Adaptive Support Ventilation Attenuates Ventilator Induced Lung Injury: Human and Animal Study

Managing the Chronically Ventilated Critically Ill Population

Advances in intensive care over the past few decades have significantly improved the chances of survival for patients with acute critical illness. However, this progress has also led to a growing population of patients who are dependent on intensive care therapies, including prolonged mechanical ventilation (PMV), after the initial acute period of critical illness. These patients are referred to as the "chronically critically ill" (CCI). CCI is a syndrome characterized by prolonged mechanical ventilation, myoneuropathies, neuroendocrine disorders, nutritional deficiencies, cognitive and psychiatric issues, and increased susceptibility to infections. It is associated with high morbidity and mortality as well as a significant increase in healthcare costs. In this article, we will review disease burden, outcomes, psychiatric effects, nutritional and ventilator weaning strategies as well as the role of palliative care for CCI with a specific focus on those requiring PMV.

The Evolution of Intermittent Mandatory Ventilation

Intermittent mandatory ventilation (IMV) is one kind of breath sequence used to classify a mode of ventilation. IMV is defined as the ability for spontaneous breaths (patient triggered and patient cycled) to exist between mandatory breaths (machine triggered or machine cycled). Over the course of more than a century, IMV has evolved into 4 distinct varieties, each with its own advantages and disadvantages in serving the goals of mechanical ventilation (ie, safety, comfort, and liberation). The purpose of this paper is to describe the evolution of IMV, review relevant supporting evidence, and discuss the rationales for each of the 4 varieties. Also included is a brief overview of the background information required for a proper perspective of the purpose and design of the innovations. Understanding these different forms of IMV is essential to recognizing the similarities and differences among many dozens of different modes of ventilation. This recognition is important for clinical application, education of caregivers, and research in mechanical ventilation.

Closed-loop ventilation

PURPOSE OF REVIEW

The last 25 years have seen considerable development in modes of closed-loop ventilation and there are now several of them commercially available. They not only offer potential benefits for the individual patient, but may also improve the organization within the intensive care unit (ICU). Clinicians are showing both greater interest and willingness to address the issues of a caregiver shortage and overload of bedside work in the ICU. This article reviews the clinical benefits of using closed-loop ventilation modes, with a focus on control of oxygenation, lung protection, and weaning.

RECENT FINDINGS

Closed-loop ventilation modes are able to maintain important physiological variables, such as oxygen saturation measured by pulse oximetry, tidal volume (VT), driving pressure (ΔP), and mechanical power (MP), within target ranges aimed at ensuring continuous lung protection. In addition, these modes adapt the ventilator support to the patient's needs, promoting diaphragm activity and preventing over-assistance. Some studies have shown the potential of these modes to reduce the duration of both weaning and mechanical ventilation.

SUMMARY

Recent studies have primarily demonstrated the safety, efficacy, and feasibility of using closed-loop ventilation modes in the ICU and postsurgery patients. Large, multicenter randomized controlled trials are needed to assess their impact on important short- and long-term clinical outcomes, the organization of the ICU, and cost-effectiveness.

Adaptive Support Ventilation and Lung-Protective Ventilation in ARDS

BACKGROUND

Adaptive support ventilation (ASV) is a partially closed-loop ventilation mode that adjusts tidal volume (V_T) and breathing frequency (f) to minimize mechanical work and driving pressure. ASV is routinely used but has not been widely studied in ARDS.

METHODS

The study was a crossover study with randomization to intervention comparing a pressure-regulated, volume-targeted ventilation mode (adaptive pressure ventilation [APV], standard of care at Beth Israel Deaconess Medical Center) set to V_T 6 mL/kg in comparison with ASV mode where V_T adjustment is automated. Subjects received standard of care (APV) or ASV and then crossed over to the alternate mode, maintaining consistent minute ventilation with 1-2 h in each mode. The primary outcome was V_T corrected for ideal body weight (IBW) before and after crossover. Secondary outcomes included driving pressure, mechanics, gas exchange, mechanical power, and other parameters measured after crossover and longitudinally.

RESULTS

Twenty subjects with ARDS were consented, with 17 randomized and completing the study (median P_aO2 /F_IO2 146.6 [128.3-204.8] mm Hg) and were mostly passive without spontaneous breathing. ASV mode produced marginally larger V_T corrected for IBW (6.3 [5.9-7.0] mL/kg IBW vs 6.04 [6.0-6.1] mL/kg IBW, P = .035). Frequency was lower with patients in ASV mode (25 [22-26] breaths/min vs 27 [22-30)] breaths/min, P = .01). In ASV, lower respiratory-system compliance correlated with smaller delivered V_T/IBW (R² = 0.4936, P = .002). Plateau (24.7 [22.6-27.6] cm H₂O vs 25.3 [23.5-26.8] cm H₂O, P = .14) and driving pressures (12.8 [9.0-15.8] cm H₂O vs 11.7 [10.7-15.1] cm H₂O, P = .29) were comparable between conventional ventilation and ASV. No adverse events were noted in either ASV or conventional group related to mode of ventilation.

CONCLUSIONS

ASV targeted similar settings as standard of care consistent with lung-protective ventilation strategies in mostly passive subjects with ARDS. ASV delivered V_T based upon respiratory mechanics, with lower V_T and mechanical power in subjects with stiffer lungs.

Efficacy of adaptive ventilation support combined with lung recruitment maneuvering for acute respiratory distress syndrome

OBJECTIVE

This study was designed to evaluate the efficacy of adaptive support ventilation (ASV) and lung recruitment maneuvering (LRM) on the hemodynamics and respiratory mechanics of patients with acute respiratory distress syndrome (ARDS).

METHODS

A total of 100 patients with ARDS admitted to the intensive care unit (ICU) of our hospital from July 2016 to October 2019 were randomly divided into the control group (n=50) receiving synchronized intermittent mandatory ventilation (SIMV) and the study group (n=50) receiving ASV + LRM. The hemodynamics, respiratory mechanics, oxygen metabolism parameters, pulmonary index of microcirculatory resistance and prognosis were compared between the two groups.

RESULTS

No significant difference was observed between the two groups in terms of baseline data (P > 0.05). Positive end-expiratory pressure (PEEP), mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), systemic vascular resistance index (SVRI), pulmonary arterial pressure (PAP), and cardiac output index (CI) were not significantly different between the two groups (P > 0.05). PEEP, peak inspiratory pressure (PIP), pulmonary vascular resistance index (PVRI), and extravascular lung water (EVLW) were lower, and arterial oxygen pressure (PaO₂), global oxygen delivery (DO₂), oxygen-uptake (VO₂), and dynamic compliance (Cdyn) were higher in the study group than in the control group (P < 0.05). Time to withdrawal, APACHE II score, and length of stay in ICU were lower in the study group than in the control group (P < 0.05).

CONCLUSION

ASV + LRM can improve respiratory mechanics, oxygen metabolism, reduce microcirculatory resistance, shorten ICU stay and alleviate the conditions of ARDS patients, but has no significant effect on hemodynamics.

Mechanisms of Mechanical Force Induced Pulmonary Vascular Endothelial Hyperpermeability

Mechanical ventilation is a supportive therapy for patients with acute respiratory distress syndrome (ARDS). However, it also inevitably produces or aggravates the original lung injury with pathophysiological changes of pulmonary edema caused by increased permeability of alveolar capillaries which composed of microvascular endothelium, alveolar epithelium, and basement membrane. Vascular endothelium forms a semi-selective barrier to regulate body fluid balance. Mechanical ventilation in critically ill patients produces a mechanical force on lung vascular endothelium when the endothelial barrier was destructed. This review aims to provide a comprehensive overview of molecular and signaling mechanisms underlying the endothelial barrier permeability in ventilator-induced lung jury (VILI).

Adaptive support ventilation attenuates postpneumonectomy acute lung injury in a porcine model

OBJECTIVES

An optimal ventilation strategy that causes as little mechanical stress and inflammation as possible is critical for patients undergoing pneumonectomy. The aim of this study was to determine whether adaptive support ventilation (ASV) can provide protective ventilation to the remaining lung after pneumonectomy with minimal mechanical stress and less inflammation than volume-control ventilation (VCV).

METHODS

In this study, 15 pigs were randomly allocated to 3 groups (n = 5 for each group): the control group, the VCV group and the ASV group. After left pneumonectomy, the VCV group was treated with the volume-control set to 20 ml/kg, and the ASV group with the mode set to achieve 60% of the minute ventilation of 2 lungs.

RESULTS

The ASV group had lower alveolar strain than the VCV group. The ASV group exhibited less lung injury and greater alveolar fluid clearance than the VCV group (13.3% vs -17.8%; P ≤ 0.018). Ventilator-induced lung injury was associated with changes in the cytokine levels in the exhaled breath condensate, differential changes in plasma and changes in the cytokines in the bronchoalveolar lavage fluid. Expression of 3 microRNAs (miR449b-3p, P ≤ 0.001; miR451-5p, P = 0.027; and miR144-5p, P = 0.008) was increased in the VCV group compared with the ASV group.

CONCLUSIONS

The ASV mode was capable of supporting rapid, shallow breathing patterns to exert lung-protective effects in a porcine postpneumonectomy model. Further investigation of microRNAs as biomarkers of ventilator-induced lung injury is warranted.