Use of dynamic compliance for open lung positive end-expiratory pressure titration in an experimental study.

OBJECTIVE: We tested whether the continuous monitoring of dynamic compliance could become a useful bedside tool for detecting the beginning of collapse of a fully recruited lung. DESIGN: Prospective laboratory animal investigation. SETTING: Clinical physiology research laboratory, University of Uppsala, Sweden. SUBJECTS: Eight pigs submitted to repeated lung lavages. INTERVENTIONS: Lung recruitment maneuver, the effect of which was confirmed by predefined oxygenation, lung mechanics, and computed tomography scan criteria, was followed by a positive end-expiratory pressure (PEEP) reduction trial in a volume control mode with a tidal volume of 6 mL/kg. Every 10 mins, PEEP was reduced in steps of 2 cm H2O starting from 24 cm H2O. During PEEP reduction, lung collapse was defined by the maximum dynamic compliance value after which a first measurable decrease occurred. Open lung PEEP according to dynamic compliance was then defined as the level of PEEP before the point of collapse. This value was compared with oxygenation (Pao2) and CT scans. MEASUREMENTS AND MAIN RESULTS: Pao2 and dynamic compliance were monitored continuously, whereas computed tomography scans were obtained at the end of each pressure step. Collapse defined by dynamic compliance occurred at a PEEP of 14 cm H2O. This level coincided with the oxygenation-based collapse point when also shunt started to increase and occurred one step before the percentage of nonaerated tissue on the computed tomography exceeded 5%. Open lung PEEP was thus at 16 cm H2O, the level at which oxygenation and computed tomography scan confirmed a fully open, not yet collapsed lung condition. CONCLUSIONS: In this experimental model, the continuous monitoring of dynamic compliance identified the beginning of collapse after lung recruitment. These findings were confirmed by oxygenation and computed tomography scans. This method might become a valuable bedside tool for identifying the level of PEEP that prevents end-expiratory collapse.

Suctioning through a double-lumen endotracheal tube helps to prevent alveolar collapse and to preserve ventilation.

OBJECTIVE: Endotracheal suctioning can cause alveolar collapse and impede ventilation. One reason is the gas flow through a single-lumen endotracheal tube (ETT) provoking a gradient between airway opening and tracheal (P(tr)) pressures. Separately extending the patient tubing limbs of a suitable ventilator into the trachea via a double-lumen ETT should maintain P(tr). Can this technique reduce the side effects? DESIGN AND SETTING: Bench and animal studies in a university hospital laboratory. INTERVENTIONS: A lung model was ventilated via single and double-lumen ETTs. Closed-system suctioning was applied with catheters introduced into the single-lumen ETT or the expiratory lumen of the double-lumen ETT via swivel adapter. Seven anesthetized pigs (lungs lavaged) underwent three runs of ventilation and suctioning through (a, b) an 8.0-mm ID single-lumen ETT, (c) a double-lumen ETT (41Ch outer diameter, OD). In (a) the single-lumen ETT was disconnected for suctioning, in (b) and (c) ventilator mode was set to continuous positive airway pressure mode, and the ETTs remained connected. MEASUREMENTS AND RESULTS: Bench: Suction through single-lumen ETTs impaired ventilation and led to strongly negative P(tr) (common: -10 to -20 mbar); the double-lumen ETT technique maintained ventilation and pressures. ANIMALS: Lung gas content (computed tomography, n=4) and arterial oxygen partial pressure, initially 1462+/-65 ml/532+/-76 mmHg, were significantly reduced by suctioning through single-lumen ETT: to 302+/-79 ml/62+/-6 mmHg with disconnection and to 851+/-211 ml/158+/-107 mmHg with closed suction. With double-lumen ETT they remained at 1377+/-95 ml/521+/-56 mmHg. CONCLUSIONS: The double-lumen ETT technique minimizes side effects of suctioning by maintaining P(tr).