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Veno-venous extracorporeal membrane oxygenation (vv-ECMO) represents one of the most advanced respiratory support for patients suffering from severe acute respiratory distress syndrome. During vv-ECMO a certain amount of extracorporeal oxygenated blood can flow back from the reinfusion into the drainage cannula without delivering oxygen to the patient. Detection and quantification of this dynamic phenomenon, defined recirculation, are critical to optimize the ECMO efficiency. Our study aimed to measure the recirculation fraction (RF) using a thermodilution technique. We built an in vitro circuit to simulate patients undergoing vv-ECMO (ECMO flow: 1.5, 3, and 4.5 L/min) with different cardiac output, using a recirculation bridge to achieve several known RFs (from 0% to 50%). The RF, computed as the ratio of the area under temperature-time curves (AUC) of the drainage and reinfusion, was significantly related to the set RF (AUC ratio (%) = 0.979 × RF (%) + 0.277%, p < 0.0001), but it was not dependent on tested ECMO and cardiac output values. A Bland-Altman analysis showed an AUC ratio bias (precision) of -0.21% for the overall data. Test-retest reliability showed an intraclass correlation coefficient of 0.993. This study proved the technical feasibility and computation validity of the applied thermodilution technique in computing vv-ECMO RF.

ImportanceData on the association of COVID-19 vaccination with intensive care unit (ICU) admission and outcomes of patients with SARS-CoV-2–related pneumonia are scarce.ObjectiveTo evaluate whether COVID-19 vaccination is associated with preventing ICU admission for COVID-19 pneumonia and to compare baseline characteristics and outcomes of vaccinated and unvaccinated patients admitted to an ICU.Design, Setting, and ParticipantsThis retrospective cohort study on regional data sets reports: (1) daily number of administered vaccines and (2) data of all consecutive patients admitted to an ICU in Lombardy, Italy, from August 1 to December 15, 2021 (Delta variant predominant). Vaccinated patients received either mRNA vaccines (BNT162b2 or mRNA-1273) or adenoviral vector vaccines (ChAdOx1-S or Ad26.COV2). Incident rate ratios (IRRs) were computed from August 1, 2021, to January 31, 2022; ICU and baseline characteristics and outcomes of vaccinated and unvaccinated patients admitted to an ICU were analyzed from August 1 to December 15, 2021.ExposuresCOVID-19 vaccination status (no vaccination, mRNA vaccine, adenoviral vector vaccine).Main Outcomes and MeasuresThe incidence IRR of ICU admission was evaluated, comparing vaccinated people with unvaccinated, adjusted for age and sex. The baseline characteristics at ICU admission of vaccinated and unvaccinated patients were investigated. The association between vaccination status at ICU admission and mortality at ICU and hospital discharge were also studied, adjusting for possible confounders.ResultsAmong the 10 107 674 inhabitants of Lombardy, Italy, at the time of this study, the median [IQR] age was 48 [28-64] years and 5 154 914 (51.0%) were female. Of the 7 863 417 individuals who were vaccinated (median [IQR] age: 53 [33-68] years; 4 010 343 [51.4%] female), 6 251 417 (79.5%) received an mRNA vaccine, 550 439 (7.0%) received an adenoviral vector vaccine, and 1 061 561 (13.5%) received a mix of vaccines and 4 497 875 (57.2%) were boosted. Compared with unvaccinated people, IRR of individuals who received an mRNA vaccine within 120 days from the last dose was 0.03 (95% CI, 0.03-0.04; P P P P P o2) and fraction of inspiratory oxygen (FiO2) at ICU admission (median [IQR]: 138 [100-180] vs 120 [90-158] mm Hg; P = .007). Factors associated with ICU and hospital mortality were higher age, premorbid heart disease, lower Pao2/FiO2 at ICU admission, and female sex (this factor only for ICU mortality). ICU and hospital mortality were similar between vaccinated and unvaccinated patients.Conclusions and RelevanceIn this cohort study, mRNA and adenoviral vector vaccines were associated with significantly lower risk of ICU admission for COVID-19 pneumonia. ICU and hospital mortality were not associated with vaccinated status. These findings suggest a substantial reduction of the risk of developing COVID-19–related severe acute respiratory failure requiring ICU admission among vaccinated people.

During the COVID-19 pandemic, a shortage of mechanical ventilators was reported and ventilator sharing between patients was proposed as an ultimate solution. Two lung simulators were ventilated by one anesthesia machine connected through two respiratory circuits and T-pieces. Five different combinations of compliances (30–50 mL × cmH2O−1) and resistances (5–20 cmH2O × L−1 × s−1) were tested. The ventilation setting was: pressure-controlled ventilation, positive end-expiratory pressure 15 cmH2O, inspiratory pressure 10 cmH2O, respiratory rate 20 bpm. Pressures and flows from all the circuit sections have been recorded and analyzed. Simulated patients with equal compliance and resistance received similar ventilation. Compliance reduction from 50 to 30 mL × cmH2O−1 decreased the tidal volume (VT) by 32% (418 ± 49 vs. 285 ± 17 mL). The resistance increase from 5 to 20 cmH2O × L−1 × s−1 decreased VT by 22% (425 ± 69 vs. 331 ± 51 mL). The maximal alveolar pressure was lower at higher compliance and resistance values and decreased linearly with the time constant (r² = 0.80, p &lt, 0.001). The minimum alveolar pressure ranged from 15.5 ± 0.04 to 16.57 ± 0.04 cmH2O. Cross-flows between the simulated patients have been recorded in all the tested combinations, during both the inspiratory and expiratory phases. The simultaneous ventilation of two patients with one ventilator may be unable to match individual patient’s needs and has a high risk of cross-interference.

Extracorporeal carbon dioxide removal (ECCO2R) is a promising strategy to manage acute respiratory failure. We hypothesized that ECCO2R could be enhanced by ventilating the membrane lung with a sodium hydroxide (NaOH) solution with high CO2 absorbing capacity. A computed mathematical model was implemented to assess NaOH–CO2 interactions. Subsequently, we compared NaOH infusion, named “alkaline liquid ventilation”, to conventional oxygen sweeping flows. We built an extracorporeal circuit with two polypropylene membrane lungs, one to remove CO2 and the other to maintain a constant PCO2 (60 ± 2 mmHg). The circuit was primed with swine blood. Blood flow was 500 mL × min−1. After testing the safety and feasibility of increasing concentrations of aqueous NaOH (up to 100 mmol × L−1), the CO2 removal capacity of sweeping oxygen was compared to that of 100 mmol × L−1 NaOH. We performed six experiments to randomly test four sweep flows (100, 250, 500, 1000 mL × min−1) for each fluid plus 10 L × min−1 oxygen. Alkaline liquid ventilation proved to be feasible and safe. No damages or hemolysis were detected. NaOH showed higher CO2 removal capacity compared to oxygen for flows up to 1 L × min−1. However, the highest CO2 extraction power exerted by NaOH was comparable to that of 10 L × min−1 oxygen. Further studies with dedicated devices are required to exploit potential clinical applications of alkaline liquid ventilation.

Patients with sepsis are poorly protected against acute respiratory acid-base derangements due to a lower noncarbonic buffer power, which is caused both by a reduction in the major noncarbonic buffers, i.e. hemoglobin and albumin, and by a reduced buffering capacity of albumin. Electrolyte shifts from and to the red blood cells determining acute variations in strong ion difference are the major buffering mechanism during acute respiratory acid-base disorders.

Background The high-flow nasal cannula (HFNC) delivers up to 60 l/min of humidified air/oxygen blend at a temperature close to that of the human body. In this study, we tested whether higher temperature and flow decrease patient comfort. In more severe patients, instead, we hypothesized that higher flow might be associated with improved comfort. Methods A prospective, randomized, cross-over study was performed on 40 acute hypoxemic respiratory failure (AHRF) patients (PaO2/FiO2 ≤ 300 + pulmonary infiltrates + exclusion of cardiogenic edema) supported by HFNC. The primary outcome was the assessment of patient comfort during HFNC delivery at increasing flow and temperature. Two flows (30 and 60 l/min), each combined with two temperatures (31 and 37 °C), were randomly applied for 20 min (four steps per patient), leaving clinical FiO2 unchanged. Toward the end of each step, the following were recorded: comfort by Visual Numerical Scale ranging between 1 (extreme discomfort) and 5 (very comfortable), together with respiratory parameters. A subgroup of more severe patients was defined by clinical FiO2 ≥ 45%. Results Patient comfort was reported as significantly higher during steps at the lower temperature (31 °C) in comparison to 37 °C, with the HFNC set at both 30 and 60 l/min (p

Limited data exist on the correlation between higher flow rates of high-flow nasal cannula (HFNC) and its physiologic effects in patients with acute hypoxemic respiratory failure (AHRF). We assessed the effects of HFNC delivered at increasing flow rate on inspiratory effort, work of breathing, minute ventilation, lung volumes, dynamic compliance and oxygenation in AHRF patients. A prospective randomized cross-over study was performed in non-intubated patients with patients AHRF and a PaO2/FiO2 (arterial partial pressure of oxygen/fraction of inspired oxygen) ratio of ≤300 mmHg. A standard non-occlusive facial mask and HFNC at different flow rates (30, 45 and 60 l/min) were randomly applied, while maintaining constant FiO2 (20 min/step). At the end of each phase, we measured arterial blood gases, inspiratory effort, based on swings in esophageal pressure (ΔPes) and on the esophageal pressure–time product (PTPPes), and lung volume, by electrical impedance tomography. Seventeen patients with AHRF were enrolled in the study. At increasing flow rate, HFNC reduced ΔPes (p

Background Lung-protective ventilation strategy suggests the use of low tidal volume, depending on ideal body weight, and adequate levels of PEEP. However, reducing tidal volume according to ideal body weight does not always prevent overstress and overstrain. On the contrary, titrating mechanical ventilation on airway driving pressure, computed as airway pressure changes from PEEP to end-inspiratory plateau pressure, equivalent to the ratio between the tidal volume and compliance of respiratory system, should better reflect lung injury. However, possible changes in chest wall elastance could affect the reliability of airway driving pressure. The aim of this study was to evaluate if airway driving pressure could accurately predict lung stress (the pressure generated into the lung due to PEEP and tidal volume). Methods One hundred and fifty ARDS patients were enrolled. At 5 and 15 cmH2O of PEEP, lung stress, driving pressure, lung and chest wall elastance were measured. Results The applied tidal volume (mL/kg of ideal body weight) was not related to lung gas volume (r2 = 0.0005 p = 0.772). Patients were divided according to an airway driving pressure lower and equal/higher than 15 cmH2O (the lower and higher airway driving pressure groups). At both PEEP levels, the higher airway driving pressure group had a significantly higher lung stress, respiratory system and lung elastance compared to the lower airway driving pressure group. Airway driving pressure was significantly related to lung stress (r2 = 0.581 p

Purpose To develop a mathematical model of oxygenation during venovenous extracorporeal membrane oxygenation (vv-ECMO). Material and methods Total oxygen consumption, cardiac output, blood flow, recirculation, intrapulmonary shunt, hemoglobin, natural lung, and membrane lung oxygen fractions were chosen as inputs. Content, partial pressure, and hemoglobin saturation of oxygen in arterial, venous, pulmonary, and extracorporeal blood were outputs. To assess accuracy and predictive power of the model, we retrospectively analyzed data of 25 vv-ECMO patients. We compiled 2 software (with numerical, 2D and 3D graphical outputs) to study the impact of each variable on oxygenation. Results The model showed high accuracy and predictive power. Raising blood flow and oxygen fraction to the membrane lung or reducing total oxygen consumption improves arterial and venous oxygenation, especially in severe cases; raising oxygen fraction to the natural lung improves oxygenation only in milder cases; raising hemoglobin always improves oxygenation, especially in the venous district; recirculation fraction severely impairs oxygenation. In severely ill patients, increasing cardiac output worsens arterial oxygenation but enhances venous oxygenation. Oxygen saturation of ECMO inlet is critical to evaluate the appropriateness of oxygen delivery. Conclusions The model with the software can be a useful teaching tool and a valuable decision-making aid for the management of hypoxic patients supported by vv-ECMO.

We hypothesized that the ventilator-related causes of lung injury may be unified in a single variable: the mechanical power. We assessed whether the mechanical power measured by the pressure–volume loops can be computed from its components: tidal volume (TV)/driving pressure (∆P aw), flow, positive end-expiratory pressure (PEEP), and respiratory rate (RR). If so, the relative contributions of each variable to the mechanical power can be estimated. We computed the mechanical power by multiplying each component of the equation of motion by the variation of volume and RR: $${\text{Power}}_{\text{rs}} = {\text{RR}} \cdot \left\{ {\Delta V^{2} \cdot \left[ {\frac{1}{2} \cdot {\text{EL}}_{\text{rs}} + {\text{RR}} \cdot \frac{{\left( {1 + I:E} \right)}}{60 \cdot I:E} \cdot R_{\text{aw}} } \right] + \Delta V \cdot {\text{PEEP}}} \right\},$$ where ∆V is the tidal volume, ELrs is the elastance of the respiratory system, I:E is the inspiratory-to-expiratory time ratio, and R aw is the airway resistance. In 30 patients with normal lungs and in 50 ARDS patients, mechanical power was computed via the power equation and measured from the dynamic pressure–volume curve at 5 and 15 cmH2O PEEP and 6, 8, 10, and 12 ml/kg TV. We then computed the effects of the individual component variables on the mechanical power. Computed and measured mechanical powers were similar at 5 and 15 cmH2O PEEP both in normal subjects and in ARDS patients (slopes = 0.96, 1.06, 1.01, 1.12 respectively, R 2 > 0.96 and p

The chapter provides a comprehensive overview on extracorporeal membrane oxygenation (ECMO) for the treatment of acute lung injury. It focuses on venovenous ECMO. The historical aspects of ECMO are explored at the light of the most recent advances linked to the H1N1 pandemic. The basic physiology of lung gas exchange is addressed, as well as the specific aspects of gas exchange through an artificial lung. A section is dedicated to the technical aspects of cannulation, setting, and equipment. The chapter also addresses the main complications of ECMO, the pharmacological approach, the management of mechanical ventilation during ECMO, and possible new trends in this approach

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.Prospective study performed between 2008 and 2011.Two university hospitals (Italy and Germany).Fifty-one patients with acute respiratory distress syndrome.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).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 (r = 0.29; p0.0001). 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; p0.05), 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).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.

To assess the time interval required to reach a new steady state of oxygenation-, ventilation-, respiratory mechanics- and hemodynamics-related variables after decreasing/increasing positive end expiratory pressure (PEEP).In 23 patients (group 1) with acute respiratory distress syndrome (ARDS), PEEP was decreased from 10 to 5 cmH2O and, after 60', it was increased from 5 to 15 cmH2O. In 21 other ARDS patients (group 2), PEEP was increased from 10 to 15 cmH2O and, after 60', decreased from 15 to 5 cmH2O. Oxygenation, ventilation, respiratory mechanics and hemodynamic variables were recorded at time 5', 15', 30' and 60' after each PEEP change.When PEEP was decreased, PaO2, PaO2/FiO2, venous admixture and arterial oxygen saturation reached their equilibrium after 5'. In contrast, when PEEP was increased, the equilibrium was not reached even after 60'. The ventilation-related variables did not change significantly with PEEP. The respiratory system compliance, when PEEP was decreased, significantly worsened only after 60'. Hemodynamics did not change significantly with PEEP. In the individual patients the change of oxygenation-related variables and of respiratory system compliance observed after 5' could predict the changes recorded after 60'. This was not possible for PaCO2.We could not find a unique equilibration time for all the considered variables. However, in general, a decremental PEEP test requires far lower equilibrium time than an incremental PEEP test, suggesting a different time course for derecruitment and recruitment patterns.

To describe the physiological meaning and the clinical application of the lung stress and strain concepts.The end-inspiratory plateau pressure and ratio of tidal volume/ideal body weight are inadequate surrogates for the end-inspiratory stress (equal to the transpulmonary pressure) and the end-inspiratory strain (change in lung volume relative to the resting volume). For a given plateau pressure or tidal volume/ideal body weight, stress and strain may vary largely due to the variability of chest wall elastance and the resting lung volume. The injurious limits of stress and strain in healthy lungs are reached when stress and strain reach the total lung capacity. This occurs when the resting lung volume (the baby lung in case of acute respiratory distress syndrome) is increased by two-fold to three-fold. As these limits are rarely reached in clinical practice and damage has been reported with stress and strain well below this upper limit, this implies the presence in the lung parenchyma of regions which act as stress raisers or pressure multipliers. These are primarily linked to the inhomogeneous distribution of local stress and strain.End-inspiratory stress and strain, as well as the lung inhomogeneity and the stress raisers, must be taken in account when setting mechanical ventilation.

RATIONALE: The effects of high positive end-expiratory pressure (PEEP) strictly depend on lung recruitability, which varies widely during acute respiratory distress syndrome (ARDS). Unfortunately, increasing PEEP may lead to opposing effects on two main factors potentially worsening the lung injury, that is, alveolar strain and intratidal opening and closing, being detrimental (increasing the former) or beneficial (decreasing the latter). OBJECTIVES: To investigate how lung recruitability influences alveolar strain and intratidal opening and closing after the application of high PEEP. METHODS: We analyzed data from a database of 68 patients with acute lung injury or ARDS who underwent whole-lung computed tomography at 5, 15, and 45 cm H(2)O airway pressure. MEASUREMENTS AND MAIN RESULTS: End-inspiratory nonaerated lung tissue was estimated from computed tomography pressure-volume curves. Alveolar strain and opening and closing lung tissue were computed at 5 and 15 cm H(2)O PEEP. In patients with a higher percentage of potentially recruitable lung, the increase in PEEP markedly reduced opening and closing lung tissue (P < 0.001), whereas no differences were observed in patients with a lower percentage of potentially recruitable lung. In contrast, alveolar strain similarly increased in the two groups (P = 0.89). Opening and closing lung tissue was distributed mainly in the dependent and hilar lung regions, and it appeared to be an independent risk factor for death (odds ratio, 1.10 for each 10-g increase). CONCLUSIONS: In ARDS, especially in patients with higher lung recruitability, the beneficial impact of reducing intratidal alveolar opening and closing by increasing PEEP prevails over the effects of increasing alveolar strain.

Lung injury caused by a ventilator results from nonphysiologic lung stress (transpulmonary pressure) and strain (inflated volume to functional residual capacity ratio).To determine whether plateau pressure and tidal volume are adequate surrogates for stress and strain, and to quantify the stress to strain relationship in patients and control subjects.Nineteen postsurgical healthy patients (group 1), 11 patients with medical diseases (group 2), 26 patients with acute lung injury (group 3), and 24 patients with acute respiratory distress syndrome (group 4) underwent a positive end-expiratory pressure (PEEP) trial (5 and 15 cm H2O) with 6, 8, 10, and 12 ml/kg tidal volume.Plateau airway pressure, lung and chest wall elastances, and lung stress and strain significantly increased from groups 1 to 4 and with increasing PEEP and tidal volume. Within each group, a given applied airway pressure produced largely variable stress due to the variability of the lung elastance to respiratory system elastance ratio (range, 0.33-0.95). Analogously, for the same applied tidal volume, the strain variability within subgroups was remarkable, due to the functional residual capacity variability. Therefore, low or high tidal volume, such as 6 and 12 ml/kg, respectively, could produce similar stress and strain in a remarkable fraction of patients in each subgroup. In contrast, the stress to strain ratio-that is, specific lung elastance-was similar throughout the subgroups (13.4 +/- 3.4, 12.6 +/- 3.0, 14.4 +/- 3.6, and 13.5 +/- 4.1 cm H2O for groups 1 through 4, respectively; P = 0.58) and did not change with PEEP and tidal volume.Plateau pressure and tidal volume are inadequate surrogates for lung stress and strain. Clinical trial registered with www.clinicaltrials.gov (NCT 00143468).

Objectives: The lung-protective strategy employs positive endexpiratory pressure to keep open otherwise collapsed lung regions (anatomical recruitment). Improvement in venous admixture with positive end-expiratory pressure indicates functional recruitment to better gas exchange, which is not necessarily related to anatomical recruitment, because of possible global/ regional perfusion modifications. Therefore, we aimed to assess the value of venous admixture (functional shunt) in estimating the fraction of nonaerated lung tissue (anatomical shunt compartment) and to describe their relationship. Design: Retrospective analysis of a previously published study. Setting: Intensive care units of four university hospitals. Patients: Fifty-nine patients with acute lung injury/acute respiratory distress syndrome. Interventions: Positive end-expiratory pressure trial at 5 and 15 cm H2O positive end-expiratory pressures. Measurements and Main Results: Anatomical shunt compartment (whole-lung computed tomography scan) and functional shunt (blood gas analysis) were assessed at 5 and 15 cm H2O positive end-expiratory pressures. Apparent perfusion ratio (perfusion per gram of nonaerated tissue/perfusion per gram of total lung tissue) was defined as the ratio of functional shunt to anatomical shunt compartment. Functional shunt was poorly correlated to the anatomical shunt compartment (r 2 .174). The apparent perfusion ratio at 5 cm H2O positive end-expiratory pressure was widely distributed and averaged 1.25 0.80. The apparent perfusion ratios at 5 and 15 cm H2O positive endexpiratory pressures were highly correlated, with a slope close to identity (y 1.10·x 0.03, r 2 .759), suggesting unchanged blood flow distribution toward the nonaerated lung tissue, when increasing positive end-expiratory pressure. Conclusions: Functional shunt poorly estimates the anatomical shunt compartment, due to the large variability in apparent perfusion ratio. Changes in anatomical shunt compartment with increasing positive end-expiratory pressure, in each individual patient, may be estimated from changes in functional shunt, only if the anatomicalfunctional shunt relationship at 5 cm H2O positive end-expiratory pressure is known. (Crit Care Med 2008; 36:669‐675)

Computed tomography (CT) has been utilized to study acute respiratory distress syndrome (ARDS) since the middle 1980s, when it revealed the inhomogeneous pattern of the lung lesion. Its advantages rely on the strict correlation between CT density and the lung physical density, allowing a quantification of lung compartments with different degrees of aeration. By CT scans, ARDS lung appeared to be "small" rather than "stiff," leading to the "baby lung" concept. The regional analysis revealed that this appearance derives from an evenly distributed lung edema, which tends, because of gravitational forces, to lie predominantly in the most dependent regions, leading to alveolar collapse. New data suggest that such a "sponge lung" is made by a "core," consolidated, lung portion, from which, through an inflammatory reaction, lung edema will spread, determining the collapsed and recruitable lung portion. The amount of recruitable lung varies among ARDS patients. This knowledge is necessary for a rational positive end-expiratory pressure (PEEP) setting because the amount of tissue maintained aerated by PEEP is closely associated with the amount of recruitable lung. CT scans may also help to diagnose ARDS because CT provides a good estimate of the high-permeability lung edema, the characteristic lesion of this syndrome.

Ventilator-induced lung injury (VILI) is a well-known side effect of mechanical ventilation. The pressures and volumes needed to induce VILI in healthy animals are far greater than pressure and volumes applied in clinical practice [1]. A possible explanation may be the presence of local pressure multipliers (stress raisers).

Chloride shift is the movement of chloride between red blood cells (RBC) and plasma (and vice versa) caused by variations in pCO2. The aim of our study was to investigate changes in plasmatic strong ion difference (SID) during acute variations in pCO2 and their possible role in the compensation for hypocapnic alkalosis.

We previously found that optoelectronic plethysmography can be used to measure the chest wall volume and its compartments: rib cage and abdomen [1]. We evaluated the breathing pattern and the chest wall displacement during pressure support (PSV) in patients with acute respiratory failure. Nine intubated patients (age 57 ± 12 years, BMI 26 ± 5 kg/m2, PaO2/FiO2 293 ± 67) were studied first at four levels of PSV (5, 10, 15, 25 cmH2O) at 10 cmH2O of PEEP and then at three levels of PEEP (5, 10, 15 cmH2O) at 10 of PSV. We measured the breathing pattern, the ribcage contribution to tidal volume (RC/VT) and the inspiratory asynchrony (IA) [2]. IA was calculated as the area enclosed by the inspiratory portion of rib cage abdomen loop and the line connecting the commencement and the terminal of inspiration. Our results suggest that only the level of PSV affects the breathing pattern. Table 1

The pressure volume (P-V) curve of the total respiratory system is drawn assuming the changes of chest wall (?Vcw) equal to the volume displaced from the syringe (?Vgas). We compared ?Vgas and ?Vcw during P-V curves obtained by supersyringe and opto-electronic plethysmography [1]. Eight sedated paralysed intubated ALI/ARDS patients (5 M/3 F, age 70 ± 13 years, BMI 25.6 ± 3 kg/m2, PaO2/FiO2 220 ± 76) were studied. During the manoeuvre ?Vcw was recorded by optoelectronic plethysmography. The volume injected and withdrawn by the supersyringe step by step (100 ml) was corrected by temperature, humidity, pressure and gas exchange [2]. The discrepancy was computed as the difference between the volume of air inflated and the chest volume measured. The compliance of the total respiratory system was measured between zero and maximum airway pressure values on the inflation (Crsinf) and deflation (Crsdef) limbs of the P-V curves. Hysteresis loops of the corrected P-Vgas and P-Vcw curves were calculated as the percentage ratio between the area of the P-V curves and the product of maximal volume by maximal pressure. Even considering thermodynamics and gas exchange correction, ?Vgas values were systematically higher than ?Vcw probably due to blood shifts from the thorax to the extremities. As a consequence, the standard supersyringe method provides an overestimation of the inspiratory and expiratory compliance of the total respiratory system on the inflation limb and an overestimation of the hysteresis area. Table 1

Background High tidal volume can cause ventilator-induced lung injury (VILI), but positive end-expiratory pressure (PEEP) is thought to be protective. We aimed to find the volumetric VILI threshold and see whether PEEP is protective per se or indirectly. Methods In 76 pigs (22 ± 2 kg), we examined the lower and upper limits (30.9–59.7 mL/kg) of inspiratory capacity by computed tomography (CT) scan at 45 cmH2O pressure. The pigs underwent a 54-h mechanical ventilation with a global strain ((tidal volume (dynamic) + PEEP volume (static))/functional residual capacity) from 0.45 to 5.56. The dynamic strain ranged from 18 to 100 % of global strain. Twenty-nine pigs were ventilated with end-inspiratory volumes below the lower limit of inspiratory capacity (group “Below”), 38 within (group “Within”), and 9 above (group “Above”). VILI was defined as death and/or increased lung weight. Results “Below” pigs did not develop VILI; “Within” pigs developed lung edema, and 52 % died before the end of the experiment. The amount of edema was significantly related to dynamic strain (edema 188–153 × dynamic strain, R2 = 0.48, p