Distinctive microcirculation of the brain during cerebral perfusion by observation with a CCD microscope

Is Maintenance of Cerebral Hypothermia the Principal Mechanism by which Retrograde Cerebral Perfusion Provides Better Brain Protection than Hypothermic Circulatory Arrest? A Study in a Porcine Model

OBJECTIVE

Retrograde cerebral perfusion (RCP) provides better brain protection than hypothermic circulatory arrest (HCA) alone. The mechanism by which RCP improves brain protection during circulatory arrest remains unknown. The purpose of the study in pigs was to determine if RCP improves brain protection mainly as a result of its ability to maintain cerebral hypothermia.

METHODS

Fifteen pigs were subjected to 120 minutes of HCA alone (HCA group, n = 5), HCA + RCP at perfusion pressures of 23 to 29 mmHg (RCP-low group, n = 5), or at perfusion pressures of 34-40 mmHg (RCP-high group, n = 5) at 15 degrees C, followed by 60 minutes of normothermic cardiopulmonary bypass (CPB). After brain temperature reached 15 degrees C, HCA was initiated with or without RCP. Temperatures in the brain, esophagus, and perfusate/blood were monitored continuously. Brain tissue blood flow was measured continuously using a laser flowmeter. Brain oxygen extraction was calculated from the oxygen contents in arterial and venous blood samples.

RESULTS

During cooling and rewarming, the change in temperature was slower in the brain than in the esophagus. A similar degree of spontaneous rewarming (from 15 degrees C to 17/18 degrees C) occurred in the brain during HCA and RCP. This indicates that RCP does not provide better maintenance of cerebral hypothermia during circulatory arrest than HCA alone. The esophageal temperature rose more slowly during RCP than during HCA alone, indicating that RCP maintains better hypothermia in the body. During RCP, the brain extracted oxygen continuously from the blood, indicating that RCP may provide nutrient flow to the brain.

CONCLUSION

In an acute pig model, maintenance of cerebral hypothermia does not appear to be the principal mechanism by which RCP provides better brain protection than HCA alone. Retrograde cerebral perfusion provides nutrient flow/oxygen to brain tissue, leading to better brain protection than HCA alone.

Experimental studies on morphological changes of microcirculation of DMN-induced liver cirrhosis after normothermic ischemia with charge-coupled device microscope

AIM

The purpose of the present experiment was to find indices for intraoperative ischemic-reperfusion injury in the cirrhotic liver.

METHODS

One percent dimethylnitrosamine (DMN) was administered intraperitoneally to liver cirrhosis (LC) groups of Wister rats on three consecutive days of each week for a period of four weeks. The rats were divided into a N60 group with 60 minute ischemia in normal livers, a LC60 group with 60 minute ischemia in cirrhotic livers, and a LC30 group with 30 minute ischemia in cirrhotic livers. Digital videotapes recorded with a pencil lens-probe charge-coupled device (CCD) microscope were analyzed with NIH Image software. In zone 3, the sinusoid diameter (SD) was measured and the volume fraction (Vv) of zone 3 was calculated in preischemia and after 10, 20, 30, and 60 min of reperfusion. At the same time, bile flow was measured.

RESULTS

The SD was significantly shorter in the cirrhotic liver groups than in the normal liver group at each point. The Vv after 60 min of reperfusion was significantly smaller in the LC60 group, with a survival rate of 0%, than in the LC30 group which had a survival rate of 67%. However, there was no significant difference in bile flow after 60 min of reperfusion in the LC30 and LC60 groups. Therefore, the Vv is suggested to be the better index for viability after ischemic-reperfusion.

CONCLUSION

SD and Vv indicate microcirculatory differences and indices in the normal and cirrhotic livers in preischemia during reperfusion.

Direct visualization of minimal cerebral capillary flow during retrograde cerebral perfusion: an intravital fluorescence microscopy study in pigs

BACKGROUND

Retrograde cerebral perfusion (RCP) is used in some centers during aortic arch surgery for brain protection during hypothermic circulatory arrest. It is still unclear however whether RCP provides adequate microcirculatory blood flow at a capillary level. We used intravital microscopy to directly visualize the cerebral capillary blood flow in a piglet model of RCP.

METHODS

Twelve pigs (weight 9.7 +/- 0.9 kg) were divided into two groups (n = 6 each): deep hypothermic circulatory arrest (DHCA) and RCP. After the creation of a window over the parietal cerebral cortex, pigs underwent 10 minutes of normothermic bypass and 40 minutes of cooling to 15 degrees C on cardiopulmonary bypass ([CPB] pH-stat, hemocrit 30%, pump flow 100 mL x kg(-1) x min(-1)). This was followed by 45 minutes of DHCA and rewarming on CPB to 37 degrees C. In the RCP group the brain was retrogradely perfused (pump flow 30 mL x kg(-1) x min(-1)) during DHCA through the superior vena cava after inferior vena cava occlusion. Plasma was labeled with fluorescein-isothiocyanate-dextran for assessing microvascular diameter and functional capillary density (FCD), defined as total length of erythrocyte-perfused capillaries per observation area. Cerebral tissue oxygenation was determined by nicotinamide adenine dinucleotide hydrogen (NADH) autofluorescence, which increases during tissue ischemia.

RESULTS

During normothermic and hypothermic antegrade cerebral perfusion the FCD did not significantly change from base line (97% +/- 14% and 96% +/- 12%, respectively). During retrograde cerebral perfusion the FCD decreased highly significantly to 2% +/- 2% of base line values (p < 0.001). Thus there was no evidence of significant capillary blood flow during retrograde cerebral perfusion. The microvascular diameter of cerebral arterioles that were slowly perfused significantly decreased to 27% +/- 6% of base line levels during RCP. NADH fluorescence progressively and significantly increased during RCP, indicating poorer tissue oxygenation. At the end of retrograde cerebral perfusion there was macroscopic evidence of significant brain edema.

CONCLUSIONS

RCP does not provide adequate cerebral capillary blood flow and does not prevent cerebral ischemia. Prolonged RCP induces brain edema. However, there might be a role for a short period of RCP to remove air and debris from the cerebral circulation after DHCA because retrograde flow could be detected in cerebral arterioles.

Experimental model to estimate intestinal viability using charge-coupled device microscopy

BACKGROUND

Intraoperative assessment of intestinal viability following release of strangulation remains difficult. The aim of this study was to establish clinical standards for the evaluation of intestinal viability by charge-coupled device (CCD) microscopy.

METHODS

A rat ileus model with strangulation for between 15 and 120 min was used. The images obtained by CCD microscopy were used to calculate maximum velocity (V (max)) ratio (ratio of V (max) of blood cell transition in the experimental segment to that in the reference segment) and S ratio (the ratio of S-the effective area of the vascular bed against the total area of the vascular bed-in the experimental segment to that in the reference segment). Rats were divided into group 1, comprising animals that survived for 7 days or more, and group 2, which consisted of animals that died within 4 days.

RESULTS

V (max) ratio and S ratio in group 1 were both significantly higher than those in group 2 (P < 0.01). No death occurred at a V (max) ratio of 0.76 or higher and an S ratio of 0.61 or more, while there were no survivors with a V (max) ratio of 0.54 or less and an S ratio of 0.51 or less.

CONCLUSION

V (max) ratio and S ratio could be used as indices for evaluation of intestinal viability.

Retrograde perfusion and true reverse brain blood flow in humans

OBJECTIVE

Reversal of brain blood flow is necessary for retrograde cerebral perfusion (RCP) to have any metabolic benefit, but RCP is commonly used with little clinical evidence of the true incidence of reverse brain blood flow and impact. S-100B is exclusive to the brain and spinal cord and released during hypothermic circulatory arrest (HCA). True reverse brain blood flow (tRBBF) during RCP may be determined by demonstrating an excess of S-100B in the effluent blood from the common carotid artery compared to blood entering the brain.

METHODS

Simultaneous blood samples were drawn from the jugular bulb and left common carotid artery during RCP at 5 min intervals in ten patients undergoing aortic surgery, utilizing HCA and subjected to blood gas, glucose and S-100B quantification. RCP was instituted at maximum pressure of 25 mmHg. Trans-cranial Doppler (TCD) continuously monitored the middle cerebral artery velocity (MCAV).

RESULTS

The mean HCA and RCP durations were 31 min (20-50 min). Reversal of MCAV was demonstrated in only 6/10 cases (mean, 6 cm/s). Veno-arterial (V-A) extraction of oxygen and glucose occurred in all cases (P<0.001), with the mean effluent pO(2) falling to 14 mmHg. V-A S-100 gradients greater than 5% were demonstrated in 8/10 cases and correlated with higher oxygen extraction (P<0.01). In patients with and without MCAV reversal, the S-100 gradients were 1. 7 and 0.3 micromol/l, respectively (P<0.01).

CONCLUSIONS

tRBBF occurred in nearly all patients. MCAV reversal appears to be a specific but insensitive guide to reverse perfusion. The de-saturation of effluent blood is not a reliable guide to true brain perfusion, and despite RCP, the brain remains ischaemic.