The effects of intrathecal hypotension on tissue perfusion and pathophysiological outcome after acute spinal cord injury

Significance of spinal cord perfusion pressure following spinal cord injury: A systematic scoping review

This scoping review systematically reviewed relevant research to summarize the literature addressing the significance of monitoring spinal cord perfusion pressure (SCPP) in acute traumatic spinal cord injury (SCI). The objectives of the review were to (1) examine the nature of research in the field of SCPP monitoring in SCI, (2) summarize the key research findings in the field, and (3) identify research gaps in the existing literature and future research priorities. Primary literature searches were conducted using databases (Medline and Embase) and expanded searches were conducted by reviewing the references of eligible articles and searches of Scopus, Web of Science core collection, Google Scholar, and conference abstracts. Relevant data were extracted from the studies and synthesis of findings was guided by the identification of patterns across studies to identify key themes and research gaps within the literature. Following primary and expanded searches, a total of 883 articles were screened. Seventy-three articles met the review inclusion criteria, including 34 original research articles. Other articles were categorized as conference abstracts, literature reviews, systematic reviews, letters to the editor, perspective articles, and editorials. Key themes relevant to the research question that emerged from the review included the relationship between SCPP and neurological recovery, the safety of monitoring pressures within the intrathecal space, and methods of intervention to enhance SCPP in the setting of acute traumatic SCI. Original research that aims to enhance SCPP by targeting increases in mean arterial pressure or reducing pressure in the intrathecal space is reviewed. Further discussion regarding where pressure within the intrathecal space should be measured is provided. Finally, we highlight research gaps in the literature such as determining the feasibility of invasive monitoring at smaller centers, the need for a better understanding of cerebrospinal fluid physiology following SCI, and novel pharmacological interventions to enhance SCPP in the setting of acute traumatic SCI. Ultimately, despite a growing body of literature on the significance of SCPP monitoring following SCI, there are still a number of important knowledge gaps that will require further investigation.

Elevated intraspinal pressure in traumatic spinal cord injury is a promising therapeutic target

The currently recommended management for acute traumatic spinal cord injury aims to reduce the incidence of secondary injury and promote functional recovery. Elevated intraspinal pressure (ISP) likely plays an important role in the processes involved in secondary spinal cord injury, and should not be overlooked. However, the factors and detailed time course contributing to elevated ISP and its impact on pathophysiology after traumatic spinal cord injury have not been reviewed in the literature. Here, we review the etiology and progression of elevated ISP, as well as potential therapeutic measures that target elevated ISP. Elevated ISP is a time-dependent process that is mainly caused by hemorrhage, edema, and blood-spinal cord barrier destruction and peaks at 3 days after traumatic spinal cord injury. Duraplasty and hypertonic saline may be promising treatments for reducing ISP within this time window. Other potential treatments such as decompression, spinal cord incision, hemostasis, and methylprednisolone treatment require further validation.

A review of spinal cord perfusion pressure guided interventions in traumatic spinal cord injury

PURPOSE

To evaluate the causality between interventions on spinal cord perfusion pressure and neurological outcome in traumatic spinal cord injury.

METHODS

A systematic review was conducted in concordance with PRISMA guidelines. The literature was found in the EMBASE, PUBMED, SCOPUS, and WEB OF SCIENCE. Eligible studies included those that reported measurements and interventions on the spinal cord perfusion pressure in either animals or patients suffering from spinal cord injury. Only studies that reported a clinical or relevant clinical outcome measure (i.e., neurophysiology) were included.

RESULTS

The search yielded 795 unique records, and six studies were included after careful review. These studies suggested a positive correlation between spinal cord perfusion pressure and neurological outcome, but conclusions on causality could not be made.

CONCLUSION

In spite of growing indications that neurological outcomes are related to the spinal cord perfusion pressure in traumatic spinal cord injuries, a solid conclusion cannot be made due to the limited literature available. Additional well-designed studies are needed to address this issue.

Cardiovascular Autonomic Dysfunction in Spinal Cord Injury: Epidemiology, Diagnosis, and Management

Spinal cord injury (SCI) disrupts autonomic circuits and impairs synchronistic functioning of the autonomic nervous system, leading to inadequate cardiovascular regulation. Individuals with SCI, particularly at or above the sixth thoracic vertebral level (T6), often have impaired regulation of sympathetic vasoconstriction of the peripheral vasculature and the splanchnic circulation, and diminished control of heart rate and cardiac output. In addition, impaired descending sympathetic control results in changes in circulating levels of plasma catecholamines, which can have a profound effect on cardiovascular function. Although individuals with lesions below T6 often have normal resting blood pressures, there is evidence of increases in resting heart rate and inadequate cardiovascular response to autonomic provocations such as the head-up tilt and cold face tests. This manuscript reviews the prevalence of cardiovascular disorders given the level, duration and severity of SCI, the clinical presentation, diagnostic workup, short- and long-term consequences, and empirical evidence supporting management strategies to treat cardiovascular dysfunction following a SCI.

Transcutaneous contrast-enhanced ultrasound imaging of the posttraumatic spinal cord

STUDY DESIGN

Experimental animal study.

OBJECTIVE

The current study aims to test whether the blood flow within the contused spinal cord can be assessed in a rodent model via the acoustic window of the laminectomy utilizing transcutaneous ultrasound.

SETTING

Department of Neurological Surgery, University of Washington, Seattle WA.

METHODS

Long-Evans rats (n = 12) were subjected to a traumatic thoracic spinal cord injury (SCI). Three days and 10 weeks after injury, animals underwent imaging of the contused spinal cord using ultrafast contrast-enhanced ultrasound with a Vantage ultrasound research system in combination with a 15 MHz transducer. Lesion size and signal-to-noise ratios were estimated via transcutaneous, subcutaneous, or epidural ultrasound acquisition through the acoustic window created by the original laminectomy.

RESULTS

Following laminectomy, transcutaneous and subcutaneous contrast-enhanced ultrasound imaging allowed for assessment of perfusion and vascular flow in the contused rodent spinal cord. An average loss of 7.2 dB from transcutaneous to subcutaneous and the loss of 5.1 dB from subcutaneous to epidural imaging in signal-to-noise ratio (SNR) was observed. The hypoperfused injury center was measured transcutaneously, subcutaneously and epidurally (5.78 ± 0.86, 5.91 ± 0.53, 5.65 ± 1.07 mm²) at 3 days post injury. The same animals were reimaged again at 10 weeks following SCI, and the area of hypoperfusion had decreased significantly compared with the 3-day measurements detected via transcutaneous, subcutaneous, and epidural imaging respectively (0.69 ± 0.05, 1.09 ± 0.11, 0.95 ± 0.11 mm², p < 0.001).

CONCLUSIONS

Transcutaneous ultrasound allows for measurements and longitudinal monitoring of local hemodynamic changes in a rodent SCI model.

Dynamic changes in intramedullary pressure 72 hours after spinal cord injury

Intramedullary pressure increases after spinal cord injury, and this can be an important factor for secondary spinal cord injury. Until now there have been no studies of the dynamic changes of intramedullary pressure after spinal cord injury. In this study, telemetry systems were used to observe changes in intramedullary pressure in the 72 hours following spinal cord injury to explore its pathological mechanisms. Spinal cord injury was induced using an aneurysm clip at T10 of the spinal cord of 30 Japanese white rabbits, while another 32 animals were only subjected to laminectomy. The feasibility of this measurement was assessed. Intramedullary pressure was monitored in anesthetized and conscious animals. The dynamic changes of intramedullary pressure after spinal cord injury were divided into three stages: stage I (steep rise) 1–7 hours, stage II (steady rise) 8–38 hours, and stage III (descending) 39–72 hours. Blood-spinal barrier permeability, edema, hemorrhage, and histological results in the 72 hours following spinal cord injury were evaluated according to intramedullary pressure changes. We found that spinal cord hemorrhage was most severe at 1 hour post-spinal cord injury and then gradually decreased; albumin and aquaporin 4 immunoreactivities first increased and then decreased, peaking at 38 hours. These results confirm that severe bleeding in spinal cord tissue is the main cause of the sharp increase in intramedullary pressure in early spinal cord injury. Spinal cord edema and blood-spinal barrier destruction are important factors influencing intramedullary pressure in stages II and III of spinal cord injury.

Contrast-enhanced ultrasound to visualize hemodynamic changes after rodent spinal cord injury

OBJECTIVE

Traumatic spinal cord injury (tSCI) causes an almost complete loss of blood flow at the site of injury (primary injury) as well as significant hypoperfusion in the penumbra of the injury. Hypoperfusion in the penumbra progresses after injury to the spinal cord and is likely to be a major contributor to progressive cell death of spinal cord tissue that was initially viable (secondary injury). Neuroprotective treatment strategies seek to limit secondary injury. Clinical monitoring of the temporal and spatial patterns of blood flow within the contused spinal cord is currently not feasible. The purpose of the current study was to determine whether ultrafast contrast-enhanced ultrasound (CEUS) Doppler allows for detection of local hemodynamic changes within an injured rodent spinal cord in real time.

METHODS

A novel ultrafast CEUS Doppler technique was developed utilizing a research ultrasound platform combined with a 15-MHz linear array transducer. Ultrafast plane-wave acquisitions enabled the separation of higher-velocity blood flow in macrocirculation from low-velocity flow within the microcirculation (tissue perfusion). An FDA-approved contrast agent (microbubbles) was used for visualization of local blood flow in real time. CEUS Doppler acquisition protocols were developed to characterize tissue perfusion both during contrast inflow and during the steady-state plateau. A compression injury of the thoracic spinal cord of adult rats was induced using iris forceps.

RESULTS

High-frequency ultrasound enabled visualization of spinal cord vessels such as anterior spinal arteries as well as central arteries (mean diameter [± SEM] 145.8 ± 10.0 µm; 76.2 ± 4.5 µm, respectively). In the intact spinal cord, ultrafast CEUS Doppler confirmed higher perfusion of the gray matter compared to white matter. Immediately after compression injury of the thoracic rodent spinal cord, spinal cord vessels were disrupted in an area of 1.93 ± 1.14 mm2. Ultrafast CEUS Doppler revealed a topographical map of local tissue hypoperfusion with remarkable spatial resolution. Critical loss of perfusion, defined as less than 40% perfusion compared to the surrounding spared tissue, was seen within an area of 2.21 ± 0.6 mm2.

CONCLUSIONS

In our current report, we introduce ultrafast CEUS Doppler for monitoring of spinal vascular structure and function in real time. Development and clinical implementation of this type of imaging could have a significant impact on the care of patients with tSCI.

Intraspinal Pressure Monitoring and Extensive Duroplasty in the Acute Phase of Traumatic Spinal Cord Injury: A Systematic Review

OBJECTIVE

The prognosis in cervical spinal cord injury is poor, and surgical and neurointensive care management need further improvement. Monitoring of the intraspinal pressure (ISP) at an early stage after traumatic spinal cord injury (tSCI) is useful clinically.

MATERIALS AND METHODS

Obtaining continuous spinal cord perfusion pressure (SCPP) measurements based on the difference between mean arterial pressure and ISP allows offering best medical and surgical treatment during this critical phase of tSCI. A search was carried out with PubMed, Embase, and Google Scholar up to January 10, 2017. Articles resulting from these searches and relevant references cited in those articles were reviewed.

RESULTS

The optimal SCPP was found to be between 90 and 100 mm Hg and mean arterial pressure of 110-130. Laminectomy alone was found to be ineffective in the reduction of ISP because it does not lower the pressure exerted by dura on the swollen spinal cord. Therefore, bony decompression with durotomy or duroplasty seems to be the procedure of choice to reduce the ISP less than 20 mm Hg.

CONCLUSIONS

A randomized controlled trial is required to determine whether laminectomy with durotomy and monitoring of ISP with SCPP optimization improve neurological recovery after tSCI.

Subacute post-traumatic ascending myelopathy after T12 burst fracture in a 32-year-old male: case report and surgical result of cervical durotomy

To draw attention to a rare neurological deterioration after spinal cord injury (SCI) and to discuss evidence supporting an increase in cerebrospinal fluid pressure (CSFP), we present an extremely rare case of subacute post-traumatic ascending myelopathy (SPAM) in which the patient sustained a T12 fracture initially resulting in paraplegia and after undergoing posterior fixation and anterior decompression. The patient was a 32-year-old healthy man who sustained a T12 burst fracture with complete paraplegia after a fall injury. The patient underwent a posterior reduction and short-segment fixation 8 h after the injury and an anterior thoracoscopic-assisted decompression on post-traumatic day 8. On post-traumatic day 21, he had a progressive neurological deterioration with dyspnoea and decreased muscle strength of both upper extremities that could not be relieved by conservative intervention. After undergoing a cervical posterior laminectomy and durotomy, the patient exhibited the clinical manifestation of brain herniation. There was no recovery of autonomous respiration, and the patient entered a coma. The patient died on post-traumatic day 25 because of cardiac and respiratory arrest. SPAM is a rare, potentially fatal neurological deterioration after SCI; however, a prompt diagnosis can be made by magnetic resonance imaging. Our observations suggest that an increase in CSFP may be the main cause of SPAM. The paraplegic level should be recorded daily so that neurological deterioration can be recognised as soon as possible.

Subacute posttraumatic ascending myelopathy: a literature review

Study design:

A literature review.

Objectives:

Our aim was to summarise the history, epidemiology, aetiological mechanism, pathological study, clinical and radiological evaluation, treatment and prognosis of subacute posttraumatic ascending myelopathy (SPAM).

Methods:

Medical literature on SPAM were searched in the PubMed, Medline, Ovid and Embase databases. The cases of SPAM reported in literature were analysed, and the history, epidemiology, aetiological mechanism, pathological study, clinical and radiological evaluation, treatment and prognosis of SPAM were summarised.

Results:

SPAM remains a relatively rare disorder occurring within the first few weeks after spinal cord injury (SCI). The incidence rate ranges from 0.42% to 1% among all SCI. SPAM is likely to occur in young and middle-aged male patients. Risk factors of SPAM include complete injury, low blood pressure, early postoperative mobilisation and nonsurgical treatment.

Conclusions:

SPAM is well recognised according to typical clinical manifestation and magnetic resonance imaging characteristics. There is no effective therapy for this neurological deterioration. The prognosis of SPAM is poor. There is usually a slight improvement of one or more level(s) below the maximal level of deterioration. The mortality rate is approximately 10%.

The relative contribution of edema and hemorrhage to raised intrathecal pressure after traumatic spinal cord injury

Raised intrathecal pressure (ITP) after traumatic spinal cord injury (SCI) is a critically important aspect of injury development that may result in significantly greater tissue damage and worsened functional outcome. Raised ITP is caused by the accumulation of blood and/or water (edema), and while their occurrence after traumatic SCI has been well established, the relative contribution of both processes to the development of ITP after SCI has not yet been determined. Accordingly, the current study investigates the temporal profile of raised ITP after traumatic SCI in relation to both hemorrhage and edema development. A closed balloon compression injury was induced at T10 in New Zealand White rabbits. Animals were thereafter assessed for spinal water content (edema), ITP, lesion and hemorrhage volume, and albumin immunoreactivity from 5 h to 1 week post-SCI. Early increases in ITP at 5 h post-injury were associated with significant increases in blood volume. ITP, however, was maximal at 3 days post-SCI, at which time there was an associated significant increase in edema that persisted for 1 week. We conclude that raised ITP after traumatic SCI is initially driven by volumetric increases in hemorrhage, while edema becomes the primary driver of ITP at 3 days post-injury.

Contrast enhanced ultrasound imaging for assessment of spinal cord blood flow in experimental spinal cord injury

Reduced spinal cord blood flow (SCBF) (i.e., ischemia) plays a key role in traumatic spinal cord injury (SCI) pathophysiology and is accordingly an important target for neuroprotective therapies. Although several techniques have been described to assess SCBF, they all have significant limitations. To overcome the latter, we propose the use of real-time contrast enhanced ultrasound imaging (CEU). Here we describe the application of this technique in a rat contusion model of SCI. A jugular catheter is first implanted for the repeated injection of contrast agent, a sodium chloride solution of sulphur hexafluoride encapsulated microbubbles. The spine is then stabilized with a custom-made 3D-frame and the spinal cord dura mater is exposed by a laminectomy at ThIX-ThXII. The ultrasound probe is then positioned at the posterior aspect of the dura mater (coated with ultrasound gel). To assess baseline SCBF, a single intravenous injection (400 µl) of contrast agent is applied to record its passage through the intact spinal cord microvasculature. A weight-drop device is subsequently used to generate a reproducible experimental contusion model of SCI. Contrast agent is re-injected 15 min following the injury to assess post-SCI SCBF changes. CEU allows for real time and in-vivo assessment of SCBF changes following SCI. In the uninjured animal, ultrasound imaging showed uneven blood flow along the intact spinal cord. Furthermore, 15 min post-SCI, there was critical ischemia at the level of the epicenter while SCBF remained preserved in the more remote intact areas. In the regions adjacent to the epicenter (both rostral and caudal), SCBF was significantly reduced. This corresponds to the previously described "ischemic penumbra zone". This tool is of major interest for assessing the effects of therapies aimed at limiting ischemia and the resulting tissue necrosis subsequent to SCI.

Venous drainage of the spine and spinal cord: a comprehensive review of its history, embryology, anatomy, physiology, and pathology

Venous drainage of the spine and spinal cord is accomplished through a complex network of venous structures compartmentalized to intrinsic, extrinsic, and extradural systems. As the literature on this topic is scarce, the following review was performed to summarize the available literature into a single coherent format. The medical literature on the spinal venous system was reviewed using online sources as well as historical documents that were not available online in regard to history, embryology, anatomy, and physiology with a particular emphasis on the pathology affecting this system. The spinal venous system is complex and variable. Proper understanding of all aspects is critical for the management of the pathology that results from its failure.

Substance P as a mediator of neurogenic inflammation after balloon compression induced spinal cord injury

Although clinical spinal cord injury (SCI) occurs within a closed environment, most experimental models of SCI create an open injury. Such an open environment precludes the measurement of intrathecal pressure (ITP), whose increase after SCI has been linked to the development of greater tissue damage and functional deficits. Raised ITP may be potentiated by edema, which we have recently shown to be associated with substance P (SP) induced neurogenic inflammation in both traumatic brain injury and stroke. The present study investigates whether SP plays a similar role as a mediator of neurogenic inflammation after SCI. A closed balloon compression injury was induced at T10 in New Zealand white rabbits. Animals were thereafter assessed for blood spinal cord barrier (BSCB) permeability, edema, ITP, histological outcome, and functional outcome from 5 h to 2 weeks post-SCI. The balloon compression model produced significant increases in BSCB permeability, edema, and ITP along with significant functional deficits that persisted for 2 weeks. Histological assessment demonstrated decreased SP immunoreactivity in the injured spinal cord while NK1 receptor immunoreactivity initially increased before returning to sham levels. In addition, aquaporin 4 immunoreactivity increased early post-SCI, implicating this water channel in the development of edema after SCI. The changes described in the present study support a role for SP as a mediator of neurogenic inflammation after SCI.

Rat model of spinal cord injury preserving dura mater integrity and allowing measurements of cerebrospinal fluid pressure and spinal cord blood flow

PURPOSES

Cerebrospinal fluid (CSF) pressure elevation may worsen spinal cord ischaemia after spinal cord injury (SCI). We developed a rat model to investigate relationships between CSF pressure and spinal cord blood flow (SCBF).

METHODS

Male Wistar rats had SCI induced at Th10 (n = 7) or a sham operation (n = 10). SCBF was measured using laser-Doppler and CSF pressure via a sacral catheter. Dural integrity was assessed using subdural methylene-blue injection (n = 5) and myelography (n = 5).

RESULTS

The SCI group had significantly lower SCBF (p < 0.0001) and higher CSF pressure (p < 0.0001) values compared to the sham-operated group. Sixty minutes after SCI or sham operation, CSF pressure was 8.6 ± 0.4 mmHg in the SCI group versus 5.5 ± 0.5 mmHg in the sham-operated group. No dural tears were found after SCI.

CONCLUSION

Our rat model allows SCBF and CSF pressure measurements after induced SCI. After SCI, CSF pressure significantly increases.

The pressure distribution of cerebrospinal fluid responds to residual compression and decompression in an animal model of acute spinal cord injury

STUDY DESIGN

In vivo large animal (pig) model study of cerebrospinal fluid (CSF) pressures after acute experimental spinal cord injury (SCI).

OBJECTIVE

To determine how the CSF pressure (CSFP) and CSF pulse pressure amplitude (CSFPPA) cranial and caudal to the injury site change after an acute SCI with subsequent thecal occlusion and decompression.

SUMMARY OF BACKGROUND DATA

Lowering intrathecal pressure via CSF drainage is currently instituted to prevent ischemia-induced SCI during thoracoabdominal aortic aneurysm surgery and was recently investigated as a potential intervention for acute traumatic SCI. However, in SCI patients, persistent extradural compression commonly occludes the subarachnoid space. This may generate a CSFP differential across the injury site, which cannot be appreciated with lumbar catheter pressure measurements.

METHODS

Anesthetized pigs were subjected to an acute contusive SCI at T11 and 8 hours of sustained compression (n = 12), or sham surgery (n = 2). CSFP was measured cranial and caudal to the injury site, using miniature pressure transducers, during compression and for 6 hours after decompression.

RESULTS

The cranial-caudal CSFP differential increased (mean, 0.39 mm Hg/h), predominantly due to increased cranial pressure. On decompression, cranial CSFP decreased (mean, -1.16 mm Hg) and caudal CSFP increased (mean, 0.65 mm Hg). The CSFP differential did not change significantly after decompression. Cranial CSFPPA was greater than caudal CSFPPA, but this differential did not change during compression. On decompression, the caudal CSFPPA increased in some but not all animals.

CONCLUSION

Although extradural compression exists at the site of injury, lumbar CSFP may not accurately indicate CSFP cranial to the injury. Decompression may provide immediate, though perhaps partial, resolution of the pressure differential. CSFPPA was not a consistent indicator of decompression in this animal model. These findings may have implications for the design of future clinical protocols in which CSFP is monitored after acute SCI.

Real-time and spatial quantification using contrast-enhanced ultrasonography of spinal cord perfusion during experimental spinal cord injury

STUDY DESIGN

Experimental study in male Wistar rats.

OBJECTIVE

To quantify temporal and spatial changes simultaneously in spinal cord blood flow and hemorrhage during the first hour after spinal cord injury (SCI), using contrast-enhanced ultrasonography (CEU).

SUMMARY OF BACKGROUND DATA

Post-traumatic ischemia and hemorrhage worsen the primary lesions induced by SCI. Previous studies did not simultaneously assess temporal and spatial changes in spinal cord blood flow.

METHODS

SCI was induced at Th10 in 12 animals, which were compared with 11 sham-operated controls. Spinal cord blood flow was measured in 7 adjacent regions of interest and in the sum of these 7 regions. Blood flow was quantified using CEU with intravenous microbubble injection. Spinal cord hemorrhage was measured on conventional B-mode sonogram slices.

RESULTS

CEU allowed us to measure the temporal and spatial changes in spinal cord blood flow in both groups. In the SCI group, spinal cord blood flow was significantly decreased in the global region of interest (P = 0.0016), at the impact site (epicenter), and in the 4 regions surrounding the epicenter, compared with the sham group. The blood flow decrease was maximum at the epicenter. No statistically significant differences between the sham groups were found for the most rostral and caudal regions of interest. Hemorrhage size increased significantly with time (P < 0.0001), from 30.3 mm(2) (±2) after 5 minutes to 39.6 mm(2) (±2.3) after 60 minutes.

CONCLUSION

CEU seems reliable for quantifying temporal and spatial changes in spinal cord blood flow. After SCI, bleeding occurs in the spinal cord parenchyma and increases significantly throughout the first hour.

Blood supply and vascular reactivity of the spinal cord under normal and pathological conditions

The authors present a review of spinal cord blood supply, discussing the anatomy of the vascular system and physiological aspects of blood flow regulation in normal and injured spinal cords. Unique anatomical functional properties of vessels and blood supply determine the susceptibility of the spinal cord to damage, especially ischemia. Spinal cord injury (SCI), for example, complicating thoracoabdominal aortic aneurysm repair is associated with ischemic trauma. The rate of this devastating complication has been decreased significantly by instituting physiological methods of protection. Traumatic SCI causes complex changes in spinal cord blood flow, which are closely related to the severity of injury. Manipulating physiological parameters such as mean arterial blood pressure and intrathecal pressure may be beneficial for patients with an SCI. Studying the physiopathological processes of the spinal cord under vascular compromise remains challenging because of its central role in almost all of the body's hemodynamic and neurofunctional processes.