An idea from Dr. Emily Junck out of Univ of Washington EM, linked below is a list of 52 landmark studies which helped evolve the practice of EM. This week’s read is from the ARDSnet trial, which showed low tidal volumes decreased mortality in ARDS and acute lung injury patients.
Past mechanical ventilation tidal volumes (TV) were 10-12 cc/kg of ideal body weight. Mortality was observed to range from 40-50% in pts with Acute Lung Injury (ALI) and Acute Resp Distress Syndrome (ARDS). Compared to the physiological 7-8 cc/kg TVs, it was hypothesized that the excessive lung stretch cause an inflammatory surge, resulting subsequent organ injury. The study hypothesized that maybe less stretch = better (lower TV), even if at the expense of decreased oxygenation or increased acidosis.
The two compared groups observed were high TV (12 cc/kg, goal plateau pressure of less/equal to 50 cc of H2O) and low TV (6 cc/kg, goal plateau pressure of less/equal to 30 cc of H2O).
Amongst several other end points, the study saw in comparison that the low TV group had:
– decreased mortality (P = 0.007), noting a 22% reduction.
– increased no. of vent-free days (P = 0.007).
– decreased no. of days of non-pulmonary organ failure (P = 0.006).
– decrease concentrations of Interleukin-6, a surrogate marker of inflammation (P = 0.002).
However, there was no statistical difference in the incidence of barotrauma, most commonly manifesting as pneumothorax (P = 0.43).
Plus ARDSnet introduced the “PEEP Ladder” used to sequentially improve oxygenation by incrementally augmenting FiO2 and PEEP.
(image from: http://crashingpatient.com/ventilator-management/ventilator-management.htm/)
Bottom Line: Lower TV = Better for injured lungs.