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Mechanical Power und beatmungsinduzierte Lungenschädigung

Artikel

Autor: Jean‑Pierre Revelly, Giorgio Iotti

Datum: 03.04.2023

In diesem Artikel werden die verschiedenen Komponenten der Mechanical Power, ihre Bedeutung in einer klinischen Situation und ihre Verwendung als Monitoring‑Parameter beleuchtet.

Mechanical Power und beatmungsinduzierte Lungenschädigung

Diese Betrachtung beschränkt sich auf die Mechanical Power (MP) während der Inspirationsphase der kontrollierten Beatmung unter der Annahme, dass es keine Atembemühungen seitens des Patienten gibt.

Aus der Physik: 

  • Mechanische Arbeit ist die Energie, die verrichtet wird, wenn ein Körper durch eine Kraft von einer Position in eine andere bewegt wird.
  • Die Leistung gibt an, welche Energiemengen in einer bestimmten Zeit umgesetzt werden.

Bei der maschinellen Beatmung ist die während der Inspiration vom Beatmungsgerät auf das Atemsystem übertrage Leistung eine übergeordnete Variable, in der die verschiedenen Elemente kombiniert sind, die eine beatmungsinduzierte Lungenschädigung (VILI) hervorrufen können (Gattinoni L, Tonetti T, Cressoni M, et al. Ventilator‑related causes of lung injury: the mechanical power. Intensive Care Med. 2016;42(10):1567‑1575. doi:10.1007/s00134‑016‑4505‑21​).

Mechanical Power bei der CMV‑Beatmung

Bei der kontrollierten mandatorischen Beatmung (CMV) mit konstantem Flow kann MP ausgedrückt werden als Arbeit pro Atemhub (W) mal Atemfrequenz (AF) (Abbildung 1) (Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303‑311. doi:10.1164/rccm.202009‑3467OC2​):

Wobei gilt:

  • Wel,PEEP entspricht der elastisch‑statischen Komponente, also der Komponente von MP, die sich auf PEEP bezieht. 
  • Wel,DP entspricht der (tidalen) elastisch‑dynamischen Komponente, also der Komponente von MP, die sich auf die Inspiration bezieht. Es wird mit einem rechtwinkligen Dreieck dargestellt. Dabei verkörpert die vertikale Seite das Tidalvolumen (Vt) und die horizontale Seite den Driving Pressure (DP). Die Steigung der dritten Seite entspricht der Compliance. 
  • Wres steht für die resistive Komponente, also die Energie, die bei jeder Inspiration abgeleitet wird, um die resistiven und viskosen Eigenschaften des Atemsystems zu überwinden. Wres wird mit einem Parallelogramm dargestellt. Dabei entspricht die Basis dem Unterschied zwischen dem Spitzendruck (Ppeak) und dem Plateaudruck (Pplat). Vt wird mit der Höhe ausgedrückt.
Diagramm, in dem drei verschiedene Komponenten von Mechanical Power dargestellt werden
Abbildung 1: Druck/Volumen‑Diagramm mit verschiedenen Komponenten von Mechanical Power (siehe Text für Erläuterungen)

Mechanical Power bei der PCV‑Beatmung

Ein ähnlicher Ansatz kann bei der druckkontrollierten Beatmung (PCV) für die Berechnung von Wel,PEEP und Wel,DP basierend auf Vt, PEEP und DP angewandt werden. Ein Näherungswert für Wres kann berechnet werden, indem die Fläche des Dreiecks mit Ppeak minus PEEP als Basis und Vt als Höhe errechnet und dann das Dreieck für Wel,DP abgezogen wird. Dieselbe Berechnung von Wres kann auch herangezogen werden, wenn Ppeak identisch mit Pplat ist (Abbildung 2) oder höher liegt (Abbildung 3), also wenn der endinspiratorische Flow null bzw. noch positiv ist. In beiden Fällen führt der Näherungswert zu einer leichten Überbewertung von Wres und somit der echten Gesamtarbeit des Beatmungsgerätes (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​).

Diagramm mit Näherungswert bei identischem Ppeak und Pplat
Abbildung 2: Näherungswert für Wres bei PCV‑Beatmung und mit identischem Ppeak und Pplat
Diagramm mit Näherungswert und einem Ppeak, der über Pplat liegt
Abbildung 3: Näherungswert für Wres bei PCV‑Beatmung und einem Ppeak, der über Pplat liegt

Ist die Mechanical Power klinisch relevant?

Zahlreiche Studienärzte haben Mechanical Power aus den Daten verschiedener Beatmungsstudien an Intensivpatienten mit (Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303‑311. doi:10.1164/rccm.202009‑3467OC2​, Tonna JE, Peltan I, Brown SM, Herrick JS, Keenan HT; University of Utah Mechanical Power Study Group. Mechanical power and driving pressure as predictors of mortality among patients with ARDS. Intensive Care Med. 2020;46(10):1941‑1943. doi:10.1007/s00134‑020‑06130‑24​, Robba C, Badenes R, Battaglini D, et al. Ventilatory settings in the initial 72 h and their association with outcome in out‑of‑hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out‑of‑hospital cardiac arrest (TTM2) trial. Intensive Care Med. 2022;48(8):1024‑1038. doi:10.1007/s00134‑022‑06756‑45​) und ohne ARDS berechnet (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/s00134‑018‑5375‑66​​, Robba C, Badenes R, Battaglini D, et al. Ventilatory settings in the initial 72 h and their association with outcome in out‑of‑hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out‑of‑hospital cardiac arrest (TTM2) trial. Intensive Care Med. 2022;48(8):1024‑1038. doi:10.1007/s00134‑022‑06756‑47​, van Meenen DMP, Algera AG, Schuijt MTU, et al. Effect of mechanical power on mortality in invasively ventilated ICU patients without the acute respiratory distress syndrome: An analysis of three randomised clinical trials. Eur J Anaesthesiol. 2023;40(1):21‑28. doi:10.1097/EJA.00000000000017788​). 
Ergebnisse dieser Analysen: 

  • Nicht‑überlebende Patienten erhielten eine viel höhere MP als Überlebende
  • Es bestand ein statistischer Zusammenhang zwischen einer steigenden MP und der Sterblichkeit auf der Intensivstation und im Krankenhaus, weniger Tagen ohne Beatmungsgerät und längeren Aufenthalten auf der Intensivstation und im Krankenhaus 

Diese retrospektiven Studien legen insgesamt nahe, dass eine zu hohe Mechanical Power nach Möglichkeit vermieden werden sollte. Dieser Schlussfolgerung liegt die Annahme zugrunde, dass ein schlechteres klinisches Behandlungsergebnis teilweise auf VILI zurückzuführen ist.

Gibt es einen sicheren MP‑Wert für alle Patienten?

Die Methoden, die zur Berechnung der MP in veröffentlichten Studien verwendet wurden, müssen genau betrachtet werden, um eine korrekte Interpretation zu ermöglichen. Je nach Verfügbarkeit der Daten ist es möglich, dass die Autoren diverse Komponenten der MP nicht berücksichtigt haben. Es ist auch umstritten, welche Methode zum Vergleichen der verschiedenen Patienten am besten geeignet ist. Ein Vorschlag umfasst eine Normalisierung der Größe des Patienten (voraussichtliches Körpergewicht), der Compliance oder des endexspiratorischen Lungenvolumens. 

Generell ist zu beachten, dass es noch keinen standardisierten Ansatz für die Berechnung der MP gibt. Ebenso wurde kein weithin akzeptierter sicherer Wert für die geschätzte MP definiert.

Ist die Mechanical Power für eine kontinuierliche Überwachung geeignet?

Individuelle Änderungen an den Einstellungen am Beatmungsgerät haben komplexe Auswirkungen auf andere Variablen der Beatmungsmechanik. Das Konzept der Mechanical Power beruht auf der implizierten Annahme, dass alle Beatmungsvariablen ein lineares Verhältnis zueinander haben und gleichermaßen zur VILI beitragen. Dies trifft jedoch nicht zu, wie am Beispiel von PEEP zu erkennen ist, dessen Verhältnis zur VILI kurvenförmig (J‑Form) ist (Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303-311. doi:10.1164/rccm.202009-3467OC2​). Es darf angenommen werden, dass es während der Inspiration ein sicheres Volumen, einen Grenzwert und eine Schädigungsszone gibt, die nicht erreicht werden sollte (Marini JJ, Rocco PRM. Which component of mechanical power is most important in causing VILI?. Crit Care. 2020;24(1):39. Published 2020 Feb 5. doi:10.1186/s13054-020-2747-49​). Das inspiratorische Flowprofil, das bei der MP nicht berücksichtigt wird, könnte eine wichtige Rolle bei der VILI spielen (Marini JJ, Crooke PS, Gattinoni L. Intra-cycle power: is the flow profile a neglected component of lung protection?. Intensive Care Med. 2021;47(5):609-611. doi:10.1007/s00134-021-06375-510​). 

Wenn auch eine Reihe von Fragen unbeantwortet bleibt, dürfte es nützlich sein, die Gesamt‑MP und ihre Komponenten zu überwachen, um die Entwicklung des einzelnen Patienten oder seine Reaktion auf Änderungen in den Beatmungseinstellungen zu bewerten. Die Mechanical Power könnte ein weiterer Faktor neben anderen Komponenten bei der klinischen Bewertung und Entscheidungsfindung werden. Zudem würde die Überwachung der MP das Sammeln hochqualitativer Daten für zukünftige prospektive Studien zum Verhältnis zwischen MP und VILI bedeutend fördern. 

Wie können wir also das Risiko einer VILI mit den Beatmungseinstellungen verringern?

Verschiedene Studienärzte haben versucht, die schädlichsten Komponenten der Beatmung zu identifizieren. Eine retrospektive Studie fasste die Beatmungsdaten von 4.500 ARDS‑Patienten, die an kontrollierten Studien teilgenommen hatten, zusammen und beurteilte mit multivariablen Modellen das Verhältnis von MP, Vt, AF und DP zur 28‑Tage‑Sterblichkeit (Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303-311. doi:10.1164/rccm.202009-3467OC2​). DP steht für Vt (mit normalisierter Compliance) und wird weithin als eine der wichtigsten Komponenten der VILI angesehen (Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372(8):747-755. doi:10.1056/NEJMsa141063911​).

Es kommt wenig überraschend, dass die Autoren einen Zusammenhang zwischen der Gesamt‑MP und der Sterblichkeit fanden. Bei der Beurteilung der verschiedenen Komponenten der MP war nur die elastisch‑dynamische Komponente (MPel,DP, also MP in Abhängigkeit von Wel,DP) statistisch relevant; die von PEEP oder der Resistance abhängigen Komponenten waren statistisch nicht relevant. MPel,DP ist bei der CMV‑ wie bei der PCV‑Beatmung besonders einfach am Patientenbett zu ermitteln.

  • MPel,DP = Vt x DP x AF / 2

Die Autoren fanden eine ähnliche Prädiktivität der Sterblichkeit, indem sie einfach DP und AF in folgendem Index vereinten:

  • 4DP+AF Index = (4 x DP) + AF

Die Autoren kamen zu folgendem Schluss: „Wenn auch die Mechanical Power mit der Sterblichkeit bei ARDS‑Patienten in Verbindung stand, so gaben ∆P und AF ebenso viel Aufschluss und konnten am Patientenbett leichter bestimmt werden. Ob eine Beatmungsstrategie auf Basis dieser Variablen das Behandlungsergebnis positiv beeinflusst, muss in randomisierten Studien geprüft werden“ (Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303-311. doi:10.1164/rccm.202009-3467OC2​).

Fußnoten

Referenzen

  1. 1. Gattinoni L, Tonetti T, Cressoni M, et al. Ventilator‑related causes of lung injury: the mechanical power. Intensive Care Med. 2016;42(10):1567‑1575. doi:10.1007/s00134‑016‑4505‑2
  2. 2. Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303‑311. doi:10.1164/rccm.202009‑3467OC
  3. 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
  4. 4. Tonna JE, Peltan I, Brown SM, Herrick JS, Keenan HT; University of Utah Mechanical Power Study Group. Mechanical power and driving pressure as predictors of mortality among patients with ARDS. Intensive Care Med. 2020;46(10):1941‑1943. doi:10.1007/s00134‑020‑06130‑2
  5. 5. Coppola S, Caccioppola A, Froio S, et al. Effect of mechanical power on intensive care mortality in ARDS patients. Crit Care. 2020;24(1):246. Published 2020 May 24. doi:10.1186/s13054‑020‑02963‑x
  6. 6. 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
  7. 7. Robba C, Badenes R, Battaglini D, et al. Ventilatory settings in the initial 72 h and their association with outcome in out‑of‑hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out‑of‑hospital cardiac arrest (TTM2) trial. Intensive Care Med. 2022;48(8):1024‑1038. doi:10.1007/s00134‑022‑06756‑4
  8. 8. van Meenen DMP, Algera AG, Schuijt MTU, et al. Effect of mechanical power on mortality in invasively ventilated ICU patients without the acute respiratory distress syndrome: An analysis of three randomised clinical trials. Eur J Anaesthesiol. 2023;40(1):21‑28. doi:10.1097/EJA.0000000000001778
  9. 9. Marini JJ, Rocco PRM. Which component of mechanical power is most important in causing VILI?. Crit Care. 2020;24(1):39. Published 2020 Feb 5. doi:10.1186/s13054‑020‑2747‑4
  10. 10. Marini JJ, Crooke PS, Gattinoni L. Intra‑cycle power: is the flow profile a neglected component of lung protection?. Intensive Care Med. 2021;47(5):609‑611. doi:10.1007/s00134‑021‑06375‑5
  11. 11. Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372(8):747‑755. doi:10.1056/NEJMsa1410639

Diagramm, in dem drei verschiedene Komponenten von Mechanical Power dargestellt werden
Abbildung 1: Druck/Volumen‑Diagramm mit verschiedenen Komponenten von Mechanical Power (siehe Text für Erläuterungen)
Diagramm mit Näherungswert bei identischem Ppeak und Pplat
Abbildung 2: Näherungswert für Wres bei PCV‑Beatmung und mit identischem Ppeak und Pplat
Diagramm mit Näherungswert und einem Ppeak, der über Pplat liegt
Abbildung 3: Näherungswert für Wres bei PCV‑Beatmung und einem Ppeak, der über Pplat liegt

Ventilator‑related causes of lung injury: the mechanical power.

Gattinoni L, Tonetti T, Cressoni M, et al. Ventilator‑related causes of lung injury: the mechanical power. Intensive Care Med. 2016;42(10):1567‑1575. doi:10.1007/s00134‑016‑4505‑2



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.

Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome.

Costa ELV, Slutsky AS, Brochard LJ, et al. Ventilatory Variables and Mechanical Power in Patients with Acute Respiratory Distress Syndrome. Am J Respir Crit Care Med. 2021;204(3):303‑311. doi:10.1164/rccm.202009‑3467OC

Rationale: Mortality in acute respiratory distress syndrome (ARDS) has decreased after the adoption of lung‑protective strategies. Lower Vt, lower driving pressure (ΔP), lower respiratory rates (RR), and higher end‑expiratory pressure have all been suggested as key components of lung protection strategies. A unifying theoretical explanation has been proposed that attributes lung injury to the energy transfer rate (mechanical power) from the ventilator to the patient, calculated from a combination of several ventilator variables.Objectives: To assess the impact of mechanical power on mortality in patients with ARDS as compared with that of primary ventilator variables such as the ΔP, Vt, and RR.Methods: We obtained data on ventilatory variables and mechanical power from a pooled database of patients with ARDS who had participated in six randomized clinical trials of protective mechanical ventilation and one large observational cohort of patients with ARDS. The primary outcome was mortality at 28 days or 60 days.Measurements and Main Results: We included 4,549 patients (38% women; mean age, 55 ± 23 yr). The average mechanical power was 0.32 ± 0.14 J · min‑1 · kg‑1 of predicted body weight, the ΔP was 15.0 ± 5.8 cm H2O, and the RR was 25.7 ± 7.4 breaths/min. The driving pressure, RR, and mechanical power were significant predictors of mortality in adjusted analyses. The impact of the ΔP on mortality was four times as large as that of the RR.Conclusions: Mechanical power was associated with mortality during controlled mechanical ventilation in ARDS, but a simpler model using only the ΔP and RR was equivalent.

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

Mechanical power and driving pressure as predictors of mortality among patients with ARDS.

Tonna JE, Peltan I, Brown SM, Herrick JS, Keenan HT; University of Utah Mechanical Power Study Group. Mechanical power and driving pressure as predictors of mortality among patients with ARDS. Intensive Care Med. 2020;46(10):1941‑1943. doi:10.1007/s00134‑020‑06130‑2

Effect of mechanical power on intensive care mortality in ARDS patients.

Coppola S, Caccioppola A, Froio S, et al. Effect of mechanical power on intensive care mortality in ARDS patients. Crit Care. 2020;24(1):246. Published 2020 May 24. doi:10.1186/s13054‑020‑02963‑x



BACKGROUND

In ARDS patients, mechanical ventilation should minimize ventilator‑induced lung injury. The mechanical power which is the energy per unit time released to the respiratory system according to the applied tidal volume, PEEP, respiratory rate, and flow should reflect the ventilator‑induced lung injury. However, similar levels of mechanical power applied in different lung sizes could be associated to different effects. The aim of this study was to assess the role both of the mechanical power and of the transpulmonary mechanical power, normalized to predicted body weight, respiratory system compliance, lung volume, and amount of aerated tissue on intensive care mortality.

METHODS

Retrospective analysis of ARDS patients previously enrolled in seven published studies. All patients were sedated, paralyzed, and mechanically ventilated. After 20 min from a recruitment maneuver, partitioned respiratory mechanics measurements and blood gas analyses were performed with a PEEP of 5 cmH2O while the remaining setting was maintained unchanged from the baseline. A whole lung CT scan at 5 cmH2O of PEEP was performed to estimate the lung gas volume and the amount of well-inflated tissue. Univariate and multivariable Poisson regression models with robust standard error were used to calculate risk ratios and 95% confidence intervals of ICU mortality.

RESULTS

Two hundred twenty-two ARDS patients were included; 88 (40%) died in ICU. Mechanical power was not different between survivors and non-survivors 14.97 [11.51-18.44] vs. 15.46 [12.33-21.45] J/min and did not affect intensive care mortality. The multivariable robust regression models showed that the mechanical power normalized to well-inflated tissue (RR 2.69 [95% CI 1.10-6.56], p = 0.029) and the mechanical power normalized to respiratory system compliance (RR 1.79 [95% CI 1.16-2.76], p = 0.008) were independently associated with intensive care mortality after adjusting for age, SAPS II, and ARDS severity. Also, transpulmonary mechanical power normalized to respiratory system compliance and to well-inflated tissue significantly increased intensive care mortality (RR 1.74 [1.11-2.70], p = 0.015; RR 3.01 [1.15-7.91], p = 0.025).

CONCLUSIONS

In our ARDS population, there is not a causal relationship between the mechanical power itself and mortality, while mechanical power normalized to the compliance or to the amount of well-aerated tissue is independently associated to the intensive care mortality. Further studies are needed to confirm this data.

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



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.

Ventilatory settings in the initial 72 h and their association with outcome in out‑of‑hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out‑of‑hospital cardiac arrest (TTM2) trial.

Robba C, Badenes R, Battaglini D, et al. Ventilatory settings in the initial 72 h and their association with outcome in out‑of‑hospital cardiac arrest patients: a preplanned secondary analysis of the targeted hypothermia versus targeted normothermia after out‑of‑hospital cardiac arrest (TTM2) trial. Intensive Care Med. 2022;48(8):1024‑1038. doi:10.1007/s00134‑022‑06756‑4



PURPOSE

The optimal ventilatory settings in patients after cardiac arrest and their association with outcome remain unclear. The aim of this study was to describe the ventilatory settings applied in the first 72 h of mechanical ventilation in patients after out‑of‑hospital cardiac arrest and their association with 6‑month outcomes.

METHODS

Preplanned sub-analysis of the Target Temperature Management-2 trial. Clinical outcomes were mortality and functional status (assessed by the Modified Rankin Scale) 6 months after randomization.

RESULTS

A total of 1848 patients were included (mean age 64 [Standard Deviation, SD = 14] years). At 6 months, 950 (51%) patients were alive and 898 (49%) were dead. Median tidal volume (VT) was 7 (Interquartile range, IQR = 6.2-8.5) mL per Predicted Body Weight (PBW), positive end expiratory pressure (PEEP) was 7 (IQR = 5-9) cmH20, plateau pressure was 20 cmH20 (IQR = 17-23), driving pressure was 12 cmH20 (IQR = 10-15), mechanical power 16.2 J/min (IQR = 12.1-21.8), ventilatory ratio was 1.27 (IQR = 1.04-1.6), and respiratory rate was 17 breaths/minute (IQR = 14-20). Median partial pressure of oxygen was 87 mmHg (IQR = 75-105), and partial pressure of carbon dioxide was 40.5 mmHg (IQR = 36-45.7). Respiratory rate, driving pressure, and mechanical power were independently associated with 6-month mortality (omnibus p-values for their non-linear trajectories: p < 0.0001, p = 0.026, and p = 0.029, respectively). Respiratory rate and driving pressure were also independently associated with poor neurological outcome (odds ratio, OR = 1.035, 95% confidence interval, CI = 1.003-1.068, p = 0.030, and OR = 1.005, 95% CI = 1.001-1.036, p = 0.048). A composite formula calculated as [(4*driving pressure) + respiratory rate] was independently associated with mortality and poor neurological outcome.

CONCLUSIONS

Protective ventilation strategies are commonly applied in patients after cardiac arrest. Ventilator settings in the first 72 h after hospital admission, in particular driving pressure and respiratory rate, may influence 6-month outcomes.

Effect of mechanical power on mortality in invasively ventilated ICU patients without the acute respiratory distress syndrome: An analysis of three randomised clinical trials.

van Meenen DMP, Algera AG, Schuijt MTU, et al. Effect of mechanical power on mortality in invasively ventilated ICU patients without the acute respiratory distress syndrome: An analysis of three randomised clinical trials. Eur J Anaesthesiol. 2023;40(1):21‑28. doi:10.1097/EJA.0000000000001778



BACKGROUND

The mechanical power of ventilation (MP) has an association with outcome in invasively ventilated patients with the acute respiratory distress syndrome (ARDS). Whether a similar association exists in invasively ventilated patients without ARDS is less certain.

OBJECTIVE

To investigate the association of mechanical power with mortality in ICU patients without ARDS.

DESIGN

This was an individual patient data analysis that uses the data of three multicentre randomised trials.

SETTING

This study was performed in academic and nonacademic ICUs in the Netherlands.

PATIENTS

One thousand nine hundred and sixty‑two invasively ventilated patients without ARDS were included in this analysis. The median [IQR] age was 67 [57 to 75] years, 706 (36%) were women.

MAIN OUTCOME MEASURES

The primary outcome was the all-cause mortality at day 28. Secondary outcomes were the all-cause mortality at day 90, and length of stay in ICU and hospital.

RESULTS

At day 28, 644 patients (33%) had died. Hazard ratios for mortality at day 28 were higher with an increasing MP, even when stratified for its individual components (driving pressure ( P  < 0.001), tidal volume ( P  < 0.001), respiratory rate ( P  < 0.001) and maximum airway pressure ( P  = 0.001). Similar associations of mechanical power (MP) were found with mortality at day 90, lengths of stay in ICU and hospital. Hazard ratios for mortality at day 28 were not significantly different if patients were stratified for MP, with increasing levels of each individual component.

CONCLUSION

In ICU patients receiving invasive ventilation for reasons other than ARDS, MP had an independent association with mortality. This finding suggests that MP holds an added predictive value over its individual components, making MP an attractive measure to monitor and possibly target in these patients.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02159196, ClinicalTrials.gov Identifier: NCT02153294, ClinicalTrials.gov Identifier: NCT03167580.

Which component of mechanical power is most important in causing VILI?

Marini JJ, Rocco PRM. Which component of mechanical power is most important in causing VILI?. Crit Care. 2020;24(1):39. Published 2020 Feb 5. doi:10.1186/s13054‑020‑2747‑4

Intra‑cycle power: is the flow profile a neglected component of lung protection?

Marini JJ, Crooke PS, Gattinoni L. Intra‑cycle power: is the flow profile a neglected component of lung protection?. Intensive Care Med. 2021;47(5):609‑611. doi:10.1007/s00134‑021‑06375‑5

Driving pressure and survival in the acute respiratory distress syndrome.

Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372(8):747‑755. doi:10.1056/NEJMsa1410639



BACKGROUND

Mechanical‑ventilation strategies that use lower end‑inspiratory (plateau) airway pressures, lower tidal volumes (VT), and higher positive end‑expiratory pressures (PEEPs) can improve survival in patients with the acute respiratory distress syndrome (ARDS), but the relative importance of each of these components is uncertain. Because respiratory‑system compliance (CRS) is strongly related to the volume of aerated remaining functional lung during disease (termed functional lung size), we hypothesized that driving pressure (ΔP=VT/CRS), in which VT is intrinsically normalized to functional lung size (instead of predicted lung size in healthy persons), would be an index more strongly associated with survival than VT or PEEP in patients who are not actively breathing.

METHODS

Using a statistical tool known as multilevel mediation analysis to analyze individual data from 3562 patients with ARDS enrolled in nine previously reported randomized trials, we examined ΔP as an independent variable associated with survival. In the mediation analysis, we estimated the isolated effects of changes in ΔP resulting from randomized ventilator settings while minimizing confounding due to the baseline severity of lung disease.

RESULTS

Among ventilation variables, ΔP was most strongly associated with survival. A 1-SD increment in ΔP (approximately 7 cm of water) was associated with increased mortality (relative risk, 1.41; 95% confidence interval [CI], 1.31 to 1.51; P<0.001), even in patients receiving "protective" plateau pressures and VT (relative risk, 1.36; 95% CI, 1.17 to 1.58; P<0.001). Individual changes in VT or PEEP after randomization were not independently associated with survival; they were associated only if they were among the changes that led to reductions in ΔP (mediation effects of ΔP, P=0.004 and P=0.001, respectively).

CONCLUSIONS

We found that ΔP was the ventilation variable that best stratified risk. Decreases in ΔP owing to changes in ventilator settings were strongly associated with increased survival. (Funded by Fundação de Amparo e Pesquisa do Estado de São Paulo and others.).