We investigated the early changes of respiratory mechanics in mechanically ventilated patients with acute respiratory failure (ARF): 8 patients after acute exacerbation of chronic airway obstruction (CAO), 8 patients with cardiogenic pulmonary edema (CPE), and 8 patients with adult respiratory distress syndrome (ARDS). The patients were studied within the first day from the onset of mechanical ventilation. Flow, changes in lung volume, and airway pressure were measured using the 900C Servo Ventilator. End-inspiratory and end-expiratory occlusions of the airway were performed to obtain respiratory compliance and resistance. We found that: (1) acute exacerbation of CAO was characterized by high respiratory resistance (reflecting in part time-constant inequalities within the lung) and severe pulmonary hyperinflation, with "intrinsic" PEEP (PEEPi) up to 22 cm H2O (mean [SD], 13.5 [6.7] cm H2O); (2) PEEPi, even if not high, was present in almost all patients with pulmonary edema, averaging 3.8 and 3.0 cm H2O in ARDS and CPE, respectively; (3) respiratory resistance was increased in patients with CPE and ARDS who had no history of airway disease; (4) patients with ARDS were characterized also by low compliance (mean [SD], 0.035 [0.005] L/cm H2O) and high resistance, the latter also reflecting a substantial component caused by time-constant inequalities; (5) in all 24 patients, static respiratory compliance (and its reciprocal, elastance) was significantly correlated with the pulmonary oxygenation index, i.e., the PaO2/PAO2 ratio. We conclude that early assessment of respiratory mechanics in mechanically ventilated patients with ARF can provide better understanding of the patients' conditions as well as guidelines for therapeutic approach and weaning attempts.

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To investigate the dose-response relationship and the time course of the effects of fenoterol (a selective beta 2-adrenergic agonist) on respiratory function in mechanically ventilated patients with acute respiratory failure due to exacerbation of chronic airflow obstruction (CAO), seven consecutive acutely ill patients were studied within 3 days of the onset of mechanical ventilation. Airflow, airway pressure, and changes in lung volume were measured with the transducers of the 900 C Servo Ventilator, the last by electronic integration. The end-expiratory lung volume (EELV), the intrinsic positive end-expiratory pressure (PEEPi), the static respiratory compliance (Cstrs), maximum and minimum respiratory resistance (Rrsmax and Rrsmin), and arterial oxygen tension (PaO2), were measured under control conditions (all patients were receiving aminophylline infused at a constant rate) 5, 15, and 30 min after administration of 4 ml aerosolized saline solution and 5, 15, and 30 min after inhalation of 0.4, 0.8, and 1.2 mg fenoterol. After the last dose, measurements were repeated at 60, 120, and 180 min. We found that, on average, while saline did not cause any significant change in respiratory mechanics, a low dose (0.4 mg) of inhaled fenoterol was followed by a rapid (5 min) and significant decrease in Rrsmax (-33%), Rrsmin (-28%), EELV (-34%), and PEEPi (-44%), with a slight but not significant further fall with higher doses. However, changes were short-lasting, and by 2 h after the end of administration were no longer significant. PaO2 dropped significantly on average, with a maximum mean fall of 15 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

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