Respiratory mechanics by least squares fitting in mechanically ventilated patients: application on flow-limited COPD patients.
OBJECTIVE
Although computerized methods of analyzing respiratory system mechanics such as the least squares fitting method have been used in various patient populations, no conclusive data are available in patients with chronic obstructive pulmonary disease (COPD), probably because they may develop expiratory flow limitation (EFL). This suggests that respiratory mechanics be determined only during inspiration.


METHODS
Eight-bed multidisciplinary ICU of a teaching hospital.


METHODS
Eight non-flow-limited postvascular surgery patients and eight flow-limited COPD patients.


METHODS
Patients were sedated, paralyzed for diagnostic purposes, and ventilated in volume control ventilation with constant inspiratory flow rate.


METHODS
Data on resistance, compliance, and dynamic intrinsic positive end-expiratory pressure (PEEPi,dyn) obtained by applying the least squares fitting method during inspiration, expiration, and the overall breathing cycle were compared with those obtained by the traditional method (constant flow, end-inspiratory occlusion method).


CONCLUSIONS
Our results indicate that (a) the presence of EFL markedly decreases the precision of resistance and compliance values measured by the LSF method, (b) the determination of respiratory variables during inspiration allows the calculation of respiratory mechanics in flow limited COPD patients, and (c) the LSF method is able to detect the presence of PEEPi,dyn if only inspiratory data are used.
Volta
Carlo A
CA
Department of Surgical, Anesthesiological and Radiological Sciences, Section of Anesthesia and Intensive Care, Ospedale S. Anna, University of Ferrara, Corso Giovecca n. 203, 44100 Ferrara, Italy. vlc@dns.unife.it
Marangoni
Elisabetta
E
Alvisi
Valentina
V
Capuzzo
Maurizia
M
Ragazzi
Riccardo
R
Pavanelli
Lina
L
Alvisi
Raffaele
R
D006801:Humans; D016018:Least-Squares Analysis; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000628:therapy*; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*