• J G Aerts, B van den Berg, A F Verbraak, and J M Bogaard.
• Respiratory Intensive Care Unit, University Hospital Dijkzigt, Erasmus University, Rotterdam, The Netherlands.
• Acta Anaesthesiol Scand. 1997 May 1; 41 (5): 607-13.

BackgroundContinuous positive airway pressure (CPAP) is known to decrease inspiratory work of breathing in patients with chronic obstructive pulmonary disease (COPD). This effect is primarily attributed to a reduction in inspiratory elastic work of breathing (Wi,el) related to a decrease in intrinsic positive end-expiratory pressure (PEEP).MethodsThe aim of this study is to design a model for computation of Wi,el on the basis of respiratory mechanics in patients with COPD, at various intrinsic PEEP- and CPAP-levels. The model was used to estimate the optimal CPAP-level with respect to the intrinsic PEEP-level in terms of reduction of Wi,el. Calculations of the decrease in Wi,el due to CPAP obtained with the model were compared to changes in Wi,el and total work of breathing (Wi,tot) determined from respiratory measurements in patients with COPD.ResultsModel calculations revealed that Wi,el was minimal whenever a CPAP-level equal to the intrinsic PEEP-level was applied. When a CPAP-level exceeding the intrinsic PEEP-level was applied, the reduction in Wi,el was less. Comparing these results to the respiratory measurements, a similar pattern in reduction of Wi,el and Wi,tot was established, although absolute values of the differences were smaller in the experimental data.ConclusionThis study indicates that in order to reduce Wi,el in patients with COPD, intrinsic PEEP should be measured and the CPAP-level adjusted to the intrinsic PEEP-level.

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