Brain damage after profoundly hypothermic circulatory arrest: Correlations between neurophysiologic and neuropathologic findings

The Expression of CD34(+)/C-kit(+) Stem Cells in Peripheral Blood in Infants After Deep Hypothermia Circulatory Arrest

To investigate the effect of deep hypothermic circulatory arrest (DHCA) on the expression of a CD34(+)/C-kit(+) progenitor cell population in peripheral blood in infants. The expression of CD34(+)/C-kit(+) stem cells in peripheral blood of 10 patients after DHCA was measured before institution of cardiopulmonary bypass (CPB) (T0), at 12-24 hours (T1) and 4-5 days (T2) after cessation of CPB, respectively. The level of CD34(+)/C-kit(+) stem cells in peripheral blood was significantly higher in the DHCA group at T1 and T2 (p<0.01). Our data show that DHCA may cause the increase of CD34(+)/C-kit(+) stem cells in peripheral blood after surgery. The role of increase of CD34(+)/C-kit(+) stem cells in peripheral blood on the beneficial effects of DHCA needs to be studied.

Interaction of temperature with hematocrit level and pH determines safe duration of hypothermic circulatory arrest

OBJECTIVE

Previous studies have demonstrated that both hematocrit level and pH influence the protection afforded by deep hypothermic circulatory arrest. The current study examines how temperature modulates the effect of hematocrit level and pH in determining a safe duration of circulatory arrest. The study also builds on previous work investigating the utility of near-infrared spectroscopy as a real-time monitor of cerebral protection during circulatory arrest.

METHODS

Seventy-six piglets (9.3 +/- 1.2 kg) underwent circulatory arrest under varying conditions with continuous monitoring by means of near-infrared spectroscopy (hematocrit level of 20% or 30%; pH-stat or alpha-stat strategy; temperature of 15 degrees C or 25 degrees C; arrest time of 60, 80, or 100 minutes). Neurologic recovery was evaluated daily by a veterinarian, and the brain was fixed in situ on postoperative day 4 to be examined on the basis of histologic score in a blinded fashion.

RESULTS

Multivariable analysis of total histologic score revealed that higher temperature, lower hematocrit level, more alkaline pH, and longer hypothermic circulatory arrest duration were predictive of more severe damage to the brain (P <.01). Regression modeling revealed that higher temperature exacerbated the disadvantage of a lower hematocrit level and longer arrest times but not pH strategy. Normalized oxyhemoglobin nadir time, derived from near-infrared spectroscopy, was positively correlated with neurologic recovery on the fourth postoperative day and with total histologic injury score (P <.0001).

CONCLUSION

Hematocrit level and pH, as well as temperature, determine the safe duration of hypothermic circulatory arrest. Near-infrared spectroscopy is a useful real-time monitor of safe duration of circulatory arrest.

Cardiopulmonary bypass in infants and children

Cardiopulmonary bypass (CPB) systems have evolved from futuristic visions of surgical pioneers to a safe and efficient tool in the therapy of treatment of cardiac disorders. There are many significant differences in the physiology between neonates and adult patients. There are currently very few congenital cardiac malformations that cannot be addressed effectively with surgical therapy. Yet, the necessity of CPB in the repair of these patients can still result in significant morbidity. A clearer understanding of the effects of CPB, hypothermia, and circulatory arrest is evolving and there is a considerable amount of research in these areas. It seems likely that modification of current CPB systems, minimization of exposure, and surgical techniques to avoid or limit the adverse effects may reduce mortality and morbidity in the future. The problems faced in these complex patients and procedures require that infant and neonatal cardiac surgery be performed in specialized centers with a multidisciplinary approach and specialized personnel. Future improvements in technology will likely result in improved long term outcome for children with congenital cardiac disease. Copyright 2000 by W.B. Saunders Company

Prediction of safe duration of hypothermic circulatory arrest by near-infrared spectroscopy

OBJECTIVE

Hypothermic circulatory arrest is widely used for adults with aortic arch disease as well as for children with congenital heart disease. At present, no method exists for monitoring safe duration of circulatory arrest. Near-infrared spectroscopy is a new technique for noninvasive monitoring of cerebral oxygenation and energy state. In the current study, the relationship between near-infrared spectroscopy data and neurologic outcome was evaluated in a survival piglet model with hypothermic circulatory arrest.

METHODS

Thirty-six piglets (9.36 +/- 0.16 kg) underwent circulatory arrest under varying conditions with continuous monitoring by near-infrared spectroscopy (temperature 15 degrees C or 25 degrees C, hematocrit value 20% or 30%, circulatory arrest time 60, 80, or 100 minutes). Each setting included 3 animals. Neurologic recovery was evaluated daily by neurologic deficit score and overall performance category. Brain was fixed in situ on postoperative day 4 and examined by histologic score.

RESULTS

Oxygenated hemoglobin signal declined to a plateau (nadir) during circulatory arrest. Time to nadir was significantly shorter with lower hematocrit value (P <.001) and higher temperature (P <.01). Duration from reaching nadir until reperfusion ("oxygenated hemoglobin signal nadir time") was significantly related to histologic score (r (s) = 0.826), neurologic deficit score (r (s) = 0.717 on postoperative day 1; 0.716 on postoperative day 4), and overall performance category (r (s) = 0.642 on postoperative day 1; 0.702 on postoperative day 4) (P <.001). All animals in which oxygenated hemoglobin signal nadir time was less than 25 minutes were free of behavioral or histologic evidence of brain injury.

CONCLUSION

Oxygenated hemoglobin signal nadir time determined by near-infrared spectroscopy monitoring is a useful predictor of safe duration of circulatory arrest. Safe duration of hypothermic circulatory arrest is strongly influenced by perfusate hematocrit value and temperature during circulatory arrest.

Neonatal cerebral oxygen regulation after hypothermic cardiopulmonary bypass and circulatory arrest

OBJECTIVE

Despite technical advances, neurologic sequelae continue to occur in neonates after heart surgery using deep hypothermic cardiopulmonary bypass (dhCPB) and circulatory arrest (DHCA). This study sought to determine the cerebral microcirculatory responses to hypoxia, hypotension, hypocapnia, and hypercapnia after dhCPB and DHCA.

DESIGN

Prospective laboratory animal trial.

SETTING

Research laboratory.

SUBJECTS

Twenty-eight newborn pigs.

INTERVENTIONS

Piglets were divided into control, dhCPB, and DHCA groups. The control group received surgery. The dhCPB group received surgery and deep hypothermic CPB for 40 mins. The DHCA group received surgery, deep hypothermic CPB for 40 mins, and circulatory arrest for 60 mins. Two hours after the intervention, cerebral microcirculatory responses were examined.

MEASUREMENTS AND MAIN RESULTS

Cerebral microcirculatory responses consisted of changes in cerebral oxygen saturation (Sco2) and pial arteriolar diameter measured by near- infrared spectroscopy and intravital microscopy, respectively. All groups experienced similar decreases in Sco2 and increases in pial arteriolar diameter in response to moderate and severe hypoxia (Pao2, 35 and 25 torr, respectively) and moderate and severe hypotension (mean pressure, 30 and 20 mm Hg, respectively). Sco2 and pial arteriolar diameter decreased to hypocapnia (Paco2, 25 torr) similarly in all groups. To hypercapnia (Paco2, 70 torr), Sco2 increased in the control group, did not change in the dhCPB group, and decreased in the DHCA group. Pial arteriolar diameter to hypercapnia increased in the control and the dhCPB groups but did not change in the DHCA group.

CONCLUSIONS

Cerebral vascular and oxygenation responses to hypoxia, hypocapnia, and hypotension were preserved after dhCPB and 1 hr of DHCA. By comparison, cerebral vascular and oxygenation responses to hypercapnia were not; both vascular and oxygenation responses were altered after DHCA, but only the oxygenation response was altered after dhCPB. These data suggest a selective disturbance in the microcirculation and/or parenchymal oxygen metabolism after DHCA and dhCPB.

Intermittent perfusion protects the brain during deep hypothermic circulatory arrest

BACKGROUND

Deep hypothermic circulatory arrest (DHCA) has been shown to cause impairment in recovery of cerebral blood flow (CBF) and cerebral metabolism (CMRO2) proportional to the duration of the DHCA period. This effect on CMRO2 may be a marker for brain injury, because CMRO2 recovers normally after cardiopulmonary bypass (CPB) when DHCA is not used. The aim of this study was to investigate the effects of intermittent perfusion during DHCA on the recovery of CMRO2 after CPB and to correlate these findings with electron microscopy (EM) of the cerebral microcirculatory bed.

METHODS

Fifteen neonatal piglets were placed on CPB and cooled to 18 degrees C. Each animal then underwent either: (1) 60 minute continuous CPB (control), (2) 60 minute uninterrupted DHCA (UI-DHCA), or (3) 60 minute DHCA with intermittent perfusion (1 minute every 15 minutes) (I-DHCA). All animals were then rewarmed and weaned from CPB. Measurements of CBF and CMRO2 were taken before and after CPB. A further 9 animals underwent CPB without DHCA (2 animals) or with DHCA (7 animals), under various conditions of arterial blood gas management, intermittent perfusion, and reperfusion time.

RESULTS

UI-DHCA resulted in significant impairment to recovery of CMRO2 after CPB (p < 0.05). Regardless of the blood gas strategy used, the EM after UI-DHCA revealed extensive damage characterized by perivascular intracellular and organelle edema, and vascular collapse. I-DHCA, on the other hand, produced a pattern of normal CMRO2 recovery identical to controls, and the EM was normal for both these groups.

CONCLUSIONS

Intermittent perfusion during DHCA is clinically practical and results in normal cerebral metabolic and ultrastructural recovery. Furthermore, the correlation between brain structure and CMRO2 suggests that monitoring CMRO2 during the operation may be an outstanding way to investigate new strategies for neuroprotection designed to reduce cerebral damage in children undergoing correction of congenital cardiac defects.

Mild hypothermia for temporary brain ischemia during cardiopulmonary support systems: report of three cases

Recovery without residual neurological damage after cardiac arrest with temporary cerebral ischemia is rare. Therefore, it is most important that every effort is made to prevent brain damage occurring immediately after successful cardiopulmonary resuscitation. We report herein the cases of three patients who suffered either cardiogenic or hypovolemic shock and were resuscitated by a cardiopulmonary support system followed by mild hypothermia. All three patients recovered completely without any neurologic damage. The outcomes of these three patients demonstrated that mild hypothermia may be important for cerebral preservation after cardiopulmonary resuscitation.

Retrograde cerebral perfusion provides limited distribution of blood to the brain: a study in pigs

OBJECTIVE

The objective of this study was to investigate flow distribution during retrograde and antegrade cerebral perfusion with India ink as a marker.

METHODS

Ten pigs received cerebral perfusion with a solution containing 50% filtered India ink for 5 minutes either antegradely through both internal carotid arteries at a flow of 180 to 200 ml/min (n = 5) or retrogradely via the superior vena cava at a flow of 300 to 500 ml/min (n = 5). The brains were then fixed for quantitative measurement of the density of ink-filled capillaries (reported as a percentage of the total selected area). The assessment was done with the use of an in-house software program.

RESULTS

In the antegrade cerebral perfusion group, the intracranial arterial and venous systems were completely filled with ink. The gray matter was colored uniformly black, and light coloring was observed in the white matter. During retrograde cerebral perfusion, the majority of ink was returned to the inferior vena cava, and only a small amount of ink was found in the innominate artery draining from the brain. Massive ink filling was observed in the sagittal sinus and other venous sinuses in all the pigs. Vessels on the surface of the brain and large vessels in the brain were also well filled with ink. However, only 10% of capillaries were filled with ink during retrograde cerebral perfusion relative to the number observed with antegrade cerebral perfusion.

CONCLUSIONS

Retrograde cerebral perfusion supplies a limited amount of blood to brain tissue, which flows mainly through superficial and large deep cerebral vessels.

Morphological investigation of the neuroprotective effects of graded hypothermia after diverse periods of global cerebral ischemia in gerbils

Hypothermia is known to be the most effective method to protect the neuronal damage induced by ischemia. In the present study, we investigated the histopathological consequences of hippocampal CA1 pyramidal neurons as well as the glial reactions in the hippocampus, after diverse periods of ischemic insult at graded intra-ischemic hypothermia ranging from 32 to 20 degrees C. Gerbils were exposed to forebrain ischemia by clamping the bilateral common carotid arteries for 5-120 min depending upon the temperatures. The morphological study was performed 7 days after ischemia or sham-operation. Histopathological evaluation of delayed neuronal death (DND) was performed by Cresyl violet (CV) staining and MAP2 immunoreactivity. Glial reactions were examined by GFAP immunostaining and isolectin B4 histochemistry, corresponding to astrocytes and microglia, respectively. The forebrain ischemia at 32 degrees C for 10 min and at 28 degrees C for 20 min did not induce DND in the CA1 region. However, the ischemia at 32 degrees C for 20 min and at 28 degrees C for 30 min caused extensive degeneration of CA1 pyramidal neurons as observed in normothermic ischemic animals. Under the condition of deep hypothermia, the ischemia for 60 min at 24 degrees C and for 120 min at 20 degrees C which were the longest durations of each temperature within the limitation of the animal survival following 7 days, induced no DND in CA1 pyramidal neurons. The reactive changes of astrocytes were observed not only in ischemic animals with DND, but also in ischemic animals without DND. Computer image analysis showed that the area fraction of GFAP-positive structures in the CA1 region was significantly increased in both ischemic cases with and without DND compared with each sham group. In contrast, the distribution of activated microglia was much more restricted to the CA1 region and they were always accompanied by DND at 7 days postischemia. The present results demonstrate the remarkable neuroprotective effect of deep hypothermia that has been widely used in cardiovascular surgeries as the cerebroprotective strategy during total circulatory cessation. The findings also suggest that even under the condition of hypothermia, glial reactions may play an important role in neuronal survival and death after ischemia.

The effect of circulatory arrest and retrograde cerebral perfusion on microtubule-associated protein 2: an immunohistochemical study in pig hippocampus

Microtubule-associated protein 2 (MAP2) immunohistochemical labeling in the hippocampus was studied to assess the protective effect of brain perfusion during surgery requiring hypothermic circulatory arrest in 24 pigs exposed to anesthesia alone (control), 120 min of complete circulatory arrest at 15 degrees C, min of retrograde cerebral perfusion at 15 degrees C, or 120 min of anterograde cerebral perfusion at 15 degrees C. Pigs were reperfused for 60 min and sacrificed. In the control anterograde perfusion groups, the intensity of MAP2 labeling was similar in all regions of the hippocampus. Circulatory arrest and retrograde perfusion resulted in significant reduction of MAP2 labeling (28% and 38% respectively of control, P < 0.001) of neurons in the CA1 region. MAP2 labeling may be useful for assessing early damage in the hippocampus in this model.

Neuronal damage after hypothermic circulatory arrest and retrograde cerebral perfusion in the pig

BACKGROUND

Antegrade and retrograde cerebral perfusion during hypothermic circulatory arrest (HCA) has been reported to provide better brain protection during operation than hypothermic circulatory arrest alone. However, the efficacy of these techniques remains to be fully determined, especially when used for prolonged periods. We used a pig model to evaluate the histopathologic consequences of HCA and the potential benefit of cerebral perfusion during HCA.

METHODS

Twenty-two pigs were divided into four groups and exposed to either anesthesia alone, 120 minutes of HCA (15 degrees C), 120 minutes of retrograde cerebral perfusion at 15 degrees C during HCA, or 120 minutes of antegrade cerebral perfusion at 15 degrees C during HCA, and then reperfused for 60 minutes under cardiopulmonary bypass at 37 degrees C. The brains were perfusion fixed at the end of the experiments and examined by light microscopy.

RESULTS

There were no morphologic changes in any areas of the brains in the anesthesia group, and very minor changes in some areas of the brains in the antegrade cerebral perfusion. group. Varying severity of neuronal damage was found in the brains of all the pigs in the HCA and retrograde cerebral perfusion groups. The severity of ischemic damage in the brain showed the following descending order: hippocampus (CA4), caudate nucleus, cerebral cortex, putamen, thalamus, Purkinje cells of the cerebellum, pons, and mesencephalic gray matter. In the hippocampus the order of damage was CA4, CA3, polymorphous layer of the dentate gyrus, prosubiculum, CA2, CA1, and granule cell layer of the dentate gyrus. The damage in the retrograde cerebral perfusion group was less severe relative to the HCA group in many areas (no significance except mesencephalic gray matter).

CONCLUSIONS

These results demonstrate that the pattern of neuronal damage in pigs subjected to HCA and retrograde cerebral perfusion differs from the traditional pattern in that the caudate nucleus and hippocampal CA4 region are the most vulnerable to ischemia-hypoxia. Our results also suggest that antegrade cerebral perfusion prevented ischemic damage to the brain and retrograde cerebral perfusion provided some protection but moderately severe damage occurred.

Retrograde cerebral perfusion does not perfuse the brain in nonhuman primates

BACKGROUND

Recently retrograde cerebral perfusion (RCP) has been advocated as an alternative to complete circulatory arrest during aortic arch surgery.

METHODS

In 19 baboons, we compared brain protection using hypothermic circulatory arrest or RCP. Animals were placed on cardiopulmonary bypass, cooled to 18 degrees C, underwent 1 hour of circulatory arrest or RCP, and were reperfused for 3 hours. Biochemical variables, cerebral blood flow (colored microsphere technique), and brain histology were assessed.

RESULTS

Release of the brain-specific ischemic marker CK-BB was similar in both groups (peak values, 123 +/- 97 U/L in the circulatory arrest group and 164 +/- 88 U/L in the RCP group; p > 0.05), as were the arteriovenous differences in glucose uptake and lactate production (p > 0.05). During RCP, significant brain flow could not be detected (0.5 +/- 0.5 mL.min-1 x 100 g-1). About 90% of the blood was shunted to the inferior caval vein, and an equilibrium in circulating microspheres was found between RCP inflow and caval vein outflow. Less than 1% of the RCP inflow returned to the aortic arch. Histologic signs of brain damage were minimal in both groups, although slightly more glial edema was found in the RCP group.

CONCLUSIONS

These data suggest that in nonhuman primates, retrograde cerebral perfusion does not perfuse the brain because of venovenous shunting.

The role of CPB management in neurobehavioral outcomes after cardiac surgery

Recent developments in techniques for managing cardiopulmonary bypass are outlined with a view toward interventions aimed at decreasing the incidence of perioperative central nervous system dysfunction and overt stroke. Recent reports assessing central nervous system dysfunction after hypothermic and normothermic cardiopulmonary bypass are reviewed and critiqued along with data assessing techniques for cerebral protection during hypothermic circulatory arrest. Controversy surrounding optimal pH management is explored along with a proposal that pH-stat may be most satisfactory to ensure better brain cooling where circulatory arrest is anticipated, whereas alpha-stat may avoid cerebral hyperemia and thus decrease the cerebral embolic load during moderate hypothermic cardiopulmonary bypass. Newer developments in cerebral monitoring techniques are also reviewed.

Long-term neurologic outcome after cardiac operation

Cardiac surgical patients face the threat of neurologic complications in all phases of their disease and its treatment. The incidence of preoperative transient ischemic attacks and stroke ranges from 5% to 14% and from 2% to 11%, respectively. The risk of preoperative cerebrovascular accidents is higher in patients with valvular disease than in those with coronary artery disease. The prevalence of postoperative neurologic disorders varies widely because of differences in defining the clinical criteria, heterogeneity of patient populations, timing of evaluation, follow-up times, study designs, and surgical and anesthesia-related procedures. Fatal cerebral damage is very rare (< 0.1%). Focal cerebral deficits, or definite stroke, are encountered in 1% to 3% of patients and minor clinical abnormalities, in 5% to 10%. Recent studies have shown that contrary to previous concepts, valve replacement does not carry essentially higher neurologic risks than coronary bypass grafting. The most common causes of operation-related neurologic disorders are microembolization or macroembolization and hypoperfusion. Although most disorders resolve early postoperatively, some deficits persist. From the neurologic standpoint, a main objective of a cardiac surgical intervention is to prevent stroke. Today, the incidence of cardiogenic cerebrovascular accidents is very low after reparative cardiac procedures. Despite surgical and anesthesia-related improvements, neurologic complications do occur. Multidimensional investigatory procedures have shown that cardiopulmonary bypass often causes cerebral dysfunction. Whether the harmful consequences are detected depends on the evaluation criteria and the investigatory methods and timing used. Further methods are needed to prevent or treat preoperative cerebrovascular accidents and particularly to improve cerebral protection during operative procedures.

Retrograde cerebral perfusion during profound hypothermia and circulatory arrest in pigs

The purpose of this study was to evaluate the use of retrograde cerebral perfusion via the superior vena cava during profound hypothermia and circulatory arrest (CA) in pigs. In three groups of 5 pigs each, group A (control) underwent cardiopulmonary bypass and normothermic CA for 1 hour, group B underwent cardiopulmonary bypass, profound hypothermia, and CA (15 degrees C nasopharyngeal) for 1 hour, and group C underwent the same procedure as group B plus retrograde cerebral perfusion. In group A none awoke. In group B, 2 of 5 did not awake and 3 of 5 awoke unable to stand, 2 with perceptive hind limb movement and 1 moving all extremities. In group C all awoke, 4 of 5 able to stand and 1 of 5 unable to stand but moving all limbs. In neurologic evaluation group B had significantly lower Tarlov scores than group C (p = 0.0090). Group B mean wake-up time, plus or minus standard error of the mean, was 124.6 +/- 4.6 minutes versus 29.2 +/- 5.1 in group C (p = 0.0090). In group B late phase CA cerebral blood flow dropped 30.9% +/- 4.8%, but in group C it rose 24.7% +/- 9.3% (p = 0.0007, pooled variance t test, two-tailed). In group B late phase CA brain oxygenation decreased 46.0% +/- 13.9% but it increased 26.1% +/- 5.4% in group C (p = 0.0013). This difference was reduced somewhat during rewarming (B, -21.2% +/- 14.9%; C, 16.4% +/- 4.7%; p = 0.043). Group B rewarming jugular venous O2 saturation was 30.8% +/- 2.5% versus 56.0% +/- 4.4% in group C (p = 0.0011). We conclude that in pigs retrograde cerebral perfusion combined with profound hypothermia during CA significantly reduces neurologic dysfunction, providing superior brain protection.

Total arch graft replacement in patients with acute type A aortic dissection

Treatment of acute type A aortic dissection with emergency total aortic arch graft replacement remains controversial. Between December 1988 and July 1993, 30 patients with this fatal disease underwent graft replacement of both the ascending aorta and total aortic arch on an emergency basis. All operations were performed with the aid of extracorporeal circulation, blood cardioplegia, selective cerebral perfusion, and open distal anastomosis. The overall early mortality rate was 23.3% (7 patients), but that in patients with complications with shock and renal/mesenteric ischemia was 57% and 66.7%, respectively. On the other hand, the mortality rate in the 23 patients (77%) in whom neither of these two risk factors was present was low (8.7%). The overall 4-year survival rate was 66.5% +/- 8.7%, and that for patients without these two risk factors was 87.0% +/- 7.0%. The present data suggest that simultaneous total arch replacement may be justified in selected patients with acute type A aortic dissection.

The use of somatosensory evoked potentials to determine the optimal degree of hypothermia during circulatory arrest

We sequentially recorded subcortical (P14) and cortical (N20) somatosensory evoked potentials (SEPs) in 32 patients undergoing deep hypothermic circulatory arrest (CA). Under normal hemodynamic conditions, hypothermia initially produced N20 disappearance at a mean nasopharyngeal temperature of 20.4 +/- 2.6 degrees C (range 14.5 to 26.1 degrees C) and P14 disappearance at a mean of 16.9 +/- 2.0 degrees C (range 12.4 to 20.2 degrees C). On rewarming, P14 reappeared at mean temperature of 19.3 +/- 4.0 degrees C (range 13.5 to 29.2 degrees C) and N20 at a mean of 21.1 +/- 4.1 degrees C (range 14.3 to 29.6 degrees C). The delay of SEP reappearance after restoration of blood flow correlated significantly with CA duration (r = 0.74 for P14, and r = 0.62 for N20; p < 0.01). Neurological recovery was uneventful in 23 patients; 5 patients presented with neurological sequelae (minor or transient in 4; no recovery from anesthesia and death after 48 hours in 1), and 4 patients died during operation. Twenty-three of 24 surviving patients in whom P14 disappearance was the criterion that hypothermia was deep enough to perform CA (duration: 17 to 94 min) had a normal neurological outcome. By contrast, all surviving patients in whom cortical SEPs disappeared at higher temperatures presented neurological sequelae. In conclusion, the neurophysiological monitoring of brain stem activity, as specifically provided by SEPs, enables determination of the optimal temperature for CA, and demonstrates superiority of SEP monitoring over the use of EEG.