Reproducable Paraplegia by Thoracic Aortic Occlusion in a Murine Model of Spinal Cord Ischemia-reperfusion

Summary

The lack of mechanistic understanding of spinal cord ischemia-reperfusion injury has hindered further adjuncts to prevent paraplegia following high risk aortic operations. Thus, the development of animal models is imperative. This manuscript demonstrates reproducible lower extremity paralysis following thoracic aortic occlusion in a murine model.

Abstract

Background
Lower extremity paralysis continues to complicate aortic interventions. The lack of understanding of the underlying pathology has hindered advancements to decrease the occurrence this injury. The current model demonstrates reproducible lower extremity paralysis following thoracic aortic occlusion.

Methods
Adult male C57BL6 mice were anesthetized with isoflurane. Through a cervicosternal incision the aorta was exposed. The descending thoracic aorta and left subclavian arteries were identified without entrance into pleural space. Skeletonization of these arteries was followed by immediate closure (Sham) or occlusion for 4 min (moderate ischemia) or 8 min (prolonged ischemia). The sternotomy and skin were closed and the mouse was transferred to warming bed for recovery.  Following recovery, functional analysis was obtained at 12 hr intervals until 48 hr.

Results
Mice that underwent sham surgery showed no observable hind limb deficit. Mice subjected to moderate ischemia for 4 min had minimal functional deficit at 12 hr followed by progression to complete paralysis at 48 hr. Mice subjected to prolonged ischemia had an immediate paralysis with no observable hind-limb movement at any point in the postoperative period. There was no observed intraoperative or post operative mortality.

Conclusion
Reproducible lower extremity paralysis whether immediate or delayed can be achieved in a murine model. Additionally, by using a median sternotomy and careful dissection, high survival rates, and reproducibility can be achieved.

Introduction

Lower extremity paralysis continues to complicate thoracoabdominal interventions. The injury, known as spinal cord ischemia-reperfusion injury (SCIR), results in paralysis in up to 20% of high risk patients¹. Surgical adjuncts such as left heart bypass, lumbar cerbrospinal fluid drains, hypothermic circulatory arrest and intercostal artery reimplantation have reduced the incidence of this complication²; however, far too many patients continue to be affected.

Clinically, spinal cord ischemia and reperfusion injury is seen as either immediate or delayed paralysis following intervention³. However, our....

Protocol

1. Preoperative Preparation and Anesthesia

1. Be sure to observe sterile technique throughout the procedure. Lay out all instruments.
2. Turn on the temperature control bed prior to anesthetic induction so that it may warm to the appropriate temperature (36.5 °C).  Power on the laser Doppler perfusion monitor so that it may boot during induction.
3. Place the mouse in the induction chamber.
   1. Carefully monitor the respiratory rate of the mouse during induction.
   2. As soon as the respiratory rate has visually slowed, remove the mouse from the induction chamber.
   3. Perform toe pinch to assess adequacy of an....

Results

Mice underwent sham surgery (n=3) or aortic occlusion for 4 (n=3) to 8 min (n=3). Postoperatively mice were graded by the Basso Mouse Score (Figure 1). Mice that underwent sham surgery had no observable functional deficits at any point postoperatively. Mice subjected to moderate ischemia (4 min) had near normal hind-limb function at 12 hr with progressive functional decline to complete paralysis by 48 hr. Mice in prolonged ischemia group (8min) had complete paralysis following surgery without any recover.......

Discussion

Paraplegia secondary to spinal cord ischemia reperfusion is the result of a complex of poorly understood pathologies⁹. While this is most commonly seen after thoracoabdominal aortic surgery, a variety of other insults such as  aortic dissections, trauma, embolic phenomena, vasculitis, and systemic hypotension¹⁰ can result in paraplegia. To gain further understanding of this injury and provide future targets to eliminate this injury, animal models have become a necessity.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
VMS Anesthesia Machine	MDS Matrx
Isoflurane	Vet One	13985-528-60	2.0% through nose cone
Induction Chamber	Vet Equip	941444
Heating Bed	Vestavia Scientific
Lazer Doppler Monitor	Moor Instruments	VMS-LDF1
5-0 Suture, Polyester	Surgidac	VD-551	Taper Needle
Microdissecting Clips	Biomedical Research Instruments	14-1030, 14-1060
Surgical Instruments	Fine Surgical Instruments		Forceps, needle holder