Understanding the Measurement of Pressure Within the Spinal Cord to Optimize Spinal Cord Perfusion Pressure Using a Porcine Model of Spinal Cord Injury.

Abstract

Recent studies have reported that monitoring spinal cord perfusion pressure (SCPP) using a pressure probe to measure "intraspinal pressure" (ISP) within the subdural space at the injury site may improve the hemodynamic management of acute spinal cord injury (SCI) patients. This study aimed to investigate, within a pig model of SCI, the relationship between the ISP measured within the subdural space and the "spinal cord pressure" (SCP) measured within the spinal cord itself. Specifically, we sought to characterize the changes to ISP and SCP over time, both rostral and caudal to the injury epicenter, and in relation to native spinal cord morphometry. Female Yucatan mini-pigs were subjected to a T10 contusion-compression injury. Pressure probes were inserted inside the spinal cord parenchyma for SCP and within the subdural space for ISP, 5-mm rostral, and caudal from the injury site. SCP and ISP were then measured over an 8-hour period post-SCI. Ultrasound images were taken before and after SCI to monitor changes in spinal cord morphometry in the early hours post-injury. Spinal cord swelling was observed in all cases; however, only half of the animals exhibited increased SCP and ISP rostrally. In these, a gradient across the injury site was observed in the ISP measured rostrally and caudally when swelling of the spinal cord filled the subdural space, and the cord was seen to be abutting against the dura. The remaining animals showed a negligible increase in ISP and SCP (<+1 mmHg). The variation in pressure response was influenced heavily by the size of the subdural space surrounding the cord. In cases where we could establish an "optimal SCPP" based on the autoregulatory function of the spinal cord, a discernible variance of approximately 10 mmHg was detected between the values derived from ISP versus SCP. These results suggest that changes in ISP and SCP after SCI are influenced by native spinal cord morphometry and that the location of measurement is important to consider, particularly in situations where the swelling of the injured cord results in an occlusion of the cerebrospinal fluid (CSF) flow through the subdural space.