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The role of spontaneous effort during mechanical ventilation: normal lung versus injured lung.

Yoshida T, Uchiyama A, Fujino Y - J Intensive Care (2015)

Bottom Line: Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration.Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis.When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

View Article: PubMed Central - PubMed

Affiliation: Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871 Japan.

ABSTRACT
The role of preserving spontaneous effort during mechanical ventilation and its interaction with mechanical ventilation have been actively investigated for several decades. Inspiratory muscle activities can lower the pleural components surrounding the lung, leading to an increase in transpulmonary pressure when spontaneous breathing effort is preserved during mechanical ventilation. Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration. However, it is important to note that these beneficial effects of preserved spontaneous effort have been demonstrated only when spontaneous effort is modest and lung injury is less severe. Recent studies have revealed the 'dark side' of spontaneous effort during mechanical ventilation, especially in severe lung injury. The 'dark side' refers to uncontrollable transpulmonary pressure due to combined high inspiratory pressure with excessive spontaneous effort and the injurious lung inflation pattern of Pendelluft (i.e., the translocation of air from nondependent lung regions to dependent lung regions). Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis. When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

No MeSH data available.


Related in: MedlinePlus

Fluid-like behavior presented in normal lung vs. solid-like behavior presented in injured lung. (A) The normal lung is traditionally considered to be a continuous elastic system—exhibiting fluid-like behavior—such that distending pressure applied to a local region of the pleura (the negative swing in pleural pressure generated by diaphragmatic contraction is −10 cm H2O) becomes generalized over the whole lung (pleural) surface (the negative swings in pleural pressure at any regions are the same −10 cm H2O). (B) In injured lung, the negative swing in pleural pressure generated by diaphragmatic contraction is not uniformly transmitted, but rather concentrated in the dependent lung regions, thus a huge difference in negative pleural pressure between nondependent and dependent lung regions was generated at the early phase of inspiration, causing Pendelluft. Adapted with permission of the Wolters Kluwer Health (Ref. [36]).
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Fig3: Fluid-like behavior presented in normal lung vs. solid-like behavior presented in injured lung. (A) The normal lung is traditionally considered to be a continuous elastic system—exhibiting fluid-like behavior—such that distending pressure applied to a local region of the pleura (the negative swing in pleural pressure generated by diaphragmatic contraction is −10 cm H2O) becomes generalized over the whole lung (pleural) surface (the negative swings in pleural pressure at any regions are the same −10 cm H2O). (B) In injured lung, the negative swing in pleural pressure generated by diaphragmatic contraction is not uniformly transmitted, but rather concentrated in the dependent lung regions, thus a huge difference in negative pleural pressure between nondependent and dependent lung regions was generated at the early phase of inspiration, causing Pendelluft. Adapted with permission of the Wolters Kluwer Health (Ref. [36]).

Mentions: Classical physiological studies have shown that pressures applied to the lung surface (through the contraction of inspiratory muscles) or to the airways (through positive-pressure ventilation) re-equilibrate by a special rearrangement of the forces within the lung so that the lung is considered to behave as a continuous elastic system, presenting with a fluid-like behavior [29,30] (Figure 3). This means that local swings in Ppl, as during usual muscle contraction, tend to be transmitted all over the lung surface, creating a fairly uniform increase in PL [31-35]. This is one of the justifications for using the esophageal pressure (Pes) to estimate overall fluctuations in Ppl in normal subjects. It is important to note that the uniform distribution of forces presented in a normal lung is the basis of an occlusion test to adjust the appropriate position of the esophageal balloon. The relationship between the change in Ppl and the change in Paw should not present near unity without a uniform distribution of forces during an occlusion test. Agostoni put the cylinder on the pleural surfaces from the apex to base, even on the diaphragmatic surface, and as a result, the local changes in Ppl during spontaneous effort were not systematically different among the pleural regions [31,32]. For this uniform distribution of forces, the preservation of spontaneous breathing effort achieves a uniform increase in ventilation at a relatively low airway pressure in normal situations (i.e., normal lung and normal respiratory drive).Figure 3


The role of spontaneous effort during mechanical ventilation: normal lung versus injured lung.

Yoshida T, Uchiyama A, Fujino Y - J Intensive Care (2015)

Fluid-like behavior presented in normal lung vs. solid-like behavior presented in injured lung. (A) The normal lung is traditionally considered to be a continuous elastic system—exhibiting fluid-like behavior—such that distending pressure applied to a local region of the pleura (the negative swing in pleural pressure generated by diaphragmatic contraction is −10 cm H2O) becomes generalized over the whole lung (pleural) surface (the negative swings in pleural pressure at any regions are the same −10 cm H2O). (B) In injured lung, the negative swing in pleural pressure generated by diaphragmatic contraction is not uniformly transmitted, but rather concentrated in the dependent lung regions, thus a huge difference in negative pleural pressure between nondependent and dependent lung regions was generated at the early phase of inspiration, causing Pendelluft. Adapted with permission of the Wolters Kluwer Health (Ref. [36]).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4940771&req=5

Fig3: Fluid-like behavior presented in normal lung vs. solid-like behavior presented in injured lung. (A) The normal lung is traditionally considered to be a continuous elastic system—exhibiting fluid-like behavior—such that distending pressure applied to a local region of the pleura (the negative swing in pleural pressure generated by diaphragmatic contraction is −10 cm H2O) becomes generalized over the whole lung (pleural) surface (the negative swings in pleural pressure at any regions are the same −10 cm H2O). (B) In injured lung, the negative swing in pleural pressure generated by diaphragmatic contraction is not uniformly transmitted, but rather concentrated in the dependent lung regions, thus a huge difference in negative pleural pressure between nondependent and dependent lung regions was generated at the early phase of inspiration, causing Pendelluft. Adapted with permission of the Wolters Kluwer Health (Ref. [36]).
Mentions: Classical physiological studies have shown that pressures applied to the lung surface (through the contraction of inspiratory muscles) or to the airways (through positive-pressure ventilation) re-equilibrate by a special rearrangement of the forces within the lung so that the lung is considered to behave as a continuous elastic system, presenting with a fluid-like behavior [29,30] (Figure 3). This means that local swings in Ppl, as during usual muscle contraction, tend to be transmitted all over the lung surface, creating a fairly uniform increase in PL [31-35]. This is one of the justifications for using the esophageal pressure (Pes) to estimate overall fluctuations in Ppl in normal subjects. It is important to note that the uniform distribution of forces presented in a normal lung is the basis of an occlusion test to adjust the appropriate position of the esophageal balloon. The relationship between the change in Ppl and the change in Paw should not present near unity without a uniform distribution of forces during an occlusion test. Agostoni put the cylinder on the pleural surfaces from the apex to base, even on the diaphragmatic surface, and as a result, the local changes in Ppl during spontaneous effort were not systematically different among the pleural regions [31,32]. For this uniform distribution of forces, the preservation of spontaneous breathing effort achieves a uniform increase in ventilation at a relatively low airway pressure in normal situations (i.e., normal lung and normal respiratory drive).Figure 3

Bottom Line: Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration.Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis.When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

View Article: PubMed Central - PubMed

Affiliation: Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871 Japan.

ABSTRACT
The role of preserving spontaneous effort during mechanical ventilation and its interaction with mechanical ventilation have been actively investigated for several decades. Inspiratory muscle activities can lower the pleural components surrounding the lung, leading to an increase in transpulmonary pressure when spontaneous breathing effort is preserved during mechanical ventilation. Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration. However, it is important to note that these beneficial effects of preserved spontaneous effort have been demonstrated only when spontaneous effort is modest and lung injury is less severe. Recent studies have revealed the 'dark side' of spontaneous effort during mechanical ventilation, especially in severe lung injury. The 'dark side' refers to uncontrollable transpulmonary pressure due to combined high inspiratory pressure with excessive spontaneous effort and the injurious lung inflation pattern of Pendelluft (i.e., the translocation of air from nondependent lung regions to dependent lung regions). Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis. When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

No MeSH data available.


Related in: MedlinePlus