Treatment with Oscillation and Open Lung Strategy ) are welcome : Timely intervention , combining therapies , strict algorithms

Recruitment of the lung is a hot topic in the treatment of patients with acute lung injury or acute respiratory distress syndrome (ARDS). We have learned from clinical and physiologic investigations that the injured lung is characterized by a reduction in volume as well as a heterogeneous distribution of aeration favoring overdistention of healthy alveoli (1). Furthermore, we must accept the fact that both endexpiratory cycling collapse and end-inspiratory overdistension promote ventilatorinduced lung injury. As a result, various maneuvers for lung recruitment and a “lung-protective strategy” are designed and presented in numerous studies. Currently, the latter has been recommended definitely (2), whereas the concept of lung recruitment has produced no proven evidence or knowledge of (deleterious) side effects. High-frequency oscillatory ventilation (HFOV) is defined as the application of extremely low tidal volume combined with a relatively high mean airway pressure using an oscillating piston pump vibrating gas at high frequency into and out of the patient. This is an old technique experiencing a renaissance today, and there are several interesting investigations using HFOV as a rescue strategy in severe ARDS (3, 4). Although the results of clinical investigations using HFOV are often impressive, the mortality rate in patients treated with HFOV remains as high as that in patients treated with conventional ventilation, and thus the “philosopher’s stone” still remains elusive. In this issue of Critical Care Medicine, Dr. Ferguson and coworkers (5) present a pilot study with an innovative design: 25 patients suffering from early ARDS were switched from conventional ventilation to HFOV (frequency 300/min 5 Hz) with an initial cycle of recruitment maneuvers (inspiratory pressure 40 cm H2O for 40 secs) followed by a stepwise decremental titration of FIO2 and mean airway pressure. Following a strict algorithm, HFOV was adjusted to oxygenation improvement and finally discontinued when patients reached a certain level. Recruitment maneuvers were performed after disconnection of the respirator for suctioning or bronchoscopy and if FIO2 had to be set 0.4. In the case of renewed deterioration during conventional ventilation, patients were put back on HFOV and then slowly weaned from it again. As a result, the PaO2/FIO2 ratio improved rapidly and significantly, and after a mean of 12 hrs of HFOV, FIO2 was markedly reduced. An average of seven recruitment maneuvers were performed per patient with a low incidence of side effects (3.3%). The present pilot study deserves attention for several reasons. First, the intervention started in a timely manner. The average duration of ventilation before enrollment was 13 hrs. In a recent study (4), mortality was found to be significantly increased in patients ventilated 3 days before HFOV (64%) in comparison with a shorter ventilation time (20%). The results of other case series (6, 7) are consistent with these findings, which leads to the conclusion that early initiation of HFOV in patients with acute lung injury at risk for additional ventilator-induced lung injury is advantageous. On the other hand, whether HFOV presents “the best lung protective ventilatory approach for ARDS” (8) has yet to be conclusively confirmed, even today. Second, the combination of therapies is innovative. Severe acute respiratory distress is a complex syndrome with multifactorial pathogenesis and a multilevel cascade of injurious pathways (9). Apart from a lung-protective ventilation concept, recent efforts to demonstrate a reduction in mortality by one single method have failed: Neither prone position (10), nor application of a drug (prostaglandin, early high-dose steroids, surfactant (11)), nor high levels of positive end-expiratory pressure (12) per se were found to decrease mortality. For recruitment maneuvers, although theoretically attractive, the database is poor and many more questions arise than answers (13). Therefore, we must pursue an innovative approach, and a well-indicated combination of strategies might be a step forward. Third, probably the most powerful aspect of the present study is the creation of a strict algorithm and explicit instructions. Management protocols and algorithms are moving into critical care medicine and will help the intensivist to use costly and aggressive therapies in a more careful and time-limited manner: For example, HFOV was stopped when defined conditions of improvement were reached. In this way a “tachyphylaxis” can be avoided and resources saved. Nevertheless, some questions remain regarding the results of the investigation by Dr. Ferguson and colleagues (5): First, most patients suffered from pulmonary ARDS (pneumonia, aspiration of gastric contents, etc.), and recent studies indicate that pulmonary and extrapulmonary ARDS (as a result of pancreatitis, peritonitis, burn, etc.) may be different pathophysiologic entities requiring different strategies (14). Is HFOV only effective in pulmonary ARDS? Second, HFOV potentially may induce barotrauma, but the incidence in the present database is low. In a Canadian retrospective investigation analyzing 156 ARDS-patients treated with HFOV (15), pneumothorax occurred in 21.8%. Can we expect the same incidence of barotrauma using the present strategy? Third, the main physiologic effect of HFOV is the application of a relatively *See also p. 479.