Respiratory compliance and resistance in mechanically ventilated patients with acute respiratory failure

Abstract

The purpose of this study was noninvasive assessment of respiratory compliance and resistance in mechanically ventilated patients with acute respiratory failure (ARF). To this end, flow, change in lung volume, and airway pressure were measured at the proximal tip of the endotracheal tubes in twenty nine critically ill unselected patients. Eleven had acute exacerbation of chronic obstructive pulmonary disease (COPD), 8 had adult respiratory distress syndrome (ARDS) and 10 had ARF of various etiologies. Static compliance (Cst,rs), 'intrinsic' PEEP (PEEPi), as well as minimum and maximum resistance (Rrs,min and Rrs,max, respectively) were obtained with end-inspiratory and end-expiratory airway occlusions. We found that: (1) PEEPi was present in all patients with COPD (up to 11.4 cmH2O) and it was not uncommon in patients with ARF without history of chronic airway disease (up to 4.1 cmH2O). (2) Without correction for PEEPi average Cst,rs was not significantly different between ARDS and COPD patients, whereas the average corrected compliance was significantly lower in ARDS patients. (3) Substantial frequency-dependence of resistance was exhibited not only by COPD patients, but also by ARDS patients.

Assessment of Factors Related to Auto-PEEP

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In our study, we investigated auto-PEEP from an epidemiological point of view and examined how much, and not how, auto-PEEP is associated with factors that are involved in the development of auto-PEEP. Surprisingly, we observed that in our sample of mechanically ventilated subjects, the variables that characterized the breathing pattern (f, T E , V T , and minute ventilation) appeared to have a marginal role in auto-PEEP in the absence of predisposing factors of the subjects (flow limitation, RS , R RS , BMI, and aging).…”

“…These conditions include increased airway resistance, a short expiratory time (T E ), a long time constant of the respiratory system ( RS ), high minute ventilation, tidal expiratory flow limitation, chronic pulmonary disease, acute respiratory failure, and obesity. 1,[8][9][10][11][12][13] Despite the known role of these causes, the quantitative effects on auto-PEEP values are unknown. Therefore, the contribution of each of the determinants of auto-PEEP is unknown, as well as which of them are associated with the risk of high auto-PEEP levels.…”

Effects of nebulized salbutamol on respiratory mechanics in adult respiratory distress syndrome

“…Firstly, we recorded between three and five regular breathing cycles and then an end-expiratory pause was performed by pressing the ventilator button in order to obtain PEEPi, as previously described [9,10]. Subsequently we allowed at least two regular breathing cycles before causing an inspiratory pause by pushing the end inspiratory hold ventilator button; we obtained a sudden decrease in airway pressure, reaching a given value (P1) that corresponds to the necessary pressure to compensate inspiratory airway resistance to airflow and, afterwards, a slower fall until a plateau value (P2) was reached; this decrease results from the viscoelastic properties of the thoracic tissue and time-constant inequalities within the pulmonary units [3,11]. P2 represents the elastic recoil pressure of the global respiratory system [12,13] and, moreover, it provided further evidence of relaxation of the respiratory muscles.…”

“…Moreover, recent studies in human patients with this syndrome [2][3][4] have proved that airflow and additional resistances are increased. Although several authors [5][6][7] have studied the efficacy of bronchodilators (BD) in patients with chronic obstructive pulmonary disease (COPD) on mechanical ventilatory support, the action of these drugs on the pulmonary mechanics in ARDS, and their clinical consequences, have been analyzed in only a few studies [4,8], in spite of their being extensively and empirically administered to these patients in intensive care units.…”

Pulmonary hyperinflation and ventilator-dependent patients

“…11.5±3.1 0.53±0.26 [40] 12.0±0.4 0.93±0.07 [52] 13.6±6.7 0.66±0.02 [61] 5.1±0.3 - [62] 4.6±0.9 0.42±0.18 [63] 7.3±2.2 0.60±0.46 [64] 9.8±0.5 0.91±0.99 [65] 5.7±0.9 0.34±0.06…”