Physiological and clinical effects of trunk inclination adjustment in patients with respiratory failure: a scoping review and narrative synthesis.

BACKGROUND: Adjusting trunk inclination from a semi-recumbent position to a supine-flat position or vice versa in patients with respiratory failure significantly affects numerous aspects of respiratory physiology including respiratory mechanics, oxygenation, end-expiratory lung volume, and ventilatory efficiency. Despite these observed effects, the current clinical evidence regarding this positioning manoeuvre is limited. This study undertakes a scoping review of patients with respiratory failure undergoing mechanical ventilation to assess the effect of trunk inclination on physiological lung parameters. METHODS: The PubMed, Cochrane, and Scopus databases were systematically searched from 2003 to 2023. INTERVENTIONS: Changes in trunk inclination. MEASUREMENTS: Four domains were evaluated in this study: 1) respiratory mechanics, 2) ventilation distribution, 3) oxygenation, and 4) ventilatory efficiency. RESULTS: After searching the three databases and removing duplicates, 220 studies were screened. Of these, 37 were assessed in detail, and 13 were included in the final analysis, comprising 274 patients. All selected studies were experimental, and assessed respiratory mechanics, ventilation distribution, oxygenation, and ventilatory efficiency, primarily within 60 min post postural change. CONCLUSION: In patients with acute respiratory failure, transitioning from a supine to a semi-recumbent position leads to decreased respiratory system compliance and increased airway driving pressure. Additionally, C-ARDS patients experienced an improvement in ventilatory efficiency, which resulted in lower PaCO2 levels. Improvements in oxygenation were observed in a few patients and only in those who exhibited an increase in EELV upon moving to a semi-recumbent position. Therefore, the trunk inclination angle must be accurately reported in patients with respiratory failure under mechanical ventilation.

Individualized estimation of arterial carbon dioxide partial pressure using machine learning in children receiving mechanical ventilation.

BACKGROUND: Measuring arterial partial pressure of carbon dioxide (PaCO2) is crucial for proper mechanical ventilation, but the current sampling method is invasive. End-tidal carbon dioxide (EtCO2) has been used as a surrogate, which can be measured non-invasively, but its limited accuracy is due to ventilation-perfusion mismatch. This study aimed to develop a non-invasive PaCO2 estimation model using machine learning. METHODS: This retrospective observational study included pediatric patients (< 18 years) admitted to the pediatric intensive care unit of a tertiary children's hospital and received mechanical ventilation between January 2021 and June 2022. Clinical information, including mechanical ventilation parameters and laboratory test results, was used for machine learning. Linear regression, multilayer perceptron, and extreme gradient boosting were implemented. The dataset was divided into 7:3 ratios for training and testing. Model performance was assessed using the R2 value. RESULTS: We analyzed total 2,427 measurements from 32 patients. The median (interquartile range) age was 16 (12-19.5) months, and 74.1% were female. The PaCO2 and EtCO2 were 63 (50-83) mmHg and 43 (35-54) mmHg, respectively. A significant discrepancy of 19 (12-31) mmHg existed between EtCO2 and the measured PaCO2. The R2 coefficient of determination for the developed models was 0.799 for the linear regression model, 0.851 for the multilayer perceptron model, and 0.877 for the extreme gradient boosting model. The correlations with PaCO2 were higher in all three models compared to EtCO2. CONCLUSIONS: We developed machine learning models to non-invasively estimate PaCO2 in pediatric patients receiving mechanical ventilation, demonstrating acceptable performance. Further research is needed to improve reliability and external validation.

End-tidal carbon dioxide and arterial to end-tidal carbon dioxide gradient are associated with mortality in patients with neurological injuries.

Pre-hospital end-tidal carbon dioxide (EtCO2) monitoring and arterial to end-tidal carbon dioxide gradient (Pa-EtCO2) have been associated with mortality in patients with traumatic brain injury. Our study aimed to analyze the association between alveolar EtCO2 or Pa-EtCO2 and mortality in patients admitted in intensive care unit (ICU) with neurological injuries. In our retrospective analysis from using large de-identified ICU databases (MIMIC-III and -IV and eICU databases), we included 2872 ICU patients with neurological injuries, identified according to the International Classification of Diseases (ICD-9 and -10), who underwent EtCO2 monitoring. We performed logistic regression and extended Cox regression to assess the association between mortality and candidate covariates, including EtCO2 and Pa-EtCO2. In-hospital mortality was 26% (n = 747). In univariate analysis, both the Pa-EtCO2 gradient and EtCO2 levels during the first 24 h were significantly associated with mortality (for a 1 mmHg increase: OR = 1.03 [CI95 1.016-1.035] and OR = 0.94 [CI95 0.923-0.953]; p < 0.001). The association remained significant in multivariate analysis. The time-varying evolution of EtCO2 was independently associated with mortality (for a 1 mmHg increase: HR = 0.976 [CI95 0.966-0.985]; p < 0.001). The time-varying Pa-EtCO2 gradient was associated with mortality only in univariate analysis. In neurocritical patients, lower EtCO2 levels at admission and throughout the ICU stay were independently associated with mortality and should be avoided.

EFFICACY OF NON-INVASIVE VENTILATION WITH EXPIRATORY WASHOUT IN STABLE COPD PATIENTS: A RANDOMIZED CROSS-OVER PILOT.

Background: A non-invasive ventilation (NIV) mask has been designed to deliver NIV with expiratory washout (EW) to improve efficacy of ventilation by optimizing clearance of expired gases from the anatomic dead-space. This study compared the performance and comfort of a novel investigational mask with EW with a conventional mask during NIV therapy.Methods: In this pilot cross-over study, participants with severe stable chronic obstructive pulmonary disease (COPD) attended a single visit to receive bi-level NIV through two masks; the investigational mask with EW, and a conventional mask. The order of mask use was randomly allocated, and each mask was used for 60-minutes with a 30-to-60-minute washout in between. The primary outcome was transcutaneous carbon dioxide (PtCO2) at 60 minutes. Other physiologic and NIV device variables were also assessed.Results: The mean difference [95% CI] in the PtCO2 between the investigational and conventional masks at 60 minutes, adjusted for baseline, was -0.74 mmHg [-2.81 to 1.33, P=0.45]. The investigational mask with EW elicited a lower tidal volume (-128.7 mL [-190.0 to -67.3], P<0.001) and minute ventilation (-2.28 L·min-1 [-3.12 to -1.43], P<0.001), and a higher leak (7.96 L·min-1 [4.39 to 11.54], P<0.001), than the conventional mask. There were no significant differences in other physiological responses or ratings of dyspnoea or comfort.Conclusions: NIV therapy delivered using a novel mask with EW was similarly effective at reducing PtCO2, while the delivered tidal volume and minute ventilation were significantly lower, when compared to a conventional mask in participants with severe COPD.

Decline in Ventilatory Ratio as a Predictor of Mortality in Adults With ARDS Receiving Prone Positioning.

BACKGROUND: Prone positioning reduces mortality in patients with moderate/severe ARDS. It remains unclear which physiological parameters could guide clinicians to assess which patients are likely to benefit from prone position. This study aimed to determine the association between relative changes in physiological parameters at 24 h of prone positioning and ICU mortality in adult subjects with ARDS. METHODS: We conducted a cohort study using the VENTILA database, including adults with ARDS receiving prone positioning. We used multivariable logistic regression to assess the association between relative changes in physiological parameters (PaO2 /FIO2 , dynamic driving pressure, PaCO2 , and ventilatory ratio defined as [minute ventilation [mL/min] × PaCO2 [mm Hg]]/[predicted body weight × 100 [mL/min] × 37.5 [mm Hg] with ICU mortality) (primary outcome). We report adjusted odds ratios with 95% CI as measures of association. RESULTS: We included 156 subjects of which 82 (53%) died in the ICU. A relative decline in the ventilatory ratio at 24 h was associated with lower ICU mortality (odds ratio 0.80 [95% CI 0.66-0.97], every 10% decrease). Relative changes in PaO2 /FIO2 (odds ratio 0.89 [95% CI 0.77-1.03], every 25% increase), PaCO2 (odds ratio 0.97 [95% CI 0.82-1.16], every 10% decrease), and dynamic driving pressure (odds ratio 0.98 [95% CI 0.89-1.07], every 10% decrease) were not associated with ICU mortality. CONCLUSIONS: In subjects with ARDS receiving prone positioning, a relative decline in the ventilatory ratio at 24 h was associated with lower ICU mortality.

Espacio muerto y destete de ventilación mecánica invasiva en residentes de la gran altitud / Dead space and weaning from invasive mechanical ventilation in high-altitude residents

RESUMEN Objetivo Determinar el valor predictivo del cálculo del espacio muerto a través de la fracción espacio muerto/volumen corriente en el destete de la ventilación mecánica invasiva en pacientes críticamente enfermos en la gran altitud. Materiales y métodos Estudio epidemiológico, observacional, analítico y prospectivo realizado en la Unidad de Terapia Intensiva Adultos del Hospital del Norte de la ciudad de El Alto, Bolivia (4090 m s. n. m. y presión barométrica de 453 mmHg) del 01 de noviembre de 2016 al 31 de marzo de 2017. Se estudiaron a los residentes de la gran altitud en ventilación mecánica invasiva. Los criterios de inclusión fueron los siguientes: a) residentes de la altitud hospitalizados en la Unidad de Terapia Intensiva en ventilación mecánica invasiva, b) pacientes con evidencia de resolución de la causa que motivó su conexión al ventilador mecánico invasivo, c) paciente con criterios e índices de destete positivos, d) prueba de respiración espontanea positivo. Las variables estudiadas fueron el espacio muerto a través de la fracción Vd/Vt y su relación con el éxito o fracaso del proceso de destete de ventilación mecánica. Se calculó la fracción Vd/Vt en los pacientes incluidos en el estudio para luego proceder al destete de la ventilación mecánica invasiva. Se dividió a los pacientes en dos grupos según la necesidad de reintubación y reconexión al ventilador mecánico dentro de las 72 horas. Resultados Se incluyeron 21 pacientes: 7 mujeres (33 %) y 14 varones (67 %). La media de edad fue 41 años con desviación estándar de 22,38 años. Dieciocho pacientes (86 %) presentaron éxito y tres (14,00 %) fracasaron en el proceso de destete de la ventilación mecánica invasiva. El valor de Vd/Vt en el grupo éxito y fracaso correspondió a 0,43 vs. 0,53 (p < 0,011109), con una sensibilidad de 0,61 y especificidad de 1; con valor predictivo positivo de 1 y valor predictivo negativo de 0,3. Conclusiones El cálculo del espacio muerto a través de la medida de la fracción espacio muerto/volumen corriente predice el éxito del destete de pacientes críticamente enfermos bajo ventilación mecánica invasiva a gran altitud.

ABSTRACT Objective To determine the predictive value of the dead space calculation through the dead space/tidal volume fraction at weaning from invasive mechanical ventilation in critically ill patients at high altitude. Materials and methods An epidemiological, observational, analytical and prospective study carried out in the Adult Intensive Care Unit of the Hospital del Norte in the city of El Alto, Bolivia (4,090 m a.s.l.; barometric pressure: 453 mm Hg) from November 01, 2016 to March 31, 2017. High-altitude residents under invasive mechanical ventilation were studied. The inclusion criteria were: a) Altitude residents hospitalized in the Invasive Mechanical Ventilation Therapy Intensive Care Unit. b) Patients with evidence of resolution of the cause that prompted their connection to the invasive mechanical ventilator. c) Patients with positive weaning criteria and rates. d) Positive spontaneous respiration test. The study variables were the dead space through the Vd/Vt fraction and its relationship with the success or failure of the weaning process from mechanical ventilation. The Vd/Vt fraction was calculated in the study patients and then weaning from invasive mechanical ventilation was performed. Patients were divided into two groups according to the need for reintubation and reconnection to the mechanical ventilator within 72 hours. Results Twenty-one (21) patients were included: 7 (33 %) women and 14 men (67 %). The mean age was 41 years with a standard deviation of 22.38 years. Eighteen (18) patients (86 %) succeeded and 3 (14 %) failed in the weaning process from invasive mechanical ventilation. The Vd/Vt values in the success and failure groups were 0.43 and 0.53 (p < 0.011109), respectively, with a sensitivity of 0.61 and specificity of 1; a positive predictive value of 1 and a negative predictive value of 0.3. Conclusions The calculation of the dead space through the measurement of the dead space/tidal volume fraction predicts the success of weaning of critically ill patients under invasive mechanical ventilation at high altitude.