Ventilator-related causes of lung injury: the mechanical power

Intensive Care Med. 2016 Oct;42(10):1567-1575. doi: 10.1007/s00134-016-4505-2. Epub 2016 Sep 12.


Purpose: We hypothesized that the ventilator-related causes of lung injury may be unified in a single variable: the mechanical power. We assessed whether the mechanical power measured by the pressure-volume loops can be computed from its components: tidal volume (TV)/driving pressure (∆P aw), flow, positive end-expiratory pressure (PEEP), and respiratory rate (RR). If so, the relative contributions of each variable to the mechanical power can be estimated.

Methods: We computed the mechanical power by multiplying each component of the equation of motion by the variation of volume and RR: [Formula: see text]where ∆V is the tidal volume, ELrs is the elastance of the respiratory system, I:E is the inspiratory-to-expiratory time ratio, and R aw is the airway resistance. In 30 patients with normal lungs and in 50 ARDS patients, mechanical power was computed via the power equation and measured from the dynamic pressure-volume curve at 5 and 15 cmH2O PEEP and 6, 8, 10, and 12 ml/kg TV. We then computed the effects of the individual component variables on the mechanical power.

Results: Computed and measured mechanical powers were similar at 5 and 15 cmH2O PEEP both in normal subjects and in ARDS patients (slopes = 0.96, 1.06, 1.01, 1.12 respectively, R (2) > 0.96 and p < 0.0001 for all). The mechanical power increases exponentially with TV, ∆P aw, and flow (exponent = 2) as well as with RR (exponent = 1.4) and linearly with PEEP.

Conclusions: The mechanical power equation may help estimate the contribution of the different ventilator-related causes of lung injury and of their variations. The equation can be easily implemented in every ventilator's software.

Keywords: ARDS; Mechanical ventilation; Respiratory mechanics; VILI.

MeSH terms

  • Adult
  • Aged
  • Airway Resistance / physiology
  • Case-Control Studies
  • Female
  • Humans
  • Logistic Models
  • Lung / physiopathology*
  • Male
  • Middle Aged
  • Positive-Pressure Respiration / methods
  • Respiratory Distress Syndrome / therapy
  • Respiratory Mechanics / physiology*
  • Tidal Volume / physiology
  • Ventilator-Induced Lung Injury / etiology*
  • Ventilators, Mechanical / adverse effects*