PII: S0022-5223(96)70468-3

Abstract

We thank Watanabe and associates for their interest in our recent article, “Pharmacologic intervention for ischemic brain edema after retrograde cerebral perfusion.”1Yoshimura N Okada M Ota T Nohara H Pharmacologic intervention for ischemic brain edema after retrograde cerebral perfusion.J THORAC CARDIOVASC SURG. 1995; 109: 1173-1181Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar We reported that the supply of oxygen or glucose by retrograde cerebral perfusion (RCP) was not enough to maintain sufficient cerebral metabolism and that this may cause brain edema after antegrade cerebral blood perfusion is resumed. We therefore recommended cerebral protection with pharmacologic agents to prevent neurologic complications during aortic arch operation with the use of RCP.1Yoshimura N Okada M Ota T Nohara H Pharmacologic intervention for ischemic brain edema after retrograde cerebral perfusion.J THORAC CARDIOVASC SURG. 1995; 109: 1173-1181Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar Although RCP is widely used with satisfactory results to protect the brain during aortic arch operation, the standards for this procedure, such as perfusion site, drainage site, perfusion pressure, flow rate, and temperature, have not yet been established.2Nojima T Magara T Nakajima Y et al.Optimal perfusion pressure for experimental retrograde cerebral perfusion.J Card Surg. 1994; 9: 548-559Crossref PubMed Scopus (52) Google Scholar We agree with Watanabe and associates that drainage from the right atrium should increase the veno-venous shunt, which may reduce the cerebral protective effect of RCP. As we explained in our article, however, the pressure gradient between the maxillary veins and systemic arteries caused retrograde cerebral blood flow, which was evidenced by desaturated blood being returned to the carotid artery. Several clinical3Yoshimura N Ataka K Okada M Yamashita C Yoshimura K Kobayashi S Ophthalmoscopic findings demonstrate reduced cerebral blood flow during retrograde cerebral perfusion.J THORAC CARDIOVASC SURG. 1995; 109: 591-593Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar, 4Yasuura K Okamoto H Ogawa Y et al.Resection of aortic aneurysms without aortic clamp technique with the aid of hypothermic total body retrograde perfusion.J THORAC CARDIOVASC SURG. 1994; 107: 1237-1243PubMed Scopus (13) Google Scholar and experimental5Usui A Hotta T Hiroura M et al.Retrograde cerebral perfusion through a superior vena caval cannula protects the brain.Ann Thorac Surg. 1992; 53: 47-53Abstract Full Text PDF PubMed Scopus (93) Google Scholar studies have suggested the existence of a veno-venous shunt that does not participate in cerebral metabolism during RCP, and the veno-venous shunt is considered a major disadvantage of RCP compared with antegrade selective cerebral perfusion. In our experimental studies, we observed that the cerebral blood flow provided during RCP was only half of that supplied during cardiopulmonary bypass with hypothermia.1Yoshimura N Okada M Ota T Nohara H Pharmacologic intervention for ischemic brain edema after retrograde cerebral perfusion.J THORAC CARDIOVASC SURG. 1995; 109: 1173-1181Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar This finding was in accord with the results of other experimental studies.2Nojima T Magara T Nakajima Y et al.Optimal perfusion pressure for experimental retrograde cerebral perfusion.J Card Surg. 1994; 9: 548-559Crossref PubMed Scopus (52) Google Scholar, 6Usui A Oohara K Liu T et al.Determination of optimum retrograde cerebral perfusion condition.J THORAC CARDIOVASC SURG. 1994; 107 (12/8/69672): 300-308PubMed Google Scholar A limitation of our study was the determination of cerebral blood flow, including veno-venous shunt flow, as Watanabe and associates pointed out. It is difficult, however, to distinguish the true functional blood flow that participates in cerebral metabolism from veno-venous shunt flow during RCP in the experimental study. Accurate measurement of the true functional blood flow, if possible, should enable us to precisely evaluate cerebral metabolism during RCP. We therefore hope that Watanabe and associates' experimental study will clarify the true functional blood flow during RCP by means of laser photometry.