Lens dislocation will appear as displacement of the small, oblong structure from this usual resting place into the anterior or posterior chamber, and has been well described in ophthalmology literature [ 12 ]. Retinal detachment has also been well described and will appear as a flat, worm-like structure in the posterior chamber that moves with eye movement and is attached at one or two points to the posterior wall. Vitreous hemorrhage will also appear in the posterior chamber as a heterogeneous mass of swirling gray material within the black globe, often likened to seaweed swaying in the waves with eye movement [ 11 , 12 , 51 ].
A relatively new application of ocular ultrasound is to indirectly assess for increased intracranial pressure ICP due to processes such as traumatic brain injury, intracranial bleeding, hydrocephalus or a hypertensive emergency. The globe provides a good acoustic window for visualization of the optic nerve, which appears as a large hypoechoic stripe posterior to the globe. Using a stricter cutoff of greater than 5. For increased ICP that is sudden onset, it has been shown that immediate intervention to decrease ICP also leads to resolution of the ultrasound findings [ 54 ].
Ocular injuries are a common presentation to the emergency department, and foreign bodies are involved in many cases. Sonography can detect foreign bodies within the globe, which typically appear as a twinkling object and a comet-tail-shaped reverberation artifact posteriorly. Ocular ultrasound has a sensitivity of However, care must be taken to avoid pressure on a potential open globe secondary to a foreign body.
If open glove is suspected, other imaging modalities such as CT are preferred [ 51 ]. Deep venous thrombosis DVT is commonly asymptomatic, however suspicion for the pathology increases with unilateral pain and swelling of an extremity. Ultrasound is the exam of choice for the initial evaluation of an extremity for DVT. The highest yield exam is for a symptomatic patient, and it has much lower sensitivity for asymptomatic extremities.
However, those who advocate for whole leg ultrasound point out that finding the isolated calf DVT obviates the need for a repeat scan at a later time, which is recommended with a negative two-point compression scan [ 12 ]. Two-point compression studies involve complete compression of the common femoral and greater saphenous vein in the inguinal area, and of the popliteal vein in the popliteal fossa of the posterior knee. The veins should compress to a very thin line, and inability to fully compress may indicate a DVT.
These structures can be better characterized by placing color Doppler over the structure and evaluating for flow. In low-flow states, squeezing the calf can help to provide extra venous return and allow easier identification [ 12 ].follow link
Emergency Medicine Ultrasound Fellowship | OHSU
Ultrasound exams of soft tissue and bone focus on superficial structures, utilizing the linear probe. The different components of soft tissue are easy to differentiate. Skin will be the hyperechoic layer just below the transducer surface, subcutaneous tissue is the hypoechoic layer below the skin, muscle will appear relatively hypoechoic more than subcutaneous tissue and feather-like with linear striations, tendons are hyperechoic and fibrillary, and bone is linear and hyperechoic with shadowing posteriorly [ 11 ].
This is differentiated from a frank fluid collection indicative of an abscess, which will require incision and drainage, versus cellulitis, which is managed using antibiotics alone [ 12 ]. Two views can be helpful as the purulent material within an abscess can have increased echogenicity and a collection may be missed, especially if it is a thin collection in the anterior-posterior plane. Sonography can be used to demonstrate nearby vasculature prior to incision and drainage of an abscess to determine optimal incision location [ 11 , 12 ]. Evaluation of tendons for potential rupture can be performed bedside, and will appear as a break in the normal linear appearance, potentially with hypoechoic hemorrhage separating the two parts [ 12 ].
A similar finding is noted in fractures. Ultrasound evaluation of bones clearly demonstrates the hyperechoic, linear cortex. In a suspected fracture, the ultrasound probe is scanned along the bone looking for defects or discontinuity of the cortex. Patient history and physical examination have poor accuracy in determining the presence of a fracture in trauma.
Ultrasound is less accurate if a fracture occurs close to a joint, but additional evidence such as soft tissue swelling or a hypoechoic hematoma adjacent to the bone provide clues that a fracture may be present [ 9 , 11 ]. When the ultrasound is used for procedural guidance, precautions are taken to keep the probe sterile. A probe cover and sterile gel are used for this purpose, and some procedural kits are found where ultrasound guidance has become more standardized.
Since most procedures using ultrasound guidance involve superficial structures, the linear probe is regularly utilized. The orientation of the probe becomes critical, as movements of equipment on the screen, such as needles, need to correlate with movement relative to the patient [ 11 ]. There are two general methods for procedure guidance using ultrasound: static and dynamic.
Static guidance usually entails either visualization of internal structures before the procedure to mark the ideal entry site, or post-procedure to verify success. Dynamic guidance entails visualization during the actual procedure [ 12 ]. Insertion of intravenous catheters using visual guidance is one of the most common procedural uses for the ultrasound [ 56 , 57 , 58 ]. Ultrasound-guided peripheral and central line placement is nearly always performed dynamically, watching the needle advance until there is successful cannulation of the vein.
Peripheral vein cannulation uses either 1. Ultrasound guidance is most useful in patients with difficult IV access, such as obese, young, IV drug abusing or prior chemotherapy patients. In general, there are two methods to visualize dynamic IV placement. In the transverse approach, the probe is held perpendicular to the vessel. The probe can be used to apply compression and differentiate artery from vein. This allows visualization of the needle tip, which appears as a bright, white dot, just as it enters the vessel below the ultrasound probe [ 11 ].
The other technique is to place the probe in line with the needle so that the vessel is visualized running across the screen from left to right, and the entire length of the needle can be visualized as it tracks through the skin and soft tissue to the vessel [ 11 ].
Central line placement follows the same principles and ultrasound has become routinely used in internal jugular and common femoral vein cannulation. While advancing the needle during central line placement, just as in landmark-based techniques, applying slight negative pressure to the syringe allows you to feel when you have punctured the vein rather than relying only on ultrasound visualization.
Once blood is withdrawn, the ultrasound probe is set aside in the sterile field while the wire is inserted. Ultrasound can then be used to verify the placement of the wire within the lumen of the vein and not the adjacent artery. Although the landmark-based approach has generally been safe, ultrasound allows several advantages including the ability to find the deepest fluid pocket and avoid inadvertent puncture of the internal organs, visualization of overlying or underlying vasculature or abnormal anatomy to avoid, and confirmation that the abdominal distension is secondary to ascites and not another disease process [ 60 , 61 ].
A prospective, randomized study involving inexperienced emergency medicine residents performing ultrasound-guided paracentesis compared to this landmark-based technique demonstrated higher success rates 95 vs.
Ultrasonography in the emergency department
Another retrospective study demonstrated the association of ultrasound guidance with lower adverse events rates such as post-paracentesis infection, hematoma, and seroma 1. The abdominal or phased array probe is typically used in a static exam, finding the best fluid pocket with the patient supine or in left lateral decubitus, marking that spot on the skin and then placing the ultrasound aside for needle insertion.
The practitioner should avoid the upper quadrants, given the proximity of the liver and spleen to the abdominal wall. Thoracentesis follows similar principles and can be used for diagnostic or therapeutic collection. Ultrasound guidance for bedside thoracentesis has resulted in overall shorter hospital stays, less overall cost and fewer complications [ 67 ]. In cases of iatrogenic pneumothorax, ultrasound guidance also reduced the number of those ultimately requiring tube thoracostomy [ 69 ]. It can also be used to estimate the size of a pleural effusion which helps to predict the utility of drainage.
In patients with a pleural effusion greater than mL, successful drainage leads to improvement in their oxygen saturation to inspired oxygen ratio [ 27 ]. Similar to a paracentesis, a phased array transducer is used with the patient either supine or sitting up, and a static exam is performed to demonstrate the deepest fluid pocket within the thoracic cavity. The diaphragm should be visualized and care should be taken to avoid the needle tip coming in close proximity to it.
Real-time ultrasound guidance can also be used to actively visualize the needle passing through the pleura and into the fluid [ 11 ]. Ultrasound can be used in tube thoracostomy pre-procedure to optimize site selection and decrease complications, or post-procedure to quickly verify correct placement. Pre-procedure ultrasound lowers the rate of iatrogenic pneumothorax 4—30 to 1. Post-procedure ultrasound can be used to detect complications such as a misplaced tube, iatrogenic pneumothorax and re-expansion pulmonary edema [ 22 , 72 , 73 ].
Extra-thoracic placement of chest tubes is estimated to complicate 0. When viewing the thorax with ultrasound, a correctly placed chest tube will disappear as it enters the thorax, but an extra-thoracic tube can be viewed in its entirety [ 74 ]. The significant drop in cardiac output in tamponade can be life-threatening, and emergent pericardiocentesis can be life-saving. As previously mentioned, ultrasound can be used to diagnose pericardial effusion and tamponade and can help in its immediate management. Ultrasound guidance allows visualization of the area of maximum fluid accumulation and real-time needle guidance to decrease complications such as inadvertent puncture of the internal mammary artery or the neurovascular bundle at the inferior edge of the ribs [ 11 , 75 , 76 ].
The traditional technique involved a subxiphoid approach and blind needle advancement until blood or fluid was withdrawn. The procedure is performed with the curvilinear or phased array transducer and can be placed either subxiphoid or in the parasternal position for viewing the pericardial effusion. The ideal site for needle placement is where the effusion has maximal depth, is closest to the skin and farthest from structures the needle could damage, such as the liver or lung.
The ultrasound beam is used to simulate the needle tract, so if the liver or lung lies above the pericardium on the screen, the needle will penetrate these structures [ 11 ]. The placement of the pericardiocentesis catheter can be confirmed using ultrasound. After the needle or catheter is deemed likely to be in the pericardial sac, a syringe filled with agitated saline can be connected and injected while viewing with the ultrasound.
The complication rate for lumbar punctures is exceedingly low; yet in patients with increased body-mass-index and excess soft tissue, the success rates can vary greatly. Anesthesia literature from Russia first mentioned the concept of ultrasound guidance used during lumbar punctures in [ 78 ].