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Ann Thorac Surg 2000;69:749
© 2000 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Boston University Medical Center, 88 E Newton St, Boston, MA 02118-2393, USA
Invited commentary
Doctor Olsson and colleagues report that the use of heparin coated bypass circuits with a reduced heparinization protocol afforded no benefit to patients undergoing thoracic aortic surgery. It is important to remember that this study was not designed to determine if heparin coated circuits afforded any benefit over standard circuits when performing thoracic aortic operations. Our group at Boston Medical Center has submitted data for publication documenting a significant impact of heparin coated circuits for operations on the thoracic aorta.
The successful implementation of a reduced heparin protocol, when using heparin coated circuits, is maximized when closed circuits, membrane oxygenations, centrifugal pumps, absence of the use of cardiotomy suction, low prime volume, heparin coated cannula with large internal lumen to minimize shear forces and normothermia, or, at most, very mild (34°C) systemic cooling are employed as a complete perfusion strategy. Using this strategy, several centers have reported excellent results with heparin coated circuits and a low heparin protocol for coronary artery bypass graft (CABG) surgery.
Our extensive clinical experience at Boston Medical Center, after our randomized trial, taught us that open cardiac procedures, especially when mechanical valves are employed, present a blood gas interface and a prosthetic valve surface occasionally leading to observable thrombus in the operative field. Thus our protocol for open cardiac valve procedures requires activated clotting times (ACT) above 400 seconds with heparin coated circuits.
The impact of profound cooling and rewarming will affect heparin metabolism and then the addition of aprotinin (regardless of dosing protocol) presents further risks for thrombotic or thromboembolic events. All our publications describe the use of a low anticoagulation protocol only with heparin coated circuits and the perfusion strategy previously described. In cases requiring significant cooling, aprotinin use, or open cardiac procedures especially with mechanical valves, heparin coated circuits must be used with a full anticoagulation protocol (ACT > 400 seconds).
Our strategy and bias is consistent with the conclusions in Dr Olsson’s study. This study is limited by too few patients with varied pathology and clinical presentations (eg dissections, aneurysms, use of full bypass for the ascending aorta and partial bypass for the descending aorta). I agree that the intense inflammation associated with major aortic surgery and the required perfusion techniques required to repair these diseases (ie open cardiac approaches, significant hypothermia, cardiotomy suction, etc) limits the effectiveness of heparin coated circuits. Attempts to employ a low anticoagulation protocol in these cases where thromboembolic risk is greatly enhanced is not prudent. Dr Olssen’s study lacks the statistical resolution to support this bias on a firm scientific basis. As always, till proven otherwise, primum non nocere.
Related Article
Ann. Thorac. Surg. 2000 69: 743-749.
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