Objectives: To develop a technique for continuously monitoring intraspinal pressure at the injury site (intraspinal pressure) after traumatic spinal cord injury.
Design: A pressure probe was placed subdurally at the injury site in 18 patients who had isolated severe traumatic spinal cord injury (American Spinal Injuries Association grades A-C). Intraspinal pressure monitoring started within 72 hours of the injury and continued for up to a week. In four patients, additional probes were inserted to simultaneously monitor subdural pressure below the injury and extradural pressure. Blood pressure was recorded from a radial artery catheter kept at the same horizontal level as the injured segment of the spinal cord. We determined the effect of various maneuvers on spinal cord perfusion pressure and spinal cord function and assessed using a limb motor score and motor-evoked potentials.
Setting: Neurosurgery and neuro-ICU covering a 3 million population in London.
Subjects: Patients with severe traumatic spinal cord injury. Control subjects without spinal cord injury (to monitor spinal cerebrospinal fluid signal and motor evoked potentials).
Interventions: Insertion of subdural spinal pressure probe.
Measurements and main results: There were no procedure-related complications. Intraspinal pressure at the injury site was higher than subdural pressure below the injury or extradural pressure. Average intraspinal pressure from the 18 patients with traumatic spinal cord injury was significantly higher than average intraspinal pressure from 12 subjects without traumatic spinal cord injury. Change in arterial PCO2, change in sevoflurane dose, and mannitol administration had no significant effect on intraspinal pressure or spinal cord perfusion pressure. Increase in inotrope dose significantly increased spinal cord perfusion pressure. Bony realignment and laminectomy did not effectively lower intraspinal pressure. Laminectomy was potentially detrimental by exposing the swollen spinal cord to compression forces applied to the skin. By intervening to increase spinal cord perfusion pressure, we could increase the amplitude of motor-evoked potentials recorded from below or just above the injury level in nine of nine patients with traumatic spinal cord injury. In two of two patients with American Spinal Injuries Association grade C traumatic spinal cord injury, higher spinal cord perfusion pressure correlated with increased limb motor score.
Conclusions: Our findings provide proof-of-principle that subdural intraspinal pressure at the injury site can be measured safely after traumatic spinal cord injury.