Ultrasound imaging and use of B-lines for functional lung evaluation in neurocritical care: A prospective, observational study

Ultrasound versus Computed Tomography Assessment of Focal Lung Aeration in Invasively Ventilated ICU Patients

It is unknown whether and to what extent the penetration depth of lung ultrasound (LUS) influences the accuracy of LUS findings. The current study evaluated and compared the LUS aeration score and two frequently used B-line scores with focal lung aeration assessed by chest computed tomography (CT) at different levels of depth in invasively ventilated intensive care unit (ICU) patients. In this prospective observational study, patients with a clinical indication for chest CT underwent a 12-region LUS examination shortly before CT scanning. LUS images were compared with corresponding regions on the chest CT scan at different subpleural depths. For each LUS image, the LUS aeration score was calculated. LUS images with B-lines were scored as the number of separately spaced B-lines (B-line count score) and the percentage of the screen covered by B-lines divided by 10 (B-line percentage score). The fixed-effect correlation coefficient (β) was presented per 100 Hounsfield units. A total of 40 patients were included, and 372 regions were analyzed. The best association between the LUS aeration score and CT was found at a subpleural depth of 5 cm for all LUS patterns (β = 0.30, p < 0.001), 1 cm for A- and B1-patterns (β = 0.10, p < 0.001), 6 cm for B1- and B2-patterns (β = 0.11, p < 0.001) and 4 cm for B2- and C-patterns (β = 0.07, p = 0.001). The B-line percentage score was associated with CT (β = 0.46, p = 0.001), while the B-line count score was not (β = 0.07, p = 0.305). In conclusion, the subpleural penetration depth of ultrasound increased with decreased aeration reflected by the LUS pattern. The LUS aeration score and the B-line percentage score accurately reflect lung aeration in ICU patients, but should be interpreted while accounting for the subpleural penetration depth of ultrasound.

Using lung ultrasound to quantitatively evaluate pulmonary water content

BACKGROUND

Increases in extravascular lung water (EVLW) can lead to respiratory failure. This study aimed to investigate whether the B-line score (BLS) was correlated with the EVLW content determined by the lung wet/dry ratio in a rabbit model.

METHODS

A total of 45 New Zealand rabbits were randomly assigned to nine groups. Among the animals, models of various lung water content levels were induced by the infusion of different volumes of warm sterile normal saline (NS) via the endotracheal tube. The arterial blood gas, spontaneous respiratory rate, and PaO₂ /FiO₂ ratio were detected before and after infusion. In addition, the B-lines were determined before and immediately after infusion in each group. Finally, both lungs were resected to determine the wet/dry ratio. In addition, all lung specimens were analyzed histologically, and EVLW was quantified using the BLS based on the number and confluence of B-lines in the intercostal space.

RESULTS

The BLS increased with increasing infusion volume. The BLS was statistically correlated with the wet/dry ratio (r² = .946) and with the PaO₂ /FiO₂ ratio (r² = .916). Furthermore, a repeatability study was performed for the lung ultrasound (LUS) technology (Bland-Altman plots), and the results suggest that LUS had favorable intraobserver and interobserver reproducibility.

CONCLUSIONS

This study is the first to suggest that the BLS can serve as a sensitive, quantitative, noninvasive, and real-time indicator of EVLW in a rabbit model of lung water accumulation. Notably, the BLS displayed an obvious correlation with the experimental gravimetry results and could also be used to predict the pulmonary oxygenation status.

Diagnostic Accuracy of Chest Radiograph, and When Concomitantly Studied Lung Ultrasound, in Critically Ill Patients With Respiratory Symptoms: A Systematic Review and Meta-Analysis

OBJECTIVES

Chest radiograph is considered the first-line diagnostic imaging modality for patients presenting with pulmonary symptoms in the ICU. In this meta-analysis, we aim to evaluate the diagnostic accuracy of chest radiograph, and when concomitantly studied lung ultrasound, in comparison with the gold-standard CT for adult critically ill patients with respiratory symptoms.

DATA SOURCES

PubMed, EMBASE, and Gray literature.

STUDY SELECTION

Studies comparing chest radiograph, and if performed lung ultrasound, with CT for adult ICU patients with respiratory symptoms.

DATA EXTRACTION

Quality was scored with Quality Assessment of Diagnostic Accuracy Studies-2, and study setting, test characteristics, and study design were extracted.

DATA SYNTHESIS

In the meta-analysis, we included 10 full-text studies, including 543 patients, and found that chest radiograph has an overall sensitivity of 49% (95% CI, 40-58%) and specificity of 92% (86-95%). In seven studies, where also lung ultrasound was studied, lung ultrasound had an overall sensitivity of 95% (92-96%) and specificity of 94% (90-97%). Substantial heterogeneity was found. A planned subgroup analysis for individual pathologies was performed. The results of four abstract-only studies, included in the systematic review, were considered unlikely to significantly influence results of our meta-analysis. Study limitations were that most studies were of low power combined with methodological limitations.

CONCLUSIONS

This meta-analysis demonstrates that chest radiograph has a low sensitivity and reasonable specificity compared with CT for detecting lung pathology in critically ill patients. The studies also investigating lung ultrasound, showed lung ultrasound to be clearly superior to chest radiograph in terms of sensitivity with similar specificity, thereby opting to be the first-line diagnostic tool in these patients.

The diagnostic accuracy for ARDS of global versus regional lung ultrasound scores - a post hoc analysis of an observational study in invasively ventilated ICU patients

Background

Semi-quantification of lung aeration by ultrasound helps to assess presence and extent of pulmonary pathologies, including the acute respiratory distress syndrome (ARDS). It is uncertain which lung regions add most to the diagnostic accuracy for ARDS of the frequently used global lung ultrasound (LUS) score. We aimed to compare the diagnostic accuracy of the global versus those of regional LUS scores in invasively ventilated intensive care unit patients.

Methods

This was a post-hoc analysis of a single-center observational study in the mixed medical–surgical intensive care unit of a university-affiliated hospital in the Netherlands. Consecutive patients, aged ≥ 18 years, and are expected to receive invasive ventilation for > 24 h underwent a LUS examination within the first 2 days of ventilation. The Berlin Definition was used to diagnose ARDS, and to classify ARDS severity. From the 12-region LUS examinations, the global score (minimum 0 to maximum 36) and 3 regional scores (the ‘anterior,’ ‘lateral,’ and ‘posterior’ score, minimum 0 to maximum 12) were computed. The area under the receiver operating characteristic (AUROC) curve was calculated and the best cutoff for ARDS discrimination was determined for all scores.

Results

The study enrolled 152 patients; 35 patients had ARDS. The global score was higher in patients with ARDS compared to patients without ARDS (median 19 [15–23] vs. 5 [3–9]; P < 0.001). The posterior score was the main contributor to the global score, and was the only score that increased significantly with ARDS severity. However, the posterior score performed worse than the global score in diagnosing ARDS, and it had a positive predictive value of only 50 (41–59)% when using the optimal cutoff. The combined anterolateral score performed as good as the global score (AUROC of 0.91 [0.85–0.97] vs. 0.91 [0.86–0.95]).

Conclusions

While the posterior score increases with ARDS severity, its diagnostic accuracy for ARDS is hampered due to an unfavorable signal-to-noise ratio. An 8-region ‘anterolateral’ score performs as well as the global score and may prove useful to exclude ARDS in invasively ventilated ICU patients.

Lung Ultrasound as a Bedside Tool for Assessment of Extravascular Lung Water in Critically Ill Head Injured Patients: An Observational Study

Introduction

Extra vascular lung water (EVLW) is defined as the amount of fluid in the interstitial and alveolar spaces. Primary aim of this study was to assess EVLW using lung USG (B lines >3 per lung field) in critically ill head injured patients.

Materials and methods

Intubated adult patients admitted in Trauma ICU with head injury (GCS 4-15) were assessed by daily chest X-ray and lung ultrasonography. Lung water content was graded based on the number of B lines per ICS with score ranging from 0-32 and categorized as low pulmonary fluid burden (0-10), moderate fluid burden (11-20) and high fluid burden (21-32).

Results

140 critically ill head injured patients were assessed for eligibility and 20 excluded. Incidence of increased EVLW using lung USG was 61.66% (74/120) and the incidence reported using chest x ray was 40.83%(49/120) and the difference was statistically significant (p value <0.001). Increased EVLW significantly increased the duration of weaning, mechanical ventilation and ICU stay (p value <0.05). Significant association was observed between APACHE II, SAPS II and GCS at admission to ICU with presence of EVLW (p value ≤0.001). Mean delay in identification of EVLW by chest X-ray (CXR) compared to lung ultrasound was 1.42±0.76 days.

Conclusion

Lung ultrasound is better than CXR for early detection of increased EVLW in critically ill head injured patients and has prognostic relevance as increased EVLW prolongs duration of mechanical ventilation and ICU stay.

How to cite this article

Gattupalli V, Jain K, et al. Lung Ultrasound as a Bedside Tool for Assessment of Extravascular Lung Water in Critically Ill Head Injured Patients: An Observational Study. Indian J Crit Care Med 2019;23(3):131-134.

Pulmonary ultrasound scoring system for intubated critically ill patients and its association with clinical metrics and mortality: A prospective cohort study

PURPOSE

Pulmonary ultrasound (PU) examination at the point-of-care can rapidly identify the etiology of acute respiratory failure (ARF) and assess treatment response. The often-subjective classification of PU abnormalities makes it difficult to document change over time and communicate findings across providers. The study goal was to develop a simple, PU scoring system that would allow for standardized documentation, have high interprovider agreement, and correlate with clinical metrics.

METHODS

In this prospective study of 250 adults intubated for ARF, a PU examination was performed at intubation, 48-hours later, and at extubation. A total lung score (TLS) was calculated. Clinical metrics and final diagnosis were extracted from the medical record.

RESULTS

TLS correlated positively with mortality (P = .03), ventilator hours (P = .003), intensive care unit, and hospital length of stay (P = .003, P = .008), and decreasing PaO₂ /FiO₂ (P < .001). Agreement of PU findings was very good (kappa = 0.83). Baseline TLS and subscores differed significantly between ARF categories (nonpulmonary, obstructive, and parenchymal disease).

CONCLUSIONS

A quick, scored, PU examination was associated with clinical metrics, including mortality among a diverse population of patients intubated for ARF. In addition to diagnostic and prognostic information at the bedside, a standardized and quantifiable approach to PU provides objectivity in serial assessment and may enhance communication of findings between providers.

B-lines score on lung ultrasound as a direct measure of respiratory dysfunction in ICU patients with acute kidney injury

PURPOSE

Fluid overload is frequently found in critically ill patients with acute kidney injury (AKI) and is associated with adverse outcomes. Lung ultrasonography (LUS) and bioimpedance spectroscopy (BIS) are potentially useful tools for the noninvasive volume assessment. We evaluated the utility of these measures, alone or in combination, in estimating the PaO₂/FiO₂ ratio in critical patients with AKI.

METHODS

In a prospective pilot observational study we included 45 patients who presented on admission or developed at any time during intensive care unit stay AKI defined according to KDIGO criteria. Patients were studied at baseline and after 48 h with LUS, BIS and arterial blood gas.

RESULTS

In the univariable analysis, the PaO₂/FiO₂ ratio was negatively correlated with the B-lines score, and this association was maintained even after adjustments. A cutoff value of 17 for the B-lines score has a sensibility of 76% and a specificity of 65% in identifying patients with PaO₂/FiO₂ < 300.

CONCLUSION

LUS can be used for functional lung evaluation and identification of patients with increase pulmonary water content and decrease PaO₂/FiO₂ ratio.

[Basic lung ultrasound. Part 2. Parenchymal diseases]

In this second part, an analysis is made of the pathology of lung parenchyma. This text is structured into different sections, including the study of atelectasias, pneumonia and abscess, interstitial/alveolar or Blines patterns, and finally an analysis is made of pulmonary embolism. With this second part, the basic knowledge to develop lung ultrasound in the anesthesia department has been presented.