, the ACT was shorter than 400 seconds. Miami, Fla) on the medical laboratory automation results Blood samples were drawn at baseline (after anes- (MLA model 1000C; Medical Laboratory Automation); (5) thetic induction and before heparin dosing), on heparin dos- antithrombin levels using a chromogenic factor Xa inhibi- ing, at the beginning of CPB, at 30, 60, and 90 minutes of tion method (Chromogenix AB, Molndal, Sweden); (6) tis- CPB, and at the termination of CPB after protamine sulfate sue factor pathway inhibitor using an enzyme-linked im- reversal. All samples were collected from an arterial line or munoassay method (American Diagnostica Inc, Greenwich, circuit port using a double-syringe technique. The first sy- Conn). ringe withdrew 10 mL of whole blood and was discarded. To determine the relation of age and hemodilution en- The second syringe was used to draw 10 mL of blood that countered during CPB to the adequacy of heparin antico- was used for ACT and subsequent testing. All whole blood agulation, markers of coagulation in the pediatric group were testing occurred within 10 seconds of acquisition. Because compared with those of adults. Activated clotting times were the HMT requires a citrated whole blood sample, residual compared with HMT values and each was correlated with blood not used for ACT testing was immediately anticoagu- subclinical markers of thrombosis (TAT complexes and lated using an evacuated tube containing 3.2% buffered so- F1.2). These correlations were done to (1) determine the dium citrate (Becton Dickinson, Franklin Lakes, NJ). A por- correlation between ACT and HMT and (2) assess the ac- tion of that citrated sample was then used to perform the curacy of the ACT and HMT level in predicting ongoing HMT contemporaneously, though the operating team
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