On-line monitoring of intrinsic PEEP in ventilator-dependent patients

Abstract

Measurement of the intrinsic positive end-expiratory pressure (PEEPi) is important in planning the management of ventilated patients. Here, a new recursive least squares method for on-line monitoring of PEEPi is proposed for mechanically ventilated patients. The procedure is based on the first-order model of respiratory mechanics applied to experimental measurements obtained from eight ventilator-dependent patients ventilated with four different ventilatory modes. The model PEEPi (PEEPi,mod) was recursively constructed on an inspiration-by-inspiration basis. The results were compared with two well-established techniques to assess PEEPi: end-expiratory occlusion to measure static PEEPi (PEEPi,st) and change in airway pressure preceding the onset of inspiratory airflow to measure dynamic PEEPi (PEEPi,dyn). PEEPi,mod was significantly correlated with both PEEPi,dyn( r = 0.77) and PEEPi,st ( r= 0.90). PEEPi,mod (5.6 ± 3.4 cmH2O) was systematically >PEEPi,dyn and PEEPi,st(2.7 ± 1.9 and 8.1 ± 5.5 cmH2O, respectively), in all the models without external PEEP. Focusing on the five patients with chronic obstructive pulmonary disease, PEEPi,mod was significantly correlated with PEEPi,st ( r = 0.71), whereas PEEPi,dyn ( r = 0.22) was not. When PEEP was set 5 cmH2O above PEEPi,st, all the methods correctly estimated total PEEP, i.e., 11.8 ± 5.3, 12.5 ± 5.0, and 12.0 ± 4.7 cmH2O for PEEPi,mod, PEEPi,st, and PEEPi,dyn, respectively, and were highly correlated (0.97–0.99). We interpreted PEEPi,mod as the lower bound of PEEPi,st and concluded that our method is suitable for on-line monitoring of PEEPi in mechanically ventilated patients.