The effects of a leukocyte-depleting filter on cerebral and renal recovery after deep hypothermic circulatory arrest

Factors influencing neurologic outcome after neonatal cardiopulmonary bypass: what we can and cannot control

Advances in cardiopulmonary bypass and surgical techniques have led to progress in the early repair of congenital heart defects in children. However, as increasing numbers survive their initial cardiac operation, an awareness is emerging that significant early and late neurologic morbidities continue to complicate otherwise successful operative repairs. Adverse neurologic outcomes after neonatal cardiac surgery are multifactorial and relate to both fixed and modifiable mechanisms. The purpose of this review is to (1) review mechanisms of brain injury after neonatal cardiopulmonary bypass, (2) examine risk factors, and (3) speculate on how investigations may improve our understanding of neurologic injury.

The Use of a Miniaturized Circuit and Bloodless Prime To Avoid Cerebral No-Reflow After Neonatal Cardiopulmonary Bypass

BACKGROUND

Our miniaturized bloodless prime circuit for neonatal cardiopulmonary bypass (CPB) has previously been shown to elicit significantly reduced systemic inflammation. We studied the effects of this circuit on cerebral reperfusion because the pathophysiology of "no-reflow" is believed to have an inflammatory component.

METHODS

Twenty neonatal piglets were randomized to CPB with miniaturized circuitry using either blood (group 1) or bloodless (group 2) prime. At 18 degrees C, piglets underwent 60 minutes of either (A) deep hypothermic circulatory arrest (DHCA) or (B) continuous low-flow bypass (DHCLF). Analysis of cerebral blood flow (CBF) was undertaken before and after CPB in addition to quantification of circulating tumor necrosis factor-alpha (TNFalpha) and intracerebral TNFalpha messenger RNA (mRNA).

RESULTS

The final hematocrit in group 2 was 22% versus 28% (p < 0.05). The CBF fell in every animal in group 1A, but increased in every animal in group 2A (p < 0.001), despite no overall change in total cardiac output. The use of DHCLF was not associated with pronounced trends in either prime group. Final serum TNFalpha concentrations were significantly higher in group 1B (3166 +/- 843 pg/mL) than group 2B (439 +/- 192 pg/mL; p < 0.05). Irrespective of the CPB strategy used, the use of a blood prime generated significantly higher levels of intracerebral TNFalpha mRNA.

CONCLUSIONS

We attribute the hyperemic cerebrovascular response to reduced inflammation through avoiding allogeneic whole blood. The analysis of circulating and intracerebral TNFalpha in this study suggests that DHCLF in conjunction with a bloodless prime might offer advantages through avoiding ischemia, no-reflow, and in addition, resulting in a significantly reduced cerebral inflammatory response.

Reperfusion injury following cerebral ischemia: pathophysiology, MR imaging, and potential therapies

Introduction

Restoration of blood flow following ischemic stroke can be achieved by means of thrombolysis or mechanical recanalization. However, for some patients, reperfusion may exacerbate the injury initially caused by ischemia, producing a so-called “cerebral reperfusion injury”. Multiple pathological processes are involved in this injury, including leukocyte infiltration, platelet and complement activation, postischemic hyperperfusion, and breakdown of the blood–brain barrier.

Methods/results and conclusions

Magnetic resonance imaging (MRI) can provide extensive information on this process of injury, and may have a role in the future in stratifying patients’ risk for reperfusion injury following recanalization. Moreover, different MRI modalities can be used to investigate the various mechanisms of reperfusion injury. Antileukocyte antibodies, brain cooling and conditioned blood reperfusion are potential therapeutic strategies for lessening or eliminating reperfusion injury, and interventionalists may play a role in the future in using some of these therapies in combination with thrombolysis or embolectomy. The present review summarizes the mechanisms of reperfusion injury and focuses on the way each of those mechanisms can be evaluated by different MRI modalities. The potential therapeutic strategies are also discussed.

Effects of Circuit Miniaturization in Reducing Inflammatory Response to Infant Cardiopulmonary Bypass by Elimination of Allogeneic Blood Products

Conventional neonatal cardiopulmonary bypass requires the use of large volumes of allogeneic blood to prevent unacceptable hemodilution. Evidence is accumulating to suggest that the use of blood products during cardiopulmonary bypass has a negative effect on clinical recovery through inflammatory side effects. This would suggest an advantage for eliminating blood use in infant cardiopulmonary bypass through circuit miniaturization. In this article, we review the data supporting this rationale and provide the results from studies in our laboratory that emphasize the benefits of circuit miniaturization.

Neonatal Brain Protection and Deep Hypothermic Circulatory Arrest: Pathophysiology of Ischemic Neuronal Injury and Protective Strategies

Deep hypothermic circulatory arrest (DHCA) has been used for the past 50 years in the surgical repair of complex congenital cardiac malformations and operations involving the aortic arch; it enables the surgeon to achieve precise anatomical reconstructions by creating a bloodless operative field. Nevertheless, DHCA has been associated with immediate and late neurodevelopmental morbidities. This review provides an overview of the pathophysiology of neonatal hypoxic brain injury after DHCA, focusing on cellular mechanisms of necrosis, apoptosis, and glutamate excitotoxicity. Techniques and strategies in neonatal brain protection include hypothermia, acid base blood gas management during cooling, and pharmacologic interventions such as the use of volatile anesthetics. Surgical techniques consist of intermittent cerebral perfusion during periods of circulatory arrest and continuous regional brain perfusion.

Partial Clamping of the Brachiocephalic Trunk for Total Ascending Aorta Replacement without Circulatory Arrest: Early and Midterm Results

BACKGROUND

The aim of this study was to evaluate in elective patients the early and midterm results of partial clamping of the brachiocephalic trunk (BCT) for total ascending aorta replacement (TAAR) without circulatory arrest. Contraindications to the procedure were BCT/aortic arch calcifications and chronic aortic dissection.

METHODS

The right radial artery was cannulated to monitor the systemic pressure after the BCT was partially clamped. A specially designed clamp was applied obliquely to occlude approximately 50% of the BCT and part of the aortic arch. The distal tip of the clamp was positioned in front of the left subclavian artery. From January 2002 to October 2003, 92 patients underwent TAAR. In 62 patients (67.4%), partial clamping of the BCT was used. Twenty of these patients underwent isolated TAAR, 27 underwent aortic valve replacement and TAAR, 11 had a Bentall operation, and 2 had a Cabrol operation. The aortic valve was spared in the remaining 2 patients. The mean (+/- SD) aortic cross-clamping and cardiopulmonary bypass times were 96 +/- 31 minutes and 116 +/- 43 minutes, respectively.

RESULTS

Early mortality was 1.6% (1 patient). No cerebrovascular accidents occurred, demonstrating the safety of the technique. The major complications were acute respiratory insufficiency in 2 cases and acute renal failure in 5. The mean follow-up time was 9.0 +/- 6.5 months. The mean 18- month and event-free survival rate was 96.6% +/- 0.9%.

CONCLUSION

Partial clamping of the BCT for TAAR without circulatory arrest provides good early and midterm clinical results. Aortic arch clamping is not associated with cerebrovascular accidents.

Adverse effects of low hematocrit during cardiopulmonary bypass in the adult: should current practice be changed?

BACKGROUND

Hemodilutional anemia during cardiopulmonary bypass can lead to inadequate oxygen delivery and, consequently, to ischemic organ injury. In adult bypass, the nadir hematocrit can vary widely with body size and prebypass hematocrit variations, yet its effects on perioperative organ dysfunction and patient outcomes remain largely unknown.

METHODS

To elucidate these effects, we retrospectively analyzed operative results and resource utilization data from 5000 consecutive cardiac operations with cardiopulmonary bypass performed on adults (1994 to 2000). Rolling decile groups (500 patients each; 75% overlapping) of increasing lowest hematocrit values were used to characterize hemodilution-outcome relationships. Intermediate-term (0 to 6 years) survival was assessed for coronary artery bypass patients (n = 3800) via Kaplan-Meier analysis in quintile subgroups based on lowest hematocrit. Multivariate logistic regression (operative mortality and morbidity) and Cox proportional hazard model (0- to 6-year mortality) analyses were used to determine independent predictors of poor outcomes.

RESULTS

Stroke, myocardial infarction, low cardiac output, cardiac arrest, renal failure, prolonged ventilation, pulmonary edema, reoperation due to bleeding, sepsis, and multiorgan failure were all significantly and systematically increased as lowest hematocrit value decreased below 22%. Consequently, intensive care requirements, hospital stays, operative costs, and operative deaths were also significantly greater as a function of hemodilution severity. Longer-term survival was improved systematically for increasing lowest hematocrit coronary artery bypass grafting quintiles; for example, 6-year survival was 80.5% and 92.3% for quintiles I (lowest hematocrit = 16.1%) and V (lowest hematocrit = 27.5%). The continuous variable lowest hematocrit was an independent predictor of (1) operative mortality, (2) prolonged cardiovascular intensive case (>2 days) and postoperative hospital (>8 days) stays, and (3) worse 0- to 6-year survival.

CONCLUSIONS

Increased hemodilution severity during cardiopulmonary bypass was associated with worse perioperative vital organ dysfunction/morbidity and increased resource use, as well as greater short- and intermediate-term mortality. We speculate that these results derive from inadequate oxygen delivery causing ischemic and/or inflammatory vital organ injury, as recently demonstrated intravitally in cerebral tissues. Although this analysis of a large observational study offers evidence linking low on-pump hematocrit values to these adverse outcomes, prospective randomized trials are needed (1) to establish whether a causal effect of hemodilution on poor outcomes actually exists and (2) to test the potential efficacy of maintaining on-pump hematocrit above 22% for improving outcomes of cardiopulmonary bypass.

Leukodepletion reduces renal injury in coronary revascularization: a prospective randomized study

BACKGROUND

Cardiopulmonary bypass (CPB) is an important contributor to renal failure, which is a well-recognized complication after coronary artery bypass grafting (CABG). Leukodepletion reduces CPB-associated inflammation and resultant end-organ injuries. However, its effectiveness in renal protection has not been evaluated in a prospective randomized clinical setting.

METHODS

Forty low-risk patients awaiting elective CABG with normal preoperative cardiac and renal function were prospectively randomized into those undergoing nonpulsatile CPB without (group A: n = 20) and with leukodepletion (group B: n = 20). Renal glomerular and tubular injury were assessed by urinary excretion of microalbumin and retinol binding protein (RBP) indexed to creatinine (Cr), respectively. Daily measurements were taken from admission to postoperative day 5. Fluid balance, serum creatinine, and blood urea were also monitored.

RESULTS

No mortality or renal complication occurred. Both groups had similar demographic makeups, Parsonnet scores, extents of coronary revascularization and, durations of CPB and aortic cross-clamping. Daily fluid balance, serum creatinine, and blood urea remained comparable in both groups throughout the study period. From equal preoperative values, a significantly higher release of urinary RBP:Cr (7,807 +/- 2,227 vs 3,942 +/- 2,528; p < 0.001) and urinary microalbumin:Cr (59.4 +/- 38.0 vs 4.7 +/- 6.7; p < 0.0001) occurred in group A, peaking on day 1 before returning to approximate baseline levels.

CONCLUSIONS

Although clinically overt renal complications were absent, sensitive indicators revealed significantly more injury to both renal tubules and glomeruli after nonpulsatile CPB without leukodepletion. These data suggest that leukocytes play an important role in post-CPB renal dysfunction, and leukodepletion may offer some renal protection in low-risk patients during CABG.

A comparison of complete blood replacement with varying hematocrit levels on neurological recovery in a porcine model of profound hypothermic (<5 degrees C) circulatory arrest

Profound hypothermia (<5 degrees C) may afford better neurological protection after circulatory arrest; however, there are theoretical concerns related to microcirculatory sludging of blood components at these ultra-low temperatures. We hypothesized that at temperatures <5 degrees C, complete blood replacement results in superior neurological outcome. Twelve Yorkshire pigs (30 kg) underwent thoracotomy, cardiopulmonary bypass (CPB), and were randomly assigned to one of three target hematocrits during circulatory arrest: 0%, 5%, 15%. Hextend (6% hetastarch in a balanced electrolyte vehicle) was used for the CPB prime and as an exchange fluid. Animals were cooled to a temperature <5 degrees C, underwent 1-h circulatory arrest, and were warmed to 35 degrees C with administration of blood to increase the hematocrit to >25% before separation from CPB. The primary outcome, peak postoperative neurobehavioral score, was compared between groups. The 0% group (mean +/- SD) had significantly (P: < 0.02) better neurobehavioral scores than the 5% and 15% groups (6.0 +/- 2.9 vs 1.3 +/- 1.0 and 1.5 +/- 0.6) respectively. Other variables (e.g., intracranial pressure) were similar between groups. In a porcine model of profound hypothermia (<5 degrees C) and circulatory arrest, complete blood replacement resulted in superior neurological outcome. This finding suggests that at ultralow temperatures, the presence of some blood component (e.g., erythrocytes, leukocytes) may be deleterious.