Article

Regional distribution of gas and tissue in acute respiratory distress syndrome. III. Consequences for the effects of positive end-expiratory pressure

Intensive Care Medicine (impact factor: 5.4). 04/2012; 26(9):1215-1227. DOI:10.1007/s001340051340 pp.1215-1227

ABSTRACT Objective: To determine whether differences in lung morphology assessed by computed tomography (CT) affect the response to positive
end-expiratory pressure (PEEP).¶Design: Prospective study over a 53-month period.¶Setting: Fourteen-bed surgical intensive care unit of a university hospital.¶Patients and participants: Seventy-one consecutive patients with early adult respiratory distress syndrome (ARDS).¶Measurements and results: Fast spiral thoracic CT was performed at zero end-expiratory pressure (ZEEP) and after implementation of PEEP 10 cmH2O. Hemodynamic and respiratory parameters were measured in both conditions. PEEP-induced overdistension and alveolar recruitment
were quantified by specifically designed software (Lungview). Overdistension occurred only in the upper lobes and was significantly
correlated with the volume of lung, characterized by a CT attenuation ranging between –900 and –800 HU in ZEEP conditions.
Cardiorespiratory effects of PEEP were similar in patients with primary and secondary ARDS. PEEP-induced alveolar recruitment
of the lower lobes was significantly correlated with their lung volume (gas + tissue) at functional residual capacity. PEEP-induced
alveolar recruitment was greater in the lower lobes with “inflammatory atelectasis” than in the lower lobes with “mechanical
atelectasis.” Lung morphology as assessed by CT markedly influenced the effects of PEEP: in patients with diffuse CT attenuations
PEEP induced a marked alveolar recruitment without overdistension, whereas in patients with lobar CT attenuations PEEP induced
a mild alveolar recruitment associated with overdistension of previously aerated lung areas. These results can be explained
by the uneven distribution of regional compliance characterizing patients with lobar CT attenuations (compliant upper lobes
and stiff lower lobes) contrasting with a more even distribution of regional compliances observed in patients with diffuse
CT attenuations.¶Conclusions: In patients with ARDS, the cardiorespiratory effects of PEEP are affected by lung morphology rather than by the cause of
the lung injury (primary versus secondary ARDS). The regional distribution of the loss of aeration and the type of atelectasis
–“mechanical” with a massive loss of lung volume, or “inflammatory” with a preservation of lung volume – characterizing the
lower lobes are the main determinants of the cardiorespiratory effects of PEEP.

Key words Acute respiratory distress syndrome–Positive end-expiratory pressure–Computed tomography–Alveolar recruitment–Lung overdistension

0 0
 · 
0 Bookmarks
 · 
36 Views
  • Source
    Article: Measurement of alveolar derecruitment in patients with acute lung injury: computerized tomography versus pressure-volume curve.
    Qin Lu, Jean-Michel Constantin, Ania Nieszkowska, Marilia Elman, Silvia Vieira, Jean-Jacques Rouby
    [show abstract] [hide abstract]
    ABSTRACT: Positive end-expiratory pressure (PEEP)-induced lung derecruitment can be assessed by a pressure-volume (P-V) curve method or by lung computed tomography (CT). However, only the first method can be used at the bedside. The aim of the study was to compare both methods for assessing alveolar derecruitment after the removal of PEEP in patients with acute lung injury or acute respiratory distress syndrome. P-V curves (constant-flow method) and spiral CT scans of the whole lung were performed at PEEPs of 15 and 0 cmH2O in 19 patients with acute lung injury or acute respiratory distress syndrome. Alveolar derecruitment was defined as the difference in lung volume measured at an airway pressure of 15 cmH2O on P-V curves performed at PEEPs of 15 and 0 cmH2O, and as the difference in the CT volume of gas present in poorly aerated and nonaerated lung regions at PEEPs of 15 and 0 cmH2O. Alveolar derecruitments measured by the CT and P-V curve methods were 373 +/- 250 and 345 +/- 208 ml (p = 0.14), respectively. Measurements by both methods were tightly correlated (R = 0.82, p < 0.0001). The derecruited volume measured by the P-V curve method had a bias of -14 ml and limits of agreement of between -158 and +130 ml in comparison with the average derecruited volume of the CT and P-V curve methods. Alveolar derecruitment measured by the CT and P-V curve methods are tightly correlated. However, the large limits of agreement indicate that the P-V curve and the CT method are not interchangeable.
    Critical care (London, England) 02/2006; 10(3):R95. · 4.61 Impact Factor
  • Source
    Article: Volumetric capnography in the mechanically ventilated patient.
    L Blanch, P V Romero, U Lucangelo
    [show abstract] [hide abstract]
    ABSTRACT: Expiratory capnogram provides qualitative information on the waveform patterns associated with mechanical ventilation and quantitative estimation of expired CO2. Volumetric capnography simultaneously measures expired CO2 and tidal volume and allows identification of CO2 from 3 sequential lung compartments: apparatus and anatomic dead space, from progressive emptying of alveoli and alveolar gas. Lung heterogeneity creates regional differences in CO2 concentration and sequential emptying contributes to the rise of the alveolar plateau and to the steeper the expired CO2 slope. The concept of dead space accounts for those lung areas that are ventilated but not perfused. In patients with sudden pulmonary vascular occlusion due to pulmonary embolism, the resultant high V/Q mismatch produces an increase in alveolar dead space. Calculations derived from volumetric capnography are useful to suspect pulmonary embolism at the bedside. Alveolar dead space is large in acute lung injury and when the effect of positive end-expiratory pressure (PEEP) is to recruit collapsed lung units resulting in an improvement of oxygenation, alveolar dead space may decrease, whereas PEEP-induced overdistension tends to increase alveolar dead space. Finally, measurement of physiologic dead space and alveolar ejection volume at admission or the trend during the first 48 hours of mechanical ventilation might provide useful information on outcome of critically ill patients with acute lung injury or acute respiratory distress syndrome.
    Minerva anestesiologica 07/2006; 72(6):577-85. · 2.66 Impact Factor
  • Source
    Article: Optimization and standardization of lung densitometry in the assessment of pulmonary emphysema.
    Berend C Stoel, Jan Stolk
    [show abstract] [hide abstract]
    ABSTRACT: Currently, lung densitometry for the assessment of pulmonary emphysema has been fully validated against pathology, pulmonary function, and health status, and it is therefore being applied in pharmacotherapeutic trials. Nevertheless, its application for the early detection of emphysema has not yet been introduced in daily clinical practice. The main reason for this is the fact that it is not yet regarded a fully optimized and standardized technique. In this work, an overview is given on the current status of different standardization aspects that play an important role in this, ie, image acquisition, choice of densitometric parameter and image processing. To address these issues, solutions have been sought from the literature and from original data from previous studies. Standardization and optimization of lung densitometry has reached a more advanced stage than has been reported so far. If normal values will become available, this technique will be feasible for clinical practice. As a result, standardization for the detection and assessment of other density-related lung diseases can be achieved in a shorter period of time.
    Investigative Radiology 12/2004; 39(11):681-8. · 4.59 Impact Factor

Show more

Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

adult respiratory distress syndrome
 
cardiorespiratory effects
 
compliant upper lobes
 
computed tomography
 
Fast spiral thoracic CT
 
gas + tissue
 
lobar CT attenuations PEEP induced
 
lower lobes
 
lung morphology
 
lung volume – characterizing
 
PEEP-induced overdistension
 
Prospective study
 
regional compliance characterizing patients
 
regional distribution
 
respiratory parameters
 
secondary ARDS
 
stiff lower lobes
 
uneven distribution
 
upper lobes
 
ZEEP conditions
 

L Puybasset