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Ann Thorac Surg 2005;79:1825
© 2005 The Society of Thoracic Surgeons
Department of Cardiovascular and Thoracic Surgery, Hôpital du Sacré-Coeur de Montréal, University of Montréal, 5400 Boulevard Gouin Ouest, Montréal, PQ H4J IC5, Canada
(E-mail: joseehsc{at}hotmail.com).
The study by Dr Coselli and colleagues could be seen by less experienced surgeons [1] as an invitation to challenge basic cardiovascular physiology. Historically, paraplegia has occurred in humans after 18 minutes of aortic cross-clamping [2]. This short period differs substantially from the 30 minutes established statistically and overquoted in the literature for the past 25 years as a safe limit of physiological insult to the spinal cord. Between the lines of this study, one can perceive the work of an outstanding team orchestrated by an exceptionally skillful surgeon and involving anesthesiologists and intensivists trained in the art of managing sudden and extreme hemodynamic disturbances.
In the series of 387 patients, only 46 had left heart bypass with a centrifugal pump, and in this group, the incidence of paraplegia was low (4%). Based on a very sophisticated statistical analysis, the conclusion of this study is rather surprising: the protective effect of the pump against paraplegia clearly demonstrated by Coselli and LeMaire [3] during resection of more extensive aneurysms (type II thoracoabdominal aneurysms necessitating longer aortic cross-clamp times) could not be reproduced for aneurysms limited to the descending thoracic aorta.
In my series of 837 resected aneurysms confined to the descending thoracic aorta, a method of perfusion was used systematically in each procedure. The overall rate of spinal cord ischemic deficit was 2.1%. It ranged from 2.3% with a Gott shunt in the first 380 patients to 1.9% with left heart bypass using a centrifugal pump in the following 457 patients. A subgroup of 165 patients underwent a repair of an acute (111) or chronic (54) traúmatic aneurysm without any incidence of paraplegia. These results suggest that in a limited aortic resection, a greater number of patent intercostal arteries coupled with maximized pump flow allows optimal perfusion of the spinal cord.
The conclusion in the present study by Dr Coselli and co-workers does not support this point of view. I suspect that their marked modification of the perfusion technique explains this apparent contradiction. In most of their patients, left heart bypass was functional only during the proximal anastomosis, which implies that the distal anastomosis was completed under ischemic conditions. If atriofemoral bypass had been used during the total aortic cross-clamp time, the protective effect on the cord may have been conclusive.
Moreover, Coselli and associates no longer measure distal perfusion pressure. I find such monitoring very valuable for pump flow regulation, particularly in hypertensive patients, in whom undesirable higher distal pressure is very prone to develop as soon as perfusion is initiated [4]. Rapid use of vasodilators to lower peripheral resistance allows preservation of more optimal bypass flow with distal pressure averaging 70 mm Hg.
I congratulate Dr Coselli and colleagues on their report. It represents a plea for safe repair of descending thoracic aortic aneurysms using a conventional, well-planned open technique. I also recognize the enormous contribution Dr Coselli has made to the specialty of thoracic aortic surgery.
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