Total and regional cerebral blood flow during perfusion from the lateral ventricle to the cisterna magna in the conscious dog: effect of hemorrhagic hypotension and retransfusion on cerebral blood flow.

This study was performed to determine if autoregulation of regional cerebral blood flow (rCBF) occurs in conscious dogs with ventriculocisternal perfusion (VCP) during moderate hypotension. Six dogs were perfused for 360 minutes using mock cerebrospinal fluid (CSF). A 120-minute control period was followed by 180 minutes of moderate hemorrhagic hypotension (mean arterial pressure (SAP) 60-80 mm Hg). The lost blood (approximately 40% of the calculated blood volume) was retransfused after 300 minutes of perfusion, and an additional 60 minutes of observation concluded the study. The rCBF was measured at 120, 240, and 360 minutes of perfusion using labeled microspheres of 15 mu diameter. Cardiac output (CO) was 2.8 +/- 0.41 liters/min at 120 minutes, decreased to 1.4 +/- 0.10 liters/min after hemorrhage, and rose after retransfusion to 2.2 +/- 0.13 liters/min. The percentage of cardiac output (%CO) received by the brain was 1.8 +/- 0.37% at 120 minutes, 3.8 +/- 0.44% at 240 minutes, and 2.2 +/- 0.22% after retransfusion (P < 0.05). There was no significant change in rCBF during hypotension. The regional cerebral blood flow was, however, significantly elevated in the thalamus, mesencephalon, pons, and medulla after retransfusion indicated a local alteration of set point in the plateau of the autoregulatory curve. Cerebral venous pH (measured in internal maxillary venous blood) decreased significantly during hemorrhage to 7.25, while cerebral arteriovenous difference of oxygen and A-VpH increased significantly during hemorrhage. Thus, autoregulation of total cerebral blood flow (CBF) during acute moderate hypotension remains intact during VCP at a rate of 0.2 ml/min using a perfusate of a constant pH and, hence, CSF-pH appears not to be of major significance for the autoregulation of CBF in moderate hypotension.