Point-of-Care Lung Ultrasound in Emergency Medicine: A Scoping Review With an Interactive Database.

BACKGROUND: This scoping review was conducted to provide an overview of the evidence of point-of-care lung ultrasound (LUS) in emergency medicine. By emphasizing clinical topics, time trends, study designs, and the scope of the primary outcomes, a map is provided for physicians and researchers to guide their future initiatives. RESEARCH QUESTION: Which study designs and primary outcomes are reported in published studies of LUS in emergency medicine? STUDY DESIGN AND METHODS: We performed a systematic search in the PubMed/MEDLINE, Embase, Web of Science, Scopus, and Cochrane Library databases for LUS studies published prior to May 13, 2023. Study characteristics were synthesized quantitatively. The primary outcomes in all papers were categorized into the hierarchical Fryback and Thornbury levels. RESULTS: A total of 4,076 papers were screened and, following selection and handsearching, 406 papers were included. The number of publications doubled from January 2020 to May 2023 (204 to 406 papers). The study designs were primarily observational (n = 375 [92%]), followed by randomized (n = 18 [4%]) and case series (n = 13 [3%]). The primary outcome measure concerned diagnostic accuracy in 319 papers (79%), diagnostic thinking in 32 (8%), therapeutic changes in 4 (1%), and patient outcomes in 14 (3%). No increase in the proportions of randomized controlled trials or the scope of primary outcome measures was observed with time. A freely available interactive database was created to enable readers to search for any given interest (https://public.tableau.com/app/profile/blinded/viz/LUSinEM_240216/INFO). INTERPRETATION: Observational diagnostic studies have been produced in abundance, leaving a paucity of research exploring clinical utility. Notably, research exploring whether LUS causes changes to clinical decisions is imperative prior to any further research being made into patient benefits.

The effects of ultrasound guidance on first-attempt success for difficult peripheral intravenous catheterization: a systematic review and meta-analysis.

Identifying patients at risk of difficult intravenous access (DIVA) and increasing the success rates of peripheral intravenous catheterization (PIVC), preferably on the first catheterization attempt, is of clinical importance. The aim of this study was to compare the use of dynamic ultrasound guidance for PIVC with the traditional technique of visualization and palpation in patients with predicted DIVA. A systematic review and meta-analysis comparing ultrasound-guided PIVC with the traditional technique was performed. Data were systematically collected through MEDLINE and EMBASE databases from inception to March 2021. Eligibility criteria included randomized controlled trials performed on patients meeting criteria for difficult catheterization comprising either (a) no palpable or visible veins, (b) previous history of difficult venous catheterization, (c) patient age less than 4 years, (d) suspicion of difficult catheterization by operator, or (e) two or more unsuccessful attempts using the traditional technique before enrollment were included. For all outcomes, a random-effects meta-analysis using the DerSimonian and Laird method was performed. The primary outcome was the first-attempt success rate, and the secondary outcomes were the overall success rate and the number of attempts for successful intravenous catheterization. Bias was assessed using the Revised Cochrane Risk of Bias tool. Seven studies with a total of 994 patients were included. Patients comprised both children and adults and settings included operating rooms, emergency departments, and intensive care units. Ultrasound guidance was associated with a higher first-attempt success rate (OR, 3.07; 95% CI, 1.66-5.65; P < 0.001). For the secondary outcomes, ultrasound guidance was associated with a higher overall success rate (OR, 3.02; 95% CI, 1.04-8.79; P = 0.04); however, this finding did not meet statistical significance in a sensitivity analysis (OR, 2.90; 95% CI, 0.71-11.93; P = 0.14). Ultrasound was not associated with a significantly different number of attempts compared with the traditional technique (difference in means, 0.14; 95% CI, -0.32 to 0.05; P = 0.15). The use of ultrasound guidance resulted in a three-fold increase in odds for the first-attempt success rate in patients with predicted DIVA compared with the traditional technique of PIVC.

Focused lung ultrasound to predict respiratory failure in patients with symptoms of COVID-19: a multicentre prospective cohort study.

Background: In this study we aimed to assess if a focused lung ultrasound examination predicts the need for mechanical ventilation, admission to an intensive care unit, high-flow oxygen treatment, death from COVID-19 within 30 days and 30-day all-cause mortality in patients with clinical suspicion of COVID-19 or PCR-verified SARS-CoV-2 infection. Methods: A multicentre prospective cohort trial was performed. Film clips from focused lung ultrasound examinations were recorded and rated by blinded observers using different scoring systems. A prediction model was built and used to test relationship between lung ultrasound scores and clinical outcomes. Diagnostic performance of scoring systems was analysed. Results: A total of 3889 film clips of 398 patients were analysed. Patients who had any of the outcomes of interest had a significantly higher ultrasound score than those who did not. Multivariable logistic regression analyses showed that lung ultrasound predicts mechanical ventilation (relative risk 2.44, 95% CI 1.32-5.52), admission to intensive care (relative risk 2.55, 95% CI 1.41-54.59) and high-flow oxygen treatment (relative risk 1.95, 95% CI 1.5-2.53) but not survival when adjusting for sex, age and relevant comorbidity. There was no diagnostic difference in area under the receiver operating characteristic curve between a scoring system using only anterolateral thorax zones and a scoring system that also included dorsal zones. Conclusion: Focused lung ultrasound in patients with clinical suspicion of COVID-19 predicts respiratory failure requiring mechanical ventilation, admission to intensive care units and the need for high-flow oxygen treatment. Thus, focused lung ultrasound may be used to risk stratify patients with COVID-19 symptoms.

Investigating effects of sodium beta-hydroxybutyrate on metabolism in placebo-controlled, bilaterally infused human leg with focus on skeletal muscle protein dynamics.

Systemic administration of beta-hydroxybutyrate (BHB) decreases whole-body protein oxidation and muscle protein breakdown in humans. We aimed to determine any direct effect of BHB on skeletal muscle protein turnover when administered locally in the femoral artery. Paired design with each subject being investigated on one single occasion with one leg being infused with BHB and the opposing leg acting as a control. We studied 10 healthy male volunteers once with bilateral femoral vein and artery catheters. One artery was perfused with saline (Placebo) and one with sodium-BHB. Labelled phenylalanine and palmitate were used to assess local leg fluxes. Femoral vein concentrations of BHB were significantly higher in the intervention leg (3.4 (3.2, 3.6) mM) compared with the placebo-controlled leg (1.9 (1.8, 2.1) mM) with a peak difference of 1.4 (1.1, 1.7) mM, p < 0.0005. Net loss of phenylalanine for BHB vs Placebo -6.7(-10.8, -2.7) nmol/min vs -8.7(-13.8, -3.7) nmol/min, p = 0.52. Palmitate flux and arterio-venous difference of glucose did not differ between legs. Under these experimental conditions, we failed to observe the direct effects of BHB on skeletal muscle protein turnover. This may relate to a combination of high concentrations of BHB (close to 2 mM) imposed systemically by spillover leading to high BHB concentrations in the saline-infused leg and a lack of major differences in concentration gradients between the two sides-implying that observations were made on the upper part of the dose-response curve for BHB and the relatively small number of subjects studied.

Remote real-time supervision via tele-ultrasound in focused cardiac ultrasound: A single-blinded cluster randomized controlled trial.

BACKGROUND: Supervision via tele-ultrasound presents a remedy for lacking on-site supervision in focused cardiac ultrasound, but knowledge of its impact is largely absent. We aimed to investigate tele-supervised physicians' cine-loop quality compared to that of non-supervised physicians and compared to that of experts. METHODS: We conducted a single-blinded cluster randomized controlled trial in an emergency department in western Denmark. Physicians with basic ultrasound competence scanned admitted patients twice. The first scan was non-supervised, and the second was non-supervised (control) or tele-supervised (intervention). Finally, experts in focused cardiac ultrasound scanned the same patient. Two blinded observers graded cine-loops recorded from all scans on a 1-5 scale. The outcome was the mean summarized scan gradings compared with a linear mixed-effects model. RESULTS: In each group, 10 physicians scanned 44 patients. From the mean summarized gradings, on a scale from 4 to 20, the second non-supervised scan grading was 10.9 (95% CI 10.2-11.7), whereas the tele-supervised grading was 12.6 (95% CI: 11.8-13.3). From the first to the second scan, tele-supervised physicians moved 9% (1.09; 95% CI: 1.00-1.19; P = 0.041) closer to the experts' quality than the non-supervised physicians. CONCLUSION: Tele-supervised physicians performed scans of better quality than non-supervised physicians. The present study supports the use of tele-supervision for physicians with basic focused ultrasound competence in a setting where on-site supervision is unavailable.

Remote Real-Time Ultrasound Supervision via Commercially Available and Low-Cost Tele-Ultrasound: a Mixed Methods Study of the Practical Feasibility and Users' Acceptability in an Emergency Department.

Minor emergency departments (ED) struggle to access sufficient expertise to supervise learners of lung and cardiac point-of-care ultrasound (POCUS). Using tele-ultrasound (tele-US) for remote supervision may remedy this situation. We aimed to evaluate the feasibility of real-time supervision via tele-US when applied to an everyday ED clinic. We conducted a mixed methods study that assessed practical feasibility, determined performance, and explored users' acceptability of supervision via tele-US. Technical performance was assessed quantitatively by the ratio in mean gray value between images on site and as received by the supervisor, and by after-compression frame rate. Qualitatively, 12 exploratory semi-structured interviews were conducted with exposed junior doctors and supervisors. Remote supervision via tele-US was performed with 10 junior doctors scanning 45 included patients. During performance assessment, neither alternating internet connection nor software significantly changed the mean gray value ratio. The lowest median frame rate of 4.6 (interquartile range [IQR]: 3.1-5.0) was found by using a 4G internet connection; the highest of 28.5 (IQR: 28.5-29.0) was found with alternative computer and local area network internet connection. In interviews, supervisors stressed the importance of preserving frame rate, and junior doctors emphasized a need for shared ultrasound terminology. In the qualitative analysis, setup mobility, accessibility, and time consumption were emphasized as being of key importance for future clinical implementations. Remote supervision via a commercially available and low-cost tele-US setup is operational for both junior doctors and supervisors when applied to lung and cardiac POCUS scans of hospitalized patients.

A low end-tidal CO2/arterial CO2 ratio during cardiopulmonary resuscitation suggests pulmonary embolism.

INTRODUCTION: Identifying reversible causes of cardiac arrest is challenging. The diagnosis of pulmonary embolism is often missed. Pulmonary embolism increases alveolar dead space resulting in low end-tidal CO2 (EtCO2) relative to arterial CO2 (PaCO2) tension. Thus, a low EtCO2/PaCO2 ratio during resuscitation may be a sign of pulmonary embolism. METHODS: Post hoc analysis of data from two porcine studies comparing ultrasonographic measurements of right ventricular diameter during resuscitation from cardiac arrest of different causes. Pigs were grouped according to cause of arrest (pulmonary embolism, hypovolemia, primary arrhythmia, hypoxia, or hyperkalaemia) and EtCO2/PaCO2 ratios were compared. RESULTS: Data from 54 pigs were analysed. EtCO2 levels at the third rhythm analysis were significantly lower when cardiac arrest was caused by pulmonary embolism than by primary arrhythmia, hypoxia and hyperkalaemia, but there was no significant difference between pulmonary embolism and hypovolemia. In contrast, PaCO2 levels were higher in cardiac arrest caused by pulmonary embolism than in the other causes of cardiac arrest. Consequently, the EtCO2/PaCO2 ratio was lower in pulmonary embolism 0.2 (95%CI 0.1-0.4), than in hypovolaemia 0.5 (95%CI 0.3-0.6), primary arrhythmia 0.7 (95%CI 0.7-0.8), hypoxia 0.5 (95%CI 0.4-0.6), and hyperkalaemia 0.6 (95%CI 0.6-0.7). CONCLUSION: A low EtCO2/PaCO2 ratio during cardiopulmonary resuscitation suggests pulmonary embolism.

Point-of-Care Ultrasound in the Periarrest Setting-Lessons Learned: A Case Report.

Point-of-care ultrasound may elucidate reversible causes of cardiac arrest, and its use is supported by international guidelines in the periarrest setting. We present a case in which the treatment of cardiac arrest caused tension pneumothoraces and cardiac tamponade by pneumopericardium. Both pneumothorax and tamponade were expected to be identified with ultrasound, but were not. Subcutaneous emphysema precluded the diagnosis of pneumothorax. Cardiac imaging was false negative for tamponade, because the latter was caused by air and not fluid. Diagnoses are not to be excluded with inconclusive point-of-care ultrasound examinations, which should prompt further clinical evaluation and imaging.

In a bed or on the floor? - The effect of realistic hospital resuscitation training: A randomised controlled trial.

INTRODUCTION: In-hospital cardiac arrest has a poor prognosis and often occurs in patients lying in a hospital bed. A bed mattress is a soft compressible surface that may decrease cardiopulmonary resuscitation (CPR) quality. Often hospital CPR training is performed with a manikin on the floor. AIM: To study CPR quality following realistic CPR training with a manikin in a bed compared with one on the floor. METHODS: We conducted a randomised controlled study. Healthcare professionals were randomised to CPR training with a manikin in a hospital bed or one on the floor. Data on CPR quality was collected from manikins. The primary outcome measure was chest compression depth. RESULTS: In total, 108 healthcare professionals (age: 40years, female: 94%) were included. The mean chest compression depth was 39mm (standard deviation (SD): 10), for the bed group compared with 38mm (SD: 9) for the floor group, p=0.49. A post hoc analysis showed that regardless of the training method, the participants who optimised their working position by jumping onto the bed or lowering the bed had a median chest compression depth of 39mm (25th-75th percentiles: 33-45) compared with 29mm (25th-75th percentiles: 23-41) for participants who did neither, p=0.04. CONCLUSION: There was no significant difference in chest compression depth between healthcare professionals who trained CPR on a manikin in a hospital bed compared with one on the floor. Chest compression depth was too shallow in both groups. Irrespective of the training method, participants who optimised their working position performed deeper chest compressions.

Timing of focused cardiac ultrasound during advanced life support - A prospective clinical study.

INTRODUCTION: Focused cardiac ultrasound can potentially identify reversible causes of cardiac arrest during advanced life support (ALS), but data on the timing of image acquisition are lacking. This study aimed to compare the quality of images obtained during rhythm analysis, bag-mask ventilations, and chest compressions. METHODS: Adult patients in cardiac arrest were prospectively included during 23 months at a Danish community hospital. Physicians who had completed basic ultrasound training performed subcostal focused cardiac ultrasound during rhythm analysis, bag-mask ventilations, and chest compressions. Image quality was categorised as either useful for interpretation or not. Two echocardiography experts rated images useful for interpretation if all the following characteristics could be determined: 1) right ventricle larger than left ventricle, 2) pericardial fluid, and 3) collapsing ventricles. RESULTS: Images were obtained from 60 of 114 patients undergoing ALS. A higher proportion of the images obtained during rhythm analysis and bag-mask ventilations were useful for interpretation when compared with chest compressions (rhythm analysis vs chest compressions: OR 2.2 (95%CI 1.3-3.8), P = 0.005; bag mask ventilations vs chest compressions: OR 2.0 (95%CI 1.1-3.7), P = 0.03). There was no difference between images obtained during rhythm analysis and bag-mask ventilations (OR 1.1 (95%CI 0.6-2.0), P = 0.74). CONCLUSION: The quality of focused cardiac ultrasound images obtained during rhythm analysis and bag-mask ventilations was superior to that of images obtained during chest compressions. There was no difference in the quality of images obtained during rhythm analysis and bag-mask ventilations. Bag-mask ventilations may constitute an overlooked opportunity for image acquisition during ALS.

The Right Ventricle Is Dilated During Resuscitation From Cardiac Arrest Caused by Hypovolemia: A Porcine Ultrasound Study.

OBJECTIVES: Dilation of the right ventricle during cardiac arrest and resuscitation may be inherent to cardiac arrest rather than being associated with certain causes of arrest such as pulmonary embolism. This study aimed to compare right ventricle diameter during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, or primary arrhythmia (i.e., ventricular fibrillation). DESIGN: Thirty pigs were anesthetized and then randomized to cardiac arrest induced by three diffrent methods. Seven minutes of untreated arrest was followed by resuscitation. Cardiac ultrasonographic images were obtained during induction of cardiac arrest, untreated cardiac arrest, and resuscitation. The right ventricle diameter was measured. Primary endpoint was the right ventricular diameter at the third rhythm analysis. SETTING: University hospital animal laboratory. SUBJECTS: Female crossbred Landrace/Yorkshire/Duroc pigs (27-32 kg). INTERVENTIONS: Pigs were randomly assigned to cardiac arrest caused by either hypovolemia, hyperkalemia, or primary arrhythmia. MEASUREMENTS AND MAIN RESULTS: At the third rhythm analysis during resuscitation, the right ventricle diameter was 32 mm (95% CI, 29-35) in the hypovolemia group, 29 mm (95% CI, 26-32) in the hyperkalemia group, and 25 mm (95% CI, 22-28) in the primary arrhythmia group. This was larger than baseline for all groups (p = 0.03). When comparing groups at the third rhythm analysis, the right ventricle was larger for hypovolemia than for primary arrhythmia (p < 0.001). CONCLUSIONS: The right ventricle was dilated during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, and primary arrhythmia. These findings indicate that right ventricle dilation may be inherent to cardiac arrest, rather than being associated with certain causes of arrest. This contradicts a widespread clinical assumption that in hypovolemic cardiac arrest, the ventricles are collapsed rather than dilated.

Detection of Pulmonary Embolism During Cardiac Arrest-Ultrasonographic Findings Should Be Interpreted With Caution.

OBJECTIVES: The aim of this study was to test the hypothesis that the right ventricle is more dilated during resuscitation from cardiac arrest caused by pulmonary embolism, compared with hypoxia and primary arrhythmia. DESIGN: Twenty-four pigs were anesthetized and cardiac arrest was induced using three different methods. Pigs were resuscitated after 7 minutes of untreated cardiac arrest. Ultrasonographic images were obtained and the right ventricular diameter was measured. SETTING: University hospital animal laboratory. SUBJECTS: Female crossbred Landrace/Yorkshire/Duroc pigs (27-32 kg). INTERVENTIONS: Pigs were randomly assigned to cardiac arrest induced by pulmonary embolism, hypoxia, or primary arrhythmia. MEASUREMENTS AND MAIN RESULTS: There was no difference at baseline. During induction of cardiac arrest, the right ventricle dilated in all groups (p < 0.01 for all). The primary endpoint was right ventricle diameter at the third rhythm analysis: 32 mm (95% CI, 29-36) for pulmonary embolism which was significantly larger than both hypoxia: 23 mm (95% CI, 20-27) and primary arrhythmia: 25 mm (95% CI, 22-28)-the absolute difference was 7-9 mm. Physicians with basic training in focused cardiac ultrasonography were able to detect a difference in right ventricle diameter of approximately 10 mm with a sensitivity of 79% (95% CI, 64-94) and a specificity of 68% (95% CI, 56-80). CONCLUSIONS: The right ventricle was more dilated during resuscitation when cardiac arrest was caused by pulmonary embolism compared with hypoxia and primary arrhythmia. However, the right ventricle was dilated, irrespective of the cause of arrest, and diagnostic accuracy by physicians with basic training in focused cardiac ultrasonography was modest. These findings challenge the paradigm that right ventricular dilatation on ultrasound during cardiopulmonary resuscitation is particularly associated with pulmonary embolism.

Clinical experience and skills of physicians in hospital cardiac arrest teams in Denmark: a nationwide study.

BACKGROUND: The quality of in-hospital resuscitation is poor and may be affected by the clinical experience and cardiopulmonary resuscitation (CPR) training. This study aimed to investigate the clinical experience, self-perceived skills, CPR training and knowledge of the guidelines on when to abandon resuscitation among physicians of cardiac arrest teams. METHODS: We performed a nationwide cross-sectional study in Denmark. Telephone interviews were conducted with physicians in the cardiac arrest teams in public somatic hospitals using a structured questionnaire. RESULTS: In total, 93 physicians (53% male) from 45 hospitals participated in the study. Median age was 34 (interquartile range: 30-39) years. Respondents were medical students working as locum physicians (5%), physicians in training (79%) and consultants (16%), and the median postgraduate clinical experience was 48 (19-87) months. Most respondents (92%) felt confident in treating a cardiac arrest, while fewer respondents felt confident in performing intubation (41%) and focused cardiac ultrasound (39%) during cardiac arrest. Median time since last CPR training was 4 (2-10) months, and 48% had attended a European Resuscitation Council (ERC) Advanced Life Support course. The majority (84%) felt confident in terminating resuscitation; however, only 9% were able to state the ERC guidelines on when to abandon resuscitation. CONCLUSION: Physicians of Danish cardiac arrest teams are often inexperienced and do not feel competent performing important clinical skills during resuscitation. Less than half have attended an ERC Advanced Life Support course, and only very few physicians know the ERC guidelines on when to abandon resuscitation.

Limited public ability to recognise and understand the universal sign for automated external defibrillators.

OBJECTIVE: To study if the public is able to recognise and understand the International Liaison Committee on Resuscitation (ILCOR) sign for automated external defibrillators (AEDs), and to explore how national resuscitation councils have adopted the sign. METHODS: A survey was conducted among travellers in an international airport serving 21 million passengers annually. Participants were asked to state the meaning of six international safety signs, one of which was the ILCOR AED sign. Also, all national resuscitation councils forming ILCOR were contacted to determine whether they recommend the ILCOR AED sign and the existence of national legislation regarding AED signage. RESULTS: In total, 493 travellers (42 nationalities) were included. Correct identification of the ILCOR AED sign was achieved by 39% (95% CI 35% to 43%). Information on AED signage was obtained from 41 of 44 (93%) national resuscitation councils; 26 councils (63%) recommended the use of the ILCOR AED sign. In two countries, the ILCOR AED sign was mandatory by law. CONCLUSIONS: There is limited public recognition and understanding of the ILCOR AED sign. The ILCOR AED sign is not unanimously recommended by national resuscitation councils worldwide. Initiatives promoting public awareness of AEDs are warranted.

Developing an emergency ultrasound app - a collaborative project between clinicians from different universities.

Focused emergency ultrasound is rapidly evolving as a clinical skill for bedside examination by physicians at all levels of education. Ultrasound is highly operator-dependent and relevant training is essential to ensure appropriate use. When supplementing hands-on focused ultrasound courses, e-learning can increase the learning effect. We developed an emergency ultrasound app to enable onsite e-learning for trainees. In this paper, we share our experiences in the development of this app and present the final product.

A framework for implementation, education, research and clinical use of ultrasound in emergency departments by the Danish Society for Emergency Medicine.

The first Danish Society for Emergency Medicine (DASEM) recommendations for the use of clinical ultrasound in emergency departments has been made. The recommendations describes what DASEM believes as being current best practice for training, certification, maintenance of acquired competencies, quality assurance, collaboration and research in the field of clinical US used in an ED.

Animal laboratory training improves lung ultrasound proficiency and speed.

BACKGROUND: Although lung ultrasound (US) is accurate in diagnosing pneumothorax (PTX), the training requirements and methods necessary to perform US examinations must be defined. OBJECTIVE: Our aim was to test whether animal laboratory training (ALT) improves the diagnostic competency and speed of PTX detection with US. METHODS: Twenty medical students without lung US experience attended a 1-day course. Didactic, practical, and experimental lectures covered the basics of US physics, US machines, and lung US, followed by hands-on training to demonstrate the signs of normal lung sliding and PTX. Each student's diagnostic skill level was tested with three subsequent examinations (at day 1, day 2, and 6-month follow-up) using experimentally induced PTX in porcine models. The outcome measures were sensitivity and specificity for US detection of PTX, self-reported diagnostic confidence, and scan time. RESULTS: The students improved their skills between the initial two examinations: sensitivity increased from 81.7% (range 69.1%-90.1%) to 100.0% (range 94.3%-100.0%) and specificity increased from 90.0% (range 82.0%-94.8%) to 98.9% (range 92.3%-100.0%); with no deterioration 6 months later. There was a significant learning curve in choosing the correct answers (p = 0.018), a 1-point increase in the self-reported diagnostic confidence (7.8-8.8 on a 10-point scale; p < 0.05), and a 1-min reduction in the mean scan time per lung (p < 0.05). CONCLUSIONS: Without previous experience and after undergoing training in an animal laboratory, medical students improved their diagnostic proficiency and speed for PTX detection with US. Lung US is a basic technique that can be used by novices to accurately diagnose PTX.

The intrapleural volume threshold for ultrasound detection of pneumothoraces: an experimental study on porcine models.

BACKGROUND: Small pneumothoraxes (PTXs) may not impart an immediate threat to trauma patients after chest injuries. However, the amount of pleural air may increase and become a concern for patients who require positive pressure ventilation or air ambulance transport. Lung ultrasonography (US) is a reliable tool in finding intrapleural air, but the performance characteristics regarding the detection of small PTXs need to be defined. The study aimed to define the volume threshold of intrapleural air when PTXs are accurately diagnosed with US and compare this volume with that for chest x-ray (CXR). METHODS: Air was insufflated into a unilateral pleural catheter in seven incremental steps (10, 25, 50, 100, 200, 350 and 500 mL) in 20 intubated porcine models, followed by a diagnostic evaluation with US and a supine anteroposterior CXR. The sonographers continued the US scanning until the PTXs could be ruled in, based on the pathognomonic US "lung point" sign. The corresponding threshold volume was noted. A senior radiologist interpreted the CXR images. RESULTS: The mean threshold volume to confirm the diagnosis of PTX using US was 18 mL (standard deviation of 13 mL). Sixty-five percent of the PTXs were already diagnosed at 10 mL of intrapleural air; 25%, at 25 mL; and the last 10%, at 50 mL. At an air volume of 50 mL, the radiologist only identified four out of 20 PTXs in the CXR pictures; i.e., a sensitivity of 20% (95% CI: 7%, 44%). The sensitivity of CXR increased as a function of volume but leveled off at 67%, leaving one-third (1/3) of the PTXs unidentified after 500 mL of insufflated air. CONCLUSION: Lung US is very accurate in diagnosing even small amounts of intrapleural air and should be performed by clinicians treating chest trauma patients when PTX is among the differential diagnoses.