Respiratory resistance and intrinsic positive end-expiratory pressure (PEEPi) in patients with the adult respiratory distress syndrome (ARDS)

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Abstract
Fourteen consecutive ARDS patients were examined within 24 h from the onset of mechanical ventilation to determine respiratory resistance (Rrs) and compliance (Cstrs), and to assess the influence of "intrinsic" positive end-expiratory pressure (PEEPi) on the measurement of Cstrs. Flow, pressure, and changes in lung volume were measured with the transducers of the Servo 900C Siemens ventilator. Airway occlusion was performed with the end-inspiratory and end-expiratory buttons of the ventilator. We found PEEPi (3.0 +/- 2.6 cm H2O) in ten of the fourteen patients. Without the correction for PEEPi, Cstrs was underestimated by 13.9 +/- 10% on average in the group as a whole (fourteen patients), and by 19.5 +/- 5.9% in the ten ARDS patients with PEEPi. Maximum and minimum respiratory resistance (Rrsmax and Rrsmin), and frequency-dependence of Rrs were also measured. On average, there was a marked frequency-dependence of resistance, as manifested by the difference between Rrsmax and Rrsmin, with an increase of both Rrsmin (7.7 +/- 4.2 cm H2O.l-1.s) and Rrsmax (14.3 +/- 5.0 cm H2O.l-1.s). The added resistance of the endotracheal tubes and ventilator tubings was flow dependent, and averaged 13.2 +/- 2.9 cm H2O.l-1.s.(ABSTRACT TRUNCATED AT 250 WORDS)