Correspondence  |   November 2016
Ventilator-induced Lung Injury: Power to the Mechanical Power
Author Notes
  • Laboratory of Pulmonary Investigation, Carlos Chagas Filho Biophysics Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil (P.R.M.R.).
  • (Accepted for publication July 14, 2016.)
    (Accepted for publication July 14, 2016.)×
Article Information
Correspondence   |   November 2016
Ventilator-induced Lung Injury: Power to the Mechanical Power
Anesthesiology 11 2016, Vol.125, 1070-1071. doi:10.1097/ALN.0000000000001297
Anesthesiology 11 2016, Vol.125, 1070-1071. doi:10.1097/ALN.0000000000001297
We read with interest the study on “Mechanical Power and Development of Ventilator-induced Lung Injury” recently published by Cressoni et al.1  in Anesthesiology. This study aimed to identify a power threshold for ventilator-induced lung injury (VILI) in noninjured lungs. The authors applied power (energy per breath times respiratory rate [RR]) above and below the threshold for VILI, as measured using computed tomography scans. Mechanical power is a function of transpulmonary driving pressure (ΔP,L), tidal volume (VT), and RR. For this purpose, piglets were ventilated with higher power (VT = 38 ml/kg and RR = 15 bpm) or at the same VT with a different RR. The authors identified the mechanical power threshold for VILI as 12 J/min, conducted further experiments at RR = 35 bpm and at powers below and above the threshold, and noted that, if mechanical power is above 12 J/min, VILI may develop. However, the absolute value of power depends on animal size, lung volume, and RR, thus limiting direct translation of this threshold to the clinical setting. In addition to the concepts of ΔP,L, energy, and power, we should consider the concept of “intensity,” i.e., the distribution of power per unit of lung surface area. If mechanical power increases without changes in lung surface area, the intensity will be higher. On the other hand, if both power and lung surface area increase, e.g., due to lung recruitment, the “intensity” may reduce or remain constant. In the presence of regional inhomogeneities of aeration, measurement of lung surface area requires careful evaluation. Alveoli may open homogeneously, present areas of overdistension, or collapse with a similar overall surface area. In these situations, the regional “intensity” is higher in the presence of alveolar inhomogeneity.
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