Targeted Perfusion Therapy in Spinal Cord Trauma

Abstract

We review state-of-the-art monitoring techniques for acute, severe traumatic spinal cord injury (TSCI) to facilitate targeted perfusion of the injured cord rather than applying universal mean arterial pressure targets. Key concepts are discussed such as intraspinal pressure and spinal cord perfusion pressure (SCPP) at the injury site, respectively, analogous to intracranial pressure and cerebral perfusion pressure for traumatic brain injury. The concept of spinal cord autoregulation is introduced and quantified using spinal pressure reactivity index (sPRx), which is analogous to pressure reactivity index for traumatic brain injury. The U-shaped relationship between sPRx and SCPP defines the optimum SCPP as the SCPP that minimizes sPRx (i.e., maximizes autoregulation), and suggests that not only ischemia but also hyperemia at the injury site may be detrimental. The observation that optimum SCPP varies between patients and temporally in each patient supports individualized management. We discuss multimodality monitoring, which revealed strong correlations between SCPP and injury site metabolism (tissue glucose, lactate, pyruvate, glutamate, glycerol), monitored by surface microdialysis. Evidence is presented that the dura is a major, but unappreciated, cause of spinal cord compression after TSCI; we thus propose expansion duroplasty as a novel treatment. Monitoring spinal cord blood flow at the injury site has revealed novel phenomena, e.g., 3 distinct blood flow patterns, local steal, and diastolic ischemia. We conclude that monitoring from the injured spinal cord in the intensive care unit is a safe technique that appears to enable optimized and individualized spinal cord perfusion.

Keywords: Blood pressure; critical care; decompression; dura; monitoring; spinal cord injury.

Fig. 1

ISP monitoring. (a) Schematic showing ISP probe between swollen cord and dura. (b) Intraoperative photo taken as an ISP probe was inserted intradurally. (c) Postoperative CT. (d) Photo of computer screen showing monitored signals including ISP, ECG, ABP, and SCPP. SCPP is ABP minus ISP. (e) Enhanced visualization of SCPP versus time. SCPP (dark line). Range of optimal (green), intermediate (yellow), and suboptimal (red) SCPPs, with sPRx color scale.

Fig. 2

ISP versus lumbar CSFP. (a) ISP ≠ CSFP when the injured cord is swollen and compressed against the dura. (b) ISP ≈ CSFP when there is CSF around the injured cord.

Fig. 3

ISP and SCPP versus outcome. (a) Mean ISP and (b) mean SCPP versus % of patients that improved by at least 1 (blue) or at least 2 (red) AIS grades. Follow-up for 9–12 months.

Fig. 4

Dural cord compression and duroplasty. (a) MRI (left) and schematic (right). The swollen cord is compressed against the dura causing 4 compartments: intrathecal above (blue), extrathecal (yellow), intrathecal at injury site (purple), and intrathecal below (green). (b) Intraoperative photo of expansion duroplasty. (c) ISP (mean ± S.D.) and (d) SCPP (mean ± S.D.) versus days after injury for 11 patients who had bony decompression + stabilization and 10 patients who had bony + dural decompression + stabilization.

Fig. 5

Multimodality monitoring after TSCI. (a) Setup for ISP + microdialysis monitoring: i) microdialysis catheter, ii) microdialysis analyzer, iii) intraoperative photo showing ISP probe + microdialysis catheter, and iv) postoperative CT showing ISP probe + microdialysis catheter. (b) LPR (left) and glutamate (right) versus time for a TSCI patient.

Fig. 6

Imaging spinal cord blood flow during surgery. (a) Schematic of setup. Laser speckle imager, infrared laser (red beam), and dorsal theca exposed after laminectomy. (b) Three patterns of spinal cord blood flow after injury (upper) termed as 1) necrosis-penumbra, 2) hyperperfusion, and 3) patchy perfusion. Spinal cord blood flow scale (bottom).