Respiratory Mechanics during the First Day of Mechanical Ventilation in Patients with Pulmonary Edema and Chronic Airway Obstruction

Abstract

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.

The effects of positive end-expiratory pressure on respiratory system mechanics and hemodynamics in postoperative cardiac surgery patients

“…Respiratory compliance or elastance and airway resistance can be readily calculated using the flow and pressure transducers incorporated into modern mechanical ventilators, if the raw signals can be connected to an external recording device (21). Among these, the constant flow inflation method has been employed by many authors (12,13,22,23).…”

Intrinsic PEEP and cardiopulmonary interaction in patients with COPD and acute ventilatory failure

“…At the end of the expiration, this positive pressure is termed auto positive end-expiratory pressure (auto PEEP) or intrinsic positive end-expiratory pressure (PEEPi) [2,3]. PEEPi and dynamic hyperinflation have been described in mechanically-ventilated chronic obstructive pulmonary disease (COPD) patients, in whom expiratory flow limitation had occurred as a consequence of dynamic airway compression [1][2][3][4][5][6][7][8]. Recent studies have suggested that, in COPD patients with expiratory flow limitation, the application of external PEEP during assisted mechanical ventilation [9], or the use of continuous positive airway pressure (CPAP) in spontaneously breathing patients [10], can counterbalance and reduce the inspiratory threshold load imposed by PEEPi, without causing further hyperinflation.…”

Predictors of weaning outcome in chronic obstructive pulmonary disease patients

“…Accordingly, in COPD, the thresholds for fR and V 'E were necessarily lower than those obtained by YANG and TOBIN [1] in a nonhomogeneous population (table 2). In the present COPD patients, the Crs,st measured during mechanical ventilation were relatively high (table 3), reflecting the fact that, in COPD patients with ARF, the Crs,st does not differ significantly from that of normal subjects [4,10], except on the first day of mechanical ventilation, when they exhibit marked dynamic hyperinflation and hence their VT impinges on the flat upper part of the static volume/pressure curve of the respiratory system [2]. It should be noted, however, that during spontaneous breathing trials COPD patients may exhibit markedly enhanced dynamic hyperinflation (DH) with concomitant decrease in Crs,st.…”