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Coda Change

Jun 5, 2018

Marcelo Amota makes the case for why driving pressures matter during mechanical ventilation in critical care. Sao Paulo, Brazil, experiences flooding every year. This exposes locals to Leptospira bacteria. The severe form of disease this causes – leptospirosis - sees patients end up on mechanical ventilators. These machines were traditionally complicated, with a huge number of settings and buttons. Marcelo Amato trained in this setting. He, alongside his colleagues, developed methods to halt bleeding in leptospirosis by manipulating ventilator settings. He calls it “protective ventilation”. It was not long before the same principles were being applied to patients suffering acute respiratory distress syndrome. Through research, Marcelo and his team concluded that driving pressures, above all other ventilator settings, were most important for patient survival. Driving pressure is the oscillation of alveolar pressure or variation of pressures inside the lungs. It is what your lungs are sensing. Although there is an obsession with tidal volume, which is displayed on ventilators, Marcello explains, driving pressures are easily calculated and more important. Marcelo discusses the increasing mortality with mechanical ventilation. The medical community, especially physiologists, are traditionally wrapped up in the concept of volutrauma. However, it is the gradient of pressures oscillating inside the lung (the driving pressure) that is causing lung injuries. So, the question became - would the lessons learnt the study on mechanical ventilation for leptospirosis be transferable to reducing risk in acute respiratory distress syndrome? Marcelo presents over twelve years of research. In doing so he highlights the changing dogma of the protective role of small tidal volumes. Research shows that the size of the tidal volume does not matter in terms of mortality. What matters is the pressure that is generated. The force with which the lung is deformed is much more important than the size of the deformation. The message: Do not look at absolute pressures, rather look at the swings in pressure. The only way a patient can survive is through a decrease in driving pressure, and not through a decrease in tidal volume.

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