title: Effects of intravenous midazolam on the work of breathing.
abstract: Midazolam at sedative doses induces an increase in upper airway resistance, but its effects on the work of breathing have not been established. The flow-resistive work of breathing and pulmonary resistance (RL) of eight healthy volunteers were measured, with either midazolam 0.1 mg/kg or placebo in a random order. Esophageal pressures were measured using a balloon-tipped catheter, airflow using a pneumotachograph. Total resistive work expressed per minute (WTOT) and per liter of ventilation (WTOT/VE), and their inspiratory (WI) and expiratory (WE) components were determined. No change was observed after placebo injection. Five minutes after midazolam injection, an increase was observed in WTOT (from 3 +/- 0.4 J/min [mean +/- SEM] at control to 6.3 +/- 1.1 J/min; P < 0.01) and in WTOT/VE (from 360 +/- 30 mJ/L at control to 1250 +/- 120 mJ/L; P < 0.01), involving both WI and WE components. An increased inspiratory RL was observed from 13.7 +/- 2.6 cm H2O.L-1.s-1 at control to 32.8 +/- 3.9 cm H2O.L-1.s-1 after midazolam. Changes in inspiratory RL were correlated to changes in WI and WI/VE (r = 0.574, P < 0.001; and r = 0.762, P < 0.001, respectively). Our results suggest that airway obstruction plays a major role in the increased work of breathing observed during sedation with midazolam.
authors.affiliation: Département d'Anesthésie-Réanimation Chirurgicale, Hospital Bichat, Paris, France.
authors.forename: P
authors.initials: P
authors.lastname: Montravers
authors.forename: B
authors.initials: B
authors.lastname: Dureuil
authors.forename: S
authors.initials: S
authors.lastname: Molliex
authors.forename: J M
authors.initials: JM
authors.lastname: Desmonts
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000187:drug effects; D006801:Humans; D008170:Lung Compliance / Q000187:drug effects; D008874:Midazolam / Q000008:administration & dosage / Q000494:pharmacology*; D012119:Respiration / Q000187:drug effects*
chemical_list: D008874:Midazolam