Mechanisms and consequences of excess exercise ventilation in fibrosing interstitial lung disease

The causes and consequences of excess exercise ventilation (EEV) in patients with fibrosing interstitial lung disease (f-ILD) were explored. Twenty-eight adults with f-ILD and 13 controls performed an incremental cardiopulmonary exercise test. EEV was defined as ventilation-carbon dioxide output (⩒E-⩒CO2) slope ≥36 L/L. Patients showed lower pulmonary function and exercise capacity compared to controls. Lower DLCO was related to higher ⩒E-⩒CO2 slope in patients (P<0.05). 13/28 patients (46.4%) showed EEV, reporting higher dyspnea scores (P=0.033). Patients with EEV showed a higher dead space (VD)/tidal volume (VT) ratio while O2 saturation dropped to a greater extent during exercise compared to those without EEV. Higher breathing frequency and VT/inspiratory capacity ratio were observed during exercise in the former group (P<0.05). An exaggerated ventilatory response to exercise in patients with f-ILD is associated with a blunted decrease in the wasted ventilation in the physiological dead space and greater hypoxemia, prompting higher inspiratory constraints and breathlessness.

Breathing control training for functional seizures: A multi-site, open-label pilot study

There are no well-validated treatments for functional seizures. While specialist psychotherapy is usually recommended, the evidence for its benefit is qualified, and it can be difficult to obtain. Given the association between hyperventilation and functional seizures we explored an alternative modality, breathing control training, in a multi-site open label pilot trial. Participants with functional seizures over the age of 16 received an hour of breathing training from a respiratory physiotherapist, with a half-hour booster session a month later. Seizure frequency and Nijmegen scores (a measure of hyperventilation) were reported at baseline and follow-up, 3-4 months later. Eighteen subjects were recruited, and 10 completed follow-up. Seven of these 10 had improved seizure frequency, and 3 did not (Wilcoxon signed rank test, p = 0.09), with seizure frequency correlating with Nijmegen score (Spearman's rank correlation = 0.75, p = 0.034). The intervention was well tolerated, with no adverse events reported. These preliminary results support a potentially new approach to treating functional seizures that should prove cost-effective and acceptable, though require confirmation by a randomised controlled trial.

Respiratory dysfunction in persistent somatic symptoms: A systematic review of observational studies

OBJECTIVE

This systematic review aims to analyze the existing literature investigating respiratory functioning in people with Persistent Somatic Symptoms (PSS) compared to healthy controls, to identify patterns of respiratory disturbances by symptom or syndrome, and describe any respiratory outcomes consistent across diagnoses.

METHODS

A systematic review following PRISMA guidelines was conducted. A comprehensive search was carried out across five databases (PubMed (NCBI), PsycArticles (Ovid), Web of Science (Core Collection), Embase, and Scopus) using two customised search strings for persistent somatic symptoms and objective respiratory parameters. Title/abstract screening and data extraction were carried out independently by two reviewers. The modified Newcastle-Ottawa Scale was used for quality assessment of the studies. Studies investigating baseline respiratory functioning in adult patients with PSS compared to healthy controls, using at least one objective respiratory were included.

RESULTS

18 studies met the inclusion criteria for the review, with a pooled sample size of n = 3245. Chronic pain conditions were found to be the most prevalent subset of diagnoses of interest, comprising six of the studies. 10 studies included measures of lung capacity, flow and/or volume, nine studies reported measures of ventilation, and four studies investigated respiratory muscle functioning. 13 of the included studies reported significant differences in at least one objective respiratory measure between groups (at rest). Scores on self-reported measures of dysnpea and breathlessness were higher in patients compared to healthy controls, while objective respiratory outcomes were varied.

CONCLUSION

The current systematic review is consistent with previous literature suggesting more pronounced experiences of breathlessness in patients with PSS, and significant disparities between reported dyspnea and objective respiratory outcomes. Research investigating the uncoupling between subjective and objective respiratory outcomes is needed to understand the mechanisms behind breathing disturbances in PSS.

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

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Respiratory Acid-Base Disorders

Respiratory acid-base disorders are often not thought of as frequently as their metabolic cousins, which occur more frequently in the emergency department. Although most respiratory and acid-base disturbances are driven by lung pathology, central nervous system and other organ systems can and do play a role as well. Although managing the airway and appropriate mechanical ventilation may be necessary, it is akin to placing a band-aid on a large wound. It is crucial for the emergency clinician to discover the etiology of the disturbance as management depends on treating the underlying etiology to prevent worsening acid-base status.

Hyperventilation Syndrome Following an Asymptomatic COVID-19 Infection

N/a.

Home-based pulmonary rehabilitation for adults with severe asthma exposed to psychosocial chronic stressors

OBJECTIVE

To evaluate the effects of a home-based pulmonary rehabilitation (PR) programme on hyperventilation symptoms, anxiety and depressive symptoms, general fatigue, health-related quality of life (HRQoL) and exercise capacity in adults with severe asthma who have been exposed to psychosocial chronic stressors.

METHODS

Data on 111 non-selected consecutive adults with severe asthma who enrolled in an 8-week home-based PR programme (weekly supervised 90-min session) was retrospectively analysed. Chronic stressors included physical, sexual and psychological violence and/or a traumatic experience related to an intensive care unit stay. Hyperventilation symptoms (Nijmegen questionnaire), Hospital Anxiety and Depression Scale, Fatigue Assessment Scale, COPD Assessment Test, Six-Minute Stepper Test and Timed-Up and Go test were assessed at baseline and after PR.

RESULTS

At baseline, participants who have been exposed to chronic stressors (n = 48, 43.2%) were younger, more often female, more often treated for anxiety and depressive disorders, and had a higher score for anxiety symptoms, hyperventilation symptoms and a poorer HRQoL, compared to those who had not been exposed to chronic stressors (p < 0.05). All the study assessments were statistically improved after PR for both groups (p < 0.001). Anxiety and depressive symptoms, fatigue and health-related quality of life questionnaires were also clinically improved based on the minimal clinically important difference.

CONCLUSION

A large proportion of adults with severe asthma, mainly women, have been exposed to chronic stressors at the time of starting a PR programme, resulting in higher anxiety symptoms and hyperventilation symptoms. However, it did not prevent these individuals from benefiting from PR.

Characterization of adolescents with functional respiratory disorders and prior history of SARS-CoV-2

BACKGROUND

The SARS-CoV-2 pandemic has caused significant pulmonary morbidity and mortality in the adult population. Children and adolescents typically show milder symptoms; however, a relevant proportion of them report persistent pulmonary symptoms even after mild SARS-CoV-2 infection. Functional respiratory disorders may be relevant differential diagnoses of persistent dyspnea. This study aims at characterizing functional respiratory disorders that may arise after SARS-CoV-2 infection regarding their clinical presentation and pulmonary function tests as well as gaining insights into the clinical course after initiation of appropriate therapy.

METHODS

This study retrospectively identified all patients referred to an outpatient clinic for pediatric pulmonology with functional respiratory disorders manifesting after proven SARS-CoV-2 infection between January 1, 2022, and October 31, 2022. Clinical history, thorough clinical examination regarding breathing patterns, and pulmonary function tests (PFTs) were taken into consideration to diagnose functional respiratory disorders.

RESULTS

Twenty-five patients (44% female) with mean (m) age = 12.73 years (SD ± 1.86) who showed distinctive features of functional respiratory disorders after SARS-CoV-2 infection (onset at m = 4.15 (± 4.24) weeks after infection) were identified. Eleven patients showed thoracic dominant breathing with insufficient ventilation, and 4 patients mainly had symptoms of inducible laryngeal obstruction. The rest (n = 10) showed overlap of these two etiologies. Most patients had a flattened inspiratory curve on spirometry and slightly elevated residual volume on body plethysmography, but values of PFTs were normal before and after standardized treadmill exercise testing. Patients were educated about the benign nature of the condition and were offered rebreathing training. All patients with follow-up (n = 5) showed normalization of the breathing pattern within 3 months.

CONCLUSIONS

Functional respiratory disorders are important differential diagnoses in persisting post-SARS-CoV-2 dyspnea in adolescents. A combination of clinical history, detailed examination of breathing patterns, and pulmonary function tests are helpful to correctly diagnose these conditions. Reassurance and rebreathing training are the mainstay of the therapy. The clinical course is favorable.

Efficacy of preoxygenation administration in volunteers, in extending the end-expiration breath-hold duration for application to abdominal radiotherapy

Background and purpose

End expiration breath hold (EEBH) is the preferred motion management method for abdominal Stereotactic Ablative Body Radiotherapy (SABR) treatments. However, multiple short EEBHs are required to complete a single treatment session. The study aimed to determine the efficacy of preoxygenation with hyperventilation in extending an EEBH duration.

Materials and methods

We randomised 10 healthy participants into two arms, each included breathing room air and oxygen at a rate of 10 L per minute (l/min) without hyperventilation for four minutes, and normally for four minutes and with hyperventilation for one minute at a rate of 20 breaths/minute for hyperventilation. The type of gas was blinded from the participants for each test. EEBH durations were then recorded, as well as systolic blood pressure, SpO₂ and heart rate. A discomfort rating was also recorded after each breath hold.

Results

A significant increase in duration of almost 50% was observed between normal breathing of room air and breathing oxygen normally followed by hyperventilation. Vital signs remained consistent between the 4 tests. The tests were well tolerated with 75% of participants recording none or minimal discomfort.

Conclusion

Preoxygenation with hyperventilation could be used to increase the EEBH duration for abdominal SABR patients which would assist in the accuracy of these treatments and possibly resulting in a reduction of overall treatment times.

Post-Hypercapnic Alkalosis: A Brief Review

Metabolic alkalosis is a common acid-base imbalance frequently observed in intensive care unit (ICU) patients and is associated with increased mortality. Post-hypercarbia alkalosis (PHA) is a type of metabolic alkalosis caused by sustained high serum bicarbonate levels following a rapid resolution of hypoventilation in patients with chronic hypercapnia due to prolonged respiratory disturbance. Common causes of chronic hypercapnia include chronic obstructive pulmonary disease (COPD), central nervous system disorders, neuromuscular disorders, and narcotic abuse. Rapid correction of hypercapnia through hyperventilation leads to a swift normalization of pCO₂, which lacks renal compensation, consequently causing an increase in plasma HCO_3- levels and severe metabolic alkalosis. Most of PHA occurs in the ICU setting requiring mechanical ventilation and can progress severe alkalemia due to secondary mineralocorticoid excess from volume depletion or decreased HCO_3- excretion from decreased glomerular filtration rate and increased proximal tubular reabsorption. PHA is associated with increased ICU stay, ventilator dependency, and mortality. Acetazolamide, a carbonic anhydrase inhibitor, has been utilized for managing PHA by inducing alkaline diuresis and reducing tubular reabsorption of bicarbonate. While acetazolamide effectively improves alkalemia, its impact on hard outcomes may be limited by factors such as patient complexity, co-administered medications, and underlying conditions contributing to alkalosis.

[Dyspnea «sine materia»]

Dyspnea is a symptom of respiratory discomfort commonly encountered in clinical practice which, in most of the cases, relates to a cardiopulmonary or a metabolic disorder. Its genesis is complex and results from numerous interactions within cortical and limbic brain areas following intero- and nociceptive stimuli. The term dyspnea «sine materia» points to a state where no clear underlying cardiopulmonary or metabolic pathology has been identified and we include here the hyperventilation syndrome and the physical deconditioning. Treatment of dyspnea «sine materia» is based on behavioural psychotherapy and on reathtletisation programme in case of physical deconditioning.

Cardiopulmonary exercise testing to indicate increased ventilatory variability in subjects with dysfunctional breathing

BACKGROUND

Dysfunctional breathing (DB) is a common, but largely underappreciated, cause of chronic dyspnea. Under visual inspection, most subjects with DB present with larger sequential changes in ventilation (V̇E) and breathing pattern (tidal volume (VT) and breathing frequency (f)) before and/or during incremental cardiopulmonary exercise testing (CPET). Currently, however, there are no objective criteria to indicate increased ventilatory variability in these subjects.

METHODS

20 chronically dyspneic subjects with DB and 10 age- and sex-matched controls performed CPET on a cycle ergometer. Cut-offs to indicate increased V̇E, VT, f, and f/VT ratio variability (Δ= highest-lowest 20 s arithmetic mean) over the last resting minute (_rest ), the 2^sd min of unloaded exercise (_unload ), and the 3^rd min of loaded exercise (_load ) were established by ROC curve analyses.

RESULTS

Subjects with DB presented with increased V̇E, higher ventilatory variability, higher dyspnea burden, and lower exercise capacity compared to controls (p<0.05). ΔV̇E_load (> 4.1 L/min), Δf_rest (> 5 breaths/min; bpm), Δf_unload (> 4 bpm), Δf_load (> 5 bpm), Δf/VT_rest (> 4.9 bpm/L), and Δf/VT_load (> 1.3 bpm/L) differentiated DB from a normal pattern (areas under the curve ranging from 0.729 to 0.845). High Δf, in particular, was associated with DB across all CPET phases.

CONCLUSIONS

This study provides objective criteria to indicate increased ventilatory variability during incremental CPET in dyspneic subjects with DB. Large variability in breathing frequency seems particularly useful in this context, a finding that should be prospectively confirmed in larger studies. This article is protected by copyright. All rights reserved.

Arterial Blood Gases in Normal Subjects at 2240 Meters Above Sea Level: Impact of Age, Gender, and Body Mass Index

Background

The values of arterial blood gases (ABG) change with altitude above sea level; empirical verification is essential because ventilatory acclimatization varies with ethnicity and a population's adaptation.

Objective

The aim of the study was to describe ABG in a healthy population residing at 2,240 meters above sea level, to identify the mean level of alveolar ventilation (PaCO₂), and to know whether a progressive increase in PaCO₂ occurs with age and the impact of increasing body mass index (BMI).

Methods

We conducted a cross-sectional study in a referral center for respiratory diseases in Mexico City. Associations among variables with correlation coefficient and regression models of PaO₂, SaO₂, and P(A-a)O₂ as dependent variables as a function of age, BMI, minute ventilation, or breathing frequency were explored.

Results

Two hundred and seventeen healthy subjects were evaluated with a mean age of 40 ± 15 years, mean of the PaO₂ was 71 ± 6 mmHg, SaO₂ 94% ± 1.6%, PaCO₂ 30.2 ± 3.4 mmHg, HCO₃ 20 ± 2 mmol/L, BE-2.9 ± 1.9 mmol/L, and the value of pH was 7.43 ± 0.02. In a linear regression, the main results were PaO₂ = 77.5-0.16*age (p < 0.0001) and with aging P(A-a)O₂ tended to increase 0.12 mmHg/year. PaCO₂ in women increased with age by 0.075 mmHg/year (p = 0.0012, PaCO₂ =26.3 + 0.075*age). SaO₂ and PaO₂ decreased significantly in women with higher BMI 0.14% and 0.52 mmHg per kg/m², (p = 0.004 and 0.002 respectively).

Conclusion

Mean PaCO₂ was 30.7 mmHg, implying a mean alveolar ventilation of around 30% above that at sea level.

Severe tachypnoea and dyspnoea due to physiological hyperventilation in pregnancy

Physiological hyperventilation and dyspnoea in pregnancy are well-established phenomena and commonly lead to a chronic respiratory alkalosis with compensatory renal excretion of bicarbonate. However, the underlying mechanism of dyspnoea during normal pregnancy remains largely undefined. Increasing progesterone levels are a primary factor leading to increased respiratory drive to ensure the rising metabolic demands of the pregnancy are met. Dyspnoea symptoms typically begin in the first or second trimester, are mild, and do not interfere with activities of daily living. We report the case of a 35-year-old female with severe physiological hyperventilation of pregnancy presenting with profound dyspnoea, tachypnoea, and presyncope from 18 weeks of gestation until delivery. Subsequent investigations revealed no identifiable underlying pathology. There remain limited reports of such severe physiological hyperventilation of pregnancy. This case highlights interesting questions regarding the respiratory physiology of pregnancy and underlying mechanisms.

The combination of hyperventilation test and graph theory parameters to characterize EEG changes in mild cognitive impairment (MCI) condition

Hyperventilation (HV) is a voluntary activity that causes changes in the neuronal firing characteristics noticeable in the electroencephalogram (EEG) signals. HV-related changes have been scribed to modulation of pO2/pCO2 blood contents. Therefore, an HV test is routinely used for highlighting brain abnormalities including those depending to neurobiological mechanisms at the basis of neurodegenerative disorders. The main aim of the present paper is to study the effectiveness of HV test in modifying the functional connectivity from the EEG signals that can be typical of a prodromal state of Alzheimer's disease (AD), the Mild Cognitive Impairment prodromal to Alzheimer condition. MCI subjects and a group of age-matched healthy elderly (Ctrl) were enrolled and subjected to EEG recording during HV, eyes-closed (EC), and eyes-open (EO) conditions. Since the cognitive decline in MCI seems to be a progressive disconnection syndrome, the approach we used in the present study is the graph theory, which allows to describe brain networks with a series of different parameters. Small world (SW), modularity (M), and global efficiency (GE) indexes were computed among the EC, EO, and HV conditions comparing the MCI group to the Ctrl one. All the three graph parameters, computed in the typical EEG frequency bands, showed significant changes among the three conditions, and more interestingly, a significant difference in the GE values between the MCI group and the Ctrl one was obtained, suggesting that the combination of HV test and graph theory parameters should be a powerful tool for the detection of possible cerebral dysfunction and alteration.

Improved simulated ventilation with a novel tidal volume and peak inspiratory pressure controlling bag valve mask: A pilot study

Introduction

The dangers of hyperventilation during resuscitation are well known. Traditional bag valve mask (BVM) devices rely on end users to control tidal volume (V_t), rate, and peak inspiratory pressures (PIP) of ventilation. The Butterfly BVM (BBVM) is a novel device intending to give greater control over these parameters. The objective of this pilot study was to compare the BBVM against a traditional device in simulated resuscitations.

Methods

Senior emergency medicine residents and fellows participated in a three-phase simulation study. First, participants used the Ambu Spur II BVM in adult and pediatric resuscitations. V_t, PIP, and rate were recorded. Second, participants repeated the resuscitations after a brief introduction to the BBVM. Third, participants were given a longer introduction to the BBVM and were tested on their ability to adjust its various settings.

Results

Nineteen participants were included in the adult arm of the study, and 16 in the pediatric arm. The BBVM restricted V_t delivered to a range of 4-8 ml/kg vs 9 ml/kg and 13 ml/kg (Ambu adult and Ambu pediatric respectively). The BBVM never exceeded target minute ventilations while the Ambu BVMs exceeded target minute ventilation in 2 of 4 tests. The BBVM failed to reliably reach higher PIP targets in one test, while the pediatric Ambu device had 76 failures of excessive PIP compared to 2 failures by the BBVM.

Conclusion

The BBVM exceeded the Ambu Spur II in delivering appropriate V_ts and in keeping PIPs below target maximums to simulated adult and pediatric patients in this pilot study.

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.

Two-handed facemask technique effectively causes hyperventilation in electroconvulsive therapy: an observational study

BACKGROUND

Electroconvulsive therapy (ECT) remains the mainstay treatment option for patients with psychiatric diseases, such as severe depression. Although various anesthetic techniques provide adequate therapeutic seizures, hyperventilation is a useful adjunct to augment seizure duration and improve seizure quality. We investigated how to efficiently use a facemask to accomplish protocolized hyperventilation and evaluate its effect on ECT seizure.

METHODS

We studied 60 patients aged ≥18 years who underwent ECT. The patients were divided into two groups according to the technique of facemask ventilation used: the one-handed (n = 30) and two-handed (n = 30) groups. Following anesthesia induction under preoxygenation conditions, hyperventilation induced hypocapnia in the one-handed facemask group with manual bag ventilation was compared to that in the two-handed facemask group with assisted pressure-controlled ventilation. Ictal and peri-ictal electroencephalogram parameters and cardiovascular responses were monitored and compared between the one-handed and two-handed groups.

RESULTS

The two-handed technique demonstrated better electroencephalogram regularity and minimized cardiovascular stress compared to the one-handed technique. These conclusions come from the fact that the one-handed technique induced a substantial volume of leaks around the facemask (201.7 ± 98.6 mL/breath), whereas minimal leaks (25.8 ± 44.6 mL/breath) with stabler and higher ventilation rate led to greater inhaled minute ventilation in the two-handed group (the one-handed group, 9.52 ± 3.94 L/min; the two-handed group, 11.95 ± 2.29 L/min; p <  0.005). At the end of ECT treatment, all parameters of blood pressure and heart rate increased significantly in both groups equally, with lower SpO₂ and more ST-segment depression on the electrocardiogram in the one-handed group. Comparing baseline values before anesthesia, ECT treatment significantly depressed ST-segment in both groups, while the degree of depression in ST-segment increased significantly in the one-handed group compared to that in the two-handed group.

CONCLUSIONS

End-tidal carbon dioxide monitoring for hyperventilation can reliably ensure hypocapnia only in the two-handed group. In ECT, the two-handed technique assisted by pressure-controlled ventilation is an effective and practical method for hyperventilation to induce adequate therapeutic seizures. While, the two-handed group with sufficient preoxygenation did not cause more cardiovascular stress than the one-handed group.

TRIAL REGISTRATION

UMIN Clinical Trials Registry 000046544, Date of registration 05/01/2022.

[Oxygenation-sensitive cardiac magnetic resonance imaging]

BACKGROUND

Oxygenation-sensitive cardiac magnetic resonance imaging (OS-CMR) is an evolving cardiac imaging technique offering new perspectives to understand, predict, and diagnose cardiac pathologies.

OBJECTIVES

To provide an overview of the basic principles of OS-CMR, the current diagnostic applications and how it may aid in future diagnostic challenges.

MATERIALS AND METHODS

Description, analysis, and interpretation of the current literature on basic research and applicational studies in both humans and animals assessing OS-CMR.

RESULTS

OS-CMR is based on the paramagnetic properties of deoxygenated hemoglobin, which is visualized by a T2*-sensitive sequence. The measured signal correlates with the oxygenation of the myocardium and can analyze vascular function during pharmacological vasodilation or vasoactive breathing exercises (hyperventilation, apnea). The herewith triggered changes in myocardial oxygenation and oxygenation reserve can be used to identify relevant stenoses in coronary artery disease. Other areas of application involve myocardial hypertrophy, microvascular dysfunction, and pulmonary hypertension.

CONCLUSION

A broad number of applications for the clinical use of OS-CMR exist so far, especially in combination with breathing exercises. OS-CMR can be conducted medication- and needle-free. Limitations involve the current lack of clinically approved, automated evaluation tools and the unavailability of vendor- and site-independent normal values.

Persistent Exertional Dyspnea and Perceived Exercise Intolerance After Mild COVID-19: A Critical Role for Breathing Dysregulation?

OBJECTIVE

After mild COVID-19, a subgroup of patients reported post-acute-phase sequelae of COVID-19 (PASC) in which exertional dyspnea and perceived exercise intolerance were common. Underlying pathophysiological mechanisms remain incompletely understood. The purpose of this study was to examine outcomes from cardiopulmonary exercise testing (CPET) in these patients.

METHODS

In this observational study, participants were patients who were referred for the analysis of PASC after mild COVID-19 and in whom CPET was performed after standard clinical workup turned out unremarkable. Cardiocirculatory, ventilatory, and metabolic responses to and breathing patterns during exercise at physiological limits were analyzed.

RESULTS

Twenty-one patients (76% women; mean age = 40 years) who reported severe disability in physical functioning underwent CPET at 32 weeks (interquartile range = 22-52) after COVID-19. Mean peak O2 uptake was 99% of predicted with normal anaerobic thresholds. No cardiovascular or gas exchange abnormalities were detected. Twenty of the 21 patients (95%) demonstrated breathing dysregulation (ventilatory inefficiency [29%], abnormal course of breathing frequency and tidal volume [57%], absent increase of end-tidal Pco2 [57%], and abnormal resting blood gases [67%]).

CONCLUSION

Breathing dysregulation may explain exertional dyspnea and perceived exercise intolerance in patients with PASC after mild COVID-19 and can be present in the absence of deconditioning. This finding warrants further study on the levels of neural control of breathing and muscle function, and simultaneously provides a potential treatment opportunity.

IMPACT

This study contributes to the understanding of persistent exertional dyspnea and perceived exercise intolerance following mild COVID-19, which is vital for the development of effective rehabilitation strategies.

Near-Infrared Spectroscopy-Guided Hyperventilation for Transient Intracranial Pressure Control during Anesthesia Induction in a Patient with Impending Uncal Herniation

Near-infrared spectroscopy (NIRS) is known to determine the adequacy of regional cerebral oxygen supply. NIRS values during anesthetic induction depends upon various factors such as anesthetic agents, inspired oxygen fraction, blood carbon dioxide levels and systemic blood pressure. Also high intracranial pressure (ICP) can lead to reduced NIRS values, secondary to increased cerebral vascular resistance induced decrease in cerebral blood flow. However optimal hyperventilation instituted as a bridge to definitive ICP management is difficult to ascertain as hypocapnia due to poorly titrated hyperventilation can potentially worsen ICP. Here we describe a novel application of NIRS-guided hyperventilation during anesthesia induction in a brain tumor patient with raised ICP features and impending uncal herniation as suggested by computed tomography (CT) scan, with ipsilateral baseline reduced NIRS values. These ipsilateral NIRS values further reduced significantly during anesthesia induction even before profound bradycardia occurred, which promptly improved to baseline following hyperventilation.

Late Onset Subacute Profound Biotinidase Deficiency Caused by a Novel Homozygous Variant c.466-3T>G in the BTD Gene

Biotinidase deficiency (BD) is an autosomal recessive disorder caused by bi-allelic mutation in the BTD gene. Clinical manifestations in BD mainly depends on residual biotinidase enzyme activity, although there are some exceptions. Broadly BD disorders are classified as profound BD and partial BD. Further profound BD can be early onset, late onset, and sometimes may be asymptomatic. Clinically late-onset profound BD can present with spectrum of manifestations ranging from single organ to multiple organ involvement, typically affecting function of brain, eye, ear, and skin. Here, a first-born child to consanguineous parents with late-onset profound BD presenting with hyperventilation secondary to lactic acidosis, hypotonia, evolving spasticity, and abnormal neuroimaging findings caused by novel homozygous variant, c.466-3T>G in the BTD gene is reported.

Caffeine alters the breathing pattern during high-intensity whole-body exercise in healthy men

PURPOSE

The current study investigated the effect of caffeine on the breathing pattern during a high-intensity whole-body exercise.

METHODS

Using a randomized, crossover, counterbalanced, and double-blind design, twelve healthy men ingested either 5 mg.kg^-1 of caffeine or cellulose (placebo) one hour before performing a high-intensity whole-body exercise (i.e., work rate corresponding to 80% of the difference between the gas exchange threshold and maximal oxygen uptake) until the limit of tolerance. Ventilatory and metabolic responses were recorded throughout the trial and at task failure.

RESULTS

Caffeine ingestion increased time to task failure in relation to the placebo (368.1 ± 49.6 s vs. 328.5 ± 56.6 s, p = 0.005). Caffeine also increased tidal volume and inspiratory time throughout the exercise (p < 0.05). Compared to task failure with placebo, task failure with caffeine intake was marked by higher (p < 0.05) minute ventilation (134.8 ± 16.4 vs. 147.6 ± 18.2 L.min^-1), the ventilatory equivalent of oxygen consumption (37.8 ± 4.2 vs. 41.7 ± 5.5 units), and respiratory exchange ratio (1.12 ± 0.10 vs. 1.19 ± 0.11 units).

CONCLUSION

In conclusion, ingestion of caffeine alters the breathing pattern by increasing tidal volume and lengthening the inspiratory phase of the respiratory cycle. These findings suggest that caffeine affects the ventilatory system, which may account, in part, for its ergogenic effects during high-intensity whole-body exercises.

[Viral meningitis: a rare cause of hyperventilation]

The etiology of hyperventilation is multifactorial. When excluding somatic causes, neurogenic hyperventilation must always be considered. Since hyperventilation itself causes neuromuscular symptoms such as paresthesia, vertigo, cephalgia, and nausea, the differential diagnosis of viral meningitis in the presence of hyperventilation is not always obvious and can easily be overlooked. Our case report shows that somatogenic causes of hyperventilation should be carefully excluded.

Neural respiratory drive in chronic thromboembolic pulmonary hypertension: Effect of balloon pulmonary angioplasty

Excessive ventilation (V̇E) during exercise, ascribed to heightened neural ventilatory drive and/or to increased "wasted" ventilation, is a feature of chronic thromboembolic pulmonary hypertension (CTEPH). In selected CTEPH patients, balloon pulmonary angioplasty (BPA) allows near-normalization of resting haemodynamic parameters but does not allow excess exercise hyperventilation to normalize. Neural ventilatory drive can be estimated by studying how arterial PCO₂ (PaCO₂), end-tidal PCO₂ (PETCO₂), V̇E and CO₂ output (V̇CO₂) change across the exercise-to-recovery transition during a cardiopulmonary exercise test. Increased "wasted" ventilation can be quantified by the physiological dead space fraction of tidal volume (VD/VT) calculated with the Enghoff simplification of the Bohr equation. These measurements were made before and after BPA in 22 CTEPH patients without significant cardiac and/or pulmonary comorbidities. Our observations suggest that before BPA, excessive hyperventilation was secondary to both heightened neural ventilatory drive and increased "wasted" ventilation; after BPA, measurements made across the exercise-to-recovery transition suggest that heightened neural ventilatory drive was no longer present.

Mathematically arterialised venous blood is a stable representation of patient acid-base status at steady state following acute transient changes in ventilation

Hyper- or hypoventilation are commonly occurring stress responses to arterial puncture around the time of blood sampling and have been shown to rapidly alter arterial blood acid–base parameters. This study aimed to evaluate a physiology-based mathematical method to transform peripheral venous blood acid–base values into mathematically arterialised equivalents following acute, transient changes in ventilation. Data from thirty patients scheduled for elective surgery were analysed using the physiology-based method. These data described ventilator changes simulating ‘hyper-’ or ‘hypoventilation’ at arterial puncture and included acid–base status from simultaneously drawn blood samples from arterial and peripheral venous catheters at baseline and following ventilatory change. Venous blood was used to calculate mathematically arterialised equivalents using the physiology-based method; baseline values were analysed using Bland–Altman plots. When compared to baseline, measured arterial and calculated arterialised values at each time point within limits of pH: ± 0.03 and PCO₂: ± 0.5 kPa, were considered ‘not different from baseline’. Percentage of values considered not different from baseline were calculated at each sampling timepoint following hyper- and hypoventilation. For the physiological method, bias and limits of agreement for pH and PCO₂ were -0.001 (-0.022 to 0.020) and -0.02 (-0.37 to 0.33) kPa at baseline, respectively. 60 s following a change in ventilation, 100% of the mathematically arterialised values of pH and PCO₂ were not different from baseline, compared to less than 40% of the measured arterial values at the same timepoint. In clinical situations where transient breath-holding or hyperventilation may compromise the accuracy of arterial blood samples, arterialised venous blood is a stable representative of steady state arterial blood.

Effects of hyperventilation with face mask on brain network in patients with epilepsy

OBJECTIVES

During the ongoing pandemic of COVID-19, wearing face masks was recommended, including patients with epilepsy doing the hyperventilation (HV) test during electroencephalogram (EEG) examination somewhere. However, evidence was still limited about the effect of HV with face mask on cortical excitability of patients with epilepsy. The motivation of this work is to make use of the graph theory of EEG to characterize the cortical excitability of patients with epilepsy when they did HV under the condition wearing a surgical face mask.

METHODS

We recruited 19 patients with epilepsy and 17 normal controls. All of participants completed two HV experiments, including HV with face mask (HV+) and HV without a mask (HV). The interval was 30 min and the sequence was random. Each experiment consisted of three segments: resting EEG, EEG of HV, and EEG of post-HV. EEG were recorded successively during each experiment. Participants were asked to evaluate the discomfort degree using a questionnaire when every HV is completed.

RESULTS

All of the participants felt more uncomfortable after HV + . Moreover, not only HV decreased small-worldness index in patients with epilepsy, but also HV + significantly increased the clustering coefficient in patients with epilepsy. Importantly, the three-way of Mask*HV*Epilepsy showed interaction in the clustering coefficient in the delta band, as well as in the path length and the small-worldness index in the theta band.

CONCLUSIONS

The results of this study indicated that patients with epilepsy showed the increased excitability of brain network during HV + . We should pay more attention to the adverse effect on brain network excitability caused by HV + in patients with epilepsy. In the clinical practice under the COVID-19 pandemic, it is important that the wearing face mask remain cautious for the individuals with epilepsy when they carried out HV behavior such as exercise (e.g., running, etc.).

Stewart analysis unmasks acidifying and alkalizing effects of ionic shifts during acute severe respiratory alkalosis

PURPOSE

Although both the Henderson-Hasselbalch method and the Stewart approach can be used to analyze acid-base disturbances and metabolic and respiratory compensation mechanisms, the latter may be superior in detecting subtle metabolic changes.

MATERIALS AND METHODS

We analyzed acid-base disturbances using both approaches in six healthy male volunteers practicing extreme voluntary hyperventilation. Arterial blood gas parameters were obtained during a breathing exercise consisting of approximately 30 cycles of powerful hyperventilation followed by breath retention for approximately 2 min.

RESULTS

Hyperventilation increased pH from 7.39 ± 0.01 at baseline to 7.74 ± 0.06, PaCO₂ decreased from 34.1 ± 1.1 to 12.6 ± 0.7 mmHg, PaO₂ increased from 116 ± 4.6 to 156 ± 4.3 mmHg. Baseline apparent strong ion difference was 42.3 ± 0.5 mEq/L, which decreased to 37.1 ± 0.7 mEq/L following hyperventilation. The strong ion gap significantly decreased following hyperventilation, with baseline levels of 10.0 ± 0.9 dropping to 6.4 ± 1.1 mEq/L.

CONCLUSIONS

Henderson-Hasselbalch analysis indicated a profound and purely respiratory alkalosis with no metabolic compensation following extreme hyperventilation. The Stewart approach revealed metabolic compensation occurring within minutes. These results challenge the long-held axiom that metabolic compensation of acute respiratory acid-base changes is a slow process.

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.

Paroxysmal dyspnea in Parkinson's disease: Respiratory dyskinesias and autonomic hyperventilation are not the same

Respiratory complaints are not uncommon in patients with Parkinson's disease (PD). While many are explained by pulmonary and cardiovascular problems unrelated to PD, secondary effects of PD, such as kyphoscoliosis, respiratory muscle rigidity, repeated pneumonias, or side effects of medication such as dyskinesias, there is a small group of patients with paroxysmal dyspnea for whom neither anxiety or other explanation has been found. This Point of View was written to call attention to this neglected, uncommon, but very distressing symptom.

Occurrence of hyperventilation-induced high amplitude rhythmic slowing with altered awareness after successful treatment of typical absence seizures and a network hypothesis

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We show that typical absence seizures (AS) and hyperventilation-induced high amplitude rhythmic slowing (HIHARS) or HIHARS with Altered Awareness (HIHARSAA) can coexist in the same patient, but never at the same time.

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We found that alkalosis and dysfunction of the same neural network are involved in both AS and HIHARS.

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AS and HIHARS should be better recognized to avoid misdiagnosis and overtreatment.

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AS and HIHARS can coexist in the same patient, but never at the same time.

Background

Typical absence seizures (AS) are epileptic phenomena typically appearing in children 4–15 years of age and can be elicited by hyperventilation (HV). Hyperventilation-induced high-amplitude rhythmic slowing (HIHARS) represents a paraphysiological response during HV and may manifest with alteration of awareness (HIHARSAA). To date, HIHARSAA has mostly been described in patients without epilepsy.

Aim

To describe five patients with treatment-responsive typical AS who, after becoming seizure free, presented with HIHARSAA.

Methods

By using video-electroencephalographic recording (Video-EEG), we describe differential clinical characteristics and ictal electrophysiological patterns of both typical AS and HIHARSAA.

Results

We demonstrate that when HIHARSAA occurs in patients with typical AS there is a temporal window between the two phenomena. This suggests that the presence of typical AS precludes the appearance of HIHARSAA.

Conclusions

We hypothesize that alkalosis and dysfunction of the same neural network are involved in both typical AS and HIHARSAA and that their distinct electroclinic manifestations are due to the involvement of different ion channels.

Significance

A better understanding of the characteristics of typical AS and HIHARSAA and of the role of alkalosis in both, can help avoiding misdiagnosis and identifying more suitable therapies for typical AS.

Safety in dermatologic procedures: anaphylaxis, vasovagal reaction, and hyperventilation

This article, part of a the series on safety in dermatologic procedures, covers the diagnosis, prevention, management, and treatment of 3 situations or conditions. The first condition we address is anaphylaxis, an uncommon but severe and potentially fatal reaction that must be recognized quickly so that urgent management coordinated with an anesthesiologist can commence. The second is fainting due to a vasovagal reaction, which is the most common complication in dermatologic surgery. This event, which occurs in 1 out of every 160 procedures, usually follows a benign course and resolves on its own. However, in patients susceptible to vasovagal reactions, syncope may lead to asystole and cardiac arrest. The third is acute hyperventilation syndrome, which is an anomalous anxiety-related increase in breathing rate beyond metabolic requirements. Brief practical recommendations for managing all 3 events are included.

Hypocapnia Induced by Hyperventilation with Indocyanine Green Kinetics Detects the Effect of Staged Carotid Angioplasty to Avoid Hyperperfusion in Patients with Impaired Cerebral Hemodynamic Reserve

Cerebral hyperperfusion syndrome (CHS) is a serious complication following carotid artery stenting (CAS). Staged angioplasty (AP) could potentially prevent CHS and hyperperfusion phenomenon (HPP) after revascularization. However, methods for measuring the effects of staged AP on cerebral hemodynamic reserve have not been established. Here, we evaluated whether indocyanine green kinetics and near-infrared spectroscopy (ICG-NIRS) with hypocapnia induced by hyperventilation can detect the effects of staged AP on hemodynamic reserve to prevent CHS after CAS. Participants comprised 44 patients at high risk of CHS, whose ipsilateral cerebrovascular reactivity (CVR) was impaired on preoperative single photon emission computed tomography (SPECT). Patients were divided into a staged AP group (n=13) and a regular CAS group (n=31). In the staged AP group, stenting was performed 3 weeks after staged AP. In the regular CAS group, 16 cases (52%) showed HPP, and five (16%) presented with CHS after CAS, while no HPP or CHS occurred in the staged AP group (p=0.001). Changes in blood flow index (BFI) and time to peak (TTP) ratio during hypocapnia calculated from ICG-NIRS indicated a significant linear relationship with preprocedural CVR on SPECT (r=-0.710, 0.632, respectively; p<0.0001 each). BFI and TTP ratios during hypocapnia were significantly improved after staged AP (p<0.001 each). Furthermore, significant linear correlations were observed between BFI and TTP ratio during hypocapnia and postoperative asymmetry index AI (r=0.405, -0.475, respectively; p<0.01 each). Hypocapnia induced by hyperventilation under ICG-NIRS appears useful for detecting the effects of staged AP on hemodynamic reserve in patients at high risk of CHS.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Safety in Dermatologic Procedures: Anaphylaxis, Vasovagal Reaction, and Hyperventilation

This article, part of a the series on safety in dermatologic procedures, covers the diagnosis, prevention, management, and treatment of 3 situations or conditions. The first condition we address is anaphylaxis, an uncommon but severe and potentially fatal reaction that must be recognized quickly so that urgent management coordinated with an anesthesiologist can commence. The second is the vasovagal reaction, which is the most common complication in dermatologic surgery. This event, which occurs in 1 out of every 160 procedures, usually follows a benign course and resolves on its own. However, in patients susceptible to vasovagal reactions, syncope may lead to asystole and cardiac arrest. The third is acute hyperventilation syndrome, which is an anomalous anxiety-related increase in breathing rate beyond metabolic requirements. Brief practical recommendations for managing all 3 events are included.

Central neurogenic hyperventilation secondary to suspected metastatic renal cell carcinoma

Central neurogenic hyperventilation (CNH) is a neurogenic disorder rarely described within Emergency Medicine literature. CNH is a primary cause of hyperventilation, most commonly due to primary central nervous system neoplasms. Patient presentation varies based on the underlying cause, and may present with a sole chief complaint of dyspnea. We present a case of an adult male with a history of deep vein thrombosis, anticoagulated on apixaban, and extensively metastatic renal cell carcinoma who presented with a two-week history of dyspnea. Evaluation in the emergency department showed a primary respiratory alkalosis with a compensatory metabolic acidosis. Diagnostic work-up failed to reveal a cardiac, pulmonary, metabolic, or toxic cause. During the emergency department course, the patient became dysarthric and altered, at which point, computed tomography scan of the head revealed a pontine hemorrhage. The hemorrhage was stabilized with prothrombin complex concentrate, but the patient's dyspnea and mental status deteriorated throughout the course of his hospitalization. While the cause of the patient's hemorrhage was not elucidated, given the patient's widely metastatic disease, it was presumed to be secondary to metastasis. Our case highlights both a unique cause of a rare disorder of hyperventilation, and a diagnostic challenge to the emergency medicine provider. It is important to consider central causes of hyperventilation in patients with dyspnea and neurologic symptoms.

Use and impact of high intensity treatments in patients with traumatic brain injury across Europe: a CENTER-TBI analysis

PURPOSE

To study variation in, and clinical impact of high Therapy Intensity Level (TIL) treatments for elevated intracranial pressure (ICP) in patients with traumatic brain injury (TBI) across European Intensive Care Units (ICUs).

METHODS

We studied high TIL treatments (metabolic suppression, hypothermia (< 35 °C), intensive hyperventilation (PaCO2 < 4 kPa), and secondary decompressive craniectomy) in patients receiving ICP monitoring in the ICU stratum of the CENTER-TBI study. A random effect logistic regression model was used to determine between-centre variation in their use. A propensity score-matched model was used to study the impact on outcome (6-months Glasgow Outcome Score-extended (GOSE)), whilst adjusting for case-mix severity, signs of brain herniation on imaging, and ICP.

RESULTS

313 of 758 patients from 52 European centres (41%) received at least one high TIL treatment with significant variation between centres (median odds ratio = 2.26). Patients often transiently received high TIL therapies without escalation from lower tier treatments. 38% of patients with high TIL treatment had favourable outcomes (GOSE ≥ 5). The use of high TIL treatment was not significantly associated with worse outcome (285 matched pairs, OR 1.4, 95% CI [1.0-2.0]). However, a sensitivity analysis excluding high TIL treatments at day 1 or use of metabolic suppression at any day did reveal a statistically significant association with worse outcome.

CONCLUSION

Substantial between-centre variation in use of high TIL treatments for TBI was found and treatment escalation to higher TIL treatments were often not preceded by more conventional lower TIL treatments. The significant association between high TIL treatments after day 1 and worse outcomes may reflect aggressive use or unmeasured confounders or inappropriate escalation strategies.

TAKE HOME MESSAGE

Substantial variation was found in the use of highly intensive ICP-lowering treatments across European ICUs and a stepwise escalation strategy from lower to higher intensity level therapy is often lacking. Further research is necessary to study the impact of high therapy intensity treatments.

TRIAL REGISTRATION

The core study was registered with ClinicalTrials.gov, number NCT02210221, registered 08/06/2014, https://clinicaltrials.gov/ct2/show/NCT02210221?id=NCT02210221&draw=1&rank=1 and with Resource Identification Portal (RRID: SCR_015582).

Prolonging deep inspiration breath-hold time to 3 min during radiotherapy, a simple solution

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A new protocol was developped to prolong deep inspiration breath-holds.

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Multiple prolonged breath-holds are achievable with minimal side effects.

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DIBH was prolonged to 3 min using HFNO and hyperventilation in breast cancer patients.

Background and purpose

Deep inspiration breath-hold is an established technique to reduce heart dose during breast cancer radiotherapy. However, modern breast cancer radiotherapy techniques with lymph node irradiation often require long beam-on times of up to 5 min. Therefore, the combination with deep inspiration breath-hold (DIBH) becomes challenging. A simple support technique for longer duration deep inspiration breath-hold (L-DIBH), feasible for daily use at the radiotherapy department, is required to maximize heart sparing.

Materials and methods

At our department, a new protocol for multiple L-DIBH of at least 2 min and 30 s was developed on 32 healthy volunteers and validated on 8 breast cancer patients during radiotherapy treatment, using a pragmatic process of iterative development, including all major stakeholders. Each participant performed 12 L-DIBHs, on 4 different days. Different methods of pre-oxygenation and voluntary hyperventilation were tested, and scored on L-DIBH duration, ease of use, and comfort.

Results

Based on 384 L-DIBHs from 32 healthy volunteers, voluntary hyperventilation for 3 min whilst receiving high-flow nasal oxygen at 40 L/min was the most promising technique. During validation, the median L-DIBH duration in prone position of 8 breast cancer patients improved from 59 s without support to 3 min and 9 s using the technique (p < 0.001).

Conclusion

A new and simple L-DIBH protocol was developed feasible for daily use at the radiotherapy center.

Is venous blood a more reliable description of acid-base state following simulated hypo- and hyperventilation?

Background

ABGs are performed in acute conditions as the reference method for assessing the acid-base status of blood. Hyperventilation and breath-holding are common ventilatory changes that occur around the time of sampling, rapidly altering the ‘true’ status of the blood. This is particularly relevant in emergency medicine patients without permanent arterial catheters, where the pain and anxiety of arterial punctures can cause ventilatory changes. This study aimed to determine whether peripheral venous values could be a more reliable measure of blood gases following acute changes in ventilation.

Methods

To allow for characterisation of ventilatory changes typical of acutely ill patients, but without the confounding influence of perfusion or metabolic disturbances, 30 patients scheduled for elective surgery were studied in a prospective observational study. Following anaesthesia, and before the start of the surgery, ventilator settings were altered to achieve a + 100% or − 60% change in alveolar ventilation (‘hyper-’ or ‘hypoventilation’), changes consistent with the anticipation of a painful arterial puncture commonly encountered in the emergency room. Blood samples were drawn simultaneously from indwelling arterial and peripheral venous catheters at baseline, and at 15, 30, 45, 60, 90 and 120 s following the ventilatory change. Comparisons between the timed arterial (or venous) samples were done using repeated-measures ANOVA, with post-hoc analysis using Bonferroni’s correction.

Results

Arterial blood pH and PCO₂ changed rapidly within the first 15–30s after both hyper- and hypoventilation, plateauing at around 60s (∆pH = ±0.036 and ∆PCO₂ = ±0.64 kPa (4.7 mmHg), respectively), with peripheral venous values remaining relatively constant until 60s, and changing minimally thereafter. Mean arterial changes were significantly different at 30s (P < 0.001) when compared to baseline, in response to both hyper- and hypoventilation.

Conclusion

This study has shown that substantial differences in arterial and peripheral venous acid-base status can be due to acute changes in ventilation, commonly seen in the ER over the 30s necessary to sample arterial blood. If changes are transient, peripheral venous blood may provide a more reliable description of acid-base status.

Comparative analysis between available challenge tests in the hyperventilation syndrome

BACKGROUND

The hyperventilation syndrome (HVS) is characterized by somatic/ psychological symptoms due to sustained hypocapnia and respiratory alkalosis without any organic disease.

OBJECTIVE

The purpose of this study was to compare ventilatory parameters and symptoms reproducibility during the hyperventilation provocation test (HVPT) and cardiopulmonary exercise test (CPET) as diagnostic tools in patients with HVS, and to identify the most frequent etiologies of the HVS by a systematic assessment.

METHODS

After exclusion of organic causes, 59 patients with HVS according to Nijmegen's questionnaire (NQ) score ≥23 with associated hypocapnia (PaCO₂/PET_CO2<35 mm Hg) were studied.

RESULTS

The most frequent comorbidities of HVS were anxiety and asthma (respectively 95% and 73% of patients). All patients described ≥3 symptoms of NQ during the HVPT vs 14% of patients during the CPET (p<0.01). For similar maximal ventilation (61 L/min during HVPT vs 60 L/min during CPET), the median level of PET_CO2 decreased from 30 mmHg at baseline to 15 mmHg during hyperventilation and increased from 31 mmHg at baseline to 34 mmHg at peak exercise (all p<0.01). No significant difference for the ventilatory parameters was found between patients with HVS (n = 16) and patients with HVS + asthma (n = 43).

CONCLUSIONS

In term of symptoms reproducibility, HVPT is a better diagnostic tool than CPET for HVS. An important proportion of patients with HVS has an atypical asthma previously misdiagnosed. The exercise-induced hyperventilation did not induce abnormal reduction in PET_CO2, suggesting that the exercise could be a therapeutic tool in HVS.

Functional Respiratory Disorders in Children

Functional respiratory disorders (FRDs) are those characterized by respiratory symptoms without anatomic or organic etiology. Clinicians caring for children encounter these disorders and should be familiar with diagnosis and treatment. FRDs encompass the habit cough syndrome and its variants, vocal cord dysfunction, hyperventilation disorders, functional dyspnea, and sighing syndrome. Failure to identify these disorders results in unnecessary testing and medication. This article reviews the clinical presentation, manifestation, and treatment of respiratory FRDs in children. How health care providers can successfully identify and treat these reversible conditions in the clinical setting is discussed.

Diagnosing and managing childhood absence epilepsy by telemedicine

The diagnosis of childhood absence epilepsy (CAE) is typically based on history and description of spells, supported by an office-based positive hyperventilation test and confirmed by routine electroencephalography (EEG). In the current coronavirus disease 2019 (COVID-19) pandemic, many pediatric neurologists have switched to telemedicine visits for nonemergent outpatient evaluations. We present a series of children diagnosed as having CAE on the basis of a positive hyperventilation test performed during remote televisits. Several of these children were begun on treatment for CAE prior to obtaining an EEG, with significant seizure reduction. Our series documents the feasibility of CAE diagnosis and management by telemedicine.

Brain and gills as internal and external ammonia sensing organs for ventilatory control in rainbow trout, Oncorhynchus mykiss

Ammonia is both a respiratory gas and a toxicant in teleost fish. Hyperventilation is a well-known response to elevations of both external and internal ammonia levels. Branchial neuroepithelial cells (NECs) are thought to serve as internal sensors of plasma ammonia (peripheral chemoreceptors), but little is known about other possible ammonia-sensors. Here, we investigated whether trout possess external sensors and/or internal central chemoreceptors for ammonia. For external sensors, we analyzed the time course of ventilatory changes at the start of exposure to high environmental ammonia (HEA, 1 mM). Hyperventilation developed gradually over 20 min, suggesting that it was a response to internal ammonia elevation. We also directly perfused ammonia solutions (0.01-1 mM) to the external surfaces of the first gill arches. Immediate hypoventilation occurred. For central chemoreceptors, we injected ammonia solutions (0.5-1.0 mM) directly onto the surface of the hindbrain of anesthetized trout. Immediate hyperventilation occurred. This is the first evidence of central chemoreception in teleost fish. We conclude that trout possess both external ammonia sensors, and dual internal ammonia sensors (perhaps for redundancy), but their roles differ. External sensors cause short term hypoventilation, which would help limit toxic waterborne ammonia uptake. When fish cannot avoid HEA, the diffusion of waterborne ammonia into the blood will stimulate both peripheral (NECs) and central (brain) chemoreceptors, resulting in hyperventilation. This hyperventilation will be beneficial in increasing ammonia excretion via the Rh metabolon system in the gills not only after HEA exposure, but also after endogenous ammonia loading from feeding or exercise.

Pharmacological Treatment of Severe Breathing Abnormalities in a Case of HNRNPU Epileptic Encephalopathy

Abnormal breathing patterns are a typical feature of Rett and Pitt-Hopkins syndrome and their variants. Their treatment can be challenging, with a risk of long-term detrimental consequences. Early infantile epileptic encephalopathy (EIEE) type 54 is a rare epileptic encephalopathy caused by pathogenic variants in the heterogeneous nuclear ribonucleoprotein U (HNRNPU) gene. Only one case has been described in the literature with episodes of hyperventilation and apnea, but treatment was not discussed. We describe the clinical and genetic features and treatment strategies in a case of EIEE type 54 and severely abnormal breathing pattern. A novel and likely pathogenic c.2277dup, p.(Pro760Serfs*5) variant in the HNRNPU gene was found in a male patient with severe episodes of hyperventilation and apnea, leading to syncope. Combination therapy with acetazolamide, alprazolam and aripiprazole led to significant clinical improvement. Although HNRNPU has not been implicated in breathing control, pathogenic variants in this gene can be associated with the development of abnormal breathing patterns reminiscent of Rett and Pitt-Hopkins syndrome. Its function as a gene expression regulator and its interaction with transcription factors offers a potential pathogenetic link between these 3 disorders. Based on our experience, treatment strategies can be similar to those already applied for patients with Pitt-Hopkins and Rett syndrome.

Safety proposals for freediving time limits should consider the metabolic-rate dependence of oxygen stores depletion

INTRODUCTION

There is no required training for breath-hold diving, making dissemination of safety protocols difficult. A recommended breath-hold dive time limit of 60 s was proposed for amateur divers. However, this does not consider the metabolic-rate dependence of oxygen stores depletion. We aimed to measure the effect of apnoea time and metabolic rate on arterial and tissue oxygenation.

METHODS

Fifty healthy participants (23 (SD 3) y, 22 women) completed four periods of apnoea for 60 s (or to tolerable limit) during rest and cycle ergometry at 20, 40, and 60 W. Apnoea was initiated after hyperventilation to achieve P_ETCO₂ of approximately 25 mmHg. Pulse oximetry, frontal lobe oxygenation, and pulmonary gas exchange were measured throughout. We defined hypoxia as SpO₂ < 88%.

RESULTS

Static and exercise (20, 40, 60 W) breath-hold break times were 57 (SD 7), 50 (11), 48 (11), and 46 (11) s (F [2.432, 119.2] = 32.0, P < 0.01). The rise in P_ETCO₂ from initiation to breaking of apnoea was dependent on metabolic rate (time × metabolic rate interaction; F [3,147] = 38.6, P < 0.0001). The same was true for the fall in SpO₂ (F [3,147] = 2.9, P = 0.03). SpO₂ fell to < 88% on 14 occasions in eight participants, all of whom were asymptomatic.

CONCLUSIONS

Independent of the added complexities of a fall in ambient pressure on ascent, the effect of apnoea time on hypoxia depends on the metabolic rate and is highly variable among individuals. Therefore, we contend that a universally recommended time limit for breath-hold diving or swimming is not useful to guarantee safety.

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

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