Utilization of mechanical power and associations with clinical outcomes in brain injured patients: a secondary analysis of the extubation strategies in neuro-intensive care unit patients and associations with outcome (ENIO) trial

Intracranial response to positive end-expiratory pressure is influenced by lung recruitability and gas distribution during mechanical ventilation in acute brain injury patients: a proof-of-concept physiological study

BACKGROUND

The effect of positive end-expiratory pressure (PEEP) on intracranial pressure (ICP) dynamics in patients with acute brain injury (ABI) remains controversial. PEEP can benefit oxygenation by promoting alveolar recruitment, but its influence on ICP is complex. The primary aims of this study were to investigate 1) how lung recruitability influences oxygenation and 2) how lung recruitability and regional gas distribution, measured via recruitment-to-inflation (RI) ratio and electrical impedance tomography (EIT), affect ICP in response to PEEP changes in critically ill patients in their early phase of ABI.

METHODS

Ten mechanically ventilated ABI patients were included. Pressure reactivity index (PRx) was estimated. Using RI manoeuvre and EIT, lung recruitability and gas distribution were assessed in response to a standardised PEEP change (from high to low levels, with a delta of 10 cmH2O). Changes in ICP (ΔICP) were calculated between high and low PEEP. Lung inhomogeneity indices (global inhomogeneity index [GI] and local inhomogeneity index [LI]) were derived from EIT. Correlations between ventilatory variables and ICP were analysed.

RESULTS

Blood oxygenation significantly decreased, going from high (14 [IQR: 12-15] cmH₂O) to low (4 [IQR: 2-5] cmH₂O) PEEP. Reducing PEEP significantly increased ICP (from 9 [IQR: 5-13] to 12 [IQR: 8-16] mmHg, p < 0.01), while cerebral perfusion pressure (CPP) improved (from 71 [IQR:67-83] to 75 [IQR: 70-84] mmHg, p = 0.03) and mean arterial pressure (MAP) increased (from 79 [IQR: 69-95] to 84 [IQR: 76-99] mmHg, p < 0.01). The RI ratio correlated significantly with ΔICP (rho = 0.87, p < 0.01), as did Vrec% (proportion of recruited volume, rho = 0.65) and GI (rho = 0.5). LI did not correlate with ΔICP. PRx was 0.30 [IQR: 0.12-0.42], indicating a deranged cerebral autoregulation.

CONCLUSIONS

Patients with a higher potential for lung recruitability had a more beneficial effect of PEEP on oxygenation. These effects should be interpreted cautiously, given that lung recruitability and global inhomogeneity of gas distribution significantly influenced the intracranial response to PEEP in ABI patients. As indicated by MAP and CPP, PEEP may impact systemic haemodynamics and cerebral perfusion when cerebral autoregulation is deranged. These findings underscore the importance of multimodal (i.e. respiratory, cerebral and haemodynamics) monitoring for optimising ventilation strategies in ABI patients and provide a framework for future research. Trial registration Registration number: NCT05363085, Date of registration: May 2022.

Association Between Mechanical Power and 28-Day All-Cause Mortality in Chronic Obstructive Pulmonary Disease Patients Undergoing Invasive Ventilation: Analysis of the MIMIC-IV Database

Purpose

Increasing evidence suggests that mechanical power (MP) is associated with mortality among patients undergoing invasive mechanical ventilation. However, the relationship between MP and mortality in chronic obstructive pulmonary disease (COPD) patients undergoing invasive ventilation remains uncertain. The aim of this study was to investigate the association between MP and 28-day all-cause mortality among COPD patients undergoing invasive ventilation.

Patients and Methods

Data were obtained from the Medical Information Mart for Intensive Care (MIMIC-IV) database. COPD patients undergoing invasive ventilation were categorized into three categories based on MP tertiles to further assess the robustness of our results. The primary outcome was 28-day all-cause mortality. The relationship between MP and 28-day all-cause mortality in COPD patients undergoing invasive ventilation was performed to evaluate restricted cubic splines and Cox proportional hazards regression analysis. Receiver operating characteristic (ROC) curves and Kaplan-Meier survival analysis were employed to evaluate and visualize the predictive value of MP for 28-day all-cause mortality. Additionally, the optimal cut-off value of MP was determined. Finally, subgroup analysis was conducted to assess the robustness of the findings.

Results

1704 COPD patients undergoing invasive ventilation (56.92% male) were included in the study. Based on the Cox regression analysis, MP was significantly associated with 28-day all-cause mortality risk in the unadjusted model (Model 1) [HR (95% CI) 1.04 (1.03-1.05), p<0.001]. However, as this is an observational study, causality cannot be inferred. Restricted cubic spline regression models revealed a linear rise in the risk of 28-day mortality as MP increased (P for non-linearity = 0.967). The area under the curve (AUC) for MP was 0.602. This study also identified an optimal cut-off value of 17.38 J/min for MP. Kaplan-Meier survival analysis demonstrated statistically significant differences in survival among invasive ventilation patients stratified by MP tertiles. Subgroup analysis of potential confounding factors indicated no significant interaction between MP and any subgroup (P for interaction: 0.114-0.967).

Conclusion

MP is associated with 28-day all-cause mortality in COPD patients undergoing invasive ventilation. The cut-off value of 17.38 J/min may serve as a reference point for clinicians in assessing disease severity. However, further research is needed to investigate the causal relationship between MP and mortality.

Mechanical power is not associated with mortality in COVID-19 mechanically ventilated patients

BACKGROUND

The relative contribution of the different components of mechanical power to mortality is a subject of debate and has not been studied in COVID-19. The aim of this study is to evaluate both the total and the relative impact of each of the components of mechanical power on mortality in a well-characterized cohort of patients with COVID-19-induced acute respiratory failure undergoing invasive mechanical ventilation. This is a secondary analysis of the CIBERESUCICOVID project, a multicenter observational cohort study including fifty Spanish intensive care units that included COVID-19 mechanically ventilated patients between February 2020 and December 2021. We examined the association between mechanical power and its components (elastic static, elastic dynamic, total elastic and resistive power) with 90-day mortality after adjusting for confounders in seven hundred ninety-nine patients with COVID-19-induced respiratory failure undergoing invasive mechanical ventilation.

RESULTS

At the initiation of mechanical ventilation, the PaO2/FiO2 ratio was 106 (78; 150), ventilatory ratio was 1.69 (1.40; 2.05), and respiratory system compliance was 35.7 (29.2; 44.5) ml/cmH2O. Mechanical power at the initiation of mechanical ventilation was 24.3 (18.9; 29.6) J/min, showing no significant changes after three days. In multivariable regression analyses, mechanical power and its components were not associated with 90-day mortality at the start of mechanical ventilation. After three days, total elastic and elastic static power were associated with higher 90-day mortality, but this relationship was also found for positive end-expiratory pressure.

CONCLUSIONS

Neither mechanical power nor its components were independently associated with mortality in COVID-19-induced acute respiratory failure at the start of MV. Nevertheless, after three days, static elastic power and total elastic power were associated with lower odds of survival. Positive end-expiratory pressure and plateau pressure, however, captured this risk in a similar manner.

Potentially modifiable ventilation factors associated with outcome in neurocritical care vs. non-neurocritical care patients: Rational and protocol for a patient-level analysis of PRoVENT, PRoVENT-iMiC and ENIO (PRIME)

INTRODUCTION

Ventilator settings and ventilation variables and parameters vary between neurocritical care and non-neurocritical care patients. We aim to compare ventilation management in neurocritical care patients versus non-neurocritical care patients under invasive mechanical ventilation support, and to determine which factors related to ventilatory management have an independent association with outcome in neurocritical patients.

METHODS AND ANALYSIS

We meta-analyze harmonized individual patient data from three observational studies ('PRactice of VENTilation in critically ill patients without ARDS' [PRoVENT], 'PRactice of VENTilation in critically ill patients in Middle-income Countries' [PRoVENT-iMiC] and 'Extubation strategies and in neuro-intensive care unit patients and associations with outcomes' [ENIO]), pooled into a database named 'PRIME'. The primary endpoint is all cause ICU mortality. Secondary endpoints are key ventilator settings and ventilation variables and parameters. To identify potentially modifiable and non-modifiable factors contributing to ICU mortality, a multivariable model will be built using demographic factors, comorbidities, illness severities, and respiratory and laboratorial variables. In analyses examining the impact of ventilatory variables on outcome, we will estimate the relative risk of ICU mortality for neurocritical and non-neurocritical care patients by dividing the study population based on key ventilator variables and parameters.

ETHICS AND DISSEMINATION

This meta-analysis will address a clinically significant research question by comparing neurocritical care with non-neurocritical care patients. As this is a meta-analysis, additional ethical committee approval is not required. Findings will be disseminated to the scientific community through abstracts and original articles in peer-reviewed journals. Furthermore, the PRIME database will be made accessible for further post-hoc analyses.

REGISTRATION

PROVENT, PROVENT-iMiC and ENIO, and the pooled database PRIME are registered at clinicaltrials.gov (NCT01868321 for PRoVENT, NCT03188770 for PRoVENT-iMiC, and NCT03400904 for ENIO, and for PRIME is pending).

Ventilation practices in acute brain injured patients and association with outcomes: the VENTIBRAIN multicenter observational study

PURPOSE

Current mechanical ventilation practices for patients with acute brain injury (ABI) are poorly defined. This study aimed to describe ventilator settings/parameters used in intensive care units (ICUs) and evaluate their association with clinical outcomes in these patients.

METHODS

An international, prospective, multicenter, observational study was conducted across 74 ICUs in 26 countries, including adult patients with ABI (e.g., traumatic brain injury, intracranial hemorrhage, subarachnoid hemorrhage, and acute ischemic stroke), who required ICU admission and invasive mechanical ventilation. Ventilatory settings were recorded daily during the first week and on days 10 and 14. ICU and 6-months mortality and 6-months neurological outcome were evaluated.

RESULTS

On admission, 2095 recruited patients (median age 58 [interquartile range 45-70] years, 66.1% male) had a median plateau pressure (Pplat) of 15 (13-18) cmH20, tidal volume/predicted body weight 6.5 (5.7-7.3) mL/Kg, driving pressure 9 (7-12) cmH20, and positive end-expiratory pressure 5 (5-8) cmH20, with no modifications in case of increased intracranial pressure (> 20 mmHg). Significant differences in practices were observed across different countries. The majority of these ventilatory settings were associated with ICU mortality, with the highest hazard ratio (HR) for Pplat (odds ratio 1.50; 95% confidence interval, CI: 1.27-1.78). The results demonstrated consistent association with 6-month mortality; less clear association was observed for neurological outcome.

CONCLUSIONS

Protective ventilation strategies are commonly used in ABI patients but with high variability across different countries. Ventilator settings during ICU stay were associated with an increased risk of ICU and 6-month mortality, but not an unfavorable neurological outcome.

Driving pressure: A useful tool for reducing postoperative pulmonary complications

The operating room is a unique environment where surgery exposes patients to non-physiological changes that can compromise lung mechanics. Therefore, raising clinicians' awareness of the potential risk of ventilator-induced lung injury (VILI) is mandatory. Driving pressure is a useful tool for reducing lung complications in patients with acute respiratory distress syndrome and those undergoing elective surgery. Driving pressure has been most extensively studied in the context of single-lung ventilation during thoracic surgery. However, the awareness of association of VILI risk and patient positioning (prone, beach-chair, park-bench) and type of surgery must be raised.

The Effect of Recruitment Maneuvers on Cerebrovascular Dynamics and Right Ventricular Function in Patients with Acute Brain Injury: A Single-Center Prospective Study

BACKGROUND

Optimization of ventilatory settings is challenging for patients in the neurointensive care unit, requiring a balance between precise gas exchange control, lung protection, and managing hemodynamic effects of positive pressure ventilation. Although recruitment maneuvers (RMs) may enhance oxygenation, they could also exert profound undesirable systemic impacts.

METHODS

The single-center, prospective study investigated the effects of RMs (up-titration of positive end-expiratory pressure) on multimodal neuromonitoring in patients with acute brain injury. Our primary focus was on intracranial pressure and secondarily on cerebral perfusion pressure (CPP) and other neurological parameters: cerebral autoregulation [pressure reactivity index (PRx)] and regional cerebral oxygenation (rSO2). We also assessed blood pressure and right ventricular (RV) function evaluated using tricuspid annular plane systolic excursion. Results are expressed as the difference (Δ) from baseline values obtained after completing the RMs.

RESULTS

Thirty-two patients were enrolled in the study. RMs resulted in increased intracranial pressure (Δ = 4.8 mm Hg) and reduced CPP (ΔCPP = -12.8 mm Hg) and mean arterial pressure (difference in mean arterial pressure = -5.2 mm Hg) (all p < 0.001). Cerebral autoregulation worsened (ΔPRx = 0.31 a.u.; p < 0.001). Despite higher systemic oxygenation (difference in partial pressure of O2 = 4 mm Hg; p = 0.001) and unchanged carbon dioxide levels, rSO2 marginally decreased (ΔrSO2 = -0.5%; p = 0.031), with a significant drop in arterial content and increase in the venous content. RV systolic function decreased (difference in tricuspid annular plane systolic excursion = -0.1 cm; p < 0.001) with a tendency toward increased RV basal diameter (p = 0.06). Grouping patients according to ΔCPP or ΔPRx revealed that those with poorer tolerance to RMs had higher CPP (p = 0.040) and a larger RV basal diameter (p = 0.034) at baseline.

CONCLUSIONS

In patients with acute brain injury, RMs appear to have adverse effects on cerebral hemodynamics. These findings might be partially explained by RM's impact on RV function. Further advanced echocardiography monitoring is required to prove this hypothesis.

Acute Respiratory Failure in Severe Acute Brain Injury

Acute respiratory failure is commonly encountered in severe acute brain injury due to a multitude of factors related to the sequelae of the primary injury. The interaction between pulmonary and neurologic systems in this population is complex, often with competing priorities. Many treatment modalities for acute respiratory failure can result in deleterious effects on cerebral physiology, and secondary brain injury due to elevations in intracranial pressure or impaired cerebral perfusion. High-quality literature is lacking to guide clinical decision-making in this population, and deliberate considerations of individual patient factors must be considered to optimize each patient's care.

Incidence and Outcomes of Acute Respiratory Distress Syndrome in Brain-Injured Patients Receiving Invasive Ventilation: A Secondary Analysis of the ENIO Study

Background: Acute respiratory distress syndrome (ARDS) is an important pulmonary complication in brain-injured patients receiving invasive mechanical ventilation (IMV). We aimed to evaluate the incidence and association between ARDS and clinical outcomes in patients with different forms of acute brain injury requiring IMV in the intensive care unit (ICU). Methods: This was a preplanned secondary analysis of a prospective, multicenter, international cohort study (NCT03400904). We included brain-injured patients receiving IMV for ≥ 24 h. ARDS was the main exposure of interest and was identified during index ICU admission using the Berlin definition. We examined the incidence and adjusted association of ARDS with ICU mortality, ICU length of stay, duration of IMV, and extubation failure. Outcomes were evaluated using mixed-effect logistic regression and cause-specific Cox proportional hazards models. Results: 1492 patients from 67 hospitals and 16 countries were included in the analysis, of whom 137 individuals developed ARDS (9.2% of overall cohort). Across countries, the median ARDS incidence was 5.1% (interquartile range [IQR] 0-10; range 0-27.3). ARDS was associated with increased ICU mortality (adjusted odds ratio (OR) 2.66; 95% confidence interval [CI], 1.29-5.48), longer ICU length of stay (adjusted hazard ratio [HR] 0.59; 95% CI, 0.48-0.73), and longer duration of IMV (adjusted HR 0.54; 95% CI, 0.44-0.67). The association between ARDS and extubation failure approached statistical significance (adjusted HR 1.48; 95% CI 0.99-2.21). Higher ARDS severity was associated with incrementally longer ICU length of stay and longer cumulative duration of IMV. Findings remained robust in a sensitivity analysis evaluating the magnitude of unmeasured confounding. Conclusions: In this cohort of acutely brain-injured patients, the incidence of ARDS was similar to that reported in other mixed cohorts of critically ill patients. Development of ARDS was associated with worse outcomes.

Mechanical Power of Ventilation: From Computer to Clinical Implications

Mechanical ventilation is a lifesaving intervention that may also induce further lung injury by exerting excessive mechanical forces on susceptible lung tissue, a phenomenon termed ventilator-induced lung injury (VILI). The concept of mechanical power (MP) aims to unify in one single variable the contribution of the different ventilatory parameters that could induce VILI by measuring the energy transfer to the lung over time. Despite an increasing amount of evidence demonstrating that high MP values can be associated with VILI development in experimental studies, the evidence regarding the association of MP and clinical outcomes remains controversial. In the present review, we describe the different determinants of VILI, the concept and computation of MP, and discuss the experimental and clinical studies related to MP. Currently, due to different limitations, the clinical application of MP is debatable. Further clinical studies are required to enhance our understanding of the relationship between MP and the development of VILI, as well as its potential impact on clinical outcomes.

Respiratory challenges and ventilatory management in different types of acute brain-injured patients

Acute brain injury (ABI) covers various clinical entities that may require invasive mechanical ventilation (MV) in the intensive care unit (ICU). The goal of MV, which is to protect the lung and the brain from further injury, may be difficult to achieve in the most severe forms of lung or brain injury. This narrative review aims to address the respiratory issues and ventilator management, specific to ABI patients in the ICU.

Brain-lung crosstalk: how should we manage the breathing brain?

Recent studies have drawn increasing attention to brain-lung crosstalk in critically ill patients. However, further research is needed to investigate the pathophysiological interactions between the brain and lungs, establish neuroprotective ventilatory strategies for brain-injured patients, provide guidance on potentially conflicting treatment priorities in patients with concomitant brain and lung injury, and enhance prognostic models to inform extubation and tracheostomy decisions. To bring together such research, BMC Pulmonary Medicine welcomes submissions to its new Collection on 'Brain-lung crosstalk'.