Utility of neuromonitoring in hypothermic circulatory arrest cases for early detection of stroke: Listening through the noise.

OBJECTIVE: Stroke remains a potentially devastating complication of aortic arch intervention. The value of neurophysiologic intraoperative monitoring (NIOM) in the early identification of stroke is unclear. We evaluated the utility of NIOM for early stroke detection in aortic arch surgery. METHODS: Across 8 years at our institution, 365 patients underwent aortic arch surgery with hypothermic circulatory arrest, and 224 cases utilized NIOM. One patient was excluded for intraoperative death. In the remaining cohort, we reviewed the incidence, timing, and location of strokes, and the incidence and nature of NIOM alerts. RESULTS: Hemiarch was performed in 154 patients and total arch replacement in 69 patients. Stroke occurred in 6.3% of all cases (14 out of 223), 15.9% of total arches (11 out of 69), and 2.0% of hemiarches (3 out of 154). There were 33 NIOM alerts (14.8%), and 9 patients had both alerts and stroke. Of these, NIOM deficits plausibly correlated with imaging findings in 7 cases (78%). Of the 5 stroke patients without NIOM alerts, 2 developed neurologic symptoms 3 days or more postoperatively, and infarcts in 3 patients did not result in sensory or motor deficits. Excluding 2 patients with late stroke, the sensitivity of NIOM for stroke detection was 75%, specificity was 88.5%, positive predictive value was 27.3%, and negative predictive value was 97.4%. CONCLUSIONS: Despite a low positive predictive value requiring a high level of discrimination when interpreting abnormal findings, NIOM has high sensitivity and specificity for the early stroke detection. Furthermore, its high negative predictive valve is reassuring for low risk of stroke in the absence of alerts.

Predictors of Acute Kidney Injury Following Aortic Arch Surgery.

BACKGROUND: Acute kidney injury (AKI) following open aortic arch surgery is a frequent complication associated with increased morbidity and mortality. The primary purpose of this study was to evaluate risk factors for postoperative AKI in patients who underwent open aortic arch surgery utilizing hypothermic circulatory arrest (HCA). MATERIALS AND METHODS: Included were 295 patients undergoing surgery between January 2011 and March 2018. AKI was defined according to Kidney Disease: Improving Global Outcomes guidelines. Preoperative and intraoperative variables were stratified by no AKI versus any AKI, and bivariate analysis was performed. Multivariable logistic regression analysis used statistically and clinically significant characteristics from the bivariate analysis. RESULTS: Of the 295 patients, 93 (32%) developed AKI. In the bivariate analysis, significant predictors of AKI included the following: history of hypertension (P < 0.001), diabetes (P = 0.03), operative urgency (P = 0.009), cardiopulmonary bypass (CPB) time (P < 0.0001), HCA time (0.02), total intraoperative transfusions (P = 0.002), and concomitant procedures (coronary artery bypass grafting, or mitral/tricuspid interventions, P = 0.0009). In the multivariable analysis, significant predictors of AKI were history of hypertension (P = 0.03) and CPB time (P = 0.02). Age, operative urgency, circulatory arrest time, and any intraoperative transfusion were not significant in the multivariable analysis. CONCLUSION: In conclusion, given that CPB time is the only modifiable risk factor identified in the analysis, approaches to reducing bypass time should continue to be the focus of decreasing risk for postoperative AKI in HCA cases.

The Buffalo Trunk Technique for Aortic Arch Reconstruction.

BACKGROUND: The frozen elephant trunk technique facilitates repair of aortic arch and proximal descending aortic pathologic processes. Commercially available hybrid grafts may simplify this approach by allowing for a single suture line, potentially streamlining the distal anastomosis and improving operative times. However, these devices are currently not readily available in United States. We developed a surgical technique, the Buffalo Trunk, to simplify the frozen elephant trunk procedure that obviates the need for a hybrid graft and decreases operating times. METHODS: Our technique uses a soft-branched graft along with a stent graft to create a distal anastomosis that incorporates the aorta, stent graft, and soft graft in a zone 2 arch reconstruction. Patient characteristics, operative times, and perioperative outcomes were analyzed. RESULTS: A total of 37 patients underwent the Buffalo Trunk procedure compared with 29 patients who underwent the traditional frozen elephant trunk. Bypass and circulatory arrest times were 34 and 18 minutes shorter, respectively, in the Buffalo Trunk group. Total blood transfusions were lower in the Buffalo Trunk group. The stroke rate was 5% and 30-day mortality occurred in 2 patients. No difference was noted in end-organ dysfunction, morbidity, and mortality between the two techniques. CONCLUSIONS: The benefits of a hybrid approach to the frozen elephant trunk can be attained without the complex industry-available technology as presented by our technique, the Buffalo Trunk. Evolution of this approach has facilitated shorter circulatory arrest time and subsequently overall decreased operative times without compromising outcomes.

Improved Mortality Associated With the Use of Extracorporeal Membrane Oxygenation.

BACKGROUND: Our objective was to evaluate the association of bridge to transplant (BTT) extracorporeal membrane oxygenation (ECMO) on survival after lung transplantation (LTx) and determine the degree to which transplant center volume affects this relationship. METHODS: Using the United Network for Organ Sharing database, we performed a retrospective cohort study evaluating the survival of patients undergoing LTx between 2005 and 2017. On the basis of previous literature, LTx centers were classified into 3 groups using their average annual LTx volume over the preceding 5 years: less than 25, 25 to 49, and more than 50. Survival of BTT ECMO and non-ECMO patients was analyzed using a log-rank test. Propensity scores for BTT ECMO were calculated, and a weighted proportional hazards model was used to compare BTT ECMO and non-ECMO patients by center volume. RESULTS: There were 20,976 patients who met inclusion criteria, with 611 (2.9%) undergoing BTT ECMO. Overall, BTT ECMO was associated with increased posttransplantation hazard of mortality (hazard ratio, 1.37; 95% confidence interval, 1.14 to 1.64). Kaplan-Meier plots by center volume suggest that BTT ECMO-associated mortality may be mitigated at high-volume LTx centers. In the propensity score-weighted proportional hazards model, we determined that when centers perform more than 35 LTxs per year, the increased hazard of BTT ECMO on mortality is no longer observed. CONCLUSIONS: BTT ECMO can be performed as a bridge to LTx without significantly increasing patient mortality in high-volume centers. Patients undergoing BTT ECMO at LTx centers that perform more than 35 LTxs annually have equivalent mortality to those who do not require ECMO before transplantation.

Toll-Like Receptor-4 Is a Mediator of Proliferation in Esophageal Adenocarcinoma.

BACKGROUND: Chronic inflammation from reflux disease has been implicated as part of the development of esophageal adenocarcinoma. Toll-like receptors (TLRs), a component of the innate immune system, have been implicated in mediating hyperplasia and metaplasia in response to inflammatory stimuli. Increased TLR4 in human esophageal cancer has been correlated with its carcinogenesis. We hypothesized that TLR4 mediates proliferation of human esophageal adenocarcinoma cells. METHODS: Normal human esophageal (HET1A) and adenocarcinoma (OE33, FLO-1) cell lines were cultured using standard techniques. TLR4 was measured at baseline and in response to reflux stimuli. All cell lines were treated with the TLR4 agonist lipopolysaccharide for 48 hours, and growth response was measured. Changes in myeloid differentiation primary response 88 (MyD88), tumor necrosis factor receptor associated factor 6 (TRAF6), and nuclear factor-κB (NF-κB) activity were measured during lipopolysaccharide treatment. All cell lines had NF-κB inhibited, and growth rate response was measured. RESULTS: TLR4 was expressed in all cell lines, with increased baseline expression in adenocarcinoma cell lines (p < 0.05). Reflux stimuli increased TLR4 expression (p < 0.01) in normal esophageal cells. After treatment with lipopolysaccharide, all cell lines showed significant increases in proliferation (p < 0.05) due to the NF-κB pathway, and their growth rate was reduced with NF-κB inhibition (p < 0.05). CONCLUSIONS: TLR4 is consistently detectable in esophageal cell lines and most highly expressed in adenocarcinoma. TLR4 expression increases in an inflammatory model of reflux disease. TLR4 activation results in increased proliferation due to the TLR4-MyD88-TRAF6-NF-κB signaling pathway, and inhibition of NF-κB leads to decreased esophageal cell growth. These findings suggest TLR4 may be a target to suppress esophageal cancer growth.

Pretreatment With Diazoxide Attenuates Spinal Cord Ischemia-Reperfusion Injury Through Signaling Transducer and Activator of Transcription 3 Pathway.

BACKGROUND: Delayed paraplegia remains a feared complication of thoracoabdominal aortic intervention. Pharmacologic preconditioning with diazoxide (DZ), an adenosine 5'-triphosphate-sensitive potassium channel opener, results in neuroprotection against ischemic insult. However, the effects of DZ in spinal cord ischemia-reperfusion injury have not been fully elucidated. We hypothesized that DZ attenuates spinal cord ischemia-reperfusion injury through the signaling transducer and activator of transcription (STAT) 3 pathway. METHODS: Adult male C57/BL6 mice received DZ (20 mg/kg) by oral gavage. Spinal cords were harvested at 0, 12, 24, 36, 48, and 60 hours after administration of DZ. The expression of phosphorylated STAT3 was assessed by Western blot analysis. Five groups were studied: DZ (DZ pretreatment, n = 8), ischemic control (phosphate-buffered saline pretreatment, n = 11), DZ + STAT3 inhibitor LY5 (DZ pretreatment + LY5, n = 8), LY5 (phosphate-buffered saline pretreatment + LY5, n = 8), and sham (without cross-clamping, n = 5). Spinal cord ischemia was induced by 4 minutes of thoracic aortic cross-clamp. Functional scoring (Basso Mouse Score) was done at 12-hour intervals until 48 hours, and spinal cords were harvested for the evaluation of B-cell lymphoma 2 expression and histologic changes. RESULTS: The expression of phosphorylated STAT3 was significantly upregulated 36 hours after the administration of DZ. The motor function in the DZ group was significantly preserved compared with all other groups. The expression of B-cell lymphoma 2 in the DZ group was significantly higher than in the ischemic control, DZ + LY5, and LY5 groups 48 hours after reperfusion. CONCLUSIONS: DZ preserves motor function in spinal cord ischemia-reperfusion injury by the STAT3 pathway. DZ may be beneficial clinically for use in spinal protection in aortic intervention.

Synergetic Induction of NGF With Diazoxide and Erythropoietin Attenuates Spinal Cord Ischemic Injury.

BACKGROUND: Paraplegia remains a significant complication of thoracoabdominal aortic intervention. We previously reported that diazoxide (DZ), enhances the neuroprotective efficacy of erythropoietin (EPO). We hypothesized that DZ and EPO combined treatment attenuates spinal cord ischemic injury through upregulation of nerve growth factor (NGF). METHODS: DZ (pretreatment) was given to adult male C57/BL6 mice by oral gavage and EPO (before surgery) was intraperitoneally injected 32 h after administration of DZ. Spinal cords were harvested 0, 2, 4, and 6 h after injection of EPO. NGF expression was analyzed by western blot. After determining the optimal time, NGF expression was compared between DZ (pretreatment) + EPO (before surgery), DZ + PBS, PBS + EPO, and PBS + PBS (ischemic control). Four groups were studied to compare the motor function after ischemia: DZ + EPO (n = 11), ischemic control (n = 9), DZ + EPO + tropomyosin receptor kinase A receptor inhibitor (n = 9), and sham (without cross-clamp, n = 4). Spinal cord ischemia was induced by a 4-min thoracic aortic cross-clamp. Functional scoring (Basso Mouse Score) was done at 12-h intervals until 48 h, and spinal cords were harvested for evaluation of NGF expression and histological changes. RESULTS: NGF expression was significantly upregulated 4 h after administration of EPO. At 4 h after injection of EPO, NGF expression in the DZ + EPO group was significantly higher than that in the other groups. DZ + EPO significantly preserved motor function compared with all other groups. At 48 h after reperfusion, the level of NGF expression in the DZ + EPO group, was significantly higher than in all other groups. CONCLUSIONS: DZ + EPO attenuates spinal cord ischemic injury through upregulation of NGF. Better understanding of this mechanism may serve to further prevent ischemic complications for aortic intervention.

Innominate Versus Axillary Artery Cannulation for the Hemiarch Repair.

BACKGROUND: Innominate artery cannulation has gained some popularity over the last decade as an alternative to axillary artery cannulation for providing selective antegrade cerebral perfusion during repair of the ascending aorta and arch. Innominate artery cannulation provides several advantages including avoidance of an additional incision and use of a larger caliber artery to provide less resistance to high flow during bypass and selective antegrade cerebral perfusion. We hypothesize that these advantages make innominate artery cannulation superior to axillary artery cannulation as it can decrease operative times and potentially decrease blood loss. METHODS: This was a single-center retrospective analysis of 206 patients who underwent hemiarch replacement between 2009 and 2017. All patients qualified including emergent cases. Groups were separated by mode of cannulation: axillary and innominate. Outcomes evaluated included cardiopulmonary bypass (CPB) time, cross-clamp time, circulatory arrest (CA) time, postoperative transfusions, intensive care unit length of stay, development of any neurological complications, end-organ failure, and mortality. Subgroup analysis was performed for elective and emergent cases. RESULTS: Axillary and innominate artery cannulation accounted for 37% (n = 77) and 67% (n = 129) of cases, respectively. There was no difference in patient characteristics except for a higher incidence of renal disease in the axillary group (16% versus 6%, P = 0.05). More emergent cases were performed in the axillary group (61% versus 17%, P < 0.001). Innominate cases had shorter CPB times (189 versus 150 min, P < 0.001) and CA (22.5 versus 11 min, P < 0.001) times overall. In the elective subgroup, CA times were shorter for the innominate cases. However, the emergent subgroup displayed no difference in operative times. Less transfusions were given in the innominate group including units of red blood cells (2 [0-6] versus 0 [0-2], P < 0.001), units of platelets (2 [1-3] versus 1 [0-2], P = 0.001), and units of plasma (6 [2-9] versus 2 [0-4], P < 0.001). A similar trend was observed in the elective subgroup. No difference in transfusions was observed in the emergent subgroup. There was no statistical difference in remaining outcomes between cases of axillary and innominate cannulation in the combined, elective, and emergent groups. CONCLUSIONS: Alternate cannulation strategies for open arch anastomoses are evolving with a trend toward using the innominate artery. These data suggest that innominate cannulation is at least equivalent to, and may be superior to, axillary cannulation. The innominate artery provides a larger conduit vessel for perfusion and this decrease in resistance to flow, allowing for faster cooling and rewarming, maybe why CPB times were lower in this group. Innominate cannulation is a safe and potentially advantageous technique for hemiarch repair.

Synergistic Reduction of Apoptosis With Diazoxide and Erythropoietin in Spinal Cord Ischemic Injury.

BACKGROUND: Paraplegia remains a devastating complication of thoracoabdominal aortic intervention. Metabolic stress induces expression of beta common receptor subunit of erythropoietin (EPO) receptor (ßcR) to exert a neuroprotective effect in spinal cord ischemia reperfusion injury (SCIR). Diazoxide (DZ) has been shown to induce ischemic tolerance. We previously reported that DZ upregulated ßcR expression and enhanced the neuroprotective effects of EPO through the upregulation of ßcR. We hypothesize that ßcR expression induced by DZ before ischemia amplifies the antiapoptotic effects of EPO in a murine model of SCIR. METHODS: Experimental groups included phosphate-buffered saline (PBS) pretreatment + PBS immediately before the operation, PBS+EPO, DZ+PBS, DZ+EPO, and sham. Spinal cord ischemia was induced by a 4-minute thoracic aortic cross-clamp. Functional scoring (Basso Mouse Score) was done at 12-hour intervals for 48 hours. Spinal cords were harvested for histologic analysis, and antiapoptotic factors (caspase 3, 8, and 9, B-cell lymphoma-2, and neuroglobin) were evaluated by Western blot analysis. RESULTS: The motor function of DZ+EPO group was significantly preserved compared with all other groups. The levels of cleaved caspase 8 and 3 in DZ+EPO were significantly lower than in the other groups. Mice treated with DZ+EPO had significantly fewer terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling-positive cells than other groups. CONCLUSIONS: Optimized upregulation of ßcR by DZ can increase the extrinsic antiapoptotic effects of EPO. Better understanding of this synergetic mechanism may serve to help prevent ischemic complications caused by aortic intervention.

Optimized induction of beta common receptor enhances the neuroprotective function of erythropoietin in spinal cord ischemic injury.

BACKGROUND: Paraplegia remains the most feared complication of complex thoracoabdominal aortic intervention. Although erythropoietin (EPO) has demonstrated neuroprotective effects in spinal cord ischemia, it does not work until expression of the beta common receptor subunit of the EPO receptor (ßcR) is induced by ischemia. We hypothesized that the ßcR can be induced by diazoxide (DZ), amplifying the neuroprotective effects of EPO in spinal cord ischemia-reperfusion injury. METHODS: For the DZ time trial, adult male C57/BL6 mice received DZ (20 mg/kg) by oral gavage. Spinal cords were harvested after 0, 12, 24, 36, and 48 hours of administration. To evaluate optimal dosing, DZ was administered at 0, 5, 10, 20, and 40 mg/kg. The expression of ßcR was assessed by Western blot analysis. Five groups were studied: PBS (pretreatment)+PBS (immediately before), PBS+EPO, DZ+PBS, DZ+EPO, and sham (without cross-clamping). Spinal cord ischemia was induced by 4 minutes of thoracic aortic cross-clamping. Functional scoring (Basso Mouse Score) was done at 12-hour intervals for 48 hours, and spinal cords were harvested for histological analysis. RESULTS: Western blot analysis demonstrated that optimal ßcR up-regulation occurred at 36 hours after DZ administration, and the optimal DZ dosage for ßcR induction was 20 mg/kg. Motor function at 48 hours after treatment was significantly better preserved in the DZ+EPO group compared with all other groups, and was significantly better preserved in the DZ only and EPO only groups compared with control (PBS+PBS). CONCLUSIONS: Pharmacologic up-regulation of ßcR with DZ can increase the efficacy of EPO in preventing spinal cord ischemia and reperfusion injury. Improved understanding of this synergetic mechanism may serve to further prevent ischemic complications for high-risk aortic intervention.

Spinal Cord Neurons Isolation and Culture from Neonatal Mice.

We present a protocol for the isolation and culture of spinal cord neurons. The neurons are obtained from neonatal C57BL/6 mice and are isolated on postnatal day 1-3. A mouse litter, usually 4-10 pups born from one breeding pair, is gathered for one experiment, and spinal cords are collected individually from each mouse after euthanasia with isoflurane. The spinal column is dissected out and then the spinal cord is released from the column. The spinal cords are then minced to increase the surface area of delivery for an enzymatic protease that allows for the neurons and other cells to be released from the tissue. Trituration is then used to release the cells into solution. This solution is subsequently fractionated in a density gradient to separate the various cells in solution, allowing for neurons to be isolated. Approximately 1-2.5 x 106 neurons can be isolated from one litter group. The neurons are then seeded onto wells coated with adhesive factors that allow for proper growth and maturation. The neurons take approximately 7 days to reach maturity in the growth and culture medium and can be used thereafter for treatment and analysis.