Can Recognition of Spinal Ischemia Be Improved? Application of Motor-Evoked Potentials, Serum Markers, and Breath Gas Analysis in an Acutely Instrumented Pig Model

Risk Factors for Spinal Cord Injury during Endovascular Repair of Thoracoabdominal Aneurysm: Review of the Literature and Proposal of a Prognostic Score

Despite recent improvements, spinal cord ischemia remains the most feared and dramatic complication following extensive aortic repair. Although endovascular procedures are associated with a lower risk compared with open procedures, this risk is still significant and must be considered. A combined medical and surgical approach may help to optimize the tolerance of the spinal cord to ischemia. The aim of this review is to describe the underlying mechanism involved in spinal cord injury during extensive endovascular aortic repair, to describe the different techniques used to improve spinal cord tolerance to ischemia-including the prophylactic or curative use of spinal drainage-and to propose our algorithm for spinal cord protection and the rational use of spinal drainage.

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.

Using serum s100-β protein as a biomarker for comparing silent brain injury in carotid endarterectomy and carotid artery stenting

BACKGROUND

S100-β protein has been introduced as a sensitive biomarker of silent cerebral injury. This study compares its serum levels before, during, and 24 hours after carotid artery stenting (CAS) and carotid endarterectomy (CEA).

METHODS

We measured serum level of S100-β in arterial blood before (S100Ba), during (S100Bb), and 24 hours after (S100Bc) CAS and CEA. We assessed differences in S100-β levels using non-parametric tests. We analyzed the relationship between carotid plaque type (echolucency) and S100-β protein level. We also examined its relation to the oximetry results in the CEA group (ipsilateral and contralateral).

RESULTS

Thirty patients were enrolled, including 15 CAS and 15 CEA patients, with no significant differences in baseline atherosclerotic characteristics. There was no significant difference in S100Ba or S100Bb levels between CAS and CEA patients. However, a significant difference was found in S100Bc: 331.3 pg/mL (IQ range 56.4-583.5) for CAS vs. 76.3 pg/mL (IQ range 29.7-117.4) for CEA (P=0.01). Type I and II plaques were associated with the higher S100Bc levels in CAS (P=0.048). S100Bc was higher in CEA patients when the contralateral cerebral hemisphere had oximetry values less than 60% (P=0.043).

CONCLUSIONS

Our study suggests that CAS might produce silent brain injury. Moreover, vulnerable plaques might be associated with higher levels of S100-β protein, especially in CAS. This pilot study demonstrates that S100-β is a useful biomarker for silent brain injury in carotid revascularization. Large scale studies are still needed to confirm these findings.

Somatosensory and transcranial motor evoked potential monitoring in a porcine model for experimental procedures

Evoked potential monitoring has evolved as an essential tool not only for elaborate neurological diagnostics, but also for general clinical practice. Moreover, it is increasingly used to guide surgical procedures and prognosticate neurological outcome in the critical care unit, e.g. after cardiac arrest. Experimental animal models aim to simulate a human-like scenario to deduct relevant clinical information for patient treatment and to test novel therapeutic opportunities. Porcine models are particularly ideal due to a comparable cardiovascular system and size. However, certain anatomic disparities have to be taken into consideration when evoked potential monitoring is used in animal models. We describe a non-invasive and reproducible set-up useful for different modalities in porcine models. We further illustrate hints to overcome multi-faceted problems commonly occurring while using this sophisticated technique. Our descriptions can be used to answer a plethora of experimental questions, and help to further facilitate experimental therapeutic innovation.