Reply to Ates and Gullu Free

We appreciate the comments by Drs Ates and Gullu and their short review, in which they conclude that selective antegrade cerebral perfusion (SACP) in combination with hypothermic circulatory arrest (HCA) should be the standard technique for the treatment of acute type A aortic dissections (AADA) [1].

In our institution, we apply this technique since 1999 in almost all patients requiring thoracic aortic surgery including the aortic arch. Up to date, we have an experience of more than 500 cases including more than 150 patients with AADA. The rationale as well as technical details of our specific technique of SACP have been published in 2003 [2].

Despite the fact that experimental and clinical work show the advantages of these combined protection technique, a number of open question remain [3,4]. Regarding the optimal temperature for SACP, it seems that temperatures around or below 20 °C provide reasonable protection for the cerebrum, associated with a reduced cerebral metabolism. Under these conditions, short periods of flow interruption—e.g. for introduction of the SACP-cannulas—are covered. Nevertheless, the optimal distribution regime is still a matter of concern, especially due to vascular resistance disturbances in the brain, triggered by the non physiological distribution. From the pathophysiological point of view, profound temperatures provide best brain protection, indicated by most complete reduction of the cerebral metabolism. Reperfusion injury can occur in these brains during rewarming, causing a rise in intracranial pressure (ICP). Since we have shown that increased ICP’s are associated with an imperfect brain protection, care has to bee taken by applying these temperatures [5]. Therefore, moderate temperatures are potentially more physiological in these settings, but inadequate flow rates and pressure drops are leading subsequently to cerebral ischemia, likewise associated with increased ICP’s.

Besides the exciting question of cerebral protection, the question for the optimal body temperature during HCA has not been answered so far. The expected requirements are hard to achieve: best protection for various organs, with different requirements concerning their oxygen consumption and a variable ischemic tolerance.

Therefore, the following questions have to be answered for a further optimal patient treatment:

1. How to adapt the flow and pressure rate to the vascular resistance in the brain according to different perfusion temperatures?

2. Define the optimal temperature and perfusion strategy for best protection of the remaining organs to prevent the ischemic/reperfusion injury during and after HCA.

Our current research focuses on these topics, hopefully leading to answer the questions and provide best care for our patients.

References