Regional distribution of gas and tissue in acute respiratory distress syndrome. III. Consequences for the effects of positive end-expiratory pressure. CT Scan ARDS Study Group. Adult Respiratory Distress Syndrome.
OBJECTIVE
To determine whether differences in lung morphology assessed by computed tomography (CT) affect the response to positive end-expiratory pressure (PEEP).


METHODS
Prospective study over a 53-month period.


METHODS
Fourteen-bed surgical intensive care unit of a university hospital.


METHODS
Seventy-one consecutive patients with early adult respiratory distress syndrome (ARDS).


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.
Puybasset
L
L
Réanimation Chirurgicale Pierre Viars, Department of Anesthesiology, Hôpital de la Pitié-Salpêtrière, University of Paris Pierre et Marie Curie, France. louis.puybasset@psl.ap-hop-paris.fr
Gusman
P
P
Muller
J C
JC
Cluzel
P
P
Coriat
P
P
Rouby
J J
JJ
D000704:Analysis of Variance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008170:Lung Compliance; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000502:physiology; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000628:therapy*; D014057:Tomography, X-Ray Computed