Heparin resistance and the potential impact on maintenance of therapeutic coagulation:

Individual Differences in Heparin Sensitivity and Their Effect on Heparin Anticoagulation During Arterial Vascular Surgery

OBJECTIVES

To investigate whether a fixed heparin dose results in adequate heparinisation levels and consequent inhibition of haemostatic activation in all patients.

METHODS

This prospective clinical pilot study included 24 patients undergoing arterial vascular surgery. Individual heparin responsiveness was assessed using the Heparin Dose Response (HDR) test, while the activated clotting time (ACT) and heparin concentration were measured to monitor the peri-procedural degree of anticoagulation. Finally, peri-operative haemostasis was evaluated with rotational thromboelastometry (ROTEM).

RESULTS

Eight patients were identified with reduced heparin sensitivity (RS group) and 16 patients with normal heparin sensitivity (NS group). Compared with the NS group, the RS group showed less prolonged ACTs after heparinisation with heparin concentrations below the calculated target heparin concentration. ROTEM revealed shorter clot formation times in the intrinsically activated coagulation test (INTEM) 3 min (114 ± 48 s vs. 210 ± 128 s) and 30 min after the initial heparin bolus (103 ± 48 s vs. 173 ± 81 s) in the RS group compared with the NS group. In the RS group, one patient developed a major thromboembolic complication.

CONCLUSIONS

This study shows that a third of the study population had reduced heparin sensitivity, which was associated with lower levels of heparinisation, and lower inhibition levels of clot initiation and clot formation. Identifying patients with reduced heparin sensitivity by monitoring the anticoagulant effect of heparin could decrease the risk of thrombotic complications after arterial vascular surgery.

[Survey of perioperative hemostasis and transfusion management in cardiac surgery: how do anesthesiologists practice?]

OBJECTIVE

To determine practices related to control of perioperative hemostasis and transfusion in patients undergoing cardiac surgery in Spain, including the extent to which protocols are being used.

METHODS

A questionnaire was created to collect information from physicians in anesthesiology and postoperative recovery care between July 1 and September 20, 2007. The physicians were asked about practice in the 12 months prior to the survey.

RESULTS

Thirty-four hospitals responded. Seventy percent reported that they did not have protocols or guidelines for the control of hemostasis during cardiac surgery. Forty-four percent did not have information on the proportion of patients who received transfusions; 47% gave transfusions to 75% of patients. The standard preoperative tests were platelet counts, activated partial thromboplastin time, and prothrombin time. Acetylsalicylic acid and clopidogrel were suspended before surgery at 15 (44%) and 25 (73%) hospitals, respectively. In cases of resistance to heparin, additional doses of the drug were injected, in combination with plasma or antithrombin in 29% and 12% of the hospitals, respectively. In the intensive postoperative recovery care unit, only 1 hospital used thromboelastography. Only 1 other hospital used a platelet function analyzer.

CONCLUSIONS

Hemostasis, perioperative coagulation, and criteria for transfusion vary widely among the hospitals surveyed. Few guidelines are available and they are not often being followed. A high percentage of patients receive transfusions, although not all hospitals can cite a figure. New technology has not been widely applied.

[Heparin resistance and antithrombin deficiency]

The phenomenon of heparin resistance (HR) is characterized by high doses of unfractionated heparin (UFH) being required to bring activated partial thromboplastin time (aPTT) and activated coagulation time (ACT) within therapeutically desired ranges, or by the impossibility of reaching these ranges. At UFH dosages > 35,000 IU/d, HR should be considered a factor. The most frequent cause of HR is deficiency of antithrombin (AT), the presence of which is essential for UFH to exert its anticoagulatory effect. AT in concentrate form may be applied to overcome AT-dependent HR. The main clinically relevant situations in which AT-dependent HR occurs, with possible indication of AT substitution, are congenital AT deficiency, asparaginase therapy, disseminated intravascular coagulation (DIC) and administration of high doses of heparin during extracorporeal circulation, where it is significant, due to the need to maintain a very high ACT (> 400 s), that use of heart-lung machines is associated with an HR incidence of approximately 20%. The following procedure is recommended when there is no DIC and when extracorporeal circulation is not used: if HR is suspected and AT activity is < or = 60%, UFH should first be reduced to 500 IU/h (to prevent bleeding complications), before AT is substituted. AT activity should then exceed 80%. Under normalized and stable AT activity, the UFH dose should be adjusted such that aPTT is within a range of 60-100 s. If anticoagulation over a longer term is indicated, then overlapping anticoagulation with a vitamin K antagonist should be started as quickly as possible.