Lack of utility of arteriojugular venous differences of lactate as a reliable indicator of increased brain anaerobic metabolism in traumatic brain injury

A Prospective Observational Feasibility Study of Jugular Bulb Microdialysis in Subarachnoid Hemorrhage

BACKGROUND

Cerebral metabolic perturbations are common in aneurysmal subarachnoid hemorrhage (aSAH). Monitoring cerebral metabolism with intracerebral microdialysis (CMD) allows early detection of secondary injury and may guide decisions on neurocritical care interventions, affecting outcome. However, CMD is a regional measuring technique that is influenced by proximity to focal lesions. Continuous microdialysis of the cerebral venous drainage may provide information on global cerebral metabolism relevant for the care of aSAH patients. This observational study aimed to explore the feasibility of jugular bulb microdialysis (JBMD) in aSAH and describe the output characteristics in relation to conventional multimodal monitoring.

METHODS

Patients with severe aSAH were included at admission or after in-house deterioration when local clinical guidelines prompted extended multimodal monitoring. Non-dominant frontal CMD, intracranial pressure (ICP), partial brain tissue oxygenation pressure (PbtO₂), and cerebral perfusion pressure (CPP) were recorded every hour. The dominant jugular vein was accessed by retrograde insertion of a microdialysis catheter with the tip placed in the jugular bulb under ultrasound guidance. Glucose, lactate, pyruvate, lactate/pyruvate ratio, glycerol, and glutamate were studied for correlation to intracranial measurements. Modified Rankin scale was assessed at 6 months.

RESULTS

Twelve adult aSAH patients were monitored during a mean 4.2 ± 2.6 days yielding 22,041 data points for analysis. No complications related to JBMD were observed. Moderate or strong significant monotonic CMD-to-JBMD correlations were observed most often for glucose (7 patients), followed by lactate (5 patients), and pyruvate, glycerol, and glutamate (3 patients). Moderate correlation for lactate/pyruvate ratio was only seen in one patient. Analysis of critical periods defined by ICP > 20, CPP < 65, or PbtO₂ < 15 revealed a tendency toward stronger CMD-to-JBMD associations in patients with many or long critical periods. Possible time lags between CMD and JBMD measurements were only identified in 6 out of 60 patient variables. With the exception of pyruvate, a dichotomized outcome was associated with similar metabolite patterns in JBMD and CMD. A nonsignificant tendency toward greater differences between outcome groups was seen in JBMD.

CONCLUSIONS

Continuous microdialysis monitoring of the cerebral drainage in the jugular bulb is feasible and safe. JBMD-to-CMD correlation is influenced by the type of metabolite measured, with glucose and lactate displaying the strongest associations. JBMD lactate correlated more often than CMD lactate to CPP, implying utility for detection of global cerebral metabolic perturbations. Studies comparing JBMD to other global measures of cerebral metabolism, e.g., PET CT or Xenon CT, are warranted.

Biochemical neuromonitoring of poor-grade aneurysmal subarachnoid hemorrhage: comparative analysis of metabolic events detected by cerebral microdialysis and by retrograde jugular vein catheterization

OBJECTIVES

In severe aneurysmal subarachnoid hemorrhage (aSAH), pathological changes in cerebral energy metabolism can be detected either by local measurements using cerebral microdialysis (cMD) together with brain tissue oxygen probe or by global measurements of arterio-jugular difference performed with retrograde jugular vein catheter. Our main objective was to compare the two methods of detection and assess whether combining biomarkers from both procedures could improve outcome prediction, which has never been studied before.

METHODS

This study included 400 sets of paired arterial and jugular venous samples and 3138 brain microdialyzates obtained from 18 poor-grade aSAH patients. Using Glasgow outcome scale (GOS), neurochemical data from unfavorable (GOS 1-3) and favorable (GOS 4-5) outcome groups were compared.

RESULTS

The lactate/pyruvate ratio was found as the most sensitive marker for predicting unfavorable outcome (90%), although not specific. In contrast, hypoxic lactate events and those of metabolic ratio (MR) < 3.44, most frequently observed in the unfavorable outcome group than in the favorable one (13.9 vs 0.9% and 33.3 vs 3.75% respectively), were shown to be more specific biomarkers (86%) to predict unfavorable outcome, but less sensitive ( < 70%). The combination of these three biomarkers improved the accuracy of outcome prediction (sensitivity 90% and specificity 71%).

DISCUSSION

Both retrograde jugular venous catheterization (RJVC) and cMD contribute to monitor poor-grade aSAH patients. In this preliminary study, we show that these two techniques are complementary and their combination increases the accuracy of outcome prediction.

The neurological wake-up test does not alter cerebral energy metabolism and oxygenation in patients with severe traumatic brain injury

BACKGROUND

The neurological wake-up test (NWT) is used to monitor the level of consciousness in patients with traumatic brain injury (TBI). However, it requires interruption of sedation and may elicit a stress response. We evaluated the effects of the NWT using cerebral microdialysis (MD), brain tissue oxygenation (PbtiO2), jugular venous oxygen saturation (SjvO2), and/or arterial-venous difference (AVD) for glucose, lactate, and oxygen in patients with severe TBI.

METHODS

Seventeen intubated TBI patients (age 16-74 years) were sedated using continuous propofol infusion. All patients received intracranial pressure (ICP) and cerebral perfusion pressure (CPP) monitoring in addition to MD, PbtiO2 and/or SjvO2. Up to 10 days post-injury, ICP, CPP, PbtiO2 (51 NWTs), MD (49 NWTs), and/or SjvO2 (18 NWTs) levels during propofol sedation (baseline) and NWT were compared. MD was evaluated at a flow rate of 1.0 μL/min (28 NWTs) or the routine 0.3 μL/min rate (21 NWTs).

RESULTS

The NWT increased ICP and CPP levels (p < 0.05). Compared to baseline, interstitial levels of glucose, lactate, pyruvate, glutamate, glycerol, and the lactate/pyruvate ratio were unaltered by the NWT. Pathological SjvO2 (<50 % or >71 %; n = 2 NWTs) and PbtiO2 (<10 mmHg; n = 3 NWTs) values were rare at baseline and did not change following NWT. Finally, the NWT did not alter the AVD of glucose, lactate, or oxygen.

CONCLUSIONS

The NWT-induced stress response resulted in increased ICP and CPP levels although it did not negatively alter focal neurochemistry or cerebral oxygenation in TBI patients.

Monitoring of acute traumatic brain injury in adults to prevent secondary brain damage

ABSTRACT: Traumatic brain injury is typically characterized by the primary injury initiating a cascade of pathologic changes that then lead to secondary brain injury. Secondary brain injury is amenable to different therapeutic options. Monitoring of otherwise occult pathologic changes involving oxygenation and metabolism is crucial for treatment decisions. Currently, decision-making is mainly based on measuring intracranial pressure and cerebral perfusion pressure. Importantly, extending neuromonitoring by including parameters reflecting cerebral perfusion, oxygenation and metabolism may improve treatment of traumatic brain injury patients by detecting neuronal damage despite optimal intracranial pressure or cerebral perfusion pressure and preventing unnecessarily aggressive treatment potentially causing local and systemic harm. In this review, the authors describe the advantages and disadvantages of contemporary, extended neuromonitoring methods in traumatic brain injury patients aimed at unmasking secondary brain damage as early as possible.

Effects of indomethacin test on intracranial pressure and cerebral hemodynamics in patients with refractory intracranial hypertension: a feasibility study

BACKGROUND

Intracranial hypertension is the final pathway of many neurocritical entities, such as spontaneous intracerebral hemorrhage (sICH) and severe traumatic brain injury (sTBI).

OBJECTIVE

This study aimed to (1) determine alterations in intracranial pressure (ICP) and cerebral hemodynamics after an indomethacin (INDO) infusion test and the related association with survival in patients with refractory intracranial hypertension (RICH) secondary to sICH or sTBI and (2) assess the safety profile after INDO.

METHODS

INDO was administered in a loading dose (0.8 mg/kg/15 min), followed by a 2-hour continuous infusion (0.5 mg/kg/h) in RICH patients with ICP greater than 20 mm Hg who did not respond to first-line therapies. Changes in ICP, cerebral perfusion pressure (CPP), and cerebrovascular variables (assessed by transcranial Doppler and jugular bulb saturation) were observed. Clinical outcome was assessed at 1 and 6 months according to the Glasgow Outcome Scale and correlated with INDO infusion test response. Analysis of INDO safety profile was conducted.

RESULTS

Thirteen sICH and 10 sTBI patients were studied. The median GCS score at admission was 6. Within 30 minutes of INDO infusion, ICP decreased (42.0 ± 13.5 vs 27.70 ± 12.7 mm Hg; Δ%: -48.4%; P < .001), and both CPP (57.7 ± 4.8 vs 71.9 ± 7.0 mm Hg; Δ%: +26.0%; P < .001) and middle cerebral artery velocity (35.2 ± 5.6 vs 42.0 ± 5.1 cm·s(-1); Δ%: +26.1%; P < .001) increased. The CPP response to a 2-hour INDO infusion test was correlated (R2 = 0.72, P < .001) with survival. No adverse events were observed after INDO.

CONCLUSION

Our findings support the effectiveness and feasibility of an INDO test in decreasing ICP and improving cerebral hemodynamics in surviving RICH patients. Future studies to evaluate different doses, lengths of infusion, and longer term effects are needed.

Neuromonitoring for Traumatic Brain Injury in Neurosurgical Intensive Care

The primary aim of neuromonitoring in patients with traumatic brain injury is early detection of secondary brain insults so that timely interventions can be instituted to prevent or treat secondary brain injury. Intracranial pressure monitoring has been a stalwart in neuromonitoring and is still very much the main parameter to guide therapy in brain injured patients in many centres. Cerebral oxygenation is also established as an important parameter for monitoring: global cerebral oxygenation is reliably measured using jugular venous oxygen saturation while brain tissue oxygen tension measurement allows focal brain oxygenation to be monitored. Near-infrared spectroscopy allows a non-invasive option for monitoring of regional cerebral oxygenation. Cerebral microdialysis makes focal measurements of markers of cellular metabolism and cellular injury and death possible, and it is in transition from being a research tool to being an important clinical tool in neuromonitoring. Multimodal monitoring allows different parameters of brain physiology and function to be monitored and can improve identification and prediction of secondary cerebral insults. Multimodal monitoring can potentially improve outcomes in patients with traumatic brain injury by promoting customised treatment strategies for individual patients in place of the commonplace practice of strict adherence to achieving the same standard physiological targets for every patient.

Cerebral oxygenation is reduced during hyperthermic exercise in humans

AIM

Cerebral mitochondrial oxygen tension (P(mito)O(2)) is elevated during moderate exercise, while it is reduced when exercise becomes strenuous, reflecting an elevated cerebral metabolic rate for oxygen (CMRO(2)) combined with hyperventilation-induced attenuation of cerebral blood flow (CBF). Heat stress challenges exercise capacity as expressed by increased rating of perceived exertion (RPE).

METHODS

This study evaluated the effect of heat stress during exercise on P(mito)O(2) calculated based on a Kety-Schmidt-determined CBF and the arterial-to-jugular venous oxygen differences in eight males [27 +/- 6 years (mean +/- SD) and maximal oxygen uptake (VO(2max)) 63 +/- 6 mL kg(-1) min(-1)].

RESULTS

The CBF, CMRO(2) and P(mito)O(2) remained stable during 1 h of moderate cycling (170 +/- 11 W, approximately 50% of VO(2max), RPE 9-12) in normothermia (core temperature of 37.8 +/- 0.4 degrees C). In contrast, when hyperthermia was provoked by dressing the subjects in watertight clothing during exercise (core temperature 39.5 +/- 0.2 degrees C), P(mito)O(2) declined by 4.8 +/- 3.8 mmHg (P < 0.05 compared to normothermia) because CMRO(2) increased by 8 +/- 7% at the same time as CBF was reduced by 15 +/- 13% (P < 0.05). During exercise with heat stress, RPE increased to 19 (19-20; P < 0.05); the RPE correlated inversely with P(mito)O(2) (r(2) = 0.42, P < 0.05).

CONCLUSION

These data indicate that strenuous exercise in the heat lowers cerebral P(mito)O(2), and that exercise capacity in this condition may be dependent on maintained cerebral oxygenation.

Methods of monitoring brain oxygenation

INTRODUCTION

Posttraumatic brain ischemia or hypoxia is a major potential cause of secondary injury that may lead to poor outcome. Avoidance, or amelioration, of this secondary injury depends on early diagnosis and intervention before permanent injury occurs. However, tools to monitor brain oxygenation continuously in the neuro-intensive care unit have been lacking.

DISCUSSION

In recent times, methods of monitoring aspects of brain oxygenation continuously by the bedside have been evaluated in several experimental and clinical series and are potentially changing the way we manage head-injured patients. These monitors have the potential to alert the clinician to possible secondary injury and enable intervention, help interpret pathophysiological changes (e.g., hyperemia causing raised intracranial pressure), monitor interventions (e.g., hyperventilation for increased intracranial pressure), and prognosticate. This review focuses on jugular venous saturation, brain tissue oxygen tension, and near-infrared spectroscopy as practical methods that may have an important role in managing patients with brain injury, with a particular focus on the available evidence in children. However, to use these monitors effectively and to understand the studies in which these monitors are employed, it is important for the clinician to appreciate the technical characteristics of each monitor, as well as respective strengths and limitations of each. It is equally important that the clinician understands relevant aspects of brain oxygen physiology and head trauma pathophysiology to enable correct interpretation of the monitored data and therefore to direct an appropriate therapeutic response that is likely to benefit, not harm, the patient.

Microdialysis in central nervous system disorders and their treatment

Central nervous system (CNS) insults elevate endogenous toxins and alter levels of indicators of metabolic disorder. These contribute to neurotrauma, neurodegenerative diseases and chronic pain and are possible targets for pharmaceutical treatment. Microdialysis samples substances in the extracellular space for chemical analysis. It has demonstrated that toxic levels of glutamate are released and that toxic levels of the reactive species O(2)(-), H(2)O(2), HO. NO and HOONO are generated upon CNS injury. Agent administration by microdialysis can also help elucidate mechanisms of damage and protection, and to identify targets for clinical application. Microdialysis sampling indicates that circuits descending from the brain to the spinal cord transmit and modulate pain signals by releasing neurotransmitter amines and amino acids. Efforts are under way to develop microdialysis into a technique for intensive care monitoring and predicting outcomes of brain insults. Finally, microdialysis sampling has demonstrated in vivo elevation of glial cell line-derived neurotrophic factor following grafting of primed fetal human neural stem cells into brain-injured rats, the first in vivo demonstration of the release of a neurotrophic factor by grafted stem cells. This increased release correlated with significantly improved spatial learning and memory.