Hyperventilation in neurological patients: from physiology to outcome evidence

Pathophysiology and Prevention of Manual-Ventilation-Induced Lung Injury (MVILI)

Manual ventilation, most commonly with a bag-valve mask, is a form of short-term ventilation used during resuscitative efforts in emergent and out-of-hospital scenarios. However, compared to mechanical ventilation, manual ventilation is an operator-dependent skill that is less well controlled and is highly subject to providing inappropriate ventilation to the patient. This article first reviews recent manual ventilation guidelines set forth by the American Heart Association and European Resuscitation Council for providing appropriate manual ventilation parameters (e.g., tidal volume and respiratory rate) in different patient populations in the setting of cardiopulmonary resuscitation. There is then a brief review of clinical and manikin-based studies that demonstrate healthcare providers routinely hyperventilate patients during manual ventilation, particularly in emergent scenarios. A discussion of the possible mechanisms of injury that can occur during inappropriate manual hyperventilation follows, including adverse hemodynamic alterations and lung injury such as acute barotrauma, gastric regurgitation and aspiration, and the possibility of a subacute, inflammatory-driven lung injury. Together, these injurious processes are described as manual-ventilation-induced lung injury (MVILI). This review concludes with a discussion that highlights recent progress in techniques and technologies for minimizing manual hyperventilation and MVILI, with a particular emphasis on tidal-volume feedback devices.

Postoperative Symptomatic Cerebral Vasospasm: Requiring Attention Following an Uneventful Resection of an Epidermoid Cyst - A Case Report and Literature Review

Cerebral vasospasm associated with epidermoid cyst can be caused by tumor content spillage, such as spontaneous rupture and postsurgical resection. Symptomatic cerebral vasospasm following the resection of an intracranial epidermoid cyst is a rare but serious complication that lacks a consensus on treatment. Case presentation: A 10-year-old girl underwent an uneventful complete resection of a left cerebellopontine angle epidermoid cyst. On the second postoperative day (POD 2), she exhibited reduced speech, confusion, and hyperventilation followed by hypocapnia. On POD 4, she developed right hemiparesis and dysphasia. Cerebral magnetic resonance imaging showed restricted diffusion areas in her left temporal and parietal lobes and the dorsal thalamus. Magnetic resonance angiograms confirmed narrowing of the proximal middle cerebral arteries, consistent with vasospasm. Conservative management, consisting of intravenous hydration and corticosteroid administration, proved effective in resolving her symptoms and radiologic vasospasm. On POD 8, the extensive restricted diffusion areas notably decreased in size. Her right hemiparesis was completely resolved, and her dysphasia gradually improved over time. At the 1-year follow-up, she exhibited moderate transcortical sensory dysphasia. To our knowledge, this study is the first to report on a pediatric case of symptomatic cerebral vasospasm following an epidermoid cyst resection. The combination of tumor content spillage and hyperventilation may contribute to the occurrence of cerebral vasospasm and subsequent ischemia. This complication should be acknowledged after a complete and uneventful resection.

Hyperventilation-Induced Nystagmus in Acute Unilateral Vestibulopathy: A Correlation with Vestibulo-ocular Reflex Gain and Clinical Implication

Hyperventilation-induced nystagmus test (HINT) is capable of generating a response in 77.2% of cases of acute unilateral vestibulopathy (AUVP); both nystagmus toward the affected side (excitatory pattern) and toward the healthy side (inhibitory pattern) have been described. The aim of the study is to investigate the clinical and prognostic role of the test by evaluating its correlation with vestibulo-ocular reflex (VOR) gain. We evaluated 33 AUVP patients by performing the HINT and video head impulse test (V-HIT) during the acute phase and then at 15 and 90 days after the onset of the symptoms. The correlation between the VOR gain of the affected side and test responses was evaluated first, phase by phase, and then considering the pattern shown during the first assessments. Patients with a negative HINT had a higher mean VOR gain than patients with a positive test at both 15 and 90 days. Patients who showed an inhibitory pattern at the first assessment had a continuous improvement in V-HIT performance, while patients with an initial excitatory response had a transient decrease in gain at the subsequent evaluation (P=.001). No difference between these 2 groups emerged at 90 days (P=.09). The finding of a negative HINT during the follow-up correlates with good V-HIT performance and could be an indicator of good recovery. The inhibitory pattern is associated with a subsequent improvement; and it would be indicative of compensation. but, despite this, the prognostic value of the test is limited.

Emerging Treatments for Subarachnoid Hemorrhage

The current landscape of therapeutic strategies for subarachnoid hemorrhage (SAH), a significant adverse neurological event commonly resulting from the rupture of intracranial aneurysms, is rapidly evolving. Through an in-depth exploration of the natural history of SAH, historical treatment approaches, and emerging management modalities, the present work aims to provide a broad overview of the shifting paradigms in SAH care. By synthesizing the historical management protocols with contemporary therapeutic advancements, patient-specific treatment plans can be individualized and optimized to deliver outstanding care for the best possible SAH-related outcomes.

Peritoneal dialysis in the setting of acute brain injury: an underappreciated modality

INTRODUCTION

Dialysis is complicated in the setting of acute brain injury (ABI) due to several factors including acute solute shifts, acid base changes, need for anticoagulation, and changes in intracranial pressure. For these reasons, continuous renal replacement therapy (CRRT) is often the chosen modality for renal replacement needs in these patients. Peritoneal dialysis (PD) is less discussed but shares many of the benefits often attributed to CRRT. We describe, from both nephrology and neurosurgical perspectives, a case successfully managed with PD.

CASE

A 25-year-old male with history of end-stage kidney disease (ESKD) secondary to focal segmental glomerulosclerosis on continuous cycling PD for 5 years presented to the hospital with headache and altered mental status. Initial imaging revealed a large intraventricular hemorrhage extending to the fourth ventricle. He underwent an emergent right depressive hemicraniectomy and clot evacuation. Post-operative imaging revealed worsening cerebral edema, intraventricular hemorrhage, and hydrocephalus. The decision was made to continue PD, noting that it retains many of the benefits of CRRT (which it is in fact, a form of) which he tolerated well until the need for a percutaneous gastrostomy tube arose. He was transiently transitioned to hemodialysis but returned to PD once his gastrostomy healed. He continued PD for 1 year without complication and eventually received a kidney transplant.

DISCUSSION

In managing patients with ABI undergoing dialysis, a number of considerations must be undertaken including avoidance of hypotension to maintain cerebral perfusion pressure and minimize ischemia reperfusion injury, avoidance of anticoagulants that can precipitate or worsen bleeding, the potential for cerebral edema due to rapid solute clearance and osmotic dissipation of therapeutic hypernatremia, and the mitigation of intracellular acidosis from bicarbonate delivery. Although underutilized, PD may potentially serve as a viable option for dialysis in the setting of ABI as demonstrated by the case presented.

Spontaneously hypertensive rats can become hydrocephalic despite undisturbed secretion and drainage of cerebrospinal fluid

BACKGROUND

Hydrocephalus constitutes a complex neurological condition of heterogeneous origin characterized by excessive cerebrospinal fluid (CSF) accumulation within the brain ventricles. The condition may dangerously elevate the intracranial pressure (ICP) and cause severe neurological impairments. Pharmacotherapies are currently unavailable and treatment options remain limited to surgical CSF diversion, which follows from our incomplete understanding of the hydrocephalus pathogenesis. Here, we aimed to elucidate the molecular mechanisms underlying development of hydrocephalus in spontaneously hypertensive rats (SHRs), which develop non-obstructive hydrocephalus without the need for surgical induction.

METHODS

Magnetic resonance imaging was employed to delineate brain and CSF volumes in SHRs and control Wistar-Kyoto (WKY) rats. Brain water content was determined from wet and dry brain weights. CSF dynamics related to hydrocephalus formation in SHRs were explored in vivo by quantifying CSF production rates, ICP, and CSF outflow resistance. Associated choroid plexus alterations were elucidated with immunofluorescence, western blotting, and through use of an ex vivo radio-isotope flux assay.

RESULTS

SHRs displayed brain water accumulation and enlarged lateral ventricles, in part compensated for by a smaller brain volume. The SHR choroid plexus demonstrated increased phosphorylation of the Na⁺/K⁺/2Cl^- cotransporter NKCC1, a key contributor to choroid plexus CSF secretion. However, neither CSF production rate, ICP, nor CSF outflow resistance appeared elevated in SHRs when compared to WKY rats.

CONCLUSION

Hydrocephalus development in SHRs does not associate with elevated ICP and does not require increased CSF secretion or inefficient CSF drainage. SHR hydrocephalus thus represents a type of hydrocephalus that is not life threatening and that occurs by unknown disturbances to the CSF dynamics.

Rapid Sequence Intubation Using the SEADUC Manual Suction Unit in a Contaminated Airway

The case presented here highlights the utility/feasibility of the SEADUC (EM Innovations, Galloway, OH) manual suction unit in clearing a contaminated airway during rapid sequence intubation. The case also highlights the importance of intubation in a patient with declining mental status in the prehospital environment. A 75-year-old woman suffered a head injury, and a helicopter emergency medical service team staffed with a physician and nurse was tasked with retrieval and transfer back to the tertiary care center. As the flight team rendezvoused with ground emergency medical services and the patient, a decision to intubate was made because of the patient's declining mental status and inability to protect her own airway. While in preparation for intubation, it was noted that the ambulance's electrical suction system was not working, and the flight crew had to resort to a SEADUC manual suction unit to clear the patient's airway of contaminants. The patient's airway was cleared, and she was successfully intubated and transported to a tertiary care center where the patient underwent an emergent neurosurgery procedure/decompression and was discharged home a few weeks later.

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.

Acute Multidisciplinary Management of Aneurysmal Subarachnoid Hemorrhage (aSAH)

Aneurysmal subarachnoid hemorrhage is a life-threatening, neurological emergency characterized by accumulation of blood in the subarachnoid space due to a ruptured aneurysm. Over the past several decades, improvements in the clinical management of aneurysmal subarachnoid hemorrhage have led to better patient outcomes. However, aneurysmal subarachnoid hemorrhage is still associated with high morbidity and mortality. During the acute phase of aneurysmal subarachnoid hemorrhage and prior to the definitive management of the aneurysm, numerous medical emergencies, such as elevated intracranial pressure and cerebral vasospasm, must be effectively managed to ensure the best possible neurological outcome. Early and rapid open communication between the clinical specialties caring for the aneurysmal subarachnoid hemorrhage patient is vital for rapid data collection, decision-making, and definitive treatment. In this narrative review, we aim to present the current guidelines for the multidisciplinary acute management of aneurysmal subarachnoid hemorrhage.

Brain relaxation using desflurane anesthesia and total intravenous anesthesia in patients undergoing craniotomy for supratentorial tumors: a randomized controlled study

BACKGROUND

Satisfactory brain relaxation is essential in neurosurgery. Desflurane anesthesia and propofol-based total intravenous anesthesia (TIVA) have different effects on cerebral hemodynamics, potentially contributing to discrepant brain relaxation. The purpose of this study was to compare the effects of desflurane and TIVA on brain relaxation in patients undergoing craniotomy for supratentorial tumors.

METHODS

In this randomized, controlled study, we enrolled patients aged 18-60 years, with ASA I-III, who were scheduled to undergo elective craniotomy for supratentorial tumors. Patients were randomly assigned in a 1:1 ratio to receive desflurane anesthesia or TIVA. The primary outcome was the proportion of satisfactory brain relaxation. Secondary outcomes included emergence and extubation times, recovery of cognitive function and postoperative complications.

RESULTS

Of 369 patients who were assessed for eligibility, 111 were randomized and 110 were included in the modified intention-to-treat analysis (55 in the desflurane group and 55 in the TIVA group). The proportion of satisfactory brain relaxation was similar between the two groups: 69% in the desflurane group and 73% in the TIVA group (RR: 0.950, 95% CI: 0.748-1.207; P = 0.675). Patients assigned to the desflurane group had shorter emergence (10 [8-13] min vs. 13 [10-20] min, P < 0.001) and extubation times (13 [10-18] min vs. 17 [13-23] min, P < 0.001), and better recovery of cognitive function at 15 min after extubation (16 [0-24] vs. 0 [0-20], P = 0.003), but experienced increased postoperative nausea and vomiting (PONV) (16 [29%] vs. 6 [11%] P = 0.017) and tachycardia (22 [40%] vs. 9 [16%], P = 0.006) during recovery.

CONCLUSIONS

Desflurane anesthesia and TIVA provide similar brain relaxation in patients without intracranial hypertension undergoing elective craniotomy. Desflurane accelerates the recovery from anesthesia but is associated with increased PONV and tachycardia during the recovery period.

TRIAL REGISTRATION

Clinicaltrial.gov (NCT04691128). Date of registration: December 31, 2020.

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.

Arterial Carbon Dioxide and Acute Brain Injury in Venoarterial Extracorporeal Membrane Oxygenation

Acute brain injury (ABI) occurs frequently in patients receiving venoarterial extracorporeal membrane oxygenation (VA-ECMO). We examined the association between peri-cannulation arterial carbon dioxide tension (PaCO 2 ) and ABI with granular blood gas data. We retrospectively analyzed adult patients who underwent VA-ECMO at a tertiary care center with standardized neuromonitoring. Pre- and post-cannulation PaCO 2 were defined as the mean of all PaCO 2 values in the 12 hours before and after cannulation, respectively. Peri-cannulation PaCO 2 drop (∆PaCO 2 ) equaled pre- minus post-cannulation PaCO 2 . ABI included intracranial hemorrhage (ICH), ischemic stroke, hypoxic-ischemic brain injury, cerebral edema, seizure, and brain death. Univariable logistic regression analysis was performed for the presence of ABI. Out of 129 VA-ECMO patients (median age = 60, 63% male), 43 (33%) patients experienced ABI. Patients had a median of 11 (interquartile range: 8-14) peri-cannulation PaCO 2 values. Comparing patients with and without ABI, pre-cannulation (39 vs. 42 mm Hg; p = 0.38) and post-cannulation (37 vs. 36 mm Hg; p = 0.82) PaCO 2 were not different. However, higher pre-cannulation PaCO 2 (odds ratio [OR] = 2.10; 95% confidence interval [CI] = 1.10-4.00; p = 0.02) and larger ∆PaCO 2 (OR = 2.69; 95% CI = 1.18-6.13; p = 0.02) were associated with ICH. In conclusion, in a cohort with granular arterial blood gas (ABG) data and a standardized neuromonitoring protocol, higher pre-cannulation PaCO 2 and larger ∆PaCO 2 were associated with increased prevalence of ICH.

Complex Permittivity of Ex-Vivo Human, Bovine and Porcine Brain Tissues in the Microwave Frequency Range

Accurate knowledge about the dielectric properties of biological tissues in the microwave frequency range may lead to advancement of biomedical applications based on microwave technology. However, the published data are very scarce, especially for human brain tissues. The aim of this work was to measure and report the complex permittivity of brain white matter, grey matter and cerebellum. Complex permittivity was measured on human, bovine and porcine brain tissues in the microwave frequency range from 0.5 to 18 GHz using an open-ended coaxial probe. The results present a valuable addition to the available data on the brain tissue complex permittivity. Some noticeable variations between the results lead to several conclusions. Complex permittivity variation within the same tissue type of the individual species was comparable to interspecies variation. The difference was prominent between human brains obtained from autopsies, while bovine brains obtained from healthy animals showed very similar complex permittivity. We hypothesize that the difference might have been caused by the basic pathologies of the patients, where the associated therapies could have affected the brain water content. We also examined the effect of excised tissue degradation on its complex permittivity over the course of three days, and the results suggest the gradual dehydration of the samples.

Cerebral Oxygen Delivery and Consumption in Brain-Injured Patients

Organism survival depends on oxygen delivery and utilization to maintain the balance of energy and toxic oxidants production. This regulation is crucial to the brain, especially after acute injuries. Secondary insults after brain damage may include impaired cerebral metabolism, ischemia, intracranial hypertension and oxygen concentration disturbances such as hypoxia or hyperoxia. Recent data highlight the important role of clinical protocols in improving oxygen delivery and resulting in lower mortality in brain-injured patients. Clinical protocols guide the rules for oxygen supplementation based on physiological processes such as elevation of oxygen supply (by mean arterial pressure (MAP) and intracranial pressure (ICP) modulation, cerebral vasoreactivity, oxygen capacity) and reduction of oxygen demand (by pharmacological sedation and coma or hypothermia). The aim of this review is to discuss oxygen metabolism in the brain under different conditions.

Association of intraoperative end-tidal carbon dioxide level with ablation volume during magnetic resonance-guided laser interstitial thermal therapy for mesial temporal lobe epilepsy

OBJECTIVE

Maximal safe ablation of target structures during magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT) is critical to achieving good seizure outcome in patients with mesial temporal lobe epilepsy (mTLE). The authors sought to determine whether intraoperative physiological variables are associated with ablation volume during MRgLiTT.

METHODS

Patients with mTLE who underwent MRgLiTT at our institution from 2014 to 2019 were retrospectively analyzed. Ablation volume was determined with volumetric analysis of intraoperative postablation MR images. Physiological parameters (systolic blood pressure [SBP], diastolic blood pressure [DBP], mean arterial pressure [MAP], end-tidal carbon dioxide [ETCO2]) measured 40 minutes prior to ablation were analyzed. Univariate and multivariate regression analyses were performed to determine independent predictors of ablation volume.

RESULTS

Forty-four patients met the inclusion criteria. The median (interquartile range) ablation volume was 4.27 (2.92-5.89) cm3, and median ablation energy was 7216 (6402-8784) J. The median MAP, SBP, DBP, and ETCO2 values measured during the 40-minute period leading up to ablation were 72.8 (66.2-81.5) mm Hg, 104.4 (96.4-114.4) mm Hg, 62.4 (54.1-69.8) mm Hg, and 34.1 (32.0-36.2) mm Hg, respectively. In univariate analysis, only total laser energy (r = 0.464, p = 0.003) and 40-minute average ETCO2 (r = -0.388, p = 0.012) were significantly associated with ablation volume. In multivariate analysis, only ETCO2 ≤ 33 mm Hg (p = 0.001) was significantly associated with ablation volume.

CONCLUSIONS

Total ablation energy and ETCO2, but not blood pressure, may significantly affect ablation volume in mTLE patients undergoing MRgLiTT. Mild hypocapnia was associated with increased extent of ablation. Intraoperative monitoring and modulation of ETCO2 may help improve extent of ablation, prediction of ablation volume, and potentially seizure outcome.

Acetazolamide modulates intracranial pressure directly by its action on the cerebrospinal fluid secretion apparatus

Background

Elevated intracranial pressure (ICP) is observed in many neurological pathologies, e.g. hydrocephalus and stroke. This condition is routinely relieved with neurosurgical approaches, since effective and targeted pharmacological tools are still lacking. The carbonic anhydrase inhibitor, acetazolamide (AZE), may be employed to treat elevated ICP. However, its effectiveness is questioned, its location of action unresolved, and its tolerability low. Here, we determined the efficacy and mode of action of AZE in the rat .

Methods

We employed in vivo approaches including ICP and cerebrospinal fluid secretion measurements in anaesthetized rats and telemetric monitoring of ICP and blood pressure in awake rats in combination with ex vivo choroidal radioisotope flux assays and transcriptomic analysis.

Results

AZE effectively reduced the ICP, irrespective of the mode of drug administration and level of anaesthesia. The effect appeared to occur via a direct action on the choroid plexus and an associated decrease in cerebrospinal fluid secretion, and not indirectly via the systemic action of AZE on renal and vascular processes. Upon a single administration, the reduced ICP endured for approximately 10 h post-AZE delivery with no long-term changes of brain water content or choroidal transporter expression. However, a persistent reduction of ICP was secured with repeated AZE administrations throughout the day.

Conclusions

AZE lowers ICP directly via its ability to reduce the choroid plexus CSF secretion, irrespective of mode of drug administration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00348-6.

Neuro-oncologic Emergencies

PURPOSE OF REVIEW

Patients with brain and spine tumors are at high risk of presenting cancer-related complications at disease presentation or during active treatment and are usually related to the type and location of the lesion. Here, we discuss presentation and management of the most common emergencies affecting patients with central nervous system neoplastic lesions.

RECENT FINDINGS

Tumor-related emergencies encompass complications in patients with central nervous system neoplasms, as well as neurologic complications in patients with systemic malignancies. Brain tumor patients are at high risk of developing multiple complications such as intracranial hypertension, brain herniation, intracranial bleeding, spinal cord compression, and others. Neuro-oncologic emergencies require immediate attention and multi-disciplinary care. These emergent situations usually need rapid decision-making and management on an inpatient basis.

Deep breathing couples CSF and venous flow dynamics

Venous system pathologies have increasingly been linked to clinically relevant disorders of CSF circulation whereas the exact coupling mechanisms still remain unknown. In this work, flow dynamics of both systems were studied using real-time phase-contrast flow MRI in 16 healthy subjects during normal and forced breathing. Flow evaluations in the aqueduct, at cervical level C3 and lumbar level L3 for both the CSF and venous fluid systems reveal temporal modulations by forced respiration. During normal breathing cardiac-related flow modulations prevailed, while forced breathing shifted the dominant frequency of both CSF and venous flow spectra towards the respiratory component and prompted a correlation between CSF and venous flow in the large vessels. The average of flow magnitude of CSF was increased during forced breathing at all spinal and intracranial positions. Venous flow in the large vessels of the upper body decreased and in the lower body increased during forced breathing. Deep respiration couples interdependent venous and brain fluid flow—most likely mediated by intrathoracic and intraabdominal pressure changes. Further insights into the driving forces of CSF and venous circulation and their correlation will facilitate our understanding how the venous system links to intracranial pressure regulation and of related forms of hydrocephalus.

Anesthesia Considerations in Neurological Emergencies

Airway obstruction and respiratory failure are common complications of neurological emergencies. Anesthesia is often employed for airway management, surgical and endovascular interventions or in the intensive care units in patients with altered mental status or those requiring burst suppression. This article provides a summary of the unique airway management and anesthesia considerations and controversies for neurologic emergencies in general, as well as for specific commonly encountered conditions: elevated intracranial pressure, neuromuscular respiratory failure, acute ischemic stroke, and acute cervical spinal cord injury.

The "Brain Stethoscope": A Non-Invasive Method for Detecting Elevated Intracranial Pressure

Introduction Minimally invasive intracranial pressure (ICP) screening has long been desired by neurosurgeons. A novel approach deriving ICP from tympanic membrane (TM) pulsation may offer the solution. The ICP waveform appears to be transmitted to the TM by the cochlear aqueduct. The resulting TM infrasonic pulsations can be measured by certain sensors. Elevated ICP alters brain compliance, which appears to yield slower rise times of the TM pulsation waveform. Measurement of this change may be useful in screening for elevated ICP. This paper investigates one such technique. Methods A stethoscope was modified for airtight external ear canal fit; the dome was exchanged for a magnetic reluctance pressure sensor, allowing measurement of TM pulsations. Analog TM pulsations were analyzed by measuring the pulsation's slope ratio between the waveform's downslope and upslope. Seventeen normal subjects (ages 18-32 years) underwent hyperventilation and tilt table testing to induce ICP changes. An algorithm processed this data and predicted the subject's ICP status. Results The slope ratio method showed consistent and stable changes with the expected alterations in ICP from the tilt test and hyperventilation maneuvers. The classification algorithm correctly identified subjects with elevated ICP in 60 of 60 independent recordings on 17 subjects. Conclusion This paper has four conclusions. First, the "brain stethoscope" can detect increased ICP from the TM pulsation waveform in healthy subjects. Second, analysis of the TM waveform using slope ratio calculations is capable of distinguishing normal versus elevated ICP. Third, the tilt and hyperventilation maneuvers showed the expected physiologic trends. Last, further studies are needed on patients with pathological ICP before the brain stethoscope can be implemented into clinical practice.

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.

Optimizing accuracy of freehand cannulation of the ipsilateral ventricle for intracranial pressure monitoring in patients with brain trauma

Background

Intracranial pressure (ICP) monitoring in traumatic brain injury (TBI) usually requires the placement of a catheter into the ipsilateral ventricle. This surgical procedure is commonly performed via a freehand method using surface anatomical landmarks as guides. The current accuracy of the catheter placement remains relatively low and even lower among TBI patients. This study was undertaken to optimize the freehand ventricular cannulation to increase the accuracy for TBI. The authors hypothesized that an optimal surgical plan of cannulation should give an operator the greatest degrees of freedom, which could be measured as the range of operation angle, range of catheter placement depth, and size of the target area.

Methods

An imaging simulation was first performed using the computed tomography (CT) images of 47 adult patients with normal brain anatomy. On the reconstructed 3D head model, four different coronal planes of ventricular cannulation were identified: a 4-cm anterior, a 2-cm anterior, a standard (central), and a 2-cm posterior plane. The degrees of freedom during the cannulation procedure were determined, including the relevant angles, lengths of cannulation, cross-sectional area, and bounding rectangle of the lateral ventricle. Next, a retrospective assessment was performed on the CT scans of another 111 patients with TBI who underwent freehand ventricular cannulation for ICP monitoring. Postoperative measurements were also performed based on CT images to calculate the accuracy and safety of catheter placement between coronal planes in practice.

Results

Our simulation results showed that the 2-cm anterior plane had more extensive degrees of freedom for ventricular cannulation, in terms of length of catheter trajectory (7% longer, P<0.001), cross-sectional area of the lateral ventricle (14% larger, P=0.046), and length of the lateral ventricle (17% wider, P<0.001) than that of the standard plane, while both the 4-cm anterior and 2-cm posterior planes did not offer advantages over the standard plane in these ways. The mean length range of catheter trajectory in the 2-cm anterior plane was 41 to 58 mm. Retrospective assessment of TBI patients with ICP monitor placement also confirmed our simulation data. It showed that the accuracy of ipsilateral ventricle cannulation in the 2-cm anterior plane was 70.6%, which was a significant increase from 42.9% in the standard plane (P=0.007).

Conclusions

Our imaging simulation and retrospective study demonstrate that different coronal planes could provide different degrees of freedom for cannulation, the 2-cm anterior plane has the greatest degrees of freedom in terms of larger target area and greater length range of the trajectory. The optimized surgical plan in this manner could improve cannulation accuracy and benefit a significant number of TBI patients.

An overview of management of intracranial hypertension in the intensive care unit

Intracranial hypertension (IH) is a clinical condition commonly encountered in the intensive care unit, which requires immediate treatment. The maintenance of normal intracranial pressure (ICP) and cerebral perfusion pressure in order to prevent secondary brain injury (SBI) is the central focus of management. SBI can be detected through clinical examination and invasive and non-invasive ICP monitoring. Progress in monitoring and understanding the pathophysiological mechanisms of IH allows the implementation of targeted interventions in order to improve the outcome of these patients. Initially, general prophylactic measures such as patient's head elevation, fever control, adequate analgesia and sedation depth should be applied immediately to all patients with suspected IH. Based on specific indications and conditions, surgical resection of mass lesions and cerebrospinal fluid drainage should be considered as an initial treatment for lowering ICP. Hyperosmolar therapy (mannitol or hypertonic saline) represents the cornerstone of medical treatment of acute IH while hyperventilation should be limited to emergency management of life-threatening raised ICP. Therapeutic hypothermia could have a possible benefit on outcome. To control elevated ICP refractory to maximum standard medical and surgical treatment, at first, high-dose barbiturate administration and then decompressive craniectomy as a last step are recommended with unclear and probable benefit on outcomes, respectively. The therapeutic strategy should be based on a staircase approach and be individualized for each patient. Since most therapeutic interventions have an uncertain effect on neurological outcome and mortality, future research should focus on both studying the long-term benefits of current strategies and developing new ones.

Mechanical ventilation in neurocritical care setting: A clinical approach

Neuropatients often require invasive mechanical ventilation (MV). Ideal ventilator settings and respiratory targets in neuro patients are unclear. Current knowledge suggests maintaining protective tidal volumes of 6-8 ml/kg of predicted body weight in neuropatients. This approach may reduce the rate of pulmonary complications, although it cannot be easily applied in a neuro setting due to the need for special care to minimize the risk of secondary brain damage. Additionally, the weaning process from MV is particularly challenging in these patients who cannot control the brain respiratory patterns and protect airways from aspiration. Indeed, extubation failure in neuropatients is very high, while tracheostomy is needed in one-third of the patients. The aim of this manuscript is to review and describe the current management of invasive MV, weaning, and tracheostomy for the main four subpopulations of neuro patients: traumatic brain injury, acute ischemic stroke, subarachnoid hemorrhage, and intracerebral hemorrhage.

Neurogenic pulmonary edema following acute stroke: The progress and perspective

Neurogenic pulmonary edema (NPE) following acute stroke is an acute respiratory distress syndrome (ARDS) with clinical characteristics that include acute onset, apparent pulmonary interstitial fluid infiltration and rapid resolution. The pathological process of NPE centers on sympathetic stimulation and fulminant release of catecholamines, which cause contraction of resistance vessels. Elevated systemic resistance forces fluid into pulmonary circulation, while pulmonary circulation overload induces pulmonary capillary pressure that elevates, and in turn damages the alveolar capillary barrier. Damage to the alveolar capillary barrier leads to pulmonary ventilation disorder, blood perfusion disorder and oxygenation disorder. Eventually, NPE will cause post-stroke patients' prognosis to further deteriorate. At present, we lack specific biological diagnostic indicators and a meticulously unified diagnostic criterion, and this results in a situation in which many patients are not recognized quickly and/or diagnosed accurately. There are no drugs that are effective against NPE. Therefore, understanding how to diagnose NPE early by identifying the risk factors and how to apply appropriate treatment to avoid a deteriorating prognosis are important scientific goals. We will elaborate the progress of NPE after acute stroke in terms of its pathophysiological mechanisms, etiology, epidemiology, clinical diagnosis and early prediction, comprehensive treatment strategies, and novel drug development. We also propose our own thinking and prospects regarding NPE.

Functional muscle strength recovery from nail gun injury to the primary motor cortex

Aim: Functional recovery following injury to the primary motor cortex is an uncommon phenomenon, given the limited ability of neurons of the adult central nervous system to regenerate. Case description: We report on a patient with near complete functional muscle strength recovery from a marked monoparesis due to nail gun injury to the medial primary motor cortex. Besides surgical decision-making, we discuss possible related mechanisms and current challenges in the regenerative processes responsible for the functional recovery. Discussion: To achieve a favorable outcome, surgical decision-making to prevent secondary damage is of upmost importance. Lesion-induced inflammatory response may potentiate endogenous neurogenesis and neuronal plasticity and potentially contribute to the regenerative process involved.