Intracranial pressure monitoring with and without brain tissue oxygen pressure monitoring for severe traumatic brain injury in France (OXY-TC): an open-label, randomised controlled superiority trial.

BACKGROUND: Optimisation of brain oxygenation might improve neurological outcome after traumatic brain injury. The OXY-TC trial explored the superiority of a strategy combining intracranial pressure and brain tissue oxygen pressure (PbtO2) monitoring over a strategy of intracranial pressure monitoring only to reduce the proportion of patients with poor neurological outcome at 6 months. METHODS: We did an open-label, randomised controlled superiority trial at 25 French tertiary referral centres. Within 16 h of brain injury, patients with severe traumatic brain injury (aged 18-75 years) were randomly assigned via a website to be managed during the first 5 days of admission to the intensive care unit either by intracranial pressure monitoring only or by both intracranial pressure and PbtO2 monitoring. Randomisation was stratified by age and centre. The study was open label due to the visibility of the intervention, but the statisticians and outcome assessors were masked to group allocation. The therapeutic objectives were to maintain intracranial pressure of 20 mm Hg or lower, and to keep PbtO2 (for those in the dual-monitoring group) above 20 mm Hg, at all times. The primary outcome was the proportion of patients with an extended Glasgow Outcome Scale (GOSE) score of 1-4 (death to upper severe disability) at 6 months after injury. The primary analysis was reported in the modified intention-to-treat population, which comprised all randomly assigned patients except those who withdrew consent or had protocol violations. This trial is registered with ClinicalTrials.gov, NCT02754063, and is completed. FINDINGS: Between June 15, 2016, and April 17, 2021, 318 patients were randomly assigned to receive either intracranial pressure monitoring only (n=160) or both intracranial pressure and PbtO2 monitoring (n=158). 27 individuals with protocol violations were not included in the modified intention-to-treat analysis. Thus, the primary outcome was analysed for 144 patients in the intracranial pressure only group and 147 patients in the intracranial pressure and PbtO2 group. Compared with intracranial pressure monitoring only, intracranial pressure and PbtO2 monitoring did not reduce the proportion of patients with GOSE score 1-4 (51% [95% CI 43-60] in the intracranial pressure monitoring only group vs 52% [43-60] in the intracranial pressure and PbtO2 monitoring group; odds ratio 1·0 [95% CI 0·6-1·7]; p=0·95). Two (1%) of 144 participants in the intracranial pressure only group and 12 (8%) of 147 participants in the intracranial pressure and PbtO2 group had catheter dysfunction (p=0.011). Six patients (4%) in the intracranial pressure and PbtO2 group had an intracrebral haematoma related to the catheter, compared with none in the intracranial pressure only group (p=0.030). No significant difference in deaths was found between the two groups at 12 months after injury. At 12 months, 33 deaths had occurred in the intracranial pressure group: 25 (76%) were attributable to the brain trauma, six (18%) were end-of-life decisions, and two (6%) due to sepsis. 34 deaths had occured in the intracranial pressure and PbtO2 group at 12 months: 25 (74%) were attributable to the brain trauma, six (18%) were end-of-life decisions, one (3%) due to pulmonary embolism, one (3%) due to haemorrhagic shock, and one (3%) due to cardiac arrest. INTERPRETATION: After severe non-penetrating traumatic brain injury, intracranial pressure and PbtO2 monitoring did not reduce the proportion of patients with poor neurological outcome at 6 months. Technical failures related to intracerebral catheter and intracerebral haematoma were more frequent in the intracranial pressure and PbtO2 group. Further research is needed to assess whether a targeted approach to multimodal brain monitoring could be useful in subgroups of patients with severe traumatic brain injury-eg, those with high intracranial pressure on admission. FUNDING: The French National Program for Clinical Research, La Fondation des Gueules Cassées, and Integra Lifesciences.

Combat Casualty Care Training: Implementation of a Simulation-Based Program in a Cross-Cultural Setting: Experience of the French Military Health Service in West Africa.

INTRODUCTION: In the French army, combat casualty care (CCC) training involves the use of simulation. The application of this pedagogic method in a cross-cultural environment has not previously been described. In this report, we explore the challenges highlighted by multiple training sessions for foreign medical providers in West Africa. METHODS: We collected the data from six 2-week courses held in Libreville, Gabon. Our main objective was to describe the course; our secondary objective was to assess our trainees' progress in their knowledge of CCC. RESULTS: The first week involved lectures, technical workshops, and single-patient simulations. The second part emphasized multiple-victim simulations and interactions with combatants and was held in the Gabonese rainforest. Sixty- two trainees undertook the six sessions. Their knowledge improved during the course, from a median score of 4 (of a maximum of 40) before to 9.5 after (p < .05). DISCUSSION: Our study is the first to describe medical-level CCC training in a cross-cultural environment. Challenges are numerous, notably differences in the expected roles of instructors and trainees. Mitigating those difficulties is possible through cultural awareness and self-awareness. Our results are limited by the absence of evaluation of improvement in the actual management of patients. CONCLUSION: CCC training using medical simulation is feasible in a cross-cultural environment.

Fibrin monomers and association with significant hemorrhage or mortality in severely injured trauma patients.

BACKGROUND: Post-traumatic hemorrhage is still the leading cause of potentially preventable death in patients with severe trauma. Traumatic-induced coagulopathy has been described as a risk factor for significant hemorrhage and mortality in this population. Fibrin monomers (FMs) are a direct marker of thrombin action, and thus reflect coagulation activation. This study sought to determine the association of FMs levels at admission with significant hemorrhage and 28-day mortality after a severe trauma. METHODS: We conducted a retrospective, observational study including all severe trauma patients admitted in a level-1 trauma center between January 2012 and December 2017. Patients with severe traumatic brain injury or previous anticoagulant / antiaggregant therapies were excluded. FMs measurements and standard coagulation test were taken at admission. Significant hemorrhage was defined as a hemorrhage requiring the transfusion of ≥ 4 Red Blood Cells units during the first 6 h. Multivariable analysis was applied to identify predictors of significant hemorrhage and a simple logistic regression analysis was applied to identify an association between FMs and 28-day mortality. RESULTS: Overall, 299 patients were included. A total of 47 (16%) experienced a significant hemorrhage. The ROC curve demonstrated that FMs had a poor accuracy to predict the occurrence of significant hemorrhage with an AUC of 0.65 (0.57-0.74). The best threshold at 92.45 µg/ml had excellent sensitivity (87%) and negative predictive value (95%), but was not independently associated with significant hemorrhage (OR = 1.5; 95%CI (0.5-4.2)). The 28-day mortality rate was 5%. In simple logistic regression analysis, FMs values ≥109.5 µg/ml were significantly associated with 28-day mortality (unadjusted OR = 13.2; 95%CI (1.7-102)). CONCLUSIONS: FMs levels at admission are not associated with the occurrence of a significant hemorrhage in patients with severe trauma. However, the excellent sensitivity and NPV of FMs could help to identify patients with a low risk of severe bleeding during hospital care. In addition, FMs levels ≥109.5 µg/ml might be predictive of 28-day mortality.

Ability of Fibrin Monomers to Predict Progressive Hemorrhagic Injury in Patients with Severe Traumatic Brain Injury.

BACKGROUND: Progressive hemorrhagic injury (PHI) is common in patients with severe traumatic brain injury (TBI) and is associated with poor outcomes. TBI-associated coagulopathy is frequent and has been described as risk factor for PHI. This coagulopathy is a dynamic process involving hypercoagulable and hypocoagulable states either one after the other either concomitant. Fibrin monomers (FMs) are a direct marker of thrombin action and thus reflect coagulation activation. This study sought to determine the ability of FM to predict PHI after severe TBI. METHODS: We conducted a prospective, observational study including all severe TBI patients admitted in the trauma center. Between September 2011 and September 2016, we enrolled patients with severe TBI into the derivation cohort. Between October 2016 and December 2018, we recruited the validation cohort on the same basis. Study protocol included FM measurements and standard coagulation test at admission and two computed tomography (CT) scans (upon arrival and at least 6 h thereafter). A PHI was defined by an increment in size of initial lesion (25% or more) or the development of a new hemorrhage in the follow-up CT scan. Multivariate logistic regression analysis was applied to identify predictors of PHI. RESULTS: Overall, 106 patients were included in the derivation cohort. Fifty-four (50.9%) experienced PHI. FM values were higher in these patients (151 [136.8-151] vs. 120.5 [53.3-151], p < 0.0001). The ROC curve demonstrated that FM had a fair accuracy to predict the occurrence of PHI with an area under curve of 0.7 (95% CI [0.6-0.79]). The best threshold was determined at 131.7 µg/ml. In the validation cohort of 54 patients, this threshold had a negative predictive value of 94% (95% CI [71-100]) and a positive predictive value of 49% (95% CI [32-66]). The multivariate logistic regression analysis identified 2 parameters associated with PHI: FM ≥ 131.7 (OR 6.8; 95% CI [2.8-18.1]) and Marshall category (OR 1.7; 95% CI [1.3-2.2]). Coagulopathy was not associated with PHI (OR 1.3; 95% CI [0.5-3.0]). The proportion of patients with an unfavorable functional neurologic outcome at 6-months follow-up was higher in patients with positive FM: 59 (62.1%) versus 16 (29.1%), p < 0.0001. CONCLUSIONS: FM levels at admission had a fair accuracy to predict PHI in patients with severe TBI. FM values ≥ 131.7 µg/ml are independently associated with the occurrence of PHI.

Anesthesia during deployment of a military forward surgical unit in low income countries: A register study of 1547 anesthesia cases.

BACKGROUND: Military anesthesia meets unique logistical, technical, tactical, and human constraints, but to date limited data have been published on anesthesia management during military operations. OBJECTIVE: This study aimed to describe and analyze French anesthetic activity in a deployed military setting. METHODS: Between October 2015 and February 2018, all patients managed by Sainte-Anne Military Hospital anesthesiologists deployed in mission were included. Anesthesia management was described and compared with the same surgical procedures in France performed by the same anesthesia team (hernia repair, lower and upper limb surgeries). Demographics, type of surgical procedure, and surgical activity were also described. The primary endpoint was to describe anesthesia management during the deployment of forward surgical teams (FST). The secondary endpoint was to compare anesthesia modalities during FST deployment with those usually used in a military teaching hospital. RESULTS: During the study period, 1547 instances of anesthesia were performed by 11 anesthesiologists during 20 missions, totaling 1237 days of deployment in nine different theaters. The majority consisted of regional anesthesia, alone (43.5%) or associated with general anesthesia (21%). Compared with France, there was a statistically significant increase in the use of regional anesthesia in hernia repair, lower and upper limb surgeries during deployment. The majority of patients were civilians as part of medical support to populations. CONCLUSION: In the context of an austere environment, the use of regional anesthesia techniques predominated when possible. These results show that the training of military anesthetists must be complete, including anesthesia, intensive care, pediatrics, and regional anesthesia.

Spontaneous Hyperventilation in Severe Traumatic Brain Injury: Incidence and Association with Poor Neurological Outcome.

BACKGROUND: Hypocapnia induces cerebral vasoconstriction leading to a decrease in cerebral blood flow, which might precipitate cerebral ischemia. Hypocapnia can be intentional to treat intracranial hypertension or unintentional due to a spontaneous hyperventilation (SHV). SHV is frequent after subarachnoid hemorrhage. However, it is understudied in patients with severe traumatic brain injury (TBI). The objective of this study was to describe the incidence and consequences on outcome of SHV after severe TBI. METHODS: We conducted a retrospective, observational study including all intubated TBI patients admitted in the trauma center and still comatose 24 h after the withdrawal of sedation. SHV was defined by the presence of at least one arterial blood gas (ABG) with both PaCO2 < 35 mmHg and pH > 7.45. Patient characteristics and outcome were extracted from a prospective registry of all intubated TBI admitted in the intensive care unit. ABG results were retrieved from patient files. A multivariable logistic regression model was developed to determine factors independently associated with unfavorable outcome (defined as a Glasgow Outcome Scale between 1 and 3) at 6-month follow-up. RESULTS: During 7 years, 110 patients fully respecting inclusion criteria were included. The overall incidence of SHV was 69.1% (95% CI [59.9-77]). Patients with SHV were more severely injured (median head AIS score (5 [4-5] vs. 4 [4-5]; p = 0.016)) and exhibited an elevated morbidity during their stay. The proportion of patients with an unfavorable functional neurologic outcome was significantly higher in patients with SHV: 40 (52.6%) versus 6 (17.6%), p = 0.0006. After adjusting for confounders, SHV remains an independent factor associated with unfavorable outcome at the 6-month follow-up (OR 4.1; 95% CI [1.2-14.4]). CONCLUSIONS: SHV is common in patients with a persistent coma after a severe TBI (overall rate: 69%) and was independently associated with unfavorable outcome at 6-month follow-up.

Management of septic shock in intermediate care unit.

BACKGROUND: While guidelines advocate goal-directed resuscitation based on timed bundles, the management of septic shock (SS) outside an ICU setting has been poorly studied in intermediate care units (IMCU). PATIENTS AND METHOD: We reviewed all cases of septic shock patients admitted to our IMCU between January 2013 and June 2014. The characteristics of sepsis, compliance of bundles, and outcomes were collected. The IMCU population was compared with the SS patients admitted to the ICU during the same period. The primary objective was to evaluate the feasibility of care in an IMCU. RESULTS: We treated 59 patients in the IMCU. Forty-three patients (73%) were fully managed in the IMCU and 16 patients (27%) were secondarily transferred to the ICU. In the first 3hours, the compliance to bundles was: blood cultures (95%), plasma lactate concentration (90%), vascular filling volume (1500ml (1000-2000)) and antibiotics (100%). A central venous line and an arterial catheter were inserted in 85% and 98.3% of the cases. At 24h, patients who were transferred to the ICU had higher lactate concentrations than the other patients (1.4±0.7mmol versus 2.9±3.4mmol; P=0.03). A 24 hours-SOFA score>4 was correlated with a transfer in ICU (OR 7,75 (95% CI 2.08-28,81; P=0.002)). CONCLUSIONS: Our work demonstrated the ability to manage SS patients solely in an IMCU. It showed that the SS resuscitation bundle can be successfully implemented outside the ICU. A lack of improvement at the 24th hour is associated with a transfer to the ICU.

Early-Onset Ventilator-Associated Pneumonia in Patients with Severe Traumatic Brain Injury: Incidence, Risk Factors, and Consequences in Cerebral Oxygenation and Outcome.

BACKGROUND: Early-onset ventilator-associated pneumonia (EOVAP) occurs frequently in severe traumatic brain-injured patients, but potential consequences on cerebral oxygenation and outcome have been poorly studied. The objective of this study was to describe the incidence, risk factors for, and consequences on cerebral oxygenation and outcome of EOVAP after severe traumatic brain injury (TBI). METHODS: We conducted a retrospective, observational study including all intubated TBI admitted in the trauma center. An EOVAP was defined as a clinical pulmonary infection score >6, and then confirmed by an invasive method. Patient characteristics, computed tomography (CT) scan results, and outcome were extracted from a prospective register of all intubated TBI admitted in the intensive care unit (ICU). Data concerning the cerebral oxygenation monitoring by PbtO2 and characteristics of EOVAP were retrieved from patient files. Multivariate logistic regression models were developed to determine the risk factors of EOVAP and to describe the factors independently associated with poor outcome at 1-year follow-up. RESULTS: During 7 years, 175 patients with severe TBI were included. The overall incidence of EOVAP was 60.6% (47.4/1000 days of ventilation). Significant risk factors of EOVAP were: therapeutic hypothermia (OR 3.4; 95% CI [1.2-10.0]), thoracic AIS score ≥3 (OR 2.4; 95% CI [1.1-5.7]), and gastric aspiration (OR 5.2, 95% CI [1.7-15.9]). Prophylactic antibiotics administration was a protective factor against EOVAP (OR 0.3, 95% CI [0.1-0.8]). EOVAP had negative consequences on cerebral oxygenation. The PbtO2 was lower during EOVAP: 23.5 versus 26.4 mmHg (p <0.0001), and there were more brain hypoxia episodes: 32 versus 27% (p = 0.03). Finally, after adjusting for confounders, an EOVAP was an independent factor associated with unfavorable neurologic functional outcome at the 1-year follow-up (OR 2.71; 95% CI [1.01-7.25]). CONCLUSIONS: EOVAP is frequent after a severe TBI (overall rate: 61%), with therapeutic hypothermia, severe thoracic lesion, and gastric aspiration as main risk factors. EOVAP had a negative impact on cerebral oxygenation measured by PbtO2 and was independently associated with unfavorable outcome at 1-year follow-up. This suggests that all precautions available should be taken to prevent EOVAP in this population.

Blunt cerebrovascular injuries in severe traumatic brain injury: incidence, risk factors, and evolution.

OBJECTIVE Blunt cerebrovascular injuries (BCVIs) affect approximately 1% of patients with blunt trauma. An antithrombotic or anticoagulation therapy is recommended to prevent the occurrence or recurrence of neurovascular events. This treatment has to be carefully considered after severe traumatic brain injury (TBI), due to the risk of intracranial hemorrhage expansion. Thus, the physician in charge of the patient is confronted with a hemorrhagic and ischemic risk. The main objective of this study was to determine the incidence of BCVI after severe TBI. METHODS The authors conducted a prospective, observational, single-center study including all patients with severe TBI admitted in the trauma center. Diagnosis of BCVI was performed using a 64-channel multidetector CT. Characteristics of the patients, CT scan results, and outcomes were collected. A multivariate logistic regression model was developed to determine the risk factors of BCVI. Patients in whom BCVI was diagnosed were treated with systemic anticoagulation. RESULTS In total, 228 patients with severe TBI who were treated over a period of 7 years were included. The incidence of BCVI was 9.2%. The main risk factors were as follows: motorcycle crash (OR 8.2, 95% CI 1.9-34.8), fracture involving the carotid canal (OR 11.7, 95% CI 1.7-80.9), cervical spine injury (OR 13.5, 95% CI 3.1-59.4), thoracic trauma (OR 7.3, 95% CI 1.1-51.2), and hepatic lesion (OR 13.3, 95% CI 2.1-84.5). Among survivors, 82% of patients with BCVI received systemic anticoagulation therapy, beginning at a median of Day 1.5. The overall stroke rate was 19%. One patient had an intracranial hemorrhagic complication. CONCLUSIONS Blunt cerebrovascular injuries are frequent after severe TBI (incidence 9.2%). The main risk factors are high-velocity lesions and injuries near cervical arteries.

Early neurological wake-up test in intubated brain-injured patients: A long-term, single-centre experience.

BACKGROUND: In prehospital setting, a severe traumatic brain injury (TBI) requires tracheal intubation, sedation and mechanical ventilation pending the initial imagery. An early neurological wake-up test (ENWT), soon after the initial imaging assessment, allows a rapid neurological reassessment. This strategy authorises an initial clinical examination of reference with which will be compared the later examinations. The main objective of this study was to describe the characteristics of the patients who underwent an ENWT, and to determine its causes of failure. METHODS: We conducted a retrospective, observational, single-centre study including all intubated TBI admitted in the trauma centre. An ENWT was defined as cessation of sedation within 24h after TBI. Data concerning patient characteristics, CT-scan results, and outcomes were extracted from a prospective register of all intubated TBI admitted in the ICU. Characteristic of ENWT and causes of failure were retrieved from patient files. A multivariate logistic regression model was developed to determine the risk factors of ENWT failure. RESULTS: During 7 years, 242 patients with intubated TBI were included. An ENWT was started in 96 patients, for an overall rate at 40%. The ENWT was stopped in 38 patients (39.5%), mostly due to neurological deterioration in 27 cases (71%) or respiratory distress in 10 cases (26%). Significant predictors of ENWT failure were: the presence of subdural hematoma with a thickness >5mm on first imagery (OR=3.2; 95%CI [1.01-10.28]), and an initial GCS score <5 (OR=7.4; 95%CI [1.92-28.43]). Prevalence of poor outcome at 1year was lesser in patients with successful ENWT compared to those with failure or absence of ENWT: 4% vs. 48% and 49% (p<0.0001). CONCLUSIONS: The ENWT is achieved in 40% of patients, with a success rate of 60.5%. In presence of a subdural hematoma with a thickness >5mm or an initial GCS score <5, an ENWT failure may be expected.

Vittel criteria for severe trauma triage: Characteristics of over-triage.

AIM: Over-triage rates related to the use of Vittel criteria are unknown. We compared severe stable trauma patients with and without significant visceral injuries. STUDY DESIGN: A single-centre retrospective analysis of a single-centre prospective cohort. PATIENTS AND METHODS: Trauma patients with at least one positive Vittel criterion from June 2010 to January 2012 in a level-1 trauma centre. Initial management included a systematic whole-body scanner. All significant lesions in stable trauma patients were recorded. RESULTS: A total of 252 trauma patients were admitted. One hundred and twenty were stable. In this group without vital distress, 72 (60%) had at least one occult lesion, 21 (17.5%) had an isolated orthopaedic injury and 27 (22.5%) had no injury. Thoracic injuries accounted for 44% of visceral injuries, abdominal for 17%, spinal for 16% and cerebral for 15%. Overall, the over-triage rate was 19%. Surgery for significant visceral injury was performed in 13 patients (18%) and arteriography in 4 patients (5.5%). Admission in an intensive care unit was required for 13 patients with occult injuries and for one patient without such a lesion (18% versus 2%, P=0.008). Hospital stays were longer in the group with visceral injuries (4±7 versus 9±8days; P=0.006). CONCLUSION: Vittel criteria use in trauma patients induces an acceptable over-triage rate. A large proportion of stable trauma patients have occult lesions. These visceral injuries frequently require special care. These data highlight the imperative need to transport major trauma patients immediately to a dedicated trauma centre and supports whole-body scanner use.

Consensus statement from the 2014 International Microdialysis Forum.

Microdialysis enables the chemistry of the extracellular interstitial space to be monitored. Use of this technique in patients with acute brain injury has increased our understanding of the pathophysiology of several acute neurological disorders. In 2004, a consensus document on the clinical application of cerebral microdialysis was published. Since then, there have been significant advances in the clinical use of microdialysis in neurocritical care. The objective of this review is to report on the International Microdialysis Forum held in Cambridge, UK, in April 2014 and to produce a revised and updated consensus statement about its clinical use including technique, data interpretation, relationship with outcome, role in guiding therapy in neurocritical care and research applications.

Tracheal intubation difficulties in the setting of face and neck burns: myth or reality?

INTRODUCTION: Face and/or neck burn (FNB) exposes patients to the double respiratory risk of obstruction and hypoxia, and these risks may require a tracheal intubation. This study aims to describe the incidence and the characteristics of difficult intubation in FNB patients. METHODS: We conducted a 5-year retrospective, single-center study including all patients meeting the following criteria: 18 years of age or older, an FNB at least 1% of burned surface area with a severity equal to or greater than the superficial second degree, and intubation and a burn center admission within the first 24 hours after the burn. Patients were compared according to the difficulty of their intubation. RESULTS: Between January 2007 and December 2011, we included 134 patients. The incidence of difficult intubation was 11.2% but was greater in the burn center than in the pre-burn center: 16.9% vs 3.5% (P = .02). The most important difference between patients with or without difficult intubation was the time between the burn injury and the intubation: 210 (105-290) vs 120 (60-180) minutes (P = .047). After multivariate analysis, an intubation performed at a burn center was independently associated with difficult intubation: odds ratio = 3.2; 95% confidence interval, 1.1-528. CONCLUSIONS: This study underlines the high incidence of difficult intubation in FNB patients, greater than 11.2%, and demonstrates that intubation is more difficult when realized at a burn center, probably because it is performed later, allowing for development of cervical and laryngeal edema.

FiO2 delivered by a turbine portable ventilator with an oxygen concentrator in an Austere environment.

BACKGROUND: Management of critically ill patients in austere environments is a logistic challenge. Availability of oxygen cylinders for the mechanically ventilated patient may be difficult in such a context. A solution is to use a ventilator able to function with an oxygen concentrator. OBJECTIVES: We tested the SeQual Integra™ (SeQual, San Diego, CA) 10-OM oxygen concentrator paired with the Pulmonetic System(®) LTV 1000 ventilator (Pulmonetic Systems, Minneapolis, MN) and evaluated the delivered fraction of inspired oxygen (FiO2) across a range of minute volumes and combinations of ventilator settings. METHODS: Two LTV 1000 ventilators were tested. The ventilators were attached to a test lung and FiO2 was measured by a gas analyzer. Continuous-flow oxygen was generated by the OC from 0.5 L/min to 10 L/min and injected into the oxygen inlet port of the LTV 1000. Several combinations of ventilator settings were evaluated to determine the factors affecting the delivered FiO2. RESULTS: The LTV 1000 ventilator is a turbine ventilator that is able to deliver high FiO2 when functioning with an oxygen concentrator. However, modifications of the ventilator settings such as increase in minute ventilation affect delivered FiO2 even if oxygen flow is constant on the oxygen concentrator. CONCLUSIONS: The ability of an oxygen concentrator to deliver high FiO2 when used with a turbine ventilator makes this method of oxygen delivery a viable alternative to cylinders in austere environments when used with a turbine ventilator. However, FiO2 has to be monitored continuously because delivered FiO2 decreases when minute ventilation is increased.

Metabolic crisis in severely head-injured patients: is ischemia just the tip of the iceberg?

Ischemia and metabolic crisis are frequent post-traumatic secondary brain insults that negatively influence outcome. Clinicians commonly mix up these two types of insults, mainly because high lactate/pyruvate ratio (LPR) is the common marker for both ischemia and metabolic crisis. However, LPR elevations during ischemia and metabolic crisis reflect two different energetic imbalances: ischemia (Type 1 LPR elevations with low oxygenation) is characterized by a drastic deprivation of energetic substrates, whereas metabolic crisis (Type 2 LPR elevations with normal or high oxygenation) is associated with profound mitochondrial dysfunction but normal supply of energetic substrates. The discrimination between ischemia and metabolic crisis is crucial because conventional recommendations against ischemia may be detrimental for patients with metabolic crisis. Multimodal monitoring, including microdialysis and brain tissue oxygen monitoring, allows such discrimination, but these techniques are not easily accessible to all head-injured patients. Thus, a new "gold standard" and adapted medical education are required to optimize the management of patients with metabolic crisis.