Proposed Guidelines for Low Molecular Weight Heparin

To the Editor:

   We read with great interest the guidelines on the use of low molecular weight heparins reported in Heart Views by Drs Abbadi and Hajir (1).

   We should like to add our experience on this topic, as we have observed an increased amount of bleeding after cardiac surgery in patients with unstable angina previously exposed to Fragmin (2).

   Because of high bioavailability and a prolonged half life, Fragmin and other low molecular weight heparins have recently been advocated as the optimal anticoagulant for patients with unstable angina when in combination with Aspirin administered twice daily (3,4).

   We carried out a study to determine whether the administration of Fragmin at a routine dose of 120u/kg/bd influenced post-operative bleeding in patients subsequently undergoing coronary artery bypass grafting (CABG) for unstable angina (2).

   A total of 390 patients undergoing first time CABG was studied prospectively and was divided into 4 groups. Group 1 was routine elective patients (n=100) who stopped Aspirin 5 days prior to surgery. Group 2 (n=60) consisted of unstable angina patients maintained on aspirin and a conventional heparin infusion. Group 3 (n=115) patients had unstable angina and were kept on Aspirin and Fragmin but their Fragmin was stopped at least 12 hours prior to surgery. In Group 4 (n=115) Fragmin was administered within 12 hours of operation.

   Post-operative blood loss at 12 hours, administration of blood and blood products, and re-sternotomy rate for bleeding or tamponade were statistically analysed with the analysis of variance.

   Significantly more blood loss was noted in Group 2 and 3 compared with Group 1 (p=0.021). Interestingly, patients in Group 4 had significantly greater 12 hour loss than all other groups (p<0.001). Groups 2 and 3 received significantly more packed red cell transfusions than Group 1 (p=0.02), while patients in Group 4 were transfused the greatest volume in the first 12 hours after surgery (p=0.047). There were no differences in the volumes of platelets and fresh frozen plasma transfused (p>0.05), or in the re-opening rate (p>0.05).

  Our data indicate that administration of Fragmin significantly promotes bleeding postoperatively compared with our control group of routine cases. The influence of Aspirin administration in the unstable angina patients has to be taken into account.

  The significantly increased volumes of packed red cells administered to unstable angina patients is also a concern as the number of donors to which the patient is exposed is increased along with the chances of infective agent transmission. There is also evidence that blood transfusion increases post-operative infections (5-7). A higher number of blood transfusions also have cost implications in this subset of unstable angina patients undergoing surgery.

   Based on these results we recommend discontinuation of low molecular weight heparin at least 12 hours before cardiac surgery.



Nicola Vitale MD
Stephen Clark DM, FRCS
Department of Cardiothoracic Surgery
Freeman Hospital,
High Heaton,
Newcastle-upon-Tyne NE7 7DN
United Kingdom



References

1. Abbadi AA, Hajir MA. Low molecular weight heparins proposed guidelines for their use. Heart Views 1999; 1:126-129

2. Clark S, Vitale N, Zacharias J, Forty J. The effect of low molecular weight heparin (Fragmin) on bleeding after cardiac surgery. 1998 Annual Meeting, The Society of Cardiothoracic Surgeons of Great Britain and Ireland. Abstract Book:142

3. FRISC Study Group. Low molecular weight heparin during instability in coronary artery disease. Lancet 1996; 347; 561-568.

4. Klein W, Buchwald A Hillis SE, et al. Comparison of low molecular weight heparin with unfractioned heparin acutely and with placebo for six weeks in the management of unstable coronary artery
disease. Circulation 1997; 96: 61-68.

5. Jensen LS. Postoperative infection and NK cell function following blood transfusion in patients undergoing elective colorectal surgery.
Brit J Surg 1992; 79: 513-516

6. Jensen LS. Cost effectiveness of blood transfusion and white cell reduction in elective colorectal surgery. Transfusion 1995; 35: 719-722.

7. Triulzi DJ. A clinical and immunologic study of blood transfusion and postoperative infection in spinal surgery. Transfusion 1992; 35: 517-524.



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