Clinical evaluation of the InnerSpace fibreoptic intracranial pressure monitoring device

Fiber-Optic Intracranial Pressure Monitoring System Using Wi-Fi-An In Vivo Study

BACKGROUND

Continuous invasive monitoring of intracranial pressure (ICP) is essential in neurocritical care for surveillance and management of raised ICP. Fluid-based systems and strain gauge microsensors remain the current standard. In the past few decades, several studies with wireless monitoring were developed aiming to reduce invasiveness and complications.

OBJECTIVE

To describe a novel Wi-Fi fiber-optic device for continuous ICP monitoring using smartphone in a swine model.

METHODS

Two ICP sensors (wireless prototype and wire-based reference) were implanted in the cerebral parenchyma of a swine model for a total of 120 minutes of continuous monitoring. Every 5 minutes, jugular veins compression was performed to evaluate ICP changes. The experimentation was divided in 3 phases for comparison and analysis.

RESULTS

Phase 1 showed agreement in ICP changes for both sensors during jugular compression and releasing, with a positive and strong Spearman correlation (r = 0.829, P < .001). Phase 2 started after inversion of the sensors in the burr holes; there was a positive and moderately weak Spearman correlation (r = 0.262, P < .001). For phase 3, the sensors were returned to the first burr holes; the prototype behaved similarly to the reference sensor, presenting a positive and moderately strong Spearman correlation (r = 0.669, P < .001).

CONCLUSION

A Wi-Fi ICP monitoring system was demonstrated in a comprehensive and feasible way. It was possible to observe, using smartphone, an adequate correlation regarding ICP variations. Further adaptations are already being developed.

Brain tissue oxygen tension and its response to physiological manipulations: influence of distance from injury site in a swine model of traumatic brain injury

OBJECTIVE The optimal site for placement of tissue oxygen probes following traumatic brain injury (TBI) remains unresolved. The authors used a previously described swine model of focal TBI and studied brain tissue oxygen tension (P_btO₂) at the sites of contusion, proximal and distal to contusion, and in the contralateral hemisphere to determine the effect of probe location on P_btO₂ and to assess the effects of physiological interventions on P_btO₂ at these different sites. METHODS A controlled cortical impact device was used to generate a focal lesion in the right frontal lobe in 12 anesthetized swine. P_btO₂ was measured using Licox brain tissue oxygen probes placed at the site of contusion, in pericontusional tissue (proximal probe), in the right parietal region (distal probe), and in the contralateral hemisphere. P_btO₂ was measured during normoxia, hyperoxia, hypoventilation, and hyperventilation. RESULTS Physiological interventions led to expected changes, including a large increase in partial pressure of oxygen in arterial blood with hyperoxia, increased intracranial pressure (ICP) with hypoventilation, and decreased ICP with hyperventilation. Importantly, P_btO₂ decreased substantially with proximity to the focal injury (contusion and proximal probes), and this difference was maintained at different levels of fraction of inspired oxygen and partial pressure of carbon dioxide in arterial blood. In the distal and contralateral probes, hypoventilation and hyperventilation were associated with expected increased and decreased P_btO₂ values, respectively. However, in the contusion and proximal probes, these effects were diminished, consistent with loss of cerebrovascular CO₂ reactivity at and near the injury site. Similarly, hyperoxia led to the expected rise in P_btO₂ only in the distal and contralateral probes, with little or no effect in the proximal and contusion probes, respectively. CONCLUSIONS P_btO₂ measurements are strongly influenced by the distance from the site of focal injury. Physiological alterations, including hyperoxia, hyperventilation, and hypoventilation substantially affect P_btO₂ values distal to the site of injury but have little effect in and around the site of contusion. Clinical interpretations of brain tissue oxygen measurements should take into account the spatial relation of probe position to the site of injury. The decision of where to place a brain tissue oxygen probe in TBI patients should also take these factors into consideration.

Intracranial pressure monitoring: why monitor?

Evidence suggests that the mortality and morbidity of acquired brain injury could be reduced if clinicians used an aggressive intracranial pressure guided approach to care. Despite nearly 50 years of evidence that intracranial pressure monitoring benefits patient care, only about half of the patients who could benefit are monitored. Some clinicians express concerns regarding risks such as bleeding, infections, and inaccuracy of the technology. Others cite cost as the reason. This article discusses the risks and benefits of intracranial pressure monitoring and the current state of evidence of why patients should be monitored.

Advances in ICP monitoring techniques

With the advent of newer devices for measuring intracranial pressure (ICP) and cerebral metabolism, more alternatives continue to rise aiming to control ICP. This manuscript presents a proposed analysis of different ICP monitoring devices in order to make appropriate selection of them in our clinical setting including general and pediatric applications. A systematic review of the literature was made analyzing the technical advances in ICP monitoring. The recent in vitro and in vivo tests as well as mathematical/computer models were reviewed. Practical applications of principles were discussed and compared based on the mode of pressure transformation. A ventricular catheter connected to an external strain gauge transducer or catheter tip pressure transducer device is considered to be the most accurate method of monitoring ICP and enables therapeutic CSF drainage. The significant infections or hemorrhage associated with ICP devices causing patients morbidity are clinically rare and should not deter the decision to monitor ICP. Parenchymal catheter tip pressure transducer devices are advantageous when ventricular ICP cannot be obtained or if there is an obstruction in the fluid couple, though they have the potential for significant measurement differences and drift due to the inability to recalibrate. Subarachnoid or subdural fluid-coupled devices and epidural ICP devices are currently less accurate. With an increasing miniaturization of the transducers, fiberoptic systems have been developed, however, there is a problem of measurement accuracy during the period of patient monitoring and external calibration should be performed frequently to ensure constant accuracy. Ventriculostomies continue to have a pivotal role in ICP control. With a rational understanding of the applications and limitations of the different ICP monitoring devices, the outcome for critically ill neurological patients is optimized.

The Camino intracranial pressure sensor: is it optimal technology? An internal audit with a review of current intracranial pressure monitoring technologies

OBJECTIVE

To audit the reliability of the Camino intracranial pressure (ICP) sensor (Camino Laboratories, San Diego, CA) in our clinical practice as part of a continuing quality assurance program, and to assess its relative usefulness as compared with currently available ICP monitoring technologies that we reviewed.

DESIGN

Prospective audit of ICP device reliability and function in 50 patients with head injuries.

METHODS

Zero drift was recorded immediately after the ICP device was removed from the patient. Dynamic frequency response bench testing of each functioning catheter from 0 to 30 Hz and static calibration testing from 0 to 100 mmHg during environmental temperature variation from 22 to 40 degrees C were carried out.

RESULTS

Zero drift (range, -13 to 22 mmHg; median, -1 mmHg) was recorded immediately after the devices were removed from patients. Seventeen (50%) of the devices tested for zero drift had absolute drifts of at least 3 mmHg. There was no correlation between recorded zero drift and duration of monitoring (r = 0.154, P = 0.207). Five sensors (10% of those tested) failed during patient monitoring and were replaced. Static and dynamic calibration tests of the functioning sensors were within the manufacturer's specifications. However, the sensitivity of the devices to environmental temperature remains a problem.

CONCLUSION

The Camino ICP sensor remains one of the most popular ICP monitoring devices for use in patients with traumatic brain injuries. However, our recent in-house assessment demonstrated the robustness of the device to be less than adequate during routine practice. In this study, more than 50% exhibited zero drift greater than 3 mmHg, which is unacceptable in a catheter tip ICP monitoring device in which zero drift and calibration cannot be checked in vivo. A review of the literature revealed that other available ICP monitoring devices may prove to be more reliable and thus more appropriate for routine clinical measurement of ICP.

Bedside invasive monitoring techniques in severe brain-injured patients

In patients with severe brain injury, brain edema, elevated intracranial pressure, and cerebral ischemia are accountable for a significant morbidity and mortality. New invasive methods of monitoring attempt to foresee the physiopathological mechanisms responsible for the production of secondary brain injuries. The available methods for monitoring severely brain-injured patients, their potential usefulness, advantages, and disadvantages are reviewed.