The pulmonary physician in critical care . 12: Acute severe asthma in the intensive care unit

Effects of Pre-Hospital Dexamethasone Administration on Outcomes of Patients with COPD and Asthma Exacerbation; a Cross-Sectional Study

Introduction

Chronic obstructive pulmonary disease (COPD) and asthma exacerbation are two common emergency situations. This study aimed to investigate the impact of pre-hospital dexamethasone initiation on treatment outcomes of these patients.

Methods

In this retrospective cross-sectional and comparative study, data from the emergency medical service (EMS) care report of patients with a final diagnosis of asthma or COPD, coded with Thailand's emergency medical triage protocol, collected between January 1, 2021, and October 31, 2022, were used. Data on baseline characteristics, emergency department length of stay (ED-LOS), and hospital admission rates were collected from electronic medical records and compared between cases with and without pre-hospital dexamethasone administration by EMS.

Results

200 patients with COPD (n = 93) and asthma (n = 107) exacerbation were enrolled. The dexamethasone-treated group had a lower but statistically non-significant hospital admission rate (71.0% versus 81.0%, absolute difference: -10%, 95% confidence interval (CI): -21.76, 1.76; p = 0.100). In patients with asthma, the dexamethasone-treated had lower median ED-LOS time (235 (IQR: 165.5-349.5) versus 322 (IQR: 238-404) minutes; p = 0.003). Dexamethasone-treated asthma patients had lower but statistically non-significant hospital admission rates (60.4% versus 78.0%, absolute difference: -17.55%, 95% CI: -34.96, -0.14; p = 0.510). In COPD patients the dexamethasone-treated and untreated groups had non-significantly lower hospital admission rates (80.8% versus 85.40%, absolute difference: -4.60%, 95% CI: -19.82, 10.63; p = 0.561) and non-significantly lower ED-LOS (232 (IQR: 150 - 346) versus 296 (IQR: 212 - 330) minutes, absolute difference: -59 (-130.81, 12.81); p = 0.106).

Conclusion

The dexamethasone administration by EMS in pre-hospital setting for management of asthma and COPD patients is beneficial in reducing the ED-LOS and need for hospital admission but its effects are not statistically significant, except regarding the ED-LOS of asthma exacerbation cases.

Multidrug Aerosol Delivery During Mechanical Ventilation

Background: In the critically ill, pulmonary vasodilators are often provided off label to intubated patients using continuous nebulization. If additional aerosol therapies such as bronchodilators or antibiotics are needed, vasodilator therapy may be interrupted. This study assesses aerosol systems designed for simultaneous delivery of two aerosols using continuous nebulization and bolus injection without interruption or circuit disconnection. Methods: One i-AIRE dual-port breath-enhanced jet nebulizer (BEJN) or two Aerogen® Solo vibrating mesh nebulizers (VMNs) were installed on the dry side of the humidifier. VMN were stacked; one for infusion and the second for bolus drug delivery. The BEJN was powered by air at 3.5 L/min, 50 psig. Radiolabeled saline was infused at 5 and 10 mL/h with radiolabeled 3 and 6 mL bolus injections at 30 and 120 minutes, respectively. Two adult breathing patterns (duty cycle 0.13 and 0.34) were tested with an infusion time of 4 hours. Inhaled mass (IM) expressed as % of initial syringe activity (IM%/min) was monitored in real time with a ratemeter. All delivered radioaerosol was collected on a filter at the airway opening. Transients in aerosol delivery were measured by calibrated ratemeter. Results: IM%/h during continuous infusion was linear and predictable, mean ± standard deviation (SD): 2.12 ± 1.45%/h, 2.47 ± 0.863%/h for BEJN and VMN, respectively. BEJN functioned without incident. VMN continuous aerosol delivery stopped spontaneously in 3 of 8 runs (38%); bolus delivery stopped spontaneously in 3 of 16 runs (19%). Tapping restarted VMN function during continuous and bolus delivery runs. Bolus delivery IM% (mean ± SD): 20.90% ± 7.01%, 30.40% ± 11.10% for BEJN and VMN, respectively. Conclusion: Simultaneous continuous and bolus nebulization without circuit disconnection is possible for both jet and mesh technology. Monitoring of VMN devices may be necessary in case of spontaneous interruption of nebulization.

Change in capnogram waveform is associated with bronchodilator response and asthma control in children

BACKGROUND

Airway hyper-reactivity, inflammation and remodeling contribute to inhomogeneity of ventilation-perfusion ratio VA·/Q· in asthma. Short-term variations in V.A/Q· can cause changes in expired capnographic indices.

OBJECTIVES

To measure acute changes in the phase 3 slope of the volumetric capnogram after β2-agonist inhalation (ΔSIII), for comparison with airway response based on FEV1 (ΔFEV1), and asthma control.

SUBJECTS AND METHODS

After ethical approval and informed consent, 72 children aged 6-18 y, followed up for asthma underwent spirometry and capnography before and after β-agonist inhalation through a spacer, using a side-stream rapid infrared analyzer. Asthma control was assessed using the GINA questionnaire.

RESULTS

Children with positive reversibility tests (defined as ΔFEV1>12%) had a significantly higher ΔSIII (m ± SE: 87.4 ± 41.4) versus those with negative tests (31.3 ± 14.0%, P = 0.001). Uncontrolled asthma was associated with a significantly larger ΔSIII (103.4 ± 64.0%, n = 7) compared to partly controlled (52.0 ± 26.1, n = 24; P = 0.009) and controlled asthma (30.8 ± 16.3, n = 41; P = 0.003). Neither Bohr dead space nor ΔFEV1 were different between asthma control groups.

CONCLUSIONS

ΔSIII was significantly larger in children with positive response to β2-agonist, and in uncontrolled asthmatics. To our knowledge these are the first data on exhaled CO₂ phase III volumetric slope change and asthma control. The observed ΔSIII could be due to an increased ventilation of inhomogeneous peripheral lung units, and merits further evaluation as a potential phenotypic biomarker in asthma.

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.

Emergency endotracheal intubation-related adverse events in bronchial asthma exacerbation: can anesthesiologists attenuate the risk?

PURPOSE

Airway management in severe bronchial asthma exacerbation (BAE) carries very high risk and should be performed by experienced providers. However, no objective data are available on the association between the laryngoscopist's specialty and endotracheal intubation (ETI)-related adverse events in patients with severe bronchial asthma. In this paper, we compare emergency ETI-related adverse events in patients with severe BAE between anesthesiologists and other specialists.

METHODS

This historical cohort study was conducted at a Japanese teaching hospital. We analyzed all BAE patients who underwent ETI in our emergency department from January 2002 to January 2014. Primary exposure was the specialty of the first laryngoscopist (anesthesiologist vs. other specialist). The primary outcome measure was the occurrence of an ETI-related adverse event, including severe bronchospasm after laryngoscopy, hypoxemia, regurgitation, unrecognized esophageal intubation, and ventricular tachycardia.

RESULTS

Of 39 patients, 21 (53.8 %) were intubated by an anesthesiologist and 18 (46.2 %) by other specialists. Crude analysis revealed that ETI performed by an anesthesiologist was significantly associated with attenuated risk of ETI-related adverse events [odds ratio (OR) 0.090, 95 % confidence interval (CI) 0.020-0.41, p = 0.001]. The benefit of attenuated risk remained significant after adjusting for potential confounders, including Glasgow Coma Score, age, and use of a neuromuscular blocking agent (OR 0.058, 95 % CI 0.010-0.35, p = 0.0020).

CONCLUSIONS

Anesthesiologist as first exposure was independently associated with attenuated risk of ETI-related adverse events in patients with severe BAE. The skill and knowledge of anesthesiologists should be applied to high-risk airway management whenever possible.

Sevoflurane therapy for life-threatening acute severe asthma: a case report

INTRODUCTION

Acute severe asthma is a life-threatening form of bronchial constriction in which the progressively worsening airway obstruction is unresponsive to the usual appropriate bronchodilator therapy. Pathophysiological changes restrict airflow, which leads to premature closure of the airway on expiration, impaired gas exchange, and dynamic hyperinflation ("air-trapping"). Additionally, patients suffering from asthma for a prolonged period of time usually have serious comorbidities. These conditions constitute a challenge during the treatment of this disease. Therapeutic interventions are designed to reduce airway resistance and improve respiratory status. To achieve therapeutic goals, appropriate bronchodilator treatment is indispensable, and mechanical ventilation under adequate sedation may also be required. The volatile anesthetic agent, sevoflurane, meets both criteria; therefore, its use can be beneficial and should be considered.

CASE PRESENTATION

A 67-yr-old Caucasian male presented with acute life-threatening asthma provoked by an assumed upper airway infection and non-steroidal anti-inflammatory drug antipyretics, complicated by chronic atrial fibrillation and hemodynamic instability. Due to frequent premature ventricular contractions, conventional treatment was considered unsafe and discontinued, and sevoflurane inhalation was initiated via the AnaConDa (Anaesthetic Conserving Device). Symptoms of life-threatening bronchospasm resolved, and the patient's respiratory status improved within hours. Adequate sedation was also achieved without any hemodynamic adverse effects.

CONCLUSION

The volatile anesthetic agent, sevoflurane, is used widely in anesthesia practice. Its utility for treatment of refractory bronchospasm has been appreciated for years; however, its administration was difficult within the environment of the intensive care unit due to the need for an anesthesia machine and a scavenging system. The introduction of the AnaConDa eliminates these obstacles and makes the use of sevoflurane safe and simple. Our case report reveals the potential of sevoflurane as a "two-in-one" (bronchodilator and sedative) drug to treat a severe acute asthma attack.

Association of center volume with outcomes in critically ill children with acute asthma

BACKGROUND

Little is known about the relation between center volume and outcomes in children requiring intensive care unit (ICU) admission for acute asthma.

OBJECTIVE

To evaluate the association of center volume with the odds of receiving positive pressure ventilation and length of ICU stay.

METHODS

Patients 2 to 18 years of age with the primary diagnosis of asthma were included (2009-2012). Center volume was defined as the average number of mechanical ventilator cases per year for any diagnoses during the study period. In multivariable analysis, the odds of receiving positive pressure ventilation (invasive and noninvasive ventilation) and ICU length of stay were evaluated as a function of center volume.

RESULTS

Fifteen thousand eighty-three patients from 103 pediatric ICUs with the primary diagnosis of acute asthma met the inclusion criteria. Seven hundred fifty-two patients (5%) received conventional mechanical ventilation and 964 patients (6%) received noninvasive ventilation. In multivariable analysis, center volume was not associated with the odds of receiving any form of positive pressure ventilation in children with acute asthma, with the exception of high- to medium-volume centers. However, ICU length of stay varied with center volume and was noted to be longer in low-volume centers compared with medium- and high-volume centers.

CONCLUSION

In children with acute asthma, this study establishes a relation between center volume and ICU length of stay. However, this study fails to show any significant relation between center volume and the odds of receiving positive pressure ventilation; further analyses are needed to evaluate this relation in more detail.

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.

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.

Factors associated with the development of severe asthma exacerbations in children

BACKGROUND

Asthma exacerbations are one of the most common causes of hospitalization in children and account for approximately 10,000 intensive care unit (ICU) admissions per year in the United States. Despite the prevalence of this disease in children, the factors associated with the development of these severe exacerbations are largely unknown.

METHODS

A retrospective case-control study was conducted involving all eligible children admitted to the hospital with asthma for a 1-year period. Potential associated factors and outcomes of children admitted to the ICU with a severe exacerbation (cases) were compared to those of children with acute asthma admitted to the ward (controls).

RESULTS

A total of 188 children were hospitalized with asthma during the study period, 57 (30%) of whom required admission to the ICU. There were no differences in age, gender, or race between cases and controls. Children admitted to the ICU were significantly more likely to have an allergy or irritant-triggered exacerbation than children admitted to the ward (OR 3.9; 95% CI 1.9-8.2; p = .0003). Additionally, children in the ICU had a significantly shorter duration of illness before being admitted to the hospital compared to those admitted to the ward (1.7 ± 2.3 vs. 3.4 ± 4.8 days; p = .002).

CONCLUSIONS

In this retrospective review, severe asthma exacerbations in children are associated with a more rapid onset of symptoms and are more likely to be associated with allergens or irritants, supporting the importance of atopy in this population.

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.

Pulmonary periarterial inflammation in fatal asthma

BACKGROUND

To date, little information has been available about pulmonary artery pathology in asthma. The pulmonary artery supplies the distal parts of the lungs and likely represents a site of immunological reaction in allergic inflammation. The objective of this study was to describe the inflammatory cell phenotype of pulmonary artery adventitial inflammation in lung tissue from patients who died of asthma.

METHODS

We quantified the different inflammatory cell types in the periarterial region of small pulmonary arteries in lung tissue from 22 patients who died of asthma [fatal asthma (FA)] and 10 control subjects. Using immunohistochemistry and image analysis, we quantified the cell density for T lymphocytes (CD3, CD4, CD8), B lymphocytes (CD20), eosinophils, mast cells (chymase and tryptase), and neutrophils in the adventitial layer of pulmonary arteries with a diameter smaller than 500 microm.

RESULTS

Our data (median/interquartile range) demonstrated increased cell density of mast cells [FA=271.8 (148.7) cells/mm2; controls=177.0 (130.3) cells/mm2, P=0.026], eosinophils [FA=23.1 (58.6) cells/mm2; controls=0.0 (2.3) cells/mm2, P=0.012], and neutrophils [FA=50.4 (85.5) cells/mm2; controls=2.9 (30.5) cells/mm2, P=0.009] in the periarterial space in FA. No significant differences were found for B and T lymphocytes or CD4+ or CD8+ subsets. Chymase/tryptase positive (MCCT) mast cells predominated over tryptase (MCT) mast cells in the perivascular arterial space in both asthma patients and controls [MCCT/(MCCT+MCT)=0.91 (0-1) in FA and 0.75 (0-1) in controls, P=0.86].

CONCLUSIONS

Our results show that the adventitial layer of the pulmonary artery participates in the inflammatory process in FA, demonstrating increased infiltration of mast cells, eosinophils, and neutrophils, but not of T and B lymphocytes.

Barotrauma not related to type of positive pressure ventilation during severe asthma exacerbations in children

BACKGROUND

Children with impending respiratory failure due to severe asthma may be treated with endotracheal intubation and mechanical ventilation. Barotrauma occurs in a significant number of these children. Non-invasive positive pressure ventilation (NPPV) has been used as an alternative intermediary therapy and potentially prevents intubation. However, the comparative risk of barotrauma associated with the use of NPPV has not been evaluated in this population.

OBJECTIVE

To determine if the mode of positive pressure delivery per se affects the likelihood of development of barotrauma.

METHODS

We retrospectively examined data from all children older than 2 years of age admitted to the Intensive Care Unit (ICU) with an asthma exacerbation between April 1997 and August 2006.

RESULTS

Of the 293 children admitted to the ICU with asthma, 45 (17%) received treatment with positive pressure ventilation: 11 received only NPPV, 29 were intubated and mechanically ventilated, and 7 children received both of these therapies. Compared with those not requiring positive pressure, children receiving positive pressure were significantly more likely to develop barotrauma during hospitalization (OR 8.9; 95% CI 2.4-32.7). However, the incidence of barotrauma did not significantly differ according to the mode of positive pressure delivery: 9% in those who received only NPPV, 14% in those who were intubated, and 14% in those who received both therapies (p = 0.92).

CONCLUSIONS

The use of positive pressure is associated with an increased risk of barotrauma in children with asthma, regardless of the mode of delivery.

The increased cost of complications in children with status asthmaticus

Status asthmaticus is one of the most common causes of admission to a pediatric intensive care unit (PICU). There is little published data, however, examining the complications associated with the treatment of status asthmaticus in children in the PICU. Our hypothesis was that children experiencing a complication would have an increased duration of hospitalization for status asthmaticus. We performed a retrospective review of the complication profile and hospital course of all children admitted to a PICU with status asthmaticus over a 9 years period. Twenty-two (8%) of the 293 children admitted to the ICU with status asthmaticus experienced one or more complications during their treatment. The most common complications were aspiration pneumonia, ventilator-associated pneumonia, pneumomediastinum, pneumothorax, and rhabdomyolysis. Intubated children were significantly more likely than non-intubated children to experience a complication (RR 15.3; 95% CI 6.7-35). Fifteen (42%) of the 36 intubated children experienced a complication. Intubated children experiencing a complication had significantly longer duration of mechanical ventilation (163 +/- 169 hr vs. 66 +/- 65 hr, P = 0.03), ICU length of stay (237 +/- 180 hr vs. 124 +/- 86 hr, P = 0.02) and hospital charges (US dollars 117,184 +/- 111,191 vs. US dollars 38,788 +/- 27,784; P = 0.001) than intubated children not experiencing a complication. In this review, complications were associated with increased morbidity and duration of hospitalization in children with status asthmaticus, particularly in those intubated as part of their therapy. This suggests that intubation and mechanical ventilation itself may increase the risk of developing a complication in this population.

The anaesthesiologist in the intensive care unit

PURPOSE OF REVIEW

This review focuses on recent knowledge in areas of anaesthesia expertise which are indispensable to intensive care unit management, including airway management, vascular access, regional analgesia and the treatment of status asthmaticus and status epilepticus.

RECENT FINDINGS

Etomidate as the sole agent for intubation in the intensive care unit has a 90% success rate, while in a prehospital setting, the addition of succinylcholine to etomidate results in a 99% success rate. In determining successful intubation, capnography and laryngoscopic/fibreoptic visualization are superior to auscultation, while auscultation is as effective as the self-inflating bulb or transillumination with the lightwand. The dorsalis pedis artery is an effective alternative to radial artery cannulation, while arterial cannulation itself can result in major adverse effects if complications arise. Ultrasound guidance in the placement of central catheters results in an improved insertion success rate. Internal jugular and subclavian lines have similar risk of haemothorax or pneumothorax, while subclavian lines are associated with the lowest incidence of infection. Midazolam, thiopentone and propofol have all been found to be efficacious in terminating refractory status epilepticus, with thiopentone resulting in a lower incidence of breakthrough seizures or treatment failure but an increased incidence of hypotension. Inhalational anaesthesia using isoflurane or desflurane has also been found to be successful in refractory status epilepticus. In the management of status asthmaticus, limiting minute volume while tolerating hypercapnia and acidosis as well as the use of inhalational anesthesia have proven effective strategies in a number of refractory cases.

SUMMARY

The anaesthesiologist's unique knowledge and skills are ideally suited to the practical management of patients in a critical care setting as well as in the treatment of the critical phases of many illnesses.

Pregnancy, delivery and the intensive care unit: need, outcome and management

PURPOSE OF REVIEW

Increasing numbers of sick pregnant and peripartum women are cared for in the intensive care unit. This review looks at the current mortality, the disease severity of admitted patients and the current need for intensive care unit and high dependency unit beds to cater for these women. It also looks at some recent advances in the treatment of some specific disease entities encountered in the intensive care unit in pregnant women and parturients which have been covered in the 2001-2002 literature.

RECENT FINDINGS

There has been a substantial fall in intensive care unit mortality in the last decade and there is a definite place for these women in intensive care unit. They represent a subgroup of severely ill patients with a need for intensive treatment and monitoring and who are worth the investment in time and money because they often recover from their acute illness to return to full productivity.

SUMMARY

The high dependency unit and intensive care unit and their role in the service to the pregnant woman and parturient are the main focus of this review which looks at the last 2 years' literature to determine the critical care services' worth and efficacy. In almost all countries, even in the smaller regional hospitals, the intensive care units and high dependency units have reduced maternal mortality and morbidity. The neonatal high dependency units have done much the same for the newborn but the neonatal literature is not reviewed for the purposes of this symposium.

Pressure control ventilation

As mechanical ventilators become increasingly sophisticated, clinicians are faced with a variety of ventilatory modes that use volume, pressure, and time in combination to achieve the overall goal of assisted ventilation. Although much has been written about the advantages and disadvantages of these increasingly complex modalities, currently there is no convincing evidence of the superiority of one mode of ventilation over another. Pressure control ventilation may offer particular advantages in certain circumstances in which variable flow rates are preferred or when pressure and volume limitation is required. The goal of this article is to provide clinicians with a fundamental understanding of the dependent and independent variables active in pressure control ventilation and describe features of the mode that may contribute to improved gas exchange and patient-ventilator synchronization.

Endotracheal intubation and pediatric status asthmaticus: site of original care affects treatment

OBJECTIVES

Status asthmaticus is a common cause of admission to a pediatric intensive care unit (PICU). Children unresponsive to medical therapies may require endotracheal intubation; however, this treatment carries significant risk, and thresholds for intubation vary. Our hypothesis was that children who sought care at community hospitals received less aggressive treatment and more frequent intubation than children who sought care at a children's hospital.

DESIGN

Retrospective cohort study.

SETTING

A university-affiliated children's hospital PICU.

PATIENTS

We retrospectively examined data from all children older than 2 yrs admitted to the PICU with status asthmaticus between April 1997 and July 2005.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 251 children admitted to the PICU with status asthmaticus, 130 initially presented to the emergency department of a children's hospital and 116 presented to the emergency department of a community hospital. Despite similar illness severity, children presenting to a community hospital were significantly more likely to be intubated than those presenting to a children's hospital (17% vs. 5%; p = .004). In addition, those children intubated at community hospitals were intubated sooner after presentation (2.4 +/- 5.2 vs. 7.5 +/- 5.8 hrs; p = .009), had shorter durations of intubation (71 +/- 73 vs. 151 +/- 81 hrs; p = .02), and had shorter PICU length of stays (129 +/- 82 vs. 230 +/- 84 hrs; p = .01).

CONCLUSIONS

Children with status asthmaticus are more likely to be intubated, and intubated sooner, at a community hospital. The shorter duration of intubation suggests that some children may not have been intubated had they presented to a children's hospital or received more aggressive therapy at their community hospital.

Pumpless extracorporeal carbon dioxide removal for life-threatening asthma

OBJECTIVE

To report the use of pumpless extracorporeal carbon dioxide removal in two cases of acute severe asthma.

DESIGN

Case reports.

SETTING

Adult general intensive care unit, Leeds General Infirmary, Leeds, UK.

PATIENTS

A 74-yr-old male and 52-yr-old female with life-threatening asthma developed progressive hypercapnia and severe acidosis that proved nonresponsive to all other therapies.

INTERVENTION

Initiation of extracorporeal arteriovenous carbon dioxide removal using the Novalung device (Novalung GmbH, Lotzenäcker 3, D-72379 Hechingen, Germany).

MAIN RESULTS

The addition of extracorporeal carbon dioxide removal to mechanical ventilation corrected hypercapnia and acidosis, allowing reduction of other supportive measures. In both cases, adequate gas exchange was maintained until their underlying condition improved sufficiently for device removal. The two patients were subsequently weaned from mechanical ventilation and made a full recovery.

CONCLUSIONS

Extracorporeal carbon dioxide removal proved to be a valuable adjunct to mechanical ventilation and other medical treatment.

Effects of water deprivation on the pharmacokinetics of theophylline and one of its metabolites, 1,3-dimethyluric acid, after intravenous and oral administration of aminophylline to rats

It has been reported that the expressions of hepatic microsomal cytochrome P450 (CYP) 1A1/2, 2B1/2 and 3A1/2 were not changed in rats with water deprivation for 72 h (rat model of dehydration) compared with the controls. It has been also reported that 1,3-dimethyluric acid (1,3-DMU) was formed from theophylline via CYP1A1/2 in rats. Hence, it could be expected that the formation of 1,3-DMU could be comparable between the two groups of rats. As expected, after both intravenous and oral administration of theophylline at a dose of 5 mg/kg to the rat model of dehydration, the AUC of 1,3-DMU was comparable to the controls. After both intravenous and oral administration of theophylline to the rat model of dehydration, the Cl(r) of both theophylline and 1,3-DMU was significantly slower than the controls. This could be due to significantly smaller urinary excretions of both theophylline and 1,3-DMU since the AUC of both theophylline and 1,3-DMU were comparable between the two groups of rats. The smaller urinary excretion of both theophylline and 1,3-DMU could be due to urine flow rate-dependent timed-interval renal clearance of both theophylline and 1,3-DMU in rats.

[Bronchial obstruction in intensive care]

Bronchial obstruction due to one of the major pulmonary diseases asthma, COPD, or emphysema are a common problem in intensive care medicine as the leading cause or as comorbidity. While in pharmacological therapy no major changes have occurred during the last few years, two major advances have been reached in ventilation therapy which are in the focus of this review. First the non invasive ventilation (NIV) has been shown to prove efficient in treating acute on chronic respiratory failure in COPD patients and is capable of shortening the duration of hospital stay. In addition NIV can be used successfully in weaning after long time ventilator therapy and improve prognosis in COPD patients. Secondly the strategy of invasive ventilation therapy has changed significantly. "Permissive hypercapnia" is unequivocally established in severe bronchial obstruction in situations of limited ventilation. When intrinsic PEEP and elevated airway resistance are present PEEP may be useful and the upper limit of airways peak pressure that we are used to in "protective ventilation" of ARDS patients can be necessary and useful to exceed.

Cell type-specific effect of hypoxia and platelet-derived growth factor-BB on extracellular matrix turnover and its consequences for lung remodeling

Hypoxia is associated with extracellular matrix remodeling in several inflammatory lung diseases, such as fibrosis, chronic obstructive pulmonary disease, and asthma. In a human cell culture model, we assessed whether extracellular matrix modification by hypoxia and platelet-derived growth factor (PDGF) involves the action of matrix metalloproteinases (MMPs) and thereby affects cell proliferation. Expression of MMP and its activity were assessed by zymography and enzyme-linked immunosorbent assay in human lung fibroblasts and pulmonary vascular smooth muscle cells (VSMCs), and synthesis of soluble collagen type I was assessed by enzyme-linked immunosorbent assay. In both cell types, hypoxia up-regulated the expression of MMP-1, -2, and -9 precursors without subsequent activation. MMP-13 was increased by hypoxia only in fibroblasts. PDGF-BB inhibited the synthesis and secretion of all hypoxia-dependent MMP via Erk1/2 mitogen-activated protein (MAP) kinase activation. Hypoxia and PDGF-BB induced synthesis of soluble collagen type I via Erk1/2 and p38 MAP kinase. Hypoxia-induced cell proliferation was blocked by antibodies to PDGF-BB or by inhibition of Erk1/2 but not by the inhibition of MMP or p38 MAP kinase in fibroblasts. In VSMCs, hypoxia-induced proliferation involved Erk1/2 and p38 MAP kinases and was further increased by fibroblast-conditioned medium or soluble collagen type I via Erk1/2. In conclusion, hypoxia controls tissue remodeling and proliferation in a cell type-specific manner. Furthermore, fibroblasts may affect proliferation of VSMC indirectly by inducing the synthesis of soluble collagen type I.

Brief review: Nondepolarizing neuromuscular blocking drugs and critical illness myopathy

PURPOSE

Critically-ill patients who receive nondepolarizing neuromuscular blocking drugs (NMBDs) may be at risk of developing profound muscle weakness that may last for months after the NMBD is discontinued, especially when large cumulative doses of NMBDs and corticosteroids are co-administered to septic, mechanically ventilated patients. This review focuses on the etiology and clinical features of critical illness myopathy (CIM), summarizes specific risk factors for its development, and discusses strategies that might be used to attenuate or even prevent the development of this potentially devastating syndrome.

CLINICAL FEATURES

The etiology of CIM is unknown. Whether it can develop in at-risk patients who undergo lengthy operations during which they receive NMBDs is also unknown. In some patients following exposure to NMBDs their motor systems are impaired secondary to loss of thick (myosin) filaments that render the muscle unexcitable to direct electrical stimulation, while the sensory system is spared. Management of patients who develop NMBD myopathy is supportive, consisting of nutritional support, physical therapy, and daily trials of decreased ventilatory support.

CONCLUSION

Recent guidelines recommend that NMBDs be used in critically ill patients only when absolutely necessary, that the depth of muscle paralysis be monitored to avoid overdosing and metabolite accumulation, and that drug administration be curtailed periodically to allow interruption of sustained NMBD effect.

Noninvasive positive pressure ventilation for the treatment of status asthmaticus in children

BACKGROUND

Noninvasive positive pressure ventilation (NPPV) has been used safely and effectively to improve gas exchange and to treat respiratory failure in a variety of disease states. Although this technique has some benefits in the treatment of status asthmaticus in adults, the use of NPPV in pediatric patients with asthma has not been described.

OBJECTIVE

To describe the use of NPPV in the treatment of pediatric status asthmaticus.

METHODS

Retrospective review of children admitted to the intensive care unit with asthma who received NPPV as part of their treatment between October 2002 and April 2004. Before and after initiation of NPPV, data were collected regarding degree of respiratory dysfunction.

RESULTS

Of seventy-nine children admitted to the intensive care unit during the study period for treatment of status asthmaticus, 5 children (mean +/- SD age, 9.6 +/- 4.2 years) were treated with NPPV. Four of the 5 children were morbidly obese, with a mean +/- SD body mass index of 32 +/- 5. There was a statistically significant improvement in respiratory rate (43 +/- 20 vs 31 +/- 12/min, P = .03) and Modified Pulmonary Index Score (13.4 +/- 1.8 vs 11.4 +/- 1.5, P = .03) after initiation of NPPV. The mean +/- SD duration of therapy was 33.2 +/- 23.9 hours, and children tolerated this therapy well, requiring little or no anxiolytics.

CONCLUSIONS

NPPV was well tolerated in this series of children with status asthmaticus and can improve subjective and objective measures of respiratory dysfunction. NPPV may be a useful adjunct in the treatment of status asthmaticus in children.

Clinical review: Mechanical ventilation in severe asthma

Respiratory failure from severe asthma is a potentially reversible, life-threatening condition. Poor outcome in this setting is frequently a result of the development of gas-trapping. This condition can arise in any mechanically ventilated patient, but those with severe airflow limitation have a predisposition. It is important that clinicians managing these types of patients understand that the use of mechanical ventilation can lead to or worsen gas-trapping. In this review we discuss the development of this complication during mechanical ventilation, techniques to measure it and strategies to limit its severity. We hope that by understanding such concepts clinicians will be able to reduce further the poor outcomes occasionally related to severe asthma.

[Acute severe asthma in older adults]

The underlying causes of acute severe or life threatening asthma are infections with respiratory viruses or Mycoplasma pneumoniae, rather than bacterial infections. In addition, exposure to various agents such as allergens, non-specific irritants or drugs, and inadequate long-term treatment may be responsible. High flow oxygen therapy, high dose topic beta(2)-agonists and systemic glucocorticosteroids should be used as baseline therapy in outpatients. In hospital, intravenous therapy-eventually including sedatives-can be administered under controlled or intensive care conditions. In patients with increasing respiratory pump weakness and alveolar hypoventilation, non-invasive and/or invasive mechanical ventilation may be required. In ventilated asthma patients permissive hypercarbia has been shown to reduce complications such as pneumothorax. Bronchoscopy and bronchial lavage are recommended for patients ventilated with increasing pressures or when atelectasis occurs.