Low-TV Ventilation: Is It the Rule for All ICU Patients?
In 2000, the Acute Respiratory Distress Syndrome Network (ARDSNet) researchers published a landmark study showing that low-tidal-volume (TV) ventilation for patients with acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) reduces mortality. Any time an intervention shows objective evidence of a mortality reduction in a critically ill patient population, the response is predictable. The physician at the bedside who is anxious to improve outcomes will enthusiastically adopt it, whereas the research and academic communities remain skeptical. That said, low-TV ventilation has generally weathered the storm thus far and continues to be recommended for patients with ARDS.

There are many patients in the intensive care unit (ICU) who do not have lung injury, though. At most of the ICUs where I have worked, the low-TV ventilation strategy (approximately 6 mL/kg) has been adopted for all patients, often not by protocol but in actual practice. I admit to using this approach myself despite knowing little about the evidence base outside of ALI. I had always figured that I was unlikely to do any harm.

This topic was the subject of an excellent point/counterpoint debate published in Chest back in 2011. In 2012, Serpa Neto and colleagues published a meta-analysis in JAMA that provided some evidence base for this practice. The patients in the low-TV group received 6.45 mL/kg ideal body weight (IBW) for 6.9 hours, and the control group received 10.6 mL/kg IBW for 6.5 hours. The researchers found that low-TV ventilation reduced lung injury, mortality, pulmonary infection, and atelectasis.

My first reaction to this article was that the results seemed too good to be true. The average duration of mechanical ventilation was very short. Is it possible that very brief periods of higher volumes could cause enough ventilator-induced lung injury to change outcomes to this degree? To me this seemed unlikely, but an editorial that accompanied the meta-analysis makes the point that there is biophysiologic support from animal data. Short exposures can apparently result in severe ventilator-induced lung injury.

What about the quality of the meta-analysis? Study populations were certainly heterogeneous and the majority of the included patients were from observational trials.

This leads me back to where I started: A low-TV ventilation strategy for all ICU patients seems like a reasonable practice, now that we have some limited data. And besides, what harm could this cause? Concerns raised seem to center around the dangers of applying a one-size-fits-all approach to the patient in the ICU. What if the patient is spontaneously breathing and taking large TVs on their own; should they be sedated to achieve 6 mL/kg IBW? Duration of mechanical ventilation was short in this meta-analysis, and patients were often perioperative; do the data apply to the average medical ICU patient on ventilator support for prolonged periods? Finally, there may be more sophisticated ways to determine the proper tidal volume for your patient.

Personally, I am going to continue to target 6 mL/kg IBW for all patients and adjust as appropriate. I'd be loath to use sedation or neuromuscular blockade to achieve this target outside of ALI or ARDS, though. And I share the concern that adopting a strict 6 mL/kg IBW protocol for all patients is likely to result in unintended, potentially harmful consequences.