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Effect of inspiration rise time on work of breathing and patient comfort during pressure support ventilation


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. The aim of this study was to investigate the effects of different IRT settings on WOB and patient comfort during pressure support ventilation.


We performed a prospective, single-blind cohort study in patients on pressure support ventilation. Ten healthy adult patients admitted to the ICU after elective facial or neck surgery were included. All patients were ventilated in the pressure support mode using a Servo 300 ventilator (Siemens, Elema, Solna, Sweden), with a positive end expiratory pressure (PEEP) of 5 cmH2O, a pressure support level of 12 cmH2O above PEEP and an inspiratory oxygen fraction of 0.40. Patients were awake and cooperative (Ramsay 2). WOB was measured with an esophageal balloon and a miniature flowmeter (Bicore system). Breathing comfort was evaluated using a visual analogue scale (VAS) ranging from 1 to 10. WOB and patient comfort was measured (in random order) at 0, 5, and 10% IRT. For statistical analysis, two-way analysis of variance was used. P < 0.05 was considered statistically significant.


An interim analysis was performed on four of a total of 10 patients. The WOB increased from 0.25 ± 0.11 J/l at 0% IRT to 0.48 ± 0.01 J/l at 5% IRT and 0.59 ± 0.21 J/l at 10% IRT (values expressed as mean ± SD). At the same time the patients comfort, as analysed by the VAS, decreased from 5.5 (4.0–7.75) at 0% IRT to 4.5 (3.0–6.5) at 5% IRT and 2.0 (1.0–3.75) at 10% IRT (values expressed as median [IQR]). Analysis of all patient data with a complete statistical analysis will be available soon.


With increasing IRT the WOB increases and patient comfort decreases. In this category of patients we therefore suggest using the shortest IRT (0%).

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Brouwer, L., Hoedemaekers, A. & van der Hoeven, J. Effect of inspiration rise time on work of breathing and patient comfort during pressure support ventilation. Crit Care 10 (Suppl 1), P38 (2006).

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