Relationship between cardiopulmonary bypass flow rate and cerebral embolization in dogs

Improving Trendelenburg position effectiveness by varying cardiopulmonary bypass flow

INTRODUCTION

Trendelenburg position (TP) is used to transport gaseous emboli away from the cerebral region during cardiac surgery. However, TP effectiveness has not been fully considered when combined with varying the cardiopulmonary bypass (CPB) flow. This study simulated the supine and TP at different pump flows and assessed the trapped emboli and embolic load entering the aortic arch branch arteries (AABA).

METHODS

A computational fluid dynamics (CFD) approach used a centrally cannulated adult patient-specific aorta model replicating a CPB circuit. Air emboli of 0.1 mm, 0.5 mm, and 1.0 mm (n = 700 each) were injected into the aorta placed in the supine position (0°) and the TP (-20°) at 2 L/min and 5 L/min. The number of emboli entering the AABA were compared. An aortic phantom flow experiment was performed to validate air bubble behaviour.

RESULTS

TP at 5 L/min had the lowest 0.1 mm mean (±SD) embolic load compared to the supine 2 L/min (55.3 ± 30.8 vs 64.3 ± 35.4). For both the supine and TP, the lower flow of 2 L/min had the highest number of simulated trapped emboli in higher elevated regions than at 5 L/min (541 ± 185 and 548 ± 191 vs 520 ± 159 and 512 ± 174), respectively. The flow experiment demonstrated that 2 L/min promoted bubble coalescence and high amounts of trapped emboli and 5 L/min transported air emboli away from the AABA.

CONCLUSIONS

TP effectiveness was improved by using CPB flow to manage air emboli. These results provide insights for predicting emboli behaviour and improving emboli de-airing procedures.

Effect of aortic cannulation depth on air emboli transport during cardiopulmonary bypass: A computational study

Introduction

Varying the insertion depth of the aortic cannula during cardiopulmonary bypass (CPB) has been investigated as a strategy to mitigate cerebral emboli, yet its effectiveness associated with CPB flow is not fully understood. We compared different arterial cannula insertion depths and pump flow influencing air microemboli entering the aortic arch branch arteries (AABA).

Methods

A computational approach used a patient-specific aorta model to evaluate four cannula locations at (1) proximal arch, (2) mid arch, (3) distal arch, and (4) descending aorta. We injected 0.1 mm microemboli (N=720) at 2 and 5 L/min and assessed the embolic load and the particle averaged transit times ( entering the AABA.

Results

Location 4 had the lowest embolic load (2 L/min: N= 63) and (5 L/min: N= 54) compared to locations 1 to 3 in the range of (N= 118 to 116 at 2 L/min:) and (N= 92 to 146 at 5 L/min). There was no significant difference between 2 L/min and 5 L/min (p = 0.31), despite 5 L/min attaining a lower mean (±standard deviation) than 2 L/min (38.0±23.4 vs 44.5±21.1), respectively. Progressing from location 1 to 4, increased 3.11s -7.40 s at 2 L/min and 1.81s -4.18s at 5 L/min.

Conclusion

It was demonstrated that the elongated cannula insertion length resulted in lower embolic loads, particularly at a higher flow rate. The numerical results suggest that CPB management could combine active flow variation with improving cannula performance and provide a foundation for a future experimental and clinical investigation to reduce surgical cerebral air microemboli.

Manual Carotid Compression is a Viable Alternative for Reduction of Cerebral Microemboli

BACKGROUND

Stroke is a devastating complication of cardiovascular surgeries, and the risk is particularly high for those requiring cardiopulmonary bypass (CPB). Embolic particles generated during the unclamping of the aortic cross-clamp may enter the cerebral circulation, lodging in small vessels. External manual compression of the carotid arteries is a non-invasive technique that has been proposed for cerebral protection during CPB procedures but is not widely deployed.

METHODS

The aim of this study is to assess the potential for cerebral emboli reduction with carotid compression using an in vitro model. Experiments were performed with a glass aortic arch model in a mock cardiovascular circuit. Small fluorescent particles were released into the circulation with and without carotid compression, and the particles visualized in the aortic midplane. The number of particles in the aorta and arch branch vessels were counted from the images before, during and following the release of carotid compression for durations of 10, 15 and 20 s. A gamma variate function was fit to the data to describe the bolus dynamics.

RESULTS

Carotid compression for 10 s reduces the number of embolic articles entering the carotid arteries by over 75%. A compression duration of 15-20 s does not result in greater particle reduction than one of 10 s.

CONCLUSION

Brief compression of the common carotid arteries during cardiovascular interventions has the potential to dramatically reduce the number of cerebral emboli and should be investigated further.

Using an automated emboli detection device in a porcine cardiopulmonary bypass (CPB) model: feasibility and considerations

The significant risk of cerebral embolism during cardiopulmonary bypass (CPB) makes monitoring of embolic events advisable already when developing new operation and coagulation management strategies for example in CPB animal models. The present study therefore evaluated in a porcine CPB model the feasibility of bilateral epicarotid Doppler signal recording and the quality of manual or automatic emboli detection. A total of 42 recordings (e.g. right carotid artery (n = 20), left carotid artery (n = 22)) were evaluated. The frequency of emboli counts was comparable for both carotid arteries. Automatic emboli detection, however, found significantly more embolic events per pig than did post-hoc manual off-line analysis of the recordings (172 +/- 217 vs. 13 +/-10). None of the brains, however, showed any emboli or infarction area either in cross-examination or in histological evaluation. In conclusion, the present study showed the feasibility of using an epicarotid Doppler device for bilateral emboli detection in a porcine CPB model. Automatic on-line emboli detection, however, reported more embolic events than did post hoc, off-line manual analysis. Possible reasons for this discrepancy are discussed.

Anesthetic technique (sufentanil versus ketamine plus midazolam) and quantitative electroencephalographic changes after cardiac surgery

OBJECTIVES

Cardiac surgery involving cardiopulmonary bypass is associated with neurologic deterioration. Several interventions, including anesthetic techniques, have been designed to limit ischemic brain damage and have been evaluated in animals. Markers of neurologic injury may facilitate the assessment of these interventions in humans.

DESIGN

A blinded randomized prospective study comparing 2 anesthetic techniques (one sufentanil-based, the other ketamine and midazolam-based) in patients undergoing cardiac surgery. Quantitative electroencephalography was used to detect postoperative neurologic injury.

SETTING

Major teaching hospital.

PARTICIPANTS

Forty-two patients aged 18 to 70 years undergoing cardiac surgery.

INTERVENTIONS

Patients were anesthetized with either a sufentanil-based or a ketamine and midazolam-based technique for cardiac surgery with cardiopulmonary bypass. Quantitative electroencephalography was performed preoperatively as well as 5 to 6 days postoperatively.

MEASUREMENTS AND MAIN RESULTS

Quantitative electroencephalography outcome did not differ (p > 0.05) between the 2 groups. It showed significant deterioration between preoperative and postoperative assessments with a decrease in faster and an increase in slower frequencies. In addition, the alpha attenuation index decreased. This may reflect a decrease in alertness. Both the intergroup comparisons and the assessment of individual changes failed to reveal significant differences between the anesthetic techniques. The adjuvant use of isoflurane correlated with less deterioration of quantitative electroencephalographic variables.

CONCLUSIONS

The use of either sufentanil-based or ketamine and midazolam-based anesthetic techniques for cardiac surgery with cardiopulmonary bypass had no effects on a marker of postoperative neurologic injury (ie, quantitative electroencephalography).

Profound reduction in brain embolization using an endoaortic baffle during bypass in swine

BACKGROUND

Cerebral embolization during cardiopulmonary bypass is an important cause of neurologic injury. This study determined whether an endoaortic baffle catheter (Cardeon Cobra Catheter; Cardeon Corporation, Cupertino, CA) could substantially reduce cerebral embolization in a swine cardiopulmonary bypass model.

METHODS

Sixteen 60 kg pigs underwent cardiopulmonary bypass; 8 animals with the Cobra baffle (Cardeon Corporation, Cupertino, CA) deployed, and 8 with the same cannula without baffle deployment. The animals were embolized with 72,000 fluorescent microspheres (97 to 100 microm) at normothermia. At the end of the experiment, the brains were removed and microspheres were isolated from eight regions.

RESULTS

During embolization, the two groups were equivalent with regard to pump flow, mean arterial pressure, temperature, Hgb and PaCO2. Deployment of the Cobra baffle reduced embolization to every brain region. Deployment of the baffle reduced total brain embolization by 89%. There was a mean of 61+/-60 emboli per gram in the control animals and 7+/-24 emboli per gram in those animals in which the baffle was deployed.

CONCLUSIONS

Cerebral embolization is profoundly reduced by use of the Cobra baffle aortic cannula. The application of this device may reduce postcardiac surgical neurologic injury.

Update on cardiopulmonary bypass

Investigations into cardiopulmonary bypass continue to refine knowledge and clinical practice. Recent investigations have emphasized neurological complications, introducing the possibility of genetic predisposition as a risk factor. Appropriate flows, pressures, and hematocrit levels during cardiopulmonary bypass continue to create controversy. Whereas previous debate has centered around appropriate temperature management, recent discussions consider the possibility that mild hypothermia after cardiopulmonary bypass might be neuroprotective. Meta-analyses and prospective investigations continue to suggest the virtual equivalence of aprotinin and lysine analogues in reducing bleeding and transfusion after cardiopulmonary bypass. Several recent studies identified the mechanisms and severity of the inflammatory response to cardiopulmonary bypass, as well as possible techniques for attenuating inflammation.

Hierarchy of regional oxygen delivery during cardiopulmonary bypass

BACKGROUND

Relative to the nonbypass state, cardiopulmonary bypass may decrease whole-body oxygen (O2) delivery. We predicted that during cardiopulmonary bypass, a hierarchy of regional blood flow and O2 delivery could be characterized.

METHODS

In 8 46.5 +/- 1.2-kg pigs, fluorescent microspheres were used to determine blood flow and O2 delivery to five organ beds before and during 37 degrees C cardiopulmonary bypass at four randomized bypass flows (1.4, 1.7, 2.0, and 2.3 L/min/m2). At completion, 18 tissue samples were obtained from the cerebral cortex (n = 4), renal cortex (n = 2), renal medulla (n = 2), pancreas (n = 3), small bowel (n = 3), and limb muscle (n = 4) for regional blood flow determination.

RESULTS

At conventional cardiopulmonary bypass flow (2.3 L/min/m2), whole-body O2 delivery was reduced by 44 +/- 6% relative to the pre-cardiopulmonary bypass state (p < 0.05). Over a range of cardiopulmonary bypass flows (2.3 to 1.7 L/min/m2), brain and kidney maintained their perfusion. Blood flow and O2 delivery to both regions were reduced when the cardiopulmonary bypass flow was reduced to 1.4 L/min/m2. However, perfusion and O2 delivery to other visceral organs (pancreas, small bowel) and skeletal muscle showed pump flow dependency over the range of flows tested.

CONCLUSIONS

This study characterizes the organ-specific hierarchy of blood flow and O2 distribution during cardiopulmonary bypass. These dynamics are relevant to clinical decisions for perfusion management.

Effect of temperature and PaCO2 on cerebral embolization during cardiopulmonary bypass in swine

BACKGROUND

Patients experience cerebral embolization during cardiopulmonary bypass (CPB). This study determined if alterations in temperature and/or PaCO2 can reduce cerebral and ocular embolization.

METHODS AND RESULTS

Forty-four pigs underwent CPB: 24 animals at 28 degrees C, and 20 at 38 degrees C. The two temperature groups were randomized to undergo embolization (67-microm fluorescent microspheres) at either hypercarbia or hypocarbia. Before and after embolization, cerebral and ocular blood flow were determined at normocarbia. Reducing temperature or PaCO2 reduced cerebral and ocular embolization. Hypocarbia reduced cerebral embolization by 60% and 45% in normothermic and hypothermic groups, respectively (p < 0.0001 and p < 0.05). Relative to normothermic animals, hypothermia reduced cerebral embolization by 37% under an elevated CO2 condition (p < 0.05), but not under hypocarbic conditions. Similarly, regardless of temperature, fewer emboli were delivered to the eye in hypocarbic animals (p < 0.05), but hypothermia did not reduce ocular embolization.

CONCLUSIONS

Cerebral embolization is determined by both temperature and PaCO2 at the time of embolization. In CPB practice, reductions in temperature and/or PaCO2 during periods of embolic risk may reduce brain injury.