Atelectasis is inversely proportional to transpulmonary pressure during weaning from ventilator support in a large animal model

Abstract

Background: In mechanically ventilated, lung injured, patients without spontaneous breathing effort, atelectasis with shunt and desaturation may appear suddenly when ventilator pressures are decreased. It is not known how such a formation of atelectasis is related to transpulmonary pressure (P L ) during weaning from mechanical ventilation when the spontaneous breathing effort is increased. If the relation between P L and atelectasis were known, monitoring of P L might help to avoid formation of atelectasis and cyclic collapse during weaning. The main purpose of this study was to determine the relation between P L and atelectasis in an experimental model representing weaning from mechanical ventilation. Methods: Dynamic transverse computed tomography scans were acquired in ten anaesthetized, surfactant-depleted pigs with preserved spontaneous breathing, as ventilator support was lowered by sequentially reducing inspiratory pressure and positive end expiratory pressure in steps. The volumes of gas and atelectasis in the lungs were correlated with P L obtained using oesophageal pressure recordings. Work of breathing (WOB) was assessed from Campbell diagrams. Results: Gradual decrease in P L in both end-expiration and endinspiration caused a proportional increase in atelectasis and decrease in the gas content (linear mixed model with an autoregressive correlation matrix; P < 0.001) as the WOB increased. However, cyclic alveolar collapse during tidal ventilation did not increase significantly. Conclusion: We found a proportional correlation between atelectasis and P L during the 'weaning process' in experimental mild lung injury. If confirmed in the clinical setting, a gradual tapering of ventilator support can be recommended for weaning without risk of sudden formation of atelectasis.

Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

“…161 Exposure to negative transpulmonary pressure, notably at the end of expiration, increases the risk of lung collapse as shown by supine pig and human cadaver imaging studies. 161,162 Negative end-expiratory transpulmonary pressures have also been consistently associated with hypoxemia and lung collapse during acute lung injury 163 and in surgical patients. 95,159 Hence, the continuous monitoring of esophageal pressure, targeting positive transpulmonary pressure, 16 has been proposed as a strategy to individualize airway pressure and maintain lung expansion during mechanical ventilation (fig.…”