How to estimate mechanical power in volume- and pressure-control ventilation

Article

Auteur: Justin Seemueller, Respiratory Clinical Specialist, Sentara Norfolk General Hospital

Date: 24.02.2021

As our understanding of VILI grows, there is a greater focus on mechanical power (MP) as a potential predictor of negative outcomes.

How to estimate mechanical power in volume- and pressure-control ventilation

Calculating MP in volume-controlled modes

Data currently suggests that a MP of 17.0 J/min is associated with higher risk of death (Serpa Neto A, Deliberato RO, Johnson AEW, et al. Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts. Intensive Care Med. 2018;44(11):1914-1922. doi:10.1007/s00134-018-5375-61). Below is the surrogate corrected method of calculating MP in Volume Control proposed by Gattinoni et al. (Giosa L, Busana M, Pasticci I, et al. Mechanical power at a glance: a simple surrogate for volume-controlled ventilation. Intensive Care Med Exp. 2019;7(1):61. Published 2019 Nov 27. doi:10.1186/s40635-019-0276-82).

Power_surr.corr= [VE x (Peak Pressure + PEEP + F/6)] / 20

If we use the corresponding values shown in the ventilator's Monitoring window, the equation is as follows:

Power_surr.corr= [ExpMinVol x (Ppeak + PEEP/CPAP + Insp Flow/6)] / 20

Figure 1 below shows the calculation using the corresponding values as shown in the Monitoring window.

Screenshot showing relevant parameters for calculating MP in volume control in monitoring window — Figure 1

Calculating MP in pressure-controlled modes

Below is a simplified method of calculating mechanical power in Pressure Control proposed by Van der Meijden et al. and Becher et al. (Becher T, van der Staay M, Schädler D, Frerichs I, Weiler N. Calculation of mechanical power for pressure-controlled ventilation. Intensive Care Med. 2019;45(9):1321-1323. doi:10.1007/s00134-019-05636-83).

MP_PCV = 0.098 x RR x VT x (∆P_insp + PEEP)

It is possible to further simplify their formula by replacing "∆P_insp + PEEP” with plateau pressure, as they are equivalent by definition. Pplateau can be measured by means of an inspiratory hold (available in the Tools window). Alternatively, an estimated value of Pplateau is displayed in the Monitoring window of Hamilton Medical ventilators. If we use the corresponding values as shown in the Monitoring window, the equation is as follows:

MP_PCV = 0.098 x fTotal x VTI x Pplateau

Figure 2 below shows the calculation using the corresponding values as shown in the Monitoring window.

These formulas may assist in identifying mechanically ventilated patients in need of earlier intervention.

Screenshot showing relevant parameters for calculating MP in pressure control in monitoring window — Figure 2

Notes en bas de page

Références

1. Serpa Neto A, Deliberato RO, Johnson AEW, et al. Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts. Intensive Care Med. 2018;44(11):1914-1922. doi:10.1007/s00134-018-5375-6
2. Giosa L, Busana M, Pasticci I, et al. Mechanical power at a glance: a simple surrogate for volume-controlled ventilation. Intensive Care Med Exp. 2019;7(1):61. Published 2019 Nov 27. doi:10.1186/s40635-019-0276-8
3. Becher T, van der Staay M, Schädler D, Frerichs I, Weiler N. Calculation of mechanical power for pressure-controlled ventilation. Intensive Care Med. 2019;45(9):1321-1323. doi:10.1007/s00134-019-05636-8

Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts.

Serpa Neto A, Deliberato RO, Johnson AEW, et al. Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts. Intensive Care Med. 2018;44(11):1914-1922. doi:10.1007/s00134-018-5375-6

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PURPOSE

Mechanical power (MP) may unify variables known to be related to development of ventilator-induced lung injury. The aim of this study is to examine the association between MP and mortality in critically ill patients receiving invasive ventilation for at least 48 h.

METHODS

This is an analysis of data stored in the databases of the MIMIC-III and eICU. Critically ill patients receiving invasive ventilation for at least 48 h were included. The exposure of interest was MP. The primary outcome was in-hospital mortality.

RESULTS

Data from 8207 patients were analyzed. Median MP during the second 24 h was 21.4 (16.2-28.1) J/min in MIMIC-III and 16.0 (11.7-22.1) J/min in eICU. MP was independently associated with in-hospital mortality [odds ratio per 5 J/min increase (OR) 1.06 (95% confidence interval (CI) 1.01-1.11); p = 0.021 in MIMIC-III, and 1.10 (1.02-1.18); p = 0.010 in eICU]. MP was also associated with ICU mortality, 30-day mortality, and with ventilator-free days, ICU and hospital length of stay. Even at low tidal volume, high MP was associated with in-hospital mortality [OR 1.70 (1.32-2.18); p < 0.001] and other secondary outcomes. Finally, there is a consistent increase in the risk of death with MP higher than 17.0 J/min.

CONCLUSION

High MP of ventilation is independently associated with higher in-hospital mortality and several other outcomes in ICU patients receiving invasive ventilation for at least 48 h.

Mechanical power at a glance: a simple surrogate for volume-controlled ventilation.

Giosa L, Busana M, Pasticci I, et al. Mechanical power at a glance: a simple surrogate for volume-controlled ventilation. Intensive Care Med Exp. 2019;7(1):61. Published 2019 Nov 27. doi:10.1186/s40635-019-0276-8

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BACKGROUND

Mechanical power is a summary variable including all the components which can possibly cause VILI (pressures, volume, flow, respiratory rate). Since the complexity of its mathematical computation is one of the major factors that delay its clinical use, we propose here a simple and easy to remember equation to estimate mechanical power under volume-controlled ventilation: [Formula: see text] where the mechanical power is expressed in Joules/minute, the minute ventilation (VE) in liters/minute, the inspiratory flow (F) in liters/minute, and peak pressure and positive end-expiratory pressure (PEEP) in centimeter of water. All the components of this equation are continuously displayed by any ventilator under volume-controlled ventilation without the need for clinician intervention. To test the accuracy of this new equation, we compared it with the reference formula of mechanical power that we proposed for volume-controlled ventilation in the past. The comparisons were made in a cohort of mechanically ventilated pigs (485 observations) and in a cohort of ICU patients (265 observations).

RESULTS

Both in pigs and in ICU patients, the correlation between our equation and the reference one was close to the identity. Indeed, the R2 ranged from 0.97 to 0.99 and the Bland-Altman showed small biases (ranging from + 0.35 to - 0.53 J/min) and proportional errors (ranging from + 0.02 to - 0.05).

CONCLUSIONS

Our new equation of mechanical power for volume-controlled ventilation represents a simple and accurate alternative to the more complex ones available to date. This equation does not need any clinical intervention on the ventilator (such as an inspiratory hold) and could be easily implemented in the software of any ventilator in volume-controlled mode. This would allow the clinician to have an estimation of mechanical power at a simple glance and thus increase the clinical consciousness of this variable which is still far from being used at the bedside. Our equation carries the same limitations of all other formulas of mechanical power, the most important of which, as far as it concerns VILI prevention, are the lack of normalization and its application to the whole respiratory system (including the chest wall) and not only to the lung parenchyma.

Calculation of mechanical power for pressure-controlled ventilation.

Becher T, van der Staay M, Schädler D, Frerichs I, Weiler N. Calculation of mechanical power for pressure-controlled ventilation. Intensive Care Med. 2019;45(9):1321-1323. doi:10.1007/s00134-019-05636-8

Link to article