Examining safety and efficacy of a fixed concentration heparin dosing strategy for anticoagulation in neonatal extracorporeal membrane oxygenation
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Objectives The paediatric intensive care unit changed heparin infusion dosing from a variable weight-based concentration to a fixed concentration strategy, when smart pump-based drug library was introduced. This change meant significantly lower rates of infusion were needed for the same dose of heparin in the neonatal population. We performed a safety and efficacy assessment of this change. Methods We performed a retrospective single-centre evaluation based on data from respiratory VA-extracorporeal membrane oxygenation (ECMO) patients weighing ≤5 kg, pre and post the change to fixed strength heparin infusion. Efficacy was analysed by distribution of activated clotting times (ACT) and heparin dose requirements between the groups. Safety was analysed using thrombotic and haemorrhagic event rates. Continuous variables were reported as median, interquartile ranges, and non-parametric tests were used. Generalised estimating equations (GEE) were used to analyse associations of heparin dosing strategy with ACT and heparin dose requirements in the first 24 h of ECMO. Incidence rate ratios of circuit related thrombotic and haemorrhagic events between groups were analysed using Poisson regression with offset for run hours. Results 33 infants (20 variable weight-based, 13 fixed concentration) were analysed. Distribution of ACT ranges and heparin dose requirements were similar between the two groups during the ECMO run and this was confirmed by GEE. Incidence rate ratios of thrombotic (fixed v weight-based) (1.9 [0.5–8], p = .37), and haemorrhagic events (0.9 [0.1–4.9], p = .95) did not show statistically significant differences. Conclusions Fixed concentration dosing of heparin was at least equally effective and safe compared to a weight-based dosing.Keywords:
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Abstract Background: Heparin is the standard drug for anticoagulation treatment and is used in many cardiac surgical interventions to prevent blood clotting. The anticoagulation status is controlled by various clotting tests. However, these tests depend on parameters like temperature, hemodilution etc. and are thus not applicable for a direct monitoring of the heparin concentration. The aim of this prospective study was to test a novel light scattering assay (LiSA) for the direct determination of heparin concentration during cardiopulmonary bypass (CPB) surgery and to compare the heparin concentrations with routinely determined activated clotting time (ACT). Methods: The patient group consisted of 50 patients undergoing coronary bypass surgery with CPB. The coagulation status was monitored by the measurement of ACT, which was performed approximately every 30 min during surgery. Parallel to each ACT measurement, the heparin concentration was measured by LiSA. Results: For 70% of the patients, ACT and heparin concentration measured by LiSA correlated reasonably over the entire time course of the intervention. For 30% of the patients, an insufficient correlation or even no correlation at all was observed. Conclusions: This study showed that LiSA enables the determination of intra-operative heparin levels. The lack of correlation between ACT and heparin concentration in a substantial group of patients shows that monitoring of heparin concentration is important. A more precise blood coagulation management, in particular, a precise administration of heparin and protamine, should be based on a combination of the measurement of heparin concentration and of ACT, but not on ACT alone.
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Activated clotting time (ACT) values were converted to heparin concentration, enabling an assessment of the accuracy of the ACT and a quantification of the prolongation imposed by bypass. Blood samples were obtained from 42 adult cardiopulmonary bypass (CPB) patients before and during bypass surgery. Samples were analysed for ACT (HemoTec ACT) and anti-factor Xa (anti-Xa) plasma heparin concentration. The mean heparin concentration calculated before bypass was an accurate reflection of plasma heparin; however, calculated values rose to around 170% of anti-Xa values upon connection to bypass. By adjusting for this rise, for 95% of cases the calculated heparin concentration would vary between 0.60 and 1.65 times anti-Xa values. Without accounting for artificial prolongation or individual sensitivities, the ACT may give values between 0.8 and 3.0 times that indicated by the anti-Xa assay. When both individual heparin sensitivities and the effects of bypass are considered, the ACT may provide a more suitable indication of heparin levels; however, typical use may overestimate heparin up to threefold.
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Data relating to the activated clotting time response to a 4 mg/kg heparin loading dose were collected prospectively in 358 patients having cardio pulmonary bypass. After excluding patients with factors known to cause relative heparin resistance or sensitivity, the activated clotting time (ACT) loading dose response ratio (ACTLORR) was calculated retrospectively in 263 patients and found to correlate significantly (p = 0.0001) with the need for extra heparin administration during bypass. Where the ACTLORR was above 5.5, 92% of patients required no additional heparin during the first 90 minutes of bypass (n = 98). Where the ACTLORR was between 4.0 and 5.0, it was far less predictive, with approximately 35% of patients requiring additional heparin. This study indicates that a large ACT response to the initial heparin loading dose (a high ACTLORR) is predictive of stable, adequate anticoagulation during the first 90 minutes of bypass, but that a low initial response is not necessarily associated with declining ACTs and the need for additional heparin administration.
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The authors compared blood loss, transfusion requirements, and heparin doses for reoperative cardiac surgery using either: a) a Duraflow (Baxter Corporation, Irvine, CA) heparin coated cardiopulmonary bypass (CPB) system or b) standard CPB. Twenty patients underwent redo cardiac surgery while supported with heparin coated CPB, and 17 patients underwent redo cardiac surgery with standard CPB. The following data are presented as mean +/- standard deviation. The heparin coated CPB circuit group received significantly less heparin than the standard CPB group (322 +/- 80 IU/kg versus 448 +/- 80 IU/kg, p < 0.01). There was no difference in blood loss in the first 24 postoperative hrs or mean transfusion requirements for the two groups. Despite the reduced dose of heparin, the mean activated clotting time in the heparin coated group was similar to the mean activated clotting time of the standard CPB group (577 +/- 98 sec versus 612 +/- 117 sec, p = ns). In conclusion, heparin coated CPB without reduced activated clotting time does not reduce transfusion requirements or blood loss in reoperative cardiac surgery. The heparin coated CPB system allows maintenance of the activated clotting time level despite reduced heparin doses.
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A change in brand suppliers of heparin at our institution resulted in a number of anecdotal reports of possible differences in potency. Both products are marketed as heparin sodium extracted from porcine intestinal mucosa. Heparin Leo is 1000 international units (British Pharmacopeia) per ml. while Hepalean is 10,000 United States Pharmacopeia (U.S.P) units per ml. Perfusion records were retrospectively reviewed for one month periods when Heparin Leo (n = 52) or Hepalean (n = 61) were used to provide anticoagulation therapy for cardiopulmonary bypass. Heparin Leo was found to be less clinically potent than Hepalean. While increasing the initial loading dose of Heparin Leo by 5% (378 vs 398 units/kg-1), the initial post load activated clotting time (ACT) was 17% lower (556 vs 666 seconds). Heparin units required per kilogram per minute of cardiopulmonary bypass were 23% higher for Heparin Leo. Additionally 8 of 52 Heparin Leo patients did not achieve an initial post load ACT of greater than 400 secs while this occurred in 2 of 61 patients treated with Hepalean. These results were statistically significant. British Pharmacopeia and United States Pharmacopeia heparin reference standards differences are insufficient to explain the discrepancies observed in this study.
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In Brief BACKGROUND: Hemostasis management has evolved to include sophisticated point-of-care systems that provide individualized dosing through heparin concentration–based anticoagulation. The Hepcon HMS Plus system (Medtronic, Minneapolis, MN) estimates heparin dose, activated clotting time (ACT), and heparin dose response (HDR). However, the accuracy of this test has not been systematically evaluated in large cohorts. METHODS: We examined institutional databases for all patients who underwent cardiac surgery with cardiopulmonary bypass (CPB) at our institution from February 2005 to July 2008. During this period, the Hepcon HMS Plus was used exclusively for assessment of heparin dosing and coagulation monitoring. Detailed demographic, surgical, laboratory, and heparin dosing data were recorded. ACT, calculated and measured HDR, and heparin concentrations were recorded. Performance of the Hepcon HMS Plus was assessed by comparison of actual and target ACT values and calculated and measured HDR. RESULTS: In 3880 patients undergoing cardiac surgery, heparin bolus dosing to a target ACT resulted in wide variation in the postheparin ACT (r2 = 0.03). The postheparin ACT did not reach the target ACT threshold in 7.4%(i.e., when target ACT was 300 s) and 16.9% (i.e., when target ACT was 350 s) of patients. Similarly, the target heparin level calculated from the HDR did not correlate with the postbolus heparin level, with 18.5% of samples differing by more than 2 levels of the assay. Calculated and measured HDR were not linearly related at any heparin level. CONCLUSIONS: The Hepcon HMS Plus system poorly estimates heparin bolus requirements in the pre-CPB period. Further prospective studies are needed to elucidate what constitutes adequate anticoagulation for CPB and how clinicians can reliably and practically assess anticoagulation in the operating room. Published ahead of print October 27, 2009
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