Lung recruitment tools

Abstract

Increased understanding of the mechanical and physical properties of the lungs and gas flow has allowed considerable advances in the field of mechanical ventilation and lung protection. Maintaining laminar flow, ‘the physiological flow’, and preventing turbulent flow during mechanical ventilation prevent atelectasis and help keep the lung open. This protects the lung from ventilator-induced lung injury (VILI). Analysis of the pressure–volume ( P/V ) curve of the respiratory system is the basis for maintaining lung protection. Lung volumes affect the dynamics of the lung and usually have a significant effect on the flow, airway resistance, lung compliance, ventilation–perfusion ratio and recruitment. Functional residual capacity (FRC) has a significant role in maintaining the structure and function of the lung, and the relationship between the FRC and closing volume (CV) is more important than considering the FRC and CV alone. Positive end-expiratory pressure (PEEP), by preventing and/or recruiting atelectatic lung regions, can maintain the lung structure and protects against VILI. The optimal PEEP, still controversial, can be determined using the following methods: (1) a decremental PEEP trial after recruitment manoeuvres with P aO2 and lung compliance guidance; (2) (quasi) static approaches or dynamic approaches based on the P/V curve; (3) based on the F iO2/PEEP table with oxygenation guidance; (4) PEEP guided by oesophageal pressure; (5) based on a computerized tomography scan or chest radiograph; and (6) using electrical impedance tomography. Recruitment manoeuvres can help to recruit atelectatic lung regions and can be accomplished by raising the transpulmonary pressure periodically and briefly to a higher level than that achieved during tidal ventilation. Clinical and experimental studies has been conducted to identify the durability of the beneficial effects of recruitment manoeuvres, when and how to perform them, early or late in the course of acute respiratory distress syndrome and with high or low PEEP, and which categories of patients will benefit from them.