Work of breathing in anesthetized patients: laryngeal mask airway versus tracheal tube

Study Objective: To compare the work of breathing associated with the laryngeal mask airway (LMA) and tracheal tube (TT) in spontaneously breathing anesthetized patients. Design: Randomized, prospective, controled trial. Setting: University teaching hospital. Subjects: 20 ASA physical status I and II patients scheduled for elective peripheral surgery with general anesthesia. Interventions and Measurements: A standardized anesthetic protocol was utilized, and patients were allowed to breathe spontaneously through a circle absorption system. Patients were randomly assigned to receive either LMA (n = 10) or TT (n = 10) for airway management. Work of breathing was determined after the patients’ ventilatory status had been allowed to stabilize for 15 minutes and before the onset of the surgical stimulus. Airflow and esophageal pressures were measured using a pneumotachograph and an esophageal balloon, respectively, and the values were subsequently integrated to determine work of breathing. Main Results: The two groups were similar with respect to demographic characteristics and the end-tidal concentrations of carbon dioxide and isoflurane. Work of breathing per minute through the LMA (1.4 ± 0.3 J/min) was significantly lower than that through the TT (1.9 ± 0.4 J/min). Conclusion: In healthy, anesthetized, spontaneously breathing patients, work of breathing is significantly lower through the LMA than the TT.