Air and its Sonographic Appearance: Understanding the Artifacts.

BACKGROUND: Although air has traditionally been considered a barrier to sonographic imaging, when encountered in unusual settings it can serve as an important indicator of various pathologic states as well. Clinician recognition and thorough understanding of the characteristic pattern of artifacts generated by air are critical for making a number of important diagnoses. CASE SERIES: We present five emergency department cases in which air was visualized in a pathologic location. Pneumothorax, pneumoperitoneum, necrotizing fasciitis, or Fournier's gangrene, and subcutaneous emphysema and pneumomediastinum, can be rapidly and easily identified on ultrasound by the presence of air artifacts. The relevant sonographic findings are described and discussed in this article. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Due to its inherent impedance mismatch with other human tissues, air has a characteristic appearance on ultrasound that includes irregular hyperechoic structures, "dirty shadowing," A-lines, and decreased visualization of deeper structures. Knowledge of the sonographic appearance of air artifacts can assist the physician in making a diagnosis, selecting appropriate additional imaging, and enlisting specialist consultation.

Reliability, Laterality and the Effect of Respiration on the Measured Corrected Flow Time of the Carotid Arteries.

BACKGROUND: Corrected flow time (FTc) measured via sonography of the carotid artery is a novel method that has shown promising results for predicting fluid responsiveness in shock states. It is a rapid and noninvasive examination that can be taught to emergency physicians with ease. However, its reliability has not been assessed, and the effects of several variables, including respiration and side of evaluation, are unclear. OBJECTIVES: The objectives were to compare carotid FTc during different phases of the respiratory cycle, (at end-inspiration and end-expiration), to compare FTc reproducibility among providers, and to compare FTc on the right and left sides in a given individual. METHODS: The FTc of both the right and left carotid arteries was measured in 16 healthy volunteers during an inspiratory hold and an expiratory hold. Examinations were completed by three sonographers blinded to previous results and were analyzed for reliability and reproducibility. RESULTS: Reliability and reproducibility were poor when comparing sonographers under all circumstances. No significant differences were found when comparing left vs. right sides of measurement regardless of respiratory phase. CONCLUSION: Although this method for predicting fluid responsiveness has many promising aspects, reproducibility between sonographers was found to be poor. No significant difference was found between the two sides of the body or respiratory phase.

Ultrasound for the evaluation of soft tissue foreign bodies before and after the addition of fluid to the surrounding interstitial space in a cadaveric model.

BACKGROUND: Point-of-care ultrasound may be used to facilitate foreign body (FB) localization and removal. We hypothesized that injection of normal saline adjacent to an FB may make it easier to detect. METHODS: The study was performed on one embalmed human cadaver. Potential FB sites were created of wood (24), metal (24), and null (24). Two sonographers evaluated each of the 72 sites both before and after a 25-gauge needle was inserted into each incision and 3 cc of normal saline was injected. Accuracy, sensitivity, and specificity were calculated both before and after injection of normal saline. Binomial tests were used to determine the statistical significance of FB detection before and after injection. A 2-tailed Student's t test was used to determine if there was a statistically significant difference between the 2 methods. RESULTS: Preinjection, 116 (81%) of the 144 interpretations (P≤ .001) were correct in their assessment of whether or not an FB was present, with a sensitivity of 81% (95% confidence interval [CI], 72%-88%) and a specificity of 79% (95% CI, 65%-90%). Postinjection, 119 (83%) of these 144 interpretations (P≤ .001) were correct in their assessment of whether or not an FB was present, with a sensitivity of 85% (95% CI, 77%-92%) and a specificity of 77% (95% CI, 63%-88%). This difference was not significant (P=.08; 95% CI, -0.04 to 0.01). DISCUSSION: Ultrasound was reasonably accurate, sensitive, and specific in identifying 1-cm metal and wood FBs. Although accuracy and sensitivity did improve after normal saline injection, this difference was not significant.