Regional distribution of lung compliance by image analysis of computed tomograms.

Computed tomography (CT) can yield quantitative information about volume distribution in the lung. By combining information provided by CT and respiratory mechanics, this study aims at quantifying regional lung compliance (CL) and its distribution and homogeneity in mechanically ventilated pigs. The animals underwent inspiratory hold maneuvers at 12 lung volumes with simultaneous CT exposure at two end-expiratory pressure levels and before and after acute lung injury (ALI) by oleic acid administration. CL and the sum of positive voxel compliances from CT were linearly correlated; negative compliance areas were found. A remarkably heterogeneous distribution of voxel compliance was found in the injured lungs. As the lung inflation increased, the homogeneity increased in healthy lungs but decreased in injured lungs. Image analysis brought novel findings regarding spatial homogeneity of compliance, which increases in ALI but not in healthy lungs by applying PEEP after a recruitment maneuver.

Perioperative steroids administration in pediatric cardiac surgery: a meta-analysis of randomized controlled trials*.

OBJECTIVE: To evaluate the effects of prophylactic perioperative corticosteroid administration, compared with placebo, on postoperative mortality and clinical outcomes (renal dysfunction, duration of mechanical ventilation, and ICU length of stay) in pediatric patients undergoing cardiac surgery with cardiopulmonary bypass. DATA SOURCES: MEDLINE and Cochrane Library were screened through August 2013 for randomized controlled trials in which perioperative steroid treatment was adopted. STUDY SELECTION: Included were randomized controlled trials conducted on pediatric population that reported clinical outcomes about mortality and morbidity. DATA EXTRACTION: Eighty citations (PubMed, 48 citations; Cochrane, 32 citations) were identified, of which 14 articles were analyzed in depth and six articles fulfilled eligibility criteria and reported mortality data (232 patients), two studies reported ICU length of stay and mechanical ventilation duration (60 patients), and two studies reported renal dysfunction (49 patients). DATA SYNTHESIS: A nonsignificant trend of reduced mortality was observed in steroid-treated patients (11 [4.7%] vs 4 [1.7%] patients; odds ratio, 0.41; 95% CI, 0.14-1.15; p = 0.089). Steroids had no effects on mechanical ventilation time (117.4 ± 95.9 hr vs 137.3 ± 102.4 hr; p = 0.43) and ICU length of stay (9.6 ± 4.6 d vs 9.9 ± 5.9 d; p = 0.8). Perioperative steroid administration reduced the prevalence of renal dysfunction (13 [54.2%] vs 2 [8%] patients; odds ratio, 0.07; 95% CI, 0.01-0.38; p = 0.002). CONCLUSION: Despite a demonstrated attenuation of cardiopulmonary bypass-induced inflammatory response by steroid administration, a systematic review of randomized controlled trials performed so far reveals that steroid administration has potential clinical advantages (lower mortality and significant reduction of renal function deterioration). A larger prospective randomized study is needed to verify clearly the effects of steroid prophylaxis in pediatric patients.

Lung regional stress and strain as a function of posture and ventilatory mode.

During positive-pressure ventilation parenchymal deformation can be assessed as strain (volume increase above functional residual capacity) in response to stress (transpulmonary pressure). The aim of this study was to explore the relationship between stress and strain on the regional level using computed tomography in anesthetized healthy pigs in two postures and two patterns of breathing. Airway opening and esophageal pressures were used to calculate stress; change of gas content as assessed from computed tomography was used to calculate strain. Static stress-strain curves and dynamic strain-time curves were constructed, the latter during the inspiratory phase of volume and pressure-controlled ventilation, both in supine and prone position. The lung was divided into nondependent, intermediate, dependent, and central regions: their curves were modeled by exponential regression and examined for statistically significant differences. In all the examined regions, there were strong but different exponential relations between stress and strain. During mechanical ventilation, the end-inspiratory strain was higher in the dependent than in the nondependent regions. No differences between volume- and pressure-controlled ventilation were found. However, during volume control ventilation, prone positioning decreased the end-inspiratory strain of dependent regions and increased it in nondependent regions, resulting in reduced strain gradient. Strain is inhomogeneously distributed within the healthy lung. Prone positioning attenuates differences between dependent and nondependent regions. The regional effects of ventilatory mode and body positioning should be further explored in patients with acute lung injury.