the-basics-of-point-of-care-ultrasound-for-the-general-pediatrician.pdf
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THE BASICS OF POINT-OF-CARE ULTRASOUND FOR THE GENERAL PEDIATRICIAN Table of Contents Section 1. Introduction and Knobology 2 Section 2. Pulmonary POC Ultrasound...
THE BASICS OF POINT-OF-CARE ULTRASOUND FOR THE GENERAL PEDIATRICIAN Table of Contents Section 1. Introduction and Knobology 2 Section 2. Pulmonary POC Ultrasound 8 Section 3. eFAST 14 Section 4. Skin/Soft Tissue POC Ultrasound 18 Section 5. Transabdominal POC of the Adolescent Female 21 Section 6. Miscellaneous - IVC, Bladder Ultrasound 23 Information and Images adapted from Doniger, Stephanie J. Pediatric Emergency and Critical Care Ultrasound. Cambridge: Cambridge University Press, 2013. Print. 1 PLEASE FILL OUT THE FOLLOWING SURVEY AT THE BEGINNING AND END OF EACH PEM ROTATION https://ufl.qualtrics.com/jfe/form/SV_5usSxaJoGJHlN4h 2 Aims Point-of-care (POC) ultrasound is an accessible clinical tool, much like the stethoscope when it was first introduced. It can be interpreted by both skilled and training physicians to augment diagnosing capacities, amplify clinical management, and improve procedural skills. Many other fields in medicine have incorporated its use into practice. Pediatrics continues to evolve in its introduction into several subspecialties, such as emergency medicine, intensive care, rheumatology, and cardiology. However, there are a number of underutilized relevant ultrasound applications that can quickly and easily be utilized in any general pediatrics office. Overall, there are many useful ultrasound modalities and techniques that can be beneficial in the outpatient and inpatient setting. It can be beneficial as it can make care safer with less procedural complications, more efficient bedside diagnosis, and less cost in a diagnostic medical world. The obvious counter arguments against ultrasound stem from their limitations and challenges. Many applications of POC ultrasound require competency and adequate bedside skill use. However, there are numerous studies that indicate that novice sonographers can learn a variety of individual ultrasound applications with good accuracy. In fact, a study indicated that 95.9% of emergency medicine residents were able to reach an “expert-level” of point-of-care ultrasound competency with 25-50 scans of a particular study. Although skepticism of its use in pediatrics exists, ultrasound is meant to be a bedside technique and requires experience. Basic concepts to point of care ultrasound should not be overlooked by a pediatrician as it is a safe and effective diagnosing tool, particularly in austere medical environments. The purpose of this introductory curriculum is to allow our pediatric trainees exposure to POC ultrasound early on in their training through in depth overviews of some common exam techniques, which include pulmonary point-of-care, eFAST, skin and musculoskeletal point-of-care, transabdominal point-of-care ultrasound for adolescent females, and evaluation of the inferior vena cava in hydration status. By exposing and immersing our pediatric residents to the ultrasound machine and transducers, we hope to provide an auxiliary method of bedside diagnosis that will continue to make our graduates well rounded pediatricians of the future. Objectives Implementation of the ultrasound curriculum expects that residents will be able to: 1. Describe the basics of how ultrasound works and knobology to another learner. 2. Perform and interpret pulmonary POC, eFAST, skin and musculoskeletal POC, transabdominal POC of an adolescent female, and IVC evaluation. 3. Acquire at least 5 scans during each pediatric trainee’s first year rotations and 10 scans during their n New second year rotation. Each scan will be verified by an attending and documented as a procedure o Innovations. 4. Inspire increased usage of POC ultrasound in an outpatient, inpatient, ED, and ICU settings. 3 Section 1. Introduction and Knobology Ultrasound Physics and Knobology (54m 00s) Ultrasound Physics and Machinery (20m 49s) https://vimeo.com/46937198 https://vimeo.com/94786374 Physics 00m 14s Transducers 14m 00s Echogenicity 1m 04s Knobology 26m 54s Transducer 2m 23s M-mode 36m 00s Planes 3m 48s Doppler 37m 26s M-Mode 06m 17s Artifacts 44m 30s Doppler 08m 00s Knobology 08m 29s Artifacts 10m 57s The pulse-echo principle in point-of-care (POC) ultrasound is based on the propagation of longitudinal sound waves into the human body and “listens” for returning echoes. Transducers contain piezoelectric ceramic crystals that convert electrical energy into sound waves at 1540 m/s, the average speed of sound in humans at body temperature. ATTENUATION is the loss of energy or weakening of sound waves. Energy is absorbed by surrounding tissues, released as heat, reflected, refracted, or scattered. Reflection is the redirection of sound waves back to its source. Refraction is the redirection of part of the sound wave as two mediums are crossed with different propagation speeds. Scattering occurs when sound waves encounter irregular surfaces or a surface smaller than the sound beam. ACOUSTIC IMPEDANCE refers to the tissue’s resistance to molecular movement, which is directly related to density. Acoustic mismatch is the largest acoustic impedance leading to lesser energy in deeper structures. Acoustic windows are sounds that go through tissues of similar acoustic impedance allowing for deeper penetration. MODES OF SCANNING A-Mode B-Mode (“B” for brightness) is the primary imaging modality in POC ultrasound with 256 shades of gray. Echogenicity stems from intensity or brightness of this imaging. ○ Hyperechoic: structures produce brighter (“whiter”) echoes ○ Hypoechoic: structures give weaker echoes than surrounding tissues ○ Isoechoic: tissues are of similar echogenicity and will be uniform ○ Anechoic: structures do not produce (“black”) echoes M-Mode (“M” for motion) records motion changes along the path of the B-mode image. An x-y plot is created where the y-axis is the distance from the transducer, and the x-axis represents time. Doppler is the change in frequency of the acoustic wave. It analyzes velocity and direction of motion, most notably blood flow. There are several types of Doppler. ○ Audible Doppler ○ Spectral (pulse wave) Doppler ○ Color Doppler shows intensity and direction of movement of higher flow states 4 Know the mnemonic “BART” for “blue away and red toward,” which depicts direction of high flow to the transducer. ○ Power Doppler is similar to Color Doppler although it is more sensitive in detecting frequency shifts in low flow states (ie. testes) TRANSDUCERS (“PROBES”) Ultrasound transducers are produced in different shapes and sizes by several manufacturers. The choice of the transducer must reflect the clinical indication and anatomy. Each transducer has a marker (“indicator”, blue dot), which allows the ultrasonographer to orient with the screen. The screen marker should be oriented to the top-left for ease. GEL is your friend! In order to transmit ultrasound waves, gel or another medium needs to be placed on the transducer footprint. There are non-sterile and sterile forms. Phased/Sector Array Transducer Flat square footprint with clustered crystals, therefore, a pie-shaped image on screen 1.5 to 4 MHz Used in the majority of pediatric cases and useful in cardiac and pulmonary POC Linear Array Transducer Flat rectangular footprint with linearly aligned crystals, therefore, a rectangular image on screen 5 to 12 MHz (highest frequency) Maximum depth of approximately 6 centimeters Useful in vascular POC and ultrasound guided procedures Curvilinear/Convex Array Transducer Curved footprint with crystals in juxtaposition, therefore, a sector-shaped image on screen ○ “Microconvex,” typically available in the NICU, are smaller versions that may be more readily used in the pediatric population. 2 to 5 MHz Useful in abdominal POC. This is rarely used in the pediatric population, unless patients are adult-size TRANSDUCER TECHNIQUES Fanning (“sweeping”) is the act of moving the transducer along an imaginary arc without removing footprint from skin Rocking is the act of tilting with one edge of the transducer off of the skin Rotating is the act of twisting clockwise or counterclockwise 5 Knobology Knobology, referred to as knowledge of “knobs” is the basic understanding of the ultrasound machine’s buttons. Different manufacturers may produce different machines. Know these four buttons on any ultrasound machine. Power. Gain. Depth. Freeze. 6 Resolution is defined as the ability to discriminate two separate objects, otherwise, overall image quality Spatial Resolution is ○ Axial resolution: discriminating objects in the scanning plane ○ Lateral resolution: discriminating objects perpendicular to the scanning plane The inter-relationship between frequency, axial resolution, and depth is fundamental. Resolution and Depth (Penetration) is dependent on Frequency. ○ High frequency >> High Attenuation >> Shallow Depth >> Low Penetration ○ Low frequency >> Low Attenuation >> Deeper Depth >> High Penetration Gain refers to the to “brightness” of the image, like on a computer monitor. As sound travels, it is attenuated through the tissue and the beam weakens. Ultrasound machines are built to counteract attenuation by making deeper images brighter. Gain allows the ultrasonographer to artificially amplify returning signals to the problem. Depth modifies distance between shallow and deeper structures. Increasing depth lengthens ultrasound wave time, which decreases the frame rate. Always begin scanning at the deepest depth. Once your structure of interest is identified, decrease depth. Tic marks alongside the screen are equivalent to 10 mm or 1 cm. Maximizing display of structure on the screen optimizes the depth setting. Zoom enlarges a select area of the image with the same pixels but decreased resolution. Freeze holds the image on the screen. The ultrasonographer can scroll through the frames leading up to the still image as a result. The cine loop, number of still images frozen at a given time, is determined by the manufacturer. 7 Artifacts Artifacts are visual effects that skew physical structures, but their presence may be normal or abnormal depending on the process. ACOUSTIC SHADOWING (“ATTENUATION ARTIFACT”) occurs when sound meets a highly reflective surface that absorb sound energy, leaving behind much less energy to penetrate deeper structures. Highly reflective structures, such as bone and calcifications, allow 30% attenuation, meaning that only 70% of sound energy returns to the transducer. Black (“clean”) shadows occur with bone and calcifications as they are highly reflective. This compares to “dirty” shadows, which occur through air and soft tissue due to acoustic impedance mismatch. Edge artifact, otherwise known as lateral cystic shadowing, arises when sound waves reach curved surfaces, such as a cyst where part of the energy beam is refracted and scattered leading to a thin shadow on each of the lateral sides of the structure. POSTERIOR ACOUSTIC ENHANCEMENT occurs as the ultrasound wave goes through areas of low energy (attenuation), such as abscesses. This allows for more “energy” to reach deeper structures. However, since the ultrasound beam will weaken (attenuate) as it propagates through the structure, the ultrasound machine does not recognize this and “autocorrects” to amplify the echoes of the deeper structures. The amplification of deeper echoes will be overcompensated and be “artificially brighter” as a result. Keep in mind that posterior acoustic enhancement can be corrected by adjusting ‘Gain.’ 8 REVERBERATION ARTIFACTS occur from soundwaves bouncing back and forth between two reflective surfaces. They present as repeating bright arcs that are equidistant, which can often be seen in the lung. 1) A-lines are repetitive equidistant horizontal flat lines seen on Lung POC Ultrasound. A-lines result from sounds reverberating between the lung pleura and the transducer distal to the brighter pleural line. 2) Ring-down (“comet tail”) artifacts occur at interfaces between tissue and air or tissue and foreign body. This appears deep to highly reflective surfaces. B-lines are a type of ring-down artifact. In fact, multiple B-lines are known as lung rockets. MIRROR IMAGE ARTIFACTS occurs when the sound wave reaches strong reflective surfaces. THORACIC ULTRASOUND https://vimeo.com/46515236 @ 8m40s The soundbeam reaches a highly reflective surface (ie. diaphragm), but instead of directly being received by the transducer, it encounters another structure, such as a nodule, and some of the beams return to the transducer while others reflect back to the highly reflective surface before returning to the transducer.Due to the time lapse, the mirror image is found in the far field of the image. The ultrasound machine makes a faulty assumption that the returning echo has only reflected once, but this is not the case. The returning mirror image appears to have returned from the deeper structure, but instead is a simply a secondary reflection. 9 Section 2. Pulmonary Point of Care Ultrasound Thoracic Ultrasound (18:56) Chest Ultrasound CASES (50:03) https://vimeo.com/46515236 https://vimeo.com/51212231 How to Scan 06m 55s B-lines 09m 37s Bat Sign 10m 55s Technique 03m 26s Lung Sliding 12m 35s Mirror Artifact 08m 40s A-lines 13m 48s Pleural Effusion 10m 42s B-lines 15m 50s Pulmonary Edema 14m 23s Pneumothorax 20m 21s Interstitial Disease 14m 42s Trauma Pneumo Algorithm 27m 35s Pneumonia 15m 15s Effusions and Hemothorax 29m 27s Limitations 16m 44s Fractures of Chest Wall 33m 16s Consolidations 36m 14s Pulmonary Contusion 38m 01s Cases 38m 20s Pereda MA, Chavez MA, Hooper-Miele CC et al. Lung Ultrasound for the Diagnosis of Pneumonia in Children: A Meta-analysis. doi: 10.1542/peds.2014-2833 Pulmonary POC can easily be implemented outpatient, in the emergency department, and on the inpatient floor. Pulmonary ultrasound has the benefits of immediate bedside diagnosis of several conditions that have traditionally depended on radiological techniques. Pulmonary ultrasound success is rooted in the evaluation of artifacts to guide diagnosis, rather than anatomical landmarks. A smaller footprint transducer is beneficial to allow for imaging between the ribs; however, it should not be small enough so that ribs cannot be visualized. Remember, artifact is integral for pulmonary point-of-care ultrasound and ribs are necessary as a reference point in comparison to the pleural line and lung sliding. A child’s thinner chest wall and smaller thoracic width allows for optimal pulmonary ultrasound. NORMAL LUNG Pleural line: hyperechoic line deep to ribs Ribs: visual reference and assist with evaluation of artifacts. Posterior shadows are normal as they follow the transducer array (Linear Transducer: parallel rib shadows and image pane will be square/rectangular vs. Phased-array transducer rib shadows are divergent and appear pie-shaped) Scanning approach Longitudinal orientation (vertical) with indicator towards the patient’s head Horizontal orientation (flat) with indicator pointed laterally in the same direction as image pane can be used for increasing the surface of the visualized pleura and very useful for lung sliding. 10 Artifacts “Bat sign”: two rib shadows with pleural line in between seen with longitudinal orientation Lung Sliding Visceral pleura gliding on the parietal pleura creates a straight hyperechoic line which is synchronized with breathing There is slight rough textured appearance to it which is due to reflexion of the ultrasound on the alveolar surface within the parenchyma Prominent lung sliding occurs at the bases where there is maximal pulmonary expansion and pleural gliding “Curtain sign” is a normal finding where aerated lung slides in the image pane covering subdiaphragmatic structures Do not confuse on left chest as cardiac movement can be confused with “lung sliding” A-lines (“A” for “air”) Reverberation artifact between pleura and transducer causing horizontal lines parallel to the pleural line that is best seen when perpendicularly scanned Generated by the presence of air (normal or pathologic) B-lines This is a type of reverberation artifact, most specifically a ring down artifact Pathologic thickening of the alveolar septa and/or fluid filling the alveoli which is surrounded by air causes hyperintense reverberation artifact and appear as “laser like” hyperechoic parallel lines 11 B-lines present with any disease that causes extravascular lung fluid +/- interstitial thickening +/- alveolar fluid accumulation. B-lines are highly sensitive for: acute respiratory distress syndrome (ARDS) infantile respiratory distress syndrome (RDS) transient tachypnea of the newborn (RRN) cardiopulmonary edema interstitial pneumonia pulmonary contusion B-lines must do the following 1) multiple hyperechoic well defined vertical lines that start at pleural line 2) move with lung sliding (respiration) 3) extend off of the screen 4) erase A-lines However, few isolated B-lines may be seen in normal lung bases therefore, greater than 3 B-lines on a scan is always pathologic and referred to as lung rockets, as normal lung will rarely have more than 8 B-lines in the entire pulmonary surface. C-lines “C” for “consolidation” C-lines are not artifact but rather the contact between soft tissue and visceral pleura Hypoechoic to intermediate echogenicity For instance, ARDS may show multiple small subpleural consolidations that are seen in more affected regions Air bronchograms can be seen within consolidations 12 M-mode essentially is reflection artifact deep to the pleural line. When dynamic, pleural movement synchronizes with a “sparkling pattern” ○ Immobile chest wall are the horizontal lines (ocean) ○ Sparkling artifact appears as grainy (sandy beach) Normal seashore sign shows waves s uperficially and beach deeper. See left side of image above. Lung pulse: “short and rapid” seashore sign due to adequate pleural contact but no pulmonary expansion. Rhythmic cardio-synchronous visceral pleural movement that appears to be a “short and rapid” version of the seashore sign. When does it occur? Complete atelectasis, Apnea, Right mainstem intubation. Abnormal stratosphere sign (pneumothorax) is caused by the lack of scatter attributed by the alveoli. Ultrasound beam immediately reflects back from the free air directly beneath the parietal pleura. Artifact deep to the pleural line will be static. All you will see are waves! PNEUMONIA & ATELECTASIS Well organized pneumonias are great conductors of ultrasound waves Pneumonia is seen primarily as an alveolar process that increases secretions in larger airways. There is no initial airway obstruction and airflow allows secretions to move to-and-fro in the bronchi dynamic air bronchogram sign = pathognomonic Surrounding B-lines differentiate pneumonia and atelectasis from other causes of consolidation PNEUMONIA: Early pneumonia: multiple small (less than 1 cm) C-lines with B-lines or confluent B-lines Hepatization of the lung is seen when dense consolidation occurs above the diaphragm ATELECTASIS: Atelectasis resorbs air distal to an occluded airway causing static air bronchograms. When lung retracts secondary to the absorption of trapped air, it causes volume reduction and brings bronchovascular structures closer and parallel. Airways with large fluid and no air movement resemble vessels (fluid bronchograms) and are typical of post-obstructive pneumonias. However vessels are hypoechoic and show a Doppler sign. 13 PULMONARY EDEMA Severe Pulmonary Edema generates sonographic white lung as B-lines overtake the entire pulmonary surface. Absent B-lines excludes cardiogenic pulmonary edema in 100% of cases. PLEURAL EFFUSION Atelectatic parenchyma is seen as soft tissue “floating” in the effusion with B-lines representative of an irregular margin of transition to the deeper aerated lungs. More easily detected in the seated patient. Visualized as an anechoic layer overlying the parenchyma INTERSTITIAL SYNDROMES (TTN and RDS) Interstitial Syndromes presents with multiple B-lines dues to an increase in extravascular fluid More easily detected in the seated patient. All Interstitial Syndromes must have: 1) 3 or more B-lines present 50% is strongly associated with a low central venous pressure, although recent studies are controversial in those less than 5 years of age. Regardless, it is a good and easy adjunct test for fluid status in any setting. The walls of the IVC should not “kiss” if adequately hydrated. 25 Patient Positioning should be in the supine position. Gentle pressure may be applied to displace bowel gas which can obstruct the view of the IVC. Subxiphoid Transverse View Place the transducer just caudal to the xiphoid process with the indicator oriented towards the patient’s right side. The transducer is oriented perpendicular to the patient’s body to achieve an accurate cross-section of the IVC. Subxiphoid Longitudinal View Same as above, but rotate the transducer 90 degrees clockwise, with the indicator pointed towards the patient’s head. The transducer should be angled slightly towards the patient’s right. 26 Bladder Volume Use the phased array transducer. Locate the pubic symphysis by manual palpation. Place the transducer immediately superior to the pubic symphysis. Slowly angle inferiorly into the pelvis. Begin with the Transverse View (indicator towards patient’s right) before the Sagittal View (indicator toward patient’s head). Always scan both planes. Freeze images to obtain measurements. A full bladder will appear spherical, and a small bladder volume will appear trapezoidal. There are several correction factors, but 0.75 is very commonly used and easily remembered. Any volume more than 3 mL is usually adequate for urine collection via catheterization in 98% of children. 27
