Hypocapnia and the injured brain: More harm than benefit:

Role of Central Sensitization Syndrome in Patients With Autonomic Symptoms

Background and Objectives

Idiosyncratic autonomic-like symptomatology, e.g., when objective autonomic tests cannot fully explain autonomic concerns, is poorly understood. We hypothesize that central sensitization plays a role in the autonomic symptoms-sings dichotomy.

Methods

This retrospective case-control study was conducted at Brigham and Women's Faulkner Hospital Autonomic Laboratory between 2022 and 2023 and analyzed patients who completed autonomic testing that included surveys (Central Sensitization Inventory [assessing central sensitization syndrome {CSS}], Compass-31 [assessing autonomic symptoms], Neuropathy Total Symptom Score-6 [assessing sensory symptoms]) and autonomic (Valsalva maneuver, deep breathing, sudomotor evaluation, and head-up tilt), cerebrovascular (cerebral blood flow velocity [CBFv]), respiratory (capnography), and neuropathic (skin biopsies for assessment of small fiber neuropathy) testing.

Results

In total, 555 patients were enrolled and 455 (78%) satisfied criteria for CSS. Patients with CSS were younger and more frequently female and had longer duration of symptoms, more comorbidities, and higher Compass-31 scores and NTSS-6 compared with non-CSS patients. Autonomic testing showed lower orthostatic end-tidal CO2 (p = 0.002) and larger orthostatic decline in CBFv (p < 0.001) in the CSS group. There was no difference in the peripheral nervous system markers (sudomotor tests and skin biopsies). The frequency of moderate autonomic failure (AF) (91.4% vs 95%, p = 0.321) was similar between the groups, but the CSS group had lower AF score (4.21 ± 3.34 vs 5.23 ± 4.08, p < 0.021).

Discussion

CSS is present in most patients with chronic autonomic concerns. Central sensitization amplifies autonomic symptoms presumably through perturbed interoceptive processing and can be an underlying mechanism driving idiosyncratic autonomic-like symptomatology. Patients with CSS had objective evidence of autonomic impairment; however, it was less severe than in non-CSS patients. Our study shows that CSS and AF coexist and both conditions need to be treated.

Timing of neurosurgical interventions for intracranial hypertension: the intensivists' and neurosurgeons' view

PURPOSE OF REVIEW

The aim of this study was to highlight clinical considerations regarding medical versus surgical management of elevated intracranial pressure (ICP), describe limitations of medical management, and summarize evidence regarding timing of neurosurgical interventions.

RECENT FINDINGS

The optimal ICP management strategy remains elusive, and substantial practice variations exist. Common risks of medical treatments include hypotension/shock, cardiac arrhythmias and heart failure, acute renal failure, volume overload, hypoxemia, and prolonged mechanical ventilation.In traumatic brain injury (TBI), recent randomized controlled trials (RCT) did not demonstrate outcome benefits for early, prophylactic decompressive craniectomy, but indicate a role for secondary decompressive craniectomy in patients with refractory elevated ICP. A recent meta-analysis suggested that when an extraventricular drain is required, insertion 24 h or less post-TBI may result in better outcomes.In large ischemic middle cerebral artery strokes, pooled analyses of three RCTs showed functional outcome benefits in patients less than 60 years who underwent prophylactic DC within less than 48 h. In intracranial hemorrhage, a recent RCT suggested outcome benefits for minimally invasive hematoma evacuation within less than 24 h.

SUMMARY

More data are needed to guide ICP targets, treatment modalities, predictors of herniation, and surgical triggers; clinical decisions should consider individual patient characteristics, and account for risks of medical and surgical treatments.

Beyond the Lungs: Extrapulmonary Effects of Non-Invasive and Invasive Ventilation Strategies

Background/Objectives: Non-invasive respiratory support and invasive mechanical ventilation are critical interventions that can induce significant changes not only in the lungs but also in extra-pulmonary organs, which are often overlooked. Understanding the extra-pulmonary effects of non-invasive respiratory support and invasive mechanical ventilation is crucial since it can help prevent or mitigate complications and improve outcomes. This narrative review explores these consequences in detail and highlights areas that require further research. Main Text: Non-invasive respiratory support and invasive mechanical ventilation can significantly impact various extrapulmonary organs. For instance, some ventilation strategies can affect venous return from the brain, which may lead to neurological sequelae. In the heart, regardless of the chosen ventilation method, increased intrathoracic pressure (ITP) can also reduce venous return to the heart. This reduction in turn can decrease cardiac output, resulting in hypotension and diminished perfusion of vital organs. Conversely, in certain situations, both ventilation strategies may enhance cardiac function by decreasing the work of breathing and lowering oxygen consumption. In the kidneys, these ventilation methods can impair renal perfusion and function through various mechanisms, including hemodynamic changes and the release of stress hormones. Such alterations can lead to acute kidney injury or exacerbate pre-existing renal conditions. Conclusions: This review emphasizes the critical importance of understanding the extensive mechanisms by which non-invasive respiratory support and invasive mechanical ventilation affect extrapulmonary organs, including neurological, cardiovascular, and renal systems. Such knowledge is essential for optimizing patient care and improving outcomes in critical care settings.

Extracorporeal Cardiopulmonary Resuscitation-Where Do We Currently Stand?

Extracorporeal cardiopulmonary resuscitation (eCPR) is a method of acute resuscitation for patients who have suffered a cardiac arrest through the utilization of an extracorporeal membrane oxygenation (ECMO) pump. The use and efficacy of eCPR is an active area of investigation with ongoing clinical investigation across the world. Since its inception, ECMO has been utilized for several conditions, but more recently, its efficacy in maintaining cerebrovascular perfusion in eCPR has generated interest in more widespread utilization, particularly in cases of out-of-hospital cardiac arrest. However, successful implementation of eCPR can be technically challenging and resource intensive and has been countered with ethical challenges beyond the scope of conventional in-hospital ECMO care. The aim of this review is to summarize the status of eCPR in the current era.

Confined spaces in space: Cerebral implications of chronic elevations of inspired carbon dioxide and implications for long-duration space travel

Cerebrovascular regulation is critically dependent upon the arterial partial pressure of carbon dioxide (P aC O 2 ${P_{{\mathrm{aC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ), owing to its effect on cerebral blood flow, tissueP C O 2 ${P_{{\mathrm{C}}{{\mathrm{O}}_{\mathrm{2}}}}}$ , tissue proton concentration, cerebral metabolism and cognitive and neuronal function. In normal environments and in the absence of pathology, at least over acute time frames, hypercapnia is usually managed readily via the respiratory chemoreflex arcs and/or acid-base buffering capacity, such that there is minimal impact on cerebrovascular and neurological function. However, in non-normal environments, such as enclosed spaces, or with pathology, extended exposures to elevations inP aC O 2 ${P_{{\mathrm{aC}}{{\mathrm{O}}_{\mathrm{2}}}}}$ can be detrimental to cerebral health. Given the direct effect of protons on cellular function, even if pH is normalized, it is feasible that higher proton concentrations could still produce detrimental effects. Although it seems that humans can work safely in mildly hypercapnic environments for extended periods, chronic respiratory acidosis can cause bone demineralization, renal calcification, perinatal developmental abnormalities, systemic inflammation and impairments in cognitive function and visuomotor skills and can produce cerebral acidosis, potentially inducing sustained alterations in cerebral function. With the advancement of new initiatives in spaceflight, including proposed long-duration missions to Mars, the study of the effects of chronic inspired CO2 on human health is relevant. In this review, we draw on evidence from preclinical, physiological and clinical research in humans to summarize the cerebral ramifications of prolonged and chronic exposures to elevated partial pressures of inspired CO2 and respiratory acidosis.

Effects of Acute Hypocapnia on Postural Standing Balance Measured by Sharpened Romberg Testing (SRT) in Healthy Subjects

INTRODUCTION

The sharpened Romberg test (SRT) is a physical maneuver that has been used to identify ataxia in individuals in resource-limited settings. Previous research has suggested that performance on balance testing may be affected by hypocapnia. In this study, we sought to determine whether acute hyperventilation-induced hypocapnia affects performance on the SRT at 501 meters above sea level.

METHODS

We recruited 22 healthy subjects. Each subject performed a baseline SRT. Subjects were then asked to hyperventilate to the point of hypocapnia, confirmed by measurement with a capnometer. Subjects were then asked to re-perform SRT. The primary endpoint was time to loss of balance, measured as time-to-stepout.

RESULTS

Time-to-stepout (TTS) on SRT at baseline had a mean ± standard deviation of 101 ± 117 s. In the hypocapnic condition, TTS was reduced to 48 ± 68 s. TTS normalized to 121 ± 132 s after recovery to normal capnic levels. Time-to-stepout was found to be significantly shorter in the hypocapnic measurement compared to the baseline measurement (P = .0128). Statistical analysis was conducted using one-tailed, paired sample T-tests using a P-value of < .05.

CONCLUSIONS

Our study found a statistically and clinically significant reduction in performance on a balance test (SRT) when exposed to acute hyperventilation-induced hypocapnia compared to a eucapnic control. Our results suggest that acute hypocapnia may contribute to neurological dysfunction independently of hypobaric hypoxia.

Association of dynamic changes in arterial partial pressure of carbon dioxide with neurological outcomes in aneurysmal subarachnoid hemorrhage

Background

Cerebral blood flow (CBF) is closely regulated by carbon dioxide (CO2). In patients with aneurysmal subarachnoid hemorrhage (aSAH), abnormal arterial partial pressure of CO2 (PaCO2) might deteriorate brain injuries. Nevertheless, the impact of dynamic PaCO2 fluctuations on neurological outcomes in aSAH patients has not been extensively studied. Our study aimed to investigate the association between dynamic PaCO2 levels and unfavorable neurological outcomes in aSAH patients.

Methods

In this retrospective observational study, we consecutively enrolled 159 aSAH patients from December 2019 to July 2021. Arterial blood gas measurements within 10 days after intensive care unit (ICU) admission for each patient were recorded to calculate the time-weighted average (TWA)-PaCO2, an indicator representing the dynamic changes in PaCO2 levels. For the association between TWA-PaCO2 levels and unfavorable neurological outcomes in aSAH patients, multivariable logistic analysis was used to explore TWA-PaCO2 levels as categorical variables, and restricted cubic spline (RCS) was used to explore TWA-PaCO2 levels as continuous variables.

Results

In multivariable logistic analysis, after adjusting confounders, when TWA-PaCO2 35-45 mmHg was as a reference, TWA-PaCO2 < 35 mmHg (odds ratio [OR] 2.15, 95 % confidence interval [CI] 0.83-5.55, P = 0.113) and TWA-PaCO2 > 45 mmHg (OR 8.31, 95 % CI 0.72-96.14, P = 0.090) were not independently associated with unfavorable neurological outcomes (modified Rankin score of 3-6). The RCS shows a "U" shape curve between TWA-PaCO2 levels and unfavorable neurological outcomes, with a nonlinear P-value of 0.023. The lowest ORs of unfavorable neurological outcomes were within PaCO2 32.8-38.1 mmHg.

Conclusions

Both lower and higher PaCO2 levels are harmful to aSAH patients. PaCO2 in the range of 32.8-38.1 mmHg is associated with lowest unfavorable neurological outcomes.

Prehospital care for traumatic brain injuries: A review of U.S. state emergency medical services protocols

Traumatic brain injury (TBIs) necessitates a rapid and comprehensive medical response to minimize secondary brain injury and reduce mortality. Emergency medical services (EMS) clinicians serve a critical role in the management of prehospital TBI, responding during an initial phase of care with significant impact on patient outcomes. We used versions two and three of the Brain Trauma Foundation (BTF) Prehospital Guidelines for the Management of Traumatic Brain Injury and the NASEMSO National Model Clinical Guidelines to determine key elements for a TBI prehospital protocol and included common factors across sources such as recommendations concerning patient monitoring, hypoxia, hypotension, hyperventilation, cerebral herniation, airway management, hyperosmolar therapy, and transport destination. We then conducted a cross-sectional evaluation of publicly available statewide EMS clinical protocols in the US to determine the degree of alignment with national guidelines. We calculated descriptive statistics for each factor in the state protocols. Despite adoption of some evidence-based recommendations for a standard approach to the prehospital management of patients with TBI, we found significant variability in statewide EMS treatment protocols for management of severe TBI, especially in the recommended frequency of patient reassessment and for the management of suspected herniation. Most statewide protocols provided guidance regarding oxygenation, ventilation, and blood pressure management that aligned with evidence-based guidelines. While most protocols did address management of oxygenation and ventilation, one in four protocols had no specific guidance for managing hypoxia and only 31% of protocols recommended avoiding hyperventilation. For the management of suspected cerebral herniation, over half of statewide protocols recommended hyperventilation, whereas only 31% explicitly advised against hyperventilation regardless of TBI severity. Interestingly, 94% of protocols do not mention the use of hyperosmolar therapy for TBI patients, neither recommending use or avoidance of hyperosmolar therapy. In conclusion, we found inconsistent adoption of national recommendations in available statewide protocols for prehospital TBI management. We identified significant gaps and variation in statewide protocols regarding patient monitoring and reassessment, as well as in several key areas of severe TBI management.

Short-Term Neurologic Complications in Patients Undergoing Extracorporeal Membrane Oxygenation Support: A Review on Pathophysiology, Incidence, Risk Factors, and Outcomes

Regardless of the type, extracorporeal membrane oxygenation (ECMO) requires the use of large intravascular cannulas and results in multiple abnormalities including non-physiologic blood flow, hemodynamic perturbation, rapid changes in blood oxygen and carbon dioxide levels, coagulation abnormalities, and a significant systemic inflammatory response. Among other sequelae, neurologic complications are an important source of mortality and long-term morbidity. The frequency of neurologic complications varies and is likely underreported due to the high mortality rate. Neurologic complications in patients supported by ECMO include ischemic and hemorrhagic stroke, hypoxic brain injury, intracranial hemorrhage, and brain death. In addition to the disease process that necessitates ECMO, cannulation strategies and physiologic disturbances influence neurologic outcomes in this high-risk population. For example, the overall documented rate of neurologic complications in the venovenous ECMO population is lower, but a higher rate of intracranial hemorrhage exists. Meanwhile, in the venoarterial ECMO population, ischemia and global hypoperfusion seem to compose a higher percentage of neurologic complications. In what follows, the literature is reviewed to discuss the pathophysiology, incidence, risk factors, and outcomes related to short-term neurologic complications in patients supported by ECMO.

The effect of CO2 on the age dependence of neurovascular coupling

Prior studies have identified variable effects of aging on neurovascular coupling (NVC). Carbon dioxide (CO2) affects both cerebral blood velocity (CBv) and NVC, but the effects of age on NVC under different CO2 conditions are unknown. Therefore, we investigated the effects of aging on NVC in different CO2 states during cognitive paradigms. Seventy-eight participants (18-78 yr), with well-controlled comorbidities, underwent continuous recordings of CBv by bilateral insonation of middle (MCA) and posterior (PCA) cerebral arteries (transcranial Doppler), blood pressure, end-tidal CO2, and heart rate during poikilocapnia, hypercapnia (5% CO2 inhalation), and hypocapnia (paced hyperventilation). Neuroactivation via visuospatial (VS) and attention tasks (AT) was used to stimulate NVC. Peak percentage and absolute change in MCAv/PCAv, were compared between CO2 conditions and age groups (≤30, 31-60, and >60 yr). For the VS task, in poikilocapnia, younger adults had a lower NVC response compared with older adults [mean difference (MD): -7.92% (standard deviation (SD): 2.37), P = 0.004], but comparable between younger and middle-aged groups. In hypercapnia, both younger [MD: -4.75% (SD: 1.56), P = 0.009] and middle [MD: -4.58% (SD: 1.69), P = 0.023] age groups had lower NVC responses compared with older adults. Finally, in hypocapnia, both older [MD: 5.92% (SD: 2.21), P = 0.025] and middle [MD: 5.44% (SD: 2.27), P = 0.049] age groups had greater NVC responses, compared with younger adults. In conclusion, the magnitude of NVC response suppression from baseline during hyper- and hypocapnia, did not differ significantly between age groups. However, the middle age group demonstrated a different NVC response while under hypercapnic conditions, compared with hypocapnia.NEW & NOTEWORTHY This study describes the effects of age on neurovascular coupling under altered CO2 conditions. We demonstrated that both hypercapnia and hypocapnia suppress neurovascular coupling (NVC) responses. Furthermore, that middle age exhibits an NVC response comparable with younger adults under hypercapnia, and older adults under hypocapnia.

Hypocapnia is associated with increased in-hospital mortality and 1 year mortality in acute heart failure patients

AIMS

Both hypercapnia and hypocapnia are common in patients with acute heart failure (AHF), but the association between partial pressure of arterial carbon dioxide (PaCO2) and AHF prognosis remains unclear. The objective of this study was to investigate the connection between PaCO2 within 24 h after admission to the intensive care unit (ICU) and mortality during hospitalization and at 1 year in AHF patients.

METHODS AND RESULTS

AHF patients were enrolled from the Medical Information Mart for Intensive Care IV database. The patients were divided into three groups by PaCO2 values of <35, 35-45, and >45 mmHg. The primary outcome was to investigate the connection between PaCO2 and in-hospital mortality and 1 year mortality in AHF patients. The secondary outcome was to assess the prediction value of PaCO2 in predicting in-hospital mortality and 1 year mortality in AHF patients. A total of 2374 patients were included in this study, including 457 patients in the PaCO2 < 35 mmHg group, 1072 patients in the PaCO2 = 35-45 mmHg group, and 845 patients in the PaCO2 > 45 mmHg group. The in-hospital mortality was 19.5%, and the 1 year mortality was 23.9% in the PaCO2 < 35 mmHg group. Multivariate logistic regression analysis showed that the PaCO2 < 35 mmHg group was associated with an increased risk of in-hospital mortality [hazard ratio (HR) 1.398, 95% confidence interval (CI) 1.039-1.882, P = 0.027] and 1 year mortality (HR 1.327, 95% CI 1.020-1.728, P = 0.035) than the PaCO2 = 35-45 mmHg group. The PaCO2 > 45 mmHg group was associated with an increased risk of in-hospital mortality (HR 1.387, 95% CI 1.050-1.832, P = 0.021); the 1 year mortality showed no significant difference (HR 1.286, 95% CI 0.995-1.662, P = 0.055) compared with the PaCO2 = 35-45 mmHg group. The Kaplan-Meier survival curves showed that the PaCO2 < 35 mmHg group had a significantly lower 1 year survival rate. The area under the receiver operating characteristic curve for predicting in-hospital mortality was 0.591 (95% CI 0.526-0.656), and the 1 year mortality was 0.566 (95% CI 0.505-0.627) in the PaCO2 < 35 mmHg group.

CONCLUSIONS

In AHF patients, hypocapnia within 24 h after admission to the ICU was associated with increased in-hospital mortality and 1 year mortality. However, the increase in 1 year mortality may be influenced by hospitalization mortality. Hypercapnia was associated with increased in-hospital mortality.

Association of Pediatric Postcardiac Arrest Ventilation and Oxygenation with Survival Outcomes

Rationale: Adult and pediatric studies provide conflicting data regarding whether post-cardiac arrest hypoxemia, hyperoxemia, hypercapnia, and/or hypocapnia are associated with worse outcomes. Objectives: We sought to determine whether postarrest hypoxemia or postarrest hyperoxemia is associated with lower rates of survival to hospital discharge, compared with postarrest normoxemia, and whether postarrest hypocapnia or hypercapnia is associated with lower rates of survival, compared with postarrest normocapnia. Methods: An embedded prospective observational study during a multicenter interventional cardiopulmonary resuscitation trial was conducted from 2016 to 2021. Patients ⩽18 years old and with a corrected gestational age of ≥37 weeks who received chest compressions for cardiac arrest in one of the 18 intensive care units were included. Exposures during the first 24 hours postarrest were hypoxemia, hyperoxemia, or normoxemia-defined as lowest arterial oxygen tension/pressure (PaO2) <60 mm Hg, highest PaO2 ⩾200 mm Hg, or every PaO2 60-199 mm Hg, respectively-and hypocapnia, hypercapnia, or normocapnia, defined as lowest arterial carbon dioxide tension/pressure (PaCO2) <30 mm Hg, highest PaCO2 ⩾50 mm Hg, or every PaCO2 30-49 mm Hg, respectively. Associations of oxygenation and carbon dioxide group with survival to hospital discharge were assessed using Poisson regression with robust error estimates. Results: The hypoxemia group was less likely to survive to hospital discharge, compared with the normoxemia group (adjusted relative risk [aRR] = 0.71; 95% confidence interval [CI] =  0.58-0.87), whereas survival in the hyperoxemia group did not differ from that in the normoxemia group (aRR = 1.0; 95% CI = 0.87-1.15). The hypercapnia group was less likely to survive to hospital discharge, compared with the normocapnia group (aRR = 0.74; 95% CI = 0.64-0.84), whereas survival in the hypocapnia group did not differ from that in the normocapnia group (aRR = 0.91; 95% CI = 0.74-1.12). Conclusions: Postarrest hypoxemia and hypercapnia were each associated with lower rates of survival to hospital discharge.

Perioperative management of adults with traumatic brain injury

Despite advances in management strategy, traumatic brain injury remains strongly associated with neurological impairment and mortality. Management of traumatic brain injury requires careful and targeted management of the physiological consequences which extend beyond the scope of the primary impact to the cranium. Here, we present a review of the principles of its acute management in adults. We outline the procedure which patients are assessed and the critical physiological variables which must be monitored to prevent further neurological damage. We describe current interventional strategies from the context of the underlying physiological mechanisms and recent clinical data and identify persisting challenges in traumatic brain injury management and potential avenues of future progress.

High ventilation breathwork practices: An overview of their effects, mechanisms, and considerations for clinical applications

High Ventilation Breathwork (HVB) refers to practices employing specific volitional manipulation of breathing, with a long history of use to relieve various forms of psychological distress. This paper seeks to offer a consolidative insight into potential clinical application of HVB as a treatment of psychiatric disorders. We thus review the characteristic phenomenological and neurophysiological effects of these practices to inform their mechanism of therapeutic action, safety profiles and future clinical applications. Clinical observations and data from neurophysiological studies indicate that HVB is associated with extraordinary changes in subjective experience, as well as with profound effects on central and autonomic nervous systems functions through modulation of neurometabolic parameters and interoceptive sensory systems. This growing evidence base may guide how the phenomenological effects of HVB can be understood, and potentially harnessed in the context of such volitional perturbation of psychophysiological state. Reports of putative beneficial effects for trauma-related, affective, and somatic disorders invite further research to obtain detailed mechanistic knowledge, and rigorous clinical testing of these potential therapeutic uses.

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.

Recent Advancements and Strategies for Overcoming the Blood-Brain Barrier Using Albumin-Based Drug Delivery Systems to Treat Brain Cancer, with a Focus on Glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive malignant tumor, and the most prevalent primary malignant tumor affecting the brain and central nervous system. Recent research indicates that the genetic profile of GBM makes it resistant to drugs and radiation. However, the main obstacle in treating GBM is transporting drugs through the blood-brain barrier (BBB). Albumin is a versatile biomaterial for the synthesis of nanoparticles. The efficiency of albumin-based delivery systems is determined by their ability to improve tumor targeting and accumulation. In this review, we will discuss the prevalence of human glioblastoma and the currently adopted treatment, as well as the structure and some essential functions of the BBB, to transport drugs through this barrier. We will also mention some aspects related to the blood-tumor brain barrier (BTBB) that lead to poor treatment efficacy. The properties and structure of serum albumin were highlighted, such as its role in targeting brain tumors, as well as the progress made until now regarding the techniques for obtaining albumin nanoparticles and their functionalization, in order to overcome the BBB and treat cancer, especially human glioblastoma. The albumin drug delivery nanosystems mentioned in this paper have improved properties and can overcome the BBB to target brain tumors.

Transcranial, Non-Invasive Evaluation of Potential Misery Perfusion During Hyperventilation Therapy of Traumatic Brain Injury Patients

Hyperventilation (HV) therapy uses vasoconstriction to reduce intracranial pressure (ICP) by reducing cerebral blood volume. However, as HV also lowers cerebral blood flow (CBF), it may provoke misery perfusion (MP), in which the decrease in CBF is coupled with increased oxygen extraction fraction (OEF). MP may rapidly lead to the exhaustion of brain energy metabolites, making the brain vulnerable to ischemia. MP is difficult to detect at the bedside, which is where transcranial hybrid, near-infrared spectroscopies are promising because they non-invasively measure OEF and CBF. We have tested this technology during HV (∼30 min) with bilateral, frontal lobe monitoring to assess MP in 27 sessions in 18 patients with traumatic brain injury. In this study, HV did not lead to MP at a group level (p > 0.05). However, a statistical approach yielded 89 events with a high probability of MP in 19 sessions. We have characterized each statistically significant event in detail and its possible relationship to clinical and radiological status (decompressive craniectomy and presence of a cerebral lesion), without detecting any statistically significant difference (p > 0.05). However, MP detection stresses the need for personalized, real-time assessment in future clinical trials with HV, in order to provide an optimal evaluation of the risk-benefit balance of HV. Our study provides pilot data demonstrating that bedside transcranial hybrid near-infrared spectroscopies could be utilized to assess potential MP.

Ventilation Targets for Patients Undergoing Mechanical Thrombectomy for Acute Ischemic Stroke: A Systematic Review

Mechanical thrombectomy (MT) has become a standard treatment for acute ischemic stroke (AIS) caused by large vessel occlusion (LVO). Recent evidence suggests that general anesthesia (GA) and mechanical ventilation do not lead to inferior neurologic outcomes if compared to non-GA. However, the guidelines lack specific recommendations for ventilation targets during MT under GA. This systematic review aims to identify ventilation strategies correlating with better neurological outcomes in AIS patients undergoing MT, particularly focusing on oxygenation and carbon dioxide (CO2) targets. A systematic search of multiple databases was conducted to identify human studies reporting the correlation between ventilation strategies and neurological outcomes in MT for AIS. Eligible studies included clinical trials, observational studies, and case-control studies. Out of 157 studies assessed, 11 met the inclusion criteria. Five studies investigated oxygenation targets, while six studies explored CO2 targets. The published studies highlighted the controversial role of supplemental normobaric oxygen therapy and its potential association with worse outcomes. Regarding CO2 targets, the studies identified a potential association between end tidal CO2 levels and functional outcomes, with hypocapnia being unfavorable. This systematic review demonstrates that the current available evidence still lacks strength to suggest specific ventilation targets, but it highlights the potential risks of hyperoxia and hypocapnia in this specific cohort of patients.

Early Changes in Arterial Partial Pressure of Carbon Dioxide and Blood Pressure After Starting Extracorporeal Membrane Oxygenation in Children: Extracorporeal Life Support Organization Database Study of Neurologic Complications

OBJECTIVE

Neurologic complications in pediatric patients supported by extracorporeal membrane oxygenation (ECMO) are common and lead to morbidity and mortality; however, few modifiable factors are known.

DESIGN

Retrospective study of the Extracorporeal Life Support Organization registry (2010-2019).

SETTING

Multicenter international database.

PATIENTS

Pediatric patients receiving ECMO (2010-2019) for all indications and any mode of support.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We investigated if early relative change in Pa co2 or mean arterial blood pressure (MAP) soon after starting ECMO was associated with neurologic complications. The primary outcome of neurologic complications was defined as a report of seizures, central nervous system infarction or hemorrhage, or brain death. All-cause mortality (including brain death) was used as a secondary outcome.Out of 7,270 patients, 15.6% had neurologic complications. Neurologic complications increased when the relative Pa co2 decreased by greater than 50% (18.4%) or 30-50% (16.5%) versus those who had a minimal change (13.9%, p < 0.01 and p = 0.046). When the relative MAP increased greater than 50%, the rate of neurologic complications was 16.9% versus 13.1% those with minimal change ( p = 0.007). In a multivariable model adjusting for confounders, a relative decrease in Pa co2 greater than 30% was independently associated with greater odds of neurologic complication (odds ratio [OR], 1.25; 95% CI, 1.07-1.46; p = 0.005). Within this group, with a relative decrease in Pa co2 greater than 30%, the effects of increased relative MAP increased neurologic complications (0.05% per BP Percentile; 95% CI, 0.001-0.11; p = 0.05).

CONCLUSIONS

In pediatric patients, a large decrease in Pa co2 and increase in MAP following ECMO initiation are both associated with neurologic complications. Future research focusing on managing these issues carefully soon after ECMO deployment can potentially help to reduce neurologic complications.

Initial Diagnosis and Management of Acutely Elevated Intracranial Pressure

Acutely elevated intracranial pressure (ICP) may have devastating effects on patient mortality and neurologic outcomes, yet its initial detection remains difficult because of the variety of manifestations that it can cause disease states it is associated with. Several treatment guidelines exist for specific disease processes such as trauma or ischemic stroke, but their recommendations may not apply to other causes. In the acute setting, management decisions must often be made before the underlying cause is known. In this review, we present an organized, evidence-based approach to the recognition and management of patients with suspected or confirmed elevated ICP in the first minutes to hours of resuscitation. We explore the utility of invasive and noninvasive methods of diagnosis, including history, physical examination, imaging, and ICP monitors. We synthesize various guidelines and expert recommendations and identify core management principles including noninvasive maneuvers, neuroprotective intubation and ventilation strategies, and pharmacologic therapies such as ketamine, lidocaine, corticosteroids, and the hyperosmolar agents mannitol and hypertonic saline. Although an in-depth discussion of the definitive management of each etiology is beyond the scope of this review, our goal is to provide an empirical approach to these time-sensitive, critical presentations in their initial stages.

Association between the time-varying arterial carbon dioxide pressure and 28-day mortality in mechanically ventilated patients with acute respiratory distress syndrome

BACKGROUND

Recent studies have shown an association between baseline arterial carbon dioxide pressure (PaCO₂) and outcomes in patients with acute respiratory distress syndrome (ARDS). However, PaCO₂ probably varies throughout the disease, and few studies have assessed the effect of longitudinal PaCO₂ on prognosis. We thus aimed to investigate the association between time-varying PaCO₂ and 28-day mortality in mechanically ventilated ARDS patients.

METHODS

In this retrospective study, we included all adult (≥ 18 years) patients diagnosed with ARDS who received mechanical ventilation for at least 24 h at a tertiary teaching hospital between January 2014 and March 2021. Patients were excluded if they received extracorporeal membrane oxygenation (ECMO). Demographic data, respiratory variables, and daily PaCO₂ were extracted. The primary outcome was 28-day mortality. Time-varying Cox models were used to estimate the association between longitudinal PaCO₂ measurements and 28-day mortality.

RESULTS

A total of 709 patients were eligible for inclusion in the final cohort, with an average age of 65 years, of whom 70.7% were male, and the overall 28-day mortality was 35.5%. After adjustment for baseline confounders, including age and severity of disease, a significant increase in the hazard of death was found to be associated with both time-varying PaCO₂ (HR 1.07, 95% CI 1.03-1.11, p<0.001) and the time-varying coefficient of variation for PaCO₂ (HR 1.24 per 10% increase, 95% CI 1.10-1.40, p<0.001) during the first five days of invasive mechanical ventilation. The cumulative proportion of exposure to normal PaCO₂ (HR 0.72 per 10% increase, 95% CI 0.58-0.89, p = 0.002) was associated with 28-day mortality.

CONCLUSION

PaCO₂ should be closely monitored in mechanically ventilated ARDS patients. The association between PaCO₂ and 28-day mortality persisted over time. Increased cumulative exposure to normal PaCO₂ was associated with a decreased risk of death.

Traumatic Brain Injury: Intraoperative Management and Intensive Care Unit Multimodality Monitoring

Traumatic brain injury is a devastating event associated with substantial morbidity. Pathophysiology involves the initial trauma, subsequent inflammatory response, and secondary insults, which worsen brain injury severity. Management entails cardiopulmonary stabilization and diagnostic imaging with targeted interventions, such as decompressive hemicraniectomy, intracranial monitors or drains, and pharmacological agents to reduce intracranial pressure. Anesthesia and intensive care requires control of multiple physiologic variables and evidence-based practices to reduce secondary brain injury. Advances in biomedical engineering have enhanced assessments of cerebral oxygenation, pressure, metabolism, blood flow, and autoregulation. Many centers employ multimodality neuromonitoring for targeted therapies with the hope to improve recovery.

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.

Efficacy and safety of remifentanil dose titration to correct the spontaneous hyperventilation in aneurysmal subarachnoid haemorrhage: protocol and statistical analysis for a prospective physiological study

INTRODUCTION

Spontaneous hyperventilation (SHV) is common in aneurysmal subarachnoid haemorrhage (aSAH). The reduction in arterial partial pressure of carbon dioxide (PaCO₂) may change the brain physiology, such as haemodynamics, oxygenation, metabolism and may lead to secondary brain injury. However, how to correct SHV safely and effectively in patients with aSAH has not been well investigated. The aim of this study is to investigate the efficacy and safety of remifentanil dose titration to correct hyperventilation in aSAH, as well as the effect of changes in PaCO₂ on cerebral blood flow (CBF).

METHODS AND ANALYSIS

This study is a prospective, single-centre, physiological study in patients with aSAH. The patients who were mechanically ventilated and who meet with SHV (tachypnoea combined with PaCO₂ <35 mm Hg and pH >7.45) will be enrolled. The remifentanil will be titrated to correct the SHV. The predetermined initial dose of remifentanil is 0.02 μg/kg/min and will be maintained for 30 min, and PaCO₂ and CBF will be measured. After that, the dose of remifentanil will be sequentially increased to 0.04, 0.06, and 0.08 μg/kg/min, and the measurements for PaCO₂ and CBF will be repeated 30 min after each dose adjustment and will be compared with their baseline values.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board of Beijing Tiantan Hospital, Capital Medical University (KY 2021-006-02) and has been registered at ClinicalTrials.gov. The results of this study will be disseminated through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

NCT04940273.

Spontaneous Hyperventilation Is Common in Patients with Spontaneous Cerebellar Hemorrhage, and Its Severity Is Associated with Outcome

BACKGROUND

The spontaneous hyperventilation (SHV) accompanying spontaneous cerebellar hemorrhage has yet to attract a sufficient amount of attention. This study aimed to analyze the incidence of SHV in spontaneous cerebellar hemorrhage patients and its risk factors as well as its association with the outcome.

METHODS

We retrospectively reviewed the medical records of all spontaneous cerebellar hemorrhage patients who underwent surgical treatment at Tongji Hospital from July 2018 to December 2020. Arterial blood gas (ABG) test results and clinical characteristics, including demographics, comorbidities, imaging features, laboratory tests, and therapy choices, were collected. The Glasgow Outcome Scale was used to assess the outcome at two weeks and six months after admission.

RESULTS

A total of 147 patients were included, and of these patients 44.9% had spontaneous hyperventilation. Hypertension (OR, 3.175; CI, 1.332-7.569), usage of sedation drugs (OR, 3.693; CI, 1.0563-8.724), and hypernatremia (OR, 2.803; CI, 1.070-7.340) seemed to positively correlate to SHV occurrence. Hematoma removal had an inverse association with SHV (OR, 0.176; CI, 0.068-0.460). Patients with poor and good outcomes had significant differences in pH, PaCO2, and HCO3- values, and the severity of SHV was associated with the PaCO2 level.

CONCLUSIONS

Spontaneous hyperventilation is common in patients with spontaneous cerebellar hemorrhage, and its severity is associated with the outcome.

Spreading Depolarization as a Therapeutic Target in Severe Ischemic Stroke: Physiological and Pharmacological Strategies

BACKGROUND

Spreading depolarization (SD) occurs nearly ubiquitously in malignant hemispheric stroke (MHS) and is strongly implicated in edema progression and lesion expansion. Due to this high burden of SD after infarct, it is of great interest whether SD in MHS patients can be mitigated by physiologic or pharmacologic means and whether this intervention improves clinical outcomes. Here we describe the association between physiological variables and risk of SD in MHS patients who had undergone decompressive craniectomy and present an initial case of using ketamine to target SD in MHS.

METHODS

We recorded SD using subdural electrodes and time-linked with continuous physiological recordings in five subjects. We assessed physiologic variables in time bins preceding SD compared to those with no SD.

RESULTS

Using multivariable logistic regression, we found that increased ETCO2 (OR 0.772, 95% CI 0.655-0.910) and DBP (OR 0.958, 95% CI 0.941-0.991) were protective against SD, while elevated temperature (OR 2.048, 95% CI 1.442-2.909) and WBC (OR 1.113, 95% CI 1.081-1.922) were associated with increased risk of SD. In a subject with recurrent SD, ketamine at a dose of 2 mg/kg/h was found to completely inhibit SD.

CONCLUSION

Fluctuations in physiological variables can be associated with risk of SD after MHS. Ketamine was also found to completely inhibit SD in one subject. These data suggest that use of physiological optimization strategies and/or pharmacologic therapy could inhibit SD in MHS patients, and thereby limit edema and infarct progression. Clinical trials using individualized approaches to target this novel mechanism are warranted.

Differential regional cerebrovascular reactivity to end-tidal gas combinations commonly seen during anaesthesia: A blood oxygenation level-dependent MRI observational study in awake adult subjects

BACKGROUND

Regional cerebrovascular reactivity (rCVR) is highly variable in the human brain as measured by blood oxygenation level-dependent (BOLD) MRI to changes in both end-tidal CO 2 and O 2 .

OBJECTIVES

We examined awake participants under carefully controlled end-tidal gas concentrations to assess how regional CVR changes may present with end-tidal gas changes seen commonly with anaesthesia.

DESIGN

Observational study.

SETTING

Tertiary care centre, Winnipeg, Canada. The imaging for the study occurred in 2019.

SUBJECTS

Twelve healthy adult subjects.

INTERVENTIONS

Cerebral BOLD response was studied under two end-tidal gas paradigms. First end-tidal oxygen (ETO 2 ) maintained stable whereas ETCO 2 increased incrementally from hypocapnia to hypercapnia (CO 2 ramp); second ETCO 2 maintained stable whereas ETO 2 increased from normoxia to hyperoxia (O 2 ramp). BOLD images were modeled with end-tidal gas sequences split into two equal segments to examine regional CVR.

MAIN OUTCOME MEASURES

The voxel distribution comparing hypocapnia to mild hypercapnia and mild hyperoxia (mean F I O 2  = 0.3) to marked hyperoxia (mean F I O 2  = 0.7) were compared in a paired fashion ( P  < 0.005 to reach threshold for voxel display). Additionally, type analysis was conducted on CO 2 ramp data. This stratifies the BOLD response to the CO 2 ramp into four categories of CVR slope based on segmentation (type A; +/+slope: normal response, type B +/-, type C -/-: intracranial steal, type D -/+.) Types B to D represent altered responses to the CO 2 stimulus.

RESULTS

Differential regional responsiveness was seen for both end-tidal gases. Hypocapnic regional CVR was more marked than hypercapnic CVR in 0.3% of voxels examined ( P  < 0.005, paired comparison); the converse occurred in 2.3% of voxels. For O 2 , mild hyperoxia had more marked CVR in 0.2% of voxels compared with greater hyperoxia; the converse occurred in 0.5% of voxels. All subjects had altered regional CO 2 response based on Type Analysis ranging from 4 ± 2 to 7 ± 3% of voxels.

CONCLUSION

In awake subjects, regional differences and abnormalities in CVR were observed with changes in end-tidal gases common during the conduct of anaesthesia. On the basis of these findings, consideration could be given to minimising regional CVR fluctuations in patients-at-risk of neurological complications by tighter control of end-tidal gases near the individual's resting values.

Association Between Partial Pressure of Carbon Dioxide and Immediate Seizures in Patients With Primary Intracerebral Hemorrhage: A Propensity-Matched Analysis

Purpose

To explore the value of partial pressure of carbon dioxide (PaCO₂) levels in arterial blood for predicting immediate seizures (ISs) in patients with primary intracerebral hemorrhage (ICH).

Methods

Demographic information and clinical data from patients with primary ICH were prospectively collected, including arterial blood gas analysis. Immediate seizures (ISs) were determined as seizures in the first 24 h after admission. Univariate and multivariate analyses were performed to assess the association of PaCO₂ levels with ISs. Propensity-score matching (PSM) analyses were adopted to reduce the baseline difference between ISs and non-ISs groups.

Results

A total of 596 patients with primary ICH were initially screened in this clinical study, 368 of whom fulfilled all the inclusion criteria [mean age, (60.46 ±12.78) years; 57.9% female patients]. ISs occurred in 30 of the 368 (8.15%) patients with primary ICH of this cohort. Patients with ISs had significantly lower PaCO₂ levels [34.35(32.38–37.53) vs. 39.45(35.90–43.43), mmHg, p < 0.001] and were younger than those without ISs [(54.57±12.15 vs. 60.99 ±12.72) years, p = 0.008]. Multivariate analysis showed that lower initial PaCO₂ (≤37.2 mmHg) level was a significant independent predictor of ISs [odds ratios (OR) 0.141, 95% confidence interval (CI) 0.057–0.351, p < 0.001], as well as younger age (OR 0.961, 95% CI 0.928–0.995, p = 0.023) and hematoma expansion (OR 0.340, 95% CI 0.134–0.863, p = 0.023). Receiver operating characteristic curve (ROC) analysis demonstrated that the optimal cutoff value of PaCO₂ level for predicting ISs was 37.20 mmHg in patients with primary ICH (the area under the curve (AUC) was 0.760 with a corresponding sensitivity of 76.67% and specificity of 67.46%, 95%CI = 0.713–0.802, p < 0.001). After PSM, the matched ISs group had significantly lower PaCO₂ levels compared with the matched non-ISs group [34.45(32.43–38.18) vs. 41.75(35.85–43.98) mmHg, p < 0.05] in the univariate analysis. The lower initial PaCO₂ level was still independent of ISs following primary ICH.

Conclusions

The lower initial PaCO₂ level was associated with an increased risk of ISs in patients with primary ICH.

The role of tranexamic acid in traumatic brain injury

Evidence from recent trials evaluating efficacy of antifibrinolytic agents in the context of traumatic brain injury may lead to changes in the management of patients with traumatic brain injury. Tranexamic acid (TXA) reduces the proteolytic action of plasmin on fibrin clots, resulting in an inhibition of fibrinolysis and stabilisation of established blood clots. There has been significant interest in use of the drug as a therapeutic agent in the context of severe haemorrhage; however, considerable controversies regarding its efficacy remain. A number of trials have demonstrated a small but significant decrease in mortality following its administration, but the results have been somewhat inconsistent and may not be generalisable. The results of the CRASH-3 trial were that there was no statistical difference in the number of traumatic brain injury related deaths (18.5% with TXA and 19.8% with placebo; relative risk [RR] 0·94; 95% confidence interval [CI] 0·86-1·02). Nonetheless, there was a subgroup of patients for whom TXA appeared to provide benefit, and this was in patients with mild and moderate injury (with a Glasgow Coma Score > 8). This is potentially a very important finding that may have huge potential implications; however, we believe it does not currently provide indisputable evidence to support the administration of TXA to all patients with TBI. Further work is required to better define the subset of patients who may benefit as well as to evaluate the long-term functional benefit in order to determine which types of severe traumatic brain injury patients would derive more benefits than harms from TXA.

Hypercapnia from Physiology to Practice

Acute hypercapnic ventilatory failure is becoming more frequent in critically ill patients. Hypercapnia is the elevation in the partial pressure of carbon dioxide (PaCO₂) above 45 mmHg in the bloodstream. The pathophysiological mechanisms of hypercapnia include the decrease in minute volume, an increase in dead space, or an increase in carbon dioxide (CO₂) production per sec. They generate a compromise at the cardiovascular, cerebral, metabolic, and respiratory levels with a high burden of morbidity and mortality. It is essential to know the triggers to provide therapy directed at the primary cause and avoid possible complications.

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.

Stroke and breathing

Stroke remains a leading cause of neurologic disability with wide ranging effects, including a variety of respiratory abnormalities. Stroke may influence the central control of the respiratory drive and breathing pattern, airway protection and maintenance, and the respiratory mechanics of inspiration and expiration. In the acute phase of stroke, the central control of breathing is affected by changes in consciousness, cerebral edema, and direct damage to brainstem respiratory centers, resulting in abnormalities in respiratory pattern and loss of airway protection. Common acute complications related to respiratory dysfunction include dysphagia, aspiration, and pneumonia. Respiratory control centers are located in the brainstem, and brainstem stroke causes specific patterns of respiratory dysfunction. Depending on the exact location and extent of stroke, respiratory failure may occur. While major respiratory abnormalities often improve over time, sleep-disordered breathing remains common in the subacute and chronic phases and worsens outcomes. Respiratory mechanics are impaired in hemiplegic or hemiparetic stroke, contributing to worse cardiopulmonary health in stroke survivors. Interventions to address the respiratory complications are under researched, and further investigation in this area is critical to improving outcomes among stroke survivors.

Neurocritical care management of poor-grade subarachnoid hemorrhage: Unjustified nihilism to reasonable optimism

BACKGROUND AND PURPOSE

Historically, overall outcomes for patients with high-grade subarachnoid hemorrhage (SAH) have been poor. Generally, between physicians, either reluctance to treat, or selectivity in treating such patients has been the paradigm. Recent studies have shown that early and aggressive care leads to significant improvement in survival rates and favorable outcomes of grade V SAH patients. With advancements in both neurocritical care and end-of-life care, non-treatment or selective treatment of grade V SAH patients is rarely justified. Current paradigm shifts towards early and aggressive care in such cases may lead to improved outcomes for many more patients.

MATERIALS AND METHODS

We performed a detailed review of the current literature regarding neurointensive management strategies in high-grade SAH, discussing multiple aspects. We discussed the neurointensive care management protocols for grade V SAH patients.

RESULTS

Acutely, intracranial pressure control is of utmost importance with external ventricular drain placement, sedation, optimization of cerebral perfusion pressure, osmotherapy and hyperventilation, as well as cardiopulmonary support through management of hypotension and hypertension.

CONCLUSIONS

Advancements of care in SAH patients make it unethical to deny treatment to poor Hunt and Hess grade patients. Early and aggressive treatment results in a significant improvement in survival rate and favorable outcome in such patients.

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.

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.

Timing, Outcome, and Risk Factors of Intracranial Hemorrhage in Acute Respiratory Distress Syndrome Patients During Venovenous Extracorporeal Membrane Oxygenation

OBJECTIVES

Intracranial hemorrhage is a serious complication in patients receiving venovenous extracorporeal membrane oxygenation during treatment of the acute respiratory distress syndrome. We analyzed timing, outcome, and risk factors of intracranial hemorrhage in patients on venovenous extracorporeal membrane oxygenation.

DESIGN

Retrospective cohort study.

SETTING

Single acute respiratory distress syndrome referral center.

PATIENTS

Patients receiving venovenous extracorporeal membrane oxygenation were identified from a cohort of 1,044 patients with acute respiratory distress syndrome. Patients developing an intracranial hemorrhage during venovenous extracorporeal membrane oxygenation therapy were compared with patients without evidence for intracranial hemorrhage. The primary objective was to assess the association of intracranial hemorrhage with 60-day mortality. Further objectives included the identification of risk factors for intracranial hemorrhage and the evaluation of clinical cutoff values.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Among 444 patients treated with venovenous extracorporeal membrane oxygenation, 49 patients (11.0% [95% CI, 8.3-14.4%]) developed an intracranial hemorrhage. The median time to intracranial hemorrhage occurrence was 4 days (95% CI, 2-7 d). Patients who developed an intracranial hemorrhage had a higher 60-day mortality compared with patients without intracranial hemorrhage (69.4% [54.4-81.3%] vs 44.6% [39.6-49.6%]; odds ratio 3.05 [95% CI, 1.54-6.32%]; p = 0.001). A low platelet count, a high positive end expiratory pressure, and a major initial decrease of Paco2 were identified as independent risk factors for the occurrence of intracranial hemorrhage. A platelet count greater than 100/nL and a positive end expiratory pressure less than or equal to 14 cm H2O during the first 7 days of venovenous extracorporeal membrane oxygenation therapy as well as a decrease of Paco2 less than 24 mm Hg during venovenous extracorporeal membrane oxygenation initiation were identified as clinical cutoff values to prevent intracranial hemorrhage (sensitivity 91% [95% CI, 82-99%], 94% [85-99%], and 67% [48-81%], respectively).

CONCLUSIONS

Intracranial hemorrhage occurs early during venovenous extracorporeal membrane oxygenation and is a determinant for 60-day mortality. Appropriate adjustment of identified modifiable risk factors might lower the prevalence of intracranial hemorrhage during venovenous extracorporeal membrane oxygenation therapy.

Acute hyperventilation increases oxygen consumption and decreases peripheral tissue perfusion in critically ill patients

PURPOSE

This study aimed to evaluate the effects of acute hyperventilation on central venous-to-arterial carbon dioxide tension difference (Pv-aCO₂), central venous oxygen saturation (ScvO₂), central venous-to-arterial CO₂ difference/arterial-central venous O₂ difference ratio (CO₂GAP-Ratio), and peripheral perfusion index (PI) in hemodynamically stable critically ill patients.

METHODS

Fifty-four mechanically ventilated patients were evaluated. The cardiac index, Pv-aCO₂, ScvO₂, CO₂GAP-Ratio, PI, and arterial and venous blood gas parameters were measured in the first set of measurements. Then, alveolar ventilation was increased by raising the respiratory rate (10 breaths/min). After a 30 min hyperventilation period, the second set of measurements was recorded.

RESULTS

Acute hyperventilation induces an increase in Pv-aCO₂ (from 3.87 ± 1.31 to 8.44 ± 1.81 mmHg, P < 0.001) and a decrease in ScvO₂(from 71.78 ± 4.82 to 66.47 ± 5.74%, P < 0.001). The CO₂GAP-Ratio was significantly increased(from 0.97 ± 0.40 to 1.74 ± 0.46, P < 0.001), and the PI showed a remarkable decrease caused by acute hyperventilation(from 1.82 ± 1.14 to 1.40 ± 0.99，P = 0.04). Hyperventilation-induced ∆_Pv-aCO₂ was negatively correlated with ∆PaCO₂(r = -0.572, P<0.001). The change in ∆_PaCO₂ was correlated with ∆_ScvO₂(r = 0.450, P<0.001). However, the left ventricular outflow tract velocity time integral (LVOT-VTI) remained unchanged during hyperventilation.

CONCLUSIONS

Acute hyperventilation induced an increase in oxygen consumption and decreased peripheral tissue perfusion in patients. For critical care patients, it is necessary to pay attention to the influence of hyperventilation on peripheral tissue perfusion indices and oxygen consumption indices.

Interleukin-6 Inhibition Reduces Neuronal Injury In A Murine Model of Ventilator-Induced Lung Injury

Mechanical ventilation is a known risk factor for delirium, a cognitive impairment characterized by frontal cortex and hippocampal dysfunction. Although interleukin-6 (IL-6) is upregulated in mechanical ventilation-induced lung injury (VILI) and may contribute to delirium, it is not known whether inhibition of systemic IL-6 mitigates delirium-relevant neuropathology. To histologically define neuropathological effects of IL-6 inhibition in an experimental VILI model. VILI was simulated in anesthetized adult mice using a 35cc/kg tidal volume mechanical ventilation model. There were two controls groups: 1) spontaneously breathing, or 2) anesthetized and mechanically ventilated with 10cc/kg tidal volume to distinguish effects of anesthesia from VILI. Two hours prior to inducing VILI, mice were treated with either anti-IL-6 antibody, anti-IL-6 receptor antibody, or saline. Neuronal injury, stress, and inflammation were assessed using immunohistochemistry. Cleaved caspase-3 (CC3), a neuronal apoptosis marker, was significantly increased in the frontal (p<0.001) and hippocampal (p<0.0001) brain regions and accompanied by significant increases in c-Fos and heat shock protein-90 in the frontal cortices of VILI mice compared to controls (p<0.001). These findings were not related to cerebral hypoxia and there was no evidence of irreversible neuronal death. Frontal and hippocampal neuronal CC3 were significantly reduced with anti-IL-6 antibody (p<0.01 and p<0.0001, respectively), anti-IL-6 receptor antibody (p<0.05 and p<0.0001, respectively) compared to saline VILI mice. VILI induces potentially reversible neuronal injury and inflammation in the frontal cortex and hippocampus, which is mitigated with IL-6 inhibition. These data suggest a potentially novel neuroprotective role of systemic IL-6 inhibition that justifies further investigation.

Effects on cerebral blood flow of position changes, hyperoxia, CO2 partial pressure variations and the Valsalva manoeuvre: A study in healthy volunteers

BACKGROUND

Maintaining adequate blood pressure to ensure proper cerebral blood flow (CBF) during surgery is challenging. Induced mild hypotension, sitting position or unavoidable intra-operative circumstances such as haemorrhage, added to variations in carbon dioxide and oxygen tensions, may influence perfusion. Several of these circumstances may coincide and it is unclear how these may affect CBF.

OBJECTIVE

To describe the variation in transcranial Doppler and regional cerebral oxygen saturation (rSO2), as a surrogate of CBF, after cardiac preload and gravitational positional changes.

DESIGN

Observational study.

SETTING

Operating room at Hospital Clínic de Barcelona.

VOLUNTEERS

Ten healthy volunteers, white, both sexes.

INTERVENTIONS

Measurements were performed in the supine, sitting and standing positions during hyperoxia, hypocapnia and hypercapnia protocols and after a Valsalva manoeuvre.

MAIN OUTCOME MEASURES

Cardiac index (CI), haemodynamic and respiratory variables, maximal and mean velocities (Vmax, Vmean) (transcranial Doppler) and rSO2 were acquired. Results were analysed using a generalised estimating equation technique.

RESULTS

CI increases more than 16% after a preload challenge were not accompanied by differences in rSO2 or Vmax - Vmean. With positional changes, Vmean decreased more than 7% (P = 0.042) from the supine to the seated position. Hyperoxia induced a cerebral rSO2 increase more than 6% (P = 0.0001) with decreases in Vmax, Vmean and CI values more than 3% (P = 0.001, 0.022 and 0.001) in the supine and standing position. During hypocapnia, CI rose more than 20% from supine to seated and standing (P = 0.0001) with a 4.5% decrease in cerebral rSO2 (P = 0.001) and a decrease of Vmax - Vmean more than 24% in all positions (P = 0.001). Hypercapnia increased cerebral rSO2 more than 17% (P = 0.001), Vmax - Vmean more than 30% (P = 0.001) with no changes in CI. After a Valsalva manoeuvre, rSO2 decreased more than 3% in the right hemisphere in the upright position (P = 0.001). Vmax - Vmean decreased more than 10% (P = 0.001) with no changes in CI.

CONCLUSION

CBF changes in response to cerebral vasoconstriction and vasodilatation were detected with rSO2 and transcranial Doppler in healthy volunteers during cardiac preload and in different body positions. Acute hypercapnia had a greater effect on recorded brain parameters than hypocapnia.

Perioperative Neurological Evaluation and Management to Lower the Risk of Acute Stroke in Patients Undergoing Noncardiac, Nonneurological Surgery: A Scientific Statement From the American Heart Association/American Stroke Association

Perioperative stroke is a potentially devastating complication in patients undergoing noncardiac, nonneurological surgery. This scientific statement summarizes established risk factors for perioperative stroke, preoperative and intraoperative strategies to mitigate the risk of stroke, suggestions for postoperative assessments, and treatment approaches for minimizing permanent neurological dysfunction in patients who experience a perioperative stroke. The first section focuses on preoperative optimization, including the role of preoperative carotid revascularization in patients with high-grade carotid stenosis and delaying surgery in patients with recent strokes. The second section reviews intraoperative strategies to reduce the risk of stroke, focusing on blood pressure control, perioperative goal-directed therapy, blood transfusion, and anesthetic technique. Finally, this statement presents strategies for the evaluation and treatment of patients with suspected postoperative strokes and, in particular, highlights the value of rapid recognition of strokes and the early use of intravenous thrombolysis and mechanical embolectomy in appropriate patients.

Hypercapnia in the critically ill: insights from the bench to the bedside

Carbon dioxide (CO2) has long been considered, at best, a waste by-product of metabolism, and at worst, a toxic molecule with serious health consequences if physiological concentration is dysregulated. However, clinical observations have revealed that 'permissive' hypercapnia, the deliberate allowance of respiratory produced CO2 to remain in the patient, can have anti-inflammatory effects that may be beneficial in certain circumstances. In parallel, studies at the cell level have demonstrated the profound effect of CO2 on multiple diverse signalling pathways, be it the effect from CO2 itself specifically or from the associated acidosis it generates. At the whole organism level, it now appears likely that there are many biological sensing systems designed to respond to CO2 concentration and tailor respiratory and other responses to atmospheric or local levels. Animal models have been widely employed to study the changes in CO2 levels in various disease states and also to what extent permissive or even directly delivered CO2 can affect patient outcome. These findings have been advanced to the bedside at the same time that further clinical observations have been elucidated at the cell and animal level. Here we present a synopsis of the current understanding of how CO2 affects mammalian biological systems, with a particular emphasis on inflammatory pathways and diseases such as lung specific or systemic sepsis. We also explore some future directions and possibilities, such as direct control of blood CO2 levels, that could lead to improved clinical care in the future.

European Resuscitation Council and European Society of Intensive Care Medicine guidelines 2021: post-resuscitation care

The European Resuscitation Council (ERC) and the European Society of Intensive Care Medicine (ESICM) have collaborated to produce these post-resuscitation care guidelines for adults, which are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. The topics covered include the post-cardiac arrest syndrome, diagnosis of cause of cardiac arrest, control of oxygenation and ventilation, coronary reperfusion, haemodynamic monitoring and management, control of seizures, temperature control, general intensive care management, prognostication, long-term outcome, rehabilitation and organ donation.

European Resuscitation Council and European Society of Intensive Care Medicine Guidelines 2021: Post-resuscitation care

The European Resuscitation Council (ERC) and the European Society of Intensive Care Medicine (ESICM) have collaborated to produce these post-resuscitation care guidelines for adults, which are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. The topics covered include the post-cardiac arrest syndrome, diagnosis of cause of cardiac arrest, control of oxygenation and ventilation, coronary reperfusion, haemodynamic monitoring and management, control of seizures, temperature control, general intensive care management, prognostication, long-term outcome, rehabilitation, and organ donation.