Serial Measurements of Serum Glial Fibrillary Acidic Protein in Moderate-Severe Traumatic Brain Injury: Potential Utility in Providing Insights into Secondary Insults and Long-Term Outcome

In patients with traumatic brain injury (TBI), serum biomarkers may have utility in assessing the evolution of secondary brain injury. A panel of nine brain-injury- associated biomarkers was measured in archived serum samples over 10 days post-injury from 100 patients with moderate-severe TBI. Among the biomarkers evaluated, serum glial fibrillary acidic protein (GFAP) had the strongest associations with summary measures of acute pathophysiology, including intracranial pressure (ICP), cerebral perfusion pressure (CPP), and brain tissue pO2 (PbtO2). Group based trajectory (TRAJ) analysis was used to identify three distinct GFAP subgroups. The low TRAJ group (n = 23) had peak levels of 9.4 + 1.2 ng/mL that declined rapidly. The middle TRAJ group (n = 48) had higher peak values (31.5 + 5.0 ng/mL) and a slower decline over time. The high TRAJ group (n = 26) had very high, sustained peak values (59.6 + 12.5 ng/mL) that even rose among some patients over 10 days. Patients in the high TRAJ group had significantly higher mortality rate than patients in low and middle TRAJ groups (26.9% vs. 7.0%, p = 0.028). The frequency of poor neurological outcome (Glasgow Outcome Score Extended [GOS-E] 1-4) was 88.5% in the high TRAJ group, 54.2% in the middle TRAJ group, and 30.4% in the low TRAJ group (p < 0.001). ICP was highest in the high TRAJ group (median 17.6 mm Hg), compared with 14.4 mmHg in the low and 15.9 mm Hg in middle TRAJ groups (p = 0.002). High TRAJ patients spent the longest time with ICP >25 mm Hg, median 23 h, compared with 2 and 6 h in the low and middle TRAJ groups (p = 0.006), and the longest time with ICP >30 mm Hg, median 5 h, compared with 0 and 1 h in the low and middle TRAJ groups, respectively (p = 0.013). High TRAJ group patients more commonly required tier 2 or 3 treatment to control ICP. The high TRAJ group had the longest duration when CPP was <50 mm Hg (p = 0.007), and PbtO2 was <10 mm Hg (p = 0.002). Logistical regression was used to study the relationship between temporal serum GFAP patterns and 6-month GOS-E. Here, the low and middle TRAJ groups were combined to form a low-risk group, and the high TRAJ group was designated the high-risk group. High TRAJ group patients had a greater chance of a poor 6-month GOS-E (p < 0.0001). When adjusting for baseline injury characteristics, GFAP TRAJ group membership remained associated with GOS-E (p = 0.003). When an intensive care unit (ICU) injury burden score, developed to quantify physiological derangements, was added to the model, GFAP TRAJ group membership remained associated with GOS-E (p = 0.014). Mediation analysis suggested that ICU burden scores were in the causal pathway between TRAJ group and 6-month mortality or GOS-E. Our results suggest that GFAP may be useful to monitor serially in moderate-severe TBI patients. Future studies in larger cohorts are needed to confirm these results.

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.

Safety profile of an intracranial multimodal monitoring bolt system for neurocritical care: a single-center experience

BACKGROUND

Intracranial multimodality monitoring (iMMM) is increasingly used in acute brain-injured patients; however, safety and reliability remain major concerns to its routine implementation.

METHODS

We performed a retrospective study including all patients undergoing iMMM at a single European center between July 2016 and January 2020. Brain tissue oxygenation probe (PbtO₂), alone or in combination with a microdialysis catheter and/or an 8-contact depth EEG electrode, was inserted using a triple-lumen bolt system and targeting normal-appearing at-risk brain area on the injured side, whenever possible. Surgical complications, adverse events, and technical malfunctions, directly associated with iMMM, were collected. A blinded imaging review was performed by an independent radiologist.

RESULTS

One hundred thirteen patients with 123 iMMM insertions were included for a median monitoring time of 9 [3-14] days. Of those, 93 (76%) patients had only PbtO₂ probe insertion and 30 (24%) had also microdialysis and/or iEEG monitoring. SAH was the most frequent indication for iMMM (n = 60, 53%). At least one complication was observed in 67/123 (54%) iMMM placement, corresponding to 58/113 (51%) patients. Misplacement was observed in 16/123 (13%), resulting in a total of 6/16 (38%) malfunctioning PbtO₂ catheters. Intracranial hemorrhage was observed in 14 iMMM placements (11%), of which one required surgical drainage. Five placements were complicated by pneumocephalus and 4 with bone fragments; none of these requires additional surgery. No CNS infection related to iMMM was observed. Seven (6%) probes were accidentally dislodged and 2 probes (2%) were accidentally broken. Ten PbtO₂ probes (8%) presented a technical malfunction after a median of 9 [ranges: 2-24] days after initiation of monitoring and 4 of them were replaced.

CONCLUSIONS

In this study, a high occurrence of complications related to iMMM was observed, although most of them did not require specific interventions and did not result in malfunctioning monitoring.

A Review of Monitoring Methods for Cerebral Blood Oxygen Saturation

In recent years, cerebral blood oxygen saturation has become a key indicator during the perioperative period. Cerebral blood oxygen saturation monitoring is conducive to the early diagnosis and treatment of cerebral ischemia and hypoxia. The present study discusses the three most extensively used clinical methods for cerebral blood oxygen saturation monitoring from different aspects: working principles, relevant parameters, current situations of research, commonly used equipment, and relative advantages of different methods. Furthermore, through comprehensive comparisons of the methods, we find that near-infrared spectroscopy (NIRS) technology has significant potentials and broad applications prospects in terms of cerebral oxygen saturation monitoring. Despite the current NIRS technology, the only bedside non-invasive cerebral oxygen saturation monitoring technology, still has many defects, it is more in line with the future development trend in the field of medical and health, and will become the main method gradually.

A management algorithm for adult patients with both brain oxygen and intracranial pressure monitoring: the Seattle International Severe Traumatic Brain Injury Consensus Conference (SIBICC)

Background

Current guidelines for the treatment of adult severe traumatic brain injury (sTBI) consist of high-quality evidence reports, but they are no longer accompanied by management protocols, as these require expert opinion to bridge the gap between published evidence and patient care. We aimed to establish a modern sTBI protocol for adult patients with both intracranial pressure (ICP) and brain oxygen monitors in place.

Methods

Our consensus working group consisted of 42 experienced and actively practicing sTBI opinion leaders from six continents. Having previously established a protocol for the treatment of patients with ICP monitoring alone, we addressed patients who have a brain oxygen monitor in addition to an ICP monitor. The management protocols were developed through a Delphi-method-based consensus approach and were finalized at an in-person meeting.

Results

We established three distinct treatment protocols, each with three tiers whereby higher tiers involve therapies with higher risk. One protocol addresses the management of ICP elevation when brain oxygenation is normal. A second addresses management of brain hypoxia with normal ICP. The third protocol addresses the situation when both intracranial hypertension and brain hypoxia are present. The panel considered issues pertaining to blood transfusion and ventilator management when designing the different algorithms.

Conclusions

These protocols are intended to assist clinicians in the management of patients with both ICP and brain oxygen monitors but they do not reflect either a standard-of-care or a substitute for thoughtful individualized management. These protocols should be used in conjunction with recommendations for basic care, management of critical neuroworsening and weaning treatment recently published in conjunction with the Seattle International Brain Injury Consensus Conference.

Electronic supplementary material

The online version of this article (10.1007/s00134-019-05900-x) contains supplementary material, which is available to authorized users.

Analysis of high-frequency PbtO2 measures in traumatic brain injury: insights into the treatment threshold

OBJECTIVE

Brain tissue hypoxia is common after traumatic brain injury (TBI). Technology now exists that can detect brain hypoxia and guide corrective therapy. Current guidelines for the management of severe TBI recommend maintaining partial pressure of brain tissue oxygen (PbtO2) > 15-20 mm Hg; however, uncertainty persists as to the optimal treatment threshold. The object of this study was to better inform the relationship between PbtO2 values and outcome for patients with TBI.

METHODS

PbtO2 measurements were prospectively and automatically collected every minute from consecutive patients admitted to the San Francisco General Hospital neurological ICU during a 6-year period. Mean PbtO2 values in TBI patients as well as the proportion of PbtO2 values below each of 75 thresholds between 0 mm Hg and 75 mm Hg over various epochs up to 30 days from the time of admission were analyzed. Patient outcomes were determined using the Glasgow Outcome Scale. The authors explored putative treatment thresholds by generating 675 separate receiver operating characteristic curves and 675 generalized linear models to examine each 1-mm Hg threshold for various epochs.

RESULTS

A total of 1,380,841 PbtO2 values were recorded in 190 TBI patients. A high proportion of PbtO2 measures were below 20 mm Hg irrespective of the examined epoch. Time below treatment thresholds was more strongly associated with outcome than mean PbtO2. A treatment window was suggested: a threshold of 19 mm Hg most robustly distinguished patients by outcome, especially from days 3-5; however, benefit was suggested from maintaining values at least as high as 33 mm Hg.

CONCLUSIONS

This analysis of high-frequency physiological data substantially informs the relationship between PbtO2 values and outcome. The results suggest a therapeutic window for PbtO2 in TBI patients along with minimum and preferred PbtO2 treatment thresholds, which may be examined in future studies. Traditional treatment thresholds that have the strongest association with outcome may not be optimal.