It is currently understood that VILI is a consequence of stress and strain placed upon lung tissue during mechanical ventilation . The severity of stress and strain induced is commonly estimated by monitoring airway pressure and tidal volumes the patient is receiving.
- Cumulative damage caused to the lung during mechanical ventilation can be expressed through mechanical power (total energy delivered in Joules per minute).
- High mechanical power has been associated with increased mortality, even where sample groups received low tidal volumes or low driving pressures.
- Simplified methods have been suggested for estimating mechanical power at the bedside.
- Further automation of these calculations through electronic medical record systems may allow for earlier interventions with the aim of improving outcomes.
It is a generally accepted practice to limit tidal volume (per IBW), plateau pressure, and driving pressure (Plat-PEEP) within acceptable ranges for lung-protective ventilation . It should also be intuitive that respiratory rate is a hypothetical multiplier of the damage induced by positive pressure ventilation . In addition, higher flow rates could also influence strain on the lung . The cumulative lung damage caused by all known variables can ultimately be expressed through mechanical power, or total energy delivered in Joules per minute. High mechanical power has been associated with increased mortality in sample groups despite receiving low tidal volume strategies; this theme has also held true in cohorts of patients receiving low driving pressure, suggesting mechanical power serves as an independent metric worth tracking .
Gattinoni et al. have utilized derivative formulas to estimate mechanical power as a metric to mitigate lung damage. The most accurate bedside method is complicated and requires clinicians to perform an inspiratory hold to measure plateau pressure for accurate resistance and elastance values . Depending on the level of sedation and patient effort, this may not always be possible.
Simplified methods have recently emerged to quickly estimate mechanical power without the need for an inspiratory hold maneuver. Gattinoni et al. proposed an acceptably accurate method for Volume Control ventilation; the simplified method was validated by comparing animal experimentation with a cohort of ICU patients from seven previously published studies [6, 7, 8, 9, 10, 11, 12]. At the cost of a small potential underestimation of actual mechanical power, the simplified method has advantages of simplicity and ease of tracking . Becher et al. have also developed a simplified method of estimation when using Pressure Control ventilation by disregarding P-ramp, and they found a high degree of correlation to reference values of mechanical power . Both of these surrogate methods have been shown to be accurate enough to justify their routine use within the clinical setting .
These new methodologies are interesting in the context of modern electronic medical record (EMR) systems, some of which can apply formulas to device integrated ventilator data. Epic is a fairly ubiquitous EMR system, and the company's system analysts have confirmed that it is possible to automatically calculate these types of shortened mechanical power formulas within new flowsheet rows. This presents an exciting prospect for generating instantaneous reports on all ventilator patients within a hospital system, who are currently receiving what might be considered unsafe levels of mechanical power. In two separate observational cohorts, a value of 17 J/min or greater was associated with a higher risk of death . In the absence of the ventilator automatically displaying estimated mechanical power within current software, the clinician can calculate it at the bedside with relative ease. By further automating through the EMR, we may achieve earlier interventions with the aim of improving mortality outcomes.
- Giosa, L., Busana, M., Pasticci, I. et al. Mechanical power at a glance: a simple surrogate for volume-controlled ventilation. ICMx 7, 61 (2019).
- Amato MB, Meade MO, Slutsky AS et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015 Feb 19;372(8):747-55.
- Hotchkiss JR Jr, Blanch L, Murias G et al. Effects of decreased respiratory frequency on ventilator-induced lung injury. Am J Respir Crit Care Med. 2000 Feb;161(2 Pt 1):463-8.
- Tonetti T, Vasques F, Rapetti F, et al. Driving pressure and mechanical power: new targets for VILI prevention. Ann Transl Med. 2017;5(14):286.
- Serpa Neto, A., Deliberato, R.O., Johnson, A.E.W. 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 44, 1914–1922 (2018).
- Cressoni M, Chiumello D, Chiurazzi C et al. Lung inhomogeneities, inflation and [18F]2-fluoro-2-deoxy-D-glucose uptake rate in acute respiratory distress syndrome. Eur Respir J. 2016 Jan;47(1):233-42. Epub 2015 Oct 22.
- Gattinoni L, Caironi P, Cressoni M et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006 Apr 27;354(17):1775-86.
- Cressoni, M., Chiumello, D., Algieri, I. et al. Opening pressures and atelectrauma in acute respiratory distress syndrome. Intensive Care Med 43, 603–611 (2017).
- Chiumello, Davide MD, Cressoni, Massimo MD, Carlesso, Eleonora MSc, et al. Bedside Selection of Positive End-Expiratory Pressure in Mild, Moderate, and Severe Acute Respiratory Distress Syndrome. Critical Care Medicine: February 2014 - Volume 42 - Issue 2 - p 252-264.
- Chiumello D, Marino A, Brioni M et al. Lung Recruitment Assessed by Respiratory Mechanics and Computed Tomography in Patients with Acute Respiratory Distress Syndrome. What Is the Relationship? Am J Respir Crit Care Med. 2016 Jun 1;193(11):1254-63.
- Chiumello, Davide MD, Mongodi, Silvia MD, Algieri, Ilaria MD, et al. Assessment of Lung Aeration and Recruitment by CT Scan and Ultrasound in Acute Respiratory Distress Syndrome Patients, Critical Care Medicine: November 2018 - Volume 46 - Issue 11 - p 1761-1768.
- Chiumello, Davide MD, Marino, Antonella MD, Cressoni, Massimo MD, et al. Pleural Effusion in Patients With Acute Lung Injury, Critical Care Medicine: April 2013 - Volume 41 - Issue 4 - p 935-944.
- Becher, T., van der Staay, M., Schädler, D. et al. Calculation of mechanical power for pressure-controlled ventilation. Intensive Care Med 45, 1321–1323 (2019).
- Chiumello, D., Gotti, M., Guanziroli, M. et al. Bedside calculation of mechanical power during volume- and pressure-controlled mechanical ventilation. Crit Care 24, 417 (2020).
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