Effectiveness of pressure support ventilation for mechanical ventilatory support in patients with status asthmaticus

Acute severe asthma: management and treatment

Patients with acute asthma attack usually access the emergency room with severe functional impairment, despite low perception of symptoms. In this scenario, early functional assessment is essential focusing on vital parameters and respiratory function, alongside perceived dyspnea. Impairment of ventilatory mechanics due to progressive dynamic pulmonary hyperinflation should be promptly treated with medical inhalation and/or intravenous therapy, reserving intensive treatment in case of non-response and/or worsening of the clinical conditions. Therapeutic planning at patient's discharge is no less important than treatment management during emergency room access as educating the patient about therapeutic adherence significantly impact long-term outcomes of asthma. With this review we aim at exploring current evidence on acute asthma attack management, focusing of pharmacological and ventilatory strategies of care and highlighting the importance of patient education once clinical stability allows discharge from the emergency department.

Is non-invasive ventilation safe in acute severe asthma?

BACKGROUND AND OBJECTIVE

The effect of non-invasive ventilation (NIV) in acute severe asthma is unclear and there are concerns regarding its safety.

METHODS

We undertook a 5-year case-control review of mortality and morbidity associated with NIV use in acute severe asthma and compared this with asthma requiring invasive mechanical ventilation (IMV) and a control group with less severe asthma without ventilatory support.

RESULTS

Eight hundred seventy-three patients had acute severe asthma of whom 30 were treated with NIV, 17 with IMV and 90 served as controls. The mean duration of NIV was 9.5 ± 7.3 h with inspiratory positive airway pressure and expiratory positive airway pressure of 11.9 ± 1.4 and 5.8 ± 1.2 cmH2 O respectively. Mortality was zero in the NIV and control groups, compared with 41% in the IMV group. None of the NIV or control groups required escalation to invasive ventilation. There were no instances of haemodynamic compromise in the NIV or control groups. Length of hospital stay was 121 ± 96 h in the NIV group and similar to the severe IMV group (136 ± 99 h, P > 0.05) and significantly longer than the control group (42 ± 40 h, P < 0.05).

CONCLUSIONS

NIV can be safely used in acute severe asthma although further work is needed to delineate the precise patient selection process.

Noninvasive ventilation in acute asthma

Noninvasive ventilation (NIV) has well-recognized benefits in acute exacerbation of chronic obstructive pulmonary disease and pulmonary edema. Its utilization in acute asthma, however, remains controversial. In this review, we describe the physiological basis to justify NIV use in acute asthma and contribute a critical appraisal of the available literature relating to this practice. A discussion of some of the more pertinent, clinically relevant practicalities is also provided. Original research articles were identified using the electronic PubMed database. Randomized controlled trials of NIV in the setting of acute asthma were selected. Retrospective observational studies were also included if they were considered to contribute to the literature review. The use of NIV in the acute asthma setting has been shown to be associated with improvements in important physiological variables including measures of airflow and respiratory rate, and lends support to further study in this field. Improvements in airflow may be a direct effect of applied positive airway pressure or an indirect effect secondary to better dispersal of aerosolized medication. Reductions observed in respiratory rate and dyspnea are likely influenced by the amount of pressure support provided. Evidence suggestive of any improvement in mortality, intubation rate, or hospital/intensive care unit length of stay, however, is lacking. Studies to date have been hampered by small numbers and a lack of demonstrable meaningful clinical outcomes. Data relating to mortality, endotracheal intubation rates, and hospital length of stay/admission should be sought in future large clinical trials.

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.

In support of pressure support

Present generation mechanical ventilators are available with advanced microprocessor-based technology. Greater emphasis is being placed on the patient controlling the ventilator, rather than the physician controlling it. Pressure support ventilation (PSV) is a form of patient-triggered ventilation that supports spontaneous breathing during mechanical ventilation. It is flow-cycled, allowing the patient to determine the inspiratory time and rate. Each spontaneous breath is terminated when inspiratory flow decelerates to a predefined percentage of peak flow. At present, strict comparisons of the usefulness of PSV with other modalities of synchronized ventilation in newborns remain limited. This article reviews the principles and clinical applications of PSV for newborns who have respiratory failure.

Status asthmaticus in children: a review

About 10% of American children have asthma, and its prevalence, morbidity, and mortality have been increasing. Asthma is an inflammatory disease with edema, bronchial constriction, and mucous plugging. Status asthmaticus in children requires aggressive treatment with beta-agonists, anticholinergics, and corticosteroids. Intubation and mechanical ventilation should be avoided if at all possible, as the underlying dynamic hyperinflation will worsen with positive-pressure ventilation. If mechanical ventilation becomes necessary, controlled hypoventilation with low tidal volume and long expiratory time may lessen the risk of barotrauma and hypotension. Unusual and nonestablished therapies for severe asthma are discussed.

Comparison of pressure support ventilation and assist-control ventilation in the treatment of respiratory failure

STUDY OBJECTIVE

To assess whether pressure support ventilation (PSV) could be used as an alternative ventilatory mode to assist-control (A/C) ventilation in the treatment of respiratory failure.

DESIGN

A short-term (4-h) prospective study in which the beneficial effect of PSV on respiratory mechanics, gas exchange, arterial oxygenation, cardiovascular hemodynamics, and oxygen consumption was compared with A/C ventilation.

SETTING

ICU of a community hospital.

PATIENTS

Forty-five patients (mean age, 62.8 [11.8] years) with respiratory failure secondary to COPD, restrictive disorders, or neuromuscular disease requiring mechanical ventilatory support in the ICU were selected for study.

INTERVENTIONS

The mean duration of mechanical ventilation before the study was 7.16 (8.64) days. Patients were switched to the PSV mode of the mechanical ventilator for a period of 4 h after which conventional A/C ventilation was resumed.

RESULTS

Patients supported with PSV compared with A/C ventilation showed significantly higher tidal volume, minute ventilation, and inspiratory time in association with significantly lower pressure in the airway and I:E ratio. With regard to gas exchange data, an increase in dead space/tidal volume ratio (VD/VT), decrease in PaO2, and statistically but not clinically significant alteration of arterial oxygenation indexes were noted. However, when patients with COPD, restrictive disorders, and neuromuscular disease were compared, significant changes in arterial oxygenation parameters were found only in patients with restrictive disorders. There were significant decreases in heart rate, systolic pulmonary artery pressure, and pulmonary capillary wedge pressure when PSV was applied. Oxygen transport and oxygen consumption were unchanged.

CONCLUSIONS

PSV could be a possible alternative to A/C ventilation in patients with respiratory failure. PSV caused an increase in VD/VT in association with a significantly lower pressure in the airway and I:E ratio. Randomized studies are needed to define the long-term benefits of both respiratory modes and the conditions in which PSV may be a valuable alternative to A/C ventilation.

Emergency management of status asthmaticus in children

Life-threatening status asthmaticus in children is sufficiently common so that all emergency departments receiving children must have a management strategy prepared for this disease. The strategy encompassing both the prehospital and the emergency department phases relies on frequent inhalation of nebulized bronchodilators (typically albuterol and ipratropium), intravenous steroids, and prompt endotracheal intubation in children with obtundation, hypoxia, or inaudible breath sounds. Death should be preventable in this disease if the child receives aggressive medical attention before respiratory arrest has developed. However, the best therapy involves prevention by ensuring that children with a history of severe asthma receive adequate anti-inflammatory therapy usually with inhaled steroids before life-threatening status asthmaticus develops.