Kathryn Radigan, MD, MSc, Assistant Professor, Pulmonary Medicine, Northwestern University, Feinberg School of Medicine
Dr. Radigan reports no financial relationships relevant to this field of study.
William Thompson, MD, Associate Professor of Medicine, University of Washington, Seattle
Early recognition of ARDS with subsequent strict adherence to low tidal volume ventilation is important for reducing mortality in the ICU.
Needham DM, et al. Timing of low tidal volume ventilation and ICU mortality in ARDS: A prospective cohort study. Am J Respir Crit Care Med 2014 Dec 5. [Epub ahead of print]
Although it has been known for more than a decade that reducing tidal volume decreases mortality in mechanically ventilated patients with acute respiratory distress syndrome (ARDS), the effects of the timing of low tidal volume ventilation has not been well studied. Needham and colleagues sought to determine the association between ICU mortality and initial tidal volume with tidal volume changes over time in ARDS patients. In this multi-site, prospective cohort study, 482 ARDS patients were recruited, with more than 11,000 twice-daily tidal volume assessments. As timely recognition of ARDS is a barrier to initiation of low tidal volume ventilation, these patients were screened with daily review of data in medical records and chest X-rays according to the American-European Consensus Conference criteria, including the need for mechanical ventilation and PaO2/FiO2 ratio < 300.
The authors showed that an increase of 1 mL/kg of predicted body weight (PBW) in initial tidal volume was associated with a 23% increase in ICU mortality (adjusted hazard ratio [HR], 1.23; 95% CI, 1.06-1.44, P = 0.008). Furthermore, there was a 15% increase in mortality, with a 1 mL/kg PBW increase in subsequent tidal volumes compared to the initial tidal volume (adjusted HR, 1.15; 95% CI, 1.02-1.29, P = 0.019). They also compared patients receiving 8 days of mechanical ventilation with a tidal volume of 6 mL/kg PBW to those receiving 10 and 8 mL/kg PBW. They found an absolute increase in ICU mortality of 7.2% (3.0-13.0%) and 2.7% (1.2-4.6%), respectively. When comparing tidal volume profiles with 4 days of 6 mL/kg PBW and 4 days of 10 mL/kg PBW, the estimated absolute increase in mortality was greater when the 10 mL/kg was used within the first 4 days vs the last 4 days of the 8-day ventilation period (4.8% [1.9-8.5%] vs 2.0% [0.6-3.9%]).
This manuscript clearly reveals the importance of adherence to low tidal volume ventilation, especially early in the development of ARDS. With this new evidence, there are two distinct concepts that will need to be stressed to the critical care population and beyond: recognition and promptness. Clinicians must be attuned to the relentlessly changing critically ill patient. Much too often, ARDS is not recognized until 12-24 hours after onset of clinical deterioration. Perhaps a prompt generated from the electronic medical record may be of benefit. If the patient meets criteria by the PaO2/FiO2 ratio, the physician is prompted to further investigate the possibility of ARDS. Once ARDS is recognized, it needs to be stressed that prompt adherence to low tidal volume ventilation will reduce the mortality of critically ill patients. The early aspect of this may be met with certain challenges, as many of the initial volumes of ARDS patients are established in the emergency department by respiratory therapists and/or by physicians who are not yet aware of the impact those initial settings may have on patient outcomes. To appropriately guide education platforms for prompt adherence, it may be helpful to investigate who is making the initial decision on volume settings (i.e., residents, ED physicians, ICU attendings, or respiratory therapists) and whether these settings are being made based on lack of education or other barriers to care (i.e., difficulty with sedation, etc). It is expected that attending presence in the ICU overnight, as well as broader educational platforms, may help with early ARDS recognition.
Although the overall message of this manuscript will benefit the delivery of critical care, I would like to exercise a word of caution with these recommendations, as the authors brought up the idea that “there may be benefit for all mechanically ventilated patients of ICU-wide protocols that default to 6 mL/kg PBW, with a specific physician order required for use of higher tidal volumes.” Although this may benefit some patients, I fear that in our enthusiasm we may go too far and may cause more harm than good. As we have all experienced, patients with low tidal volume ventilation may need excessive amounts of sedation to tolerate the low volumes. In efforts to provide low tidal volume ventilation, many of our patients may receive excessive sedation that may lead to worse outcomes, including prolonged mechanical ventilation. We must use caution, investigate further, and not confuse a broadly useful guideline with a prescription for all.
This manuscript supports the idea that early diagnosis and intervention for many issues in the ICU is critical: antibiotics in septic shock, resuscitation for patients with gastrointestinal bleeding, anticoagulation for pulmonary embolism, and now low tidal volume ventilation for ARDS. Perhaps the best treatment of our critically ill patients can be summarized by early and aggressive recognition and treatment, especially for those interventions known to improve patient outcomes.