Objective:

To define which would be the mechanical power (using a mathematical model that can apply to possible causes for lung injury) used by a ventilator, in patients undergoing invasive mechanical ventilation in spontaneous PAV (proportional assist ventilation).

Material and methods:

The mechanical and distention powers are calculated using the equations:

${\mathrm{p}\mathrm{o}\mathrm{d}\mathrm{e}\mathrm{r}\mathrm{}\mathrm{m}\mathrm{e}\mathrm{c}\mathrm{a}\mathrm{n}\mathrm{i}\mathrm{c}\mathrm{o}}_{\mathrm{r}\mathrm{s}}=FR.\left\{∆{\mathrm{V}}^2.\mathrm{}\left[\frac{1}{2}.{\mathrm{E}\mathrm{L}}_{\mathrm{r}\mathrm{s}}\mathrm{}+\mathrm{}\mathrm{F}\mathrm{R}.\mathrm{}\frac{\left(1\mathrm{}+\mathrm{}\mathrm{I}:\mathrm{}\mathrm{E}\right)}{60\mathrm{}.\mathrm{}\mathrm{I}\mathrm{}:\mathrm{}\mathrm{E}}\mathrm{}.\mathrm{}{\mathrm{R}}_{\mathrm{a}\mathrm{w}}\right]\mathrm{}+∆\mathrm{V}\mathrm{}.\mathrm{}\mathrm{P}\mathrm{E}\mathrm{E}\mathrm{P}\right\}$

2. Mechanical power rs = (0.098) . (FR . ΔV) . (Ppeak − ½ . ΔP)

3. PD = (0.098) . (PPL − PEEP) . Vt . RF

Sixty patients were selected, half of them with invasive mechanical ventilation PAV in spontaneous mode, estimating the plateau pressure (P pl ) though tidal volume value (Vt), distensibility (C rs ), and the positive pressure at the end of a normal exhalation (PEEPt) given by the mechanical ventilator.

Results:

Data from 60 patients undergoing invasive mechanical ventilation was included, 30 of them through spontaneous modality: proportional assist ventilation (PAV), from which 100% had a successful ventilator tube removal; 30 patients were paired as controls with controlled modalities, with age 65 years (SD ± 15), 63% were men, with the general parameters: mean respiratory frequency (RF) of 18 (SD ± 5.5) min-1, mean Vt of 0.46 (SD ± 0.1) Lts, mean C rs of 55 (SD ± 22) mL/cm H2O, PEEPt of 7.6 (SD ± 3.3) cm H2O, peak pressure (Ppico) 20.4 (SD ± 6.9) cm H2O, Ppl of 17.05 (SD ± 5.8) cm H2O. When comparing the mechanical power, all the results were inferior in patients with spontaneous modality versus patients undergoing controlled modality ventilation, determining the following values: 6.98 (SD ± 1.69) versus 18.49 (SD ± 8.20) J/min (p < 0.001), 7.17 (SD ± 1.67) versus 20.92 (SD ± 9.05) J/min (p < 0.001) and of 4.6 (SD ± 1.64) versus 12.33 (SD ± 7.04) J/min (p < 0.001), in the equations 1, 2, and 3 respectively, with an average value for the patients undergoing spontaneous modality of 6.25 (SD ± 1.66) J/min.

Conclusions:

The probability of determining a mean value for the mechanical power used in patients undergoing invasive mechanical ventilation on a PAV mode may allow to obtain a standard parameter to follow under the context of its estimated equivalence in physiological conditions, mainly for patients in whom lung protective measures are desired in order to obtain a positive progress and the eventual removal of the invasive ventilation.

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