Chest
Volume 106, Issue 5, November 1994, Pages 1401-1406
Journal home page for Chest

Clinical Investigations: Asthma
Respiratory Mechanics in Status Asthmaticus: Effects of Inhalational Anesthesia

https://doi.org/10.1378/chest.106.5.1401Get rights and content

The incidence and severity of bronchial asthma has increased considerably in recent years. As a result, the number of patients requiring mechanical ventilation and more intensive medical therapy for treatment of refractory asthma has also increased. Despite this, available information concerning the quantitative changes in respiratory mechanics and the response to treatment that occur in such patients is limited. The present study describes the abnormalities in respiratory mechanics and the response to isoflurane anesthesia observed in three adults mechanically ventilated for treatment of status asthmaticus. Airway pressure, flow, and volume were measured during controlled mechanical ventilation in which the airway was periodically occluded in order to determine respiratory system mechanics. In two patients, the volume of hyperinflation and expiratory volume-flow relationship were also obtained. Inspiratory and expiratory indices of respiratory resistance were markedly abnormal. These abnormalities were associated with significant dynamic hyperinflation and high levels of intrinsic PEEP. Expiratory flow limitation was also identified in two patients by failure of low levels of applied positive end-expiratory pressure (PEEP) to alter the expiratory volume-flow relationship. Indices of respiratory resistance as well as the magnitude of dynamic hyperinflation and intrinsic PEEP improved considerably with isoflurane administration, after having been refractory to intensive conventional bronchodilator therapy. In summary, these results demonstrate the severity of abnormalities in respiratory mechanics present in ventilated patients with status asthmaticus and the potential therapeutic efficacy of inhalational anesthesia in this setting.

Section snippets

Subjects

Three patients (two male, one female) with status asthmaticus refractory to conventional medical treatment were studied in the medical intensive care units of three McGill University teaching hospitals. In each case, the diagnosis of asthma had been previously established by the medical history and the presence of reversible airway obstruction.3 Each patient had severe bronchospasm associated with marked respiratory distress and acute respiratory acidosis necessitating urgent endotracheal

Results

Individual values for Rmax, Rmin, and Crs before and during isoflurane anesthesia are provided in Figure 1. Baseline values of Rmax and Rmin were markedly elevated and decreased considerably with isoflurane. Crs was variably reduced and did not change significantly with isoflurane. In patient 2, a dose-response curve of isoflurane was obtained. As can be seen in Figure 2, the lowest isoflurane concentration used reduced Rmax and Rmin with further improvement at the higher concentrations while

Discussion

This study shows the severity of abnormalities in respiratory function that occur in status asthmaticus and the effects of isoflurane on various indices of respiratory system mechanics in this setting. Previous reports have described a number of abnormalities in respiratory mechanics in ventilated patients with status asthmaticus.14, 15, 16 These include increases in inspiratory and expiratory resistance as well as the development of dynamic hyperinflation with PEEPi. However, to our knowledge,

ACKNOWLEDGMENTS

The authors wish to thank Dr. Andrew Scott and the staff of the Montreal General Hospital, the Royal Victoria Hospital, and the Montreal Chest Hospital Centre for their help and cooperation.

References (31)

  • RanieriVM et al.

    Effects of positive end-expiratory pressure on alveolar recruitment and gas exchange in patients with adult respiratory distress syndrome.

    Am Rev Respir Dis

    (1991)
  • BroseghiniC et al.

    Respiratory mechanics during the first day of mechanical ventilation in patients with pulmonary edema and chronic airway obstruction.

    Am Rev Respir Dis

    (1988)
  • RossiA et al.

    Respiratory mechanics in mechanically ventilated patients with respiratory failure.

    J Appl Physiol

    (1985)
  • BatesJHT et al.

    Interrupter resistance elucidated by alveolar pressure measurement in open-chest normal dogs.

    J Appl Physiol

    (1988)
  • GottfriedSB et al.

    Noninvasive determination of respiratory system mechanics during mechanical ventilation for acute respiratory failure.

    Am Rev Respir Dis

    (1985)
  • Cited by (0)

    Supported in part by the Medical Research Council of Canada, the Respiratory Health Network of Centres of Excellence, the Canadian Cystic Fibrosis Foundation, and the J.T. Costello Memorial Research Fund

    Presented in part at the Annual Meeting of the American Thoracic Society, Miami, May 17, 1992.

    Recipient of research fellowship awards from the Canadian Lung Association and the Fonds de la Recherche en Sante du Quebec.

    Medical Research Scholar of the Fonds de la Recherche en Sante du Quebec.

    View full text