Determinants of acute kidney injury during high-power mechanical ventilation: secondary analysis from experimental data

BACKGROUND

The individual components of mechanical ventilation may have distinct effects on kidney perfusion and on the risk of developing acute kidney injury; we aimed to explore ventilatory predictors of acute kidney failure and the hemodynamic changes consequent to experimental high-power mechanical ventilation.

METHODS

Secondary analysis of two animal studies focused on the outcomes of different mechanical power settings, including 78 pigs mechanically ventilated with high mechanical power for 48 h. The animals were categorized in four groups in accordance with the RIFLE criteria for acute kidney injury (AKI), using the end-experimental creatinine: (1) NO AKI: no increase in creatinine; (2) RIFLE 1-Risk: increase of creatinine of > 50%; (3) RIFLE 2-Injury: two-fold increase of creatinine; (4) RIFLE 3-Failure: three-fold increase of creatinine; RESULTS: The main ventilatory parameter associated with AKI was the positive end-expiratory pressure (PEEP) component of mechanical power. At 30 min from the initiation of high mechanical power ventilation, the heart rate and the pulmonary artery pressure progressively increased from group NO AKI to group RIFLE 3. At 48 h, the hemodynamic variables associated with AKI were the heart rate, cardiac output, mean perfusion pressure (the difference between mean arterial and central venous pressures) and central venous pressure. Linear regression and receiving operator characteristic analyses showed that PEEP-induced changes in mean perfusion pressure (mainly due to an increase in CVP) had the strongest association with AKI.

CONCLUSIONS

In an experimental setting of ventilation with high mechanical power, higher PEEP had the strongest association with AKI. The most likely physiological determinant of AKI was an increase of pleural pressure and CVP with reduced mean perfusion pressure. These changes resulted from PEEP per se and from increase in fluid administration to compensate for hemodynamic impairment consequent to high PEEP.

Impact of mechanical power and positive end expiratory pressure on central vs. mixed oxygen and carbon dioxide related variables in a population of female piglets

INTRODUCTION

The use of the pulmonary artery catheter has decreased overtime; central venous blood gases are generally used in place of mixed venous samples. We want to evaluate the accuracy of oxygen and carbon dioxide related parameters from a central versus a mixed venous sample, and whether this difference is influenced by mechanical ventilation.

MATERIALS AND METHODS

We analyzed 78 healthy female piglets ventilated with different mechanical power.

RESULTS

There was a significant difference in oxygen-derived parameters between samples taken from the central venous and mixed venous blood (Sv ¯ $$ \overline{v} $$ O2 = 74.6%, ScvO2 = 83%, p < 0.0001). Conversely, CO2-related parameters were similar, with strong correlation. Ventilation with higher mechanical power and PEEP increased the difference between oxygen saturations, (Δ[ScvO2-Sv ¯ $$ \overline{v} $$ O2 ] = 7.22% vs. 10.0% respectively in the low and high MP groups, p = 0.020); carbon dioxide-related parameters remained unchanged (p = 0.344).

CONCLUSIONS

The venous oxygen saturation (central or mixed) may be influenced by the effects of mechanical ventilation. Therefore, central venous data should be interpreted with more caution when using higher mechanical power. On the contrary, carbon dioxide-derived parameters are more stable and similar between the two sampling sites, independently of mechanical power or positive end expiratory pressures.

Estimation of normal lung weight index in healthy female domestic pigs

INTRODUCTION

Lung weight is an important study endpoint to assess lung edema in porcine experiments on acute respiratory distress syndrome and ventilatory induced lung injury. Evidence on the relationship between lung-body weight relationship is lacking in the literature. The aim of this work is to provide a reference equation between normal lung and body weight in female domestic piglets.

MATERIALS AND METHODS

177 healthy female domestic piglets from previous studies were included in the analysis. Lung weight was assessed either via a CT-scan before any experimental injury or with a scale after autopsy. The animals were randomly divided in a training (n = 141) and a validation population (n = 36). The relation between body weight and lung weight index (lung weight/body weight, g/kg) was described by an exponential function on the training population. The equation was tested on the validation population. A Bland-Altman analysis was performed to compare the lung weight index in the validation population and its theoretical value calculated with the reference equation.

RESULTS

A good fit was found between the validation population and the exponential equation extracted from the training population (RMSE = 0.060). The equation to determine lung weight index from body weight was: [Formula: see text] At the Bland and Altman analyses, the mean bias between the real and the expected lung weight index was - 0.26 g/kg (95% CI - 0.96-0.43), upper LOA 3.80 g/kg [95% CI 2.59-5.01], lower LOA - 4.33 g/kg [95% CI = - 5.54-(- 3.12)].

CONCLUSIONS

This exponential function might be a valuable tool to assess lung edema in experiments involving 16-50 kg female domestic piglets. The error that can be made due to the 95% confidence intervals of the formula is smaller than the one made considering the lung to body weight as a linear relationship.

End-Tidal to Arterial PCO2 Ratio as Guide to Weaning from Veno-Venous Extra-Corporeal Membrane Oxygenation

RATIONALE

Weaning from veno-venous extracorporeal membrane oxygenation (VV-ECMO) is based on oxygenation and not on carbon dioxide elimination.

OBJECTIVE

To predict readiness to wean from VV-ECMO Methods: In this multicenter study of mechanically ventilated adults with severe acute respiratory distress syndrome (ARDS) receiving VV-ECMO, we investigated a variable based on CO2 elimination. The study included a prospective interventional study of a physiological cohort (n=26), and a retrospective clinical cohort (n=638).

MEASUREMENTS AND MAIN RESULTS

Weaning failure in the clinical and physiological cohorts were respectively 37% and 42%. The main cause of failure in the physiological cohort was high inspiratory effort or respiratory rate. All patients exhaled similar amounts of CO2 but in patients who failed the weaning trial minute ventilation was higher to maintain the PaCO2 unchanged. The effort to eliminate one unit-volume of CO2, was double in failing patients [68·9 (42·4-123) vs. 39 (20·1-57) [cmH2O/(L/min)], p=0.007], owing to the higher physiological dead space [68 (58.73) % vs. 54 (41,.64) %; p=0.012]. PetCO2/PaCO2 ratio was a clinical variable strongly associated with weaning outcome at baseline was the, AUC: 0.87 (95%CI 0·71 - one). Similarly, the PetCO2/PaCO2 ratio was associated with weaning outcome in the "clinical cohort" both pre-weaning trial (OR 4·14; 95% CI 1·32 - 12·2; p=0·015), and at a sweep gas flow of zero (OR 13·1; 95% CI 4-44·4; p<0·001).

CONCLUSION

The primary reason for weaning failure from VV-ECMO is high effort to eliminate CO2. A higher PetCO2/PaCO2 ratio was associated with greater likelihood of weaning from VV-ECMO.

Mechanical power thresholds during mechanical ventilation: An experimental study

The extent of ventilator-induced lung injury may be related to the intensity of mechanical ventilation--expressed as mechanical power. In the present study, we investigated whether there is a safe threshold, below which lung damage is absent. Three groups of six healthy pigs (29.5 ± 2.5 kg) were ventilated prone for 48 h at mechanical power of 3, 7, or 12 J/min. Strain never exceeded 1.0. PEEP was set at 4 cmH2 O. Lung volumes were measured every 12 h; respiratory, hemodynamics, and gas exchange variables every 6. End-experiment histological findings were compared with a control group of eight pigs which did not undergo mechanical ventilation. Functional residual capacity decreased by 10.4% ± 10.6% and 8.1% ± 12.1% in the 7 J and 12 J groups (p = 0.017, p < 0.001) but not in the 3 J group (+1.7% ± 17.7%, p = 0.941). In 3 J group, lung elastance, PaO2 and PaCO2 were worse compared to 7 J and 12 J groups (all p < 0.001), due to lower ventilation-perfusion ratio (0.54 ± 0.13, 1.00 ± 0.25, 1.78 ± 0.36 respectively, p < 0.001). The lung weight was lower (p < 0.001) in the controls (6.56 ± 0.90 g/kg) compared to 3, 7, and 12 J groups (12.9 ± 3.0, 16.5 ± 2.9, and 15.0 ± 4.1 g/kg, respectively). The wet-to-dry ratio was 5.38 ± 0.26 in controls, 5.73 ± 0.52 in 3 J, 5.99 ± 0.38 in 7 J, and 6.13 ± 0.59 in 12 J group (p = 0.03). Vascular congestion was more extensive in the 7 J and 12 J compared to 3 J and control groups. Mechanical ventilation (with anesthesia/paralysis) increase lung weight, and worsen lung histology, regardless of the mechanical power. Ventilating at 3 J/min led to better anatomical variables than at 7 and 12 J/min but worsened the physiological values.

Role of Fluid and Sodium Retention in Experimental Ventilator-Induced Lung Injury

Background: Ventilator-induced lung injury (VILI) via respiratory mechanics is deeply interwoven with hemodynamic, kidney and fluid/electrolyte changes. We aimed to assess the role of positive fluid balance in the framework of ventilation-induced lung injury.

Methods:Post-hoc analysis of seventy-eight pigs invasively ventilated for 48 h with mechanical power ranging from 18 to 137 J/min and divided into two groups: high vs. low pleural pressure (10.0 ± 2.8 vs. 4.4 ± 1.5 cmH₂O; p < 0.01). Respiratory mechanics, hemodynamics, fluid, sodium and osmotic balances, were assessed at 0, 6, 12, 24, 48 h. Sodium distribution between intracellular, extracellular and non-osmotic sodium storage compartments was estimated assuming osmotic equilibrium. Lung weight, wet-to-dry ratios of lung, kidney, liver, bowel and muscle were measured at the end of the experiment.

Results: High pleural pressure group had significant higher cardiac output (2.96 ± 0.92 vs. 3.41 ± 1.68 L/min; p < 0.01), use of norepinephrine/epinephrine (1.76 ± 3.31 vs. 5.79 ± 9.69 mcg/kg; p < 0.01) and total fluid infusions (3.06 ± 2.32 vs. 4.04 ± 3.04 L; p < 0.01). This hemodynamic status was associated with significantly increased sodium and fluid retention (at 48 h, respectively, 601.3 ± 334.7 vs. 1073.2 ± 525.9 mmol, p < 0.01; and 2.99 ± 2.54 vs. 6.66 ± 3.87 L, p < 0.01). Ten percent of the infused sodium was stored in an osmotically inactive compartment. Increasing fluid and sodium retention was positively associated with lung-weight (R² = 0.43, p < 0.01; R² = 0.48, p < 0.01) and with wet-to-dry ratio of the lungs (R² = 0.14, p < 0.01; R² = 0.18, p < 0.01) and kidneys (R² = 0.11, p = 0.02; R² = 0.12, p = 0.01).

Conclusion: Increased mechanical power and pleural pressures dictated an increase in hemodynamic support resulting in proportionally increased sodium and fluid retention and pulmonary edema.

Mobilizing Carbon Dioxide Stores. An Experimental Study

Rationale: Understanding the physiology of CO₂ stores mobilization is a prerequisite for intermittent extracorporeal CO₂ removal (ECCO₂R) in patients with chronic hypercapnia.Objectives: To describe the dynamics of CO₂ stores.Methods: Fifteen pigs (61.7 ± 4.3 kg) were randomized to 48 hours of hyperventilation (group "Hyper," n = 4); 48 hours of hypoventilation (group "Hypo," n = 4); 24 hours of hypoventilation plus 24 hours of normoventilation (group "Hypo-Baseline," n = 4); or 24 hours of hypoventilation plus 24 hours of hypoventilation plus ECCO₂R (group "Hypo-ECCO₂R," n = 3). Forty-eight hours after randomization, the current [Formula: see text]e was reduced by 50% in every pig.Measurements and Main Results: We evaluated [Formula: see text]co₂, [Formula: see text]o₂, and metabolic [Formula: see text]co₂ ([Formula: see text]o₂ times the metabolic respiratory quotient). Changes in the CO₂ stores were calculated as [Formula: see text]co₂ - metabolic V̇co₂. After 48 hours, the CO₂ stores decreased by 0.77 ± 0.17 l kg^-1 in group Hyper and increased by 0.32 ± 0.27 l kg^-1 in group Hypo (P = 0.030). In group Hypo-Baseline, they increased by 0.08 ± 0.19 l kg^-1, whereas in group Hypo-ECCO₂R, they decreased by 0.32 ± 0.24 l kg^-1 (P = 0.197). In the second 24-hour period, in groups Hypo-Baseline and Hypo-ECCO₂R, the CO2 stores decreased by 0.15 ± 0.09 l kg^-1 and 0.51 ± 0.06 l kg^-1, respectively (P = 0.002). At the end of the experiment, the 50% reduction of [Formula: see text]e caused a Pa_CO2 rise of 9.3 ± 1.1, 32.0 ± 5.0, 16.9 ± 1.2, and 11.7 ± 2.0 mm Hg h^-1 in groups Hyper, Hypo, Hypo-Baseline, and Hypo-ECCO₂R, respectively (P < 0.001). The Pa_CO2 rise was inversely related to the previous CO₂ stores mobilization (P < 0.001).Conclusions: CO₂ from body stores can be mobilized over 48 hours without reaching a steady state. This provides a physiological rationale for intermittent ECCO₂R in patients with chronic hypercapnia.

Monitoring lung impedance changes during long-term ventilator-induced lung injury ventilation using electrical impedance tomography

OBJECTIVE

The target of this methodological evaluation was the feasibility of long-term monitoring of changes in lung conditions by time-difference electrical impedance tomography (tdEIT). In contrast to ventilation monitoring by tdEIT, the monitoring of end-expiratory (EELIC) or end-inspiratory (EILIC) lung impedance change always requires a reference measurement.

APPROACH

To determine the stability of the used Pulmovista 500^® EIT system, as a prerequisite it was initially secured on a resistive phantom for 50 h. By comparing the slopes of EELIC for the whole lung area up to 48 h from 36 pigs ventilated at six positive end-expiratory pressure (PEEP) levels from 0 to 18 cmH₂O we found a good agreement (range of r ² = 0.93-1.0) between absolute EIT (aEIT) and tdEIT values. This justified the usage of tdEIT with its superior local resolution compared to aEIT for long-term determination of EELIC.

MAIN RESULTS

The EELIC was between -0.07 Ωm day^-1 at PEEP 4 and -1.04 Ωm day^-1 at PEEP 18 cmH₂O. The complex local time pattern for EELIC was roughly quantified by the new parameter, centre of end-expiratory change (CoEEC), in equivalence to the established centre of ventilation (CoV). The ventrally located mean of the CoV was fairly constant in the range of 42%-46% of thorax diameter; however, on the contrary, the CoEEC shifted from about 40% to about 75% in the dorsal direction for PEEP levels of 14 and 18 cmH₂O.

SIGNIFICANCE

The observed shifts started earlier for higher PEEP levels. Changes of EELI could be precisely monitored over a period of 48 h by tdEIT on pigs.

Fluid administration for acute circulatory dysfunction using basic monitoring

This review aims at evaluating the role and the effectiveness of basic hemodynamic monitoring to guide and to titrate fluid administration during acute circulatory dysfunction. Fluid infusion is a cornerstone of the management of acute circulatory dysfunction. This is a time-related situation, which should be promptly faced to avoid multi organ dysfunction. For this purpose, the recognition of clinical signs of acute circulatory dysfunction is of pivotal importance. A prompt fluid resuscitation in the early phase of acute circulatory failure is a key and recommended intervention, on the other hand the hemodynamic targets and the safety limits indicating whether or not stopping this treatment in already resuscitated patients are still undefined. Bedside clinical examination has been demonstrated to be a reliable instrument to recognize the mismatch between cardiac function and peripheral oxygen demand. Mottling skin and capillary refill time have been recently proposed using a semi-quantitative approach as reliable tool to guide shock therapy; lactate level, central venous oxygen saturation and venous-to-arterial CO₂ tension difference are also useful to track the effect of the therapies overtime. Finally, the availability of echocardiography miniaturization of the machines has boosted this technique as part of the daily clinical assessment of patient, inside and outside the intensive care units (ICUs).

Reclassifying Acute Respiratory Distress Syndrome

RATIONALE

The ratio of Pa_O2 to Fi_O2 (P/F) defines acute respiratory distress syndrome (ARDS) severity and suggests appropriate therapies.

OBJECTIVES

We investigated 1) whether a 150-mm-Hg P/F threshold within the range of moderate ARDS (100-200 mm Hg) would define two subgroups that were more homogeneous; and 2) which criteria led the clinicians to apply extracorporeal membrane oxygenation (ECMO) in severe ARDS.

METHODS

At the 150-mm-Hg P/F threshold, moderate patients were split into mild-moderate (n = 50) and moderate-severe (n = 55) groups. Patients with severe ARDS (Fi_O2 not available in three patients) were split into higher (n = 63) and lower (n = 18) Fi_O2 groups at an 80% Fi_O2 threshold.

MEASUREMENTS AND MAIN RESULTS

Compared with mild-moderate ARDS, patients with moderate-severe ARDS had higher peak pressures, Pa_CO2, and pH. They also had heavier lungs, greater inhomogeneity, more noninflated tissue, and greater lung recruitability. Within 84 patients with severe ARDS (P/F < 100 mm Hg), 75% belonged to the higher Fi_O2 subgroup. They differed from the patients with severe ARDS with lower Fi_O2 only in Pa_CO2 and lung weight. Forty-one of 46 patients treated with ECMO belonged to the higher Fi_O2 group. Within this group, the patients receiving ECMO had higher Pa_CO2 than the 22 non-ECMO patients. The inhomogeneity ratio, total lung weight, and noninflated tissue were also significantly higher.

CONCLUSIONS

Using the 150-mm-Hg P/F threshold gave a more homogeneous distribution of patients with ARDS across the severity subgroups and identified two populations that differed in their anatomical and physiological characteristics. The patients treated with ECMO belonged to the severe ARDS group, and almost 90% of them belonged to the higher Fi_O2 subgroup.

Effects of regional perfusion block in healthy and injured lungs

Background

Severe hypoperfusion can cause lung damage. We studied the effects of regional perfusion block in normal lungs and in the lungs that had been conditioned by lavage with 500 ml saline and high V_T (20 ml kg⁻¹) ventilation.

Methods

Nineteen pigs (61.2 ± 2.5 kg) were randomized to five groups: controls (n = 3), the right lower lobe block alone (n = 3), lavage and high V_T (n = 4), lung lavage, and high V_T plus perfusion block of the right (n = 5) or left (n = 4) lower lobe. Gas exchange, respiratory mechanics, and hemodynamics were measured hourly. After an 8-h observation period, CT scans were obtained at 0 and 15 cmH₂O airway pressure.

Results

Perfusion block did not damage healthy lungs. In conditioned lungs, the left perfusion block caused more edema in the contralateral lung (777 ± 62 g right lung vs 484 ± 204 g left; p < 0.05) than the right perfusion block did (581 ± 103 g right lung vs 484 ± 204 g left; p n.s.). The gas/tissue ratio, however, was similar (0.5 ± 0.3 and 0.8 ± 0.5; p n.s.). The lobes with perfusion block were not affected (gas/tissue ratio right 1.6 ± 0.9; left 1.7 ± 0.5, respectively). Pulmonary artery pressure, PaO₂/FiO₂, dead space, and lung mechanics were more markedly affected in animals with left perfusion block, while the gas/tissue ratios were similar in the non-occluded lobes.

Conclusions

The right and left perfusion blocks caused the same “intensity” of edema in conditioned lungs. The total amount of edema in the two lungs differed because of differences in lung size. If capillary permeability is altered, increased blood flow may induce or increase edema.

Electronic supplementary material

The online version of this article (10.1186/s40635-017-0161-2) contains supplementary material, which is available to authorized users.

The future of mechanical ventilation: lessons from the present and the past

The adverse effects of mechanical ventilation in acute respiratory distress syndrome (ARDS) arise from two main causes: unphysiological increases of transpulmonary pressure and unphysiological increases/decreases of pleural pressure during positive or negative pressure ventilation. The transpulmonary pressure-related side effects primarily account for ventilator-induced lung injury (VILI) while the pleural pressure-related side effects primarily account for hemodynamic alterations. The changes of transpulmonary pressure and pleural pressure resulting from a given applied driving pressure depend on the relative elastances of the lung and chest wall. The term ‘volutrauma’ should refer to excessive strain, while ‘barotrauma’ should refer to excessive stress. Strains exceeding 1.5, corresponding to a stress above ~20 cmH₂O in humans, are severely damaging in experimental animals. Apart from high tidal volumes and high transpulmonary pressures, the respiratory rate and inspiratory flow may also play roles in the genesis of VILI. We do not know which fraction of mortality is attributable to VILI with ventilation comparable to that reported in recent clinical practice surveys (tidal volume ~7.5 ml/kg, positive end-expiratory pressure (PEEP) ~8 cmH₂O, rate ~20 bpm, associated mortality ~35%). Therefore, a more complete and individually personalized understanding of ARDS lung mechanics and its interaction with the ventilator is needed to improve future care. Knowledge of functional lung size would allow the quantitative estimation of strain. The determination of lung inhomogeneity/stress raisers would help assess local stresses; the measurement of lung recruitability would guide PEEP selection to optimize lung size and homogeneity. Finding a safety threshold for mechanical power, normalized to functional lung volume and tissue heterogeneity, may help precisely define the safety limits of ventilating the individual in question. When a mechanical ventilation set cannot be found to avoid an excessive risk of VILI, alternative methods (such as the artificial lung) should be considered.

Driving pressure and mechanical power: new targets for VILI prevention

Several factors have been recognized as possible triggers of ventilator-induced lung injury (VILI). The first is pressure (thus the 'barotrauma'), then the volume (hence the 'volutrauma'), finally the cyclic opening-closing of the lung units ('atelectrauma'). Less attention has been paid to the respiratory rate and the flow, although both theoretical considerations and experimental evidence attribute them a significant role in the generation of VILI. The initial injury to the lung parenchyma is necessarily mechanical and it could manifest as an unphysiological distortion of the extracellular matrix and/or as micro-fractures in the hyaluronan, likely the most fragile polymer embedded in the matrix. The order of magnitude of the energy required to break a molecular bond between the hyaluronan and the associated protein is 1.12×10^-16 Joules (J), 70-90% higher than the average energy delivered by a single breath of 1L assuming a lung elastance of 10 cmH₂O/L (0.5 J). With a normal statistical distribution of the bond strength some polymers will be exposed each cycle to an energy large enough to rupture. Both the extracellular matrix distortion and the polymer fractures lead to inflammatory increase of capillary permeability with edema if a pulmonary blood flow is sufficient. The mediation analysis of higher vs. lower tidal volume and PEEP studies suggests that the driving pressure, more than tidal volume, is the best predictor of VILI, as inferred by increased mortality. This is not surprising, as both tidal volume and respiratory system elastance (resulting in driving pressure) may independently contribute to the mortality. For the same elastance driving pressure is a predictor similar to plateau pressure or tidal volume. Driving pressure is one of the components of the mechanical power, which also includes respiratory rate, flow and PEEP. Finding the threshold for mechanical power would greatly simplify assessment and prevention of VILI.

Positive end-expiratory pressure: how to set it at the individual level

The positive end-expiratory pressure (PEEP), since its introduction in the treatment of acute respiratory failure, up to the 1980s was uniquely aimed to provide a viable oxygenation. Since the first application, a large debate about the criteria for selecting the PEEP levels arose within the scientific community. Lung mechanics, oxygen transport, venous admixture thresholds were all proposed, leading to PEEP recommendations from 5 up to 25 cmH₂O. Throughout this period, the main concern was the hemodynamics. This paradigm changed during the 1980s after the wide acceptance of atelectrauma as one of the leading causes of ventilator induced lung injury. Accordingly, the PEEP aim shifted from oxygenation to lung protection. In this framework, the prevention of lung opening and closing became an almost unquestioned dogma. Consequently, as PEEP keeps open the pulmonary units opened during the previous inspiratory phase, new methods were designed to identify the 'optimal' PEEP during the expiratory phase. The open lung approach requires that every collapsed unit potentially openable is opened and maintained open. The methods to assess the recruitment are based on imaging (computed tomography, electric impedance tomography, ultrasound) or mechanically-driven gas exchange modifications. All the latest assume that whatever change in respiratory system compliance is due to changes in lung compliance, which in turn is uniquely function of the recruitment. Comparative studies, however, showed that the only possible approach to measure the amount of collapsed tissue regaining inflation is the CT scan. In fact, all the other methods estimate as recruitment the gas entry in pulmonary units already open at lower PEEP, but increasing their compliance at higher PEEP. Since higher PEEP is usually more indicated (also for oxygenation) when the recruitability is higher, as occurs with increasing severity, a meaningful PEEP selection requires the assessment of recruitment. The Berlin definition may help in this assessment.

Mesenchymal stromal cell-derived extracellular vesicles rescue radiation damage to murine marrow hematopoietic cells

Mesenchymal stromal cells (MSCs) have been shown to reverse radiation damage to marrow stem cells. We have evaluated the capacity of MSC-derived extracellular vesicles (MSC-EVs) to mitigate radiation injury to marrow stem cells at 4 h to 7 days after irradiation. Significant restoration of marrow stem cell engraftment at 4, 24 and 168 h post irradiation by exposure to MSC-EVs was observed at 3 weeks to 9 months after transplant and further confirmed by secondary engraftment. Intravenous injection of MSC-EVs to 500cGy exposed mice led to partial recovery of peripheral blood counts and restoration of the engraftment of marrow. The murine hematopoietic cell line, FDC-P1 exposed to 500cGy, showed reversal of growth inhibition, DNA damage and apoptosis on exposure to murine or human MSC-EVs. Both murine and human MSC-EVs reverse radiation damage to murine marrow cells and stimulate normal murine marrow stem cell/progenitors to proliferate. A preparation with both exosomes and microvesicles was found to be superior to either microvesicles or exosomes alone. Biologic activity was seen in freshly isolated vesicles and in vesicles stored for up to 6 months in 10% dimethyl sulfoxide at -80 °C. These studies indicate that MSC-EVs can reverse radiation damage to bone marrow stem cells.

[Health surveillance for employees who work in "areas suspected of pollution" or confined]

About medical aspects related to the work involving confined spaces Neil McManus, one of the leading world expert on the topic, points out that now a days, besides what is required for general work environmental, no specific data can be found in the literature on health surveillance programs for workers engaged in activities in confined environments. Although there are activities in confined environments, which may include the adoption of operating procedures and protection systems similar to those one used in manufacturing jobs (e.g., use of PPE as respiratory mask and protective clothing, etc.) we must, however, emphasize that activities in confined environments involve specific working conditions of particular physical / psychological stress for employees. Working in these spaces has as consequences issues not found in other situations (being confined, difficulties in the movement, unable to access / exit, uncomfortable postures, etc.) and also, in emergency, it may involve difficulties with activities offirst aid or extraction of the worker injured and in some cases even obstruct them. Therefore we believe that it is important to begin a debate on the topic and to indicate what should be the physical requirements of the employees who have been called to work in this particular workplace.

[Criteria of the OCRA method in evaluating the structural assembly of aircrafts: preliminary data]

In the aircraft productive sector, the risk assessment of repetitive occupational activities through the OCRA method presents some major obstacles: - high number of different tasks (more than 20) carried out during the work shift. - definite identification of the number of technical actions per cycle. Risk assessment through the traditional OCRA method provides in this sector a index which varies according to the sampling of the occupational tasks, rather than reflecting the effective risk level. The study raises an OCRA-based method which is applicable in the aircraft production sector and defines the overall ergonomic load for homogeneous groups of exposed workers, based on production data specified for each aircraft model.

[Mechanisms causing chronic renal injury in kidney disease and their possible reversibility]

Much study has been dedicated to the understanding of the mechanisms leading to the progression of renal injury and to the development of strategies to limit this progression or possibly induce tissue regeneration. Among several identified mechanisms, the role of angiotensin II is widely recognized. Moreover, the progression of glomerular damage is characterized by capillary loss, reduction of the proliferative response, and production of antiangiogenic factors. Several lines of evidence support the potential effect of therapeutic startegies aimed at interfering with angiotensin II or stimulating angiogenesis in order to reduce the progression of renal injury. Recent work has underlined the potential of strategies involving the use of stem cells. Different populations of stem cells have been identified in the adult kidney. During renal injury, stem cells derived from the bone marrow that migrate through the circulation to the kidney may contribute to tissue repair. The regenerative potential of stem cells could be exploited by administration of ex vivo expanded stem cell populations or by the development of techniques to expand and differentiate local stem cells.

[Ion pair HPLC determination of p-aminobenzoic acid as an impurity in procaine and procainamide hydrochlorides]

A simple, specific and sensitive high-performance liquid chromatographic method for the determination of p-amino benzoic acid (PABA) as impurity in procaine and procainamide hydrochlorides has been developed. The compounds were chromatographed on reversed phase C-18 using water-methanol-acetonitrile solvent system containing sodium lauryl sulphate ion-pair reagent.