Residual Volume

BackgroundAlveolar volume measured according to the American Thoracic Society-European Respiratory Society (ATS-ERS) guidelines during the single breath diffusion test can be underestimated when there is maldistribution of ventilation. Therefore, the alveolar volume calculated by taking into account the ATS-ERS guidelines was compared to the alveolar volume measured from sequentiallly collected samples of the expired volume in two groups of individuals: COPD patients and healthy individuals. The aim of this study was to investigate the effects of the maldistribution of ventilation on the real estimate of alveolar volume and to evaluate some indicators suggestive of the presence of maldistribution of ventilation.MethodsThirty healthy individuals and fifty patients with moderate-severe COPD were studied. The alveolar volume was measured either according to the ATS-ERS guidelines or considering the whole expired volume subdivided into five quintiles. An index reflecting the non-uniformity of the distribution of ventilation was then derived (DeltaVA/VE).ResultsSignificant differences were found when comparing the two measurements and the alveolar volume by quintiles appeared to have increased progressively towards residual volume in healthy individuals and much more in COPD patients. Therefore, DeltaVA/VE resulted in an abnormal increase in COPD.ConclusionThe results of our study suggest that the alveolar volume during the single breath diffusion test should be measured through the collection of a sample of expired volume which could be more representative of the overall gas composition, especially in the presence of uneven distribution of ventilation. Further studies aimed at clarifying the final effects of this way of calculating the alveolar volume on the measure of DLCO are needed. DeltaVA/VE is an index that can help assess the severity of inhomogeneity in COPD patients.

BackgroundPulmonary aspiration of gastric contents is a serious clinical complication, particularly in patients receiving enteral nutrition or undergoing anesthesia. Gastric residual volume (GRV) is a commonly used surrogate marker that can identify delayed gastric emptying and enteral nutrition intolerance, both of which may increase the risk of aspiration. Traditional methods for measuring GRV are invasive and lack standardization. Point-of-care ultrasound (PoCUS) has emerged as a promising, noninvasive bedside alternative. Despite its growing clinical use, there is still no consolidated guidance on PoCUS procedures for GRV assessment in adult patients.ObjectiveThis scoping review aims to map and synthesize the available evidence on procedural techniques, interpretation criteria, and decision-making applications related to PoCUS for GRV assessment.MethodsThis scoping review will follow the JBI Collaboration methodology and will be reported in accordance with the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols extension for Scoping Reviews) guidelines. The PCC (population, concept, and context) mnemonic guided the formulation of the research question. Systematic searches will be conducted in MEDLINE, CINAHL, Embase, Scopus, Cochrane Library, and LILACS, as well as in gray literature sources. Eligible sources will include primary studies, reviews, and clinical guidelines focused on PoCUS for GRV assessment in adults (aged ≥18 years). Two independent reviewers will perform study screening and data extraction. The synthesis will be structured using the I-AIM (indication, acquisition, interpretation, and medical decision-making) framework. Results will be summarized narratively, in tables, and through visual representations such as flowcharts and conceptual diagrams.ResultsThis protocol was registered on the Open Science Framework registry on August 21, 2025. The literature search began on April 3, 2026, with study selection and data extraction planned for May 2026. The final results are expected to be submitted for publication in July 2026. As this is a protocol study, no results are available yet.ConclusionsThis review will identify and categorize the procedures, technical parameters, and clinical applications of PoCUS for GRV assessment in adult patients. By mapping the existing evidence, the findings may inform future research, educational curricula, and the development of clinical guidelines for nurses. In addition, the review will highlight methodological gaps and variations in practice that may affect the safe and effective use of PoCUS across diverse health care settings.

Background/objectivesElevated gastric residual volume (GRV) is traditionally read as feeding intolerance, and randomized trials in general intensive care units (ICUs) have discredited its routine use. Whether this holds in neurocritical patients is unknown.MethodsThis exploratory, hypothesis-generating single-center retrospective cohort study comprised 355 neurosurgical ICU adults with documented GRV (2022-2026)-the exposure was a peak GRV ≥ 250 mL, the institutional feeding-hold threshold (n = 32). Three explanations were examined: prognosis (Firth penalized regression for in-hospital mortality), nutrition (standardized mean differences with causal mediation), and intracranial pathology (rank-based partial correlation between patient-level maxima of GRV and intracranial pressure (ICP) in the same early ICU window, plus trajectory phenotyping).ResultsElevated GRV was not significantly associated with in-hospital mortality (adjusted odds ratio 1.46; 95% confidence interval (CI) 0.52-3.65) and was not associated with greater deterioration in laboratory-based systemic inflammatory/nutritional indices than in comparators, with null mediation. The patient-level maxima of GRV and ICP were correlated before adjustment (ρ = 0.28) and 0.19 after full adjustment (95% CI -0.001 to 0.37, p = 0.051; 10 exposed of 109), and intracranial hypertension (ICP > 22 mmHg) occurred in 90% of exposed versus 61% of unexposed monitored patients. A high-GRV trajectory phenotype was the youngest class yet showed the most frequent intracranial hypertension, although its membership and persistence were highly sensitive to missing-data handling.ConclusionsIn neurocritical patients receiving enteral tube feeding with documented GRV monitoring, elevated GRV was not associated with greater deterioration in laboratory-based systemic inflammatory/nutritional indices, whereas a possible association with higher early ICP was observed in a small, monitored subset. Because the ICP-monitored subset was small, these exploratory, hypothesis-generating findings do not establish a brain-gut signal. They raise the hypothesis that elevated GRV in this setting may reflect intracranial rather than solely gastrointestinal processes and require prospective confirmation with temporally paired measurements.