title: Different low constant flows can equally determine the lower inflection point in acute respiratory distress syndrome patients.
abstract: Among the possible techniques to obtain the pressure-volume (P x V) curve at the bedside the low constant flow (CF) is the easiest and quickest one. However, the best value for CF to perform a good semi-static P x V curve is still to be determined. The purpose of this study was to evaluate the influence of 4 different CFs (1, 2, 5, and 10 L/min) on determination of lower inflection point of the P x V curve (L-Pflex) and upper inflection point of the P x V curve (U-Pflex) on the maximum slope and on the inspiratory work of breathing (up to volume of 1.35 L; inspiratory work L/cm H2O), comparing the volume estimated from the CF with the measured volume obtained by the respiratory inductive plethysmograph. The design was a prospective study, and the setting was an adult medical intensive care unit of a university hospital. There were 7 acute respiratory distress syndrome (ARDS) patients, less than 5 days of installation, after the standardization of lung volume history received sequentially from 4 different low inspiratory CFs in 2 trials. The P x V curve lasted from 73 +/- 1.6 s (1 L/min) to 8.8 +/- 0.69 s (10 L/min). The L-Pflex differed in the 2 performed trials (p = 0.04). There was no difference of L-Pflex among the 4 CFs comparing the 3 methods (p = 0.072) used for its calculation as well as comparing the estimated and the measured volume (p = 0.456). The maximum slope decreased significantly while increasing the flow from 1 to 10 L/min just in the estimated volume (p = 0.03). The inspiratory work did not increase with the increment of the flow either in the estimated volume (p = 0.217) or in the measured volume (p = 0.149). The U-Pflex differed among the trials (p = 0.003) and the methods used for its calculation (p < 0.01). Constant flows from 1 to 10 L/min can equally determine L-Pflex in ARDS patients and is an easy and quick way to obtain the L-Pflex in order to optimize positive end expiratory pressure (PEEP) in ARDS patients.
authors.affiliation: Respiratory Intensive Care Unit, Pulmonary Division of the School of Medicine, University of São Paulo, Brazil.
authors.forename: A M
authors.initials: AM
authors.lastname: Gama
authors.forename: E C
authors.initials: EC
authors.lastname: Meyer
authors.forename: A M
authors.initials: AM
authors.lastname: Gaudêncio
authors.forename: M A
authors.initials: MA
authors.lastname: Grunauer
authors.forename: M B
authors.initials: MB
authors.lastname: Amato
authors.forename: C R
authors.initials: CR
authors.lastname: de Carvalho
authors.forename: C S
authors.initials: CS
authors.lastname: Barbas
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010991:Plethysmography; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics