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

Retrograde perfusion through superior vena cava reaches the brain during circulatory arrest

Background

The optimal technique for brain perfusion during circulatory arrest remains controversial. Concern exists that retrograde cerebral perfusion (RCP) via the superior vena cava (SVC) is unable to perfuse the brain. We evaluated whether RCP blood circulates through the brain parenchyma in humans during deep hypothermic circulatory arrest (DHCA). We hypothesized that a significant difference in the levels of S-100β (a protein with very high neuro-sensitivity) between the blood infused in the SVC and the effluent blood returning in the left carotid artery (CA) during RCP, should be regarded as a sign of the circulation of RCP blood through the brain parenchyma.

Methods

We enrolled 10 non-consecutive patients undergoing elective arch-surgery using DHCA and RCP. Circulating S-100β levels were measured at baseline and immediately before DHCA. During DHCA and RCP the difference in S-100β between the SVC and the CA was evaluated after 10 minutes of arrest and immediately before resumption of the circulation. S-100β levels were evaluated using enzyme-linked immunosorbent assay (ELISA).

Results

Mean DHCA duration was 22.4±7.9 minutes. Mean S-100β level at baseline was 92.5±54.9 µg/L. After 10 minutes of DHCA the level of S-100β in the CA was significantly higher than in the SVC (936.9±326.3 vs. 810.9±307.4 µg/L, P=0.0021). This difference was enhanced at the second DHCA sample (1113.8±334.2 vs. 920.5±340.0 µg/L, P=0.0002). There was a statistically significant correlation between the duration of DHCA and the percent difference in S-100β level between the SVC and the CA (Pearson's correlation coefficient =0.902).

Conclusions

RCP is able to perfuse the brain parenchyma in humans during DHCA.

Effects of Cryotherapy after Contusion Using Real-Time Intravital Microscopy

PURPOSE

To examine effects of local tissue cooling on contusion-induced microvascular hemodynamics and leukocytes behavior using real-time intravital microscopy.

METHODS

Male Wistar rats (N = 21, 130-150 g) were randomly assigned to intensive cooling group (3 degrees C, N = 7), a moderate cooling group (27 degrees C, N = 7), or control group (37 degrees C, N = 7). Contusion was induced by dropping a plastic ball on exposed cremaster muscle. After 5 min, the cremaster muscle was superfused with a saline solution for 10 min at controlled temperature of either 3 degrees C (cooling), 27 degrees C (moderate cooling), or 37 degrees C (control). Microvascular hemodynamics (vessel internal diameter, blood flow rate and erythrocyte velocity) and leukocyte behavior (rolling and adhesion) were measured from recorded videotapes in the same venules before and after contusion, and after cooling.

RESULTS

Cooling-induced vasoconstriction was marked at 3 degrees C and moderate at 27 degrees C compared with that at 37 degrees C. Blood flow rate and erythrocyte velocity were markedly lower at 3 degrees C compared to 37 degrees C. At 27 degrees C, erythrocyte velocity was higher than that at 37 degrees C, but blood flow rate was maintained at a level similar to that at 37 degrees C. The number of rolling and adhering leukocytes at 3 degrees C and 27 degrees C were significantly less than at 37 degrees C.

CONCLUSION

Our results suggest that local tissue cooling, similar to cryotherapy, improves edema and inflammatory reaction, and may be useful for reducing inflammatory response without inhibiting blood flow after contusion.

Reducing risk in infant cardiopulmonary bypass: the use of a miniaturized circuit and a crystalloid prime improves cardiopulmonary function and increases cerebral blood flow

Advances in perfusion strategies have played an important role in improving outcomes following repair of complex congenital heart defects. The influence of cooling strategy, temperature, duration of circulatory arrest, and specific method of cerebral perfusion on neurologic morbidity have been extensively characterized. Similarly, the ability of pharmacologic agents to modulate the post-cardiopulmonary bypass (CPB) inflammatory response has been previously elucidated in both the laboratory and clinical arena. However, modification of the circuit and priming components have received comparably less attention. We recently showed that employment of a miniaturized circuit and a bloodless prime reduce inflammation and have salutary effects on cardiopulmonary function following hypothermic low-flow perfusion (HLF), and that this circuit may also improve cerebral protection following both deep hypothermic circulatory arrest and HLF. The current report, therefore, reviews current strategies utilized to minimize post-CPB inflammation and highlights the empirical evidence from our laboratory demonstrating the beneficial role of a miniaturized extracorporeal circuit in this context.