Effect of Positive End-expiratory Pressure on Regional Ventilation Distribution during Mechanical Ventilation after Surfactant Depletion

Bayat, Sam; Porra, Liisa; Albu, Gergely; Suhonen, Heikki; Strengell, Satu; Suortti, P.; Sovijärvi, Anssi; Peták, Ferenc; Habre, Walid

doi:10.1097/aln.0b013e318291c165

Cited by 33 publications

(47 citation statements)

References 43 publications

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“…This difference is unlikely to affect the lung volume estimates in a normal lungs, however may gain importance after lung lavage where the airway closures may lead to trapped air in the lung periphery. Using a similar experimental model where the regional lung ventilation was assessed by synchrotron imaging, we recently demonstrated that air trapping may be encountered at PEEP level of 3 cmH 2 O [17]. Considering that the maximum amount of such lung regions with trapped air does not exceed 10%, the impact of this phenomenon on our results is minor.…”

Section: Discussionmentioning

confidence: 94%

“…The pathogenesis of this severe pulmonary disorder is far more complex then the loss of surfactant function. Nonetheless, the present model mimics lung collapsibility and the loss or regional lung ventilation with increased heterogeneity, particularly at low PEEP levels [17]. Atelectasis development was evidenced from the marked and significant decreases in EELV MBW,He (-38 ± 5.3%, p < 0.005) and ELV (-65 ± 4.2%, p < 0.001) at PEEP 0.…”

Section: Discussionmentioning

confidence: 99%

“…Atelectasis development was evidenced from the marked and significant decreases in EELV MBW,He (-38 ± 5.3%, p < 0.005) and ELV (-65 ± 4.2%, p < 0.001) at PEEP 0. The lavage-induced changes in EELV CT were less obvious, since lung volume variable includes all aerated structures including those with trapped air [17]. To avoid time effects in our findings, the order of PEEP was randomized within a set of recordings.…”

Section: Discussionmentioning

confidence: 99%

“…This was manifested both in the excellent correlations between EELV MBW,He and EELV CT (Figure 4) and the good agreement (Figure 5). The importance of this finding stems from the fact that multiple breath washout technique by using ultrasonic flow meter has been applied commonly in experimental [6,10,17,20] and clinical studies [2,21-26]. However, the relationship of EELV MBW,He obtained by this approach was not related to that obtained by using a reference method in patients with acute lung injury based on CT imaging [7], and the validity of this variable has not been evaluated.…”

Section: Discussionmentioning

confidence: 99%

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Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging

et al. 2014

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BackgroundBedside assessment of lung volume in clinical practice is crucial to adapt ventilation strategy. We compared bedside measures of lung volume by helium multiple-breath washout technique (EELVMBW,He) and effective lung volume based on capnodynamics (ELV) to those assessed from spiral chest CT scans (EELVCT) under different PEEP levels in control and surfactant-depleted lungs.MethodsLung volume was assessed in anaesthetized mechanically ventilated rabbits successively by measuring i) ELV by analyzing CO2 elimination traces during the application of periods of 5 consecutive alterations in inspiratory/expiratory ratio (1:2 to 1.5:1), ii) measuring EELVMBW,He by using helium as a tracer gas, and iii) EELVCT from CT scan images by computing the normalized lung density. All measurements were performed at PEEP of 0, 3 and 9 cmH2O in random order under control condition and following surfactant depletion by whole lung lavage.ResultsVariables obtained with all techniques followed sensitively the lung volume changes with PEEP. Excellent correlation and close agreement was observed between EELVMBW,He and EELVCT (r = 0.93, p < 0.0001). ELV overestimated EELVMBW,He and EELVCT in normal lungs, whereas this difference was not evidenced following surfactant depletion. These findings resulted in somewhat diminished but still significant correlations between ELV and EELVCT (r = 0.58, p < 0.001) or EELVMBW,He (0.76, p < 0.001) and moderate agreements.ConclusionsLung volume assessed with bedside techniques allow the monitoring of the changes in the lung aeration with PEEP both in normal lungs and in a model of acute lung injury. Under stable pulmonary haemodynamic condition, ELV allows continuous lung volume monitoring, whereas EELVMBW,He offers a more accurate estimation, but intermittently.

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging

et al. 2014

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“…Instead, the radiologic pattern may be of diffusely distributed moderately aerated tissue 6 . Though the volume of aerated lung may be appreciable in diffuse injury 7 , aerated and non-aerated lung are co-localized such that lung tissue interdependence 8,9 may be important. It is unlikely that the same relationship among inflation, deformation, and injury is at play when a given V T inflates a separate aerated lung compartment, compared with where aeration and non-aeration are diffusely intermingled.…”

Section: Introductionmentioning

confidence: 99%

Visualizing the Propagation of Acute Lung Injury

et al. 2016

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Background Mechanical ventilation worsens acute respiratory distress syndrome, but this secondary “ventilator-associated” injury is variable and difficult to predict. The authors aimed to visualize the propagation of such ventilator-induced injury, in the presence (and absence) of a primary underlying lung injury, and to determine the predictors of propagation. Methods Anesthetized rats (n = 20) received acid aspiration (hydrochloric acid) followed by ventilation with moderate tidal volume (VT). In animals surviving ventilation for at least 2 h, propagation of injury was quantified by using serial computed tomography. Baseline lung status was assessed by oxygenation, lung weight, and lung strain (VT/expiratory lung volume). Separate groups of rats without hydrochloric acid aspiration were ventilated with large (n = 10) or moderate (n = 6) VT. Results In 15 rats surviving longer than 2 h, computed tomography opacities spread outward from the initial site of injury. Propagation was associated with higher baseline strain (propagation vs. no propagation [mean ± SD]: 1.52 ± 0.13 vs. 1.16 ± 0.20, P < 0.01) but similar oxygenation and lung weight. Propagation did not occur where baseline strain was less than 1.29. In healthy animals, large VT caused injury that was propagated inward from the lung periphery; in the absence of preexisting injury, propagation did not occur where strain was less than 2.0. Conclusions Compared with healthy lungs, underlying injury causes propagation to occur at a lower strain threshold and it originates at the site of injury; this suggests that tissue around the primary lesion is more sensitive. Understanding how injury is propagated may ultimately facilitate a more individualized monitoring or management.

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Hyperpolarized gas diffusion MRI for the study of atelectasis and acute respiratory distress syndrome

et al. 2014

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Considerable uncertainty remains about the best ventilator strategies for the mitigation of atelectasis and associated airspace stretch in patients with acute respiratory distress syndrome (ARDS). In addition to several immediate physiological effects, atelectasis increases the risk of ventilator-associated lung injury (VALI), which has been shown to significantly worsen ARDS outcomes. A number of lung imaging techniques have made substantial headway in clarifying the mechanisms of atelectasis. This paper reviews the contributions of CT, PET, and conventional MRI to understanding this phenomenon. In doing so, it also reveals several important shortcomings inherent to each of these approaches. Once these shortcomings have been made apparent, we describe how hyperpolarized gas magnetic resonance imaging (HP MRI)—a technique that is uniquely able to assess responses to mechanical ventilation and lung injury in peripheral airspaces—is poised to fill several of these knowledge gaps. The HP-MRI-derived apparent diffusion coefficient (ADC) quantifies the restriction of 3He diffusion by peripheral airspaces, thereby obtaining pulmonary structural information at an extremely small scale. Lastly, this paper reports the results of a series of experiments that measured ADC in mechanically ventilated rats in order to investigate (i) the effect of atelectasis on ventilated airspaces; (ii) the relationship between positive end-expiratory pressure (PEEP), hysteresis, and the dimensions of peripheral airspaces; and (iii) the ability of PEEP and surfactant to reduce airspace dimensions after lung injury. An increase in ADC was found to be a marker of atelectasis-induced overdistension. With recruitment, higher airway pressures were shown to reduce stretch rather than worsen it. Moving forward, HP MRI has significant potential to shed further light on the atelectatic processes that occur during mechanical ventilation.

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Effect of Positive End-expiratory Pressure on Regional Ventilation Distribution during Mechanical Ventilation after Surfactant Depletion

Cited by 33 publications

References 43 publications

Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging

Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging

Visualizing the Propagation of Acute Lung Injury

Hyperpolarized gas diffusion MRI for the study of atelectasis and acute respiratory distress syndrome

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