title: Influence of hypotension and nerve root section on the ability to mobilize the spinal cord during spine surgery. An experimental study in a pig model.
abstract: BACKGROUND
  The correction of severe spinal deformities by an isolated posterior approach often involves cord manipulation together with hypotensive anesthesia. To date, the efficiency of methods to increase the tolerance of the cord to displacement and the influence of hypotension on this tolerance is yet to be assessed.
  
  
  OBJECTIVE
  The objective of this study was to determine the limits of cord displacement before the disappearance of neurophysiologic signals. The influence of the type of force applied, the section of the roots, and the induced hypotension on the cord's tolerance to displacement was also assessed.
  
  
  METHODS
  Experimental study using a domestic pig model.
  
  
  METHODS
  Successive records of cord-to-cord motor evoked potentials were obtained during displacement maneuvers. Displacing forces were released immediately after the absence of neurophysiologic signals.
  
  
  METHODS
  Surgical procedures were performed under conventional general anesthesia. The spinal cord and nerve roots from T6 to T10 levels were exposed by excision of the posterior elements, allowing for free cord movement. Three groups were established according to the method of spinal cord displacement: the separation (Group 1, n=5), the root stump pull (Group 2, n=5), and the torsion groups (Group 3, n=5). An electromechanical external device was used to apply the displacing forces. The three displacement tests were repeated after sectioning the adjacent nerve roots. The experiments were first carried out under normotension and afterward under induced hypotension.
  
  
  RESULTS
  In Group 1, evoked potential disappeared with a displacement of 10.1±1.6 mm with unharmed roots and 15.3±4.7 mm after the sectioning of four adjacent roots (p<.01). After induced hypotension, potentials were lost at 4.0±1.2 mm (p<.01). In Group 2, the absence of potentials occurred at 20.0±4.3 mm and increased to 23.5±2.1 mm (p<.05) after cutting the two contralateral roots. Under hypotensive conditions, the loss of neurophysiologic signals was detected at 5.3±1.2 mm (p<.01). In Group 3, the cord allowed torsion of 95.3±.2° that increased to 112.4±7.1° if the contralateral roots were cut. Under hypotension, the loss of potentials was found at 20±6.2° (p<.01).
  
  
  CONCLUSIONS
  In this experimental model, it was possible to displace the thoracic spinal cord by a distance superior to the spinal cord width without suffering neurophysiologic changes. The limits of cord displacement increase when the adjacent nerve roots are sacrificed. Induced hypotension had a dramatic effect on the tolerance of the spinal cord for displacement. This work has an important clinical significance because induced hypotension during specific spine surgery procedures requiring spinal cord manipulation in humans may increase the risk of neurologic spinal cord injury.
authors: Institute for Research on Musculoskeletal Disorders, School of Medicine, Valencia Catholic University, Quevedo 2, Valencia 46001, Spain. Electronic address: carlos.barrios@uv.es.
authors: Carlos
authors: C
authors: Barrios
authors: Division of Pediatric Orthopedics, Hospital Son Espases, Carretera de Valldemossa, 79, 07120 Palma de Mallorca, Islas Baleares, Spain.
authors: Gabriel
authors: G
authors: Pizá-Vallespir
authors: Department of Pediatric Orthopedics, Hospital Ramón y Cajal, Ctra. de Colmenar Viejo, km. 9.100, Madrid 28034, Spain.
authors: Jesús
authors: J
authors: Burgos
authors: Department of Clinical Neurophysiology, Hospital Ramón y Cajal, Ctra. de Colmenar Viejo, km. 9.100, Madrid 28034, Spain.
authors: Gema
authors: G
authors: De Blas
authors: Department of Clinical Neurophysiology, Hospital Ramón y Cajal, Ctra. de Colmenar Viejo, km. 9.100, Madrid 28034, Spain.
authors: Elena
authors: E
authors: Montes
authors: Spine Surgery Unit, Hospital La Fraternidad-Muprexpa, Paseo de la Habana, 83-85, Madrid 28036, Spain.
authors: Eduardo
authors: E
authors: Hevia
authors: Laboratory of Neural Repair, Hospital Nacional de Paraplégicos, Finca La Peraleda, s/n, Toledo 45071, Spain.
authors: Jorge E
authors: JE
authors: Collazos-Castro
authors: Department of Experimental Surgery, Hospital Ramón y Cajal, Ctra. de Colmenar Viejo, km. 9.100, Madrid 28034, Spain.
authors: Carlos
authors: C
authors: Correa
mesh_terms: D000818:Animals; D019054:Evoked Potentials, Motor / Q000502:physiology; D007022:Hypotension; D023421:Models, Animal; D009068:Movement; D011183:Postoperative Complications; D012307:Risk Factors; D013116:Spinal Cord / Q000502:physiology*; D013119:Spinal Cord Injuries / Q000209:etiology; D013126:Spinal Nerve Roots / Q000502:physiology / Q000601:surgery*; D013131:Spine / Q000601:surgery*; D034421:Sus scrofa; D013552:Swine
keywords: EMG; Induced hypotension; Nerve root section; Neurologic surgical complications; Neurophysiologic monitoring; Spinal cord injury