Cardiac-gated intracranial elastance in a swine model of raised intracranial pressure: a novel method to assess intracranial pressure-volume dynamics

Open cranium model for the study of cerebrovascular dynamics in intracranial hypertension

BACKGROUND

Significant research has been devoted to developing noninvasive approaches to neuromonitoring. Clinical validation of such approaches is often limited, with minimal data available in the clinically relevant elevated ICP range.

NEW METHOD

To allow ultrasound-guided placement of an intraventricular catheter and to perform simultaneous long-duration ICP and ultrasound recordings of cerebral blood flow, we developed a large unilateral craniectomy in a swine model. We also used a microprocessor-controlled actuator for intraventricular saline infusion to reliably and reversibly manipulate ICP according to pre-determined profiles.

RESULTS

The model was reproducible, resulting in over 80 hours of high-fidelity, multi-parameter physiological waveform recordings in twelve animals, with ICP ranging from 2 to 78 mmHg. ICP elevations were reversible and reproducible according to two predetermined profiles: a stepwise elevation up to an ICP of 30-35 mmHg and return to normotension, and a clinically significant plateau wave. Finally, ICP was elevated to extreme levels of greater than 60 mmHg, simulating extreme clinical emergency.

COMPARISON WITH EXISTING METHODS

Existing methods for ICP monitoring in large animals typically relied on burr-hole approaches for catheter placement. Accurate catheter placement can be difficult in pigs, given the thickness of their skull. Additionally, ultrasound is significantly attenuated by the skull. The open cranium model overcomes these limitations.

CONCLUSIONS

The hemicraniectomy model allowed for verified placement of the intraventricular catheter, and reversible and reliable ICP manipulation over a wide range. The large dural window additionally allowed for long-duration recording of cerebral blood flow velocity from the middle cerebral artery.

Neurovascular Interventions for Neurotrauma: From Treatment of Injured Vessels to Treatment of the Injured Brain?

Traumatic brain injury is often associated with a direct or secondary neurovascular pathology. In this review, we present recent advancements in endovascular neurosurgery that enable accurate and effective vessel reconstruction with emphasis on its role in early diagnosis, the expanding use of flow diversion in pseudoaneurysms, and traumatic arteriovenous fistulas. In addition, future directions in which catheter-based interventions could potentially affect traumatic brain injury are described: targeting blood brain barrier integrity using the advantages of intra-arterial drug delivery of blood brain barrier stabilizers to prevent secondary brain edema, exploring the impact of endovascular venous access as a means to modulate venous outflow in an attempt to reduce intracranial pressure and augment brain perfusion, applying selective intra-arterial hypothermia as a neuroprotection method mitigating some of the risks conferred by systemic cooling, trans-vessel wall delivery of regenerative therapy agents, and shifting attention using multimodal neuromonitoring to post-traumatic vasospasm to further characterize the role it plays in secondary brain injury. Thus, we believe that the potential of endovascular tools can be expanded because they enable access to the "highways" governing perfusion and flow and call for further research focused on exploring these routes because it may contribute to novel endovascular approaches currently used for treating injured vessels, harnessing them for treatment of the injured brain.

Intraorbital pressure-volume characteristics in a piglet model: In vivo pilot study

Intracranial pressure measurement is frequently used for diagnosis in neurocritical care but cannot always accurately predict neurological deterioration. Intracranial compliance plays a significant role in maintaining cerebral blood flow, cerebral perfusion pressure, and intracranial pressure. This study's objective was to investigate the feasibility of transferring external pressure into the eye orbit in a large-animal model while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures. The experimental system comprised a specifically designed pressure applicator that can be placed and tightly fastened onto the eye. A pressure chamber made from thin, elastic, non-allergenic film was attached to the lower part of the applicator and placed in contact with the eyelid and surrounding tissues of piglets' eyeballs. External pressure was increased from 0 to 20 mmHg with steps of 1 mmHg, from 20 to 30 mmHg with steps of 2 mmHg, and from 30 to 50 mmHg with steps of 5 mmHg. An invasive pressure sensor was used to measure intraorbital pressure directly. An equation was derived from measured intraorbital and external pressures (intraorbital pressure = 0.82 × external pressure + 3.12) and demonstrated that external pressure can be linearly transferred to orbit tissues with a bias (systematic error) of 3.12 mmHg. This is close to the initial intraorbital pressure within the range of pressures tested. We determined the relationship between intraorbital compliance and externally applied pressure. Our findings indicate that intraorbital compliance can be controlled across a wide range of 1.55 to 0.15 ml/mmHg. We observed that external pressure transfer into the orbit can be achieved while maintaining a clinically acceptable pressure gradient between intraorbital and external pressures.

Intracranial pressure: current perspectives on physiology and monitoring

Intracranial pressure (ICP) monitoring is now viewed as integral to the clinical care of many life-threatening brain insults, such as severe traumatic brain injury, subarachnoid hemorrhage, and malignant stroke. It serves to warn of expanding intracranial mass lesions, to prevent or treat herniation events as well as pressure elevation which impedes nutrient delivery to the brain. It facilitates the calculation of cerebral perfusion pressure (CPP) and the estimation of cerebrovascular autoregulatory status. Despite advancements in our knowledge emanating from a half century of experience with this technology, important controversies remain related even to fundamental aspects of ICP measurements, including indications for monitoring, ICP treatment thresholds, and management of intracranial hypertension. Here, we review the history of ICP monitoring, the underlying pathophysiology as well as current perspectives on why, when and how ICP monitoring is best used. ICP is typically assessed invasively but a number of emerging, non-invasive technologies with inherently lower risk are showing promise. In selected cases, additional neuromonitoring can be used to assist in the interpretation of ICP monitoring information and adapt directed treatment accordingly. Additional efforts to expand the evidence base relevant to ICP monitoring, related technologies and management remain a high priority in neurosurgery and neurocritical care.

Intracranial Pulsating Balloon-Based Cardiac-Gated ICP Modulation Impact on Brain Oxygenation: A Proof-of-Concept Study in a Swine Model

BACKGROUND

Brain oxygenation improvement is a sought-after goal in neurocritical care patients. Previously, we have shown that cerebral blood flow improvement by cardiac-gated intracranial pressure (ICP) modulation using an intracranial pulsating balloon is feasible in a swine model. We sought to explore specific ICP modulation protocols to assess the feasibility of influencing brain oxygenation.

METHODS

A previously presented electrocardiogram (ECG)-gated intracranial balloon pump in which volume, timing, and duty cycle of balloon inflation could be altered was used. Different protocols were tested in a swine model of normal and elevated ICP attained by intracranial fluid infusion with continuous monitoring of physiological parameters, and brain tissue oxygen tension (PbtO₂) was measured at baseline and after device activation.

RESULTS

We studied five swine, subjected to two main protocols differing in their phase relative to the cardiac cycle. In reduced brain perfusion status (ICP > 20 mm Hg, PbtO₂ < 15 mm Hg), the late-diastolic-early-systolic (Inflation/deflation) protocol showed consistent elevation in PbtO₂ (+ 9%, p < 0.01), coupled with ICP reduction (- 12%, p < 0.01), whereas the early-systolic-late-diastolic (inflation/deflation) protocol resulted in PbtO₂ reduction (- 4%, p < 0.01), coupled with ICP increase (+ 5% above baseline, p < 0.01). No significant changes in brain oxygenation or ICP were observed at normal perfusion status (ICP < 20 mm Hg, PbtO₂ > 15 mm Hg).

CONCLUSIONS

Intracranial cardiac-gated balloon pump activation can influence cerebral oxygenation and raise PbtO₂ above threshold values. This study supports the concept of late-diastolic pressure rise, coupled with early-systolic pressure drop, as a potential effector of flow augmentation leading to improve brain tissue oxygenation. Further studies are warranted to assess the translational potential of using an intracranial cardiac-gated balloon pump device to improve brain tissue oxygenation.