ELASTIC WORK OF BREATHING DURING CONTINUOUS POSITIVE AIRWAY PRESSURE IN INTUBATED PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE (THEORETICAL-ANALYSIS AND EXPERIMENTAL VALIDATION)

Background: Continuous positive airway pressure (CPAP) is known to dec rease inspiratory work of breathing in patients with chronic obstructi ve 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). Metho ds: The aim of this study is to design a model for computation of Wi,e l on the basis of respiratory mechanics in patients with COPD, at vari ous intrinsic PEEP- and CPAP-levels. The model was used to estimate th e 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 C PAP obtained with the model were compared to changes in Wi,el and tota l work of breathing (Wi,tot) determined from respiratory measurements in patients with COPD. Results: Model calculations revealed that Wi,el was minimal whenever a CPAP-level equal to the intrinsic PEEP-level w as applied. When a CPAP-level exceeding the intrinsic PEEP-level was a pplied, the reduction in Wi,el was less. Comparing these results to th e respiratory measurements, a similar pattern in reduction of Wi,el an d Wi,tot was established, although absolute values of the differences were smaller in the experimental data. Conclusion: This study indicate s 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-l evel. (C) Acta Anaesthesiologica Scandinavica 41 (1997).