The neurology of acutely failing respiratory mechanics

Identification and Management of Acute Neuromuscular Respiratory Failure in the ICU

Respiratory failure is a common and potentially life-threatening complication of neuromuscular diseases. Prompt recognition and accurate diagnosis of new or worsening chronic neuromuscular disease have important clinical management and prognostic implications. In this article, we present an approach to the acute presentation of undifferentiated neuromuscular respiratory failure in the ICU and guidance for determination and respiratory management of the underlying disorder.

Muscarinic cholinergic modulation of cardiovascular variables in spinal cord injured rats

Spinal cord injury (SCI) leads not only to major impairments in sensorimotor control but also to dramatic dysregulation of autonomic functions including major cardiovascular disturbances. Consequently, individuals with SCI endure daily episodic hypo/hypertension and are at increased risk for cardiovascular disease. Several studies have suggested that an intrinsic spinal coupling mechanism between motor and sympathetic neuronal networks exist and that propriospinal cholinergic neurons may be responsible for a synchronized activation of both somatic and sympathetic outputs. We therefore investigated in the present study, the effect of cholinergic muscarinic agonists on cardiovascular parameters in freely moving adult rats after SCI. Female Sprague-Dawley rats were implanted with radiotelemetry sensors for long-term in vivo monitoring of blood pressure (BP). From BP signal, we calculated heart rate (HR) and respiratory frequency. We first characterized the physiological changes occurring after a SCI performed at the T3-T4 level in our experimental model system. We then investigated the effects on BP, HR and respiration, of the muscarinic agonist oxotremorine using one variant that crossed the blood brain barrier (Oxo-S) and one that does not (Oxo-M) in both Pre- and Post-SCI animals. After SCI, both HR and respiratory frequency increased. BP values exhibited an immediate profound drop before progressively increasing over the three-week post-lesion period but remained below control values. A spectral analysis of BP signal revealed the disappearance of the low frequency component of BP (0.3-0.6 Hz) referred to as Mayer waves after SCI. In Post-SCI animals, central effects mediated by Oxo-S led to an increase in HR and MAP, a slowdown in respiratory frequency and to an increased power in the 0.3-0.6 Hz frequency band. This study unravels some of the mechanisms by which muscarinic activation of spinal neurons could contribute to partial restoration of BP after SCI.

Methods and Applications in Respiratory Physiology: Respiratory Mechanics, Drive and Muscle Function in Neuromuscular and Chest Wall Disorders

Individuals with neuromuscular and chest wall disorders experience respiratory muscle weakness, reduced lung volume and increases in respiratory elastance and resistance which lead to increase in work of breathing, impaired gas exchange and respiratory pump failure. Recently developed methods to assess respiratory muscle weakness, mechanics and movement supplement traditionally employed spirometry and methods to evaluate gas exchange. These include recording postural change in vital capacity, respiratory pressures (mouth and sniff), electromyography and ultrasound evaluation of diaphragmatic thickness and excursions. In this review, we highlight key aspects of the pathophysiology of these conditions as they impact the patient and describe measures to evaluate respiratory dysfunction. We discuss potential areas of physiologic investigation in the evaluation of respiratory aspects of these disorders.

Disordered breathing in severe cerebral illness - towards a conceptual framework

Despite potentially life-threatening symptoms of disordered breathing in severe cerebral illness, there are no clear recommendations on diagnostic and therapeutic strategies for these patients. To identify types of breathing disorders observed in severely neurological comprised patients, to direct further research on classification, pathophysiology, diagnosis and treatment for disordered breathing in cerebral disease. Data including polygraphy, transcutaneous capnometry, blood gas analysis and radiological examinations of patients with severe cerebral illness and disordered breathing admitted to the neurological intensive care were analyzed. Patients (15) presented with acquired central hypoventilation syndrome (ACHS), central bradypnea, central tachypnea, obstructive, mixed and central apneas and hypopneas, Cheyne Stokes respiration, ataxic (Biot's) breathing, cluster breathing and respiration alternans. Severe cerebral illness may result in an ACHS and in a variety of disorders of the respiratory rhythm. Two of these, abrupt switches between breathing patterns and respiration alternans, suggest the existence of a rhythmogenic respiratory network. Polygraphy, transcutaneous capnometry, blood gas analysis and MRI are promising tools for diagnosis and research alike.

The role of extracellular vesicles in traumatic brain injury-induced acute lung injury

Acute lung injury (ALI), a common complication after traumatic brain injury (TBI), can evolve into acute respiratory distress syndrome (ARDS) and has a mortality rate of 30%-40%. Secondary ALI after TBI exhibits the following typical pathological features: infiltration of neutrophils into the alveolar and interstitial space, alveolar septal thickening, alveolar edema, and hemorrhage. Extracellular vesicles (EVs) were recently identified as key mediators in TBI-induced ALI. Due to their small size and lipid bilayer, they can pass through the disrupted blood-brain barrier (BBB) into the peripheral circulation and deliver their contents, such as genetic material and proteins, to target cells through processes such as fusion, receptor-mediated interactions, and uptake. Acting as messengers, EVs contribute to mediating brain-lung cross talk after TBI. In this review, we aim to summarize the mechanism of EVs in TBI-induced ALI, which may provide new ideas for clinical treatment.

Kv1.1 subunits localize to cardiorespiratory brain networks in mice where their absence induces astrogliosis and microgliosis

Cardiorespiratory collapse following a seizure is a suspected cause of sudden unexpected death in epilepsy (SUDEP), the leading cause of epilepsy-related mortality. In the commonly used Kcna1 gene knockout (Kcna1^-/-) mouse model of SUDEP, cardiorespiratory profiling reveals an array of aberrant breathing patterns that could contribute to risk of seizure-related mortality. However, the brain structures mediating these respiratory abnormalities remain unknown. We hypothesize that Kv1.1 deficiency in respiratory control centers of the brain contribute to respiratory dysfunction in Kcna1^-/- mice leading to increased SUDEP risk. Thus, in this study, we first used immunohistochemistry to map expression of Kv1.1 protein in cardiorespiratory brain regions of wild-type Kcna1^+/+ (WT) mice. Next, GFAP and Iba1 immunostaining was used to test for the presence of astrogliosis and microgliosis, respectively, in the cardiorespiratory centers of Kcna1^-/- mice, which could be indicative of seizure-related brain injury that could impair breathing. In WT mice, we detected Kv1.1 protein in all cardiorespiratory centers examined, including the basolateral amygdala, dorsal respiratory group, dorsal motor nucleus of vagus, nucleus ambiguus, ventral respiratory column, and pontine respiratory group, as well as chemosensory centers including the retrotrapezoid and median raphae nuclei. Extensive gliosis was observed in the same areas in Kcna1^-/- mice suggesting that seizure-associated brain injury could contribute to respiratory abnormalities.

Correlation Between Respiratory Accessory Muscles and Diaphragm Pillars MRI and Pulmonary Function Test in Late-Onset Pompe Disease Patients

Objectives: Pompe disease is a rare genetic disease produced by mutations in the GAA gene leading to progressive skeletal and respiratory muscle weakness. T1-weighted magnetic resonance imaging is useful to identify fatty replacement in skeletal muscles of late-onset Pompe disease (LOPD) patients. Previous studies have shown that replacement by fat correlates with worse results of muscle function tests. Our aim was to investigate if fat replacement of muscles involved in the ventilation process correlated with results of the spirometry and predicted respiratory muscle impairment in LOPD patients over time.

Materials and Methods: We studied a cohort of 36 LOPD patients followed up annually in our center for a period of 4 years. We quantified muscle fat replacement using Mercuri score of the thoracic paraspinal and abdominal muscles and the pillars of the diaphragm. We correlated the combined Mercuri scores of these areas with spirometry results and the need of respiratory support.

Results: We found a statistically significant correlation (Spearman test, p < 0.05; coefficient of correlation > 0.6) between forced vital capacity seated and lying and fat fraction score of all muscle groups studied. The group of patients who needed respiratory support had higher fat fraction scores than patients not requiring ventilatory support. Higher fat replacement in these areas correlated with worse progression in spirometry values over time.

Conclusions: Fat replacement of paraspinal, abdominal, and trunk muscles correlates with results of spirometry and is able to predict worsening in respiratory muscle function tests that could lead to an emerging ventilatory dysfunction. Therefore, the identification of fat replacement in these muscle groups should lead to a closer monitorization of patients. Radiologic evaluation of diaphragm pillars in T1-weighted imaging axial sequences could also be helpful to predict respiratory insufficiency.

Single and sequential voluntary cough in children with chronic spinal cord injury

We investigated the impact of spinal cord injury (SCI) on cough capacity in 10 children (Mean ± SD, age 8 ± 4 years) and compared it to 15 typically developing children (age 8 ± 3 years). Participants underwent spirometry, single and sequential cough assessment with surface-electromyography from respiratory muscles. Inspiratory phase duration, inspiratory phase peak flow, inspiratory phase rise time, compression phase duration, expiratory phase rise time, expiratory phase peak airflow (EPPF) and cough volume acceleration (CVA) parameters of single and sequential cough were measured. Root mean square (RMS) values of right pectoralis-major, intercostal, rectus-abdominus (RA), and oblique (OB) muscles were calculated and mean of three trials were compared. The significance criterion was set at P < 0.05. The SCI group produced significantly lower lung volumes, EPPF, CVA, and RMS values of RA and OB during expiratory phases of single and sequential coughs. The decrease in activation in expiratory muscles in the SCI group accounts for the impaired expiratory flow and may contribute to risk of respiratory complications.

Mechanical ventilation in Guillain-Barré syndrome

Introduction: Up to 30% of patients with Guillain-Barré syndrome (GBS) develop respiratory failure requiring intensive care unit (ICU) admission and mechanical ventilation. Progressive weakness of the respiratory muscles is the leading cause of acute respiratory distress and respiratory failure with hypoxia and/or hypercarbia. Bulbar weakness may compromise airway patency and predispose patients to aspiration pneumonia. Areas covered: Clinical questions related to the use of mechanical ventilation include but are not limited to: When to start? Invasive or noninvasive? When to wean from mechanical ventilation? When to perform tracheostomy? How to manage complications of GBS in the ICU including nosocomial infection, ventilator-associated pneumonia, and ICU-acquired weakness? In this narrative review, the authors summarize the up-to-date knowledge of the incidence, pathophysiology, evaluation, and general management of respiratory failure in GBS. Expert opinion: Respiratory failure in GBS merits more attention from caregivers. Emergency intubation may lead to life-threatening complications. Appropriate methods and time point of intubation and weaning, an early tracheostomy, and predictive prophylaxis of complications benefit patients' long-term prognosis.

Successful treatment of a 12-year-old boy with Guillain-Barré syndrome requiring tracheostomy due to respiratory muscle paralysis: A case report

Childhood Guillain-Barré syndrome (GBS) occasionally leads to respiratory failure early after onset, requiring long-term ventilation management after tracheal intubation. However, patients requiring tracheostomy management are rare. In the present study, a case of a 12-year-old boy with GBS who required artificial respiration management due to rapid progression of respiratory muscle paralysis is reported. Intravenous immunoglobulin (IVIg) and pulse steroid therapy were provided; however, both were ineffective and tracheostomy was necessary 26 days after onset. A second course of IVIg and pulse steroid therapy was administered on day 34. With continued rehabilitation, the patient was able to walk long distances on day 74 and was subsequently discharged on day 89. In cases of severe GBS, when IVIg and pulse steroid therapy do not improve the respiratory muscle strength of the patient, early tracheostomy may improve the patient's quality of life during artificial respiration management.

Amyotrophic Lateral Sclerosis and the Respiratory System

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that always affects the respiratory muscles. It is characterized by degeneration of motor neurons in the brain and spinal cord. Respiratory complications are the most common causes of death in ALS and typically occur within 3 to 5 years of diagnosis. Because ALS affects both upper and lower motor neurons, it causes hyperreflexia, spasticity, muscle fasciculations, muscle atrophy, and weakness. It ultimately progresses to functional quadriplegia. ALS most commonly begins in the limbs, but in about one-third of cases it begins in the bulbar muscles responsible for speech and swallowing.

The clinical management of neuromuscular disorders in intensive care

Life-threatening neuromuscular disorders affect a small, but growing group of patients in the intensive care unit who present special management problems, as well as great therapeutic opportunities. In inflammatory conditions, a cure is often possible, and for chronic, genetic or degenerative conditions, achieving the previous level of function is the target. Neuromuscular experts and intensivists need to cooperate closely to achieve the best possible outcomes. They need to acquire a very specific set of skills, including both a thorough understanding of the mechanics of ventilation as well as familiarity with the diagnostic categories of genetic and of autoimmune diseases. This review of the clinical management of adult neuromuscular disease in the ICU aims to provide an overview of the most important conditions encountered in the ICU and a practical approach to their diagnosis, monitoring, and treatment.

Neuromuscular problems in the ICU

PURPOSE OF REVIEW

Patients with acute life-threatening neuromuscular disease require close cooperation between neuromuscular and intensive care specialists to achieve the best possible outcomes. The problems encountered by these patients are different from those in traditional neuromuscular practice, and neurologists consulting in the ICU need a specific skill set to provide useful guidance. However, outcomes can be very good if treatment is instituted effectively. This review aims to provide an overview of the most important neuromuscular conditions encountered in the ICU and enable a practical approach to patient management.

RECENT FINDINGS

New research has provided improved knowledge of the impact of acute neuromuscular failure on the mechanics of respiration, on the categories of neuromuscular disease in the ICU, and on the main factors influencing outcomes. Pitfalls and risks in ICU treatment are better understood.

SUMMARY

Evidence-based algorithms for monitoring and treatment have been developed. These advances enhance the role of the neuromuscular specialist in acute care. The principles of best practice are discussed in this review.

Invasive versus non-invasive ventilation for acute respiratory failure in neuromuscular disease and chest wall disorders

BACKGROUND

Acute respiratory failure is a common life-threatening complication of acute onset neuromuscular diseases, and may exacerbate chronic hypoventilation in patients with neuromuscular disease or chest wall disorders. Standard management includes oxygen supplementation, physiotherapy, cough assistance, and, whenever needed, antibiotics and intermittent positive pressure ventilation. Non-invasive mechanical ventilation (NIV) via nasal, buccal or full-face devices has become routine practice in many centres.

OBJECTIVES

The primary objective of this review was to compare the efficacy of non-invasive ventilation with invasive ventilation in improving short-term survival in acute respiratory failure in people with neuromuscular disease and chest wall disorders. The secondary objectives were to compare the effects of NIV with those of invasive mechanical ventilation on improvement in arterial blood gas after 24 hours and lung function measurements after one month, incidence of barotrauma and ventilator-associated pneumonia, duration of mechanical ventilation, length of stay in the intensive care unit and length of hospital stay.

SEARCH METHODS

We searched the following databases on 11 September 2017: the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE and Embase. We also searched conference proceedings and clinical trials registries.

SELECTION CRITERIA

We planned to include randomised or quasi-randomised trials with or without blinding. We planned to include trials performed in children or adults with acute onset neuromuscular diseases or chronic neuromuscular disease or chest wall disorders presenting with acute respiratory failure that compared the benefits and risks of invasive ventilation versus NIV.

DATA COLLECTION AND ANALYSIS

Two review authors reviewed searches and independently selected studies for assessment. We planned to follow standard Cochrane methodology for data collection and analysis.

MAIN RESULTS

We did not identify any trials eligible for inclusion in the review.

AUTHORS' CONCLUSIONS

Acute respiratory failure is a life-threatening complication of acute onset neuromuscular disease and of chronic neuromuscular disease and chest wall disorders. We found no randomised trials on which to elaborate evidence-based practice for the use of non-invasive versus invasive mechanical ventilation. For researchers, there is a need to design and conduct new randomised trials to compare NIV with invasive ventilation in acute neuromuscular respiratory failure. These trials should anticipate variations in treatment responses according to disease condition (acute onset versus acute exacerbation on chronic neuromuscular diseases) and according to the presence or absence of bulbar dysfunction.