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J Thorac Cardiovasc Surg 1994;108:993-994
© 1994 Mosby, Inc.

LETTERS TO THE EDITOR

Cerebral metabolism during retrograde cerebral perfusion

Second Department of Surgery
Shiga University of Medical Science
Otsu, Shiga 520-21, Japan

To the Editor:

Usui and associates ¹ recently reported their findings regarding optimal perfusion pressure during retrograde cerebral perfusion (RCP) in dogs, and the authors are to be congratulated on their results They measured cerebral blood flow, cerebrospinal fluid pressure, oxygen consumption, and carbon dioxide elimination during cardiopulmonary bypass and RCP. They analyzed those data in great detail and determined the optimal perfusion pressure to be 25 mm Hg. Clinical applications of various RCP procedures have been reported, but the changes in cerebral metabolism during RCP have not been clarified. Theirs was the first experimental study to suggest the optimal perfusion pressure for RCP, and the experimental model they used perfused oxygenated blood via bilateral maxillary veins to avoid venous valves that would interfere with RCP. No previous experimental model has been devised to assess RCP simply.

We ^2-5 performed experiments on cerebral metabolism during RCP using a similar experimental model in adult mongrel dogs. Partial cardiopulmonary bypass was carried out at a flow rate of 100 ml/kg per minute to induce hypothermia (nasopharyngeal temperature at 20° C). After circulatory arrest, RCP was performed for 60 minutes at this temperature. RCP was performed with oxygenated blood via catheters placed in the bilateral maxillary veins. The retrograde cerebral flow rate was regulated to maintain a mean perfusion pressure at 20 mm Hg in the external jugular vein. During RCP the cannulas placed in superior and inferior venae cavae (SVC and IVC) were clamped. In our study, ² the nasopharyngeal temperature increased slowly during hypothermic circulatory arrest, but the temperature was maintained in a narrow range without surface cooling during RCP. Oxygen consumption values suggested that a considerable amount of oxygen could be supplied to cerebral tissue and carbon dioxide excretion by RCP. In addition, the data on cerebral excess lactate indicated that RCP maintained aerobic metabolism during 60 minutes of RCP. Cerebral tissue adenosine triphosphate concentration was significantly higher than that after 60 minutes of circulatory arrest. It is speculated that this aerobic metabolism reflected storage in the form of high-energy phosphates. Maintenance of the adenosine triphosphate level during RCP indicates the possibility of extending the safe duration of hypothermic circulatory arrest. We also evaluated the water content of cerebral tissue as an indicator of cerebral edema. The water content of cerebral tissue after 60 minutes of RCP was significantly higher than that after circulatory arrest. RCP increases the venous and cerebrospinal fluid pressure, which can be major factors in brain edema. In addition, we ^2-4 evaluated the effects of pulsatile flow during RCP,and "venous" pulsatile flow successfully reduced cerebral edema.

In another study, we ⁵ investigated the effects on cerebral metabolism of clamping the blood flow from the IVC cannula during RCP. Usui and associates ¹ used an experimental model in which both the SVC and IVC were clamped during RCP. Clamping the blood flow from the IVC during RCP is an important procedure. In our study, the percentage of returned blood volume, oxygen consumption, carbon dioxide excretion, and oxygen saturation of the returned blood were significantly higher in the IVC-clamped group than those in the IVC-unclamped group. The serum creatine kinase BB level was significantly lower in the IVC-clamped group.

In conclusion, RCP may provide adequate metabolic support for the brain during circulatory arrest and interruption of the venous blood flow through the IVC cannula.

References

1. Usui A, Oohara K, Liu T-1, et al. Determination of optimal retrograde cerebral perfusion conditions. J THORAC CARDIOVASC SURG 1994;107:300-8.
   
2. Nojima T, Mori A, Watarida S, Onoe M. Cerebral metabolism and effects of pulsatile flow during retrograde cerebral perfusion. J Cardiovasc Surg 1993;34:483-92.
   
3. Nojima T, Mori A, Watarida S, et al. Experimental studies of pulsatile retrograde cerebral perfusion. J Jpn Assoc Thorac Surg 1994;42:175-80.
   
4. Mori A. Retrograde cerebral perfusion using pulsatile flow under condition of profound hypothermia. Ann Thorac Surg 1993;56:1497-8.
   
5. Nojima T, Mori A, Watarida S, et al. Experimental studies on retrograde cerebral perfusion: efficacy of clamping of the venous blood flow through IVC cannula. Jpn J Thorac Surg 1993;46:690-4.
   

This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Nojima, T. Articles by Nakajima, Y. Search for Related Content PubMed Articles by Nojima, T. Articles by Nakajima, Y.