Ventilation Strategies: Recruitment Maneuvers

Lorenzo Ball and Paolo Pelosi

Introduction

Acute respiratory distress syndrome (ARDS) is characterized by refractory hypoxemia, reduced lung compliance [1], and increased lung inhomogeneity [2]. After the landmark studies carried out in the early 2000s, the so-called protective ventilation, comprising a low tidal volume (V_T) titrated to 6 mL/kg of predicted body weight and positive end-expiratory pressure (PEEP), has gained wide acceptance in the management of patients with ARDS, as it showed an improvement in mortality [3]. However, low tidal volumes are associated with cyclic opening and closing of collapsed lung regions, in a potentially harmful mechanism referred to as atelectrauma

[4]. The use of PEEP is currently recommended to prevent this phenomenon and maintain patency of alveoli, but the use of high pressures can be associated with barotrauma. Both atelectrauma and volutrauma are putative mechanisms of ventilator-induced lung injury (VILI) [5]; therefore the clinician should balance between these two conditions while ensuring an acceptable gas exchange to the patient [6].

Recruitment maneuvers (RMs) are transient procedures that increase the transpulmonary pressure, with the aim of obtaining a mechanical reopening of collapsed lung units [7]. The first assessment of these techniques dates back to two decades ago, when the concept of lung recruitment has been studied. There are several arguments that provide a pathophysiological rationale supporting the implementation of RMs as part of the ventilatory setting in ARDS, as sedation, neuromuscular blockade, and the absence of sigh reflex facilitate the alveolar collapse. RMs have been implemented in protocols for ventilation in ARDS and constitute a common but debated part of the management of these patients. In a recent meta-analysis, the

L. Ball, MD • P. Pelosi, MD, FERS (*)

IRCCS AOU San Martino-IST, Department of Surgical Sciences and Integrated Diagnostics, University of Genoa, Largo Rosanna Benzi 8, 16131 Genoa, Italy e-mail: This email address is being protected from spam bots, you need Javascript enabled to view it ; This email address is being protected from spam bots, you need Javascript enabled to view it

contribution to mortality reduction in moderate/severe ARDS of RMs was estimated around 6% [8]. This improvement in outcome is relatively small, contributing to a high degree of variability in the techniques, timing, and protocols implementing RMs in the clinical and research practice.

In fact, there are several unclear aspects that hinder a widely accepted approach to RMs. The techniques and timings are still under investigation, and it is not clear which subgroups of patients are more likely to take benefit from RMs. Already opened alveoli are at risk of overinflation, and the result of a RM in some case only consists in the achievement of an anatomical rather than functional recruitment, without improvement of gas exchange and potentially worsening hypoxia in the longer term [7]. Nonetheless, safety concerns must be taken into account, as the airway pressure increase can lead to a hemodynamic impairment and hypotension, due to an increased workload for right ventricle, left ventricle underfilling, or worsening of a pre-existing diastolic dysfunction [9, 10]. In addition to this, the optimal ventilatory settings and PEEP titration after RMs are still controversial. For all these reasons, guidelines for the use of RMs are still lacking.

The aim of this chapter is to illustrate the physiologic rationale and mechanism of RMs, the different techniques to perform RMs, their clinical effects and safety, as well as clinical tools to assess the efficacy of RMs.