![]() ![]() Might these low-volumes lead to atelectrauma and worsening VILI in a certain subset of patients? Is there a way to quantify the degree of de-recruitment? To better estimate the size of the baby lung?Īnd so a division was born. Anatomic studies have demonstrated that ideal body weight is a poor predictor of of lung volumes in patients with ARDS (8). It is unclear if this empirically low dose is appropriate for everyone. However, the ARMA cohort provides little guidance on whether such an empiric strategy is superior to a more individualized approach. Essentially, the ARMA trial demonstrated that an empiric low-tidal volume strategy is superior to an empiric high-tidal volume strategy. In the two trials that did identify a benefit of low-tidal volume ventilation, the ARMA cohort and the Amato et al cohort, both ventilated their control group at concerningly high volumes (12cc/kg) (7). Conversely, in the patients with high pre-randomization compliance, those randomized to the low tidal-volume group demonstrated an increased mortality.Īdditionally, the three trials that failed to find a benefit of low-tidal volume ventilation employed a control group in which the mean tidal volume was approximately 10 cc/kg of ideal body weight, very similar to the pre-randomization tidal volumes in the ARMA trial. In the patients with low-pulmonary compliance, patients randomized to the low-tidal volume arm demonstrated a significant improvement in mortality when compared to those in the traditional tidal volume group. In this document, the authors examined the patients in the ARMA cohort based off the individual patient’s lung compliance at the time of randomization. ![]() Even more interesting was a subgroup analysis of the ARMA data performed by Deans et al in Critical Care Medicine in 2005 (6). In the group of patients who met inclusion criteria but were not enrolled in the ARMA cohort because of technical reasons, the overall mortality was 31.7%, almost identical to the 31% reported in the low-tidal volume group (6). The median prescribed tidal volume just prior to randomization was 10cc/kg, leading to an increase in tidal volumes in the majority of patients randomized to the traditional ventilation group. In fact, the traditional ventilator strategy at the time ARMA was enrolling was to vary tidal volumes based on the individual lung compliance of the patient. The control arm, termed the traditional ventilation group, was exposed to extraordinarily high tidal volumes. The authors found an 8.8% increase in mortality at 180-days following intubation in patients randomized to the traditional ventilation group (31% vs 38.8%).Īnd yet despite these impressive results, it is important to realize what the ARMA trial truly demonstrated. The benefits demonstrated in the ARMA trial were impressive. The trial was stopped early after enrolling only 861 patients when an interim analysis demonstrated a significant improvement in mortality in the patients randomized to the low-tidal volume group. The low-tidal volume group prescribed 4-6 cc kg of ideal body weight with a maximum plateau pressure of 30 mmHg. ![]() The first, which the called traditional, prescribed 12cc/kg of tidal volume, with a maximum plateau pressure of 50 mmHg. This trial, performed by the ARDSNET research group, randomized patients admitted to 10 centers with ARDS (defined as P/F ratio of less than 300 and bilateral pulmonary infiltrates of non-cardiac origin) to two ventilator strategies. It was not until the ARMA trial, published in the NEJM in 2000 that low-tidal volume ventilation demonstrated a statistically significant improvement in mortality (5). In fact, the first few trials examining the efficacy of low-tidal volume strategies failed to find a survival benefit when compared to more traditional ventilatory strategies (2,3,4). Despite the universal acceptance of low-tidal volume for the management of ARDS, the evidence supporting lung protective ventilation is far more controversial than its fabled repute. And while its logistical implementation has not caught up with its theoretical acceptance, this is likely due more to a fault in our ability to recognize patients who are at risk for ARDS and ventilator induced lung injury (VILI), rather than a lack of acceptance of the premise of lung protective ventilatory strategies (1). The use of lung protective ventilation has become ubiquitous in the culture of critical care medicine. The great tragedy of Science - the slaying of a beautiful hypothesis by an ugly fact. ![]()
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