Airway pressure release ventilation reduces the increase in bronchoalveolar lavage fluid high-mobility group box-1 levels and lung water in experimental acute respiratory distress syndrome induced by lung lavage

Pulmonary Interstitial Matrix and Lung Fluid Balance From Normal to the Acutely Injured Lung

This review analyses the mechanisms by which lung fluid balance is strictly controlled in the air-blood barrier (ABB). Relatively large trans-endothelial and trans-epithelial Starling pressure gradients result in a minimal flow across the ABB thanks to low microvascular permeability aided by the macromolecular structure of the interstitial matrix. These edema safety factors are lost when the integrity of the interstitial matrix is damaged. The result is that small Starling pressure gradients, acting on a progressively expanding alveolar barrier with high permeability, generate a high transvascular flow that causes alveolar flooding in minutes. We modeled the trans-endothelial and trans-epithelial Starling pressure gradients under control conditions, as well as under increasing alveolar pressure (Palv) conditions of up to 25 cmH2O. We referred to the wet-to-dry weight (W/D) ratio, a specific index of lung water balance, to be correlated with the functional state of the interstitial structure. W/D averages ∼5 in control and might increase by up to ∼9 in severe edema, corresponding to ∼70% loss in the integrity of the native matrix. Factors buffering edemagenic conditions include: (i) an interstitial capacity for fluid accumulation located in the thick portion of ABB, (ii) the increase in interstitial pressure due to water binding by hyaluronan (the "safety factor" opposing the filtration gradient), and (iii) increased lymphatic flow. Inflammatory factors causing lung tissue damage include those of bacterial/viral and those of sterile nature. Production of reactive oxygen species (ROS) during hypoxia or hyperoxia, or excessive parenchymal stress/strain [lung overdistension caused by patient self-induced lung injury (P-SILI)] can all cause excessive inflammation. We discuss the heterogeneity of intrapulmonary distribution of W/D ratios. A W/D ∼6.5 has been identified as being critical for the transition to severe edema formation. Increasing Palv for W/D > 6.5, both trans-endothelial and trans-epithelial gradients favor filtration leading to alveolar flooding. Neither CT scan nor ultrasound can identify this initial level of lung fluid balance perturbation. A suggestion is put forward to identify a non-invasive tool to detect the earliest stages of perturbation of lung fluid balance before the condition becomes life-threatening.

A narrative review of advanced ventilator modes in the pediatric intensive care unit

Respiratory failure is a common reason for pediatric intensive care unit admission. The vast majority of children requiring mechanical ventilation can be supported with conventional mechanical ventilation (CMV) but certain cases with refractory hypoxemia or hypercapnia may require more advanced modes of ventilation. This paper discusses what we have learned about the use of advanced ventilator modes [e.g., high-frequency oscillatory ventilation (HFOV), high-frequency percussive ventilation (HFPV), high-frequency jet ventilation (HFJV) airway pressure release ventilation (APRV), and neurally adjusted ventilatory assist (NAVA)] from clinical, animal, and bench studies. The evidence supporting advanced ventilator modes is weak and consists of largely of single center case series, although a few RCTs have been performed. Animal and bench models illustrate the complexities of different modes and the challenges of applying these clinically. Some modes are proprietary to certain ventilators, are expensive, or may only be available at well-resourced centers. Future efforts should include large, multicenter observational, interventional, or adaptive design trials of different rescue modes (e.g., PROSpect trial), evaluate their use during ECMO, and should incorporate assessments through volumetric capnography, electric impedance tomography, and transpulmonary pressure measurements, along with precise reporting of ventilator parameters and physiologic variables.

Airway pressure release ventilation versus low tidal volume ventilation for patients with acute respiratory distress syndrome/acute lung injury: a meta-analysis of randomized clinical trials

Background

It is uncertain whether airway pressure release ventilation (APRV) is better than low tidal volume ventilation (LTVV) for patients with acute respiratory distress syndrome (ARDS). The purpose of this meta-analysis was to compare APRV and LTVV on patients with ARDS.

Methods

Randomized controlled trials (RCTs) comparing outcomes in ARDS ventilator therapy with APRV or LTVV were identified using Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica Database (EMBASE), Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science, the Cochrane Library, and The Chinese Biomedicine Literature Database (SinoMed) from inception to March 2019.

Results

A total of 7 RCTs with a 405 patients were eligible for our meta-analysis. The results revealed that APRV was associated with lower hospital mortality [405 patients; odds ratio (OR), 0.57; 95% confidence interval (CI), 0.37-0.88; P=0.01], a shorter time of ventilator therapy [373 patients; mean difference (MD), 5.36; 95% CI, 1.99-8.73; P=0.002], and intensive care unit (ICU) stay (315 patients; MD, -4.50; 95% CI, -6.56 to -2.44; P<0.0001), better respiratory system compliance on day 3 (202 patients; MD, 8.19; 95% CI, 0.84-15.54; P=0.03), arterial partial pressure of oxygen/fraction of inspired oxygen (PaO2/FiO2) on day 3 (294 patients; MD, 44.40; 95% CI, 16.05-72.76; P=0.002), and higher mean arterial pressure (MAP) on day 3 (285 patients; MD, 4.18; 95% CI, 3.10-5.25; P<0.00001). There was no statistical difference in the incidence of pneumothorax (170 patients; OR, 0.40; 95% CI, 0.12-1.34; P=0.14).

Conclusions

The meta-analysis showed that APRV could reduce hospital mortality, duration of ventilation and ICU stay, improve lung compliance, oxygenation index, and MAP compared with LTVV for patients with ARDS. We found APRV to be a safe and effective ventilation mode for patients with ARDS.

HMGB1 and inflammatory cytokines in experimental acute lung injury induced in rabbits

ABSTRACT The aim of this work was to measure HMGB1, TNF-alpha, and IL-8 in bronchoalveolar lavage (BAL), serum and TLR2 and TLR4mRNA expression in lung tissue of rabbits with two grades of acute lung injury (ALI). The animals were randomly assigned to groups with severe (S) and mild/moderate (MM) ALI, induced with warm saline, and a control group. HMGB1, TNF-alpha, IL-8, TLR2mRNA and TLR4mRNA were measured after ALI induction. The results showed increased levels of IL-8, TNF-alpha, HMGB1 and TLR4mRNA in the ALI groups. HMGB1, IL-8 and TNF-alpha concentrations in BAL were higher in S compared MM. Increased TLR4mRNA was observed in S and MM versus control. The results suggest an early participation of HMGB1 in ALI together with IL-8 and TNF-alpha and association with severity. TLR4 has early expression and role in ALI pathophysiology but is not associated with severity.

The safety and efficacy of airway pressure release ventilation in acute respiratory distress syndrome patients: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

The acute respiratory distress syndrome (ARDS) is a critical illness with high mortality and a worse prognosis. Mechanical ventilation (MV) is currently considered to be one of the most effective methods of treating ARDS. In this meta-analysis, we discussed the efficacy of airway pressure release ventilation (APRV) in treating ARDS.

METHODS

Following the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA), Ovid Medline, Embase, and PubMed were systematically searched with the keywords of "ARDS" and "APRV". The studies containing the treatment of APRV in ARDS were included. According to the MV protocol used in the studies, the comparison was undertaken between the APRV group vs low tidal volume (LTV) group and synchronized intermittent mandatory ventilation (SIMV) group. The relative risk (RR) and the standard mean difference with 95% confidence intervals (CI) were used for the comparison between groups.

RESULTS

Fourteen studies with 2096 patients were included in the meta-analysis. The average increasing rate of PaO2/FiO2 was 75.4% in the APRV group vs 44.1% in the non-APRV group. No significant differences were found in mortality and duration of ICU stay between APRV vs LTV (P = .073 and P = .404) and APRV vs SIMV (P = .370 and P = .894).

CONCLUSION

The APRV protocol would have a higher increase in the PaO2/FiO2 ratio, which was a safe protocol with a compatible effect comparing to LTV and SIMV.

Experimental study of airway pressure release ventilation in the treatment of acute respiratory distress syndrome

Airway pressure release ventilation (APRV) is a ventilator mode which has demonstrated potential benefits in acute respiratory distress syndrome (ARDS) patients. We therefore sought to compare relevant pulmonary data and safety outcomes of this mode to the conventional ventilation and sustained inflation. Canines admitted after intravenous injection of oleic acid requiring mechanical ventilation were randomly divided into 3 groups (n=6), namely conventional ventilation group, low tidal volume ventilation with recruitment group (LTV+SI) and APRV group. The changes of oxygenation, ventilation, airway pressure, inflammatory reaction and hemodynamics at the basic state were observed at 0, 1, 2 and 4 h during the experiment. The levels of PaO₂/FiO₂ in APRV group were higher than LTV+SI group at 2 and 4 h (P<0.05). In APRV group, the PCO₂ levels at 1, 2 and 4 h is much lower than LTV+SI group (P<0.05). Outcome variables showed no differences between APRV, LVT+SI and conventional mechanical ventilation for plateau airway pressure (24±1 vs. 29±3 vs. 25±4), mean arterial pressure (92.9±16.5 vs. 85.8±21.4 vs. 88.7±24.4), cardiac index (4.3±1.7 vs. 3.5±1.9 vs. 3.4±2.1), ERO₂ (13.4±10.3 vs. 16.1±6.8 vs. 17.6±9.1), lac (2.5±1.7 vs. 3.1±1.6 vs. 3.9±1.9), tumor necrosis factor (TNF)-α (132±11 vs. 140±6 vs. 195±13) and matrix metalloproteinase (MMP)-9. For canines sustaining acute respiratory distress syndrome requiring mechanical ventilation, APRV can significantly improve oxygenation and keep hemodynamic stability compared with LTV+SI. The results of TNF-α and MMP-9 suggest that APRV could be as protective for ARDS as LTV with recruitment group.

The 30-year evolution of airway pressure release ventilation (APRV)

Airway pressure release ventilation (APRV) was first described in 1987 and defined as continuous positive airway pressure (CPAP) with a brief release while allowing the patient to spontaneously breathe throughout the respiratory cycle. The current understanding of the optimal strategy to minimize ventilator-induced lung injury is to "open the lung and keep it open". APRV should be ideal for this strategy with the prolonged CPAP duration recruiting the lung and the minimal release duration preventing lung collapse. However, APRV is inconsistently defined with significant variation in the settings used in experimental studies and in clinical practice. The goal of this review was to analyze the published literature and determine APRV efficacy as a lung-protective strategy. We reviewed all original articles in which the authors stated that APRV was used. The primary analysis was to correlate APRV settings with physiologic and clinical outcomes. Results showed that there was tremendous variation in settings that were all defined as APRV, particularly CPAP and release phase duration and the parameters used to guide these settings. Thus, it was impossible to assess efficacy of a single strategy since almost none of the APRV settings were identical. Therefore, we divided all APRV studies divided into two basic categories: (1) fixed-setting APRV (F-APRV) in which the release phase is set and left constant; and (2) personalized-APRV (P-APRV) in which the release phase is set based on changes in lung mechanics using the slope of the expiratory flow curve. Results showed that in no study was there a statistically significant worse outcome with APRV, regardless of the settings (F-ARPV or P-APRV). Multiple studies demonstrated that P-APRV stabilizes alveoli and reduces the incidence of acute respiratory distress syndrome (ARDS) in clinically relevant animal models and in trauma patients. In conclusion, over the 30 years since the mode's inception there have been no strict criteria in defining a mechanical breath as being APRV. P-APRV has shown great promise as a highly lung-protective ventilation strategy.

Airway pressure release ventilation: improving oxygenation: indications, rationale, and adverse events associated with airway pressure release ventilation in patients with acute respiratory distress syndrome for advance practice nurses

Airway pressure release ventilation (APRV) is a mode of ventilation that has been around since the 1980s and was originally viewed as a type of continuous positive pressure mode of ventilation. Conceptually, APRV can be thought of as a type of inverse-ratio, pressure-controlled, intermittent mandatory ventilation during which the maintenance of spontaneous breathing and prolonged application of high mean airway pressure contribute to the clinical benefits. The aim of this review article was to familiarize the bedside clinician working in the intensive care unit with the theory and rationale behind this mode of ventilation. The potential advantages and disadvantages of APRV will also be discussed to empower the advance practice clinician and bedside nurse to advocate for their patient diagnosed with the often-high mortality disease of acute respiratory distress syndrome.

Inhaled aerosolized insulin ameliorates hyperglycemia-induced inflammatory responses in the lungs in an experimental model of acute lung injury

Introduction

Previous studies have shown that patients with diabetes mellitus appear to have a lower prevalence of acute lung injury. We assumed that insulin prescribed to patients with diabetes has an anti-inflammatory property and pulmonary administration of insulin might exert beneficial effects much more than intravenous administration.

Methods

Twenty-eight mechanically ventilated rabbits underwent lung injury by saline lavage, and then the animals were allocated into a normoglycemia group (NG), a hyperglycemia group (HG), an HG treated with intravenous insulin (HG-VI) group or an HG treated with aerosolized insulin (HG-AI) group with continuous infusion of different fluid solutions and treatments: normal saline, 50% glucose, 50% glucose with intravenous insulin, or 50% glucose with inhaled aerosolized insulin, respectively. After four hours of treatment, the lungs and heart were excised en bloc, and then high-mobility group B1 concentration in bronchoalveolar lavage fluid, interleukin-8 and toll-like receptor 4 mRNA expression in bronchoalveolar lavage fluid cells, and lung myeloperoxidase activity were measured.

Results

Treatment with both aerosolized insulin and intravenous insulin attenuated toll-like receptor 4 mRNA expressions in the bronchoalveolar lavage fluid cells. Interleukin-8 and toll-like receptor 4 mRNA expression was significantly lower in the HG-AI group than in the HG-IV group. The lung myeloperoxidase activity in the normal healthy group showed significantly lower levels compared to the NG group but not different compared to those of the HG, HG-VI and HG-AI groups.

Conclusions

The results suggest that insulin attenuates inflammatory responses in the lungs augmented by hyperglycemia in acute lung injury and the insulin's efficacy may be better when administered by aerosol.

The effect of APRV ventilation on ICP and cerebral hemodynamics

BACKGROUND

Airway pressure release ventilation (APRV) is an alternative approach to the low-tidal volume "open-lung" ventilation strategy. APRV is associated with a higher mean airway pressure than conventional ventilation and has therefore not been evaluated in patients with acute neurological injuries.

METHODS

Case report.

RESULTS

We report a patient with severe progressive hypoxemia following a subarachnoid hemorrhage who was converted from pressure-controlled mechanical ventilation to APRV. This change in ventilatory mode was associated with a significant improvement in oxygenation and alveolar ventilation with an associated increase in cerebral blood flow and a negligible increase in intracranial pressure.

CONCLUSION

APRV may safely be applied to neurocritically ill patients, and that this mode of ventilation may increase cerebral blood flow without increasing intracranial pressure.