Different Low Constant Flows Can Equally Determine the Lower Inflection Point in Acute Respiratory Distress Syndrome Patients

• Published in: Artificial organs 2001-11, Vol.25 (11), p.882-889
• Main Authors: Gama, Ana Maria Casati Nogueira, Meyer, Eduardo Correa, Gaudêncio, Ana Maria Araújo Silva, Grunauer, Michelle Andrade, Amato, Marcelo Britto Passos, De Carvalho, Carlos Roberto Ribeiro, Barbas, Carmen Sílvia Valente
• Format: Article
• Language: English
• Subjects: Acute respiratory distress syndrome; Adult; Constant flow technique; Female; Humans; Male; Mechanical ventilation; Middle Aged; Pflex; Plethysmography; Positive end expiratory pressure; Positive-Pressure Respiration; Pressure-volume curves; Prospective Studies; Respiratory Distress Syndrome, Adult - physiopathology; Respiratory Distress Syndrome, Adult - therapy; Respiratory Mechanics
• ISSN: 0160-564X; 1525-1594
• DOI: 10.1046/j.1525-1594.2001.06898.x

: Among the possible techniques to obtain the pressure–volume (P × 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 semistatic P × 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 × V curve (L‐Pflex) and upper inflection point of the P × 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 × 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.