A statistical analysis of factors predisposing patients to heparin resistance Tanee Chan 1 , Nian Chih Hwang 2 and Chong Hee Lim 1 1 Department of Cardiothoracic Surgery, National Heart Centre, Singapore; 2 Department of Anaesthesia and Surgical Intensive Care, Singapore General Hospital, Singapore Heparin resistance (HR) is occasionally encountered in cardiac surgery. The objective of this study is to identify possible factors predisposing patients to heparin resis- tance. Four hundred patients scheduled for elective cardiac surgery requiring the use of cardiopulmonary bypass (CPB) were enrolled in this study. Data collection included: demographic data, types of preoperative anti- coagulant/antiplatelet therapy, preoperative haemato- logical and biochemical laboratory results, medical condition, baseline activated clotting time (ACT) and infusion volume prior to heparinisation. Patients who require 5 mg/kg or more to achieve ACT greater than 400 seconds before CPB were considered to be heparin resistant. All data was tested with a preliminary uni- variate analysis and factors associated with HR (p value B /0.05) were entered into a multivariate logistic regression analysis. Factors associated with HR with a p value B /0.05 are considered predictors for HR. Thirty-two (8.0%) of the 400 patients fulfilled the criteria for HR. Preoperative heparin (p  /0.025), low molecular weight heparin (p  /0.049), plateletcount ] /300,000/ml (p  /0.022) and albumin plasma concentration 5 /35 g/dl 0,  /0.044) are significantly associated with HR. HR patients also tend to require more volume replacement prior to CPB to maintain haemodynamic stability p  /0.007). Perfusion (2006) 21, 99  /103. Introduction Identification of factors responsible for the develop- ment of reduced sensitivity to heparin has important implications for cardiac surgery with cardiopulmon- ary bypass (CPB), because inadequate anticoagula- tion during this procedure can have profound thrombotic and haemorrhagic consequences. Many studies on heparin resistance (HR) have identified several factors, including antithrombin III (AT-III) deficiency induced by preoperative administration of heparin, 1  4 enhanced factor VII activity, 5 throm- bocytopenia, 6 preoperative use of an intra-aortic balloon pump (IABP) 1 , high preoperative platelet counts, 1 and endocarditis. 7 However, these factors may not always be observed in a population who exhibit HR. The objective of this study is to identify factors that may predispose patients undergoing cardiac surgery to HR with the use of statistical analysis tools. Methods All consecutive adult patients scheduled for elective cardiac surgeries requiring the use of CPB from April to November 2002 at the National Heart Centre, Singapore were prospectively included in this study. Data collection included: 1. Demographic data 2. Types of preoperative anticoagulant/antiplate- let therapy 3. Preoperative haematological and biochemical laboratory results [haematocrit (%), total white cell count (  / 10 9 /L), platelets (  / 10 9 /L), pro- thrombin time (sec), partial thromboplastin time (sec), albumin (g/L), protein (g/L) and creatinine (mmol/L)] 4. Medical condition 5. Baseline activated clotting time (ACT) 6. Total infusion volume prior to heparinization 7. Approximate hours of fasting before induction of general anaesthesia In addition, any prebypass aprotinin administra- tion and IABP support were also recorded. The data selections were based on our current clinical knowledge and previous studies. 1  8 Patients under- going emergency operations were excluded from this study. Address for correspondence: Tanee Chan, Senior Perfusionist, Department of Cardiothoracic Surgery, Perfusion Service, National Heart Centre, c/o Mistri Wing, 17, Third Hospital Avenue, Singapore 168752, Singapore. Email: perfusionist@nhc.com Perfusion 2006; 21: 99  /103 # 2006 Edward Arnold (Publishers) Ltd 10.1191/0267659106pf855oa