**4. Procedural ultrasound**

scan [11, 52, 53]. The globe provides a good acoustic window for visualization of the optic nerve, which appears as a large hypoechoic stripe posterior to the globe. ONSD is measured 3 mm posterior to the optic disc and is normally less than 5 mm. Using a stricter cutoff of greater than 5.8 mm for increased ICP (>20 mmHg) yields a sensitivity of 90% and specificity of 84% [51]. ONSD has mixed reviews for real-time trending of ICP. 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]. However, for sustained increases in ICP, ONSD does not appear to

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 87.5% and a specificity of 85.2% for foreign bodies, and is more reliable in the detection of metallic material. 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]. Lesser utilized ocular exams include demonstration of the ocular vasculature using color Doppler to evaluate for central retinal artery and central retinal vein occlusion, and evaluation of the posterior orbital space for hemorrhage (hypoechoic area) or distortion/flattening of the posterior globe ("guitar pick

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. As the clinical relevance of isolated calf DVT is controversial, most radiology performed and POCUS DVT exams focus on the larger vessels above the knee [12, 13]. 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. False positives can occur if structures such as a lymph node, Baker's cyst or pseudoaneurysm, are mistaken for a noncompressible vessel. 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

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

normalize in real time with measures to decrease ICP [53].

154 Essentials of Accident and Emergency Medicine

sign"), indicative of a retrobulbar hematoma [51].

**3.8. DVT ultrasound**

easier identification [12].

**3.9. Soft tissue and bone ultrasound**

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].

#### **4.1. Venous cannulation**

Insertion of intravenous catheters using visual guidance is one of the most common procedural uses for the ultrasound [56–58]. 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 1.5-inch cannulated needle, or a longer angiocath for deeper veins. Ultrasound guidance is most useful in patients with difficult IV access, such as obese, young, IV drug abusing or prior chemotherapy patients. In patients with difficult to obtain IV access, ultrasound-guided IV placement was demonstrated to be consistently twice as fast and decrease the total number of punctures needed by an average of two, but still had variable success (80–90%) [9]. Physicians with greater ultrasound experience have more than 60% increased success rates between ultrasound and landmark guidance compared to novice practitioners with no ultrasound background [9, 56, 59].

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. They should also avoid 11 and 2 o'clock angles of the abdomen to prevent inadvertently puncturing the inferior epigastric arteries, a known cause of hemorrhagic complications [66]. A pocket of 3–4 cm between the abdominal wall and the free-floating loops of bowel is adequate and is

The Evolving Role of Ultrasound in Emergency Medicine http://dx.doi.org/10.5772/intechopen.74777 157

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]. Specifically, ultrasound reduces the rates of iatrogenic pneumothorax by 29%, which complicates 20–39% of physical exam-guided thoracenteses [68]. In cases of iatrogenic pneumothorax, ultrasound guidance also reduced the number of those ultimately requiring tube thoracostomy [69]. Ultrasound increases the accuracy of site selection by 26% and decreases the number of unsuccessful attempts [70]. 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 500 mL, successful drainage leads to improvement in their oxygen saturation to inspired oxygen ratio [27]. With the patient supine, a distance from the thoracic wall to the visceral pleura over 5 cm at the posterior axillary line can

identify an effusion larger than 500 mL (90% specificity and 100% sensitivity) [24, 71].

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. A depth of 15 mm between the visceral and parietal pleura over three sequential intercostal spaces is adequate to perform the procedure. Realtime ultrasound guidance can also be used to actively visualize the needle passing through

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 1.3–6.7%), helps avoid intercostal vessels and allows visualization of aberrant anatomy that can lead to complications. Postprocedure 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 0.5–2.6% of attempts, and ultrasound has demonstrated a sensitivity of 83–100% and specificity of 83–100% for differentiating intra- and extra-thoracic placement [74]. 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

usually found in the lateral-most aspect of the abdomen [11].

the pleura and into the fluid [11].

**4.3. Pericardiocentesis**

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. The depth of the desired vessel is measured and needle is inserted at the same distance distal to the ultrasound probe at a 45° angle. 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. The use of ultrasound in central line placement has led to reduction in complications by 78%, reduction in attempts needed by 40% and reduction in unsuccessful cannulation by 64% [9, 12].

#### **4.2. Paracentesis and thoracentesis**

Paracentesis can be performed for both diagnostic sampling and/or therapeutic drainage. 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]. Physical exam itself has poor reliability in the diagnosis of ascites, and ultrasound demonstrated improved sensitivity (94% compared to 50%) and specificity (82 vs. 29%) in detection [62]. In landmark-based paracentesis, success is determined mainly by the overall volume of ascites, success rates are 44% for 300 mL and 78% for 500 mL, but virtually never successful with volume is less than 50 mL [63]. 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. 61%, P = 0.0003) [64]. Another retrospective study demonstrated the association of ultrasound guidance with lower adverse events rates such as post-paracentesis infection, hematoma, and seroma (1.4 vs. 4.7%, p = 0.01) [65].

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. They should also avoid 11 and 2 o'clock angles of the abdomen to prevent inadvertently puncturing the inferior epigastric arteries, a known cause of hemorrhagic complications [66]. A pocket of 3–4 cm between the abdominal wall and the free-floating loops of bowel is adequate and is usually found in the lateral-most aspect of the abdomen [11].

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]. Specifically, ultrasound reduces the rates of iatrogenic pneumothorax by 29%, which complicates 20–39% of physical exam-guided thoracenteses [68]. In cases of iatrogenic pneumothorax, ultrasound guidance also reduced the number of those ultimately requiring tube thoracostomy [69]. Ultrasound increases the accuracy of site selection by 26% and decreases the number of unsuccessful attempts [70]. 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 500 mL, successful drainage leads to improvement in their oxygen saturation to inspired oxygen ratio [27]. With the patient supine, a distance from the thoracic wall to the visceral pleura over 5 cm at the posterior axillary line can identify an effusion larger than 500 mL (90% specificity and 100% sensitivity) [24, 71].

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. A depth of 15 mm between the visceral and parietal pleura over three sequential intercostal spaces is adequate to perform the procedure. Realtime 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 1.3–6.7%), helps avoid intercostal vessels and allows visualization of aberrant anatomy that can lead to complications. Postprocedure 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 0.5–2.6% of attempts, and ultrasound has demonstrated a sensitivity of 83–100% and specificity of 83–100% for differentiating intra- and extra-thoracic placement [74]. 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].

#### **4.3. Pericardiocentesis**

or a longer angiocath for deeper veins. Ultrasound guidance is most useful in patients with difficult IV access, such as obese, young, IV drug abusing or prior chemotherapy patients. In patients with difficult to obtain IV access, ultrasound-guided IV placement was demonstrated to be consistently twice as fast and decrease the total number of punctures needed by an average of two, but still had variable success (80–90%) [9]. Physicians with greater ultrasound experience have more than 60% increased success rates between ultrasound and landmark

guidance compared to novice practitioners with no ultrasound background [9, 56, 59].

vessel [11].

**4.2. Paracentesis and thoracentesis**

156 Essentials of Accident and Emergency Medicine

hematoma, and seroma (1.4 vs. 4.7%, p = 0.01) [65].

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. The depth of the desired vessel is measured and needle is inserted at the same distance distal to the ultrasound probe at a 45° angle. 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

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. The use of ultrasound in central line placement has led to reduction in complications by 78%, reduction

in attempts needed by 40% and reduction in unsuccessful cannulation by 64% [9, 12].

Paracentesis can be performed for both diagnostic sampling and/or therapeutic drainage. 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]. Physical exam itself has poor reliability in the diagnosis of ascites, and ultrasound demonstrated improved sensitivity (94% compared to 50%) and specificity (82 vs. 29%) in detection [62]. In landmark-based paracentesis, success is determined mainly by the overall volume of ascites, success rates are 44% for 300 mL and 78% for 500 mL, but virtually never successful with volume is less than 50 mL [63]. 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. 61%, P = 0.0003) [64]. Another retrospective study demonstrated the association of ultrasound guidance with lower adverse events rates such as post-paracentesis infection,

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. Using ultrasound, the initial approach in over 80% of patients was changed to an apical puncture site due to better fluid accumulation here [75, 77].

**4.5. Endotracheal intubation confirmation and tracheostomy**

within the esophagus [88].

**5. Conclusion**

tent organ or vessel injury.

Intubation is a common procedure performed in emergency medicine and has high rates of first pass success [86]. However, one of the well-known complications is accidental endobronchial intubation which would result in ventilation of only one lung, or intra-esophageal intubation which would result in neither lung being ventilated. As many as 55% of these endobronchial intubations are missed by auscultation of the bilateral lung fields alone, and in cases of poor cardiac output (e.g., cardiac arrest), patients may lack sufficient circulation to the lungs to expel enough carbon dioxide for accurate capnography [87]. Ultrasound has demonstrated utility in verifying the correct placement of the endotracheal tube (ETT) directly and indirectly [9, 88]. Indirect verification involves demonstration of pleural sliding in the anterior, midclavicular line bilaterally once the ETT is placed. This technique would be limited in the setting of a pneumothorax [31, 87]. Direct verification involves real-time visualization during intubation with the probe placed midline over the trachea in the suprasternal notch. Evidence of successful intubation is seen as a single air artifact, and unsuccessful, esophageal intubation would be apparent as a double air artifact (air in the tube and the trachea). The direct method has overall sensitivity of 98.9, with 100% specificity in noncardiac arrest patients, and 75% specificity in cardiac arrest patients [89]. This technique is limited if the trachea lies directly over the esophagus, as it would obscure visualization of the air artifact

The Evolving Role of Ultrasound in Emergency Medicine http://dx.doi.org/10.5772/intechopen.74777 159

If intubation is ultimately unsuccessful, ultrasound can also provide guidance in cricothyroidotomy [9]. Inaccurate landmark identification using digital palpation is one of the leading causes of cricothyroidotomy failure and complication [90]. Excess soft tissue in the neck can result in significant difficulty palpating and identifying the thyroid and cricoid cartilage. Ultrasound has demonstrated increased reliability in identification of the cricothyroid membrane and its use has the potential to decrease moderate-severe injuries to the trachea and

Ultrasound has helped to transform the practice of emergency medicine by providing an efficient and powerful tool that allows rapid information acquisition and subsequently informed, quick decision-making. Its utility continues to expand and, with technological advancements, it will continue to become more versatile and widespread in its use, not only in the emergency department, but in the prehospital and more austere settings. It allows the emergency physician to expedite care by decreasing time needed to obtain imaging and speak with consultants or to order additional tests or treatments based on the findings. It decreases procedural complications by allowing real-time guidance of needles along specific tracts, avoiding inadver-

Ultrasound education is established as an essential part of all emergency medicine residencies, as well as some general surgery residencies, and is offered as an accredited fellowship. As physicians graduate from these training programs, the expectations of their ultrasound

larynx by up to one third compared to landmark-based technique [90].

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. A "snow-storm" of bubbles, showing as white dots, will be seen within the pericardial sac if the catheter is correctly placed, or may be apparent within the ventricle if the myocardium was penetrated during the procedure [9, 11].

#### **4.4. Lumbar puncture**

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 1971 [78]. Following this publication, further anesthesia literature has documented a reduced number of unsuccessful attempts, fewer interspaces punctured, and decreased needle repositioning within the skin when using pre-procedure ultrasound guidance [79–81]. Ultrasound was recently demonstrated to be a preferred rescue method in failed neonatal lumbar punctures [82]. Likewise, a 2005 case series demonstrated its utility in localization in three failed adult lumbar punctures performed by experienced physicians [83]. In patients with difficulty to palpate landmarks, ultrasound has proven value to identify the lumbar vertebral landmarks as well as other relevant structures that help to guide a lumbar puncture [84, 85].

As the best utility in ultrasound guidance is experienced in patients with a high amount of overlying soft tissue, a curvilinear transducer will typically be the choice probe to gain a greater amount of depth. The transducer is placed parallel to the vertebral column at first to view the spinous processes and the desired para-vertebral space. The spinous processes will be hyperechoic and rounded, and there will be a notable gap where the space occurs. Ultrasound allows alignment in both the vertical as well as the horizontal axis, providing an exact point for needle puncture to optimize success. Real-time guidance is generally not performed given the difficulty of needle insertion with one hand while holding the probe, and typically static guidance and skin marking are sufficient [11].

#### **4.5. Endotracheal intubation confirmation and tracheostomy**

Intubation is a common procedure performed in emergency medicine and has high rates of first pass success [86]. However, one of the well-known complications is accidental endobronchial intubation which would result in ventilation of only one lung, or intra-esophageal intubation which would result in neither lung being ventilated. As many as 55% of these endobronchial intubations are missed by auscultation of the bilateral lung fields alone, and in cases of poor cardiac output (e.g., cardiac arrest), patients may lack sufficient circulation to the lungs to expel enough carbon dioxide for accurate capnography [87]. Ultrasound has demonstrated utility in verifying the correct placement of the endotracheal tube (ETT) directly and indirectly [9, 88]. Indirect verification involves demonstration of pleural sliding in the anterior, midclavicular line bilaterally once the ETT is placed. This technique would be limited in the setting of a pneumothorax [31, 87]. Direct verification involves real-time visualization during intubation with the probe placed midline over the trachea in the suprasternal notch. Evidence of successful intubation is seen as a single air artifact, and unsuccessful, esophageal intubation would be apparent as a double air artifact (air in the tube and the trachea). The direct method has overall sensitivity of 98.9, with 100% specificity in noncardiac arrest patients, and 75% specificity in cardiac arrest patients [89]. This technique is limited if the trachea lies directly over the esophagus, as it would obscure visualization of the air artifact within the esophagus [88].

If intubation is ultimately unsuccessful, ultrasound can also provide guidance in cricothyroidotomy [9]. Inaccurate landmark identification using digital palpation is one of the leading causes of cricothyroidotomy failure and complication [90]. Excess soft tissue in the neck can result in significant difficulty palpating and identifying the thyroid and cricoid cartilage. Ultrasound has demonstrated increased reliability in identification of the cricothyroid membrane and its use has the potential to decrease moderate-severe injuries to the trachea and larynx by up to one third compared to landmark-based technique [90].
