Positive End-Expiratory Pressure and Respiratory Rate Modify the Association of Mechanical Power and Driving Pressure With Mortality Among Patients With Acute Respiratory Distress Syndrome

Association between mechanical power and intensive care unit mortality in Korean patients under pressure-controlled ventilation

BACKGROUND

Mechanical power (MP) has been reported to be associated with clinical outcomes. Because the original MP equation is derived from paralyzed patients under volume-controlled ventilation, its application in practice could be limited in patients receiving pressure-controlled ventilation (PCV). Recently, a simplified equation for patients under PCV was developed. We investigated the association between MP and intensive care unit (ICU) mortality.

METHODS

We conducted a retrospective analysis of Korean data from the Fourth International Study of Mechanical Ventilation. We extracted data of patients under PCV on day 1 and calculated MP using the following simplified equation: MPPCV = 0.098 ∙ respiratory rate ∙ tidal volume ∙ (ΔPinsp + positive end-expiratory pressure), where ΔPinsp is the change in airway pressure during inspiration. Patients were divided into survivors and non-survivors and then compared. Multivariable logistic regression was performed to determine association between MPPCV and ICU mortality. The interaction of MPPCV and use of neuromuscular blocking agent (NMBA) was also analyzed.

RESULTS

A total of 125 patients was eligible for final analysis, of whom 38 died in the ICU. MPPCV was higher in non-survivors (17.6 vs. 26.3 J/min, P<0.001). In logistic regression analysis, only MPPCV was significantly associated with ICU mortality (odds ratio, 1.090; 95% confidence interval, 1.029-1.155; P=0.003). There was no significant effect of the interaction between MPPCV and use of NMBA on ICU mortality (P=0.579).

CONCLUSIONS

MPPCV is associated with ICU mortality in patients mechanically ventilated with PCV mode, regardless of NMBA use.

The Impact of Mechanical Energy Assessment on Mechanical Ventilation: A Comprehensive Review and Practical Application

Mechanical ventilation (MV) provides basic organ support for patients who have acute hypoxemic respiratory failure, with acute respiratory distress syndrome as the most severe form. The use of excessive ventilation forces can exacerbate the lung condition and lead to ventilator-induced lung injury (VILI); mechanical energy (ME) or power can characterize such forces applied during MV. The ME metric combines all MV parameters affecting the respiratory system (ie, lungs, chest, and airways) into a single value. Besides evaluating the overall ME, this parameter can be also related to patient-specific characteristics, such as lung compliance or patient weight, which can further improve the value of ME for characterizing the aggressiveness of lung ventilation. High ME is associated with poor outcomes and could be used as a prognostic parameter and indicator of the risk of VILI. ME is rarely determined in everyday practice because the calculations are complicated and based on multiple equations. Although low ME does not conclusively prevent the possibility of VILI (eg, due to the lung inhomogeneity and preexisting damage), individualization of MV settings considering ME appears to improve outcomes. This article aims to review the roles of bedside assessment of mechanical power, its relevance in mechanical ventilation, and its associations with treatment outcomes. In addition, we discuss methods for ME determination, aiming to propose the most suitable method for bedside application of the ME concept in everyday practice.

Invasive mechanical ventilation in patients with acute respiratory distress syndrome receiving extracorporeal support: a narrative review of strategies to mitigate lung injury

Veno-venous extracorporeal membrane oxygenation is indicated in patients with acute respiratory distress syndrome and severely impaired gas exchange despite evidence-based lung protective ventilation, prone positioning and other parts of the standard algorithm for treating such patients. Extracorporeal support can facilitate ultra-lung-protective ventilation, meaning even lower volumes and pressures than standard lung-protective ventilation, by directly removing carbon dioxide in patients needing injurious ventilator settings to maintain sufficient gas exchange. Injurious ventilation results in ventilator-induced lung injury, which is one of the main determinants of mortality in acute respiratory distress syndrome. Marked reductions in the intensity of ventilation to the lowest tolerable levels under extracorporeal support may be achieved and could thereby potentially mitigate ventilator-induced lung injury and theoretically patient self-inflicted lung injury in spontaneously breathing patients with high respiratory drive. However, the benefits of this strategy may be counterbalanced by the use of continuous deep sedation and even neuromuscular blocking drugs, which may impair physical rehabilitation and impact long-term outcomes. There are currently a lack of large-scale prospective data to inform optimal invasive ventilation practices and how to best apply a holistic approach to patients receiving veno-venous extracorporeal membrane oxygenation, while minimising ventilator-induced and patient self-inflicted lung injury. We aimed to review the literature relating to invasive ventilation strategies in patients with acute respiratory distress syndrome receiving extracorporeal support and discuss personalised ventilation approaches and the potential role of adjunctive therapies in facilitating lung protection.

Venovenous extracorporeal CO2 removal to support ultraprotective ventilation in moderate-severe acute respiratory distress syndrome: A systematic review and meta-analysis of the literature

BACKGROUND

A strategy that limits tidal volumes and inspiratory pressures, improves outcomes in patients with the acute respiratory distress syndrome (ARDS). Extracorporeal carbon dioxide removal (ECCO₂R) may facilitate ultra-protective ventilation. We conducted a systematic review and meta-analysis to evaluate the efficacy and safety of venovenous ECCO₂R in supporting ultra-protective ventilation in moderate-to-severe ARDS.

METHODS

MEDLINE and EMBASE were interrogated for studies (2000-2021) reporting venovenous ECCO₂R use in patients with moderate-to-severe ARDS. Studies reporting ≥10 adult patients in English language journals were included. Ventilatory parameters after 24 h of initiating ECCO₂R, device characteristics, and safety outcomes were collected. The primary outcome measure was the change in driving pressure at 24 h of ECCO₂R therapy in relation to baseline. Secondary outcomes included change in tidal volume, gas exchange, and safety data.

RESULTS

Ten studies reporting 421 patients (PaO₂:FiO₂ 141.03 mmHg) were included. Extracorporeal blood flow rates ranged from 0.35-1.5 L/min. Random effects modelling indicated a 3.56 cmH₂O reduction (95%-CI: 3.22-3.91) in driving pressure from baseline (p < .001) and a 1.89 mL/kg (95%-CI: 1.75-2.02, p < .001) reduction in tidal volume. Oxygenation, respiratory rate and PEEP remained unchanged. No significant interactions between driving pressure reduction and baseline driving pressure, partial pressure of arterial carbon dioxide or PaO₂:FiO₂ ratio were identified in metaregression analysis. Bleeding and haemolysis were the commonest complications of therapy.

CONCLUSIONS

Venovenous ECCO₂R permitted significant reductions in ∆P in patients with moderate-to-severe ARDS. Heterogeneity amongst studies and devices, a paucity of randomised controlled trials, and variable safety reporting calls for standardisation of outcome reporting. Prospective evaluation of optimal device operation and anticoagulation in high quality studies is required before further recommendations can be made.