Immediate post-operative effects of tracheotomy on respiratory function during mechanical ventilation

INTRODUCTION Tracheotomy is widely performed in the intensive care unit after long-term oral intubation. The present study investigates the immediate influence of tracheotomy on respiratory mechanics and blood gases during mechanical ventilation. METHODS Tracheotomy was performed in 32 orally intubated patients for 10.5 +/- 4.66 days (all results are means +/- standard deviations). Airway pressure, flow and arterial blood gases were recorded immediately before tracheotomy and half an hour afterwards. Respiratory system elastance (Ers), resistance (Rrs) and end-expiratory pressure (EEP) were evaluated by multiple linear regression. Respiratory system reactance (Xrs), impedance (Zrs) and phase angle (phirs) were calculated from Ers and Rrs. Comparisons of the mechanical parameters, blood gases and pH were performed with the aid of the Wilcoxon signed-rank test (P = 0.05). RESULTS Ers increased (7 +/- 11.3%, P = 0.001), whereas Rrs (-16 +/- 18.4%, P = 0.0003), Xrs (-6 +/- 11.6%, P = 0.006) and phi rs (-14.3 +/- 16.8%, P = <0.001) decreased immediately after tracheotomy. EEP, Zrs, blood gases and pH did not change significantly. CONCLUSION Lower Rrs but also higher Ers were noted immediately after tracheotomy. The net effect is a non-significant change in the overall Rrs (impedance) and the effectiveness of respiratory function. The extra dose of anaesthetics (beyond that used for sedation at the beginning of the procedure) or a higher FiO2 (fraction of inspired oxygen) during tracheotomy or aspiration could be related to the immediate elastance increase.