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Evaluation of Recruitment Maneuver Effects

A single standard, repeatable and reliable mean to evaluate the effectiveness of a recruitment maneuver, is not universally accepted: it is still debated which is the best method to assess the efficacy of RMs. The assessment should be based on a thoughtful clinical judgment, relying on information derived from different monitoring techniques, and anatomical and functional evaluation should be integrated. The physiological parameters most commonly assessed include the PaO2/FiO2 ratio, pulmonary compliance, and the pressure-volume (P-V) curve. Imaging techniques can be extremely helpful and comprise computed tomography (CT), lung ultrasonography (LUS), and electric impedance tomography (EIT).

Blood Gas Analysis and PaO2/FiO2 Ratio

In the clinical practice, one of the most evaluated clinical outcome is the PaO2/FiO2 ratio, for its low cost, widespread availability, and ease of interpretation. Furthermore, it is intrinsically associated with the severity of ARDS [39] and is rapidly influenced by an effective RM. Transcutaneous SpO2 is a rough estimate of PaO2 and can be used to monitor in real time the modifications of gas exchange, and to verify that during the apnea phase of the RM, the oxygenation remains within a safety range. After the RM, a decrease of PaCO2 is usually observed consensually to the increase of the SpO2 and PaO2/FiO2 ratio, adding completeness to the overall evaluation. The major limit of blood gas analysis parameters is that they are strongly influenced by other variables. Before a RM, the baseline intrinsic recruitability of the lung and gas exchange are both related to the severity of ARDS [13, 40]: the PaO2/FiO2 ratio could show greater improvement in the most severe ARDS forms, compared to the mild ones [40]. Moreover, a transient improvement of gas exchange does not necessarily translate in improved outcome, as it might be achieved at the price of a higher risk for barotrauma and VILI. The ventilatory settings, including PEEP level and the cardiac output, can influence the PaO2/FiO2 ratio, leading to a misinterpretation of the evaluation of RMs [20]. Therefore, the PaO2/FiO2 ratio assessed by blood gas analysis and the SpO2 represent the two most widely available parameters used to evaluate RMs but, assessing the efficacy of the RM only on oxygenation, does not give a complete description of the recruitment and should be a part of an integrated evaluation.

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