Limits...
Optimizing positive end-expiratory pressure by oscillatory mechanics minimizes tidal recruitment and distension: an experimental study in a lavage model of lung injury.

Zannin E, Dellaca RL, Kostic P, Pompilio PP, Larsson A, Pedotti A, Hedenstierna G, Frykholm P - Crit Care (2012)

Bottom Line: Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5).EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O.Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Introduction: It is well established that during mechanical ventilation of patients with acute respiratory distress syndrome cyclic recruitment/derecruitment and overdistension are potentially injurious for lung tissues. We evaluated whether the forced oscillation technique (FOT) could be used to guide the ventilator settings in order to minimize cyclic lung recruitment/derecruitment and cyclic mechanical stress in an experimental model of acute lung injury.

Methods: We studied six pigs in which lung injury was induced by bronchoalveolar lavage. The animals were ventilated with a tidal volume of 6 ml/kg. Forced oscillations at 5 Hz were superimposed on the ventilation waveform. Pressure and flow were measured at the tip and at the inlet of the endotracheal tube respectively. Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5). Positive end-expiratory pressure (PEEP) was increased from 0 to 24 cm H2O in steps of 4 cm H2O and subsequently decreased from 24 to 0 in steps of 2 cm H2O. At each PEEP step CT scans and EX5 were assessed at end-expiration and end-inspiration.

Results: During deflation the relationship between both end-expiratory and end-inspiratory EX5 and PEEP was a U-shaped curve with minimum values at PEEP = 13.4 ± 1.0 cm H2O (mean ± SD) and 13.0 ± 1.0 cm H2O respectively. EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O. At this PEEP level, CT did not show any substantial sign of intra-tidal recruitment/derecruitment or expiratory lung collapse.

Conclusions: Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration. The optimal PEEP strategy based on end-expiratory EX5 minimized intra-tidal recruitment/derecruitment as assessed by CT, and the concurrent attenuation of intra-tidal variations of EX5 suggests that it may also minimize tidal mechanical stress.

Show MeSH

Related in: MedlinePlus

Respiratory system resistance (Rrs), oscillatory elastance (EX5), percentage volume of non-aerated tissue (VtissNA%), lung gas volume (Vgas) at end-expiration (closed symbols) and at end-inspiration (open symbols) during the incremental and decremental positive end-expiratory pressure (PEEP) trial as a function of PEEP. Data are reported as mean and SD. Significance of differences between inspiration and expiration: *P <0.01, +P <0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3672594&req=5

Figure 2: Respiratory system resistance (Rrs), oscillatory elastance (EX5), percentage volume of non-aerated tissue (VtissNA%), lung gas volume (Vgas) at end-expiration (closed symbols) and at end-inspiration (open symbols) during the incremental and decremental positive end-expiratory pressure (PEEP) trial as a function of PEEP. Data are reported as mean and SD. Significance of differences between inspiration and expiration: *P <0.01, +P <0.05.

Mentions: Figure 2 shows mean data from all pigs. As expected, Rrs decreased with increasing PEEP. The relationship between EX5 and PEEP was U-shaped both at end-expiration and at end-inspiration. EX5 was higher (higher tension applied to the tissues, lower compliance) at end-inspiration (0.15 ± 0.10 cm H2O/ml) than at end-expiration (0.08 ± 0.90 cm H2O/ml) and during incremental PEEP steps than during the decremental PEEP series. Both end-inspiratory and end-expiratory EX5 reached their minimum values (maximum values of compliance) during the deflation series at a PEEP level of 12 and 14 cm H2O respectively. The difference between end-inspiratory and end-expiratory EX5 was higher during the incremental than during the decremental PEEP series and reached its minimum during deflation at a PEEP level of 12 cm H2O.


Optimizing positive end-expiratory pressure by oscillatory mechanics minimizes tidal recruitment and distension: an experimental study in a lavage model of lung injury.

Zannin E, Dellaca RL, Kostic P, Pompilio PP, Larsson A, Pedotti A, Hedenstierna G, Frykholm P - Crit Care (2012)

Respiratory system resistance (Rrs), oscillatory elastance (EX5), percentage volume of non-aerated tissue (VtissNA%), lung gas volume (Vgas) at end-expiration (closed symbols) and at end-inspiration (open symbols) during the incremental and decremental positive end-expiratory pressure (PEEP) trial as a function of PEEP. Data are reported as mean and SD. Significance of differences between inspiration and expiration: *P <0.01, +P <0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3672594&req=5

Figure 2: Respiratory system resistance (Rrs), oscillatory elastance (EX5), percentage volume of non-aerated tissue (VtissNA%), lung gas volume (Vgas) at end-expiration (closed symbols) and at end-inspiration (open symbols) during the incremental and decremental positive end-expiratory pressure (PEEP) trial as a function of PEEP. Data are reported as mean and SD. Significance of differences between inspiration and expiration: *P <0.01, +P <0.05.
Mentions: Figure 2 shows mean data from all pigs. As expected, Rrs decreased with increasing PEEP. The relationship between EX5 and PEEP was U-shaped both at end-expiration and at end-inspiration. EX5 was higher (higher tension applied to the tissues, lower compliance) at end-inspiration (0.15 ± 0.10 cm H2O/ml) than at end-expiration (0.08 ± 0.90 cm H2O/ml) and during incremental PEEP steps than during the decremental PEEP series. Both end-inspiratory and end-expiratory EX5 reached their minimum values (maximum values of compliance) during the deflation series at a PEEP level of 12 and 14 cm H2O respectively. The difference between end-inspiratory and end-expiratory EX5 was higher during the incremental than during the decremental PEEP series and reached its minimum during deflation at a PEEP level of 12 cm H2O.

Bottom Line: Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5).EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O.Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Introduction: It is well established that during mechanical ventilation of patients with acute respiratory distress syndrome cyclic recruitment/derecruitment and overdistension are potentially injurious for lung tissues. We evaluated whether the forced oscillation technique (FOT) could be used to guide the ventilator settings in order to minimize cyclic lung recruitment/derecruitment and cyclic mechanical stress in an experimental model of acute lung injury.

Methods: We studied six pigs in which lung injury was induced by bronchoalveolar lavage. The animals were ventilated with a tidal volume of 6 ml/kg. Forced oscillations at 5 Hz were superimposed on the ventilation waveform. Pressure and flow were measured at the tip and at the inlet of the endotracheal tube respectively. Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5). Positive end-expiratory pressure (PEEP) was increased from 0 to 24 cm H2O in steps of 4 cm H2O and subsequently decreased from 24 to 0 in steps of 2 cm H2O. At each PEEP step CT scans and EX5 were assessed at end-expiration and end-inspiration.

Results: During deflation the relationship between both end-expiratory and end-inspiratory EX5 and PEEP was a U-shaped curve with minimum values at PEEP = 13.4 ± 1.0 cm H2O (mean ± SD) and 13.0 ± 1.0 cm H2O respectively. EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O. At this PEEP level, CT did not show any substantial sign of intra-tidal recruitment/derecruitment or expiratory lung collapse.

Conclusions: Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration. The optimal PEEP strategy based on end-expiratory EX5 minimized intra-tidal recruitment/derecruitment as assessed by CT, and the concurrent attenuation of intra-tidal variations of EX5 suggests that it may also minimize tidal mechanical stress.

Show MeSH
Related in: MedlinePlus