Data From Advanced Respiratory Monitoring During Alveolar Recruitment Maneuvers (ARM). A Prospective Observational Study

During general anaesthesia, ventilation disorders with atelectasis, derecruitment of posteroinferior zones and reduced functional residual capacity (FRC) occur in relation to the operative position, the effect of neuromuscular block and general anaesthesia. These conditions of poor pulmonary aeration favor postoperative respiratory complications and are responsible for excess mortality in the perioperative period.

Alveolar recruitment maneuvers (ARMs) are ventilatory strategies used during general anesthesia that aim to restore lung aeration with a Positive End Expiratory Pressure (PEEP) sufficient to keep the lungs open afterwards. These maneuvers can be performed in a variety of ways but generally involve gradually increasing the level of airway pressure, followed by a stepwise decrease to an end-expiratory pressure (PEEP) level decided by the practitioner based on monitoring data and considering the clinical outcome and hemodynamic tolerance of the maneuver.

Atelectasis essentially occurs when the pressure in the alveolus at the end of expiration is lower than the pressure that allows the alveolus to remain open (critical opening pressure). The principle is to transiently increase transpulmonary pressure (TTP) (the difference between airway pressure (Paw) and pleural pressure) above the critical opening pressure.

Maintaining alveolar end-expiratory pressure (PEEP) after the maneuver is essential to avoid de-recruitment. The concept of the alveolar recruitment maneuver is very popular in our specialty. The benefits and importance of this alveolar recruitment strategy were initially identified in intensive care patients. Particular attention is now being paid to lung-free patients in the operating theatre, especially those with obesity, during long prone surgeries and during laparoscopic abdominal surgery. Currently, the benefits of ARM are also being seen, with a reduced risk of serious pulmonary and extra-pulmonary complications in the first 7 days postoperatively for this type of patient.

Currently, these maneuvers are performed directly on ventilators that incorporate an automated, programmable procedure. The technique consists in gradually increasing inspiratory pressure to 40 cmH2O and PEEP to 20 cmH2O, the incremental phase. As soon as the maximum pressure level is reached, a progressive decrement phase follows. Three parameters need to be set: maximum inspiratory pressure, maximum PEEP and maneuver duration. The level of PEEP at which the alveoli theoretically remain open is determined by monitoring the patient's compliance and tidal volume. This pulmonary hyperinflation not only has a major impact on hemodynamics but also presents a risk of barotrauma. ARM is currently performed without transpulmonary pressure measurement and with this procedure.