Clinical review: Mechanical ventilation in severe asthma

A systematic review on the use of sevoflurane in the management of status asthmaticus in adults

BACKGROUND

To conduct a systematic review looking into the use of sevoflurane in the management of status asthmaticus (SA) in adults.

METHODS

We performed a systematic search on PubMed, EMBASE, and The Cochrane Library - CENTRAL through 23rd August 2023, restricting to studies reported in English. We included studies reporting use of sevoflurane in asthmatics beyond its use as an anaesthetic agent in surgeries i.e. in the emergency department (ED) and critical care setting, and focused on patient's clinical parameters, ventilation pressures and weaning of invasive ventilation.

RESULTS

A total of 13 publications fulfilled the inclusion criteria, comprising of 18 cases. All publications were of case reports/ series and conference abstracts, and no randomised trials were available. Most patients required intubation despite best medical management before sevoflurane administration, and high airway pressures and respiratory acidosis were apparent. There was significant heterogeneity regarding severity of asthma, treatment instituted, and the delivery, duration and concentration of sevoflurane administered. Many of the studies also did not quantify the changes in parameters pre- and post-sevoflurane. Sixteen patients experienced improvements in clinical status with sevoflurane administration-one required escalation to extracorporeal membrane oxygenation (ECMO), and another did not survive.

CONCLUSION

The systematic review suggests sevoflurane can be a valuable treatment option in SA. As these cases are rare and heterogenous, further prospective case series are needed to support this.

Severe asthma exacerbation: Changes in patient characteristics, management, and outcomes from 1997 to 2016 in 40 ICUs in the greater Paris area

Background

Despite advances in asthma treatments, severe asthma exacerbation (SAE) remains a life-threatening condition in adults, and there is a lack of data derived from adult patients admitted to intensive care units (ICUs) for SAE. The current study investigated changes in adult patient characteristics, management, and outcomes of SAE over a 20-year period in 40 ICUs in the greater Paris area.

Methods

In this retrospective observational study, admissions to 40 ICUs in the greater Paris area for SAE from January 1, 1997, to December 31, 2016 were analyzed. The primary outcome was the proportion of ICU admissions for SAE during 5-year periods. Secondary outcomes were ICU and hospital mortality, and the use of mechanical ventilation and catecholamine. Multivariate analysis was performed to assess factors associated with ICU mortality.

Results

A total of 7049 admissions for SAE were recorded. For each 5-year period, the proportion decreased over time, with SAE accounting for 2.84% of total ICU admissions (n=2841) between 1997 and 2001, 1.76% (n=1717) between 2002 and 2006, 1.05% (n=965) between 2007 and 2011, and 1.05% (n=1526) between 2012 and 2016. The median age was 46 years (interquartile range [IQR]: 32-59 years), 55.41% were female, the median Simplified Acute Physiology Score II was 20 (IQR: 13-28), and 19.76% had mechanical ventilation. The use of mechanical ventilation remained infrequent throughout the 20-year period, whereas the use of catecholamine decreased. ICU and hospital mortality rates decreased. Factors associated with ICU mortality were renal replacement therapy, catecholamine, cardiac arrest, pneumothorax, acute respiratory distress syndrome, sepsis, and invasive mechanical ventilation (IMV). Non-survivors were older, had more severe symptoms, and were more likely to have received IMV.

Conclusion

ICU admission for SAE remains uncommon, and the proportion of cases decreased over time. Despite a slight increase in symptom severity during a 20-year period, ICU and hospital mortality decreased. Patients requiring IMV had a higher mortality rate.

Factors associated with prolonged mechanical ventilation in children with pulmonary failure: Cohort study from the LARed Network registry

OBJECTIVES

To identify factors associated with prolonged mechanical ventilation (pMV) in pediatric patients in pediatric intensive care units (PICUs).

DESIGN

Secondary analysis of a prospective cohort.

SETTING

PICUs in centers that are part of the LARed Network between April 2017 and January 2022.

PARTICIPANTS

Pediatric patients on mechanical ventilation (IMV) due to respiratory causes. We defined IMV time greater than the 75th percentile of the global cohort.

INTERVENTIONS

None.

MAIN VARIABLES OF INTEREST

Demographic data, diagnoses, severity scores, therapies, complications, length of stay, morbidity, and mortality.

RESULTS

1698 children with MV of 8±7 days were included, and pIMV was defined as 9 days. Factors related to admission were age under 6 months (OR 1.61, 95% CI 1.17-2.22), bronchopulmonary dysplasia (OR 3.71, 95% CI 1.87-7.36), and fungal infections (OR 6.66, 95% CI 1.87-23.74), while patients with asthma had a lower risk of pIMV (OR 0.30, 95% CI 0.12-0.78). Regarding evolution and length of stay in the PICU, it was related to ventilation-associated pneumonia (OR 4.27, 95% CI 1.79-10.20), need for tracheostomy (OR 2.91, 95% CI 1.89-4.48), transfusions (OR 2.94, 95% CI 2.18-3.96), neuromuscular blockade (OR 2.08, 95% CI 1.48-2.93), high-frequency ventilation (OR 2.91, 95% CI 1.89-4.48), and longer PICU stay (OR 1.13, 95% CI 1.10-1.16). In addition, mean airway pressure greater than 13cmH2O was associated with pIMV (OR 1.57, 95% CI 1.12-2.21).

CONCLUSIONS

Factors related to IMV duration greater than 9 days in pediatric patients in PICUs were identified in terms of admission, evolution, and length of stay.

Predicting the risk of acute respiratory failure among asthma patients-the A2-BEST2 risk score: a retrospective study

Objectives

Acute respiratory failure (ARF) is a common complication of bronchial asthma (BA). ARF onset increases the risk of patient death. This study aims to develop a predictive model for ARF in BA patients during hospitalization.

Methods

This was a retrospective cohort study carried out at two large tertiary hospitals. Three models were developed using three different ways: (1) the statistics-driven model, (2) the clinical knowledge-driven model, and (3) the decision tree model. The simplest and most efficient model was obtained by comparing their predictive power, stability, and practicability.

Results

This study included 398 patients, with 298 constituting the modeling group and 100 constituting the validation group. Models A, B, and C yielded seven, seven, and eleven predictors, respectively. Finally, we chose the clinical knowledge-driven model, whose C-statistics and Brier scores were 0.862 (0.820-0.904) and 0.1320, respectively. The Hosmer-Lemeshow test revealed that this model had good calibration. The clinical knowledge-driven model demonstrated satisfactory C-statistics during external and internal validation, with values of 0.890 (0.815-0.965) and 0.854 (0.820-0.900), respectively. A risk score for ARF incidence was created: The A2-BEST2 Risk Score (A2 (area of pulmonary infection, albumin), BMI, Economic condition, Smoking, and T2(hormone initiation Time and long-term regular medication Treatment)). ARF incidence increased gradually from 1.37% (The A2-BEST2 Risk Score ≤ 4) to 90.32% (A2-BEST2 Risk Score ≥ 11.5).

Conclusion

We constructed a predictive model of seven predictors to predict ARF in BA patients. This predictor's model is simple, practical, and supported by existing clinical knowledge.

Anesthesia Machine and New Modes of Ventilation

Mechanical ventilation is ubiquitous in the operating room. This article explores the anesthesia machine as a ventilator, examining its unique features and differences from ventilators designed for long-term use. It will describe standard and nonstandard modes of ventilation. The reader will develop a more nuanced understanding of how to tailor ventilation and oxygenation strategies based on patient and anesthetic scenarios as well as with the assistance of new technologies.

Extracorporeal Membrane Oxygenation (ECMO): A Life Saver in Near-Fatal Asthma

Near-fatal asthma (NFA) is a life-threatening condition that represents the most severe clinical phenotype of asthma and can progress to fatal asthma. Patients with NFA do not respond adequately to conventional medical therapy and urgent intervention is needed to provide adequate oxygenation by invasive mechanical ventilation. While mechanical ventilation is a potentially life-saving intervention, it could cause lung injury, barotrauma, and dynamic hyperinflation due to high ventilator settings resulting in hemodynamic instability. Extracorporeal membrane oxygenation (ECMO) provides full respiratory support with adequate gas exchange in patients with NFA and improves survival rate. We present a case of a young female patient who presented with NFA, and her clinical condition was worsening despite invasive positive pressure mechanical ventilation.

VIVID: In Vivo End-to-End Molecular Communication Model for COVID-19

As an alternative to ongoing efforts for vaccine development, scientists are exploring novel approaches to provide innovative therapeutics, such as nanoparticle- and stem cell-based treatments. Thus, understanding the transmission and propagation dynamics of coronavirus inside the respiratory system has attracted researchers' attention. In this work, we model the transmission and propagation of coronavirus inside the respiratory tract, starting from the nasal area to alveoli using molecular communication theory. We performed experiments using COMSOL, a finite-element multiphysics simulation software, and Python-based simulations to analyze the end-to-end communication model in terms of path loss, delay, and gain. The analytical results show the correlation between the channel characteristics and pathophysiological properties of coronavirus. For the initial 50% of the maximum production rate of virus particles, the path loss increases more than 16 times than the remaining 50%. The delayed response of the immune system and increase in the absorption of virus particles inside the respiratory tract delay the arrival of virus particles at the alveoli. Furthermore, the results reveal that the virus load is more in case of asthmatic patients as compared to the normal subjects.

Difficulty Ventilating: A Case Report on Ventilation Considerations of an Intubated Asthmatic Undergoing Air Medical Critical Care Transport

The air medical transport of intubated patients is a high-risk mission that requires preplanning before helicopter launch. This case describes a scenario in which the helicopter emergency medical services (HEMS) team was unable to ventilate a patient because of the mechanical limitations of the transport ventilator. The HEMS mission was ultimately aborted, and the patient had to be transported by a ground crew equipped with a hospital-based ventilator. In addition to the optimal medical management of the patient in status asthmaticus, critical care transport crews must be familiar with the treatment of patients exhibiting extremely high peak airway pressures. Specifically, ventilator manipulations as well as the technical specifications of the transport ventilator may preclude the patient from being transported by the HEMS team. It is imperative that the patient's current ventilator setting be evaluated before the launch of the aircraft to prevent any possible delays in patient care.

Evaluation and management of the critically ill adult asthmatic in the emergency department setting

INTRODUCTION

Asthma is a common reason for presentation to the Emergency Department and is associated with significant morbidity and mortality. While patients may have a relatively benign course, there is a subset of patients who present in a critical state and require emergent management.

OBJECTIVE

This narrative review provides evidence-based recommendations for the assessment and management of patients with severe asthma.

DISCUSSION

It is important to consider a broad differential diagnosis for the cause and potential mimics of asthma exacerbation. Once the diagnosis is determined, the majority of the assessment is based upon the clinical examination. First line therapies for severe exacerbations include inhaled short-acting beta agonists, inhaled anticholinergics, intravenous steroids, and magnesium. Additional therapies for refractory cases include parenteral epinephrine or terbutaline, helium‑oxygen mixture, and consideration of ketamine. Intravenous fluids should be administered, as many of these patients are dehydrated and at risk for hypotension if they receive positive pressure ventilatory support. Noninvasive positive pressure ventilation may prevent the need for endotracheal intubation. If mechanical ventilation is required, it is important to avoid breath stacking by setting a low respiratory rate and allowing permissive hypercapnia. Patients with severe asthma exacerbations will require intensive care unit admission.

CONCLUSIONS

This review provides evidence-based recommendations for the assessment and management of severe asthma with a focus on the emergency clinician.

Acute Severe Asthma in Adolescent and Adult Patients: Current Perspectives on Assessment and Management

Asthma is a chronic airway inflammatory disease that is associated with variable expiratory flow, variable respiratory symptoms, and exacerbations which sometimes require hospitalization or may be fatal. It is not only patients with severe and poorly controlled asthma that are at risk for an acute severe exacerbation, but this has also been observed in patients with otherwise mild or moderate asthma. This review discusses current aspects on the pathogenesis and pathophysiology of acute severe asthma exacerbations and provides the current perspectives on the management of acute severe asthma attacks in the emergency department and the intensive care unit.

Anesthetic Considerations for Patients Undergoing Bronchial Thermoplasty

Bronchial thermoplasty (BT) is a novel, Food and Drug Administration-approved nondrug treatment for patients whose asthma remains uncontrolled despite traditional pharmacotherapy. BT involves application of controlled radiofrequency energy to reduce airway smooth muscle in large- and medium-sized airways. Although BT is often performed under general anesthesia, anesthetic management strategies for BT are poorly described. We describe the anesthetic management of 7 patients who underwent 19 BT treatments in a tertiary academic medical center.

Acute severe asthma complicated with tension pneumothorax and hemopneumothorax

A 47-year-old patient presented to the emergency room with an attack of acute severe asthma. In spite of all primary measures, the patient was deteriorating. Arterial blood gases showed hypercarbia and acidemia. The patient was shifted to the intensive care unit connected to noninvasive ventilation for 3 h, without any obvious improvement. Decision was taken to intubate, ventilate, and keep her deeply sedated. On the 4^th day of ventilation, the patient developed sudden tension pneumothorax and she was near to arrest. Management for tension pneumothorax was immediate and successful. After that, chest X-ray and computerized tomography scan showed hemopneumothorax, for which a chest tube was inserted in both chest sides and blood transfusion was initiated immediately. After this incidence, the patient's parameters improved dramatically. Four days later, the patient was extubated and kept in intensive care unit till the chest tubes were removed and then shifted to the ward and discharged on day 15 from admission.

Safety and effectiveness of albuterol solutions with and without benzalkonium chloride when administered by continuous nebulization

PURPOSE

The results of a study to determine if rates of poor response differ in patients receiving continuous nebulized albuterol (CNA) therapy with or without the preservative benzalkonium chloride are presented.

METHODS

A retrospective analysis of the records of all patients who received CNA therapy at a large academic medical center from July 2015 to January 2016 was conducted. Data from patient evaluations performed before and after a change to benzalkonium chloride-containing albuterol were collected. The primary outcome was the rate of poor patient response, defined as a composite endpoint. Secondary outcomes included duration of therapy, dosing requirements, and duration of supplemental oxygen therapy.

RESULTS

There was no significant difference in rates of poor response between patients exposed (n = 80) and patients not exposed (n = 48) to benzalkonium chloride (16% and 17%, respectively; p = 0.95). The cohort not exposed to benzalkonium chloride had a median CNA duration of 7.0 hours, as compared with 10.5 hours for the cohort exposed to benzalkonium chloride, but this difference was not significant (p = 0.19). There were no significant differences between the benzalkonium chloride-exposed and nonexposed cohorts in the maximum dosing requirement (12.6 mg/hr versus 12.8 mg/hr, p = 0.89) or median duration of supplemental oxygen use (27.5 hours versus 16.5 hours, p = 0.77).

CONCLUSION

A study of hospitalized patients receiving CNA detected no significant difference in the frequency of poor response to therapy between groups receiving benzalkonium chloride-free versus benzalkonium chloride-containing albuterol products.

Inhalation Techniques Used in Patients with Respiratory Failure Treated with Noninvasive Mechanical Ventilation

The administration of aerosolized medication is a basic therapy for patients with numerous respiratory tract diseases, including obstructive airway diseases (OADs), cystic fibrosis (CF), and infectious airway diseases. The management and care for patients requiring mechanical ventilation remains one of the greatest challenges for medical practitioners, both in intensive care units (ICUs) and pulmonology wards. Aerosol therapy is often necessary for patients receiving noninvasive ventilation (NIV), which may be stopped for the time of drug delivery and administered through a metered-dose inhaler or nebulizer in the traditional way. However, in most severe cases, this may result in rapid deterioration of the patient's clinical condition. Unfortunately, only limited number of original well-planned studies addressed this problem. Due to inconsistent information coming from small studies, there is a need for more precise data coming from large prospective real life studies on inhalation techniques in patients receiving NIV.

Mechanically Ventilating the Severe Asthmatic

The management of the critically ill patients with asthma can be rather challenging. Potentially devastating complications relating to this presentation include hypoxemia, worsening bronchospasm, pulmonary aspiration, tension pneumothorax, dynamic hyperinflation, hypotension, dysrhythmias, and seizures. In contrast to various other pathologies requiring mechanical ventilation, acute asthma is generally associated with better outcomes. This review serves as a practical guide to the physician managing patients with severe acute asthma requiring mechanical ventilation. In addition to specifics relating to endotracheal intubation, we also discuss the interpretation of ventilator graphics, the recommended mode of ventilation, dynamic hyperinflation, permissive hypercapnia, as well as the role of extracorporeal membrane oxygenation and noninvasive mechanical ventilation.

Recommendations for mechanical ventilation of critically ill children from the Paediatric Mechanical Ventilation Consensus Conference (PEMVECC)

Purpose

Much of the common practice in paediatric mechanical ventilation is based on personal experiences and what paediatric critical care practitioners have adopted from adult and neonatal experience. This presents a barrier to planning and interpretation of clinical trials on the use of specific and targeted interventions. We aim to establish a European consensus guideline on mechanical ventilation of critically children.

Methods

The European Society for Paediatric and Neonatal Intensive Care initiated a consensus conference of international European experts in paediatric mechanical ventilation to provide recommendations using the Research and Development/University of California, Los Angeles, appropriateness method. An electronic literature search in PubMed and EMBASE was performed using a combination of medical subject heading terms and text words related to mechanical ventilation and disease-specific terms.

Results

The Paediatric Mechanical Ventilation Consensus Conference (PEMVECC) consisted of a panel of 15 experts who developed and voted on 152 recommendations related to the following topics: (1) general recommendations, (2) monitoring, (3) targets of oxygenation and ventilation, (4) supportive measures, (5) weaning and extubation readiness, (6) normal lungs, (7) obstructive diseases, (8) restrictive diseases, (9) mixed diseases, (10) chronically ventilated patients, (11) cardiac patients and (12) lung hypoplasia syndromes. There were 142 (93.4%) recommendations with “strong agreement”. The final iteration of the recommendations had none with equipoise or disagreement.

Conclusions

These recommendations should help to harmonise the approach to paediatric mechanical ventilation and can be proposed as a standard-of-care applicable in daily clinical practice and clinical research.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-017-4920-z) contains supplementary material, which is available to authorized users.

A comparison of synchronized intermittent mandatory ventilation and pressure-regulated volume control ventilation in elderly patients with acute exacerbations of COPD and respiratory failure

BACKGROUND

COPD is the third leading cause of death worldwide. Acute exacerbations of COPD may cause respiratory failure, requiring intensive care unit admission and mechanical ventilation. Intensive care unit patients with acute exacerbations of COPD requiring mechanical ventilation have higher mortality rates than other hospitalized patients. Although mechanical ventilation is the most effective intervention for these conditions, invasive ventilation techniques have yielded variable effects.

OBJECTIVE

We evaluated pressure-regulated volume control (PRVC) ventilation treatment efficacy and preventive effects on pulmonary barotrauma in elderly COPD patients with respiratory failure.

PATIENTS AND METHODS

Thirty-nine intubated patients were divided into experimental and control groups and treated with the PRVC and synchronized intermittent mandatory ventilation - volume control methods, respectively. Vital signs, respiratory mechanics, and arterial blood gas analyses were monitored for 2-4 hours and 48 hours.

RESULTS

Both groups showed rapidly improved pH, partial pressure of oxygen (PaO2), and PaO2 per fraction of inspired O2 levels and lower partial pressure of carbon dioxide (PaCO2) levels. The pH and PaCO2 levels at 2-4 hours were lower and higher, respectively, in the test group than those in the control group (P<0.05 for both); after 48 hours, blood gas analyses showed no statistical difference in any marker (P>0.05). Vital signs during 2-4 hours and 48 hours of treatment showed no statistical difference in either group (P>0.05). The level of peak inspiratory pressure in the experimental group after mechanical ventilation for 2-4 hours and 48 hours was significantly lower than that in the control group (P<0.05), while other variables were not significantly different between groups (P>0.05).

CONCLUSION

Among elderly COPD patients with respiratory failure, application of PRVC resulted in rapid improvement in arterial blood gas analyses while maintaining a low peak inspiratory pressure. PRVC can reduce pulmonary barotrauma risk, making it a safer protective ventilation mode than synchronized intermittent mandatory ventilation - volume control.

Brazilian recommendations of mechanical ventilation 2013. Part I

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumonia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Mechanical ventilation for severe asthma

Acute exacerbations of asthma can lead to respiratory failure requiring ventilatory assistance. Noninvasive ventilation may prevent the need for endotracheal intubation in selected patients. For patients who are intubated and undergo mechanical ventilation, a strategy that prioritizes avoidance of ventilator-related complications over correction of hypercapnia was first proposed 30 years ago and has become the preferred approach. Excessive pulmonary hyperinflation is a major cause of hypotension and barotrauma. An appreciation of the key determinants of hyperinflation is essential to rational ventilator management. Standard therapy for patients with asthma undergoing mechanical ventilation consists of inhaled bronchodilators, corticosteroids, and drugs used to facilitate controlled hypoventilation. Nonconventional interventions such as heliox, general anesthesia, bronchoscopy, and extracorporeal life support have also been advocated for patients with fulminant asthma but are rarely necessary. Immediate mortality for patients who are mechanically ventilated for acute severe asthma is very low and is often associated with out-of-hospital cardiorespiratory arrest before intubation. However, patients who have been intubated for severe asthma are at increased risk for death from subsequent exacerbations and must be managed accordingly in the outpatient setting.

Brazilian recommendations of mechanical ventilation 2013. Part I

Perspectives on invasive and noninvasive ventilatory support for critically ill patients are evolving, as much evidence indicates that ventilation may have positive effects on patient survival and the quality of the care provided in intensive care units in Brazil. For those reasons, the Brazilian Association of Intensive Care Medicine (Associação de Medicina Intensiva Brasileira - AMIB) and the Brazilian Thoracic Society (Sociedade Brasileira de Pneumologia e Tisiologia - SBPT), represented by the Mechanical Ventilation Committee and the Commission of Intensive Therapy, respectively, decided to review the literature and draft recommendations for mechanical ventilation with the goal of creating a document for bedside guidance as to the best practices on mechanical ventilation available to their members. The document was based on the available evidence regarding 29 subtopics selected as the most relevant for the subject of interest. The project was developed in several stages, during which the selected topics were distributed among experts recommended by both societies with recent publications on the subject of interest and/or significant teaching and research activity in the field of mechanical ventilation in Brazil. The experts were divided into pairs that were charged with performing a thorough review of the international literature on each topic. All the experts met at the Forum on Mechanical Ventilation, which was held at the headquarters of AMIB in São Paulo on August 3 and 4, 2013, to collaboratively draft the final text corresponding to each sub-topic, which was presented to, appraised, discussed and approved in a plenary session that included all 58 participants and aimed to create the final document.

Development of learning objectives and a validated testing tool for management of pediatric mechanical ventilation*

OBJECTIVES

Graduate medical education is shifting toward an outcome-based paradigm, where physicians are evaluated for competency using well-defined criteria. Our aim was to learning objectives and a testing tool to assess competency in the management of mechanical ventilation for infants, children, and adolescents and to verify that the test was reliable and valid.

DESIGN

Prospective reliability and validity study.

SETTING

Large, university-affiliated academic hospital.

SUBJECTS

Sixty-one total subjects from five different academic centers divided into three groups of varying experience. The groups were second- and third-year pediatric residents (Novice), second- and third-year pediatric critical care fellows (Advanced), and pediatric critical care faculty (Expert).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Ten learning objectives considered important for the management of pediatric mechanical ventilation were developed from expert opinion and current evidence. Based on these objectives, a 35-question multiple choice, knowledge- and case-based test was created. Content validity was achieved by consensus of three experts in pediatric critical care medicine evaluating whether the questions reflected the learning objectives and the responses were consistent with current practice and evidence-based medicine. The test was then administered to the three groups to establish construct validity. The "Novice" group scored a mean of 34.6% (95% CI, 28-41%), the "Advanced" group a mean of 59.4% (95% CI, 53-65%), and the "Expert" group a mean of 74.8% (95% CI, 69-80%), with p less than 0.01 for all comparisons. As determined by Hoyt's analysis, the reliability coefficient was 0.89, reflecting excellent reliability.

CONCLUSIONS

This is the first description of specific learning objectives for management of pediatric mechanical ventilation and the first validated and reliable testing tool for assessing knowledge. This tool could be used by fellowship programs to assess fellow competency and identify knowledge gaps in this area prior to completion of training. Further work must be done to determine the criteria for determination of competency.

Is pressure-regulated volume control mode appropriate for severely obstructed patients?

PURPOSE

Management of mechanical ventilation in severely obstructed patients remains controversial. Pressure-regulated volume control ventilation (PRVCV) has been suggested to be the best option, as it should ensure a prefixed tidal volume at the lowest peak inspiratory pressure. We sought to determine the accuracy of the delivered volume, compared with the programmed volume, when using PRVCV.

MATERIALS AND METHODS

Experimental work performing ventilation simulations using volume control ventilation (VCV), PRVCV, and pressure control ventilation (PCV). Each mode was tested at tidal volumes (TVs) of 200 and 500 mL at both low and high airway resistance. Evita XL and Servo-i ventilators were used.

RESULTS

At 200 ml TV with high resistance, volume delivered with Evita XL was 165 mL (95% confidence interval, 158-169) in VCV, 117 mL (95% confidence interval, 117-120) in PCV, and 120 (95% confidence interval, 115-121) in PRVCV (P<.001). Volume delivered with Servo-i was 133 mL (95% confidence interval, 130-136) in VCV, 108 mL (95% confidence interval, 104-111) in PCV, and 104 (95% confidence interval, 101-108) in PRVCV (P<.001).

CONCLUSIONS

In high-resistance simulations, the delivered volume was lower when using PCV or PRVCV modes than VCV mode. Pressure control ventilation or PRVCV may fail to provide programmed TV, ultimately leading to hypoventilation of the patient.

Acute respiratory failure

Acute respiratory failure is common in critically ill children, who are at increased risk of respiratory embarrassment because of the developmental variations in the respiratory system. Although multiple etiologies exist, pneumonia and bronchiolitis are most common. Respiratory system monitoring has evolved, with the clinical examination remaining paramount. Invasive tests are commonly replaced with noninvasive monitors. Children with ALI/ARDS have better overall outcomes than adults, although data regarding specific therapies are still lacking. Most children will have some degree of long-term physiologic respiratory compromise after recovery from ALI/ARDS. The physiologic basis for respiratory failure and its therapeutic options are reviewed here.

Medical emergencies: pulmonary embolism and acute severe asthma

In this, the second of two articles covering specific medical emergencies, we discuss the definitions, epidemiology, pathophysiology, acute and chronic management of pulmonary embolus and acute severe asthma.

Human versus Computer Controlled Selection of Ventilator Settings: An Evaluation of Adaptive Support Ventilation and Mid-Frequency Ventilation

Background. There are modes of mechanical ventilation that can select ventilator settings with computer controlled algorithms (targeting schemes). Two examples are adaptive support ventilation (ASV) and mid-frequency ventilation (MFV). We studied how different clinician-chosen ventilator settings are from these computer algorithms under different scenarios. Methods. A survey of critical care clinicians provided reference ventilator settings for a 70 kg paralyzed patient in five clinical/physiological scenarios. The survey-derived values for minute ventilation and minute alveolar ventilation were used as goals for ASV and MFV, respectively. A lung simulator programmed with each scenario's respiratory system characteristics was ventilated using the clinician, ASV, and MFV settings. Results. Tidal volumes ranged from 6.1 to 8.3 mL/kg for the clinician, 6.7 to 11.9 mL/kg for ASV, and 3.5 to 9.9 mL/kg for MFV. Inspiratory pressures were lower for ASV and MFV. Clinician-selected tidal volumes were similar to the ASV settings for all scenarios except for asthma, in which the tidal volumes were larger for ASV and MFV. MFV delivered the same alveolar minute ventilation with higher end expiratory and lower end inspiratory volumes. Conclusions. There are differences and similarities among initial ventilator settings selected by humans and computers for various clinical scenarios. The ventilation outcomes are the result of the lung physiological characteristics and their interaction with the targeting scheme.

Beyond the guidelines: fatal and near-fatal asthma

While asthma is extremely common, fatal and near fatal asthma is rare and often preventable if there is early recognition of symptom progression and appropriate intervention. In the past decade, asthma mortality has progressively declined in association with the widespread use of inhaled corticosteroids and asthma care plans. Management of life threatening asthma requires patient education to ensure the proper use of medications and to enable the patient to recognize when additional therapy for poorly controlled asthma is required. There is some evidence that suggests that the overly aggressive use of asthma medications when treating a severe exacerbation may contribute to morbidity. Because of the risks of air trapping and barotrauma associated with partial airway obstruction, it is best to avoid mechanical ventilation if possible but when this is used, low tidal volumes, longer exhalation times, and permissive hypercarbia can minimize these risks. There is the promise that a better understanding of asthma immunology and severe asthma "phenotypes" will lead to better prevention and therapy.

Severe Asthma

Despite vast improvements in the care of children with asthma over the past decades, asthma remains a common cause of admission to pediatric intensive care units. During the 1990s asthma prevalence and hospital admissions increased in the United States and worldwide. The increase occurred in both males and females and across all ethnic groups. However, the largest increases occurred in children of low socioeconomic status living in urban settings. Recent asthma statistics should be interpreted with consideration of changes made in the method for reporting asthma prevalence (Fig. 23-1). From 1980 to 1996, the National Health Interview Survey (NHIS) conducted by the CDC measured pediatric asthma prevalence as the percentage of children with asthma in the past 12 months. Since 1997, asthma prevalence estimates have been defined as: having received an asthma diagnosis, currently having the disease at the time of the interview, and experiencing an attack in the past year. The more specific definition may have led to a reduction in the number of children reported to have asthma.

Management of severe asthma exacerbation in children

BACKGROUND

Asthma is a common disease in children and acute severe asthma exacerbation can be life-threatening. This article aims to review recent advances in understanding of risk factors, pathophysiology, diagnosis and treatment of severe asthma exacerbation in children.

DATA SOURCES

Articles concerning severe asthma exacerbation in children were retrieved from PubMed. Literatures were searched with MeSH words "asthma", "children", "severe asthma exacerbation" and relevant cross references.

RESULTS

Severe asthma exacerbation in children requires aggressive treatments with β2-agonists, anticholinergics, and corticosteroids. Early initiation of inhaled β-agonists and systemic use of steroids are recommended. Other agents such as magnesium and aminophylline have some therapeutic benefits. When intubation and mechanical ventilation are needed, low tidal volume, controlled hypoventilation with lower-than-traditional respiratory rates and permissive hypercapnia can be applied.

CONCLUSIONS

Researchers should continue to detect the risk factors, pathophysiology, diagnosis and treatment of severe asthma exacerbation in children. More studies especially randomized controlled trials are required to evaluate the efficacy and safety of standard and new therapies.

Acute lung failure

Lung failure is the most common organ failure seen in the intensive care unit. The pathogenesis of acute respiratory failure (ARF) can be classified as (1) neuromuscular in origin, (2) secondary to acute and chronic obstructive airway diseases, (3) alveolar processes such as cardiogenic and noncardiogenic pulmonary edema and pneumonia, and (4) vascular diseases such as acute or chronic pulmonary embolism. This article reviews the more common causes of ARF from each group, including the pathological mechanisms and the principles of critical care management, focusing on the supportive, specific, and adjunctive therapies for each condition.

Analytic review: management of life-threatening asthma in adults

Asthma remains a troubling health problem despite the availability of effective treatment. A small but significant number of asthmatics experience life-threatening attacks culminating in intensive care unit admission. Standard treatment includes high dose systemic corticosteroids and inhaled bronchodilators. Patients with especially severe attacks may develop respiratory failure and need endotracheal intubation and mechanical ventilation. Severe airway obstruction may lead to dynamic hyperinflation and the possibility of hemodynamic collapse and barotrauma. Fortunately, most intubated asthmatics survive if physicians adhere to key management principles intended to avoid or minimize hyperinflation. The purpose of this review is to discuss the pathogenesis of life-threatening asthma and to provide practical guidance to promote rationale, safe, and effective management.

The use of non-invasive ventilation for life-threatening asthma attacks: Changes in the need for intubation

BACKGROUND AND OBJECTIVE

Although non-invasive ventilation (NIV) has been shown to be effective in a wide variety of respiratory diseases, its role in severe asthma attacks remains uncertain. The aim of this study was to clarify the effectiveness of NIV in patients experiencing severe attacks of asthma.

METHODS

A retrospective cohort study was performed, comparing the periods November 1999-October 2003 (pre-introduction of NIV) and November 2004-October 2008 (post-introduction of NIV). The data and clinical outcomes for patients who experienced severe attacks of asthma, and who fulfilled the inclusion criteria, were retrieved and compared.

RESULTS

Fifty events (48 patients) from the pre-NIV period and 57 events (54 patients) from the post-NIV period, which required hospitalization, were included in the analysis. Nine of the 50 pre-NIV events (mean PaO(2)/fraction of inspired O(2) (FiO(2)) 241 +/- 161; PaCO(2) 79 +/- 40) were treated primarily by endotracheal intubation (ETI), while 17 of the 57 post-NIV events (PaO(2)/FiO(2) 197 +/- 132, P = 0.39; PaCO(2) 77 +/- 30, P = 0.95) were treated primarily by NIV. The rate of ETI decreased in the post-NIV period (2/57 (3.5%) vs 9/50 (18%), P = 0.01). NIV was started earlier than mechanical ventilation (MV) with ETI (mean time interval between arrival and start of MV 171.7 +/- 217.9 min vs 38.5 +/- 113.8 min for NIV, P < 0.05). In the post-NIV cohort, there was a trend towards a reduction in the duration of MV with ETI or NIV (36.9 +/- 38.4 h vs 20.3 +/- 35.8 h, P = 0.09), and hospital stay was shortened (12.6 +/- 4.2 vs 8.4 +/- 2.8 days, P < 0.01). No deaths occurred during this period as a consequence of asthma attacks.

CONCLUSIONS

The need for ETI in patients with severe attacks of asthma was decreased after introduction of NIV. The ready availability of NIV enabled the rapid commencement of MV and may decrease the need for ETI. NIV is an acceptable and useful method of stabilizing patients experiencing severe attacks of asthma.

Noninvasive ventilation and low-flow veno-venous extracorporeal carbon dioxide removal as a bridge to lung transplantation in a child with refractory hypercapnic respiratory failure due to bronchiolitis obliterans

OBJECTIVE

To report the successful management of end-stage hypercapnic respiratory failure through the association of noninvasive mechanical ventilation and a novel automated device (Decapsmart) of low-flow veno-venous extracorporeal CO2 removal.

DESIGN

Case report.

SETTINGS

Pediatric intensive care unit at a tertiary care children's hospital.

PATIENT

A pediatric patient affected by bronchiolitis obliterans with refractory hypercapnic respiratory failure. The patient received successful lung transplantation after respiratory support with noninvasive mechanical ventilation and a novel automated device of low-flow veno-venous extracorporeal CO2 removal.

INTERVENTIONS

Treatment of end-stage hypercapnic respiratory failure with the association of noninvasive ventilation and low-flow veno-venous extracorporeal CO2 removal as a bridge to lung transplantation.

MEASUREMENTS AND MAIN RESULTS

Respiratory support controlling hypercapnia, limiting volutrauma, barotraumas, and preventing the incidence of ventilator-associated pneumonia/lung colonization.

CONCLUSION

Noninvasive mechanical ventilation and Decapsmart have proven efficacious in managing refractory hypercapnic respiratory failure in a pediatric patient awaiting lung transplantation.

Review article: management of acute severe and near-fatal asthma

Despite a decline in the Australian overall asthma mortality, near-fatal/critical asthma continues to be a significant management issue for emergency physicians and intensivists. Near-fatal asthma is a unique subtype of asthma, with a variety of clinical presentations, requiring rapid and aggressive intervention. The pharmacological and non-pharmacological management of near-fatal asthma remains very complex. The present review discusses recent advances and evidence for current available strategies targeting this time critical emergency.

Reversal of bronchial obstruction with bi-level positive airway pressure and nebulization in patients with acute asthma

Jet nebulization (JN) and non-invasive mechanical ventilation (NIMV) through bi-level pressure is commonly used in emergency and intensive care of patients experiencing an acute exacerbation of asthma. However, a scientific basis for effect of JN coupled with NIMV is unclear. Objective. To evaluate the effect of jet nebulization administered during spontaneous breathing with that of nebulization with NIV at two levels of inspiratory and expiratory pressures resistance in patients experiencing an acute asthmatic episode. Methods. A prospective, randomized controlled study of 36 patients with severe asthma (forced expiratory volume in 1 second [FEV(1)] less than 60% of predicted) selected with a sample of patients who presented to the emergency department. Subjects were randomized into three groups: control group (nebulization with the use of an unpressured mask), experimental group 1 (nebulization and non-invasive positive pressure with inspiratory positive airway pressure [IPAP] = 15 cm H(2)O, and expiratory positive airway pressure [EPAP] = 5 cm H(2)O), and experimental group 2 (nebulization and non-invasive positive pressure with IPAP = 15 cm H(2)O and EPAP = 10 cm H(2)O). Bronchodilators were administered with JN for all groups. Dependent measures were recorded before and after 30 minutes of each intervention and included respiratory rate (RR), heart rate (HR), oxygen saturation (SpO(2)), peak expiratory flow (PEF), forced expiratory volume in 1 second (FEV(1)), forced vital capacity (FVC), and forced expiratory flow between 25 and 75% (FEF(25-75)). Results. The group E2 showed an increase of the peak expiratory flow (PEF), forced vital capacity (FVC), FEV(1) (p < 0.03) and F(25-75%) (p < 0.000) when compared before and 30 minutes after JN+NIMV. In group E1 the PFE (p < 0.000) reached a significant increase after JN+ NIMV. RR decreased before and after treatment in group E1 only (p = 0.04). Conclusion. Nebulization coupled with NIV in patients with acute asthma has the potential to reduce bronchial obstruction and symptoms secondary to augmented PEF compared with nebulization during spontaneous breathing. In reversing bronchial obstruction, this combination appears to be more efficacious when a low pressure delta is used in combination with a high positive pressure at the end of expiration.

Intravenous ketamine in a dissociating dose as a temporizing measure to avoid mechanical ventilation in adult patient with severe asthma exacerbation

BACKGROUND

Patients experiencing severe asthma exacerbations occasionally deteriorate to respiratory failure requiring endotracheal intubation and mechanical ventilation. Mechanical ventilation in this setting exposes the patients to substantial iatrogenic risk and should be avoided if at all possible.

OBJECTIVES

To describe the use of intravenous ketamine in acute asthma exacerbation.

CASE REPORT

We present a case of severe asthma exacerbation in an adult female patient who failed to improve with standard therapies, but promptly improved with the administration of intravenous ketamine (0.75 mg/kg i.v. bolus followed by continuous drip of 0.15 mg/kg/h).

SUMMARY

This case suggests that intravenous ketamine given in a dissociative dose may be an effective temporizing measure to avoid mechanical ventilation in adult patients with severe asthma exacerbations.