Total circulatory arrest as a support modality in congenital heart surgery: review and current evidence

The use of total circulatory arrest (TCA)/deep hypothermic circulatory arrest (DHCA) as a support modality in congenital heart surgery is a time-tested strategy. However, with technological advances, the widespread use of this technique has decreased. Adjunctive cerebral perfusion with continuous cardiopulmonary bypass (CPB) gradually has become more popular with a view to reduce the complications related to DHCA. In addition, better neuromonitoring and neuroprotective strategies have made DHCA much safer. However, the level of evidence to support the best way to protect the brain during congenital heart surgery is insufficient. This review analyzes the history, physiology, techniques of DHCA, as well as other alternative strategies like selective cerebral perfusion and presents the current available evidence.

Neuroprotective Strategies in Repair and Replacement of the Aortic Arch

Aortic arch surgery is a technical challenge, and cerebral protection during distal anastomosis is a continued topic of controversy and discussion. The physiologic effects of hypothermic arrest and adjunctive cerebral perfusion have yet to be fully defined, and the optimal strategies are still undetermined. This review highlights the historical context, physiological rationale, and clinical efficacy of various neuroprotective strategies during arch operations.

Diffusion-weighted imaging detects early brain injury after hypothermic circulatory arrest in pigs

OBJECTIVES

Cerebral injury is a complication of surgery with deep hypothermic circulatory arrest (DHCA). This study aimed to evaluate diffusion-weighted imaging (DWI) for the early detection of brain injury after DHCA in an animal model.

METHODS

Twelve healthy, adult, male miniature pigs were randomly divided into the DHCA (to receive DHCA; n = 6) and the control (sham surgery under anaesthesia; n = 6) groups. All animals received DWI, T1-weighted imaging (T1WI) and T2WI the day before surgery, 7 h postoperatively and 24 h postoperatively. Histopathological evaluation of the brain tissues was performed in the DHCA group using the Fluoro-Jade C staining to detect neuronal degeneration, the Nissl staining to show neuronal morphology and the TUNEL assay for apoptosis. The Cohen's kappa coefficient was used to compare the results of DWI with those of the histopathological evaluation.

RESULTS

All animals survived surgery. In the control group, no new focal brain lesions were detected by postoperative DWI, T1WI or T2WI. In the DHCA group, new focal brain lesions were detected as early as 7 h postoperatively by DWI but not T1WI or T2WI. All three imaging sequences revealed abnormalities 24 h after surgery. In sections from areas showing abnormalities on DWI, the Fluoro-Jade C staining detected neuronal degeneration, the Nissl staining showed morphological abnormalities and the TUNEL assay demonstrated apoptotic cells. The Cohen's kappa statistics showed agreement between DWI findings and the results of all 3 histopathological examinations (TUNEL: kappa = 0.553; Nissl: kappa = 0.652; Fluoro-Jade C: kappa = 0.778; all P < 0.001).

CONCLUSIONS

DWI is superior to T1WI or T2WI for the early detection of neurological lesions after DHCA in pigs.

A novel augmented venous-drainage model of cardiopulmonary bypass for deep hypothermic circulatory arrest without blood priming

Objective:

Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) are commonly used in cardiac surgery. However, the mortality and morbidity are still high in practice. Developing novel protective stategies and elucidating the underlying mechanisms for the pathophysiological consequences of DHCA have been hampered because of the absence of a satisfactory recovery animal model. The aim of this study was to establish a novel and safe DHCA model without blood priming in rats to study the pathophysiology of potential complications.

Methods:

Ten adult male Sprague-Dawley rats (age, 14-16 weeks; weight, 200-300g) were used. The entire CPB circuit consisted of a modified reservoir, a custom-designed small-volume membrane oxygenator, a roller pump and a home-made heat exchanger, all of which were connected via silicon tubing. The volume of the priming solution was less than 10 ml. The right jugular vein, right carotid artery and left femoral artery were cannulated. The blood was drained from the right atrium through the right jugular vein and fed back to the rat via the left femoral artery. CPB was commenced at a full flow rate. The animals were cooled to a pericranial temperature of 18°C and then subjected to 45 minutes of DHCA with global ischemia. Circulatory arrest was followed by rewarming and over 60 minutes of reperfusion. CPB was terminated carefully. Blood in the circuit was centrifuged and slowly transfused to achieve optimal hematocrit. Blood gas and hemodynamic parameters were recorded at each time point before CPB, during CPB and after CPB.

Results:

All CPB and DHCA processes were achieved successfully. No rat died in our research. Blood gas analyses at different times were normal. Cardiac function and blood pressure were stable after the operation. The vital signs of all the rats were stable.

Conclusion:

The novel augmented venous-drainage CPB and DHCA model in rats could be established successfully without blood priming.

Anesthetic Considerations for Surgery on the Aortic Arch

Aortic arch surgery requires meticulous teamwork in the true perioperative sense. Planning and communication at all phases from preoperative evaluation, through intraoperative management, to postoperative care should be well coordinated between surgical, anesthesia, perfusion, and intensive care unit teams. This review discusses intraoperative management from the anesthesiologist’s perspective, with particular emphasis on transesophageal echo evaluation and coagulation management.

Anesthetic management of patent ductus arteriosus in adults

Patent ductus arteriosus (PDA) is an extracardiac left to right shunt. It should be corrected at an early age, but some patients may survive into adult life even without repair. Anesthetic management for adult patients with PDA poses many challenges for the anesthesiologist due to alterations in the cardiopulmonary physiology. We report successful anesthesia management of a case of an adult patient of PDA with moderate pulmonary artery hypertension with infective endarteritis (two large mobile vegetations at the pulmonary end of the duct).

Effect of Hypothermia-Induced Respiratory Arrest on Cerebral Circulation in Rats

Intravital microscopy was employed to examine cerebral circulation in rats assessed by blood flow in the venules with diameter of 10-30 μ during immersion hypothermia continued to the moment of respiratory arrest and for 10 min thereafter. Circulation in the cerebral microvessels continued during severe hypothermia, and it went on even after hypothermic respiratory arrest while the heart was beating. In pial venules, the blood continued to fl ow for 8-10 min after respiratory arrest.

An experimental study to replace the thoracic descending aorta for pigs with a self-made sutureless blood vessel

To simplify the procedure of blood vessel replacement operation and shorten the vascular anastomosis time, we developed a special artificial blood vessel which can be connected to native blood vessels without suture. The self-made sutureless blood vessel (SMSBV) was made from two titanium connectors and a Gore-Tex graft. To investigate blood compatibility and histocompatibility of the SMSBV, we carried thoracic descending aorta replacement using either SMSBV or Gore-Tex, respectively, in pigs. The aortic clamp time and the operative blood loss in the experimental group (using SMSBV) were less than those in the control group (using Gore-Tex). The whole blood hematocrit, platelet count, plasma soluble P-selectin, plasma free hemoglobin, and interleukins 2, 6 at each time point were not different significantly between the two groups. Light microscopy and transmission electron microscopy examination showed there were layers of vascular smooth muscle cells and endothelial cells adhered in the inner wall of artificial blood vessel without any signs of thrombosis. Based on the result, we have drawn the conclusion that the application of SMSBV can significantly shorten the vascular anastomosis time, reduce operative blood loss, and show good blood and tissue compatibility.

Relative Higher Hematocrit Attenuates the Cerebral Excitatory Amino Acid Elevation Induced by Deep Hypothermic Circulatory Arrest in Rats

Hemodilution is a commonly used technique in cardiopulmonary bypass (CPB) and deep hypothermic circulation arrest (DHCA). Our previous study showed that lower hematocrit aggravated the brain injury after DCHA. Because the excitatory amino acids are critical pathways of ischemic neuronal damage, the purpose of the present study was to investigate the effects of different degrees of hemodilution on the excitatory amino acid content in different brain areas after DHCA Adult Sprague-Dawley rats were randomly divided into four groups: group I hematocrit (Hct) 10% (H1), group II Hct 20% (H2), group III Hct 30% (H3), and control group (C). All animals except those in the control group underwent DHCA at 18°C for 90 minutes. Different degrees of hemodilution were accomplished by changing the composition and volume of the priming solution used in CPB. High-performance liquid chromatography was used to determine the concentration of glutamate (Glu), aspartate (Asp), glycine (Gly), gamma-aminobutyric acid (GABA), and taurine (Tau) in the cerebral cortex, hippocampus, and thalamus. We found that the concentration of these five amino acids in the hippocampus and cortex were all increased after DHCA. Glu, Asp, and Gly in the hippocampus and cortex were significantly lower in the Hct 30% group than in the other two groups (p<0.05). There was no significant difference in the GABA and Tau concentrations among the three groups. In summary, excitatory amino acids increased significantly after DHCA, and relative higher hematocrit attenuates this response.

Establishment of a novel rat model without blood priming during normothermic cardiopulmonary bypass

OBJECTIVE

An effective animal model was needed for research on the pathophysiology of cardiopulmonary bypass (CPB). Rat models were considered suitable for research into CPB, recently. The aim of the article is to establish a simple and safe CPB model without blood priming in rats, containing the advantages of controlling temperature precisely, being similar to the clinical process and laying the foundation for the further study of a deep hypothermic circulatory arrest (DHCA) model.

MATERIALS AND METHODS

Ten Sprague-Dawley rats, divided into a CPB group (n=7) and a sham group (n=3), received sevoflurane inhalation anesthesia and were maintained in an anesthesia state by intubation. The entire CPB circuit consisted of a reservoir, a membrane oxygenator, a roller pump, a heat exchanger and a heat cooler, all of which were connected via silicon tubes. The volume of the priming solution, composed of 6% HES130/0.4 and 125 IU heparin, was less than 12 ml. In the CPB group, a 22G catheter was placed in the left femoral artery for monitoring arterial blood pressure, a 20G catheter was placed in a tail artery for arterial inflow and a homemade, multiorificed catheter was inserted into a right jugular vein for venous drainage. After 90 minutes, the CPB process was terminated when vital signs were stable. In the sham group, the same surgical process was conducted except for the venous drainage. Post-oxygenator blood gas and hemodynamic parameters were measured at each time point before CPB, during CPB and after CPB.

RESULTS

All CPB processes were successfully achieved. Blood gas analysis and hemodynamic parameters of each time point were in accordance with normal ranges. The vital signs of all rats were stable.

CONCLUSION

The establishment of CPB without blood priming in rats can be achieved successfully. The rat model could be used to study short-term or long-term organ injury mechanisms caused by CPB. Furthermore, on the basis of the precise control of temperature and the depth of anesthesia, the DHCA model in rats could be developed further to study pathophysiological changes of neurological and other organ functions in the future.

Anesthetic protection of neurons injured by hypothermia and rewarming: roles of intracellular Ca2+ and excitotoxicity

BACKGROUND

Mild hypothermia is neuroprotective after cerebral ischemia but surgery involving profound hypothermia (PH, temperature less than 18°C) is associated with neurologic complications. Rewarming (RW) from PH injures hippocampal neurons by glutamate excitotoxicity, N-methyl-D-aspartate receptors, and intracellular calcium. Because neurons are protected from hypoxia-ischemia by anesthetic agents that inhibit N-methyl-D-aspartic acid receptors, we tested whether anesthetics protect neurons from damage caused by PH/RW.

METHODS

Organotypic cultures of rat hippocampus were used to model PH/RW injury, with hypothermia at 4°C followed by RW to 37°C and assessment of cell death 1 or 24 h later. Cell death and intracellular Ca were assessed with fluorescent dye imaging and histology. Anesthetic agents were present in the culture media during PH and RW or only RW.

RESULTS

Injury to hippocampal CA1, CA3, and dentate neurons after PH and RW involved cell swelling, cell rupture, and adenosine triphosphate (ATP) loss; this injury was similar for 4 through 10 h of PH. Isoflurane (1% and 2%), sevoflurane (3%) and xenon (60%) reduced cell loss but propofol (3 μM) and pentobarbital (100 μM) did not. Isoflurane protection involved reduction in N-methyl-D-aspartate receptor-mediated Ca influx during RW but did not involve γ-amino butyric acid receptors or KATP channels. However, cell death increased over the next day.

CONCLUSION

Anesthetic protection of neurons rewarmed from 4°C involves suppression of N-methyl-D-aspartate receptor-mediated Ca overload in neurons undergoing ATP loss and excitotoxicity. Unlike during hypoxia/ischemia, anesthetic agents acting predominantly on γ-aminobutyric acid receptors do not protect against PH/RW. The durability of anesthetic protection against cold injury may be limited.