Increased extravascular lung water reduces the efficacy of alveolar recruitment maneuver in acute respiratory distress syndrome

The Nature of Recruitment and De-Recruitment and Its Implications for Management of ARDS

Recruitment maneuvers in ARDS are used to improve oxygenation and lung mechanics by applying high airway pressures to reopen collapsed or obstructed peripheral airways and alveoli. In the early 1990s, recruitment maneuvers became a central feature of a variant form of lung-protective ventilation known as open-lung ventilation. This strategy is based on the belief that repetitive opening and closing of distal airspaces induces shear injury and therefore contributes both to ventilator-induced lung injury and ARDS-associated mortality. However, the largest multi-center randomized controlled trial of open-lung ventilation in moderate to severe ARDS reported that recruitment maneuver plateau pressures of 50-60 cm H₂O were associated with significantly higher mortality compared to traditional lung-protective ventilation. Despite being based on well conducted preclinical and clinical recruitment maneuver studies, the higher mortality associated with the open-lung ventilation strategy requires re-examining the assumptions and conclusions drawn from those previous studies. This narrative review examines the evidence used to design recruitment maneuver strategies. We also review the radiologic, rheologic, and histopathologic evidence regarding the nature of lung injury and the phenomena of recruitment and de-recruitment as it informs our perceptions of recruitment potential in ARDS. Major lung-protective ventilation clinical trial data and other clinical data are also examined to assess the practical necessity of recruitment maneuvers in ARDS and whether a subset of cases might benefit from pursuing recruitment maneuver therapy. Finally, a less a radical approach to recruitment maneuvers is offered that might achieve the goals of recruitment maneuvers with less risk of harm.

Ventilator-associated lung injury in the intensive care unit and operating room – what's new?

The prophylaxis of ventilator-associated lung injury (VALI) and postoperative pulmonary complications (PPC) is of utmost importance to reduce complications both in the perioperative period of major surgery and in the intensive care unit (ICU).

Protective approach to mechanical ventilation comprises a wide range of measures reducing the damage of the lung tissue associated with the stress and strain phenomena. The implementation of the strategy of high positive end-expiratory pressure (PEEP) in combination with alveolar recruitment maneuver has numerous limitations and requires further personalized approaches.

When lung injury is self-induced by a patient, it becomes an important contributor to VALI and should be timely diagnosed and prevented both before initiation of mechanical support and during the restoration of spontaneous breathing. This review highlights the key mechanisms of VALI and current understanding of protective ventilation. The concept of damaging energy as well as approaches to the personalized optimization of respiratory settings are discussed in detail. Particular attention is paid to the prognostication of the risk factors of VALI and PPC.

The Contribution of Surface Tension-Dependent Alveolar Septal Stress Concentrations to Ventilation-Induced Lung Injury in the Acute Respiratory Distress Syndrome

In the acute respiratory distress syndrome (ARDS), surface tension, T, is likely elevated. And mechanical ventilation of ARDS patients causes ventilation-induced lung injury (VILI), which is believed to be proportional to T. However, the mechanisms through which elevated T may contribute to VILI have been under-studied. This conceptual analysis considers experimental and theoretical evidence for static and dynamic mechanical mechanisms, at the alveolar scale, through which elevated T exacerbates VILI; potential causes of elevated T in ARDS; and T-dependent means of reducing VILI. In the last section, possible means of reducing T and improving the efficacy of recruitment maneuvers during mechanical ventilation of ARDS patients are discussed.

Protective ventilation from ICU to operating room: state of art and new horizons

The prevention of ventilator-associated lung injury (VALI) and postoperative pulmonary complications (PPC) is of paramount importance for improving outcomes both in the operating room and in the intensive care unit (ICU). Protective respiratory support includes a wide spectrum of interventions to decrease pulmonary stress-strain injuries. The motto 'low tidal volume for all' should become routine, both during major surgery and in the ICU, while application of a high positive end-expiratory pressure (PEEP) strategy and of alveolar recruitment maneuvers requires a personalized approach and requires further investigation. Patient self-inflicted lung injury is an important type of VALI, which should be diagnosed and mitigated at the early stage, during restoration of spontaneous breathing. This narrative review highlights the strategies used for protective positive pressure ventilation. The emerging concepts of damaging energy and power, as well as pathways to personalization of the respiratory settings, are discussed in detail. In the future, individualized approaches to protective ventilation may involve multiple respiratory settings extending beyond low tidal volume and PEEP, implemented in parallel with quantifying the risk of VALI and PPC.

Alveolar recruitment maneuver attenuates extravascular lung water in acute respiratory distress syndrome

BACKGROUND

The alveolar recruitment maneuver (RM) has been reported to improve oxygenation in acute respiratory distress syndrome (ARDS) and may be related to reduced extravascular lung water (EVLW) in animals. This study was designed to investigate the effects of RM on EVLW in patients with ARDS.

METHODS

An open label, prospective, randomized controlled trial including patients with ARDS was conducted in hospitals in North Taiwan between 2010 and 2016. The patients were divided into 2 groups (with and without RM). The primary endpoint was the comparison of the EVLW index between the 2 groups.

RESULTS

Twenty-four patients with ARDS on mechanical ventilator support were randomized to receive ventilator treatment with RM (RM group, n = 12) or without RM (non-RM group, n = 12). Baseline demographic characteristics were similar between the 2 groups. After recruitment, the day 3 extravascular lung water index (EVLWI) (25.3 ± 9.3 vs 15.5 ± 7.3 mL/kg, P = .008) and the arterial oxygen tension/fractional inspired oxygen ratio (PaO2/FiO2) (132.3 ± 43.5 vs 185.6 ± 38.8 mL/kg, P = .003) both improved over that of day 1. However, both EVLWI and PaO2/FiO2 did not significantly change from day 1 to 3 in the non-RM group.

CONCLUSION

RM is a feasible method for improving oxygenation and the EVLW index in patients with ARDS, as well as for decreasing ventilator days and intensive care unit stay duration.

Postperfusion lung syndrome: Respiratory mechanics, respiratory indices and biomarkers

Postperfusion lung syndrome is rare but lethal. Secondary inflammatory response was the popularly accepted theory for the underlying etiology. Respiratory index (RI) and arterial oxygen tension/fractional inspired oxygen can be reliable indices for the diagnosis of this syndrome as X-ray appearance is always insignificant at the early stage of the onset. Evaluations of extravascular lung water content and pulmonary compliance are also helpful in the definite diagnosis. Multiorgan failure and triple acid-base disturbances that might develop secondary to postperfusion lung syndrome are responsible for the poor prognosis and increased mortality rather than postperfusion lung syndrome itself. Mechanical ventilation with low tidal volume (TV) and proper positive end-expiratory pressure can be an effective treatment strategy. Use of ulinastatin and propofol may benefit the patients through different mechanisms.

Recruitment manoeuvres in acute respiratory distress syndrome: Little evidence for routine use

The use of alveolar recruitment manoeuvres for the treatment of acute respiratory distress syndrome is a topic of uncertainty in current critical care practice. Acute respiratory distress syndrome leads to inflammatory atelectasis, which challenges the gas exchange properties of the lung. Recruitment of atelectatic lung tissue requires elevation of transpulmonary pressure. Transpulmonary pressure can be suppressed at a given airway pressure when pleural pressures are elevated. The present review discusses recruitment of lung tissue in detail, highlighting the key research in the field. Differing techniques for recruiting lung tissue, as well as various outcome measures to determine efficacy, are analyzed and critiqued. The commonly used sustained inflation manoeuvre is perhaps regarded as the only strategy to recruit the lung, explaining its prevalence. Staircase recruitment with positive end-expiratory pressure titration is shown to be an equally - if not more - effective therapy that devotes attention to the maintenance of lung recruitment.