Effects of Inspiration Rise Time on Work of Breathing and Comfort of Conscious Patients on Mechanical Ventilation

Introduction Pressure Support Ventilation is widely used in patients in the ICU. Matching the patient's respiratory needs with adequate ventilator settings is necessary to ensure a low work of breathing (WOB) and maximal patient comfort. The inspiratory rise time (IRT) determines the time to reach the selected airway pressure. A short IRT results in a high peak inspiratory flow and a short time to reach that peak, but is also associated with the development of turbulent flow, resulting in increased WOB. Aim of this study is to investigate the effects of different IRT settings on WOB and patient comfort during pressure support ventilation.

Methods We will performed a prospective, single blind cohort study in patients on Pressure Support Ventilation. 10 healthy adult patients admitted to the ICU after elective facial or neck surgery will be included. All patients will be ventilated in pressure support mode using a Servo 300 ventilator (Siemens. Elema, Solna, Sweden), with a positive end expiratory pressure of 5 cm H2O, pressure support level of 12 cm H2O above PEEP and an inspiratory oxygen fraction of 0.40. Patients have to be awake and cooperative (Ramsay 2). WOB will be measured with an esophageal balloon, and miniature flowmeter (Bicore system). Breathing comfort will be evaluated using a visual analogue scale (VAS) ranging from 1 to 10. WOB and patient comfort will be measured (in random order) at 0, 5, and 10% IRT. For statistical analysis the two-way analysis of variance will used. A p value of < 0.05 will be considered statistically significant.