OBJECTIVE: To assess the effect of a decrease in respiratory rate on dynamic hyperinflation, as determined by changes in plateau airway pressure, in patients with status asthmaticus whose baseline minute ventilation approximated 10 L/min. DESIGN: Observational descriptive study. SETTING: Medical intensive care unit. PATIENTS: Twelve patients with severe asthma mechanically ventilated in the assist control mode with a tidal volume of 613 +/- 100 mL and an inspiratory flow rate of 79 +/- 4 L/min. INTERVENTIONS: A decrease in respiratory rate from 18 to 12 and 6 breaths/min. MEASUREMENTS AND MAIN RESULTS: Plateau airway pressure decreased by approximately 2 cm H2O (25.4 +/- 2.8 vs. 23.3 +/- 2.6 cm H2O, p <.01) when respiratory rate was decreased from 18 to 12 breaths/min (increase in expiratory time 1.7 secs) and by a similar amount (23.3 +/- 2.6 vs. 21.3 +/- 2.9 cm H2O, p <.01) when respiratory rate was decreased from 12 to 6 breaths/min (increase in expiratory time 5 secs). Peak airway pressure was similar at the three respiratory rates (66.8 +/- 8.7 vs. 66.4 +/- 9.5 vs. 67.8 +/- 11.1 cm H2O at 18, 12, and 6 breaths/min, respectively). End-expiratory flow rates (n = 7) were 61.4 +/- 12.6, 38.6 +/- 4.5, and 23.1 +/- 5.8 mL/sec at respiratory rates of 18, 12, and 6 breaths/min, respectively. CONCLUSIONS: Prolongation of expiratory time decreases dynamic hyperinflation in patients with status asthmaticus, as evidenced by a reduction in plateau airway pressure, but the magnitude of this effect is relatively modest when baseline minute ventilation is < or = 10 L/min, because of the low end-expiratory flow rates. Since flow progressively decreases throughout expiration, the reduction in dynamic hyperinflation resulting from a given prolongation of expiratory time will depend on the baseline respiratory rate (i.e., less reduction in dynamic hyperinflation at a lower respiratory rate). Changes in peak airway pressure may not always reflect the changes in dynamic hyperinflation that result from prolongation of expiratory time.
OBJECTIVE: To assess the effect of a decrease in respiratory rate on dynamic hyperinflation, as determined by changes in plateau airway pressure, in patients with status asthmaticus whose baseline minute ventilation approximated 10 L/min. DESIGN: Observational descriptive study. SETTING: Medical intensive care unit. PATIENTS: Twelve patients with severe asthma mechanically ventilated in the assist control mode with a tidal volume of 613 +/- 100 mL and an inspiratory flow rate of 79 +/- 4 L/min. INTERVENTIONS: A decrease in respiratory rate from 18 to 12 and 6 breaths/min. MEASUREMENTS AND MAIN RESULTS: Plateau airway pressure decreased by approximately 2 cm H2O (25.4 +/- 2.8 vs. 23.3 +/- 2.6 cm H2O, p <.01) when respiratory rate was decreased from 18 to 12 breaths/min (increase in expiratory time 1.7 secs) and by a similar amount (23.3 +/- 2.6 vs. 21.3 +/- 2.9 cm H2O, p <.01) when respiratory rate was decreased from 12 to 6 breaths/min (increase in expiratory time 5 secs). Peak airway pressure was similar at the three respiratory rates (66.8 +/- 8.7 vs. 66.4 +/- 9.5 vs. 67.8 +/- 11.1 cm H2O at 18, 12, and 6 breaths/min, respectively). End-expiratory flow rates (n = 7) were 61.4 +/- 12.6, 38.6 +/- 4.5, and 23.1 +/- 5.8 mL/sec at respiratory rates of 18, 12, and 6 breaths/min, respectively. CONCLUSIONS: Prolongation of expiratory time decreases dynamic hyperinflation in patients with status asthmaticus, as evidenced by a reduction in plateau airway pressure, but the magnitude of this effect is relatively modest when baseline minute ventilation is < or = 10 L/min, because of the low end-expiratory flow rates. Since flow progressively decreases throughout expiration, the reduction in dynamic hyperinflation resulting from a given prolongation of expiratory time will depend on the baseline respiratory rate (i.e., less reduction in dynamic hyperinflation at a lower respiratory rate). Changes in peak airway pressure may not always reflect the changes in dynamic hyperinflation that result from prolongation of expiratory time.
Authors: Rick Hodder; M Diane Lougheed; J Mark FitzGerald; Brian H Rowe; Alan G Kaplan; R Andrew McIvor Journal: CMAJ Date: 2009-11-09 Impact factor: 8.262
Authors: Maria Paula Caramez; Joao B Borges; Mauro R Tucci; Valdelis N Okamoto; Carlos R R Carvalho; Robert M Kacmarek; Atul Malhotra; Irineu Tadeu Velasco; Marcelo B P Amato Journal: Crit Care Med Date: 2005-07 Impact factor: 7.598
Authors: Carsten Lott; Anatolij Truhlář; Anette Alfonzo; Alessandro Barelli; Violeta González-Salvado; Jochen Hinkelbein; Jerry P Nolan; Peter Paal; Gavin D Perkins; Karl-Christian Thies; Joyce Yeung; David A Zideman; Jasmeet Soar Journal: Notf Rett Med Date: 2021-06-10 Impact factor: 0.826