Lung ultrasonography may provide an indirect estimation of lung porosity and airspace geometry.

BACKGROUND: Echographic vertical artifacts (B-lines) in chest ultrasonography have often been associated with pathological patterns. A scientifically sound explanation of these artifacts has not yet been proposed. OBJECTIVES: The 'spongy' nature of the lung in its liquid and solid components and the changes that take place in peripheral airspace (PAS) geometry might be the key point to understanding these phenomena. METHODS: Six excised right rabbit lungs were obtained. Each lung underwent direct ultrasound evaluation in two different conditions: at complete tissue elastic recoil volume and at pulmonary expansion volume achieved by applying a constant positive pressure of 12 cm H2O. Lung volumes and densities were reported in both conditions. Histological examination was performed on three naturally collapsed lungs and on three lungs under positive pressure inflation after having been fixed in formalin solution. RESULTS: Mean volumes of naturally collapsed lungs and fixed expanded lungs were 11.2 ± 0.36 and 44.83 ± 3.03 ml, respectively. Mean densities were 0.622 ± 0.016 and 0.155 ± 0.007 g/ml, respectively. Ultrasound evaluation of collapsed lungs showed dense vertical artifacts and a 'white lung' pattern, while the evaluation of expanded lungs showed hyperechoic line and horizontal artifacts of reflection. Histological evaluation showed a different PAS geometry in collapsed lungs caused by alveolar size reduction and shape changes with unfolded and closed units modifying the peripheral porosity of the frothy nature of the lung. CONCLUSIONS: Airspace geometry, frothy nature and porosity are the determinants of the different behavior of ultrasound interacting with the subpleural lung parenchyma. Chest ultrasound may thus be interpreted as an indirect 'estimator' of lung porosity.

Contrast enhanced ultrasound vs chest x-ray to determine correct central venous catheter position.

PURPOSES: We aimed to analyze the diagnostic accuracy of contrast enhanced ultrasonography (CEUS), compared with chest x-ray (CXR), in the detection of correct central venous line (CVL) placement. Our hypothesis was to verify whether CEUS could substitute CXR as a reference standard for correct placement of CVL or function as a triage test to limit the execution of CXR only for selected patients. BASIC PROCEDURES: CEUS was carried out in 71 non consecutive patients to verify the correct positioning of a central venous line. Sensitivity, specificity, positive and negative predictive values, and likelihood ratios of CEUS compared to CXR, with their respective 95% confidence interval (CI), were calculated. MAIN FINDINGS: CXR identified 6 CVL misplacements (8,4%, CI 95% 3,2%-18%). Four of these were intravascular and 2 in the right atrium. CEUS identified only 3 misplacements, of which 1 was intravascular and 2 intracardiac. Using CXR as a reference standard, and considering intravascular and intracardiac malpositioning altogether, the sensitivity, specificity, and positive and negative likelihood ratio of CEUS were 33% (95% CI, 0%-71%), 98% (95% CI, 95%-100%), 21%, 7%, 0%, and 68%, respectively. The negative and positive predictive values were 94% (95% CI, 89%-100%) and 67% (95% CI, 13%-100%). PRINCIPAL CONCLUSIONS: CEUS can't substitute CXR, or become a triage test in selected patients, in evaluating the correct tip position after CVL placement.

Sonographic interstitial syndrome: the sound of lung water.

OBJECTIVE: Ultrasound lung comets (ULCs) now have an acknowledged correlation with extravascular lung water, but they present in different orders and numbers in different pathologic pulmonary entities. How these artifacts are created is not yet known, and the literature gives discordant hypotheses. Understanding their formation is the first step in understanding lung disease. The purpose of this study was to show the morphologic and genetic variability of interstitial lung disease studied with echography and thus to propose a unitary mechanism for the formation of ULCs. METHODS: This study included 3 parts: (1) a retrospective analysis of echographic lung images of patients with interstitial syndrome; (2) an analysis of the literature for definitions of the size of the pulmonary lobule; and (3) an experimental model of different air-water interfaces scanned with varying ultrasonic frequencies. RESULTS: The retrospective analysis of echographic lung images included 176 patients with diffuse ULCs: 118 patients had acute pulmonary edema; 18 had acute lung injury/acute respiratory distress syndrome; and 40 were premature neonates with respiratory distress syndrome. Experimental models permitted us to discover that ring-down artifacts are produced only by single and double layers of bubbles in specific structural settings. CONCLUSIONS: Reverberation between bubbles with a critical radius seems to be at the origin of ring-down artifacts. Echographic manifestations of interstitial lung disease, whose genesis lies in the partial air loss of lobes and segments, are acoustic phenomena originating from variations in the tissue-fluid relationship of the lung. A correlation between anatomopathologic characteristics and structures of sonographic artifacts could allow more rapid and noninvasive diagnoses.

Occult traumatic pneumothorax: diagnostic accuracy of lung ultrasonography in the emergency department.

BACKGROUND: The role of chest ultrasonography (US) in the diagnosis of pneumothorax (PTX) has been established, but how it compares with lung CT scanning in the diagnosis of radiooccult PTX and in the determination of its topographic extension has not yet been completely evaluated. OBJECTIVE: To determine the diagnostic accuracy of chest US in the emergency department (ED) in the diagnosis of occult PTX in trauma patients and to define its ability to determine PTX extension. DESIGN: An 18-month prospective study. PATIENTS: A total of 109 conscious, spontaneously breathing patients who had been admitted to the ED for chest trauma or polytrauma. METHODS: All eligible patients underwent a standard anteroposterior supine chest radiograph (Rx) and a spiral CT lung scan within 1 h of ED admission. Lung US was carried out by an operator who was unaware of the other examination results, both for diagnosis and for the quantitative delimitation of the PTX. RESULTS: Twenty-five traumatic PTXs were detected in the 218 hemithoraxes (109 patients; 2 patients had a bilateral PTX) evaluated by spiral CT scan; of these, only 13 of 25 PTXs (52%) were revealed by chest Rx (sensitivity, 52%; specificity, 100%), while 23 of 25 PTXs (92%) were identified by lung US with one false-positive result (sensitivity, 92%; specificity, 99.4%). In 20 of 25 cases, there was agreement on the extension of the PTX between CT lung scan and lung US with a mean difference of 1.9 cm (range, 0 to 4.5 cm) in the localization of retroparietal air extension; chest Rx was not able to give quantitative results. CONCLUSIONS: Lung US scans carried out in the ED detect occult PTX and its extension with an accuracy that is almost as high as the reference standard (CT scanning).

Validation of a novel index of hemorrhage using a lower body negative pressure shock model.

BACKGROUND: Vital signs are late indicators of blood loss in trauma patients. Indexed Heart to Arm Time (iHAT) is a non-invasive index based on a modified pulse transit time (mPTT) indexed to the time between R waves on the electrocardiogram (RR interval). We aimed to investigate how early iHAT is able to detect central hypovolemia during the progression from mild to severe simulated hemorrhage induced by applying lower body negative pressure (LBNP). METHODS: Thirty healthy volunteers were enrolled. Central hypovolemia was induced by application of increasing LBNP from 0 to -80 mmHg. At every step, non-invasive blood pressure, heart rate, cardiac echo Doppler measurements and iHAT were recorded. RESULTS: Aortic flow Velocity Time Integral (VTI) reduction from 21.8±3.7 (baseline) to 11.2±3 cm (-70 mmHg) (P<0.001) was progressive with LBNP increase and represented a significant change in stroke volume and preload and induced an increase in heart rate from 69±2 to 107±4 bpm. iHAT increased from 34.2±4.65% (baseline) to 53.9±14.34% (-80 mmHg), P<0.001. The increase in iHAT became significant after -30 mmHg level was reached, corresponding to 500-1000 mL blood loss. CONCLUSIONS: iHAT measures both the reduction in preload and the parabolic heart rate increase due to the linear decrease in stroke volume. iHAT was able to detect a progressive central volume loss in a model of hemorrhage in healthy volunteers undergoing LBNP. A rising trend in iHAT can be a useful marker for progressive volume loss during moderate to severe bleeding.

Ultrasound-guided pleural puncture in supine or recumbent lateral position - feasibility study.

BACKGROUND: The aim of this study is to evaluate feasibility, safety and efficacy of accessing the pleural space with the patient supine or in lateral recumbent position, under constant ultrasonic guidance along the costophrenic sinus. METHODS: All patients with pleural effusion, referred to thoracentesis or pleural drainage from February 2010 to January 2011 in two institutions, were drained either supine or in lateral recumbent position through an echomonitored cannulation of the costophrenic sinus. The technique is described in detail and an analysis of safety and feasibility is carried out. RESULTS: One hundred and one thoracenteses were performed on 76 patients and 30 pigtail catheters were inserted in 30 patients (for a total of 131 pleural procedures in 106 patients enrolled). The feasibility of the procedures was 100% and in every case it was possible to follow real time needle tip passage in the pleural space.Ninety eight thoracenteses (97%) and all catheter drainages were successfully completed. Four thoracenteses were stopped because of the appearance of complications while no pigtail drainage procedure was stopped. After 24 hour follow up, one chest pain syndrome (1.3% of completed thoracenteses) and two pneumothoraces (1.4%) occurred. The mean acquisition time of pleural space was 76 ± 9 seconds for thoracentesis and 185 ± 46 seconds for drainage insertion (p < 0.05). CONCLUSIONS: This study highlights the safety and efficacy of this technique of real time echo-monitored pleural space puncture, that offers a more comfortable patient position, an easier approach for the operator, a very low rate of complications with short acquisition time of pleural space.

Ex vivo lung sonography: morphologic-ultrasound relationship.

Ultrasound (US) interstitial syndrome is a sonographic lung pattern characterized by the presence of acoustic artifacts (B-lines and white lung). The purpose of this study was to demonstrate how interstitial syndrome is determined by acoustic interactions in lungs of variable density and in healthy organs deflated to a nonphysiologic level of density. Normal rabbit lungs were studied ex vivo by US at varying known degrees of inflation, and their histologic appearances were described. In this experimental setting, US interstitial syndrome recognizes a mechanism related to tissue density or porosity. Artifacts (B-lines and white lung) appear in the normal rabbit lung through air-dependent increases in density. As in pathologic conditions, US interstitial syndrome can be reproduced in histologically normal lungs that are deflated to a critical level (>0.45 g/mL) of density, which is not achievable under physiologic conditions.

"Synthetic" comets: a new look at lung sonography.

Ultrasound interstitial syndrome is an echographic pattern of the lung characterized by the presence of multiple acoustic artifacts called "comets" or B-lines. It correlates to increase in extravascular lung water and to interstitial lung disease. From the physical and genetic point of view, the characteristics and the entity of this correlation have not yet been studied. The purpose of this study was to extrapolate past observations and demonstrate how comets or B-lines are artifactual images whose formation is linked to ultrasound interactions on discretely aerated tissues of variable density. Echographic comets were studied by scanning a wet synthetic, partially aerated polyurethane sponge (phantom). Density of the phantom in different drying phases was measured and correlated to the presence of echographic artifacts. Artifacts (comets) showed a different concentration from a completely white artifactual field to presence of rare comets. Their density correlates with porosity and geometry of the phantom. In our opinion, comets represent superficial, artifactual, density and geometry correlated phenomenon due to the acoustic permeability of a broken (collapsed) specular reflector, normally present when the phantom is dry.