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.

Ischemic Spinal Cord Injury-Experimental Evidence and Evolution of Protective Measures.

BACKGROUND: Paraplegia remains one of the most devastating complications of descending and thoracoabdominal aortic repair. The aim of this review is to outline the current state of art in the rapidly developing field of spinal cord injury research. METHODS: A review of PubMed and Web of Science databases was performed using the following terms and their combinations: spinal cord, injury, ischemia, ischemia-reperfusion, ischemic spinal cord injury, paraplegia, paraparesis. Articles published before July 2019 were screened and included if considered relevant. RESULTS: The review focuses on the topic of spinal cord injury and the developments concerning methods of monitoring, diagnosing, and preventing spinal cord injury. CONCLUSIONS: Translation of novel technologies from bench to bedside and into everyday clinical practice is challenging; however, each of the developing areas holds great promise in spinal cord injury prevention.

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.

Management of aortic root in type A dissection: Bentall approach.

BACKGROUND: We analyzed the results of the modified Bentall procedure in a high-risk group of patients presenting with acute type A aortic dissection (ATAAD). METHODS: ATAAD patients undergoing a modified Bentall between 1996 and 2018 (n = 314) were analyzed. Mechanical composite conduits were used in 45%, and biological ones using either a bioprosthesis implanted into an aortic graft (33%) or xeno-/homograft root conduits (22%) in the rest. Preoperative malperfusion was present in 34% of patients and cardiopulmonary resuscitation required in 9%. RESULTS: Concomitant arch procedures consisted of hemiarch in 56% and total arch/elephant trunk in 34%, while concomitant coronary artery surgery was required in 20%. The average cross-clamp and cardiopulmonary bypass times were 126 ± 43 and 210 ± 76 min, respectively, while the average circulatory arrest times were 29 ± 17 min. A total of 69 patients (22%) suffered permanent neurologic deficit, while myocardial infarction occurred in 18 cases (6%) and low cardiac output syndrome in 47 (15%). The in-hospital mortality rate was 17% due to intractable low cardiac output syndrome (n = 29), major brain injury (n = 16), multiorgan failure (n = 6), and sepsis (n = 2). The independent predictors of in-hospital mortality were critical preoperative state (odds ratio [OR], 5.6; p < .001), coronary malperfusion (OR, 3.6; p = .002), coronary artery disease (OR, 2.6; p = .033), and prior cerebrovascular accident (OR, 5.6; p = .002). CONCLUSIONS: The modified Bentall operation, along with necessary concomitant procedures, can be performed with good early results in high-risk ATAAD patients presenting.

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.