Pressure-controlled ventilation in children with severe status asthmaticus

Anesthetic considerations in children with asthma

Due to the high prevalence of asthma and general airway reactivity, anesthesiologists frequently encounter children with asthma or asthma-like symptoms. This review focuses on the epidemiology, the underlying pathophysiology, and perioperative management of children with airway reactivity, including controlled and uncontrolled asthma. It spans from preoperative optimization to optimized intraoperative management, airway management, and ventilation strategies. There are three leading causes for bronchospasm (1) mechanical (eg, airway manipulation), (2) non-immunological anaphylaxis (anaphylactoid reaction), and (3) immunological anaphylaxis. Children with increased airway reactivity may benefit from a premedication with beta-2 agonists, non-invasive airway management, and deep removal of airway devices. While desflurane should be avoided in pediatric anesthesia due to an increased risk of bronchospasm, other volatile agents are potent bronchodilators. Propofol is superior in blunting airway reflexes and, therefore, well suited for anesthesia induction in children with increased airway reactivity.

Overview of severe asthma, with emphasis on pediatric patients: a review for practitioners

Asthma is the most common life-threatening chronic disease in children. Although guidelines exist for the diagnosis and treatment of asthma, treatment of severe, pediatric asthma remains difficult. Limited studies in the pediatric population on new asthma therapies, complex issues with adolescence and adherence, health disparities, and unequal access to guideline-based care complicate the care of children with severe, persistent asthma. The purpose of this review is to provide an overview of asthma, including asthma subtypes, comorbidities, and risk factors, to discuss diagnostic considerations and pitfalls and existing treatments, and then present existing and emerging therapeutic approaches to asthma management. An improved understanding of asthma heterogeneity, clinical characteristics, inflammatory patterns, and pathobiology can help further guide the management of severe asthma in children. More studies are needed in the pediatric population to understand emerging therapeutics application in children. Effective multimodal strategies tailored to individual characteristics and a commitment to address risk factors, modifiers, and health disparities may help reduce the burden of asthma in the USA.

Emergency department treatment of asthma in children: A review

Asthma is the most common chronic illness in children, with >700,000 emergency department (ED) visits each year. Asthma is a respiratory disease characterized by a combination of airway inflammation, bronchoconstriction, bronchial hyperresponsiveness, and variable outflow obstruction, with clinical presentations ranging from mild to life-threatening. Standardized ED treatment can improve patient outcomes, including fewer hospital admissions. Informed by the most recent guidelines, this review focuses on the optimal approach to diagnosis and treatment of children with acute asthma exacerbations who present to the ED.

Pathophysiology, research challenges, and clinical management of smoke inhalation injury

Smoke inhalation injury is a serious medical problem that increases morbidity and mortality after severe burns. However, relatively little attention has been paid to this devastating condition, and the bulk of research is limited to preclinical basic science studies. Moreover, no worldwide consensus criteria exist for its diagnosis, severity grading, and prognosis. Therapeutic approaches are highly variable depending on the country and burn centre or hospital. In this Series paper, we discuss understanding of the pathophysiology of smoke inhalation injury, the best evidence-based treatments, and challenges and future directions in diagnostics and management.

Ventilation strategies in paediatric inhalation injury

Inhalation injury increases morbidity and mortality in burns victims. While the diagnosis remains largely clinical, bronchoscopy is also helpful to diagnose and grade the severity of any injury. Inhalation injury results from direct thermal injury or chemical irritation of the respiratory tract, systemic toxicity from inhaled substances, or a combination of these factors. While endotracheal intubation is essential in cases where upper airway obstruction may occur, it has its own risks and should not be performed prophylactically in all cases of inhalation injury. The evidence-base informing the selection of optimal ventilation strategy in inhalation injury is sparse, and most recommendations are based on extrapolation from (largely adult) studies in acute respiratory distress syndrome (ARDS). Conventional ventilation using a lung-protective approach (i.e. low tidal volume, limited plateau pressure, and permissive hypercarbia) is recommended as the initial approach if invasive ventilation is required; various rescue strategies may become necessary if there is a poor response. The efficacy of many widely used pharmacologic adjuncts in inhalation injury remains uncertain. Further research is urgently required to address these gaps in our knowledge.

Anesthesia and ventilation strategies in children with asthma: part II - intraoperative management

PURPOSE OF REVIEW

As asthma is a frequent disease especially in children, anesthetists are increasingly providing anesthesia for children requiring elective surgery with well controlled asthma but also for those requiring urgent surgery with poorly controlled or undiagnosed asthma. This second part of this two-part review details the medical and ventilatory management throughout the perioperative period in general but also includes the perioperative management of acute bronchospasm and asthma exacerbations in children with asthma.

RECENT FINDINGS

Multiple observational trials assessing perioperative respiratory adverse events in healthy and asthmatic children provide the basis for identifying risk reduction strategies. Mainly, animal experiments and to a small extent clinical data have advanced our understanding of how anesthetic agents effect bronchial smooth muscle tone and blunt reflex bronchoconstriction. Asthma treatment outside anesthesia is well founded on a large body of evidence.Perioperative prevention strategies have increasingly been studied. However, evidence on the perioperative management, including mechanical ventilation strategies of asthmatic children, is still only fair, and further research is required.

SUMMARY

To minimize the considerable risk of perioperative respiratory adverse events in asthmatic children, perioperative management should be based on two main pillars: the preoperative optimization of asthma treatment (please refer to the first part of this two-part review) and - the focus of this second part of this review - the optimization of anesthesia management in order to optimize lung function and minimize bronchial hyperreactivity in the perioperative period.

Anesthesia and ventilation strategies in children with asthma: part I - preoperative assessment

PURPOSE OF REVIEW

Asthma is a common disease in the pediatric population, and anesthetists are increasingly confronted with asthmatic children undergoing elective surgery. This first of this two-part review provides a brief overview of the current knowledge on the underlying physiology and pathophysiology of asthma and focuses on the preoperative assessment and management in children with asthma. This also includes preoperative strategies to optimize lung function of asthmatic children undergoing surgery. The second part of this review focuses on the immediate perioperative anesthetic management including ventilation strategies.

RECENT FINDINGS

Multiple observational trials assessing perioperative respiratory adverse events in healthy and asthmatic children provide the basis for identifying risk factors in the patient's (family) history that aid the preoperative identification of at-risk children. Asthma treatment outside anesthesia is well founded on a large body of evidence. Optimization and to some extent intensifying asthma treatment can optimize lung function, reduce bronchial hyperreactivity, and minimize the risk of perioperative respiratory adverse events.

SUMMARY

To minimize the considerable risk of perioperative respiratory adverse events in asthmatic children, a good understanding of the underlying physiology is vital. Furthermore, a thorough preoperative assessment to identify children who may benefit of an intensified medical treatment thereby minimizing airflow obstruction and bronchial hyperreactivity is the first pillar of a preventive perioperative management of asthmatic children. The second pillar, an individually adjusted anesthesia management aiming to reduce perioperative adverse events, is discussed in the second part of this review.

Outcomes of invasive mechanical ventilation in children and adolescents hospitalized due to status asthmaticus in United States: a population based study

OBJECTIVE

Current national estimates of and outcomes of Invasive Mechanical Ventilation (MV) in status asthmaticus (SA) are unclear. The objective of this study is to estimate the incidence and outcomes of MV in hospitalized SA children and adolescents.

METHODS

We used the Nationwide Inpatient Sample (NIS, 2009-2010), the largest all-payer hospital discharge database in United States. All hospitalizations (age ≤21 years) with a primary diagnosis of SA were selected. MV was identified using ICD-9-CM procedure codes. Multivariable regression analyses were used to examine the association between MV and outcomes (Length of Stay (LOS) and Hospital Charges (HC)).

RESULTS

Over the study period, of the 250 718 SA hospitalizations, MV was needed for <96 h in 0.37% hospitalizations and 0.18% had MV for ≥96 h. Complications occurred in 12.4% (30 991) of all hospitalizations with pneumonia (10.8%) being the most common. A total of 65 patients died in hospitals (the overall in-hospital mortality [IHM] rate was 0.03%). About 55 of these deaths occurred among those who had MV (4% IHM rate for those receiving MV). The mean LOS and hospital HC included without MV (2.1 d, $11 921) MV < 96 h (4.8 d, $52 201); MV > 96 h (15.6 d, $200 336). After adjustment for patient/hospital level factors, the need for MV was associated with significantly higher LOS and HC (p < 0.0001). Those who had MV<96 h (OR = 2.58, 95% CI = 1.77-3.77) or MV ≥ 96 h (OR = 6.23, 95% CI = 3.87-10.03) had higher risk of developing pneumonia.

CONCLUSIONS

Although MV is infrequently needed in children and adolescents hospitalized for SA (0.55% incidence rate), it is associated with higher IHM rate and significant hospital resource utilization.

Demographics, clinical course, and outcomes of children with status asthmaticus treated in a pediatric intensive care unit: 8-year review

OBJECTIVE

This study was done to understand the demographics, clinical course, and outcomes of children with status asthmaticus treated in a tertiary care pediatric intensive care unit (PICU).

METHODS

The medical charts of all patients above 5 years of age admitted to the PICU at Nationwide Children's Hospital, Columbus, OH, USA, with status asthmaticus from 2000 to 2007 were reviewed retrospectively. Data from 222 encounters by 183 children were analyzed.

RESULTS

The mean age at admission in years was 11 ± 3.8. The median PICU stay was 1 day (range, 1-12 days) and median hospital stay was 3 days. The ventilated group (n = 17) stayed a median of 2 days longer in the PICU and hospital. Nearly half of the children (n = 91; 50%) did not receive daily controller asthma medications. Adherence to asthma medications was reported in 125 patient charts of whom 43 (34%) were compliant. Exposure to smoking was reported in 167 of whom 70 (42%) were exposed. Among patients receiving metered dose inhaler (MDI), only 39 (18%) were using it with a spacer. Among 105 patient charts asthma severity data were available, of them 21 (20%) were labeled as mild intermittent, 29 (28%) were mild persistent, 26 (25%) were moderate persistent, and 29 (28%) were severe persistent. Compared to children with only one PICU admission during the study period (n = 161), children who had multiple PICU admissions (n = 22) experienced more prior emergency department visits and hospitalizations for asthma symptoms. There were no fatalities.

CONCLUSION

Asthmatics with any disease severity are at risk for life-threatening asthma exacerbations requiring PICU stay, especially those who are not adherent with their daily medications.

Pediatric status asthmaticus

Status asthmaticus is a frequent cause of admission to a pediatric intensive care unit. Prompt assessment and aggressive treatment are critical. First-line or conventional treatment includes supplemental oxygen, aerosolized albuterol, and corticosteroids. There are several second-line treatments available; however, few comparative studies have been performed and in the absence of good evidence-based treatments, the use of these therapies is highly variable and dependent on local practice and provider preference. In this article the pathophysiology and treatment of status asthmaticus is discussed, and the literature regarding second-line treatments is critically assessed to apply an evidence basis to the treatment of this severe disease.

Fatal and near-fatal asthma in children: the critical care perspective

OBJECTIVE

To characterize the clinical course, therapies, and outcomes of children with fatal and near-fatal asthma admitted to pediatric intensive care units (PICUs).

STUDY DESIGN

This was a retrospective chart abstraction across the 8 tertiary care PICUs of the Collaborative Pediatric Critical Care Research Network (CPCCRN). Inclusion criteria were children (aged 1-18 years) admitted between 2005 and 2009 (inclusive) for asthma who received ventilation (near-fatal) or died (fatal). Data collected included medications, ventilator strategies, concomitant therapies, demographic information, and risk variables.

RESULTS

Of the 261 eligible children, 33 (13%) had no previous history of asthma, 218 (84%) survived with no known complications, and 32 (12%) had complications. Eleven (4%) died, 10 of whom had experienced cardiac arrest before admission. Patients intubated outside the PICU had a shorter duration of ventilation (median, 25 hours vs 84 hours; P < .001). African-Americans were disproportionately represented among the intubated children and had a shorter duration of intubation. Barotrauma occurred in 15 children (6%) before admission. Pharmacologic therapy was highly variable, with similar outcomes.

CONCLUSION

Of the children ventilated in the CPCCRN PICUs, 96% survived to hospital discharge. Most of the children who died experienced cardiac arrest before admission. Intubation outside the PICU was correlated with shorter duration of ventilation. Complications of barotrauma and neuromyopathy were uncommon. Practice patterns varied widely among the CPCCRN sites.

Refractive errors and corrections for OCT images in an inflated lung phantom

Visualization and correct assessment of alveolar volume via intact lung imaging is important to study and assess respiratory mechanics. Optical Coherence Tomography (OCT), a real-time imaging technique based on near-infrared interferometry, can image several layers of distal alveoli in intact, ex vivo lung tissue. However optical effects associated with heterogeneity of lung tissue, including the refraction caused by air-tissue interfaces along alveoli and duct walls, and changes in speed of light as it travels through the tissue, result in inaccurate measurement of alveolar volume. Experimentally such errors have been difficult to analyze because of lack of 'ground truth,' as the lung has a unique microstructure of liquid-coated thin walls surrounding relatively large airspaces, which is difficult to model with cellular foams. In addition, both lung and foams contain airspaces of highly irregular shape, further complicating quantitative measurement of optical artifacts and correction. To address this we have adapted the Bragg-Nye bubble raft, a crystalline two-dimensional arrangement of elements similar in geometry to alveoli (up to several hundred μm in diameter with thin walls) as an inflated lung phantom in order to understand, analyze and correct these errors. By applying exact optical ray tracing on OCT images of the bubble raft, the errors are predicted and corrected. The results are validated by imaging the bubble raft with OCT from one edge and with a charged coupled device (CCD) camera in transillumination from top, providing ground truth for the OCT.

Status asthmaticus in the medical intensive care unit: a 30-year experience

OBJECTIVES

To investigate the characteristics, trends in management (permissive hypercapnia; mechanical ventilation (MV); neuromuscular blockade) and their impact on complications and outcomes in Status Asthmaticus (SA).

METHODS

We performed a retrospective observational study of subjects admitted with SA to a single multidisciplinary MICU over a 30-year period. All laboratory, radiologic, respiratory care, physician notes and orders were extracted from an electronic medical record (EMR) maintained during the entire duration of the study.

RESULTS

Two hundred and twenty-seven subjects were admitted with 280 episodes of SA. While subjects reflected our regional population (52% Hispanic), African Americans were over-represented (22%) and Caucasians under-represented (21%). Thirty-eight percent reported childhood asthma, 27% were steroid dependent (10% in the last 10 years), and 18% had a recent steroid taper. One hundred and thirty-nine (61.2%) required intubation. The duration of hospitalization was similar between mechanically ventilated and non-ventilated subjects (5.8±4.41 vs. 6.8±7.22 days; p=0.07). The overall complication rate remained low irrespective of the use of permissive hypercapnia or mode of mechanical ventilation (overall mortality 0.4%; pneumothorax 2.5%; pneumonia 2.9%). The frequency of SA declined significantly in the last 10 years of the study (12.4 vs. 3.2 cases/year).

CONCLUSIONS

Despite the frequent use of mechanical ventilation, mortality/complication rates remained extremely low. MV did not significantly increase the duration of hospitalization. At our institution, the frequency of SA significantly decreased despite an increase in emergency room visits for asthma.

Trends in admissions for pediatric status asthmaticus in New Jersey over a 15-year period

OBJECTIVE

Status asthmaticus accounts for a large portion of the morbidity and mortality associated with asthma, but we know little about its epidemiology. We describe here the hospitalization characteristics of children with status asthmaticus, how they changed over time, and how they differed between hospitals with and without PICUs.

PATIENTS AND METHODS

We used administrative data from New Jersey that included all hospitalizations in the state from 1992, 1995, and 1999-2006. We identified children with status asthmaticus by using International Classification of Diseases, Ninth Revision, diagnosis codes that indicate status asthmaticus and the use of mechanical ventilation by using procedure codes. We designated hospitals with a PICU as "PICU hospitals" and those without as "adult hospitals."

RESULTS

We identified 28 309 admissions of children with status asthmaticus (22.8% of all asthma hospitalizations). From 1992 to 2006, the rate of hospital admissions decreased by half (from 1.98 in 1000 to 0.93 in 1000 children), and there was a 70% decrease in the number of children admitted to adult hospitals. The rate of ICU care in PICU hospitals more than tripled. However, the rate of mechanical ventilation remained low, and the number of deaths was small and unchanged (n=14 total). Hospital costs climbed from $6.6 million to $9.5 million.

CONCLUSIONS

Although fewer children are being admitted with status asthmaticus, the proportion of patients managed in PICUs is climbing. There has been no substantial change in rates of mechanical ventilation or death. Additional research is needed to better understand how patients and physicians decide on the appropriate site for hospital care and how that choice affects outcome.

Dynamics of tidal volume and ventilation heterogeneity under pressure-controlled ventilation during bronchoconstriction: a simulation study

The difference in effectiveness between volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) on mechanically ventilated patients during bronchoconstriction is not totally clear. PCV is thought to deliver a more uniform distribution of ventilation than VCV, but the delivered tidal volume could be unstable and affected by changes in the degree of constriction. To explore the magnitude of these effects, we ran numerical simulations with both modes of ventilation in a network model of the lung in which we incorporated not only the pressure and flow dynamics along the airways but also the effect of cycling pressures and tissue tethering forces during breathing on the dynamic equilibrium of the airway smooth muscle (ASM) (Venegas et al., Nature 434: 777-782). These simulations provided an illustration of changes in airway radii, the total delivered tidal volume stability, and distribution of ventilation following a transition from VCV to PCV and during progressively increasing ASM activation level. These simulations yielded three major results. First, the ventilation heterogeneity and patchiness in ventilation during steady-state VCV were substantially reduced after the transition to PCV. Second, airway radius, tidal volume, and the distribution of ventilation under severe bronchoconstriction were highly sensitive to the setting of inspiratory pressure selected for PCV and to the degree of activation of the ASM. Third, the dynamic equilibrium of active ASM exposed to cycling forces is the major contributor to these effects. These insights may provide a theoretical framework to guide the selection of ventilation mode, the adjustment of ventilator settings, and the interpretation of clinical observations in mechanically ventilated asthmatic patients.

Experience with use of extracorporeal life support for severe refractory status asthmaticus in children

Introduction

Severe status asthmaticus (SA) in children may require intubation and mechanical ventilation with a subsequent increased risk of death. In the patient with SA and refractory hypercapnoeic respiratory failure, use of extracorporeal life support (ECLS) has been anecdotally reported for carbon dioxide removal and respiratory support. We aimed to review the experience of a single paediatric centre with the use of ECLS in children with severe refractory SA, and to compare this with international experience from the Extracorporeal Life Support Organization (ELSO) registry.

Methods

All paediatric patients (aged from 1 to 17 years) with primary International Classification of Diseases (ICD)-9 diagnoses of SA receiving ECLS for respiratory failure from both the Children's Healthcare of Atlanta at Egleston (Children's at Egleston) database and the ELSO registry were reviewed.

Results

Thirteen children received ECLS for refractory SA at the Children's at Egleston from 1986 to 2007. The median age of the children was 10 years (range 1 to 16 years). Patients generally received aggressive use of medical and anaesthetic therapies for SA before cannulation with a median partial pressure of arterial carbon dioxide (PaCO₂) of 130 mmHg (range 102 to 186 mmHg) and serum pH 6.89 (range 6.75 to 7.03). The median time of ECLS support was 95 hours (range 42 to 395 hours). All 13 children survived without neurological sequelae. An ELSO registry review found 64 children with SA receiving ECLS during the same time period (51 excluding the Children's at Egleston cohort). Median age, pre-ECLS PaCO₂ and pH were not different in non-Children's ELSO patients. Overall survival was 60 of 64 (94%) children, including all 13 from the Children's at Egleston cohort. Survival was not significantly associated with age, pre-ECLS PaCO₂, pH, cardiac arrest, mode of cannulation or time on ECLS. Significant neurological complications were noted in 3 of 64 (4%) patients; patients with neurological complications were not significantly more likely to die (P = 0.67).

Conclusions

Single centre and ELSO registry experience provide results of a cohort of children with refractory SA managed with ECLS support. Further study is necessary to determine if use of ECLS in this setting produces better outcomes than careful mechanical ventilation and medical therapy alone.

Permissive hypercapnia

Mechanical ventilation using high tidal volume (VT) and transpulmonary pressure can damage the lung, causing ventilator-induced lung injury. Permissive hypercapnia, a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure, has been accepted progressively in critical care for adult, pediatric, and neonatal patients requiring mechanical ventilation and is one of the central components of current protective ventilatory strategies.

Asthma

Asthma has been recognized as a disease since the earliest times. In the Corpus Hippocraticum, Hippocrates used the term “ασθμα” to indicate any form of breathing difficulty manifesting itself by panting. Aretaeus of Cappadocia, a well-known Greek physician (second century A.D.), is credited with providing the first detailed description of an asthma attack [13], and to Celsus it was a disease with wheezing and noisy, violent breathing. In the history of Rome, we find many members of the Julio-Claudian family affected with probable atopic respiratory disorders: Caesar Augustus suffered from bronchoconstriction, seasonal rhinitis as well as a highly pruritic skin disease. Claudius suffered from rhinoconjunctivitis and Britannicus was allergic to horse dander [529]. Maimonides (1136–1204) warned that to neglect treatment of asthma could prove fatal, whereas until the 19th century, European scholars defined it as “nervous asthma,” a term that was given to mean a defect of conductivity of the ninth pair of cranial nerves.

Metabolic acidosis as an underlying mechanism of respiratory distress in children with severe acute asthma

OBJECTIVE

1) To alert the clinician that increasing rate and depth of breathing during treatment of acute asthma may be a manifestation of metabolic acidosis with hyperventilation rather than worsening airway obstruction; and 2) to describe the frequency of metabolic acidosis with hyperventilation in children with severe acute asthma admitted to our pediatric intensive care unit.

DESIGN

Retrospective medical record review.

SETTING

University-affiliated children's hospital.

PATIENTS

All patients admitted to the pediatric intensive care unit with a diagnosis of asthma between January 1, 2005, and December 31, 2005.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Fifty-three patients with asthma (median age 7.8 yrs, range 0.7-17.9 yrs; 35 [66%] male; 46 [87%] black and 7 [13%] white) were admitted to the pediatric intensive care unit during the study period. Fifteen (28%) patients developed metabolic acidosis with hyperventilation (pH <7.35, Pco2 <35 torr [4.6 kPa], and base excess < or = -7 mmol/L) during their hospital course. Of these, lactic acid was assessed in four patients and was elevated in each; all had hyperglycemia (blood glucose >120 mg/dL [6.7 mmol/L]). Patients who developed metabolic acidosis with hyperventilation received asthma therapy similar to that received by patients who did not develop the disorder. Metabolic acidosis resolved contemporaneously with tapering of beta2-adrenergic agonists and administration of supportive care. All patients survived.

CONCLUSIONS

Metabolic acidosis with hyperventilation manifesting as respiratory distress can occur in children with severe acute asthma. A pathophysiologic rationale exists for the contribution of beta2-adrenergic agents to the development of this acid-base disorder. Failure to recognize metabolic acidosis as the underlying mechanism of respiratory distress may lead to inappropriate intensification of bronchodilator therapy. Supportive care and tapering of beta2-adrenergic agents are recommended to resolve this condition.

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.

Early administration of two intravenous bolus of aminophylline added to the standard treatment of children with acute asthma

OBJECTIVES

Evaluate the efficacy of adding two intravenous bolus of aminophylline to the standard treatment of acute asthma episode in children admitted to the pediatric emergency room (PER).

METHODS

Between March 2001 and February 2002, 60 children (2-5 years old), admitted to the PER at Hospital de Clínicas de Porto Alegre (Brazil), due to an episode of acute asthma, refractory to conventional therapy (an oral dose of steroids and at least three doses of inhaled albuterol, associated or not with oxygen) were enrolled in a randomized, double blind, placebo controlled clinical trial. The randomization was performed in blocks of 10 patients, who received a "bronchodilator solution" (either saline or aminophylline), in two doses: on arrival at the PER and again 6h later. The intervention group received aminophylline 5mg/kg/dose diluted in normal saline (NS) solution up to a 20 mL volume, while the placebo group received plain NS, both in an infusion rate of 1 cc/min. The main outcomes were total length of hospital stay, length of supplemental oxygen use, number of bronchodilator nebulizations and/or aerosol inhalations performed and patient destination. The groups were compared using the Students t-test, Mann-Whitney test and Chi-Square test, accepting p<0.05 as significant.

RESULTS

Comparing the main outcomes, we did not find differences between the placebo and aminophylline groups: 29.0+/-14.7 versus 26.2+/-13.4 beta-agonist nebulizations per patient (p=0.46); 2.4+/-10.6 versus 5.6+/-14.2 aerosol inhalations per patient (p=0.32); 24.7+/-30.0 versus 26.0+/-25.2h for oxygen supplement (p=0.86); 43.2+/-30.0 versus 43.6+/-23.7h for length of hospital stay (p=0.95). We also did not find differences between the two groups related to the blood pressure, heart rate, respiratory rate and oxygen saturation.

CONCLUSION

In children aged 2-5 years admitted to a PER with asthma, two intravenous doses of 5mg/kg of aminophylline given 6h apart did not change the length of stay in hospital, the number of nebulizations given or the duration of oxygen therapy required. We are unable to tell whether there would be benefit with higher doses of aminophylline designed to give levels in the usual therapeutic range.

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.

Current management of status asthmaticus in the pediatric ICU

Status asthmaticus (SA) in the pediatric ICU (PICU) can progress to a life-threatening emergency. The goal of management is to improve hypoxemia, improve bronchoconstriction, and decrease airway edema through the administration of continuous nebulized beta2 adrenergic agonist with intermittent anticholinergics, corticosteroids, and oxygen. Adjunctive therapies, such as magnesium, methylxanthines, intravenous beta-agonists, heliox, and noninvasive ventilation should be considered in the child who fails to respond to initial therapies. The restoration of adequate pulmonary functions, resolution of airway obstruction, and avoidance of mechanical ventilation should guide management. This article reviews the pathophysiology, assessment, and management of the child who has SA in the PICU to provide the critical care nurse with current information to facilitate optimal care.