J Thorac Cardiovasc Surg 1994;108:994
© 1994 Mosby, Inc.
Cerebral metabolism during retrograde cerebral perfusion
Akihiko Usui, MD
Department of Thoracic Surgery
Nagoya University, School of Medicine
65 Tsurumai, Shouwa-ku
Nagoya 466, Japan
Reply to the Editor:
The comments of Dr Nojima and his colleagues regarding our article "Determination of Optimum Retrograde Cerebral Perfusion Conditions"
1 are appreciated. We tried to clarify the optimal perfusion condition of retrograde cerebral perfusion (RCP) in the experimental study using adult mongrel dogs to measure cerebral tissue blood flow, oxygen consumption, and cerebrospinal fluid pressure. RCP was established by perfusing oxygenated blood via bilateral internal maxillary veins, clamping the bicaval cannulas, and opening the aortic cannula by gravity to the cardiotomy reservoir in the hypothermic condition (20° C). RCP was performed as the external jugular venous pressure was changed from 15 to 35 mm Hg in increments of 5 mm Hg. RCP with an external jugular venous pressure of 25 mm Hg provided about half the cerebral tissue blood flow of cardiopulmonary bypass with a flow rate of 1000 ml/min. It decreased significantly as an external jugular venous pressure was decreased from 25 to 15 mm Hg but did not increased significantly as external jugular venous pressure was increased from 25 to 35 mm Hg. Whole-body oxygen consumption during RCP in an external jugular venous pressure of 25 mm Hg was one quarter of that during hypothermic cardiopulmonary bypass and varied with the external jugular venous pressure. The cerebrospinal fluid pressure varied in proportion to the external jugular venous pressure, showing a slightly lower value. High external jugular venous pressure was associated with high intracranial pressure, which restricted cerebral tissue blood flow. RCP with high jugular venous pressure and high intracranial pressure also may cause brain edema. We think that the optimum venous pressure of RCP is the lowest pressure that provides effective cerebral tissue blood flow and also the highest pressure under which brain edema does not result. We concluded that an external jugular venous pressure of 25 mm Hg can be used safely with the maximum cerebral tissue blood flow. However, we have not estimated brain edema during RCP. Dr. Nojima and associates evaluated the water content of cerebral tissue as an indicator of brain edema. They measured the water content of cerebral tissue after 60 minutes of RCP and reported that it was significantly higher than after circulatory arrest. They also mentioned the effects of pulsatile flow during RCP. They said that the venous pulsatile flow successfully reduced brain edema. Brain edema is one of the major problems associated with RCP. It occasionally causes serious neurologic deficiency. We believe that keeping the venous pressure under 25 mm Hg is a step toward reducing brain edema. The venous pulsatile flow may be another useful means to reduce brain edema.
Dr. Nojima and his colleagues also performed a comparative study between 60 minutes of RCP and circulatory arrest in the hypothermic condition. In their study RCP maintained nasopharyngeal temperature in a narrow range without surface cooling and provided a considerable amount of oxygen to cerebral tissue, maintaining aerobic metabolism and keeping a high level of cerebral tissue adenosine triphosphate concentration. We 2 performed the same comparative study between 60 minutes of RCP at an external jugular venous pressure of 25 mm Hg and circulatory arrest in the hypothermic condition. RCP reduced oxygen debt during the study by providing oxygen and also cooled the brain better than circulatory arrest. Cerebral tissue oxygen tension decreased slightly, and cerebral tissue carbon dioxide tension increased slowly during RCP. These changes were smaller than those seen with circulatory arrest. Tissue concentrations of adenosine triphosphate in the brain remained relatively high during RCP but decreased rapidly during circulatory arrest. Dr. Nojima reported that RCP maintained aerobic metabolism during 60 minutes of RCP. In our study RCP did not maintain aerobic metabolism sufficiently, but we also reached the conclusion that RCP may reduce ischemic damage to the brain and may safely extend the cerebral circulatory interruption time. 2,3
Dr. Nojima mentioned the efficacy of clamping the blood flow from the inferior vena cava (IVC) cannula during RCP. We 4 also performed RCP by perfusing blood via the superior vena cava (SVC) and draining blood from the IVC and aorta. In this model only 20% of perfused blood via the SVC was returned through the aorta and the rest drained from the IVC. Whereas the blood that returned via the aorta was significantly desaturated even at hypothermia, the blood that returned via the IVC did not show desaturation even at normothermia. The SVC system has many connections to the IVC system. Therefore, the blood perfused via the SVC runs into the IVC system through these connections. When the IVC is clamped during RCP, most of the blood perfused via the SVC runs through the SVC system, and the blood that runs into the IVC system perfuses the visceral organ retrogradely. Therefore, we also recommend clamping the IVC cannula during RCP for protection of both the brain and visceral organs.
References
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Usui A, Oohara K, Lin T, et al. Determination of optimum retrograde cerebral perfusion conditions. J THORAC CARDIOVASC SURG 1994;107;300-8.
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Usui A, Oohara K, Lin T, et al. Comparative experimental study between retrograde cerebral perfusion and circulatory arrest. J THORAC CARDIOVASC SURG 1994;107:1228-36.[Abstract/Free Full Text]
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Usui A, Hotta T, Hiroura M, et al. Cerebral metabolism and function during normothermic retrograde cerebral perfusion. Cardiovasc Surg 1993;1:107-12.[Medline]
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Usui A, Hotta T, Hiroura M, et al. Retrograde cerebral perfusion through a superior vena caval cannula protects the brain. Ann Thorac Surg 1992;53:47-53.[Abstract]
