Mechanical Ventilation during ECMO: Best Practices

Adults and children who require extracorporeal membrane oxygenation for respiratory failure remain at risk for ongoing lung injury if ventilator management is not optimized. This review serves as a guide to assist the bedside clinician in ventilator titration for patients on extracorporeal membrane oxygenation, with a focus on lung-protective strategies. Existing data and guidelines for extracorporeal membrane oxygenation ventilator management are reviewed, including non-conventional ventilation modes and adjunct therapies.

Diaphragm Neurostimulation Assisted Ventilation in Critically Ill Patients

Diaphragm neurostimulation consists of placing electrodes directly on or in proximity to the phrenic nerve(s) to elicit diaphragmatic contractions. Since its initial description in the 18th century, indications have shifted from cardiopulmonary resuscitation to long-term ventilatory support. Recently, the technical development of devices for temporary diaphragm neurostimulation has opened up the possibility of a new era for the management of mechanically ventilated patients. Combining positive pressure ventilation with diaphragm neurostimulation offers a potentially promising new approach to the delivery of mechanical ventilation which may benefit multiple organ systems. Maintaining diaphragm contractions during ventilation may attenuate diaphragm atrophy and accelerate weaning from mechanical ventilation. Preventing atelectasis and preserving lung volume can reduce lung stress and strain and improve homogeneity of ventilation, potentially mitigating ventilator-induced lung injury. Furthermore, restoring the thoracoabdominal pressure gradient generated by diaphragm contractions may attenuate the drop in cardiac output induced by positive pressure ventilation. Experimental evidence suggests diaphragm neurostimulation may prevent neuroinflammation associated with mechanical ventilation. This review describes the historical development and evolving approaches to diaphragm neurostimulation during mechanical ventilation and surveys the potential mechanisms of benefit. The review proposes a research agenda and offers perspectives for the future of diaphragm neurostimulation assisted mechanical ventilation for critically ill patients.

A cortactin CTTN coding SNP contributes to lung vascular permeability and inflammatory disease severity in African descent subjects

The cortactin gene (CTTN), encoding an actin-binding protein critically involved in cytoskeletal dynamics and endothelial cell (EC) barrier integrity, contains single nucleotide polymorphisms (SNPs) associated with severe asthma in Black patients. As loss of lung EC integrity is a major driver of mortality in the Acute Respiratory Distress Syndrome (ARDS), sepsis, and the acute chest syndrome (ACS), we speculated CTTN SNPs that alter EC barrier function will associate with clinical outcomes from these types of conditions in Black patients. In case-control studies, evaluation of a nonsynonymous CTTN coding SNP Ser484Asn (rs56162978, G/A) in a severe sepsis cohort (725 Black subjects) revealed significant association with increased risk of sepsis mortality. In a separate cohort of sickle cell disease (SCD) subjects with and without ACS (177 SCD Black subjects), significantly increased risk of ACS and increased ACS severity (need for mechanical ventilation) was observed in carriers of the A allele. Human lung EC expressing the cortactin S484N transgene exhibited: (i) delayed EC barrier recovery following thrombin-induced permeability; (ii) reduced levels of critical Tyr486 cortactin phosphorylation; (iii) inhibited binding to the cytoskeletal regulator, nmMLCK; and (iv) attenuated EC barrier-promoting lamellipodia dynamics and biophysical responses. ARDS-challenged Cttn+/- heterozygous mice exhibited increased lung vascular permeability (compared to wild-type mice) which was significantly attenuated by IV delivery of liposomes encargoed with CTTN WT transgene but not by CTTN S484N transgene. In summary, these studies suggest that the CTTN S484N coding SNP contributes to severity of inflammatory injury in Black patients, potentially via delayed vascular barrier restoration.

Extra Corporeal Membrane Oxygenation in the Treatment of Human Immunodeficiency Virus-Related P. jirovecii Pneumonia

Despite the undeniable complexity one may encounter while managing critically ill patients with human immunodeficiency virus infection (HIV), intensive care unit-related mortality has declined in recent years, not only because of more efficacious antiretroviral therapy (ART) but also due to the advances in critical support. However, the use of extracorporeal membrane oxygenation (ECMO) in these patients remains controversial. We report four cases of HIV-infected patients with Pneumocystis jirovecii pneumonia (PJP) and acute respiratory distress syndrome (ARDS) treated with ECMO support and discuss its indications and possible role in the prevention of barotrauma and ventilator- induced lung injury (VILI). The eventually favorable clinical course of the patients that we present suggests that although immune status is an important aspect in the decision to initiate ECMO support, this technology can provide real benefit in some patients with severe HIV-related refractory ARDS.

High-frequency oscillatory ventilation in children: A systematic review and meta-analysis

BACKGROUND

High-frequency oscillatory ventilation (HFOV) is an alternative mechanical ventilation mode proposed to reduce ventilator-induced lung injuries and improve clinical outcomes. The aim of this study was to determine the effects of HFOV compared to conventional mechanical ventilation (CMV) when used in children with hypoxemic respiratory failure.

METHODS

The literature search was conducted to identify all studies published before December 2020. Eligible studies included a population aged between 28 days and 18 years old, presented original data from randomized controlled trials (RCTs) or observational studies, compared the use of HFOV with CMV. Meta-analyses of the pooled data were performed by using random-effects models with inverse-variance weighting.

RESULTS

A total of 11 studies (2605 cases) were included, most of them evaluating patients with acute respiratory distress syndrome. The mean age of participants was 8.2 months and the mean oxygenation index of those included in the RCTs was 24.4. The effect of HFOV on mortality was not significant, and clinically significant harm or benefit could not be excluded (risk ratio [RR], 0.93; 95% confidence interval [CI], 0.72 to 1.20). No significant difference between groups was found in duration of mechanical ventilation (-2.23; 95% CI, -5.07 to 0.61), treatment failure (RR, 0.28; 95% CI, 0.08 to 1.02), and occurrence of barotrauma (RR, 0.88; 95% CI, 0.39 to 1.99).

CONCLUSION

The scarce evidence currently available does not allow us to conclude that HFOV has advantages over CMV and further studies are needed to clarify its role in the treatment of acute hypoxemic respiratory failure in children.

Patient-Self Inflicted Lung Injury: A Practical Review

Patients with severe lung injury usually have a high respiratory drive, resulting in intense inspiratory effort that may even worsen lung damage by several mechanisms gathered under the name “patient-self inflicted lung injury” (P-SILI). Even though no clinical study has yet demonstrated that a ventilatory strategy to limit the risk of P-SILI can improve the outcome, the concept of P-SILI relies on sound physiological reasoning, an accumulation of clinical observations and some consistent experimental data. In this review, we detail the main pathophysiological mechanisms by which the patient’s respiratory effort could become deleterious: excessive transpulmonary pressure resulting in over-distension; inhomogeneous distribution of transpulmonary pressure variations across the lung leading to cyclic opening/closing of nondependent regions and pendelluft phenomenon; increase in the transvascular pressure favoring the aggravation of pulmonary edema. We also describe potentially harmful patient-ventilator interactions. Finally, we discuss in a practical way how to detect in the clinical setting situations at risk for P-SILI and to what extent this recognition can help personalize the treatment strategy.

Lung ultrasound guided pulmonary recruitment during mechanical ventilation in neonates: A case series

BACKGROUND

Recently, the first report of lung ultrasound (LUS) guided recruitment during open lung ventilation in neonates has been published. LUS guided recruitment can change the approach to open lung ventilation, which is currently performed without any measure of lung function/lung expansion in the neonatal population.

METHODS

We included all the newborn infants that underwent a LUS-guided recruitment maneuver during mechanical ventilation as a rescue attempt for an extremely severe respiratory condition with oxygen saturation/fraction of inspired oxygen (SpO2/FIO2) ratio below 130 or the inability to wean off mechanical ventilation.

RESULTS

We report a case series describing 4 LUS guided recruitment maneuvers, underlying crucial aspects of this technique that can improve the effectiveness of the procedure. In particular, we describe a novel pattern (the S-pattern) that allows us to distinguish the recruitable from the unrecruitable lung and guide the pressure titration phase. Additionally, we describe the optimal LUS-guided patient positioning.

CONCLUSIONS

We believe that the inclusion of specifications regarding patient positioning and the S-pattern in the LUS-guided protocol may be beneficial for the success of the procedure.

Extracorporeal membrane oxygenation in critically ill neonatal and pediatric patients with acute respiratory failure: a guide for the clinician

Intro: Extracorporeal membrane oxygenation for neonatal and pediatric respiratory failure continues to demonstrate improving outcomes, largely due to advances in technology along with refined management strategies despite mounting patient acuity and complexity. Successful use of ECMO requires thoughtful initiation and candidacy strategies, along with reducing the risk of ventilator induced lung injury and the progression to multiorgan failure.Areas Covered: This review describes current ECMO management strategies for neonatal and pediatric patients with acute refractory respiratory failure and summarizes relevant published literature. ECMO initiation and candidacy, along with ventilator and sedation management, are highlighted. Additionally, rapidly expanding areas of interest such as anticoagulation strategies, transfusion thresholds, rehabilitation on ECMO, and drug pharmacokinetics are described.Expert Opinion: Over the last few decades, published studies supporting ECMO use for acute refractory respiratory failure, along with institutional experience, have resulted in increased utilization although more randomized-controlled trials are needed. Future research should focus on filling the knowledge gaps that remain regarding anticoagulation, transfusion thresholds, ventilator strategies, sedation, and approaches to rehabilitation to subsequently implement into clinical practice. Additionally, efforts should focus on well-designed trials, including population pharmacokinetic studies, to develop dosing recommendations.

Review of the Mechanisms of Ventilator Induced Lung Injury and the Principles of Intraoperative Lung Protective Ventilation

Intraoperative ventilator induced lung injury is associated with development of postoperative pulmonary complications. Despite advances in modes and methods of mechanical ventilation, postoperative pulmonary complications remain as one of the leading causes of adverse outcomes following surgery and anesthesia. In an attempt to reduce the incidence of postoperative pulmonary complications, the use of an intraoperative ventilatory technique to minimize lung injury has been introduced. Lung protective ventilation typically entails the use of a physiologic tidal volume, positive end expiratory pressure, extended inspiratory time, and an alveolar recruitment maneuver. The goal of intraoperative lung protective ventilation is to prevent or at least minimize development of ventilator induced lung injury by maintaining a homogeneous lung and alveolar stability during and after a surgical procedure. To appreciate the value of the application of an intraoperative lung protective ventilation strategy, the pathophysiology and developmental processes of ventilator induced lung injury must first be understood. The primary purpose of this paper is to provide a basic understanding of the relationship between conventional intraoperative mechanical ventilation, pulmonary derangement and lung injury as well as a rationale for the use of individualized lung protective ventilation to optimize surgical patient pulmonary outcomes.

Dynamic Airway Driving Pressure and Outcomes in Children With Acute Hypoxemic Respiratory Failure

BACKGROUND

Limited adult data suggest that airway driving pressure might better reflect the potential risk for lung injury than tidal volume based on ideal body weight, and the parameter correlates with mortality in ARDS. There is a lack of data about the effect of driving pressure on mortality in pediatric ARDS. This study aimed to evaluate the effect of driving pressure on morbidity and mortality of children with acute hypoxemic respiratory failure.

METHODS

This retrospective cohort study was performed in a tertiary level pediatric ICU. Children who received invasive mechanical ventilation for acute hypoxemic respiratory failure (defined as [Formula: see text] < 300 within 24 h after intubation), in a 2-y period were included. The cohort was divided into 2 groups based on the highest dynamic driving pressure (ΔP, calculated as the difference between peak inspiratory pressure and PEEP) in the first 24 h, with a cutoff value of 15 cm H₂O.

RESULTS

Of the 380 children who were mechanically ventilated during the study period, 101 children who met eligibility criteria were enrolled. Common diagnoses were pneumonia (n = 51), severe sepsis (n = 24), severe dengue (n = 10), and aspiration pneumonia (n = 7). In comparison to the group with high ΔP (ie, ≥ 15 cm H₂O), children in the group with low ΔP (ie, < 15 cm H₂O) had significantly lower median (interquartile range) duration of ventilation (5 [4-6] d vs 8 [6-11] d, P < .001], ICU length of stay (6 [5-8] d vs 12 [8-15] d, P < .001], and more ventilator-free days at day 28 (23 [20-24] vs 17 [0-22] d, P < .001). Logistic regression analysis also suggested driving pressure as an independent predictor of morbidity after adjusting for confounding variables. However, there was no statistically significant difference in mortality between the 2 groups (17% in low ΔP vs 24% in high ΔP, P = .38). Subgroup analysis of 65 subjects who fulfilled ARDS criteria yielded similar results with respect to mortality and morbidity.

CONCLUSIONS

Below a threshold of 15 cm H₂O, ΔP was associated with significantly decreased morbidity in children with acute hypoxemic respiratory failure.

Antenatal Endotoxin Impairs Lung Mechanics and Increases Sensitivity to Ventilator-Induced Lung Injury in Newborn Rat Pups

Perinatal inflammation due to chorioamnionitis and ventilator-induced lung injury (VILI) at birth is independent risk factors for the development of bronchopulmonary dysplasia (BPD). We have previously shown that antenatal endotoxin (ETX) causes abnormal lung structure and function in 2-week-old rats, but whether ETX impairs lung mechanics at birth and increases risk for VILI is unknown. Fetal rats were exposed to 10 μg endotoxin or saline via intra-amniotic injection. At birth (D0) or 7 days (D7), rats received 90 min of lung protective ventilation [PROTECT group; tidal volume (Vt) = 6 ml/kg with positive end expiratory pressure (PEEP) = 2 cmH₂O]; P20 ventilation [plateau pressure (Pplat) = 20 cmH₂O, PEEP = 0]; or P24 ventilation (Pplat = 24 cmH₂O, PEEP = 0, only applied to D7). Prior to prolonged ventilation at D0, endotoxin-exposed rats had decreased compliance and inspiratory capacity (IC) compared to controls. At D7, endotoxin was associated with reduced compliance. High-pressure ventilation (P20 and P24) tended to increase IC and compliance in all saline-treated groups. Ventilation at D0 with P20 increased IC and compliance when applied to saline-treated but not endotoxin-exposed pups. At D7, P24 ventilation of endotoxin-exposed pups increased elastance, bronchoalveolar lavage protein content, and IL-1b and TEN-C mRNA expression in comparison to the saline group. In summary, antenatal endotoxin exposure alters lung mechanics at birth and 1 week of life and increases susceptibility to VILI as observed in lung mechanics, alveolocapillary barrier injury, and inflammatory mRNA expression. We speculate that antenatal inflammation primes the lung for a more marked VILI response, suggesting an adverse synergistic effect of antenatal and postnatal exposures.

Successful conservative managements of extensive pneumatoceles in a preterm girl: A case report

We describe a preterm girl with severe respiratory distress syndrome, which was managed with mechanical ventilation. She developed severe ventilator induced lung injury, causing extensive unilateral emphysema. CT-scan of the lungs corresponded with extensive pneumatoceles. She was managed conservatively, using neurally adjusted ventilatory assist, with success and was extubated on day of life 38. She was discharged home without any respiratory support at 39 weeks of postmenstrual age. Our case illustrates the ongoing risk of severe ventilator induced lung injury and highlights a unique injury pattern in a preterm newborn that was managed conservatively using neurally adjusted ventilatory assist with an excellent outcome.

SOX11 and FAK participate in the stretch‑induced mechanical injury to alveolar type 2 epithelial cells

The aim of the present study was to explore the potential role of SOX11 in the stretch-induced mechanical injury to alveolar type 2 epithelial (AT2) cells. A cell stretch (CS) test was used to induce mechanical injury to primary cultured AT2 cells. Wound healing, adhesion, cell viability assays and flow cytometry were performed to evaluate the migration, adhesion, viability and apoptosis of AT2 cells. Changes in the invasive ability of AT2 cells were detected using a Transwell invasion assay. To further explore the underlying molecular mechanisms, reverse transcription-quantitative PCR and western blot analysis were used to assess the expression levels of SOX11, FAK, Akt, caspase-3/8, p65 and matrix metal-loproteinase (MMP)7. Co-immunoprecipitation (Co-IP) and luciferase reporter assays were used to detect the interaction between SOX11 and FAK. CS reduced the invasion, migration and adhesion, and increased the apoptosis of AT2 cells. It also resulted in the downregulation of SOX11 and FAK expression in AT2 cells. The overexpression of SOX11 reversed these changes, whereas the knockdown of SOX11 aggravated the deterioration of the aforementioned biological behaviors and the apoptosis of the AT2 cells following CS. The overexpression of SOX11 upregulated the FAK and Akt expression levels, and downregulated caspase-3/8 expression, whereas the silencing of SOX11 reversed these changes following CS. Furthermore, the effects of SOX11 overexpression were inhibited by FAK antagonism. The results of Co-IP demonstrated that SOX11 and FAK were bound together, and that the expression of FAK was significantly increased in the SOX11 overexpression group. Luciferase assays revealed that the luciferase activity and the mRNA expression of FAK were significantly increased following transfection with pcDNA SOX11 and pGL3 FAK promoter. Co-IP and luciferase assays revealed that SOX11 directly regulated the expression of FAK. On the whole, the present study demonstrates that the downregulated expression of SOX11 and FAK are involved in the stretch-induced mechanical injury to AT2 cells. The over-expression of SOX11 significantly alleviates AT2 cell injury through the upregulation of FAK and Akt, and the inhibition of apoptosis. These findings suggest that the activation of SOX11 and FAK may be potential preventive and therapeutic options for ventilator-induced lung injury.

Anesthetic considerations for lung resection: preoperative assessment, intraoperative challenges and postoperative analgesia

This article is intended to provide a general overview of the anesthetic management for lung resection surgery including the preoperative evaluation of the patient, factors influencing the intraoperative anesthetic management and options for postoperative analgesia. Lung cancer is the leading cause of death among cancer patients in the United States. In patients undergoing lung resection, perioperative pulmonary complications are the major etiology of morbidity and mortality. Risk stratification of patients should be part of the preoperative assessment to predict their risk of short-term vs. long-term pulmonary complications. Improvements in surgical technique and equipment have made video assisted thoracoscopy and robotically assisted thoracoscopy the procedures of choice for thoracic surgeries. General anesthesia including lung isolation has become essential for optimizing visualization of the operative lung but may itself contribute to pulmonary complications. Protective lung ventilation strategies may not prevent acute lung injury from one-lung ventilation, but it may decrease the amount of overall lung injury by using small tidal volumes, positive end expiratory pressure, low peak and plateau airway pressures and low inspired oxygen fraction, as well as by keeping surgical time as short as possible. Because of the high incidence of chronic post-thoracotomy pain syndrome following thoracic surgery, which can impact a patient's normal daily activities for months to years after surgery, postoperative analgesia is a necessary part of the anesthetic plan. Multiple options such as thoracic epidural analgesia, intravenous narcotics and several nerve blocks can be considered in order to prevent or attenuate chronic pain syndromes. Enhanced recovery after thoracic surgery is a relatively new topic with many elements taken from the experience with colorectal surgery. The goal of enhanced recovery is to improve patient outcome by improving organ function and decreasing postoperative complications, and therefore decreasing length of hospital stay.

High-frequency oscillatory ventilation: A narrative review

High-frequency oscillatory ventilation (HFOV) is a lung-protective strategy that can be utilized in the full spectrum of patient populations ranging from neonatal to adults with acute lung injury. HFOV is often utilized as a rescue strategy when conventional mechanical ventilation (CV) has failed. HFOV uses low tidal volumes and constant mean airway pressures in conjunction with high respiratory rates to provide beneficial effects on oxygenation and ventilation, while eliminating the traumatic “inflate–deflate” cycle imposed by CV. Although statistical evidence supporting HFOV is particularly low, potential benefits for its application in many clinical manifestations still remain. High-frequency oscillation is a safe and effective rescue mode of ventilation for the treatment of acute respiratory distress syndrome (ARDS). All patients who have ventilator-induced lung injury (VILI) or are at risk of developing VILI or ARDS would be suitable candidates for HFOV, especially those who have failed conventional mechanical ventilation. This narrative aims to provide a review of HFOV vis-à-vis its indications, contraindications, hazards, parameters to monitoring, patient selection, clinical goals, mechanisms of action, controls for optimizing ventilation and oxygenation, clinical application in ARDS, and a comparison with other modes of mechanical ventilation.

Cross-sectional analysis on publication status and age representation of clinical studies addressing mechanical ventilation and ventilator-induced lung injury in infants and children

OBJECTIVES

We determined the number and time-to-public availability of study results of published and unpublished clinical studies in paediatric mechanical ventilation (MV) and ventilator-induced lung injury (VILI), which were registered as completed on ClinicalTrials.gov. Furthermore, we explored the pattern of represented research study subtopics and the corresponding study populations.

SETTING

Literature search based on ClinicalTrials.gov, PubMed and Google Scholar from 9 July 2017 to 27 September 2017.

PRIMARY AND SECONDARY OUTCOME MEASURES

Assessment, if studies included in our analysis had been published. Assessment of primary research focus, patient enrolment and age representation of the analysed studies.

RESULTS

We identified n=109 registered and completed clinical studies on paediatric MV and VILI (enrolment: 22 233 participants). 71% were published, including data from 18 647 subjects. 29% of studies were unpublished, containing data from 3586 subjects. Median time-to-public availability of study results was 22 (IQR, 12.8-41.5) months. The most important study subtopics were biophysical and technical aspects of MV (32 studies), administration of drugs to mitigate VILI through various mechanisms (40 studies) and diagnostic procedures (16 studies). n=66/109 (61%) studies exclusively focused on children below 1 year of age and n=2/109 (2%) exclusively on children between 1 and 14 years.

CONCLUSIONS

One-third of clinical studies in paediatric MV and VILI registered as completed on ClinicalTrials.gov remained unpublished and contained data on 3586 study participants. The overall median time-to-public availability of study results was longer than the deadline of 12 months mandated by the Food and Drug Administration Amendment Act of 2007. Important and clinically relevant research study subtopics were represented in the research questions investigated in paediatric MV and VILI. The study population was skewed towards children younger than 1 year which indicates, that there is a substantial need for clinical VILI research in older children.

Detection of optimal PEEP for equal distribution of tidal volume by volumetric capnography and electrical impedance tomography during decreasing levels of PEEP in post cardiac-surgery patients

Background

Homogeneous ventilation is important for prevention of ventilator-induced lung injury. Electrical impedance tomography (EIT) has been used to identify optimal PEEP by detection of homogenous ventilation in non-dependent and dependent lung regions. We aimed to compare the ability of volumetric capnography and EIT in detecting homogenous ventilation between these lung regions.

Methods

Fifteen mechanically-ventilated patients after cardiac surgery were studied. Ventilator settings were adjusted to volume-controlled mode with a fixed tidal volume (Vt) of 6–8 ml kg⁻¹ predicted body weight. Different PEEP levels were applied (14 to 0 cm H₂O, in steps of 2 cm H₂O) and blood gases, Vcap and EIT were measured.

Results

Tidal impedance variation of the non-dependent region was highest at 6 cm H₂O PEEP, and decreased significantly at 14 cm H₂O PEEP indicating decrease in the fraction of Vt in this region. At 12 cm H₂O PEEP, homogenous ventilation was seen between both lung regions. Bohr and Enghoff dead space calculations decreased from a PEEP of 10 cm H₂O. Alveolar dead space divided by alveolar Vt decreased at PEEP levels ≤6 cm H₂O. The normalized slope of phase III significantly changed at PEEP levels ≤4 cm H₂O. Airway dead space was higher at higher PEEP levels and decreased at the lower PEEP levels.

Conclusions

In postoperative cardiac patients, calculated dead space agreed well with EIT to detect the optimal PEEP for an equal distribution of inspired volume, amongst non-dependent and dependent lung regions. Airway dead space reduces at decreasing PEEP levels.

Mitochondrial damage pathways in ventilator induced lung injury (VILI): an update

Although reduced tidal volumes have improved patient survival during ventilation for acute lung injury, further improvements will require pharmacologic interventions of the cellular pathways for inflammation and injury. We previously reported that pretreatment with mitochondrial targeted mtDNA repair enzymes largely prevented lung injury and inflammation during a protocol for moderately severe ventilation induced lung injury. GSH/GSSG ratios indicated that free radical production had been reduced to baseline levels by treatment. The central role of the alveolar macrophages and cellular mechanisms of injury are discussed. This includes a rapid calcium entry and mitochondrial production of excessive reactive oxygen species. Excessive ROS can then result in activation of the NLRP3 inflammasome and secretion of IL-1 and IL-18 by caspase-1. A simultaneous activation of NFkB to transcribe pro forms of the cytokines is stimulated by damage associated molecular pattern (DAMP) recognition receptors. These are primarily TLR4 responding to various cellular damage products and TLR9 responding to mtDNA fragments that appear to be primarily involved. Intervention in these pathways could result in useful future clinical treatments.

Lung Recruitment Strategies During High Frequency Oscillatory Ventilation in Preterm Lambs

Background: High frequency oscillatory ventilation (HFOV) is considered a lung protective ventilation mode in preterm infants only if lung volume is optimized. However, whilst a "high lung volume strategy" is advocated for HFOV in preterm infants this strategy is not precisely defined. It is not known to what extent lung recruitment should be pursued to provide lung protection. In this study we aimed to determine the relationship between the magnitude of lung volume optimization and its effect on gas exchange and lung injury in preterm lambs. Methods: 36 surfactant-deficient 124-127 d lambs commenced HFOV immediately following a sustained inflation at birth and were allocated to either (1) no recruitment (low lung volume; LLV), (2) medium- (MLV), or (3) high lung volume (HLV) recruitment strategy. Gas exchange and lung volume changes over time were measured. Lung injury was analyzed by post mortem pressure-volume curves, alveolar protein leakage, gene expression, and histological injury score. Results: More animals in the LLV developed a pneumothorax compared to both recruitment groups. Gas exchange was superior in both recruitment groups compared to LLV. Total lung capacity tended to be lower in the LLV group. Other parameters of lung injury were not different. Conclusions: Lung recruitment during HFOV optimizes gas exchange but has only modest effects on lung injury in a preterm animal model. In the HLV group aiming at a more extensive lung recruitment gas exchange was better without affecting lung injury.

Prone positioning acute respiratory distress syndrome patients

Prone position has been used in acute respiratory distress syndrome (ARDS) patients for more than 40 years in ICU. After having demonstrated its capability to significantly improve oxygenation in a large number of patients, sometimes dramatically, this procedure has been found to prevent ventilator-induced lung injury, the primary concern for the intensivists managing ARDS patients. Over the time, several trials have been done, which regularly improved and refined from each other. At the end, significant improvement in survival has been demonstrated in the most severe ARDS patients, at a threshold of 100-150 mmHg PaO₂/FiO₂ ratio. The effect of proning on survival cannot be predicted and seems unrelated with both severity of oxygenation impairment and oxygenation response to proning. The rate of complication is declining with the increase in centers expertise. The pressure sores are more frequent in prone and require a special attention. Prone position is a key component of lung protective mechanical ventilation and should be used as a first line therapy in association with low tidal volume and neuromuscular blocking agents in patients with severe ARDS.

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.

Expression of aquaporins 1 and 5 in a model of ventilator-induced lung injury and its relation to tidal volume

NEW FINDINGS

What is the central question of this study? Although different studies have attempted to find factors that influence the expression of aquaporins (AQPs) in the lung in different situations, to date no research group has explored the expression of AQP1 and AQP5 jointly in rats mechanically ventilated with different tidal volumes in a model of ventilator-induced lung injury. What is the main finding? Mechanical ventilation with a high tidal volume causes lung injury and oedema, increasing lung permeability. In rats ventilated with a high tidal volume, the pulmonary expression of AQP1 decreases. We analysed the expression of aquaporins 1 and 5 and its relation with tidal volume in a model of ventilator-induced lung injury. Forty-two rats were used. Six non-ventilated animals were killed (control group). The remaining rats were ventilated for 2 h with different tidal volumes (group 7ML with 7 ml kg^-1 and group 20ML with 20 ml kg^-1 ) and a respiratory rate of 90 breaths min^-1 . Lung oedema was measured, and the expression of AQP1 and AQP5 was determined by Western immunoblotting and measurement of mRNA. Lung oedema and alveolar-capillary membrane permeability were significantly increased in the animals of group 20ML compared with the control group. Expression of AQP1 was decreased in groups 7ML and 20ML compared with the control group. In conclusion, mechanical ventilation with a high tidal volume causes lung injury and oedema, increasing lung permeability. In rats ventilated with a high tidal volume, the pulmonary expression of AQP1 decreases.

Liquid extracorporeal carbon dioxide removal: use of THAM (tris-hydroxymethyl aminomethane) coupled to hemofiltration to control hypercapnic acidosis in a porcine model of protective mechanical ventilation

A promising approach to facilitate protective mechanical ventilation is the use of extracorporeal CO2 removal techniques. Several strategies based on membrane gas exchangers have been developed. However, these techniques are still poorly available. The goal of this study was to assess the efficacy and safety of THAM infusion coupled to hemofiltration for the management of hypercapnic acidosis. A severe respiratory acidosis was induced in seven anesthetized pigs. Five of them were treated with THAM 8-mmol·kg(-1)·h(-1) coupled to hemofiltration (THAM+HF group) at 100 mL·kg(-1)·h(-1). After 18-hours of treatment the THAM infusion was stopped but hemofiltration was kept on until 24-hours. The 2 other animals were treated with THAM but without hemofiltration. After 1-hour of treatment in THAM+HF, PaCO2 rapidly decreased from a median of 89.0 (IQR) (80.0, 98.0) to 71.3 (65.8, 82.0) mmHg (P<0.05), while pH increased from 7.12 (7.01, 7.15) to 7.29 (7.27, 7.30) (P<0.05). Thereafter PaCO2 remained stable between 60-70 mmHg, while pH increased above 7.4. After stopping THAM at 18 hours of treatment a profound rebound effect was observed with severe hypercapnic acidosis. The most important side effect we observed was hyperosmolality, which reached a maximum of 330 (328, 332) mOsm·kg H2O(-1) at T18. The animals treated only with THAM developed severe hypercapnia, despite the fact that pH returned to normal values, and died after 12 hours. Control-group had an uneven evolution until the end of the experiment. A combined treatment with THAM coupled to hemofiltration may be an effective treatment to control severe hypercapnic acidosis.

Ventilator Weaning and Spontaneous Breathing Trials; an Educational Review

The term "weaning" is used to describe the gradual process of decreasing ventilator support. It is estimated that 40% of the duration of mechanical ventilation is dedicated to the process of weaning. Spontaneous breathing trial (SBT) assesses the patient's ability to breathe while receiving minimal or no ventilator support. The collective task force in 2001 stated that the process of SBT and weaning should start by assessing whether the underlying cause of respiratory failure has been resolved or not. Weaning predictors are parameters that are intended to help clinicians predict whether weaning attempts will be successful or not. Although the international consensus conference in 2005 did not recommend their routine use for clinical decision making, researchers did not stop working in this area. In the present article, we review some of the recent studies about weaning predictors, criteria, procedure, as well as assessment for extubation a mechanically ventilated patient.

Saikosaponin-d attenuates ventilator-induced lung injury in rats

Saikosaponin-d is one of the main bioactive components in the traditional Chinese medicine Bupleurum falcatum L and possesses anti-inflammatory and immune-modulatory properties. The current study aimed to investigate the protective effects of saikosaponin-d on ventilator-induced lung injury (VILI) in rats. We found that saikosaponin-d treatment significantly attenuated the pathological changes of lungs induced by mechanical ventilation. Administration of saikosaponin-d reduced the pulmonary neutrophil infiltration as well as the MPO concentrations. Saikosaponin-d also decreased the expression of pro-inflammatory cytokines including MIP-2, IL-6 and TNF-α. Meanwhile, the expression of anti-inflammatory mediators, such as TGF-β1 and IL-10, was obviously elevated after saikosaponin-d administration. Saikosaponin-d remarkably reduced the oxidative stress and apoptosis rate in lung tissues. On the molecular level, saikosaponin-d treatment obviously downregulated the expression of caspases-3 and the pro-apoptotic protein bax, and promoted the expression level of anti-apoptotic protein bcl-2. Collectively, our study demonstrated that saikosaponin-d may attenuate ventilator induced lung injury through inhibition of inflammatory responses, oxidative stress and apoptosis.

MECHANICAL VENTILATION FOR THE LUNG TRANSPLANT RECIPIENT

Mechanical ventilation (MV) is an important aspect in the intraoperative and early postoperative management of lung transplant (LTx)-recipients. There are no randomized-controlled trials of LTx-recipient MV strategies; however there are LTx center experiences and international survey studies reported. The main early complication of LTx is primary graft dysfunction (PGD), which is similar to the adult respiratory distress syndrome (ARDS). We aim to summarize information pertinent to LTx-MV, as well as PGD, ARDS, and intraoperative MV and to synthesize these available data into recommendations. Based on the available evidence, we recommend lung-protective MV with low-tidal-volumes (≤6 mL/kg predicted body weight [PBW]) and positive end-expiratory pressure for the LTx-recipient. In our opinion, the MV strategy should be based on donor characteristics (donor PBW as a parameter of actual allograft size), rather than based on recipient characteristics; however this donor-characteristics-based protective MV is based on indirect evidence and requires validation in prospective clinical studies.

Minimising ventilator induced lung injury in preterm infants

Ventilator induced lung injury continues to occur at an unacceptably high rate, which is inversely related to gestational age. Although the "new BPD" may not be entirely avoidable in the extremely premature infant, recognition of risk factors and adoption of an appropriate ventilatory strategy, along with continuous real time monitoring, may help to minimise lung damage. This paper will review the pathogenesis of ventilator induced lung injury and strategies that may mitigate it.