Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome

Mechanical ventilation in acute respiratory distress syndrome: The open lung revisited

Acute respiratory distress syndrome (ARDS) is still related to high mortality and morbidity rates. Most patients with ARDS will require ventilatory support. This treatment has a direct impact upon patient outcome and is associated to major side effects. In this regard, ventilator-associated lung injury (VALI) is the main concern when this technique is used. The ultimate mechanisms of VALI and its management are under constant evolution. The present review describes the classical mechanisms of VALI and how they have evolved with recent findings from physiopathological and clinical studies, with the aim of analyzing the clinical implications derived from them. Lastly, a series of knowledge-based recommendations are proposed that can be helpful for the ventilator assisted management of ARDS at the patient bedside.

Extracorporeal carbon dioxide removal (ECCO2R) in patients with acute respiratory failure

PURPOSE

To review the available knowledge related to the use of ECCO₂R as adjuvant strategy to mechanical ventilation (MV) in various clinical settings of acute respiratory failure (ARF).

METHODS

Expert opinion and review of the literature.

RESULTS

ECCO₂R may be a promising adjuvant therapeutic strategy for the management of patients with severe exacerbations of COPD and for the achievement of protective or ultra-protective ventilation in patients with ARDS without life-threatening hypoxemia. Given the observational nature of most of the available clinical data and differences in technical features and performances of current devices, the balance of risks and benefits for or against ECCO₂R in such patient populations remains unclear CONCLUSIONS: ECCO₂R is currently an experimental technique rather than an accepted therapeutic strategy in ARF-its safety and efficacy require confirmation in clinical trials.

Successful Treatment of Refractory Hypoxemia Secondary to Disseminated Histoplasmosis Using Extracorporeal Membrane Oxygenation Support

Refractory hypoxemia secondary to acute respiratory distress syndrome (ARDS) is associated with high mortality. Extracorporeal membraneoxygenation (ECMO) is an accepted strategy for treating refractory hypoxemia in patients with ARDS but is relatively contraindicated in the setting of systemic infections. We present a case of successful ECMO use in a host with refractory hypoxemia secondary to disseminated histoplasmosis with fungemia and discuss our management approach to this difficult patient.

Limiting ventilator-associated lung injury in a preterm porcine neonatal model

PURPOSE

Preterm infants are prone to respiratory distress syndrome (RDS), with severe cases requiring mechanical ventilation for support. However, there are no clear guidelines regarding the optimal ventilation strategy. We hypothesized that airway pressure release ventilation (APRV) would mitigate lung injury in a preterm porcine neonatal model.

METHODS

Preterm piglets were delivered on gestational day 98 (85% of 115day term), instrumented, and randomized to volume guarantee (VG; n=10) with low tidal volumes (5.5cm³kg^-1) and PEEP 4cmH₂O or APRV (n=10) with initial ventilator settings: P_High 18cmH₂O, P_Low 0cmH₂O, T_High 1.30s, T_Low 0.15s. Ventilator setting changes were made in response to clinical parameters in both groups. Animals were monitored continuously for 24hours.

RESULTS

The mortality rates between the two groups were not significantly different (p>0.05). The VG group had relatively increased oxygen requirements (F_iO₂ 50%±9%) compared with the APRV group (F_iO₂ 28%±5%; p>0.05) and a decrease in PaO₂/FiO₂ ratio (VG 162±33mmHg; APRV 251±45mmHg; p<0.05). The compliance of the VG group (0.51±0.07L·cmH₂O^-1) was significantly less than the APRV group (0.90±0.06L·cmH₂O^-1; p<0.05).

CONCLUSION

This study demonstrates that APRV improves oxygenation and compliance as compared with VG. This preliminary work suggests further study into the clinical uses of APRV in the neonate is warranted.

LEVEL OF EVIDENCE

Not Applicable (Basic Science Animal Study).

pRotective vEntilation with veno-venouS lung assisT in respiratory failure: A protocol for a multicentre randomised controlled trial of extracorporeal carbon dioxide removal in patients with acute hypoxaemic respiratory failure

One of the few interventions to demonstrate improved outcomes for acute hypoxaemic respiratory failure is reducing tidal volumes when using mechanical ventilation, often termed lung protective ventilation. Veno-venous extracorporeal carbon dioxide removal (vv-ECCO₂R) can facilitate reducing tidal volumes. pRotective vEntilation with veno-venouS lung assisT (REST) is a randomised, allocation concealed, controlled, open, multicentre pragmatic trial to determine the clinical and cost-effectiveness of lower tidal volume mechanical ventilation facilitated by vv-ECCO₂R in patients with acute hypoxaemic respiratory failure. Patients requiring intubation and mechanical ventilation for acute hypoxaemic respiratory failure will be randomly allocated to receive either vv-ECCO₂R and lower tidal volume mechanical ventilation or standard care with stratification by recruitment centre. There is a need for a large randomised controlled trial to establish whether vv-ECCO₂R in acute hypoxaemic respiratory failure can allow the use of a more protective lung ventilation strategy and is associated with improved patient outcomes.

Acute respiratory distress syndrome

Acute respiratory distress syndrome presents as hypoxia and bilateral pulmonary infiltrates on chest imaging in the absence of heart failure sufficient to account for this clinical state. Management is largely supportive, and is focused on protective mechanical ventilation and the avoidance of fluid overload. Patients with severe hypoxaemia can be managed with early short-term use of neuromuscular blockade, prone position ventilation, or extracorporeal membrane oxygenation. The use of inhaled nitric oxide is rarely indicated and both β2 agonists and late corticosteroids should be avoided. Mortality remains at approximately 30%.

Extracorporeal Life Support: Physiological Concepts and Clinical Outcomes

Extracorporeal life support (ECLS) describes a system that involves drainage from the venous circulation and return via an oxygenator into the arterial circulation (veno-arterial extracorporeal membrane oxygenation). ECLS provides effective cardiopulmonary support, but the parallel circulation has complex effects on the systemic and pulmonary circulatory physiology. An understanding of the physiological changes is fundamental to the management of ECLS. In this review, the key physiological concepts and the implications on the clinical management of ECLS are discussed. In addition, the clinical outcomes associated with ECLS in cardiogenic shock are systematically reviewed. The paucity of clinical trials on ECLS highlights the need for randomized trials to guide the selection of patients.

Acute respiratory distress syndrome: the heart side of the moon

PURPOSE OF REVIEW

Circulatory failure is a frequent complication during acute respiratory distress syndrome (ARDS) and is associated with a poor outcome. This review aims at clarifying the mechanisms of circulatory failure during ARDS.

RECENT FINDINGS

For the past decades, the right ventricle (RV) has gained a crucial interest since many authors confirmed the high incidence of acute cor pulmonale during ARDS and showed a potential role of the acute cor pulmonale in the poor outcome of ARDS patients. The most important recent progress demonstrated in ARDS ventilatory strategy is represented by the prone position, which has a huge beneficial effect on RV afterload. This review will focus on the mechanisms responsible for the RV dysfunction/failure during ARDS and on the strategy, which allows improving the right ventricular function.

SUMMARY

The RV has a pivotal role in the circulatory failure of ARDS patients. The ventilatory strategy during ARDS has to pay a peculiar attention to the RV to rigorously control its afterload.

Open lung approach ventilation abolishes the negative effects of respiratory rate in experimental lung injury

BACKGROUND

We recently reported that a high respiratory rate was associated with less inflammation than a low respiratory rate, but caused more pulmonary edema in a model of ARDS when an ARDSNet ventilatory strategy was used. We hypothesized that an open lung approach (OLA) strategy would neutralize the independent effects of respiratory rate on lung inflammation and edema. This hypothesis was tested in an ARDS model using two clinically relevant respiratory rates during OLA strategy.

METHODS

Twelve piglets were subjected to an experimental model of ARDS and randomized into two groups: LRR (20 breaths/min) and HRR (40 breaths/min). They were mechanically ventilated for 6 h according to an OLA strategy. We assessed respiratory mechanics, hemodynamics, and extravascular lung water (EVLW). At the end of the experiment, wet/dry ratio, regional histology, and cytokines were evaluated.

RESULTS

After the ARDS model was established, Cdyn,rs decreased from 21 ± 3.3 to 9.0 ± 1.8 ml/cmH2 O (P < 0.0001). After the lung recruitment maneuver, Cdyn,rs increased to the pre-injury value. During OLA ventilation, no differences in respiratory mechanics, hemodynamics, or EVLW were observed between groups. Wet/dry ratio and histological scores were not different between groups. Cytokine quantification was similar and showed a homogeneous distribution throughout the lung in both groups.

CONCLUSION

Contrary to previous findings with the ARDSNet strategy, respiratory rate did not influence lung inflammatory response or pulmonary edema during OLA ventilation in experimental ARDS. This indicates that changing the respiratory rate when OLA ventilation is used will not exacerbate lung injury.

End-inspiratory pause prolongation in acute respiratory distress syndrome patients: effects on gas exchange and mechanics

Background

End-inspiratory pause (EIP) prolongation decreases dead space-to-tidal volume ratio (Vd/Vt) and PaCO₂. We do not know the physiological benefits of this approach to improve respiratory system mechanics in acute respiratory distress syndrome (ARDS) patients when mild hypercapnia is of no concern.

Methods

The investigation was conducted in an intensive care unit of a university hospital, and 13 ARDS patients were included. The study was designed in three phases. First phase, baseline measurements were taken. Second phase, the EIP was prolonged until one of the following was achieved: (1) EIP of 0.7 s; (2) intrinsic positive end-expiratory pressure ≥1 cmH₂O; or (3) inspiratory–expiratory ratio 1:1. Third phase, the Vt was decreased (30 mL every 30 min) until PaCO₂ equal to baseline was reached. FiO₂, PEEP, airflow and respiratory rate were kept constant.

Results

EIP was prolonged from 0.12 ± 0.04 to 0.7 s in all patients. This decreased the Vd/Vt and PaCO₂ (0.70 ± 0.07 to 0.64 ± 0.08, p < 0.001 and 54 ± 9 to 50 ± 8 mmHg, p = 0.001, respectively). In the third phase, the decrease in Vt (from 6.3 ± 0.8 to 5.6 ± 0.8 mL/Kg PBW, p < 0.001) allowed to decrease plateau pressure and driving pressure (24 ± 3 to 22 ± 3 cmH₂O, p < 0.001 and 13.4 ± 3.6 to 10.9 ± 3.1 cmH₂O, p < 0.001, respectively) and increased respiratory system compliance from 29 ± 9 to 32 ± 11 mL/cmH₂O (p = 0.001). PaO₂ did not significantly change.

Conclusions

Prolonging EIP allowed a significant decrease in Vt without changes in PaCO₂ in passively ventilated ARDS patients. This produced a significant decrease in plateau pressure and driving pressure and significantly increased respiratory system compliance, which suggests less overdistension and less dynamic strain.

Lung hyperaeration assessment by computed tomography: correction of reconstruction-induced bias

Background

Computed tomography (CT) reconstruction parameters, such as slice thickness and convolution kernel, significantly affect the quantification of hyperaerated parenchyma (V_HYPER%). The aim of this study was to investigate the mathematical relation between V_HYPER% calculated at different reconstruction settings, in mechanically ventilated and spontaneously breathing patients with different lung pathology.

Methods

In this retrospective observational study, CT scans of patients of the intensive care unit and emergency department were collected from two CT scanners and analysed with different kernel-thickness combinations (reconstructions): 1.25 mm soft kernel, 5 mm soft kernel, 5 mm sharp kernel in the first scanner; 2.5 mm slice thickness with a smooth (B41s) and a sharp (B70s) kernel on the second scanner. A quantitative analysis was performed with Maluna® to assess lung aeration compartments as percent of total lung volume. CT variables calculated with different reconstructions were compared in pairs, and their mathematical relationship was analysed by using quadratic and power functions.

Results

43 subjects were included in the present analysis. Image reconstruction parameters influenced all the quantitative CT-derived variables. The most relevant changes occurred in the hyperaerated and normally aerated volume compartments. The application of a power correction formula led to a significant reduction in the bias between V_HYPER% estimations (p < 0.001 in all cases). The bias in V_HYPER% assessment did not differ between lung pathology nor ventilation mode groups (p > 0.15 in all cases).

Conclusions

Hyperaerated percent volume at different reconstruction settings can be described by a fixed mathematical relationship, independent of lung pathology, ventilation mode, and type of CT scanner.

Airway driving pressure and lung stress in ARDS patients

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 < 0.0001 and r² = 0.353 p < 0.0001 at 5 and 15 cmH₂O of PEEP). For a lung stress of 24 and 26 cmH₂O, the optimal cutoff value for the airway driving pressure were 15.0 cmH₂O (ROC AUC 0.85, 95 % CI = 0.782–0.922); and 16.7 (ROC AUC 0.84, 95 % CI = 0.742–0.936).

Conclusions

Airway driving pressure can detect lung overstress with an acceptable accuracy. However, further studies are needed to establish if these limits could be used for ventilator settings.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1446-7) contains supplementary material, which is available to authorized users.

Ultrasonography for the assessment of lung recruitment maneuvers

Lung collapse is a known complication that affects most of the patients undergoing positive pressure mechanical ventilation. Such atelectasis and airways closure lead to gas exchange and lung mechanics impairment and has the potential to develop an inflammatory response in the lungs. These negative effects of lung collapse can be reverted by a lung recruitment maneuver (RM) i.e. a ventilatory strategy that resolves lung collapse by a brief and controlled increment in airway pressures. However, an unsolved question is how to assess such RM at the bedside. The aim of this paper is to describe the usefulness of lung sonography (LUS) to conduct and personalize RM in a real-time way at the bedside. LUS has favorable features to assess lung recruitment due to its high specificity and sensitivity to detect lung collapse together with its non-invasiveness, availability and simple use.

Biotrauma and Ventilator-Induced Lung Injury: Clinical Implications

The pathophysiological mechanisms by which mechanical ventilation can contribute to lung injury, termed "ventilator-induced lung injury" (VILI), is increasingly well understood. "Biotrauma" describes the release of mediators by injurious ventilatory strategies, which can lead to lung and distal organ injury. Insights from preclinical models demonstrating that traditional high tidal volumes drove the inflammatory response helped lead to clinical trials demonstrating lower mortality in patients who underwent ventilation with a lower-tidal-volume strategy. Other approaches that minimize VILI, such as higher positive end-expiratory pressure, prone positioning, and neuromuscular blockade have each been demonstrated to decrease indices of activation of the inflammatory response. This review examines the evolution of our understanding of the mechanisms underlying VILI, particularly regarding biotrauma. We will assess evidence that ventilatory and other "adjunctive" strategies that decrease biotrauma offer great potential to minimize the adverse consequences of VILI and to improve the outcomes of patients with respiratory failure.

Effects of the open lung concept following ARDSnet ventilation in patients with early ARDS

BACKGROUND

Ventilation with low tidal volume (VT) is well recognized as a protective approach to patients with acute respiratory distress syndrome (ARDS), but the optimal level of positive end-expiratory pressure (PEEP) remains uncertain. This study aims to evaluate two protective ventilatory strategies sequentially applied in patients with early ARDS.

METHODS

In this prospective cohort study, fifteen patients were ventilated during 24 h with positive end-expiratory pressure (PEEP) adjusted according to the ARDSnet low-PEEP table (ARDSnet-24 h). During the next 24 h, nine patients with PaO2/FIO2 ratio below 350 mmHg were ventilated with PEEP titrated according to the Open Lung Concept protocol (ARDSnet + OLC). In the other six patients, regardless of their PaO2/FIO2 ratio, the ARDSnet remained for a further 24 h (ARDSnet-48 h). Ventilatory variables, arterial blood-gas and cytokine were obtained at baseline, 24 and 48 h. Additionally, whole-lung-computed tomography was acquired at 24 and 48 h.

RESULTS

A sustained improvement in PaO2/FIO2 ratio (P = 0.008) with a decrease in collapsed regions (P = 0.008) was observed in the ARDSnet + OLC group compared with the ARDSnet-24 h group. A reduction in IL-6 in plasma (P < 0.02) was observed throughout the protocol in the ARDSnet + OLC group. Compared with the ARDSnet-48 h group, the ARDSnet + OLC presented smaller amounts of collapsed areas (P = 0.018) without significant differences in hyperinflated regions and in driving and plateau pressures.

CONCLUSIONS

In this set of patients with early ARDS, mechanical ventilation with an individually tailored PEEP sustained improved pulmonary function with better aeration, without significant increase in hyperinflated areas".

TRIAL REGISTRATION

Brazilian Clinical Trials Registry (ReBec). RBR-5zm9pr. 04th November 2015.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Echocardiographic parameters of right ventricular function predict mortality in acute respiratory distress syndrome: a pilot study

Right ventricular (RV) dysfunction in acute respiratory distress syndrome (ARDS) contributes to increased mortality. Our aim is to identify reproducible transthoracic echocardiography (TTE) parameters of RV dysfunction that can be used to predict outcomes in ARDS. We performed a retrospective single-center cohort pilot study measuring tricuspid annular plane systolic excursion (TAPSE), Tei index, RV-fractional area change (RV-FAC), pulmonary artery systolic pressure (PASP), and septal shift, reevaluated by an independent blinded cardiologist (JK). Thirty-eight patients were included. Patients were divided on the basis of 30-day survival. Thirty-day mortality was 47%. Survivors were younger than nonsurvivors. Survivors had a higher pH, PaO2∶FiO2 ratio, and TAPSE. Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II), and Sequential Organ Failure Assessment (SOFA) scores were lower in survivors. TAPSE has the strongest association with increased 30-day mortality from date of TTE. Accordingly, TAPSE has a strong positive correlation with PaO2∶FiO2 ratios, and Tei index has a strong negative correlation with PaO2∶FiO2 ratios. Septal shift was associated with lower PaO2∶FiO2 ratios. Decrease in TAPSE, increase in Tei index, and septal shift were seen in the severe ARDS group. In multivariate logistic regression models, TAPSE maintained a significant association with mortality independent of age, pH, PaO2∶FiO2 ratios, positive end expiratory pressure, PCO2, serum bicarbonate, plateau pressures, driving pressures, APACHE II, SAPS II, and SOFA scores. In conclusion, TAPSE and other TTE parameters should be used as novel predictive indicators for RV dysfunction in ARDS. These parameters can be used as surrogate noninvasive RV hemodynamic measurements to be manipulated to improve mortality in patients with ARDS and contributory RV dysfunction.

Impact of Recruitment on Static and Dynamic Lung Strain in Acute Respiratory Distress Syndrome

BACKGROUND

Lung strain, defined as the ratio between end-inspiratory volume and functional residual capacity, is a marker of the mechanical load during ventilation. However, changes in lung volumes in response to pressures may occur in injured lungs and modify strain values. The objective of this study was to clarify the role of recruitment in strain measurements.

METHODS

Six oleic acid-injured pigs were ventilated at positive end-expiratory pressure (PEEP) 0 and 10 cm H2O before and after a recruitment maneuver (PEEP = 20 cm H2O). Lung volumes were measured by helium dilution and inductance plethysmography. In addition, six patients with moderate-to-severe acute respiratory distress syndrome were ventilated with three strategies (peak inspiratory pressure/PEEP: 20/8, 32/8, and 32/20 cm H2O). Lung volumes were measured in computed tomography slices acquired at end-expiration and end-inspiration. From both series, recruited volume and lung strain (total, dynamic, and static) were computed.

RESULTS

In the animal model, recruitment caused a significant decrease in dynamic strain (from [mean ± SD] 0.4 ± 0.12 to 0.25 ± 0.07, P < 0.01), while increasing the static component. In patients, total strain remained constant for the three ventilatory settings (0.35 ± 0.1, 0.37 ± 0.11, and 0.32 ± 0.1, respectively). Increases in tidal volume had no significant effects. Increasing PEEP constantly decreased dynamic strain (0.35 ± 0.1, 0.32 ± 0.1, and 0.04+0.03, P < 0.05) and increased static strain (0, 0.06 ± 0.06, and 0.28 ± 0.11, P < 0.05). The changes in dynamic and total strain among patients were correlated to the amount of recruited volume. An analysis restricted to the changes in normally aerated lung yielded similar results.

CONCLUSION

Recruitment causes a shift from dynamic to static strain in early acute respiratory distress syndrome.

Predicting ventilator-induced lung injury using a lung injury cost function

Managing patients with acute respiratory distress syndrome (ARDS) requires mechanical ventilation that balances the competing goals of sustaining life while avoiding ventilator-induced lung injury (VILI). In particular, it is reasonable to suppose that for any given ARDS patient, there must exist an optimum pair of values for tidal volume (VT) and positive end-expiratory pressure (PEEP) that together minimize the risk for VILI. To find these optimum values, and thus develop a personalized approach to mechanical ventilation in ARDS, we need to be able to predict how injurious a given ventilation regimen will be in any given patient so that the minimally injurious regimen for that patient can be determined. Our goal in the present study was therefore to develop a simple computational model of the mechanical behavior of the injured lung in order to calculate potential injury cost functions to serve as predictors of VILI. We set the model parameters to represent normal, mildly injured, and severely injured lungs and estimated the amount of volutrauma and atelectrauma caused by ventilating these lungs with a range of VT and PEEP. We estimated total VILI in two ways: 1) as the sum of the contributions from volutrauma and atelectrauma and 2) as the product of their contributions. We found the product provided estimates of VILI that are more in line with our previous experimental findings. This model may thus serve as the basis for the objective choice of mechanical ventilation parameters for the injured lung.

Ultra-protective ventilation and hypoxemia

Partial extracorporeal CO₂ removal allows a decreasing tidal volume without respiratory acidosis in patients with acute respiratory distress syndrome. This, however, may be associated with worsening hypoxemia, due to several mechanisms, such as gravitational and reabsorption atelectasis, due to a decrease in mean airway pressure and a critically low ventilation-perfusion ratio, respectively. In addition, an imbalance between alveolar and artificial lung partial pressures of nitrogen may accelerate the process. Finally, the decrease in the respiratory quotient, leading to unrecognized alveolar hypoxia and monotonous low plateau pressures preventing critical opening, may contribute to hypoxemia.

[Respiratory monitoring of pediatric patients in the Intensive Care Unit]

Respiratory monitoring plays an important role in the care of children with acute respiratory failure. Therefore, its proper use and correct interpretation (recognizing which signals and variables should be prioritized) should help to a better understanding of the pathophysiology of the disease and the effects of therapeutic interventions. In addition, ventilated patient monitoring, among other determinations, allows to evaluate various parameters of respiratory mechanics, know the status of the different components of the respiratory system and guide the adjustments of ventilatory therapy. In this update, the usefulness of several techniques of respiratory monitoring including conventional respiratory monitoring and more recent methods are described. Moreover, basic concepts of mechanical ventilation, their interpretation and how the appropriate analysis of the information obtained can cause an impact on the clinical management of the patient are defined.

Visualizing the Propagation of Acute Lung Injury

BACKGROUND

Mechanical ventilation worsens acute respiratory distress syndrome, but this secondary "ventilator-associated" injury is variable and difficult to predict. The authors aimed to visualize the propagation of such ventilator-induced injury, in the presence (and absence) of a primary underlying lung injury, and to determine the predictors of propagation.

METHODS

Anesthetized rats (n = 20) received acid aspiration (hydrochloric acid) followed by ventilation with moderate tidal volume (V(T)). In animals surviving ventilation for at least 2 h, propagation of injury was quantified by using serial computed tomography. Baseline lung status was assessed by oxygenation, lung weight, and lung strain (V(T)/expiratory lung volume). Separate groups of rats without hydrochloric acid aspiration were ventilated with large (n = 10) or moderate (n = 6) V(T).

RESULTS

In 15 rats surviving longer than 2 h, computed tomography opacities spread outward from the initial site of injury. Propagation was associated with higher baseline strain (propagation vs. no propagation [mean ± SD]: 1.52 ± 0.13 vs. 1.16 ± 0.20, P < 0.01) but similar oxygenation and lung weight. Propagation did not occur where baseline strain was less than 1.29. In healthy animals, large V(T) caused injury that was propagated inward from the lung periphery; in the absence of preexisting injury, propagation did not occur where strain was less than 2.0.

CONCLUSIONS

Compared with healthy lungs, underlying injury causes propagation to occur at a lower strain threshold and it originates at the site of injury; this suggests that tissue around the primary lesion is more sensitive. Understanding how injury is propagated may ultimately facilitate a more individualized monitoring or management.

Personalizing mechanical ventilation for acute respiratory distress syndrome

Lung-protective ventilation with low tidal volumes remains the cornerstone for treating patient with acute respiratory distress syndrome (ARDS). Personalizing such an approach to each patient's unique physiology may improve outcomes further. Many factors should be considered when mechanically ventilating a critically ill patient with ARDS. Estimations of transpulmonary pressures as well as individual's hemodynamics and respiratory mechanics should influence PEEP decisions as well as response to therapy (recruitability). This summary will emphasize the potential role of personalized therapy in mechanical ventilation.

Effects of different levels of end-expiratory pressure on hemodynamic, respiratory mechanics and systemic stress response during laparoscopic cholecystectomy

OBJECTIVE

General anesthesia causes reduction of functional residual capacity. And this decrease can lead to atelectasis and intrapulmonary shunting in the lung. In this study we want to evaluate the effects of 5 and 10cmH₂O PEEP levels on gas exchange, hemodynamic, respiratory mechanics and systemic stress response in laparoscopic cholecystectomy.

METHODS

American Society of Anesthesiologist I-II physical status 43 patients scheduled for laparoscopic cholecystectomy were randomly selected to receive external PEEP of 5cmH₂O (PEEP 5 group) or 10cmH₂O PEEP (PEEP 10 group) during pneumoperitoneum. Basal hemodynamic parameters were recorded, and arterial blood gases (ABG) and blood sampling were done for cortisol, insulin and glucose level estimations to assess the systemic stress response before induction of anesthesia. Thirty minutes after the pneumoperitoneum, the respiratory and hemodynamic parameters were recorded again and ABG and sampling for cortisol, insulin, and glucose levels were repeated. Lastly hemodynamic parameters were recorded; ABG analysis and sampling for stress response levels were taken after 60minutes from extubation.

RESULTS

There were no statistical differences between the two groups about hemodynamic and respiratory parameters except mean airway pressure (P_mean). P_mean, compliance and PaO₂; pH values were higher in 'PEEP 10 group'. Also, PaCO₂ values were lower in 'PEEP 10 group'. No differences were observed between insulin and lactic acid levels in the two groups. But postoperative cortisol level was significantly lower in 'PEEP 10 group'.

CONCLUSION

Ventilation with 10cmH₂O PEEP increases compliance and oxygenation, does not cause hemodynamic and respiratory complications and reduces the postoperative stress response.

The standard of care of patients with ARDS: ventilatory settings and rescue therapies for refractory hypoxemia

Purpose

Severe ARDS is often associated with refractory hypoxemia, and early identification and treatment of hypoxemia is mandatory. For the management of severe ARDS ventilator settings, positioning therapy, infection control, and supportive measures are essential to improve survival.

Methods and results

A precise definition of life-threating hypoxemia is not identified. Typical clinical determinations are: arterial partial pressure of oxygen < 60 mmHg and/or arterial oxygenation < 88 % and/or the ratio of PaO₂/FIO₂ < 100. For mechanical ventilation specific settings are recommended: limitation of tidal volume (6 ml/kg predicted body weight), adequate high PEEP (>12 cmH₂O), a recruitment manoeuvre in special situations, and a ‘balanced’ respiratory rate (20-30/min). Individual bedside methods to guide PEEP/recruitment (e.g., transpulmonary pressure) are not (yet) available. Prone positioning [early (≤ 48 hrs after onset of severe ARDS) and prolonged (repetition of 16-hr-sessions)] improves survival. An advanced infection management/control includes early diagnosis of bacterial, atypical, viral and fungal specimen (blood culture, bronchoalveolar lavage), and of infection sources by CT scan, followed by administration of broad-spectrum anti-infectives. Neuromuscular blockage (Cisatracurium ≤ 48 hrs after onset of ARDS), as well as an adequate sedation strategy (score guided) is an important supportive therapy. A negative fluid balance is associated with improved lung function and the use of hemofiltration might be indicated for specific indications.

Conclusions

A specific standard of care is required for the management of severe ARDS with refractory hypoxemia.

Lung ventilation strategies for acute respiratory distress syndrome: a systematic review and network meta-analysis

To identify the best lung ventilation strategy for acute respiratory distress syndrome (ARDS), we performed a network meta-analysis. The Cochrane Central Register of Controlled Trials, EMBASE, MEDLINE, CINAHL, and the Web of Science were searched, and 36 eligible articles were included. Compared with higher tidal volumes with FiO2-guided lower positive end-expiratory pressure [PEEP], the hazard ratios (HRs) for mortality were 0.624 (95% confidence interval (CI) 0.419-0.98) for lower tidal volumes with FiO2-guided lower PEEP and prone positioning and 0.572 (0.34-0.968) for pressure-controlled ventilation with FiO2-guided lower PEEP. Lower tidal volumes with FiO2-guided higher PEEP and prone positioning had the greatest potential to reduce mortality, and the possibility of receiving the first ranking was 61.6%. Permissive hypercapnia, recruitment maneuver, and low airway pressures were most likely to be the worst in terms of all-cause mortality. Compared with higher tidal volumes with FiO2-guided lower PEEP, pressure-controlled ventilation with FiO2-guided lower PEEP and lower tidal volumes with FiO2-guided lower PEEP and prone positioning ventilation are associated with lower mortality in ARDS patients. Lower tidal volumes with FiO2-guided higher PEEP and prone positioning ventilation and lower tidal volumes with pressure-volume (P-V) static curve-guided individual PEEP are potential optimal strategies for ARDS patients.

Safety and Efficacy of Combined Extracorporeal CO2 Removal and Renal Replacement Therapy in Patients With Acute Respiratory Distress Syndrome and Acute Kidney Injury: The Pulmonary and Renal Support in Acute Respiratory Distress Syndrome Study

OBJECTIVE

To assess the safety and efficacy of combining extracorporeal CO2 removal with continuous renal replacement therapy in patients presenting with acute respiratory distress syndrome and acute kidney injury.

DESIGN

Prospective human observational study.

SETTINGS

Patients received volume-controlled mechanical ventilation according to the acute respiratory distress syndrome net protocol. Continuous venovenous hemofiltration therapy was titrated to maintain maximum blood flow and an effluent flow of 45 mL/kg/h with 33% predilution.

PATIENTS

Eleven patients presenting with both acute respiratory distress syndrome and acute kidney injury required renal replacement therapy.

INTERVENTIONS

A membrane oxygenator (0.65 m) was inserted within the hemofiltration circuit, either upstream (n = 7) or downstream (n = 5) of the hemofilter. Baseline corresponded to tidal volume 6 mL/kg of predicted body weight without extracorporeal CO2 removal. The primary endpoint was 20% reduction in PaCO2 at 20 minutes after extracorporeal CO2 removal initiation. Tidal volume was subsequently reduced to 4 mL/kg for the remaining 72 hours.

MEASUREMENTS AND MAIN RESULTS

Twelve combined therapies were conducted in the 11 patients. Age was 70 ± 9 years, Simplified Acute Physiology Score II was 69 ± 13, Sequential Organ Failure Assessment score was 14 ± 4, lung injury score was 3 ± 0.5, and PaO2/FIO2 was 135 ± 41. Adding extracorporeal CO2 removal at tidal volume 6 mL/kg decreased PaCO2 by 21% (95% CI, 17-25%), from 47 ± 11 to 37 ± 8 Torr (p < 0.001). Lowering tidal volume to 4 mL/kg reduced minute ventilation from 7.8 ± 1.5 to 5.2 ± 1.1 L/min and plateau pressure from 25 ± 4 to 21 ± 3 cm H2O and raised PaCO2 from 37 ± 8 to 48 ± 10 Torr (all p < 0.001). On an average of both positions, the oxygenator's blood flow was 410 ± 30 mL/min and the CO2 removal rate was 83 ± 20 mL/min. The oxygenator blood flow (p <0.001) and the CO2 removal rate (p = 0.083) were higher when the membrane oxygenator was placed upstream of the hemofilter. There was no safety concern.

CONCLUSIONS

Combining extracorporeal CO2 removal and continuous venovenous hemofiltration in patients with acute respiratory distress syndrome and acute kidney injury is safe and allows efficient blood purification together with enhanced lung protective ventilation.

Role of extracorporeal membrane oxygenation in adult respiratory failure: an overview

Extracorporeal membrane oxygenation (ECMO) provides complete or partial support of the heart and lungs. Ever since its inception in the 1960s, it has been used across all age groups in the management of refractory respiratory failure and cardiogenic shock. While it has gained widespread acceptance in the neonatal and pediatric physician community, ECMO remains a controversial therapy for Acute Respiratory Distress Syndrome (ARDS) in adults. Its popularity was revived during the swine flu (H1N1) pandemic and advancements in technology have contributed to its increasing usage. ARDS continues to be a potentially devastating condition with significant mortality rates. Despite gaining more insights into this entity over the years, mechanical ventilation remains the only life-saving, yet potentially harmful intervention available for ARDS. ECMO shows promise in this regard by offering less dependence on mechanical ventilation, thereby potentially reducing ventilator-induced injury. However, the lack of rigorous clinical data has prevented ECMO from becoming the standard of care in the management of ARDS. Therefore, the results of two large ongoing randomized trials, which will hopefully throw more light on the role of ECMO in the management of this disease entity, are keenly awaited. In this article we will provide a basic overview of the development of ECMO, the types of ECMO, the pathogenesis of ARDS, different ventilation strategies for ARDS, the role of ECMO in ARDS and the role of ECMO as a bridge to lung transplantation.

Feasibility and safety of low-flow extracorporeal carbon dioxide removal to facilitate ultra-protective ventilation in patients with moderate acute respiratory distress sindrome

Background

Mechanical ventilation with a tidal volume (V_T) of 6 mL/kg/predicted body weight (PBW), to maintain plateau pressure (P_plat) lower than 30 cmH₂O, does not completely avoid the risk of ventilator induced lung injury (VILI). The aim of this study was to evaluate safety and feasibility of a ventilation strategy consisting of very low V_T combined with extracorporeal carbon dioxide removal (ECCO₂R).

Methods

In fifteen patients with moderate ARDS, V_T was reduced from baseline to 4 mL/kg PBW while PEEP was increased to target a plateau pressure – (P_plat) between 23 and 25 cmH₂O. Low-flow ECCO₂R was initiated when respiratory acidosis developed (pH < 7.25, PaCO₂ > 60 mmHg). Ventilation parameters (V_T, respiratory rate, PEEP), respiratory compliance (C_RS), driving pressure (DeltaP = V_T/C_RS), arterial blood gases, and ECCO₂R system operational characteristics were collected during the period of ultra-protective ventilation. Patients were weaned from ECCO₂R when PaO₂/FiO₂ was higher than 200 and could tolerate conventional ventilation settings. Complications, mortality at day 28, need for prone positioning and extracorporeal membrane oxygenation, and data on weaning from both MV and ECCO₂R were also collected.

Results

During the 2 h run in phase, V_T reduction from baseline (6.2 mL/kg PBW) to approximately 4 mL/kg PBW caused respiratory acidosis (pH < 7.25) in all fifteen patients. At steady state, ECCO₂R with an average blood flow of 435 mL/min and sweep gas flow of 10 L/min was effective at correcting pH and PaCO₂ to within 10 % of baseline values. PEEP values tended to increase at V_T of 4 mL/kg from 12.2 to 14.5 cmH₂O, but this change was not statistically significant. Driving pressure was significantly reduced during the first two days compared to baseline (from 13.9 to 11.6 cmH₂O; p < 0.05) and there were no significant differences in the values of respiratory system compliance. Rescue therapies for life threatening hypoxemia such as prone position and ECMO were necessary in four and two patients, respectively. Only two study-related adverse events were observed (intravascular hemolysis and femoral catheter kinking).

Conclusions

The low-flow ECCO₂R system safely facilitates a low volume, low pressure ultra-protective mechanical ventilation strategy in patients with moderate ARDS.

Current Applications for the Use of Extracorporeal Carbon Dioxide Removal in Critically Ill Patients

Mechanical ventilation in patients with respiratory failure has been associated with secondary lung injury, termed ventilator-induced lung injury. Extracorporeal venovenous carbon dioxide removal (ECCO₂R) appears to be a feasible means to facilitate more protective mechanical ventilation or potentially avoid mechanical ventilation in select patient groups. With this expanding role of ECCO₂R, we aim to describe the technology and the main indications of ECCO₂R.

Experimental blunt chest trauma--cardiorespiratory effects of different mechanical ventilation strategies with high positive end-expiratory pressure: a randomized controlled study

Background

Uncertainty persists regarding the optimal ventilatory strategy in trauma patients developing acute respiratory distress syndrome (ARDS). This work aims to assess the effects of two mechanical ventilation strategies with high positive end-expiratory pressure (PEEP) in experimental ARDS following blunt chest trauma.

Methods

Twenty-six juvenile pigs were anesthetized, tracheotomized and mechanically ventilated. A contusion was applied to the right chest using a bolt-shot device. Ninety minutes after contusion, animals were randomized to two different ventilation modes, applied for 24 h: Twelve pigs received conventional pressure-controlled ventilation with moderately low tidal volumes (V_T, 8 ml/kg) and empirically chosen high external PEEP (16cmH₂O) and are referred to as the HP-CMV-group. The other group (n = 14) underwent high-frequency inverse-ratio pressure-controlled ventilation (HFPPV) involving respiratory rate of 65breaths · min⁻¹, inspiratory-to-expiratory-ratio 2:1, development of intrinsic PEEP and recruitment maneuvers, compatible with the rationale of the Open Lung Concept. Hemodynamics, gas exchange and respiratory mechanics were monitored during 24 h. Computed tomography and histology were analyzed in subgroups.

Results

Comparing changes which occurred from randomization (90 min after chest trauma) over the 24-h treatment period, groups differed statistically significantly (all P values for group effect <0.001, General Linear Model analysis) for the following parameters (values are mean ± SD for randomization vs. 24-h): PaO₂ (100 % O₂) (HFPPV 186 ± 82 vs. 450 ± 59 mmHg; HP-CMV 249 ± 73 vs. 243 ± 81 mmHg), venous admixture (HFPPV 34 ± 9.8 vs. 11.2 ± 3.7 %; HP-CMV 33.9 ± 10.5 vs. 21.8 ± 7.2 %), PaCO₂ (HFPPV 46.9 ± 6.8 vs. 33.1 ± 2.4 mmHg; HP-CMV 46.3 ± 11.9 vs. 59.7 ± 18.3 mmHg) and normally aerated lung mass (HFPPV 42.8 ± 11.8 vs. 74.6 ± 10.0 %; HP-CMV 40.7 ± 8.6 vs. 53.4 ± 11.6 %). Improvements occurring after recruitment in the HFPPV-group persisted throughout the study. Peak airway pressure and V_T did not differ significantly. HFPPV animals had lower atelectasis and inflammation scores in gravity-dependent lung areas.

Conclusions

In this model of ARDS following unilateral blunt chest trauma, HFPPV ventilation improved respiratory function and fulfilled relevant ventilation endpoints for trauma patients, i.e. restoration of oxygenation and lung aeration while avoiding hypercapnia and respiratory acidosis.

High respiratory rate is associated with early reduction of lung edema clearance in an experimental model of ARDS

BACKGROUND

The independent impact of respiratory rate on ventilator-induced lung injury has not been fully elucidated. The aim of this study was to investigate the effects of two clinically relevant respiratory rates on early ventilator-induced lung injury evolution and lung edema during the protective ARDSNet strategy. We hypothesized that the use of a higher respiratory rate during a protective ARDSNet ventilation strategy increases lung inflammation and, in addition, lung edema associated to strain-induced activation of transforming growth factor beta (TGF-β) in the lung epithelium.

METHODS

Twelve healthy piglets were submitted to a two-hit lung injury model and randomized into two groups: LRR (20 breaths/min) and HRR (40 breaths/min). They were mechanically ventilated during 6 h according to the ARDSNet strategy. We assessed respiratory mechanics, hemodynamics, and extravascular lung water (EVLW). At the end of the experiment, the lungs were excised and wet/dry ratio, TGF-β pathway markers, regional histology, and cytokines were evaluated.

RESULTS

No differences in oxygenation, PaCO2 levels, systemic and pulmonary arterial pressures were observed during the study. Respiratory system compliance and mean airway pressure were lower in LRR group. A decrease in EVLW over time occurred only in the LRR group (P < 0.05). Wet/dry ratio was higher in the HRR group (P < 0.05), as well as TGF-β pathway activation. Histological findings suggestive of inflammation and inflammatory tissue cytokines were higher in LRR.

CONCLUSION

HRR was associated with more pulmonary edema and higher activation of the TGF-β pathway. In contrast with our hypothesis, HRR was associated with less lung inflammation.

Mechanisms and clinical consequences of acute lung injury

Acute respiratory distress syndrome (ARDS) was first described in 1967, and since then there have been a large number of studies addressing its pathogenesis and therapies. Despite intense research efforts, very few therapies for ARDS have been shown to be effective other than the use of lung protection strategies. The scarcity of therapeutic choices is related to the intricate pathogenesis of the syndrome and to insensitive and aspecific criteria to diagnose this profound acute respiratory failure. The aim of this paper is to summarize advances of new ARDS definitions and provide an overview of new relevant signaling pathways that mediate acute lung injury.

Physiology versus evidence-based guidance for critical care practice

Evidence based medicine is an attempt to optimize the medical decision process through methods primarily based on evidence coming from meta-analyses, systematic reviews, and randomized controlled trials ("evidence-based medicine"), rather than on "clinical judgment" alone. The randomized trials are the cornerstones of this process. However, the randomized trials are just a method to prove or disprove a given hypothesis, which, in turn, derives from a general observation of the reality (premises or theories). In this paper we will examine some of the most recent randomized trials performed in Intensive Care, analyzing their premises, hypothesis and outcome. It is quite evident that when the premises are wrong or too vague the unavoidable consequences will be a negative outcome. We should pay when designing the trial an equal attention in defining premises and hypothesis that we pay for the trial conduction.

Open Lung in Lateral Decubitus With Differential Selective Positive End-Expiratory Pressure in an Experimental Model of Early Acute Respiratory Distress Syndrome

OBJECTIVE

After lung recruitment, lateral decubitus and differential lung ventilation may enable the titration and application of optimum-selective positive end-expiratory pressure values for the dependent and nondependent lungs. We aimed at compare the effects of optimum-selective positive end-expiratory pressure with optimum global positive end-expiratory pressure on regional collapse and aeration distribution in an experimental model of acute respiratory distress syndrome.

DESIGN

Prospective laboratory investigation.

SETTING

University animal research laboratory.

SUBJECTS

Seven piglets.

INTERVENTIONS

A one-hit injury acute respiratory distress syndrome model was established by repeated lung lavages. After replacing the tracheal tube by a double-lumen one, we initiated lateral decubitus and differential ventilation. After maximum-recruitment maneuver, decremental positive end-expiratory pressure titration was performed. The positive end-expiratory pressure corresponding to maximum dynamic compliance was defined globally (optimum global positive end-expiratory pressure) and for each individual lung (optimum-selective positive end-expiratory pressure). After new maximum-recruitment maneuver, two steps were performed in randomized order (15 min each): ventilation applying the optimum global positive end-expiratory pressure and the optimum-selective positive end-expiratory pressure. CT scans were acquired at end expiration and end inspiration.

MEASUREMENTS AND MAIN RESULTS

Aeration homogeneity was evaluated as a nondependent/dependent ratio (percent of total gas content in upper lung/percent of total gas content in lower lung) and tidal recruitment as the difference in the percent mass of nonaerated tissue between expiration and inspiration. At the end of the 15-minute optimum-selective positive end-expiratory pressure, compared with the optimum global positive end-expiratory pressure, resulted in 1) decrease in the percent mass of collapse in the lower lung at expiratory CT (19% ± 15% vs 4% ± 5%; p = 0.03); 2) decrease in the nondependent/dependent ratio between the optimum global positive end-expiratory pressure-expiratory-CT and optimum-selective positive end-expiratory pressure-expiratory-CT (3.7 ± 1.2 vs 0.8 ± 0.5; p = 0.01); 3) decrease in the nondependent/dependent ratio between the optimum global positive end-expiratory pressure-inspiratory-CT and optimum-selective positive end-expiratory pressure-inspiratory-CT (2.8 ± 1.1 vs 0.6 ± 0.3; p = 0.01); and 4) less tidal recruitment (p = 0.049).

CONCLUSIONS

After maximum lung recruitment, lateral decubitus and differential lung ventilation enabled the titration of optimum-selective positive end-expiratory pressure values for the dependent and the nondependent lungs, made possible the application of an optimized regional open lung approach, promoted better aeration distribution, and minimized lung tissue inhomogeneities.

Real-time images of tidal recruitment using lung ultrasound

Background

Ventilator-induced lung injury is a form of mechanical damage leading to a pulmonary inflammatory response related to the use of mechanical ventilation enhanced by the presence of atelectasis. One proposed mechanism of this injury is the repetitive opening and closing of collapsed alveoli and small airways within these atelectatic areas—a phenomenon called tidal recruitment. The presence of tidal recruitment is difficult to detect, even with high-resolution images of the lungs like CT scan. The purpose of this article is to give evidence of tidal recruitment by lung ultrasound.

Findings

A standard lung ultrasound inspection detected lung zones of atelectasis in mechanically ventilated patients. With a linear probe placed in the intercostal oblique position. We observed tidal recruitment within atelectasis as an improvement in aeration at the end of inspiration followed by the re-collapse at the end of expiration. This mechanism disappeared after the performance of a lung recruitment maneuver.

Conclusions

Lung ultrasound was helpful in detecting the presence of atelectasis and tidal recruitment and in confirming their resolution after a lung recruitment maneuver.

Electronic supplementary material

The online version of this article (doi:10.1186/s13089-015-0036-2) contains supplementary material, which is available to authorized users.

Acute cor pulmonale during protective ventilation for acute respiratory distress syndrome: prevalence, predictors, and clinical impact

RATIONALE

Increased right ventricle (RV) afterload during acute respiratory distress syndrome (ARDS) may induce acute cor pulmonale (ACP).

OBJECTIVES

To determine the prevalence and prognosis of ACP and build a clinical risk score for the early detection of ACP.

METHODS

This was a prospective study in which 752 patients with moderate-to-severe ARDS receiving protective ventilation were assessed using transesophageal echocardiography in 11 intensive care units. The study cohort was randomly split in a derivation (n = 502) and a validation (n = 250) cohort.

MEASUREMENTS AND MAIN RESULTS

ACP was defined as septal dyskinesia with a dilated RV [end-diastolic RV/left ventricle (LV) area ratio >0.6 (≥1 for severe dilatation)]. ACP was found in 164 of the 752 patients (prevalence of 22 %; 95 % confidence interval 19-25 %). In the derivation cohort, the ACP risk score included four variables [pneumonia as a cause of ARDS, driving pressure ≥18 cm H2O, arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2) ratio <150 mmHg, and arterial carbon dioxide partial pressure ≥48 mmHg]. The ACP risk score had a reasonable discrimination and a good calibration. Hospital mortality did not differ between patients with or without ACP, but it was significantly higher in patients with severe ACP than in the other patients [31/54 (57 %) vs. 291/698 (42 %); p = 0.03]. Independent risk factors for hospital mortality included severe ACP along with male gender, age, SAPS II, shock, PaO2/FiO2 ratio, respiratory rate, and driving pressure, while prone position was protective.

CONCLUSIONS

We report a 22 % prevalence of ACP and a poor outcome of severe ACP. We propose a simple clinical risk score for early identification of ACP that could trigger specific therapeutic strategies to reduce RV afterload.

Mechanical ventilation for ARDS patients--for a better understanding of the 2012 Surviving Sepsis Campaign Guidelines

The mortality rate among patients suffering acute respiratory distress syndrome (ARDS) remains high despite implementation at clinical centers of the lung protective ventilatory strategies recommended by the International Guidelines for Management of Severe Sepsis and Septic Shock, 2012. This suggests that such strategies are still sub-optimal for some ARDS patients. For these patients, tailored use of ventilator settings should be considered, including: further reduction of tidal volumes, administration of neuromuscular blocking agents if the patient’s spontaneous breathing is incompatible with mechanical ventilation, and adjusting positive end-expiratory pressure (PEEP) settings based on transpulmonary pressure levels.

Respiratory monitoring with electrical impedance tomography for lung protective ventilation and alveolar recruitment maneuver in a patient with a single lung transplant and early graft dysfunction

A case is presented on a patient who underwent left single lung transplantation for emphysema type COPD. There was early graft dysfunction gradeiii during the immediate postoperative period, which required the implantation of an extracorporeal membrane oxygenator (ECMO). Respirator ventilatory parameters were adjusted to avoid lung distension, low tidal volume (Vc) (280ml), high respiratory rates (20rpm), and a positive pressure at end expiration (PEEP) level of 8cmH2O. On monitoring the pulmonary tidal volume distribution by bedside electrical impedance tomography (EIT), it was noted that most of the tidal volume was distributed in the native lung emphysema. An alveolar recruitment manoeuvre was performed, under control of the EIT, that enabled the current volume and distribution and the pressures required to ventilate the transplanted lung to be observed.