Adverse effects of prolonged hyperventilation in patients with severe head injury: a randomized clinical trial

Short-term mild hyperventilation on intracranial pressure, cerebral autoregulation, and oxygenation in acute brain injury patients: a prospective observational study

Current guidelines suggest a target of partial pressure of carbon dioxide (PaCO2) of 32-35 mmHg (mild hypocapnia) as tier 2 for the management of intracranial hypertension. However, the effects of mild hyperventilation on cerebrovascular dynamics are not completely elucidated. The aim of this study is to evaluate the changes of intracranial pressure (ICP), cerebral autoregulation (measured through pressure reactivity index, PRx), and regional cerebral oxygenation (rSO2) parameters before and after induction of mild hyperventilation. Single center, observational study including patients with acute brain injury (ABI) admitted to the intensive care unit undergoing multimodal neuromonitoring and requiring titration of PaCO2 values to mild hypocapnia as tier 2 for the management of intracranial hypertension. Twenty-five patients were included in this study (40% female), median age 64.7 years (Interquartile Range, IQR = 45.9-73.2). Median Glasgow Coma Scale was 6 (IQR = 3-11). After mild hyperventilation, PaCO2 values decreased (from 42 (39-44) to 34 (32-34) mmHg, p < 0.0001), ICP and PRx significantly decreased (from 25.4 (24.1-26.4) to 17.5 (16-21.2) mmHg, p < 0.0001, and from 0.32 (0.1-0.52) to 0.12 (-0.03-0.23), p < 0.0001). rSO2 was statistically but not clinically significantly reduced (from 60% (56-64) to 59% (54-61), p < 0.0001), but the arterial component of rSO2 (ΔO2Hbi, changes in concentration of oxygenated hemoglobin of the total rSO2) decreased from 3.83 (3-6.2) μM.cm to 1.6 (0.5-3.1) μM.cm, p = 0.0001. Mild hyperventilation can reduce ICP and improve cerebral autoregulation, with minimal clinical effects on cerebral oxygenation. However, the arterial component of rSO2 was importantly reduced. Multimodal neuromonitoring is essential when titrating PaCO2 values for ICP management.

Development of a piglet model for cerebrovascular autoregulation assessment with altered PaCO2

Introduction

Cerebrovascular autoregulation (CA) capacity can be impaired in the aftermath of acute brain injuries. Altered physiological states, such as hypo- and hypercapnia, affect CA. Although these effects have been demonstrated in several animal experiments, the exact effect of PaCO₂ on the plateau of cerebral blood flow (CBF) across the spectrum of arterial blood pressures has not been fully disclosed.

Research question

The aim was to explore pial vasodynamics in response to changing PaCO₂ in a porcine cranial window model, as preparation for an experimental setup in which the CBF plateau position is investigated under different PaCO₂ conditions.

Material and methods

Five piglets were brought under anesthesia, intubated, ventilated and instrumented with a cranial window through which pial arteriolar diameters could be microscopically observed. By changing ventilation to either hyper- or hypoventilation we were able to investigate a range of PaCO2 from 25 till 90 mmHg.

Results

Altering the respiratory rate to manipulate PaCO₂ by ventilation appeared to be feasible and reliable.

Discussion and conclusion

We found that ETCO₂ reliably represents PaCO₂ in our model. Pial arteriolar diameter changes followed the direction of PaCO₂ changes, but the effect of PaCO₂ on the diameters was not linear. Only in the hypercapnia setting did we observe a clear and consistent vasodilation of the pial arterioles.

Acute Lung Injury after Cardiopulmonary Resuscitation: A Narrative Review

Although cardiopulmonary resuscitation (CPR) includes lifesaving maneuvers, it might be associated with a wide spectrum of iatrogenic injuries. Among these, acute lung injury (ALI) is frequent and yields significant challenges to post-cardiac arrest recovery. Understanding the relationship between CPR and ALI is determinant for refining resuscitation techniques and improving patient outcomes. This review aims to analyze the existing literature on ALI following CPR, emphasizing prevalence, clinical implications, and contributing factors. The review seeks to elucidate the pathogenesis of ALI in the context of CPR, assess the efficacy of CPR techniques and ventilation strategies, and explore their impact on post-cardiac arrest outcomes. CPR-related injuries, ranging from skeletal fractures to severe internal organ damage, underscore the complexity of managing post-cardiac arrest patients. Chest compression, particularly when prolonged and vigorous, i.e., mechanical compression, appears to be a crucial factor contributing to ALI, with the concept of cardiopulmonary resuscitation-associated lung edema (CRALE) gaining prominence. Ventilation strategies during CPR and post-cardiac arrest syndrome also play pivotal roles in ALI development. The recognition of CPR-related lung injuries, especially CRALE and ALI, highlights the need for research on optimizing CPR techniques and tailoring ventilation strategies during and after resuscitation.

Trending Ability of End-Tidal Capnography Monitoring During Mechanical Ventilation to Track Changes in Arterial Partial Pressure of Carbon Dioxide in Critically Ill Patients With Acute Brain Injury: A Monocenter Retrospective Study

BACKGROUND

Changes in arterial partial pressure of carbon dioxide (Pa co2 ) may alter cerebral perfusion in critically ill patients with acute brain injury. Consequently, international guidelines recommend normocapnia in mechanically ventilated patients with acute brain injury. The measurement of end-tidal capnography (Et co2 ) allows its approximation. Our objective was to report the agreement between trends in Et co2 and Pa co2 during mechanical ventilation in patients with acute brain injury.

METHODS

Retrospective monocenter study was conducted for 2 years. Critically ill patients with acute brain injury who required mechanical ventilation with continuous Et co2 monitoring and with 2 or more arterial gas were included. The agreement was evaluated according to the Bland and Altman analysis for repeated measurements with calculation of bias, and upper and lower limits of agreement. The directional concordance rate of changes between Et co2 and Pa co2 was evaluated with a 4-quadrant plot. A polar plot analysis was performed using the Critchley methods.

RESULTS

We analyzed the data of 255 patients with a total of 3923 paired ΔEt co2 and ΔPa co2 (9 values per patient in median). Mean bias by Bland and Altman analysis was -8.1 (95 CI, -7.9 to -8.3) mm Hg. The directional concordance rate between Et co2 and Pa co2 was 55.8%. The mean radial bias by polar plot analysis was -4.4° (95% CI, -5.5 to -3.3) with radial limit of agreement (LOA) of ±62.8° with radial LOA 95% CI of ±1.9°.

CONCLUSIONS

Our results question the performance of trending ability of Et co2 to track changes in Pa co2 in a population of critically ill patients with acute brain injury. Changes in Et co2 largely failed to follow changes in Pa co2 in both direction (ie, low concordance rate) and magnitude (ie, large radial LOA). These results need to be confirmed in prospective studies to minimize the risk of bias.

Clinical practice and effect of carbon dioxide on outcomes in mechanically ventilated acute brain-injured patients: a secondary analysis of the ENIO study

PURPOSE

The use of arterial partial pressure of carbon dioxide (PaCO2) as a target intervention to manage elevated intracranial pressure (ICP) and its effect on clinical outcomes remain unclear. We aimed to describe targets for PaCO2 in acute brain injured (ABI) patients and assess the occurrence of abnormal PaCO2 values during the first week in the intensive care unit (ICU). The secondary aim was to assess the association of PaCO2 with in-hospital mortality.

METHODS

We carried out a secondary analysis of a multicenter prospective observational study involving adult invasively ventilated patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH), intracranial hemorrhage (ICH), or ischemic stroke (IS). PaCO2 was collected on day 1, 3, and 7 from ICU admission. Normocapnia was defined as PaCO2 > 35 and to 45 mmHg; mild hypocapnia as 32-35 mmHg; severe hypocapnia as 26-31 mmHg, forced hypocapnia as < 26 mmHg, and hypercapnia as > 45 mmHg.

RESULTS

1476 patients (65.9% male, mean age 52 ± 18 years) were included. On ICU admission, 804 (54.5%) patients were normocapnic (incidence 1.37 episodes per person/day during ICU stay), and 125 (8.5%) and 334 (22.6%) were mild or severe hypocapnic (0.52 and 0.25 episodes/day). Forced hypocapnia and hypercapnia were used in 40 (2.7%) and 173 (11.7%) patients. PaCO2 had a U-shape relationship with in-hospital mortality with only severe hypocapnia and hypercapnia being associated with increased probability of in-hospital mortality (omnibus p value = 0.0009). Important differences were observed across different subgroups of ABI patients.

CONCLUSIONS

Normocapnia and mild hypocapnia are common in ABI patients and do not affect patients' outcome. Extreme derangements of PaCO2 values were significantly associated with increased in-hospital mortality.

Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest

INTRODUCTION

Little is known about the impact of tidal volumes delivered by emergency medical services (EMS) to adult patients with out-of-hospital cardiac arrest (OHCA). A large urban EMS system changed from standard adult ventilation bags to small adult bags. We hypothesized that the incidence of return of spontaneous circulation (ROSC) at the end of EMS care would increase after this change.

METHODS

We performed a retrospective analysis evaluating adults treated with advanced airway placement for nontraumatic OHCA between January 1, 2015 and December 31, 2021. We compared rates of ROSC, ventilation rate, and mean end tidal carbon dioxide (ETCO2) by minute before and after the smaller ventilation bag implementation using linear and logistic regression.

RESULTS

Of the 1,994 patients included, 1,331 (67%) were treated with a small adult bag. ROSC at the end of EMS care was lower in the small bag cohort than the large bag cohort, 33% vs 40% (p = 0.003). After adjustment, small bag use was associated with lower odds of ROSC at the end of EMS care [OR 0.74, 95% CI 0.61 - 0.91]. Ventilation rates did not differ between cohorts. ETCO2 values were lower in the large bag cohort (33.2 ± 17.2 mmHg vs. 36.9 ± 19.2 mmHg, p < 0.01).

CONCLUSION

Use of a small adult bag during OHCA was associated with lower odds of ROSC at the end of EMS care. The effects on acid base status, hemodynamics, and delivered minute ventilation remain unclear and warrant additional study.

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.

Impact of Hypo- and Hyper-capnia on Spreading Depolarizations in Rat Cerebral Cortex

Patients with traumatic brain injury are typically maintained at low-normal levels of arterial partial pressure of carbon dioxide (PaCO2) to counteract the risk of elevated intracranial pressure during intensive care. However, several studies suggest that management at hypercarbic levels may have therapeutic benefit. Here we examined the impact of CO2 levels on spreading depolarizations (SD), a mechanism and marker of acute lesion development in stroke and brain trauma. In an acute preparation of mechanically ventilated (30/70 O2/N2) female rats, SDs were evoked by cortical KCl application and monitored by electrophysiology and laser doppler flowmetry; CO2 levels were adjusted by ventilator settings and supplemental CO2. During 90 min of KCl application, rats were maintained at hypocapnia (end-tidal CO2 22 ± 2 mmHg) or hypercapnia (57 ± 4 mmHg) but did not differ significantly in arterial pH (7.31 ± 0.10 vs. 7.22 ± 0.08, p = 0.31) or other variables. Surprisingly, there was no difference between groups in the number of SDs recorded (10.7 ± 4.2 vs. 11.7 ± 3.1; n = 3 rats/group; p = 0.75) nor in SD durations (64 ± 27 vs. 69 ± 37 sec, p = 0.54). In separate experiments (n = 3), hypoxia was induced by decreasing inhaled O2 to 10% and single SDs were induced under interleaved conditions of hypo-, normo-, and hypercapnia. No differences in SD duration were observed. In both normoxia and hypoxia experiments, however, mean arterial pressures were negatively correlated with SD durations (normoxia R2 = -0.29; hypoxia R2 = -0.61, p's < 0.001). Our results suggest that any therapeutic benefit of elevated CO2 therapy may be dependent on an acidic shift in pH or may only be observed in conditions of focal brain injury.

Are We Ready for Clinical Therapy based on Cerebral Autoregulation? A Pro-con Debate

Cerebral autoregulation (CA) is a physiological mechanism that maintains constant cerebral blood flow regardless of changes in cerebral perfusion pressure and prevents brain damage caused by hypoperfusion or hyperperfusion. In recent decades, researchers have investigated the range of systemic blood pressures and clinical management strategies over which cerebral vasculature modifies intracranial hemodynamics to maintain cerebral perfusion. However, proposed clinical interventions to optimize autoregulation status have not demonstrated clear clinical benefit. As future trials are designed, it is crucial to comprehend the underlying cause of our inability to produce robust clinical evidence supporting the concept of CA-targeted management. This article examines the technological advances in monitoring techniques and the accuracy of continuous assessment of autoregulation techniques used in intraoperative and intensive care settings today. It also examines how increasing knowledge of CA from recent clinical trials contributes to a greater understanding of secondary brain injury in many disease processes, despite the fact that the lack of robust evidence influencing outcomes has prevented the translation of CA-guided algorithms into clinical practice.

Intracranial Pressure Monitoring and Treatment Thresholds in Acute Neural Injury: A Narrative Review of the Historical Achievements, Current State, and Future Perspectives

Since its introduction in the 1960s, intracranial pressure (ICP) monitoring has become an indispensable tool in neurocritical care practice and a key component of the management of moderate/severe traumatic brain injury (TBI). The primary utility of ICP monitoring is to guide therapeutic interventions aimed at maintaining physiological ICP and preventing intracranial hypertension. The rationale for such ICP maintenance is to prevent secondary brain injury arising from brain herniation and inadequate cerebral blood flow. There exists a large body of evidence indicating that elevated ICP is associated with mortality and that aggressive ICP control protocols improve outcomes in severe TBI patients. Therefore, current management guidelines recommend a cerebral perfusion pressure (CPP) target range of 60-70 mm Hg and an ICP threshold of >20 or >22 mm Hg, beyond which therapeutic intervention should be initiated. Though our ability to achieve these thresholds has drastically improved over the past decades, there has been little to no change in the mortality and morbidity associated with moderate-severe TBI. This is a result of the "one treatment fits all" dogma of current guideline-based care that fails to take individual phenotype into account. The way forward in moderate-severe TBI care is through the development of continuously derived individualized ICP thresholds. This narrative review covers the topic of ICP monitoring in TBI care, including historical context/achievements, current monitoring technologies and indications, treatment methods, associations with patient outcome and multi-modal cerebral physiology, present controversies surrounding treatment thresholds, and future perspectives on personalized approaches to ICP-directed therapy.

Association between prehospital end-tidal carbon dioxide levels and mortality in patients with suspected severe traumatic brain injury

PURPOSE

Severe traumatic brain injury is a leading cause of mortality and morbidity, and these patients are frequently intubated in the prehospital setting. Cerebral perfusion and intracranial pressure are influenced by the arterial partial pressure of CO₂ and derangements might induce further brain damage. We investigated which lower and upper limits of prehospital end-tidal CO₂ levels are associated with increased mortality in patients with severe traumatic brain injury.

METHODS

The BRAIN-PROTECT study is an observational multicenter study. Patients with severe traumatic brain injury, treated by Dutch Helicopter Emergency Medical Services between February 2012 and December 2017, were included. Follow-up continued for 1 year after inclusion. End-tidal CO₂ levels were measured during prehospital care and their association with 30-day mortality was analyzed with multivariable logistic regression.

RESULTS

A total of 1776 patients were eligible for analysis. An L-shaped association between end-tidal CO₂ levels and 30-day mortality was observed (p = 0.01), with a sharp increase in mortality with values below 35 mmHg. End-tidal CO₂ values between 35 and 45 mmHg were associated with better survival rates compared to < 35 mmHg. No association between hypercapnia and mortality was observed. The odds ratio for the association between hypocapnia (< 35 mmHg) and mortality was 1.89 (95% CI 1.53-2.34, p < 0.001) and for hypercapnia (≥ 45 mmHg) 0.83 (0.62-1.11, p = 0.212).

CONCLUSION

A safe zone of 35-45 mmHg for end-tidal CO₂ guidance seems reasonable during prehospital care. Particularly, end-tidal partial pressures of less than 35 mmHg were associated with a significantly increased mortality.

CAB versus ABC approach for resuscitation of patients following traumatic injury: Toward improving patient safety and survival

INTRODUCTION

Though a circulation-airway-breathing (CAB) resuscitation sequence is now widely accepted in administering CPR over the airway-breathing-circulation (ABC) sequence following cardiac arrest, current evidence and guidelines vary considerably for complex polytraumas, with some prioritizing management of the airway and others advocating for initial treatment of hemorrhage. This review aims to evaluate existing literature comparing ABC and CAB resuscitation sequences in adult trauma patients in-hospital to direct future research and guide evidence-based recommendations for management.

METHODS

A literature search was conducted on PubMed, Embase, and Google Scholar until September 29, 2022. Articles were assessed for comparison between CAB and ABC resuscitation sequences, adult trauma patients, in-hospital treatment, patient volume status, and clinical outcomes.

RESULTS

Four studies met the inclusion criteria. Two studies compared the CAB and ABC sequences specifically in hypotensive trauma patients, one study evaluated the sequences in trauma patients with hypovolemic shock, and one study in patients with all types of shock. Hypotensive trauma patients who underwent rapid sequence intubation before blood transfusion had a significantly higher mortality rate than those who had blood transfusion initiated first (50 vs 78% P < 0.05) and a significant drop in blood pressure. Patients who subsequently experienced post-intubation hypotension (PIH) had increased mortality over those without PIH. overall mortality was higher in patients that developed PIH (mortality, n (%): PIH = 250/753 (33.2%) vs 253/1291 (19.6%), p < 0.001).

CONCLUSION

This study found that hypotensive trauma patients, especially those with active hemorrhage, may benefit more from a CAB approach to resuscitation, as early intubation may increase mortality secondary to PIH. However, patients with critical hypoxia or airway injury may still benefit more from the ABC sequence and prioritization of the airway. Future prospective studies are needed to understand the benefits of CAB with trauma patients and identify which patient subgroups are most affected by prioritizing circulation before airway management.

Hypocapnia is an independent predictor of in-hospital mortality in acute heart failure

AIMS

Acute heart failure (AHF) poses a major threat to hospitalized patients for its high mortality rate and serious complications. The aim of this study is to determine whether hypocapnia [defined as the partial pressure of arterial carbon dioxide (PaCO₂ ) below 35 mmHg] on admission could be associated with in-hospital all-cause mortality in AHF.

METHODS AND RESULTS

A total of 676 patients treated in the coronary care unit for AHF were retrospectively analysed, and the study endpoint was in-hospital all-cause mortality. The 1:1 propensity score matching (PSM) analysis, Kaplan-Meier curve, and Cox regression model were used to explore the association between hypocapnia and in-hospital all-cause mortality in AHF. Receiver operating characteristic (ROC) curve and Delong's test were used to assess the performance of hypocapnia in predicting in-hospital all-cause mortality in AHF. The study cohort included 464 (68.6%) males and 212 (31.4%) females, and the median age was 66 years (interquartile range 56-74 years). Ninety-eight (14.5%) patients died during hospitalization and presented more hypocapnia than survivors (76.5% vs. 45.5%, P < 0.001). A 1:1 PSM was performed between hypocapnic and non-hypocapnic patients, with 264 individuals in each of the two groups after matching. Compared with non-hypocapnic patients, in-hospital mortality was significantly higher in hypocapnic patients both before (22.2% vs. 6.8%, P < 0.001) and after (20.8% vs. 8.7%, P < 0.001) PSM. Kaplan-Meier curve showed a significantly higher probability of in-hospital death in patients with hypocapnia before and after PSM (both P < 0.001 for the log-rank test). Multivariate Cox regression analysis showed that hypocapnia was an independent predictor of AHF mortality both before [hazard ratio (HR) 2.22; 95% confidence interval (CI) 1.23-3.98; P = 0.008] and after (HR 2.19; 95% CI 1.18-4.07; P = 0.013) PSM. Delong's test showed that the area under the ROC curve was improved after adding hypocapnia into the model (0.872, 95% CI 0.839-0.901 vs. 0.855, 95% CI 0.820-0.886, P = 0.028). PaCO₂ was correlated with the estimated glomerular filtration rate (r = 0.20, P = 0.001), left ventricular ejection fraction (r = 0.13, P < 0.001), B-type natriuretic peptide (r = -0.28, P < 0.001), and lactate (r = -0.15, P < 0.001). Kaplan-Meier curve of PaCO₂ tertiles and multivariate Cox regression analysis showed that the lowest PaCO₂ tertile was associated with increased risk of in-hospital mortality in AHF (all P < 0.05).

CONCLUSIONS

Hypocapnia is an independent predictor of in-hospital mortality for AHF.

Mechanical Ventilation in Patients with Traumatic Brain Injury: Is it so Different?

Patients with traumatic brain injury (TBI) frequently require invasive mechanical ventilation and admission to an intensive care unit. Ventilation of patients with TBI poses unique clinical challenges, and careful attention is required to ensure that the ventilatory strategy (including selection of appropriate tidal volume, plateau pressure, and positive end-expiratory pressure) does not cause significant additional injury to the brain and lungs. Selection of ventilatory targets may be guided by principles of lung protection but with careful attention to relevant intracranial effects. In patients with TBI and concomitant acute respiratory distress syndrome (ARDS), adjunctive strategies include sedation optimization, neuromuscular blockade, recruitment maneuvers, prone positioning, and extracorporeal life support. However, these approaches have been largely extrapolated from studies in patients with ARDS and without brain injury, with limited data in patients with TBI. This narrative review will summarize the existing evidence for mechanical ventilation in patients with TBI. Relevant literature in patients with ARDS will be summarized, and where available, direct data in the TBI population will be reviewed. Next, practical strategies to optimize the delivery of mechanical ventilation and determine readiness for extubation will be reviewed. Finally, future directions for research in this evolving clinical domain will be presented, with considerations for the design of studies to address relevant knowledge gaps.

Treatments for intracranial hypertension in acute brain-injured patients: grading, timing, and association with outcome. Data from the SYNAPSE-ICU study

PURPOSE

Uncertainties remain about the safety and efficacy of therapies for managing intracranial hypertension in acute brain injured (ABI) patients. This study aims to describe the therapeutical approaches used in ABI, with/without intracranial pressure (ICP) monitoring, among different pathologies and across different countries, and their association with six months mortality and neurological outcome.

METHODS

A preplanned subanalysis of the SYNAPSE-ICU study, a multicentre, prospective, international, observational cohort study, describing the ICP treatment, graded according to Therapy Intensity Level (TIL) scale, in patients with ABI during the first week of intensive care unit (ICU) admission.

RESULTS

2320 patients were included in the analysis. The median age was 55 (I-III quartiles = 39-69) years, and 800 (34.5%) were female. During the first week from ICU admission, no-basic TIL was used in 382 (16.5%) patients, mild-moderate in 1643 (70.8%), and extreme in 295 cases (eTIL, 12.7%). Patients who received eTIL were younger (median age 49 (I-III quartiles = 35-62) vs 56 (40-69) years, p < 0.001), with less cardiovascular pre-injury comorbidities (859 (44%) vs 90 (31.4%), p < 0.001), with more episodes of neuroworsening (160 (56.1%) vs 653 (33.3%), p < 0.001), and were more frequently monitored with an ICP device (221 (74.9%) vs 1037 (51.2%), p < 0.001). Considerable variability in the frequency of use and type of eTIL adopted was observed between centres and countries. At six months, patients who received no-basic TIL had an increased risk of mortality (Hazard ratio, HR = 1.612, 95% Confidence Interval, CI = 1.243-2.091, p < 0.001) compared to patients who received eTIL. No difference was observed when comparing mild-moderate TIL with eTIL (HR = 1.017, 95% CI = 0.823-1.257, p = 0.873). No significant association between the use of TIL and neurological outcome was observed.

CONCLUSIONS

During the first week of ICU admission, therapies to control high ICP are frequently used, especially mild-moderate TIL. In selected patients, the use of aggressive strategies can have a beneficial effect on six months mortality but not on neurological outcome.

The effect of hyperventilation versus normoventilation on cerebral oxygenation using near infrared spectroscopy in children undergoing posterior fossa tumor resection: A randomized controlled cross-over trial

BACKGROUND

This study aims to compare the effect of two different ventilation strategies on cerebral oxygenation in children undergoing posterior fossa tumor excision surgeries.

METHODS

Children scheduled for posterior fossa tumor surgeries were enrolled in this randomized, double-blinded, controlled cross-over trial. After induction of general anesthesia and positioning, participants were randomized to have mild hyperventilation for 30 min (phase 1) followed by normal ventilation for another 30 min (phase2) (early hyperventilation group, n = 23), or normal ventilation for 30 min (phase 1) followed by hyperventilation for 30 min (phase 2) (early normoventilation group, n = 19). Our primary outcome was cerebral oxygenation, measured using near-infrared spectroscopy (NIRS). Other outcomes included the intracranial pressure (ICP), brain relaxation score at the end of phase 1, and frequency of nadir NIRS.

RESULTS

Forty-two children were available for final per protocol analysis. The cerebral oxygenation decreased after the hyperventilation phase compared to the baseline values and the corresponding phases of normoventilation. The mean difference [95% confidence intervals (CI)] in cerebral oxygen saturation between the hyperventilation and normal ventilation readings was 13.45 ± 1.14% [11.14-15.76] and 11.47 ± 0.96% [11.14-15.76] in the left and right sides, respectively (p-values <0.0001). Both carryover and period effects were not significant. The ICP at the end of phase 1 did not differ between the two groups: 22.12 ± 3.75 mmHg vs. 23.26 ± 4.33, mean difference [95%CI]: -0.78 [-3.05 to 1.5], p = 0.49. Brain relaxation score was similar in the two groups.

CONCLUSION

In children undergoing posterior fossa craniotomy, moderate hyperventilation reduced cerebral oxygenation without significant improvement of the surgical brain relaxation or the ICP.

Brain-Lung Crosstalk: Management of Concomitant Severe Acute Brain Injury and Acute Respiratory Distress Syndrome

Purpose of Review

To summarize pathophysiology, key conflicts, and therapeutic approaches in managing concomitant severe acute brain injury (SABI) and acute respiratory distress syndrome (ARDS).

Recent Findings

ARDS is common in SABI and independently associated with worse outcomes in all SABI subtypes. Most landmark ARDS trials excluded patients with SABI, and evidence to guide decisions is limited in this population. Potential areas of conflict in the management of patients with both SABI and ARDS are (1) risk of intracranial pressure (ICP) elevation with high levels of positive end-expiratory pressure (PEEP), permissive hypercapnia due to lung protective ventilation (LPV), or prone ventilation; (2) balancing a conservative fluid management strategy with ensuring adequate cerebral perfusion, particularly in patients with symptomatic vasospasm or impaired cerebrovascular blood flow; and (3) uncertainty about the benefit and harm of corticosteroids in this population, with a mortality benefit in ARDS, increased mortality shown in TBI, and conflicting data in other SABI subtypes. Also, the widely adapted partial pressure of oxygen (PaO2) target of > 55 mmHg for ARDS may exacerbate secondary brain injury, and recent guidelines recommend higher goals of 80-120 mmHg in SABI. Distinct pathophysiology and trajectories among different SABI subtypes need to be considered.

Summary

The management of SABI with ARDS is highly complex, and conventional ARDS management strategies may result in increased ICP and decreased cerebral perfusion. A crucial aspect of concurrent management is to recognize the risk of secondary brain injury in the individual patient, monitor with vigilance, and adjust management during critical time windows. The care of these patients requires meticulous attention to oxygenation and ventilation, hemodynamics, temperature management, and the neurological exam. LPV and prone ventilation should be utilized, and supplemented with invasive ICP monitoring if there is concern for cerebral edema and increased ICP. PEEP titration should be deliberate, involving measures of hemodynamic, pulmonary, and brain physiology. Serial volume status assessments should be performed in SABI and ARDS, and fluid management should be individualized based on measures of brain perfusion, the neurological exam, and cardiopulmonary status. More research is needed to define risks and benefits in corticosteroids in this population.

Optimal Arterial Blood Gas Tensions for the Prognosis of Favorable Neurological Outcomes in Survivors after Extracorporeal Cardiopulmonary Resuscitation

Our aim is to assess the optimal levels of oxygen and carbon dioxide for the prognosis of favorable neurologic outcomes in survivors after extracorporeal cardiopulmonary resuscitation (ECPR). We obtained the mean levels of PaCO₂ and PaO₂ in arterial blood gas samples 72 h after ECPR. The primary outcome was the neurological status, according to the Cerebral Performance Categories (CPC) scale, upon discharge. Of 119 (48.6%) survivors, 95 (38.8%) had favorable neurologic outcomes (CPC 1 or 2). There was a U-shaped relationship between mean arterial blood gas tensions and poor neurological outcomes. The risk of poor neurological outcome was lowest in patients with the second tertile of mean PaCO₂ (30–42 mm Hg) and PaO₂ (120–160 mm Hg). In a multivariable analysis, third tertile of mean PaCO₂, third tertile of mean PaO₂, age, shockable rhythm, out of hospital cardiac arrest, duration of cardiopulmonary resuscitation, and ECPR at cardiac catheterization lab were found to be significantly associated with poor neurologic outcomes. Additionally, hypercapnia and extreme hyperoxia were found to be significantly associated with poor neurological outcomes after ECPR. Therefore, maintaining adequate arterial levels of oxygen and carbon dioxide may be important for favorable neurological prognoses in survivors after ECPR.

Noninvasive and invasive mechanical ventilation for neurologic disorders

Patients with acute neurologic injuries frequently require mechanical ventilation due to diminished airway protective reflexes, cardiopulmonary failure secondary to neurologic insults, or to facilitate gas exchange to precise targets. Mechanical ventilation enables tight control of oxygenation and carbon dioxide levels, enabling clinicians to modulate cerebral hemodynamics and intracranial pressure with the goal of minimizing secondary brain injury. In patients with acute spinal cord injuries, neuromuscular conditions, or diseases of the peripheral nerve, mechanical ventilation enables respiratory support under conditions of impending or established respiratory failure. Noninvasive ventilatory approaches may be carefully considered for certain disease conditions, including myasthenia gravis and amyotrophic lateral sclerosis, but may be inappropriate in patients with Guillain-Barré syndrome or when relevant contra-indications exist. With regard to discontinuing mechanical ventilation, considerable uncertainty persists about the best approach to wean patients, how to identify patients ready for extubation, and when to consider primary tracheostomy. Recent consensus guidelines highlight these and other knowledge gaps that are the focus of active research efforts. This chapter outlines important general principles to consider when initiating, titrating, and discontinuing mechanical ventilation in patients with acute neurologic injuries. Important disease-specific considerations are also reviewed where appropriate.

Multisystem Involvement in Post-acute Sequelae of COVID-19 (PASC)

OBJECTIVE

To describe cerebrovascular, neuropathic and autonomic features of post-acute sequelae of COVID-19 (PASC).

METHODS

This retrospective study evaluated consecutive patients with chronic fatigue, brain fog and orthostatic intolerance consistent with PASC. Controls included postural tachycardia syndrome patients (POTS) and healthy participants. Analyzed data included surveys and autonomic (Valsalva maneuver, deep breathing, sudomotor and tilt tests), cerebrovascular (cerebral blood flow velocity (CBFv) monitoring in middle cerebral artery), respiratory (capnography monitoring) and neuropathic (skin biopsies for assessment of small fiber neuropathy) testing and inflammatory/autoimmune markers.

RESULTS

Nine PASC patients were evaluated 0.7±0.3 years after a mild COVID-19 infection, treated as home observations. Autonomic, pain, brain fog, fatigue and dyspnea surveys were abnormal in PASC and POTS (n=10), compared to controls (n=15). Tilt table test reproduced the majority of PASC symptoms. Orthostatic CBFv declined in PASC (-20.0±13.4%) and POTS (-20.3±15.1%), compared to controls (-3.0±7.5%,p=0.001) and was independent of end-tidal carbon dioxide in PASC, but caused by hyperventilation in POTS. Reduced orthostatic CBFv in PASC included both subjects without (n=6) and with (n=3) orthostatic tachycardia. Dysautonomia was frequent (100% in both PASC and POTS) but was milder in PASC (p=0.013). PASC and POTS cohorts diverged in frequency of small fiber neuropathy (89% vs. 60%) but not in inflammatory markers (67% vs. 70%). Supine and orthostatic hypocapnia was observed in PASC.

INTERPRETATION

PASC following mild COVID-19 infection is associated with multisystem involvement including: 1) cerebrovascular dysregulation with persistent cerebral arteriolar vasoconstriction; 2) small fiber neuropathy and related dysautonomia; 3) respiratory dysregulation; 4) chronic inflammation. This article is protected by copyright. All rights reserved.

Perioperative Management of Polytrauma Patients with Severe Traumatic Brain Injury Undergoing Emergency Extracranial Surgery: A Narrative Review

Managing the acute phase after a severe traumatic brain injury (TBI) with polytrauma represents a challenging situation for every trauma team member. A worldwide variability in the management of these complex patients has been reported in recent studies. Moreover, limited evidence regarding this topic is available, mainly due to the lack of well-designed studies. Anesthesiologists, as trauma team members, should be familiar with all the issues related to the management of these patients. In this narrative review, we summarize the available evidence in this setting, focusing on perioperative brain protection, cardiorespiratory optimization, and preservation of the coagulative function. An overview on simultaneous multisystem surgery (SMS) is also presented.

Overview of Acute Ischemic Stroke Evaluation and Management

Stroke is a major contributor to death and disability worldwide. Prior to modern therapy, post-stroke mortality was approximately 10% in the acute period, with nearly one-half of the patients developing moderate-to-severe disability. The most fundamental aspect of acute stroke management is "time is brain". In acute ischemic stroke, the primary therapeutic goal of reperfusion therapy, including intravenous recombinant tissue plasminogen activator (IV TPA) and/or endovascular thrombectomy, is the rapid restoration of cerebral blood flow to the salvageable ischemic brain tissue at risk for cerebral infarction. Several landmark endovascular thrombectomy trials were found to be of benefit in select patients with acute stroke caused by occlusion of the proximal anterior circulation, which has led to a paradigm shift in the management of acute ischemic strokes. In this modern era of acute stroke care, more patients will survive with varying degrees of disability post-stroke. A comprehensive stroke rehabilitation program is critical to optimize post-stroke outcomes. Understanding the natural history of stroke recovery, and adapting a multidisciplinary approach, will lead to improved chances for successful rehabilitation. In this article, we provide an overview on the evaluation and the current advances in the management of acute ischemic stroke, starting in the prehospital setting and in the emergency department, followed by post-acute stroke hospital management and rehabilitation.

PaCO2-management in the neuro-critical care of patients with subarachnoid hemorrhage

The partial pressure of carbon dioxide (PaCO2) in the arterial blood is a strong vasomodulator affecting cerebral blood flow and the risk of cerebral edema and ischemia after acute brain injury. In turn, both complications are related to poor outcome in patients with aneurysmal subarachnoid hemorrhage (aSAH). We aimed to analyze the effect of PaCO2 levels on the course and outcome of aSAH. All patients of a single institution treated for aSAH over 13.5 years were included (n = 633). Daily PaCO2 values from arterial blood gas measurements were recorded for up to 2 weeks after ictus. The study endpoints were: delayed cerebral ischemia (DCI), need for decompressive craniectomy due to increased intracranial pressure > 20 mmHg refractory to conservative treatment and poor outcome at 6-months follow-up (modified Rankin scale > 2). By correlations with the study endpoints, clinically relevant cutoffs for the 14-days mean values for the lowest and highest daily PaCO2 levels were defined by receiver operating characteristic curve analysis. Association with the study endpoints for the identifies subgroups was analyzed using multivariate analysis. The optimal range for PaCO2 values was identified between 30 and 38 mmHg. ASAH patients with poor initial condition (WFNS 4/5) were less likely to show PaCO2 values within the range of 30-38 mmHg (p < 0.001, OR = 0.44). In the multivariate analysis, PaCO2 values between 30 and 38 mmHg were associated with a lower risk for decompressive craniectomy (p = 0.042, aOR = 0.27), DCI occurrence (p = 0.035; aOR = 0.50), and poor patient outcome (p = 0.004; aOR = 0.42). The data from this study shows an independent positive association between low normal mean PaCO2 values during the acute phase of aSAH and patients' outcome. This effect might be attributed to the reduction of intracranial hypertension and alterations in the cerebral blood flow.

Transcranial color-coded duplex sonography assessment of cerebrovascular reactivity to carbon dioxide: an interventional study

Background

The investigation of CO₂ reactivity (CO₂-CVR) is used in the setting of, e.g., traumatic brain injury (TBI). Transcranial color-coded duplex sonography (TCCD) is a promising bedside tool for monitoring cerebral hemodynamics. This study used TCCD to investigate CO₂-CVR in volunteers, in sedated and mechanically ventilated patients without TBI and in sedated and mechanically ventilated patients in the acute phase after TBI.

Methods

This interventional investigation was performed between March 2013 and February 2016 at the surgical ICU of the University Hospital of Zurich. Ten volunteers (group 1), ten sedated and mechanically ventilated patients (group 2), and ten patients in the acute phase (12–36 h) after severe TBI (group 3) were included. CO₂-CVR to moderate hyperventilation (∆ CO₂ -5.5 mmHg) was assessed by TCCD.

Results

CO₂-CVR was 2.14 (1.20–2.70) %/mmHg in group 1, 2.03 (0.15–3.98) %/mmHg in group 2, and 3.32 (1.18–4.48)%/mmHg in group 3, without significant differences among groups.

Conclusion

Our data did not yield evidence for altered CO₂-CVR in the early phase after TBI examined by TCCD.

Trial registration

Part of this trial was performed as preparation for the interventional trial in TBI patients (clinicaltrials.gov NCT03822026, 30.01.2019, retrospectively registered).

Intraoperative end-tidal carbon dioxide and postoperative mortality in major abdominal surgery: a historical cohort study

PURPOSE

There is a paucity of data on the effect of intraoperative end-tidal carbon dioxide (EtCO₂) levels on postoperative mortality. The purpose of this study was to investigate the relationship between intraoperative EtCO₂ and 90-day mortality in patients undergoing major abdominal surgery under general anesthesia.

METHODS

We conducted a historical cohort study of patients undergoing major abdominal surgery under general anesthesia at Kyoto University Hospital. We measured the intraoperative EtCO₂, and patients with a mean EtCO₂ value < 35 mm Hg were classified as low EtCO₂. The time effect was determined based on minutes below an EtCO₂ of 35 mm Hg, and cumulative effects were evaluated by measuring the area under the threshold of 35 mm Hg for each patient.

RESULTS

Of 4,710 patients, 1,374 (29%) had low EtCO₂ and 55 (1.2%) died within 90 days of surgery. Multivariable Cox regression analysis-adjusted for age, American Society of Anesthesiologists Physical Status classification, sex, laparoscopic surgery, emergency surgery, blood loss, mean arterial pressure, duration of surgery, type of surgery, and chronic obstructive pulmonary disease-revealed an association between low EtCO₂ and 90-day mortality (adjusted hazard ratio, 2.2; 95% confidence interval [CI], 1.2 to 3.8; P = 0.006). In addition, severity of low EtCO₂ was associated with an increased 90-day mortality (area under the threshold; adjusted hazard ratio; 2.9, 95% CI, 1.2 to 7.4; P =0.02); for long-term exposure to an EtCO₂ < 35 mm Hg (≥ 226 min), the adjusted hazard ratio for increased 90-day mortality was 2.3 (95% CI, 0.9 to 6.0; P = 0.08).

CONCLUSION

A mean intraoperative EtCO₂ < 35 mm Hg was associated with increased postoperative 90-day mortality.

Optimal Targets of the First 24-h Partial Pressure of Carbon Dioxide in Patients with Cerebral Injury: Data from the MIMIC-III and IV Database

BACKGROUND

It is generally believed that hypercapnia and hypocapnia will cause secondary injury to patients with craniocerebral diseases, but a small number of studies have shown that they may have potential benefits. We assessed the impact of partial pressure of arterial carbon dioxide (PaCO₂) on in-hospital mortality of patients with craniocerebral diseases. The hypothesis of this research was that there is a nonlinear correlation between PaCO₂ and in-hospital mortality in patients with craniocerebral diseases and that mortality rate is the lowest when PaCO₂ is in a normal range.

METHODS

We identified patients with craniocerebral diseases from Medical Information Mart for Intensive Care third and fourth edition databases. Cox regression analysis and restricted cubic splines were used to examine the association between PaCO₂ and in-hospital mortality.

RESULTS

Nine thousand six hundred and sixty patients were identified. A U-shaped association was found between the first 24-h PaCO₂ and in-hospital mortality in all participants. The nadir for in-hospital mortality risk was estimated to be at 39.5 mm Hg (p for nonlinearity < 0.001). In the subsequent subgroup analysis, similar results were found in patients with traumatic brain injury, metabolic or toxic encephalopathy, subarachnoid hemorrhage, cerebral infarction, and other encephalopathies. Besides, the mortality risk reached a nadir at PaCO₂ in the range of 35-45 mm Hg. The restricted cubic splines showed a U-shaped association between the first 24-h PaCO₂ and in-hospital mortality in patients with other intracerebral hemorrhage and cerebral tumor. Nonetheless, nonlinearity tests were not statistically significant. In addition, Cox regression analysis showed that PaCO₂ ranging 35-45 mm Hg had the lowest death risk in most patients. For patients with hypoxic-ischemic encephalopathy and intracranial infections, the first 24-h PaCO₂ and in-hospital mortality did not seem to be correlated.

CONCLUSIONS

Both hypercapnia and hypocapnia are harmful to most patients with craniocerebral diseases. Keeping the first 24-h PaCO₂ in the normal range (35-45 mm Hg) is associated with lower death risk.

Management of arterial partial pressure of carbon dioxide in the first week after traumatic brain injury: results from the CENTER-TBI study

Purpose

To describe the management of arterial partial pressure of carbon dioxide (PaCO₂) in severe traumatic brain-injured (TBI) patients, and the optimal target of PaCO₂ in patients with high intracranial pressure (ICP).

Methods

Secondary analysis of CENTER-TBI, a multicentre, prospective, observational, cohort study. The primary aim was to describe current practice in PaCO₂ management during the first week of intensive care unit (ICU) after TBI, focusing on the lowest PaCO₂ values. We also assessed PaCO₂ management in patients with and without ICP monitoring (ICP_m), and with and without intracranial hypertension. We evaluated the effect of profound hyperventilation (defined as PaCO₂ < 30 mmHg) on long-term outcome.

Results

We included 1100 patients, with a total of 11,791 measurements of PaCO₂ (5931 lowest and 5860 highest daily values). The mean (± SD) PaCO₂ was 38.9 (± 5.2) mmHg, and the mean minimum PaCO₂ was 35.2 (± 5.3) mmHg. Mean daily minimum PaCO₂ values were significantly lower in the ICP_m group (34.5 vs 36.7 mmHg, p < 0.001). Daily PaCO₂ nadir was lower in patients with intracranial hypertension (33.8 vs 35.7 mmHg, p < 0.001). Considerable heterogeneity was observed between centers. Management in a centre using profound hyperventilation (HV) more frequently was not associated with increased 6 months mortality (OR = 1.06, 95% CI = 0.77–1.45, p value = 0.7166), or unfavourable neurological outcome (OR 1.12, 95% CI = 0.90–1.38, p value = 0.3138).

Conclusions

Ventilation is manipulated differently among centers and in response to intracranial dynamics. PaCO₂ tends to be lower in patients with ICP monitoring, especially if ICP is increased. Being in a centre which more frequently uses profound hyperventilation does not affect patient outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00134-021-06470-7.

European Stroke Organisation (ESO) guidelines on the management of space-occupying brain infarction

Space-occupying brain oedema is a potentially life-threatening complication in the first days after large hemispheric or cerebellar infarction. Several treatment strategies for this complication are available, but the size and quality of the scientific evidence on which these strategies are based vary considerably. The aim of this Guideline document is to assist physicians in their management decisions when treating patients with space-occupying hemispheric or cerebellar infarction. These Guidelines were developed based on the European Stroke Organisation (ESO) standard operating procedure and followed the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. A working group identified 13 relevant questions, performed systematic reviews and meta-analyses of the literature, assessed the quality of the available evidence, and wrote evidence-based recommendations. An expert consensus statement was provided if not enough evidence was available to provide recommendations based on the GRADE approach. We found high-quality evidence to recommend surgical decompression to reduce the risk of death and to increase the chance of a favourable outcome in adult patients aged up to and including 60 years with space-occupying hemispheric infarction who can be treated within 48 hours of stroke onset, and low-quality evidence to support this treatment in older patients. There is continued uncertainty about the benefit and risks of surgical decompression in patients with space-occupying hemispheric infarction if this is done after the first 48 hours. There is also continued uncertainty about the selection of patients with space-occupying cerebellar infarction for surgical decompression or drainage of cerebrospinal fluid. These Guidelines further provide details on the management of specific subgroups of patients with space-occupying hemispheric infarction, on the value of monitoring of intracranial pressure, and on the benefits and risks of medical treatment options. We encourage new high-quality studies assessing the risks and benefits of different treatment strategies for patients with space-occupying brain infarction.

Association of Ventilation during Initial Trauma Resuscitation for Traumatic Brain Injury and Post-Traumatic Outcomes: A Systematic Review

OBJECTIVES

In the absence of evidence of acute cerebral herniation, normal ventilation is recommended for patients with traumatic brain injury (TBI). Despite this recommendation, ventilation strategies vary during the initial management of patients with TBI and may impact outcome. The goal of this systematic review was to define the best evidence-based practice of ventilation management during the initial resuscitation period.

METHODS

A literature search of PubMed, CINAHL, and SCOPUS identified studies from 2009 through 2019 addressing the effects of ventilation during the initial post-trauma resuscitation on patient outcomes.

RESULTS

The initial search yielded 899 articles, from which 13 were relevant and selected for full-text review. Six of the 13 articles met the inclusion criteria, all of which reported on patients with TBI. Either end-tidal carbon dioxide (ETCO2) or partial pressure carbon dioxide (PCO2) were the independent variables associated with mortality. Decreased rates of mortality were reported in patients with normal PCO2 or ETCO2.

CONCLUSIONS

Normoventilation, as measured by ETCO2 or PCO2, is associated with decreased mortality in patients with TBI. Preventing hyperventilation or hypoventilation in patients with TBI during the early resuscitation phase could improve outcome after TBI.

End-tidal to arterial carbon dioxide gradient is associated with increased mortality in patients with traumatic brain injury: a retrospective observational study

Early definitive airway protection and normoventilation are key principles in the treatment of severe traumatic brain injury. These are currently guided by end tidal CO2 as a proxy for PaCO2. We assessed whether the difference between end tidal CO2 and PaCO2 at hospital admission is associated with in-hospital mortality. We conducted a retrospective observational cohort study of consecutive patients with traumatic brain injury who were intubated and transported by Helicopter Emergency Medical Services to a Level 1 trauma center between January 2014 and December 2019. We assessed the association between the CO2 gap-defined as the difference between end tidal CO2 and PaCO2-and in-hospital mortality using multivariate logistic regression models. 105 patients were included in this study. The mean ± SD CO2 gap at admission was 1.64 ± 1.09 kPa and significantly greater in non-survivors than survivors (2.26 ± 1.30 kPa vs. 1.42 ± 0.92 kPa, p < .001). The correlation between EtCO2 and PaCO2 at admission was low (Pearson's r = .287). The mean CO2 gap after 24 h was only 0.64 ± 0.82 kPa, and no longer significantly different between non-survivors and survivors. The multivariate logistic regression model showed that the CO2 gap was independently associated with increased mortality in this cohort and associated with a 2.7-fold increased mortality for every 1 kPa increase in the CO2 gap (OR 2.692, 95% CI 1.293 to 5.646, p = .009). This study demonstrates that the difference between EtCO2 and PaCO2 is significantly associated with in-hospital mortality in patients with traumatic brain injury. EtCO2 was significantly lower than PaCO2, making it an unreliable proxy for PaCO2 when aiming for normocapnic ventilation. The CO2 gap can lead to iatrogenic hypoventilation when normocapnic ventilation is aimed and might thereby increase in-hospital mortality.

Emergency medical services protocols for traumatic brain injury in the United States: A call for standardization

BACKGROUND

Traumatic brain injury (TBI) with acute elevation in intracranial pressure (ICP) is a neurologic emergency associated with significant morbidity and mortality. In addition to indicated trauma resuscitation, emergency department (ED) management includes empiric administration of hyperosmolar agents, rapid diagnostic imaging, anticoagulation reversal, and early neurosurgical consultation. Despite optimization of in-hospital care, patient outcomes may be worsened by variation in prehospital management. In this study, we evaluate geographic variation between emergency medical services (EMS) protocols for patients with suspected TBI.

METHODS

We performed a cross-sectional analysis of statewide EMS protocols in the United States in December 2020 and included all complete protocols published on government websites. Outcome measures were defined to include protocols or orders for the following interventions, given TBI: (1) hyperventilation and end-tidal capnography (EtCO2) goals, (2) administration of hyperosmolar agents, (3) tranexamic acid (TXA) administration for isolated head injury, (4) non-invasive management including head-of-bed elevation, and (5) hemodynamic goals.

RESULTS

We identified 32 statewide protocols including Washington, D.C., 4 of which did not include specific guidance for TBI. Of 28 states providing ventilatory guidance, 22/28 (78.6%) recommend hyperventilation, with 17/22 (77.3%) restricting hyperventilation to signs of acute herniation. The remaining 6 states prohibited hyperventilation. Regarding EtCO2 goals among states permitting hyperventilation, 17/22 (77.3%) targeted an EtCO2 of < 35 mmHg, while 5/22 (22.7%) provided no guide EtCO2 for hyperventilation. Rhode Island was the only state identified that included hypertonic saline (3%), and Delaware was the only state that allowed TXA in the setting of isolated TBI with GCS ≤ 12. Only 15/32 (46.9%) identified states recommend head-of-bed elevation. For blood pressure goals, 12/28 (42.9%) of states set minimum systolic blood pressure at 90 mmHg, while 10/28 (35.7%) set other SBP goals. The remaining 6/28 (21.4%) did not provide TBI-specific SBP goals.

CONCLUSIONS

There is wide variation among civilian prehospital protocols for traumatic brain injury. Prehospital care within the first "golden hour" may dramatically affect patient outcomes. Neurocritical care providers should be mindful of geographic variation in local protocols when designing and evaluating quality improvement interventions and should aim to standardize prehospital care protocols.

Effect of Implementing the Out-of-Hospital Traumatic Brain Injury Treatment Guidelines: The Excellence in Prehospital Injury Care for Children Study (EPIC4Kids)

STUDY OBJECTIVE

We evaluate the effect of implementing the out-of-hospital pediatric traumatic brain injury guidelines on outcomes in children with major traumatic brain injury.

METHODS

The Excellence in Prehospital Injury Care for Children study is the preplanned secondary analysis of the Excellence in Prehospital Injury Care study, a multisystem, intention-to-treat study using a before-after controlled design. This subanalysis included children younger than 18 years who were transported to Level I trauma centers by participating out-of-hospital agencies between January 1, 2007, and June 30, 2015, throughout Arizona. The primary and secondary outcomes were survival to hospital discharge or admission for children with major traumatic brain injury and in 3 subgroups, defined a priori as those with moderate, severe, and critical traumatic brain injury. Outcomes in the preimplementation and postimplementation cohorts were compared with logistic regression, adjusting for risk factors and confounders.

RESULTS

There were 2,801 subjects, 2,041 in preimplementation and 760 in postimplementation. The primary analysis (postimplementation versus preimplementation) yielded an adjusted odds ratio of 1.16 (95% confidence interval 0.70 to 1.92) for survival to hospital discharge and 2.41 (95% confidence interval 1.17 to 5.21) for survival to hospital admission. In the severe traumatic brain injury cohort (Regional Severity Score-Head 3 or 4), but not the moderate or critical subgroups, survival to discharge significantly improved after guideline implementation (adjusted odds ratio = 8.42; 95% confidence interval 1.01 to 100+). The improvement in survival to discharge among patients with severe traumatic brain injury who received positive-pressure ventilation did not reach significance (adjusted odds ratio = 9.13; 95% confidence interval 0.79 to 100+).

CONCLUSION

Implementation of the pediatric out-of-hospital traumatic brain injury guidelines was not associated with improved survival when the entire spectrum of severity was analyzed as a whole (moderate, severe, and critical). However, both adjusted survival to hospital admission and discharge improved in children with severe traumatic brain injury, indicating a potential severity-based interventional opportunity for guideline effectiveness. These findings support the widespread implementation of the out-of-hospital pediatric traumatic brain injury guidelines.

Hyperventilation in Adult TBI Patients: How to Approach It?

Hyperventilation is a commonly used therapy to treat intracranial hypertension (ICTH) in traumatic brain injury patients (TBI). Hyperventilation promotes hypocapnia, which causes vasoconstriction in the cerebral arterioles and thus reduces cerebral blood flow and, to a lesser extent, cerebral blood volume effectively, decreasing temporarily intracranial pressure. However, hyperventilation can have serious systemic and cerebral deleterious effects, such as ventilator-induced lung injury or cerebral ischemia. The routine use of this therapy is therefore not recommended. Conversely, in specific conditions, such as refractory ICHT and imminent brain herniation, it can be an effective life-saving rescue therapy. The aim of this review is to describe the impact of hyperventilation on extra-cerebral organs and cerebral hemodynamics or metabolism, as well as to discuss the side effects and how to implement it to manage TBI patients.

Prognostic effects of arterial carbon dioxide levels in patients hospitalized into the cardiac intensive care unit for acute heart failure

AIMS

Although both hypercapnia and hypocapnia are common in acute heart failure (AHF) patients, routine assessment of arterial blood gas is not recommended. Additionally, no association between hypercapnia and increased mortality has been found, and the prognostic value of hypocapnia in AHF patients remains to be elucidated. In this observational study, we aimed to investigate the relationship between partial pressure of arterial carbon dioxide (PaCO2), especially low PaCO2, and long-term mortality in AHF patients.

METHODS AND RESULTS

Acute heart failure patients hospitalized in the cardiac intensive care unit of our institution between 2007 and 2011 were screened. All eligible patients were divided into two groups based on the inflection point (i.e. 31.0 mmHg) of the 3-knot cubic spline curve of the hazard ratio (HR), with a PaCO2 of 40 mmHg as a reference. The association between PaCO2 levels and all-cause mortality was assessed using Cox proportional hazards regression models. Among 435 patients with a median follow-up of 1.8 years, 115 (26.4%) died. Adjusted analysis with relevant variables as confounders indicated that PaCO2 <31 mmHg was significantly associated with increased all-cause mortality [HR 1.71, 95% confidence interval (CI) 1.05-2.79; P = 0.032]. When PaCO2 was considered as a continuous variable, the lower was the log-transformed PaCO2, the greater was the increased risk of mortality (HR 0.71, 95% CI 0.52-0.96; P = 0.024).

CONCLUSIONS

In AHF patients, lower PaCO2 at admission was associated with increased long-term mortality risk.

Escalate and De-Escalate Therapies for Intracranial Pressure Control in Traumatic Brain Injury

Severe traumatic brain injury (TBI) is frequently associated with an elevation of intracranial pressure (ICP), followed by cerebral perfusion pressure (CPP) reduction. Invasive monitoring of ICP is recommended to guide a step-by-step “staircase approach” which aims to normalize ICP values and reduce the risks of secondary damage. However, if such monitoring is not available clinical examination and radiological criteria should be used. A major concern is how to taper the therapies employed for ICP control. The aim of this manuscript is to review the criteria for escalating and withdrawing therapies in TBI patients. Each step of the staircase approach carries a risk of adverse effects related to the duration of treatment. Tapering of barbiturates should start once ICP control has been achieved for at least 24 h, although a period of 2–12 days is often required. Administration of hyperosmolar fluids should be avoided if ICP is normal. Sedation should be reduced after at least 24 h of controlled ICP to allow neurological examination. Removal of invasive ICP monitoring is suggested after 72 h of normal ICP. For patients who have undergone surgical decompression, cranioplasty represents the final step, and an earlier cranioplasty (15–90 days after decompression) seems to reduce the rate of infection, seizures, and hydrocephalus.

Mechanical ventilation in patients with acute brain injury: recommendations of the European Society of Intensive Care Medicine consensus

Purpose

To provide clinical practice recommendations and generate a research agenda on mechanical ventilation and respiratory support in patients with acute brain injury (ABI).

Methods

An international consensus panel was convened including 29 clinician-scientists in intensive care medicine with expertise in acute respiratory failure, neurointensive care, or both, and two non-voting methodologists. The panel was divided into seven subgroups, each addressing a predefined clinical practice domain relevant to patients admitted to the intensive care unit (ICU) with ABI, defined as acute traumatic brain or cerebrovascular injury. The panel conducted systematic searches and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) method was used to evaluate evidence and formulate questions. A modified Delphi process was implemented with four rounds of voting in which panellists were asked to respond to questions (rounds 1–3) and then recommendation statements (final round). Strong recommendation, weak recommendation, or no recommendation were defined when > 85%, 75–85%, and < 75% of panellists, respectively, agreed with a statement.

Results

The GRADE rating was low, very low, or absent across domains. The consensus produced 36 statements (19 strong recommendations, 6 weak recommendations, 11 no recommendation) regarding airway management, non-invasive respiratory support, strategies for mechanical ventilation, rescue interventions for respiratory failure, ventilator liberation, and tracheostomy in brain-injured patients. Several knowledge gaps were identified to inform future research efforts.

Conclusions

This consensus provides guidance for the care of patients admitted to the ICU with ABI. Evidence was generally insufficient or lacking, and research is needed to demonstrate the feasibility, safety, and efficacy of different management approaches.

Electronic supplementary material

The online version of this article (10.1007/s00134-020-06283-0) contains supplementary material, which is available to authorized users.

The effects of arterial CO2 on the injured brain: Two faces of the same coin

Serum levels of carbon dioxide (CO₂) closely regulate cerebral blood flow (CBF) and actively participate in different aspects of brain physiology such as hemodynamics, oxygenation, and metabolism. Fluctuations in the partial pressure of arterial CO₂ (PaCO₂) modify the aforementioned variables, and at the same time influence physiologic parameters in organs such as the lungs, heart, kidneys, and the gastrointestinal tract. In general, during acute brain injury (ABI), maintaining normal PaCO₂ is the target to be achieved. Both hypercapnia and hypocapnia may comprise secondary insults and should be avoided during ABI. The risks of hypocapnia mostly outweigh the potential benefits. Therefore, its therapeutic applicability is limited to transient and second-stage control of intracranial hypertension. On the other hand, inducing hypercapnia could be beneficial when certain specific situations require increasing CBF. The evidence supporting this claim is very weak. This review attempts providing an update on the physiology of CO₂, its risks, benefits, and potential utility in the neurocritical care setting.

End-tidal and arterial carbon dioxide gradient in serious traumatic brain injury after prehospital emergency anaesthesia: a retrospective observational study

OBJECTIVES

In the UK, 20% of patients with severe traumatic brain injury (TBI) receive prehospital emergency anaesthesia (PHEA). Current guidance recommends an end-tidal carbon dioxide (ETCO2) of 4.0-4.5 kPa (30.0-33.8 mm Hg) to achieve a low-normal arterial partial pressure of CO2 (PaCO2), and reduce secondary brain injury. This recommendation assumes a 0.5 kPa (3.8 mm Hg) ETCO2-PaCO2 gradient. However, the gradient in the acute phase of TBI is unknown. The primary aim was to report the ETCO2-PaCO2 gradient of TBI patients at hospital arrival.

METHODS

A retrospective cohort study of adult patients with serious TBI, who received a PHEA by a prehospital critical care team in the East of England between 1 April 2015 and 31 December 2017. Linear regression was performed to test for correlation and reported as R-squared (R2). A Bland-Altman plot was used to test for paired ETCO2 and PaCO2 agreement and reported with 95% CI. ETCO2-PaCO2 gradient data were compared with a two-tailed, unpaired, t-test.

RESULTS

107 patients were eligible for inclusion. Sixty-seven patients did not receive a PaCO2 sample within 30 min of hospital arrival and were therefore excluded. Forty patients had complete data and were included in the final analysis; per protocol. The mean ETCO2-PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg), with moderate correlation (R2=0.23, p=0.002). The Bland-Altman bias was 1.7 (95% CI 1.4 to 2.0) kPa with upper and lower limits of agreement of 3.6 (95% CI 3.0 to 4.1) kPa and -0.2 (95% CI -0.8 to 0.3) kPa, respectively. There was no evidence of a larger gradient in more severe TBI (p=0.29). There was no significant gradient correlation in patients with a coexisting serious thoracic injury (R2=0.13, p=0.10), and this cohort had a larger ETCO2-PaCO2 gradient, 2.0 (±1.1) kPa (15.1 mm Hg), p=0.01. Patients who underwent prehospital arterial blood sampling had an arrival PaCO2 of 4.7 (±0.2) kPa (35.1 mm Hg).

CONCLUSION

There is only moderate correlation of ETCO2 and PaCO2 at hospital arrival in patients with serious TBI. The mean ETCO2-PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg). Lower ETCO2 targets than previously recommended may be safe and appropriate, and there may be a role for prehospital PaCO2 measurement.

Ventilation in Simulated Out-of-Hospital Cardiac Arrest Resuscitation Rarely Meets Guidelines

OBJECTIVE

The American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care recommend ventilation rates of eight to ten breaths per minute or two ventilations every 30 compressions, and tidal volumes between 500-600 ml. However, compliance with these guidelines is mainly unknown. The objective of this study is to estimate the proportion of simulated adult OHCA cases that meet guideline-based ventilation targets.

METHODS

We conducted a blinded prospective observational study of standardized simulated cases of EMS-witnessed adult OHCA. During scheduled training sessions, resuscitations were performed by high-quality CPR trained EMS teams composed of four on-duty, full-time EMT/Paramedics from a large urban fire-based EMS agency. A high-fidelity simulation center allowed complete audio and video monitoring from a control room. Rescuers were unaware of the study, or that ventilation practices were being observed. All interventions, including airway and ventilation strategies, were at the discretion of the clinical team. A calibrated Laerdal SimMan 3 G manikin and associated Laerdal Debrief Viewer software recorded ventilation rate, tidal volume, and minute ventilation. Simulations achieving median ventilation rate 7-10 breaths/min, tidal volume 500-600 ml, and minute ventilation 3.5-6 liters/min were considered meeting guideline-based targets.

RESULTS

A total of 106 EMS teams were included in the study. Only 3/106 [2.8% (95% CI: 0.6-8.0)] of the EMS teams demonstrated ventilation characteristics meeting all guideline-based targets. The median ventilation rate was 5.8 breaths/min (IQR 4.4-7.7 breaths/min) with 26/106 [24.5% (95% CI: 17.2-33.7)] between 7-10 breaths/min. The median tidal volume was 413.5 ml (IQR 280.5-555.4 ml), with 18/106 [17.0% (95% CI: 10.9-25.5)] between 500-600 ml. The median minute ventilation was 2.4 L/min (IQR 1.2-3.6 L/min) with 16/106 [15.1% (95% CI: 9.4-23.3)] between 3.5-6.0 L/min.

CONCLUSION

During simulated adult OHCA resuscitation attempts, ventilation practices rarely met guideline-based targets, despite being performed by well-trained EMS providers. Methods should be developed to monitor and ensure high-quality ventilation during actual OHCA resuscitation attempts.

Neurocritical Management of Traumatic Acute Subdural Hematomas

Acute subdural hematoma (ASDH) has been a major part of traumatic brain injury. Intracranial hypertension may be followed by ASDH and brain edema. Regardless of the complicated pathophysiology of ASDH, the extent of primary brain injury underlying the ASDH is the most important factor affecting outcome. Ongoing intracranial pressure (ICP) increasing lead to cerebral perfusion pressure (CPP) decrease and cerebral blood flow (CBF) decreasing occurred by CPP decrease. In additionally, disruption of cerebral autoregulation, vasospasm, decreasing of metabolic demand may lead to CBF decreasing. Various protocols for ICP lowering were introduced in neuro-trauma field. Usage of anti-epileptic drugs (AEDs) for ASDH patients have controversy. AEDs may reduce the risk of early seizure (<7 days), but, does not for late-onset epilepsy. Usage of anticoagulants/antiplatelets is increasing due to life-long medical disease conditions in aging populations. It makes a difficulty to decide the proper management. Tranexamic acid may use to reducing bleeding and reduce ASDH related death rate. Decompressive craniectomy for ASDH can reduce patient's death rate. However, it may be accompanied with surgical risks due to big operation and additional cranioplasty afterwards. If the craniotomy is a sufficient management for the ASDH, endoscopic surgery will be good alternative to a conventional larger craniotomy to evacuate the hematoma. The management plan for the ASDH should be individualized based on age, neurologic status, radiologic findings, and the patient's conditions.

Sevoflurane with opioid or dexmedetomidine infusions in dogs undergoing intracranial surgery: a retrospective observational study

This study reports the clinical use of two sevoflurane-based anesthetic techniques in dogs undergoing craniectomy. Twenty-one animals undergoing elective rostrotentorial or transfrontal craniectomy for brain tumor excision, anesthetized with sevoflurane, were enrolled in this retrospective, observational study. Anesthetic records were allocated to two groups: Sevo-Op (sevoflurane and short acting opioid infusion): 8 dogs and Sevo-Dex (sevoflurane and dexmedetomidine infusion): 13 dogs. Average mean arterial pressure (MAP), heart rate, end-tidal carbon dioxide, end-tidal sevoflurane and intraoperative infusion rates during surgery were calculated. Presence of intra-operative and post-operative bradycardia, tachycardia, hypotension, hypertension, hypothermia, hyperthermia was recorded. Time to endotracheal extubation, intraoperative occurrence of atrioventricular block, postoperative presence of agitation, seizures, use of labetalol and dexmedetomidine infusion were also recorded. Data from the two groups were compared with Fisher's exact test and unpaired t tests with Welch's correction. Odds ratio (OR) and 95% confidence interval (CI) were calculated for categorical variables. Intra-operatively, MAP was lower in Sevo-Op [85 (± 6.54) vs. 97.69 (± 7.8) mmHg, p = 0.0009]. Time to extubation was longer in Sevo-Dex [37.69 (10–70) vs. 19.63 (10–25), p = 0.0033]. No differences were found for the other intra-operative and post-operative variables investigated. Post-operative hypertension and agitation were the most common complications (11 and 12 out of 21 animals, respectively). These results suggest that the infusion of dexmedetomidine provides similar intra-operative conditions and post-operative course to a short acting opioid infusion during sevoflurane anesthesia in dogs undergoing elective rostrotentorial or transfrontal intracranial surgery.

Assessment of Dynamic Intracranial Compliance in Children with Severe Traumatic Brain Injury: Proof-of-Concept

Background and Aims

Intracranial compliance refers to the relationship between a change in intracranial volume and the resultant change in intracranial pressure (ICP). Measurement of compliance is useful in managing cardiovascular and respiratory failure; however, there are no contemporary means to assess intracranial compliance. Knowledge of intracranial compliance could complement ICP and cerebral perfusion pressure (CPP) monitoring in patients with severe traumatic brain injury (TBI) and may enable a proactive approach to ICP management. In this proof-of-concept study, we aimed to capitalize on the physiologic principles of intracranial compliance and vascular reactivity to CO₂, and standard-of-care neurocritical care monitoring, to develop a method to assess dynamic intracranial compliance.

Methods

Continuous ICP and end-tidal CO₂ (ETCO₂) data from children with severe TBI were collected after obtaining informed consent in this Institutional Review Board-approved study. An intracranial pressure-PCO₂ Compliance Index (PCI) was derived by calculating the moment-to-moment correlation between change in ICP and change in ETCO₂. As such, “good” compliance may be reflected by a lack of correlation between time-synched changes in ICP in response to changes in ETCO₂, and “poor” compliance may be reflected by a positive correlation between changes in ICP in response to changes in ETCO₂.

Results

A total of 978 h of ICP and ETCO₂ data were collected and analyzed from eight patients with severe TBI. Demographic and clinical characteristics included patient age 7.1 ± 5.8 years (mean ± SD); 6/8 male; initial Glasgow Coma Scale score 3 [3–7] (median [IQR]); 6/8 had decompressive surgery; 7.1 ± 1.4 ICP monitor days; ICU length of stay (LOS) 16.1 ± 6.8 days; hospital LOS 25.9 ± 8.4 days; and survival 100%. The mean PCI for all patients throughout the monitoring period was 0.18 ± 0.04, where mean ICP was 13.7 ± 2.1 mmHg. In this cohort, PCI was observed to be consistently above 0.18 by 12 h after monitor placement. Percent time spent with PCI thresholds > 0.1, 0.2, and 0.3 were 62% [24], 38% [14], and 23% [15], respectively. The percentage of time spent with an ICP threshold > 20 mmHg was 5.1% [14.6].

Conclusions

Indirect assessment of dynamic intracranial compliance in TBI patients using standard-of-care monitoring appears feasible and suggests a prolonged period of derangement out to 5 days post-injury. Further study is ongoing to determine if the PCI—a new physiologic index, complements utility of ICP and/or CPP in guiding management of patients with severe TBI.

Electronic supplementary material

The online version of this article (10.1007/s12028-020-01004-3) contains supplementary material, which is available to authorized users.