DOI: 10.1213/00000539-199804001-00024

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Issn Print: 0003-2999

Publication Date: 1998/04/01


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ADVERSE HEMOSTATIC EFFECTS OF MODIFIED ULTRAFILTRATION AS ASSESSED BY THROMBOELASTOGRAPHY

M.E. Barron; A. Weisinger; R. Perryman

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Introduction The introduction in 1991 of Modified Ultrafiltration (MUF) postcardiopulmonary bypass (CPB) in pediatric cardiac surgery has been shown to reduce many of the deleterious effects of CPB [1,2]. In addition, it has been shown to improve outcome and reduce postoperative morbidity in certain patient groups. [3] However, MUF has been criticized because of anecdotal experiences of increased bleeding post-CPB [4]. Thromboelastography (TEG) has been shown to provide an evaluation of the functional integrity of the coagulation system from initial clot formation to clot retraction/dissolution. [5] This study sought to assess the hemostatic/coagulation effects of MUF in infants and young children as assessed by TEG.
Materials and Methods Following institutional approval and parental consent, 45 children undergoing primary surgical correction of congenital heart disease were prospectively studied. CPB was performed using a membrane oxygenator (Minimax; Medtronic, Minneapolis, MN). All patients received an Isolyte-whole blood prime. Modified ultrafiltration was performed immediately following separation from CPB according to the method of Naik. [1] The Sorin PTS 5327 pediatric blood cardioplegia system with a bypass loop incorporating a Minntech HPH 400 hemoconcentrator was used for MUF (Sorin Biomedical, Inc. Irvine, CA). The Hemocor HPH 400 hemoconcentrator has a molecular weight cut-off of 65,000 Daltons. Baseline 1% celite activated TEG's were performed post-induction of anesthesia.
The effects of MUF on TEG were analyzed by comparing each pre-MUF TEG with the corresponding post-MUF TEG. TEG's were performed on the Haemoscope thromboelastograph (Haemoscope Corp. Skokie, ILL.) using 1 ml of whole blood with 4.0 IU of lyophilized Heparinase 1 in a 1% celite vial. Hematocrit, platelet count, and fibrinogen levels were also measured pre- and post-MUF as surrogate markers of the concentration effects of MUF.
All values presented are group means of the patient population. The nonparametric Wilcoxon signed rank test was used for all comparisons (pre-MUF vs. post MUF), and a p valve Results 37 children successfully completed the study protocol. Demographic and procedural data include: age-12.4 mo, weight-7.3 kg, CPB time -64 min., MUF time - 13.1 min, and the MUF ultrafiltate removed - 420ml. The mean increase in HCT was 9.0%, with a mean increase in platelet count and fibrinogen level of 20, 500 k/mm3 and 38mg/dL, respectively. The post-MUF fibrinogen level was only 129 mg/dL. All patients had pre-CPB TEG profiles consistent with a normal TEG index. Every patient demonstrated a deterioration of the TEG index as a result of MUF. The mean changes in each of the five measured values of the TEG tracing were: (Table 1)
Conclusions This study confirms the concentration effects of MUF by increasing RBC mass, higher platelet counts, and minor increases in fibrinogen levels; while removing approximately 60mlkg of combined ultrafiltrate from the CPB circuit and the patient. However, despite the apparent quantitative increase in coagulation markers, there was a uniform worsening in all 5 measured TEG variables; with significant increases in the R and K times, and a marked decrease in the alpha angle. These observations are consistent with thrombin formation and fibrinogen genesis disorders, and further dysfunction of the platelet-fibrinogen interaction. This may be due to an increase in circulating heparin activity due to MUF and the prolonged exposure to the CPB apparatus. Monitoring of coagulation status using thromboelastography is markedly altered by MUF and further correlation with clinical bleeding is warranted.
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