Objective: To evaluate the physiological effects of decannulation on breathing patterns and respiratory mechanics by comparing mouth breathing (MB) to tracheal breathing (TB) in tracheostomized patients.
Design and setting: Prospective cross-over study in a critical and neuromuscular care unit.
Patients and methods: Nine consecutive neuromuscular tracheostomized patients. Flow, esophageal pressure, gastric pressure, expiratory gas, and arterial blood gases were measured during MB and TB.
Results: MB induced an increase in tidal volume (from 330+/-60 ml to 400+/-80 ml) without changing respiratory frequency, inspiratory time, or arterial CO(2) pressure. This ventilation increase was due to a significant increase in physiological dead space (from 156+/-67 to 230+/-82 ml) and was associated with significant increases in work of breathing (from 6.9+/-3.4 to 9.1+/-3.3 J/min), transdiaphragmatic pressure swing (from 10+/-4 to 12.5+/-7 cmH(2)O), diaphragmatic pressure-time product per minute (from 214+/-100 to 271+/-92 cmH(2)O s(-1) min(-1)), and oxygen uptake (from 206+/-30 to 229+/-34 ml/min). Upper airway resistance did not differ from in vitro tracheostomy tube resistance. In addition, total lung-airway resistance, dynamic pulmonary compliance, and intrinsic positive end-expiratory pressure were similar in both conditions.
Conclusions: Decannulation resulted in a dead space increase with no other detectable additional loading. It increased work of breathing by more than 30%. Decannulation deserves special attention in patients with restrictive respiratory disease.