Evolution Over Time of Ventilatory Management and Outcome of Patients With Neurologic Disease

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.

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.

Pressure-support compared with pressure-controlled ventilation mitigates lung and brain injury in experimental acute ischemic stroke in rats

BACKGROUND

We aimed to evaluate the pulmonary and cerebral effects of low-tidal volume ventilation in pressure-support (PSV) and pressure-controlled (PCV) modes at two PEEP levels in acute ischemic stroke (AIS).

METHODS

In this randomized experimental study, AIS was induced by thermocoagulation in 30 healthy male Wistar rats. After 24 h, AIS animals were randomly assigned to PSV or PCV with VT = 6 mL/kg and PEEP = 2 cmH2O (PSV-PEEP2 and PCV-PEEP2) or PEEP = 5 cmH2O (PSV-PEEP5 and PCV-PEEP5) for 2 h. Lung mechanics, arterial blood gases, and echocardiography were evaluated before and after the experiment. Lungs and brain tissue were removed for histologic and molecular biology analysis. The primary endpoint was diffuse alveolar damage (DAD) score; secondary endpoints included brain histology and brain and lung molecular biology markers.

RESULTS

In lungs, DAD was lower with PSV-PEEP5 than PCV-PEEP5 (p < 0.001); interleukin (IL)-1β was lower with PSV-PEEP2 than PCV-PEEP2 (p = 0.016) and PSV-PEEP5 than PCV-PEEP5 (p = 0.046); zonula occludens-1 (ZO-1) was lower in PCV-PEEP5 than PCV-PEEP2 (p = 0.042). In brain, necrosis, hemorrhage, neuropil edema, and CD45 + microglia were lower in PSV than PCV animals at PEEP = 2 cmH2O (p = 0.036, p = 0.025, p = 0.018, p = 0.011, respectively) and PEEP = 5 cmH2O (p = 0.003, p = 0.003, p = 0.007, p = 0.003, respectively); IL-1β was lower while ZO-1 was higher in PSV-PEEP2 than PCV-PEEP2 (p = 0.009, p = 0.007, respectively), suggesting blood-brain barrier integrity. Claudin-5 was higher in PSV-PEEP2 than PSV-PEEP5 (p = 0.036).

CONCLUSION

In experimental AIS, PSV compared with PCV reduced lung and brain injury. Lung ZO-1 reduced in PCV with PEEP = 2 versus PEEP = 5 cmH2O, while brain claudin-5 increased in PSV with PEEP = 2 versus PEEP = 5 cmH2O.

The effect of age on clinical outcomes in critically ill brain-injured patients

PURPOSE

We studied the impact of age on survival and functional recovery in brain-injured patients.

METHODS

We performed an observational cohort study of all consecutive adult patients with brain injury admitted to ICU in 8 years. To estimate the optimal cut-off point of the age associated with unfavorable outcomes (mRS 3-6), receiver operating characteristic (ROC) curve analyses were used. Multivariate logistic regression analyses were performed to identify prognostic factors for unfavorable outcomes.

RESULTS

We included 619 brain-injured patients. We identified 60 years as the cut-off point at which the probability of unfavorable outcomes increases. Patients ≥ 60 years had higher severity scores at ICU admission, longer duration of mechanical ventilation, longer ICU and hospital stays, and higher mortality. Factors identified as associated with unfavorable outcomes (mRS 3-6) were an advanced age (≥ 60 years) [Odds ratio (OR) 4.59, 95% confidence interval (CI) 2.73-7.74, p < 0.001], a low GCS score (≤ 8 points) [OR 3.72, 95% CI 1.95-7.08, p < 0.001], the development of intracranial hypertension [OR 5.52, 95% CI 2.70-11.28, p < 0.001], and intracerebral hemorrhage as the cause of neurologic disease [OR 3.87, 95% CI 2.34-6.42, p < 0.001].

CONCLUSION

Mortality and unfavorable functional outcomes in critically ill brain-injured patients were associated with older age (≥ 60 years), higher clinical severity (determined by a lower GCS score at admission and the development of intracranial hypertension), and an intracerebral hemorrhage as the cause of neurologic disease.

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'.

Mechanical Ventilation in Patients with Traumatic Brain Injury: Is it so Different?

Patients with traumatic brain injury (TBI) frequently require invasive mechanical ventilation and admission to an intensive care unit. Ventilation of patients with TBI poses unique clinical challenges, and careful attention is required to ensure that the ventilatory strategy (including selection of appropriate tidal volume, plateau pressure, and positive end-expiratory pressure) does not cause significant additional injury to the brain and lungs. Selection of ventilatory targets may be guided by principles of lung protection but with careful attention to relevant intracranial effects. In patients with TBI and concomitant acute respiratory distress syndrome (ARDS), adjunctive strategies include sedation optimization, neuromuscular blockade, recruitment maneuvers, prone positioning, and extracorporeal life support. However, these approaches have been largely extrapolated from studies in patients with ARDS and without brain injury, with limited data in patients with TBI. This narrative review will summarize the existing evidence for mechanical ventilation in patients with TBI. Relevant literature in patients with ARDS will be summarized, and where available, direct data in the TBI population will be reviewed. Next, practical strategies to optimize the delivery of mechanical ventilation and determine readiness for extubation will be reviewed. Finally, future directions for research in this evolving clinical domain will be presented, with considerations for the design of studies to address relevant knowledge gaps.

"THE MANTLE" bundle for minimizing cerebral hypoxia in severe traumatic brain injury

To ensure neuronal survival after severe traumatic brain injury, oxygen supply is essential. Cerebral tissue oxygenation represents the balance between oxygen supply and consumption, largely reflecting the adequacy of cerebral perfusion. Multiple physiological parameters determine the oxygen delivered to the brain, including blood pressure, hemoglobin level, systemic oxygenation, microcirculation and many factors are involved in the delivery of oxygen to its final recipient, through the respiratory chain. Brain tissue hypoxia occurs when the supply of oxygen is not adequate or when for some reasons it cannot be used at the cellular level. The causes of hypoxia are variable and can be analyzed pathophysiologically following "the oxygen route." The current trend is precision medicine, individualized and therapeutically directed to the pathophysiology of specific brain damage; however, this requires the availability of multimodal monitoring. For this purpose, we developed the acronym "THE MANTLE," a bundle of therapeutical interventions, which covers and protects the brain, optimizing the components of the oxygen transport system from ambient air to the mitochondria.

Validation of the flow index to detect low inspiratory effort during pressure support ventilation

Background

Bedside assessment of low levels of inspiratory effort, which are probably insufficient to prevent muscle atrophy, is challenging. The flow index, which is derived from the analysis of the inspiratory portion of the flow–time waveform, has been recently introduced as a non-invasive parameter to evaluate the inspiratory effort. The primary objective of the present study was to provide an external validation of the flow index to detect low inspiratory effort.

Methods

Datasets containing flow, airway pressure, and esophageal pressure (P_es)–time waveforms were obtained from a previously published study in 100 acute brain-injured patients undergoing pressure support ventilation. Waveforms data were analyzed offline. A low inspiratory effort was defined by one of the following criteria, work of breathing (WOB) less than 0.3 J/L, P_es–time product (PTP_es) per minute less than 50 cmH₂O•s/min, or inspiratory muscle pressure (P_mus) less than 5 cmH₂O, adding “or occurrence of ineffective effort more than 10%” for all criteria. The flow index was calculated according to previously reported method. The association of flow index with P_es-derived parameters of effort was investigated. The diagnostic accuracy of the flow index to detect low effort was analyzed.

Results

Moderate correlations were found between flow index and WOB, P_mus, and PTP_es per breath and per minute (Pearson’s correlation coefficients ranged from 0.546 to 0.634, P < 0.001). The incidence of low inspiratory effort was 62%, 51%, and 55% using the definition of WOB, PTP_es per minute, and P_mus, respectively. The area under the receiver operating characteristic curve for flow index to diagnose low effort was 0.88, 0.81, and 0.88, for the three respective definition. By using the cutoff value of flow index less than 2.1, the diagnostic performance for the three definitions showed sensitivity of 0.95–0.96, specificity of 0.57–0.71, positive predictive value of 0.70–0.84, and negative predictive value of 0.90–0.93.

Conclusions

The flow index is associated with P_es-based inspiratory effort measurements. Flow index can be used as a valid instrument to screen low inspiratory effort with a high probability to exclude cases without the condition.

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

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 (V_T) 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.

Effects of Positive End-Expiratory Pressure on Lung Recruitment, Respiratory Mechanics, and Intracranial Pressure in Mechanically Ventilated Brain-Injured Patients

Background: The pathophysiological effects of positive end-expiratory pressure (PEEP) on respiratory mechanics, lung recruitment, and intracranial pressure (ICP) in acute brain-injured patients have not been completely elucidated. The primary aim of this study was to assess the effects of PEEP augmentation on respiratory mechanics, quantitative computed lung tomography (qCT) findings, and its relationship with ICP modifications. Secondary aims included the assessment of the correlations between different factors (respiratory mechanics and qCT features) with the changes of ICP and how these factors at baseline may predict ICP response after greater PEEP levels.

Methods: A prospective, observational study included mechanically ventilated patients with acute brain injury requiring invasive ICP and who underwent two-PEEP levels lung CT scan. Respiratory system compliance (Crs), arterial partial pressure of carbon dioxide (PaCO₂), mean arterial pressure (MAP), data from qCT and ICP were obtained at PEEP 5 and 15 cmH₂O.

Results: Sixteen examinations (double PEEP lung CT and neuromonitoring) in 15 patients were analyzed. The median age of the patients was 54 years (interquartile range, IQR = 39–65) and 53% were men. The median Glasgow Coma Scale (GCS) at intensive care unit (ICU) admission was 8 (IQR = 3–12). Median alveolar recruitment was 2.5% of total lung weight (−1.5 to 4.7). PEEP from 5 to 15 cmH₂O increased ICP [median values from 14.0 (11.2–17.5) to 23.5 (19.5–26.8) mmHg, p < 0.001, respectively]. The amount of recruited lung tissue on CT was inversely correlated with the change (Δ) in ICP (rho = −0.78; p = 0.0006). Additionally, ΔCrs (rho = −0.77, p = 0.008), ΔPaCO₂ (rho = 0.81, p = 0.0003), and ΔMAP (rho = −0.64, p = 0.009) were correlated with ΔICP. Baseline Crs was not predictive of ICP response to PEEP.

Conclusions: The main factors associated with increased ICP after PEEP augmentation included reduced Crs, lower MAP and lung recruitment, and increased PaCO₂, but none of these factors was able to predict, at baseline, ICP response to PEEP. To assess the potential benefits of increased PEEP in patients with acute brain injury, hemodynamic status, respiratory mechanics, and lung morphology should be taken into account.