To the Editor:
With interest we read the “Clinical Concepts and Commentary” by Goldenberg et al.1 about lung-protective ventilation in the operating room. We congratulate the authors for their word of caution and farsightedness. We fully agree that low tidal volumes (VT) are an essential part of lung-protective ventilation in patients with acute respiratory syndrome, but we would like to point out that even VT of 6 ml/kg ideal body weight have been shown to be too high in severe cases.2 This emphasizes that the concept of protective ventilation is far more complex than often suggested when referred to protective ventilation as using low VT.
This specifically applies to several publications about intraoperative ventilation in patients with healthy lungs for which the titles often suggest that low VT is the main element of protective ventilation.3 However, only very few trials, including our own study,4 restricted their intervention to this factor. Goldenberg et al. acknowledged our work but incorrectly stated that “no recruitment maneuvers” were performed. All patients received a lung expansion maneuver consisting of three manual bag ventilations with a maximum pressure of 40 cm H2O shortly before extubation.4 Despite this effort, significantly more patients ventilated with low VT had atelectasis directly after surgery. Thus, a single recruitment maneuver with manual bag inflations before extubation is not sufficient to counterbalance the effects of low VT when a low positive-end expiratory pressure (PEEP) of 5 cm H2O is used. Therefore, we call into question the conclusion by Goldenberg et al. that “during anesthesia, protective ventilation is beneficial when both lower VT and a recruitment strategy are included, but not when lower VT used alone.” We would rather stress that neither the optimal combination of PEEP and VT nor the best recruitment strategy is known yet.
New insight into the role of PEEP and recruitment maneuvers comes from the results of the PROtective Ventilation using HIgh versus LOw positive end-expiratory pressure trial.5 In this study, 900 patients undergoing upper abdominal surgery were ventilated with 8 ml/kg ideal body weight and randomly assigned to PEEP of 12 cm H2O plus multiple recruitment maneuvers or PEEP of 2 cm H2O or less without recruitment maneuvers. There was no difference in postoperative pulmonary complications between the two groups, but in patients ventilated with high PEEP, intraoperative hypotension was a major problem. As a consequence, neither high PEEP nor regular recruitment maneuvers per se are lung protective with regard to postoperative pulmonary complications but cause clinically important adverse effects.
Goldenberg et al. summarize “that the ideal approach to intraoperative ventilation…remains unknown.” Taking into account that so many open questions remain, even without discussing the role of hypercapnia6 or inspiratory oxygen concentration,7 we believe that their conclusion cannot be overemphasized.
The authors declare no competing interests.