Objective: Although computerised methods of analysis of respiratory system mechanics, such as the Least Squares Fitting (LSF) method, have been successfully applied in different patient populations, no conclusive data are available for COPD patients probably because they may develop expiratory flow limitation (EFL). The latter suggests the respiratory mechanics be determined only during inspiration. Setting: Eight bed multidisciplinary ICU of a teaching Hospital Patients: Eight non flow limited Post Vascular Surgery patients and eight flow limited COPD patients. Intervention: Patients were sedated, paralysed for diagnostic purposes and ventilated in volume control ventilation with constant inspiratory flow rate. Measurements: Data of resistance, compliance and dynamic intrinsic positive end expiratory pressure (PEEPi,dyn) obtained by applying the LSF method during inspiration, expiration and the whole breathing cycle were compared with those obtained by the traditional method (constant flow, end-inspiratory occlusion method). Results and conclusion: Our results indicate that 1) the presence of EFL markedly decreased the precision of resistance and compliance values measured by the LSF method 2) the determination of respiratory variables during inspiration allows the calculation of respiratory mechanics in flow limited COPD patients; 3) the LSF method is able to detect the presence of PEEPi,dyn if only inspiratory data is used.
Respiratory mechanics by least squares fitting in mechanically ventilated patients: application on flow-limited COPD patients
VOLTA, Carlo Alberto;RAGAZZI, Riccardo;PAVANELLI, Lina;ALVISI, Raffaele
2002
Abstract
Objective: Although computerised methods of analysis of respiratory system mechanics, such as the Least Squares Fitting (LSF) method, have been successfully applied in different patient populations, no conclusive data are available for COPD patients probably because they may develop expiratory flow limitation (EFL). The latter suggests the respiratory mechanics be determined only during inspiration. Setting: Eight bed multidisciplinary ICU of a teaching Hospital Patients: Eight non flow limited Post Vascular Surgery patients and eight flow limited COPD patients. Intervention: Patients were sedated, paralysed for diagnostic purposes and ventilated in volume control ventilation with constant inspiratory flow rate. Measurements: Data of resistance, compliance and dynamic intrinsic positive end expiratory pressure (PEEPi,dyn) obtained by applying the LSF method during inspiration, expiration and the whole breathing cycle were compared with those obtained by the traditional method (constant flow, end-inspiratory occlusion method). Results and conclusion: Our results indicate that 1) the presence of EFL markedly decreased the precision of resistance and compliance values measured by the LSF method 2) the determination of respiratory variables during inspiration allows the calculation of respiratory mechanics in flow limited COPD patients; 3) the LSF method is able to detect the presence of PEEPi,dyn if only inspiratory data is used.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
