Impact of distal aortic perfusion on 'segmental steal' depleting spinal cord blood flow-a quantitative experimental approach.

OBJECTIVES: Aortic steal is an underestimated risk factor for intraoperative spinal cord ischaemia. A negative effect on spinal cord perfusion in thoraco-abdominal aneurysm repair has been suspected if blood drains away from the cord initiated by a reversal of the arterial pressure gradient. The amount of blood and pressure loss via back-bleeding of segmental arteries and the impact of distal aortic perfusion (DaP) have not been analysed yet. The aim of our study was to quantify 'segmental steal' in vivo during simulated thoraco-abdominal aneurysm repair and to determine the impact of DaP on steal and spinal cord perfusion. METHODS: Ten juvenile pigs were put on cardiopulmonary bypass with DaP and visceral arteries were ligated. 'Segmental steal' was quantified by draining against gravity with/without DaP. Blood volume of 'segmental steal' was quantified and microspheres were injected for Post mortem spinal cord perfusion analysis. 'Segmental steal' was quantified with/without DaP-and with stopped DaP. RESULTS: Quantification revealed a significantly higher steal on cardiopulmonary bypass with DaP with a mean difference of 24(11) ml/min. In all spinal cord segments, blood flow was diminished during steal drainage on DaP, compared to 'no steal'. The least perfused region was the low thoracic to upper lumbar segment. CONCLUSIONS: 'Segmental steal' is a relevant threat to spinal cord perfusion-even with the utilization of DaP-diminishing spinal cord perfusion. The blood volume lost by back-bleeding of segmental arteries is not to be underestimated and occlusion of segmental arteries should be considered in thoraco-abdominal aneurysm repair.

Mapping the collateral network: Optimal near-infrared spectroscopy optode placement.

BACKGROUND: Paraplegia after extensive aortic procedures is a disastrous complication, and maintenance of adequate spinal cord perfusion/oxygenation is pivotal to its prevention. Collateral network (CN) near-infrared spectroscopy (cnNIRS) has been introduced as a noninvasive method for indirect spinal cord oxygenation monitoring. However, the CN has not been investigated in its entirety using this monitoring modality. This study aimed to identify the optimal cnNIRS positioning in an acute large animal model for routine clinical use. METHODS: The paraspinous CN was measured from the high thoracic region to the low lumbar region (T4-L5) using cnNIRS in 10 juvenile pigs (plus reference data from 7 animals) during aortic ischemia and reperfusion. These data were compared with data on direct regional tissue perfusion of the CN and the spinal cord. RESULTS: After aortic cross-clamping, cnNIRS at the mid-thoracic to the low lumbar level decreased rapidly to a nadir at 10 minutes of distal ischemia (mean difference, 18.3 ± 11% to 44.5 ± 9%; P < .001 to .045), with more pronounced changes in the caudal regions. High thoracic cnNIRS remained stable (mean difference, 4.3 ± 4%; P = .915). Measurements of cnNIRS, CN, and spinal cord regional perfusion demonstrated comparable curve progressions starting from the mid-thoracic region (r = 0.5-0.7; P < .001). CONCLUSIONS: cnNIRS is capable of detecting relevant changes during ischemia and reperfusion from the mid-thoracic level downward with characteristic oxygenation patterns corresponding to CN and spinal cord regional perfusion. For extensive aortic procedures, noninvasive cnNIRS placement appears to be useful from the mid-thoracic level (T7-T9) to the lower lumbar level (L3-L5) and also may serve as a versatile monitoring method for procedures limited to the proximal thoracic aorta.

Relevance and Recommendations for the Application of Cardioplegic Solutions in Cardiopulmonary Bypass Surgery in Pigs.

Cardioplegic solutions play a major role in cardiac surgery due to the fact that they create a silent operating field and protect the myocardium against ischemia and reperfusion injury. For studies on cardioplegic solutions, it is important to compare their effects and to have a valid platform for preclinical testing of new cardioplegic solutions and their additives. Due to the strong anatomical and physiological cardiovascular similarities between pigs and humans, porcine models are suitable for investigating the effects of cardioplegic solutions. This review provides an overview of the results of the application of cardioplegic solutions in adult or pediatric pig models over the past 25 years. The advantages, disadvantages, limitations, and refinement strategies of these models are discussed.

Effect of cerebrospinal fluid pressure elevation on spinal cord perfusion during aortic cross-clamping with distal aortic perfusion.

OBJECTIVES: Distal aortic perfusion (DaP) is a widely accepted protective adjunct facilitating early reinstitution of visceral perfusion during extended thoracic and thoraco-abdominal aortic repair. DaP has also been suggested to secure distal inflow to the paraspinal collateral network via the hypogastric arteries and thereby reduce the risk of spinal cord ischaemia. However, an increase in cerebrospinal fluid (CSF) pressure is frequently observed during thoracoabdominal aortic aneurysm repair. The aim of this study was to evaluate the effects of DaP on regional spinal cord blood flow (SCBF) during descending aortic cross-clamping and iatrogenic elevation of cerebrospinal fluid pressure. METHODS: Eight juvenile pigs underwent central cannulation for cardiopulmonary bypass according to our established experimental protocol followed by aortic cross-clamping of the descending thoracic and abdominal aorta-mimicking sequential aortic clamping-with the initiation of DaP. Thereafter, CSF pressure elevation was induced by the infusion of blood plasma until baseline CSF pressure was tripled. At each time-point, microspheres of different colours were injected allowing for regional SCBF analysis. RESULTS: DaP led to a pronounced hyperperfusion of the distal spinal cord [SCBF up to 480%, standard deviation (SD): 313%, compared to baseline]. However, DaP provided no or only limited additional flow to the upper and middle segments of the spinal cord (C1-Th7: 5% of baseline, SD: 5%; Th8-L2: 24%, SD: 39%), which was compensated by proximal flow only at C1-Th7 level. Furthermore, DaP could not counteract an experimental CSF pressure elevation, which led to a further decrease in regional SCBF most pronounced in the mid-thoracic spinal cord segment. CONCLUSIONS: Protective DaP during thoraco-abdominal aortic repair may be associated with inadequate spinal protection particularly at the mid-thoracic spinal cord level ('watershed area') and result in the adverse effect of a potentially dangerous hyperperfusion of the distal spinal cord segments.

Experimental near-infrared spectroscopy-guided minimally invasive segmental artery occlusion.

OBJECTIVES: Minimally invasive staged segmental artery (SA) coil- and plug embolization is a new method for paraplegia prevention associated with extensive aortic procedures. Near-infrared spectroscopy of the paraspinal collateral network (cnNIRS) has emerged as a non-invasive method for spinal cord monitoring. The aim of this study was to evaluate cnNIRS to guide minimally invasive SA occlusion. METHODS: In a chronic large animal experiment, 18 juvenile pigs underwent two-stage minimally invasive staged SA coil- and plug embolization for complete SA occlusion. Coil-embolization was performed either by SA main stem occlusion (characteristic of pig anatomy) or separately for the left- and right SA. Lumbar cnNIRS was recorded during and after the procedure. Neurological status was assessed up to 3 days after complete SA occlusion. RESULTS: Mean time from SA coil embolization to minimum cnNIRS values was 11 ± 5 min with an average decrease from 101 ± 2% to 78 ± 8% of baseline (difference: -23 ± 9, P < 0.001). Lumbar cnNIRS demonstrated significant differences between left and right when SAs were occluded separately in all cases (-7 ± 4%, 1 min after first SA occlusion; P = 0.001). Permanent paraplegia occurred in 2 (11%) and any kind of neurological deficit-temporary or permanent-in 7 animals (39%). Association between lumbar cnNIRS and neurological outcome after minimally invasive staged SA coil- and plug embolization suggests positive correlation (R = 0.5, P = 0.052). CONCLUSIONS: Lumbar cnNIRS independently reacts to unilateral SA occlusion. cnNIRS-guided SA occlusion is feasible and may become a useful adjunct facilitating adequate and complete vessel occlusion.

Near real-time bedside detection of spinal cord ischaemia during aortic repair by microdialysis of the cerebrospinal fluid.

OBJECTIVES: Spinal cord ischaemia (SCI) remains the most devastating complication after thoraco-abdominal aortic aneurysm (TAAA) repair. Its early detection is crucial if therapeutic interventions are to be successful. Cerebrospinal fluid (CSF) is readily available and accessible to microdialysis (MD) capable of detecting metabolites involved in SCI [i.e. lactate, pyruvate, the lactate/pyruvate ratio (LPR), glucose and glycerol] in real time. Our aim was to evaluate the feasibility of CSF MD for the real-time detection of SCI metabolites. METHODS: In a combined experimental and translational approach, CSF MD was evaluated (i) in an established experimental large animal model of SCI with 2 arms: (a) after aortic cross-clamping (AXC, N = 4), simulating open TAAA repair and (b) after total segmental artery sacrifice (Th4-L5, N = 8) simulating thoracic endovascular aortic repair. The CSF was analysed utilizing MD every 15 min. Additionally, CSF was collected hourly from 6 patients undergoing open TAAA repair in a high-volume aortic reference centre and analysed using CSF MD. RESULTS: In the experimental AXC group, CSF lactate increased 3-fold after 10 min and 10-fold after 60 min of SCI. Analogously, the LPR increased 5-fold by the end of the main AXC period. Average glucose levels demonstrated a 1.5-fold increase at the end of the first (preconditioning) AXC period (0.60±0.14 vs 0.97±0.32 mmol/l); however, they decreased below (to 1/3 of) baseline levels (0.60±0.14 vs 0.19±0.13 mmol/l) by the end of the experiment (after simulated distal arrest). In the experimental segmental artery sacrifice group, lactate levels doubled and the LPR increased 3.3-fold within 30 min and continued to increase steadily almost 5-fold 180 min after total segmental artery sacrifice (P < 0.05). In patients undergoing TAAA repair, lactate similarly increased 5-fold during ischaemia, reaching a maximum at 6 h postoperatively. In 2 patients with intraoperative SCI, indicated by a decrease in the motor evoked potential of >50%, the LPR increased by 200%. CONCLUSIONS: CSF is widely available during and after TAAA repair, and CSF MD is feasible for detection of early anaerobic metabolites of SCI. CSF MD is a promising new tool combining bedside availability and real-time capacity to potentially enable rapid detection of imminent SCI, thereby maximizing chances to prevent permanent paraplegia in patients with TAAA.

Detrimental effects of cerebrospinal fluid pressure elevation on spinal cord perfusion: first-time direct detection in a large animal model.

OBJECTIVES: Cerebrospinal fluid (CSF) drainage is routinely utilized to mitigate perioperative and postoperative spinal cord ischaemia in open and endovascular thoraco-abdominal aortic aneurysm repair to prevent permanent paraplegia. Clinical decision-making in the vulnerable perioperative period, however, is still based on limited clinical and experimental data. Our aim was to investigate the isolated effect of CSF pressure elevation on spinal cord perfusion in an established large animal model. METHODS: Ten juvenile pigs with normal (native) arterial inflow (patent segmental arteries and collaterals) underwent iatrogenic CSF pressure elevation (×2, ×3, ×4 from their individual baseline pressure). Each pressure level was maintained for 30 min to mimic clinical response time. After the quadrupling of CSF pressure, the dural sac was slowly depressurized against gravity allowing CSF pressure to passively return to baseline values. Measurements were taken 30 and 60 min after normalization, and microspheres for regional blood flow analysis were injected at each time point. RESULTS: Spinal cord perfusion decreased significantly at all mid-thoracic to lumbar cord segments at the doubling of CSF pressure and declined to values <53% compared to baseline when pressure was quadrupled. Normalizing CSF pressure led to an intense hyperperfusion of up to 186% at the cervical level and 151% within the lumbar region. CONCLUSIONS: CSF pressure elevation results in a relevant impairment of spinal cord blood supply. Close perioperative and postoperative monitoring of CSF pressure is crucial for maintaining sufficient spinal cord perfusion. Radical and rapid withdrawal of CSF is followed by significant hyperperfusion in all spinal cord segments and may lead to 'drainage-related' iatrogenic reperfusion injury-aggravating the risk of delayed spinal cord injury-and should therefore be avoided.

The role of dietary non-heme iron load and peripheral nerve inflammation in the development of peripheral neuropathy (PN) in obese non-diabetic leptin-deficient ob/ob mice.

INTRODUCTION: Here, we investigated inflammatory signs of peripheral nerves in leptin-deficient obese ob/ob mice and the modulating effects of the exogenous iron load. METHODS: Ob/ob and ob/+ control mice were fed with high, standard, or low iron diet for four months. RESULTS: We found intraepidermal nerve fiber degeneration in foot skin and low-grade neuropathic abnormalities including mildly slowed motor and compound sensory nerve conduction velocities and low-grade macrophage and T-cell infiltration without overt neuropathology in sciatic nerves of all ob/ob mice. Low dietary iron load caused more pronounced abnormalities than high iron load in ob/ob mice. DISCUSSION: Our data suggest that dietary non-heme iron deficiency may be a modulating factor in the pathogenesis of peripheral neuropathy in obese ob/ob mice with metabolic syndrome. Once the mechanisms can be further elucidated, how low dietary iron augments peripheral nerve degeneration and dysfunction via pro-inflammatory pathways and new therapeutic strategies could be developed. ABBREVIATIONS: CMAP: compound muscle action potential; cSNCV: compound sensory nerve conduction velocity; IENFD: intraepidermal nerve fiber density; LDL: low-density lipoprotein; MetS: metabolic syndrome; MNCV: motor conduction velocity; NCV: nerve conduction velocity; PN: peripheral neuropathy; PNS: peripheral nervous system; STZ: streptozotocin; T2D: type 2 diabetes mellitus; TNF alpha: tumor necrosis factor alpha; WHO: World Health Organization.

Evaluation of conventional and frozen elephant trunk techniques on spinal cord blood flow in an animal model.

OBJECTIVES: The treatment of patients with extensive thoracic aortic disease involving the arch and descending aorta is often performed using the frozen elephant trunk technique (FET). Spinal cord blood flow (SCBF) in cervical, thoracic and lumbar sections prior, during and after aortic arch surgery were compared in conventional elephant trunk (cET) and FET technique in a pig model. METHODS: German Landrace pigs (75-85 kg) underwent aortic arch surgery using the FET (n = 8) or cET (n = 8) techniques. The E-vita Open hybrid stent graft was applied in all FET animals. Regional SCBF was measured 4 times: (i) before cardiopulmonary bypass, (ii) after 1 h, (iii) after 3 h, and (iv) after 6 h of reperfusion using fluorescence microspheres. Spinal cord segments were examined histopathologically and by immunohistochemistry. RESULTS: SCBF in FET decreased significantly from 0.13 ± 0.03 to 0.05 ± 0.02 ml/min/g after 1 h (P = 0.047). While at 3 h of reperfusion, SCBF increased and was comparable to baseline (0.09 ± 0.01 ml/min/g), beyond this time SCBF decreased again (0.05 ± 0.02 ml/min/g). A similar trend was found for SCBF in the cET group (baseline: 0.16 ± 0.04 ml/min/g, 1 h reperfusion: 0.02 ± 0.01 ml/min/g, 3 h reperfusion: 0.03 ± 0.01 ml/min/g and 6 h reperfusion: 0.02 ± 0.01 ml/min/g, P = 0.019). Cervical, thoracic and lumbar SCBF were also comparable in both groups. Histological analyses of spinal cord showed no differences in necrosis between cET and FET, while no differences were found for hypoxia-inducible factor-1α and apoptosis-inducing factor. In contrast, oxidative stress and caspase-induced apoptosis were higher in cET versus FET. CONCLUSIONS: The SCBF changed significantly during extensive aortic arch surgery with circulatory arrest and moderate hypothermia, but such changes were comparable between the FET and cET groups. The implantation of hybrid stent graft did not influence SCBF in thoracic and lumbar segments of the spinal cord. The immunohistological examination showed no differences between cET and FET regarding ischaemic damage and hypoxia-induced effects in spinal cord segments.

Reno-protective effects of epigallocatechingallate in a small piglet model of extracorporeal circulation.

Cardiopulmonary bypass still often is a necessary tool in cardiac surgery in particular in the correction of congenital heart defects in small infants. Nevertheless, among the complications linked to extracorporeal circulation (ECC) with cardiopulmonary bypass (CPB) in both infants and adults one of the most serious problems is renal impairment. Since this might be caused by ischemia/reperfusion injury and accumulation of free radicals, we used (-)-epigallocatechin-3-gallate (EGCG), a derivate from green tea, which is known to possess antioxidant, antiapoptotic and NO-scavenging properties in order to find out whether EGCG may protect the kidney. 23 four-week-old Angler Sattelschwein-piglets (8-15 kg) were divided into three groups: control-group (n=7), ECC-group (n=10), EGCG-group (n=6). The ECC- and EGCG-group were thoracotomized and underwent CPB for 120 min followed by a 90-min recovery-time. The EGCG-group received 10 mg/kg EGCG before and after CPB. Histology revealed that CPB led to widening of Bowman's capsule, and to vacuolization of proximal tubular cells (p<0.05) which could be prevented by EGCG (p<0.05). Using immunohistology, we found significant nuclear translocation of hypoxia-inducible-factor-1-alpha (HIF-1-alpha) and increased nitrotyrosine formation in the ECC-group. Both were significantly (p<0.05) inhibited by EGCG. ECC-induced loss of energy-rich phosphates was prevented by EGCG. In blood samples we found that CPB resulted in increases in creatinine and urea (in serum) and led to loss of total protein (p<0.05), which all was not present in EGCG-treated animals. We conclude that CPB causes damage in the kidney which can be attenuated by EGCG.

Sutureless mitral valve replacement with bioprostheses and Nitinol attachment rings: feasibility in acute pig experiments.

OBJECTIVE: There is a need for fast, minimally invasive sutureless replacement of mitral valves. METHODS: Unchanged FDA-approved biological valve prostheses were sutured to Nitinol attachment rings (Endosmart, Stutensee, Germany) that were covered with textile (devices). The lower flange of the device was stretched in ice water and maintained in a stretched position with stretching sutures. In 9 acute pig experiments through a limited left thoracotomy, a single suture was placed around the mitral annulus, the device was positioned, the annular suture tied, the stretching sutures retracted, and the device activated by warm saline. Position of the device, heart and valve function, coronary arteries, left ventricular outflow tract, and surrounding structures were observed with transoesophageal echocardiography, left ventricular and coronary angiograms, and pathologic examination at autopsy. RESULTS: The devices could be easily navigated to the mitral valve annulus and actuated within seconds. Three devices were placed with warm blood in the operative field and were tilted or dislocated at autopsy. In the other 6 devices, transesophageal echocardiography and left ventricular and coronary angiography demonstrated normal prosthetic valve and heart function, without valvular or para-device leakage, and with normal aortic valve and coronary arteries. At autopsy in these 6 cases, the devices were strongly fixed at the anatomic mitral valve annulus, without abnormalities of the device, heart valve prosthesis, left ventricular outflow tract, or aortic valve ostium. CONCLUSIONS: Nitinol attachments rings combined with unchanged biological valve prostheses can make fast and strong sutureless replacement of the mitral valve feasible in acute pig experiments. Applicators that constrain and release the device mechanically need to be developed.