Sonographic Optic Nerve Sheath Diameter as an Estimate of Intracranial Pressure in Adult Trauma

Authors: Strumwasser A, Kwan RO, Yeung L, Miraflor E, Ereso A, Castro-Moure F, Patel A, Sadjadi J, Victorino GP.

Department of Surgery, University of California, San Francisco-East Bay, Oakland, California.

BACKGROUND: Intracranial pressure (ICP) is currently measured with invasive monitoring. Sonographic optic nerve sheath diameter (ONSD) may provide a noninvasive estimate of ICP. Our hypothesis was that bedside ONSD accurately estimates ICP in acutely injured patients. The specific aims were (1) to determine the accuracy of ONSD in estimating elevated ICP, (2) to correlate ONSD and ICP in unilateral and bilateral head injuries, and (3) to determine the effect of ICP monitor placement on ONSD measurements.

MATERIALS AND METHODS: A blinded prospective study of adult trauma patients requiring ICP monitoring was performed at a University-based urban trauma center. The ONSD was measured by ultrasound pre- and post-placement of an ICP monitor (Camino Bolt or Ventriculostomy).

RESULTS: One-hundred fourteen measurements were obtained in 10 trauma patients requiring ICP monitoring. Pre- and post-ONSD were compared with side of injury in the presence of an ICP monitor. ROC analysis demonstrated ONSD poorly estimates elevated ICP (AUC = 0.36). Overall sensitivity, specificity, PPV, NPV, and accuracy for estimating ICP with ONSD were 36%, 38%, 40%, 16%, and 37%. Poor correlation of ONSD to ICP was observed with unilateral (R(2) = 0.45, P < 0.01) and bilateral (R(2) = 0.21, P = 0.01) injuries. ICP monitor placement did not affect ONSD measurements on the right (P = 0.5), left (P = 0.4), or right and left sides combined (P = 0.3).

CONCLUSIONS: Sonographic ONSD as a surrogate for elevated ICP in lieu of invasive monitoring is not reliable due to poor accuracy and correlation.

Can chronic increased intracranial pressure or exposure to repetitive intermittent intracranial pressure elevations raise your risk for Alzheimer’s disease?

Author: Wostyn P

Over a decade ago, I formulated the hypothesis that cumulative effects of exposure to high intracranial pressure (ICP) may contribute to the development of Alzheimer's disease (AD), though not necessarily in an exclusive way. In addition to individual ICP characteristics (high 'physiological' ICP) and diseases causing ICP elevation, various activities with significant Valsalva effort, such as weightlifting and wind instrument playing, can generate very high ICPs. Recent studies of normal-pressure hydrocephalus (NPH), glaucoma and Alzheimer's disease provide supportive evidence for this hypothesis. A number of studies have shown a high incidence of AD related lesions in patients with NPH, which is known to be associated with prolonged elevation of ICP in a majority of cases. In both NPH and AD, an important decrease in cerebrospinal fluid (CSF) production was calculated. According to researchers in the US, the resulting CSF stagnation with impaired clearance and accumulation of neurotoxic substances may play an important role in the onset and progression of AD. They tested the hypothesis that improving CSF turnover by means of an investigational low-flow ventriculoperitoneal shunt will delay the progression of dementia in patients with Alzheimer's disease. With regard to the observed decrease in CSF production in patients suffering from NPH, it was postulated that chronic increased ICP causes downregulation of CSF production. It is hypothesized here that repetitive intermittent ICP elevations also may lead to downregulation of CSF production due to long-term cumulative effects. If the latter proves to be true, then both chronic increased ICP and repeated exposures to increased ICP (e.g., repetitive Valsalva maneuvers) may cause a similar cascade of CSF circulatory failure events leading to AD over time. Furthermore, AD may be causally related to increased ICP through other pathomechanisms. Additional supportive evidence for the role of a pressure factor in the pathogenesis of AD comes from studies concerning glaucoma. Elevated intraocular pressure (IOP) is a hallmark of glaucoma. Recently, similarities in pathophysiology between glaucoma and AD have been noted, with increased processing of amyloid precursor protein (APP) and up-regulation of beta-amyloid protein expression in retinal ganglion cells (RGCs). Given this link between AD and glaucoma, evidence for a causal relationship between repetitive intermittent ICP elevations and AD is gained from research indicating that high resistance wind instrument playing raises IOP and may result in glaucomatous damage. To test the validity of the hypothesis that exposure to repetitive but nonsustained ICP elevations may predispose to AD a non-invasive, epidemiological study is proposed in this paper.

Impact of intracranial pressure monitor prophylaxis on central nervous system infections and bacterial multi-drug resistance

Authors: Stoikes NF, Magnotti LJ, Hodges TM, Weinberg JA, Schroeppel TJ, Savage SA, Fischer PE, Fabian TC, Croce MA.

BACKGROUND:
Routine intracranial pressure monitor (ICP) prophylaxis is not practiced at our institution. Nevertheless, some patients receive de facto prophylaxis as a result of the use of antibiotics for injuries such as open or facial fractures. We tested the hypothesis that prophylactic antibiotics do not reduce the incidence of central nervous system (CNS) infections but instead are associated with the acquisition of multi-drug resistant (MDR) bacterial infections.

METHODS:
Patients admitted to the trauma intensive care unit (TICU) from January, 2001 through December, 2004 with blunt, non-operative traumatic brain injury who were managed solely with an ICP monitor were identified from our trauma registry and divided into two groups: (1) Those receiving no antibiotics prior to or during ICP monitoring (NONE; n = 71); and (2) those already receiving antibiotics at the time of ICP monitor insertion (PRO; n = 84). Groups were stratified on the basis of age, Injury Severity Score (ISS), Glasgow Coma Scale (GCS) Score, base excess (BE), ICP days, transfusions in 24 h, ICU days, ventilator days, head Abbreviated Injury Score (AIS), and chest AIS. The study groups did not differ with respect to age, ISS, GCS, BE, ICP days, 24-h transfusions, ICU days, ventilator days, head AIS, or length of stay. In all, 183 patients were identified, of whom 28 died within seven days and were excluded from the analysis. All patients were followed until discharge for both CNS infections and subsequent infectious complications.

RESULTS:
Only two patients, both in the PRO group, developed CNS infection. Both infectious complications (0.7 vs 1.4 per patient; p < 0.05) and infections secondary to MDR pathogens (0.03 vs. 0.33 per patient; p < 0.01) were significantly more common in the PRO group. Twenty-nine percent of the ventilator-associated pneumonias and 33% of the blood stream infections in the PRO group were MDR, whereas only two blood stream infections in the NONE group (4% of the total infections) were MDR.

CONCLUSIONS:
The routine use of prophylactic antibiotics for ICP monitor insertion is not warranted. This practice does not reduce the CNS infection rate and is associated with more MDR pathogens in any subsequent infectious complications.

Intracranial pressure: why we monitor it, how to monitor it, what to do with the number and what’s the future?

Authors: Andrea Lavinio and David K. Menon.

Improved ICP probes, antibiotic-impregnated ventricular catheters and multimodality, computerized systems allow ICP monitoring and individualized optimization of brain physiology. Noninvasive technologies for ICP and cerebral perfusion pressure assessment are being tested in the clinical arena. Computerized morphological analysis of the ICP pulse-waveform can provide an indicator of global cerebral perfusion.

Monitoring and interpretation of intracranial pressure

Authors: M Czosnyka and J Pickard

Although there is no "Class I" evidence, ICP monitoring is useful, if not essential, in head injury, poor grade subarachnoid haemorrhage, stroke, intracerebral haematoma, meningitis, acute liver failure, hydrocephalus, benign intracranial hypertension, craniosynostosis etc. Information which can be derived from ICP and its waveforms includes cerebral perfusion pressure (CPP), regulation of cerebral blood flow and volume, CSF absorption capacity, brain compensatory reserve, and content of vasogenic events. Some of these parameters allow prediction of prognosis of survival following head injury and optimisation of "CPP-guided therapy". In hydrocephalus CSF dynamic tests aid diagnosis and subsequent monitoring of shunt function.

Noninvasive intracranial compliance from MRI-based measurements of transcranial blood and CSF flows: indirect versus direct approach

Authors: Tain RW, Alperin N.

Intracranial compliance (ICC) determines the ability of the intracranial compartment to accommodate an increase in volume without a large increase in intracranial pressure (ICP). The clinical utilization of ICC is limited by the invasiveness of current measurement. Several investigators attempted to estimate ICC noninvasively, from magnetic resonance imaging (MRI) measurements of cerebral blood and cerebral spinal fluid flows, either using indirect measures of ICC or directly by measuring the ratio of the changes in intracranial volume and pressure during the cardiac cycle. The indirect measures include the phase lag between the cerebrospinal fluid (CSF) and its driving force, either arterial inflow or net transcranial blood flow. This study compares the sensitivity of phase-based and amplitude-based measures of ICC to changes in ICC. In vivo volumetric blood and CSF flows measured by MRI phase contrast from healthy volunteers and from patients with elevated ICP were used for the comparison. An RLC circuit model of the craniospinal system was utilized to simulate the effect of a change in ICC on the CSF flow waveform. The simulations demonstrated that amplitude-based measures of ICC are considerably more sensitive than phase-based measures, and among the amplitude-based measures, the ICC index provides the most reliable estimate of ICC.

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