Antonella Marino

Lung Inhomogeneity in Patients with Acute Respiratory Distress Syndrome

RATIONALE Pressures and volumes needed to induce ventilator-induced lung injury in healthy lungs are far greater than those applied in diseased lungs. A possible explanation may be the presence of local inhomogeneities acting as pressure multipliers (stress raisers). OBJECTIVES To quantify lung inhomogeneities in patients with acute respiratory distress syndrome (ARDS). METHODS Retrospective quantitative analysis of CT scan images of 148 patients with ARDS and 100 control subjects. An ideally homogeneous lung would have the same expansion in all regions; lung expansion was measured by CT scan as gas/tissue ratio and lung inhomogeneities were measured as lung regions with lower gas/tissue ratio than their neighboring lung regions. We defined as the extent of lung inhomogeneities the fraction of the lung showing an inflation ratio greater than 95th percentile of the control group (1.61). MEASUREMENTS AND MAIN RESULTS The extent of lung inhomogeneities increased with the severity of ARDS (14 ± 5, 18 ± 8, and 23 ± 10% of lung volume in mild, moderate, and severe ARDS; P < 0.001) and correlated with the physiologic dead space (r(2) = 0.34; P < 0.0001). The application of positive end-expiratory pressure reduced the extent of lung inhomogeneities from 18 ± 8 to 12 ± 7% (P < 0.0001) going from 5 to 45 cm H2O airway pressure. Lung inhomogeneities were greater in nonsurvivor patients than in survivor patients (20 ± 9 vs. 17 ± 7% of lung volume; P = 0.01) and were the only CT scan variable independently associated with mortality at backward logistic regression. CONCLUSIONS Lung inhomogeneities are associated with overall disease severity and mortality. Increasing the airway pressures decreased but did not abolish the extent of lung inhomogeneities.

Bedside selection of positive end-expiratory pressure in mild, moderate, and severe acute respiratory distress syndrome.

Objective:Positive end-expiratory pressure exerts its effects keeping open at end-expiration previously collapsed areas of the lung; consequently, higher positive end-expiratory pressure should be limited to patients with high recruitability. We aimed to determine which bedside method would provide positive end-expiratory pressure better related to lung recruitability. Design:Prospective study performed between 2008 and 2011. Setting:Two university hospitals (Italy and Germany). Patients:Fifty-one patients with acute respiratory distress syndrome. Interventions:Whole lung CT scans were taken in static conditions at 5 and 45 cm H2O during an end-expiratory/end-inspiratory pause to measure lung recruitability. To select individual positive end-expiratory pressure, we applied bedside methods based on lung mechanics (ExPress, stress index), esophageal pressure, and oxygenation (higher positive end-expiratory pressure table of lung open ventilation study). Measurements and Main Results:Patients were classified in mild, moderate and severe acute respiratory distress syndrome. Positive end-expiratory pressure levels selected by the ExPress, stress index, and absolute esophageal pressures methods were unrelated with lung recruitability, whereas positive end-expiratory pressure levels selected by the lung open ventilation method showed a weak relationship with lung recruitability (r2 = 0.29; p < 0.0001). When patients were classified according to the acute respiratory distress syndrome Berlin definition, the lung open ventilation method was the only one which gave lower positive end-expiratory pressure levels in mild and moderate acute respiratory distress syndrome compared with severe acute respiratory distress syndrome (8 ± 2 and 11 ± 3 cm H2O vs 15 ± 3 cm H2O; p < 0.05), whereas ExPress, stress index, and esophageal pressure methods gave similar positive end-expiratory pressure values in mild, moderate, and severe acute respiratory distress syndrome. The positive end-expiratory pressure selected by the different methods were unrelated to each other with the exception of the two methods based on lung mechanics (ExPress and stress index). Conclusions:Bedside positive end-expiratory pressure selection methods based on lung mechanics or absolute esophageal pressures provide positive end-expiratory pressure levels unrelated to lung recruitability and similar in mild, moderate, and severe acute respiratory distress syndrome, whereas the oxygenation-based method provided positive end-expiratory pressure levels related with lung recruitability progressively increasing from mild to moderate and severe acute respiratory distress syndrome.

Pleural effusion in patients with acute lung injury : a CT scan study

Objectives:Pleural effusion is a frequent finding in patients with acute respiratory distress syndrome. To assess the effects of pleural effusion in patients with acute lung injury on lung volume, respiratory mechanics, gas exchange, lung recruitability, and response to positive end-expiratory pressure. Design, Setting, and Patients:A total of 129 acute lung injury or acute respiratory distress syndrome patients, 68 analyzed retrospectively and 61 prospectively, studied at two University Hospitals. Interventions:Whole-lung CT was performed during two breath-holding pressures (5 and 45 cm H2O). Two levels of positive end-expiratory pressure (5 and 15 cm H2O) were randomly applied. Measurements:Pleural effusion volume was determined on each CT scan section; respiratory system mechanics, gas exchange, and hemodynamics were measured at 5 and 15 cm H2O positive end-expiratory pressure. In 60 patients, elastances of lung and chest wall were computed, and lung and chest wall displacements were estimated. Results:Patients were divided into higher and lower pleural effusion groups according to the median value (287 mL). Patients with higher pleural effusion were older (62 ± 16 yr vs. 54 ± 17 yr, p < 0.01) with a lower minute ventilation (8.8 ± 2.2 L/min vs. 10.1 ± 2.9 L/min, p < 0.01) and respiratory rate (16 ± 5 bpm vs. 19 ± 6 bpm, p < 0.01) than those with lower pleural effusion. Both at 5 and 15 cm H2O of positive end-expiratory pressure PaO2/FIO2, respiratory system elastance, lung weight, normally aerated tissue, collapsed tissue, and lung and chest wall elastances were similar between the two groups. The thoracic cage expansion (405 ± 172 mL vs. 80 ± 87 mL, p < 0.0001, for higher pleural effusion group vs. lower pleural effusion group) was greater than the estimated lung compression (178 ± 124 mL vs. 23 ± 29 mL, p < 0.0001 for higher pleural effusion group vs. lower pleural effusion group, respectively). Conclusions:Pleural effusion in acute lung injury or acute respiratory distress syndrome patients is of modest entity and leads to a greater chest wall expansion than lung reduction, without affecting gas exchange or respiratory mechanics.

Lung recruitability in ARDS H1N1 patients

Dear Editor, In 2009, a newly identified H1N1 virus rapidly led to a worldwide pandemic infection [1]. The mortality rate was 5–7% in hospitalized patients and approximately 20% among those admitted to the intensive care unit (ICU) [2]. The H1N1 infection occasionally developed into acute respiratory distress syndrome (ARDS), and in some cases the hypoxemia was so severe as to require advanced rescue therapies, such as extracorporeal support. To the best of our knowledge, however, the quantitative characteristics of the ARDS due to the H1N1 virus as assessed by computed tomography (CT) have not yet been reported. We report here three patients with severe ARDS associated to H1N1 infection who were admitted to our ICU and in whom lung weight, edema, and recruitability were evaluated by a lung CT scan and subsequently by the PEEP test. Patient 1 was aged 49 years and had a body mass index (BMI) and a PaO2/ FiO2 of 42.5 kg/m 2 and 170 at PEEP 10 cmH2O, respectively; patient 2 was aged 42 years and had a BMI and a PaO2/FiO2 of 34.7 kg/m 2 and 108 at PEEP 10 cmH2O, respectively; patient 3 was aged 49 years and had a BMI and a PaO2/FiO2 of 26.2 kg/m 2

Comparison of measurement methods: an endless application of wrong statistical methods

Dear Editor, We were recently asked by a number of colleagues to perform an agreement analysis between two measurement methods using the statistical methods shown in Becker et al. [1]. At first glance, we were delighted with the correct use of the method proposed by Bland and Altman [2] and with the non-parametric Passing– Bablock regression [3], as well as with the very high number of measurements (dots in the figures). However, further study very quickly led to a change of opinion for the following reasons:

ARDS onset time and prognosis: is it a turtle and rabbit race?

According to the last Berlin definition, ARDS is a form of acute diffuse lung injury occurring in patients with predisposing risk factors, onset within one week of a known clinical insult or new/worsening respiratory symptoms, presence of bilateral opacities on the chest radiographs not fully explained by effusions, lobar/lung collapse, or nodules, respiratory failure not fully explained by cardiac failure or fluid overload, and hypoxemia. It can be classified as mild (200 mmHg < PaO2/FiO2 ≤300 mmHg or 27 kPa < PaO2/FiO2 ≤40 kPa), moderate (100 mmHg < PaO2/FiO2 ≤200 mmHg or 13 kPa < PaO2/FiO2 ≤27 kPa) or severe (PaO2/FiO2 ≤100 mmHg or PaO2/FiO2 ≤13 kPa) (1).

The Humidification During Noninvasive Ventilation

The humidification and heating (i.e., the conditioning) of medical gases is now a well-established clinical practice in intubated patients receiving invasive ventilatory support. The two most commonly used humidifying devices are the heated humidifier and the heat and moisture exchanger. At the present time, there is no information on the optimal level of the humidity of inspired gases during noninvasive ventilation (NIV). The American National Standard Institute suggested, although not directly for NIV, that 10 mgH2O/l of AH is the lowest acceptable level needed to minimize mucosal damage in the upper airways. The NIV can be delivered by a facial mask or by a helmet. Differently from the face mask, the higher internal volume of the helmet (12–15 l vs. 0.3 l) generates a mixing chamber between the expired and inspired medical gases, thus increasing the level of temperature and humidity. By delivering CPAP (continuous positive airway pressure) with a common ventilator by helmet, the level of humidity was higher than the minimum required level. On the contrary, by applying CPAP with continuous CPAP flow, it seems reasonable to use a heated humidifier. When using a face mask, a heated humidifier or heat moisture exchanger should always be used.