Over the last decade, our understanding of VILI has grown exponentially and in the last couple years, the concept of mechanical power has gained popularity.
Finally, it seems like we are moving from the very simplistic 6ml/kg/IBW, and the debate of whether the volumes or the pressures are the responsible for the injury (both).
The mechanical power (the energy delivered from the ventilator per minute) incorporates all the components delivered from the ventilator (tidal volume, flow, inspiratory pressure, inspiratory time, PEEP, Respiratory rate) and it is a good comprehensive concept that involve complex engineering, mathematical and physics concept that most of clinicians including myself have hard time totally comprehending.
So are we there yet? No, we are getting closer but there are much more questions to be answered and more work to be done.
– Are the simplified available equations accurate?
– Should we target a specific number?
– How about the actively breathing patient? Is the total work done by the ventilator and the patient are in series (additive) or in parallel (subtractive), possibly different in different ventilator modes?
– How about the trans-pulmonary mechanical power? Do we have to worry about the energy transferred to the chest wall including the diaphragm? And does it cause diaphragmatic injury?
– Should we index the numbers to IBW or Aeriated lung ?
– How about the energy dissipated as heat, does that count as injurious to the respiratory system?
– Should we worry about if the energy or work delivered is elastic work (work against the elastance of the respiratory system) or resistive work (work against the airway resistance)?
– We always concentrate on the injury to the alveoli which is understandable, but how about the lung matrix and interstitial space, are they safe?
– Should we incorporate multiple modalities measurements (e.g. EIT, Esophageal balloon, plethysmography, US, etc) to the mechanical power?
-Finally, we need continuous measurements of accurate mechanical power numbers while we adjust our ventilator settings as doubtfully clinicians will be calculating those equations every time adjustments done.
There are probably some answers to the above questions or possibly more questions that hopefully will have answers to.
The important thing is, we are making progress and on the right track
