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<< An Evidence-Based Approach To Emergency Ultrasound

Ultrasound For Procedural Guidance

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Ultrasound For Procedural Guidance

Ultrasound For Procedural Guidance

The use of ultrasound for procedural guidance has been well-established in the radiology literature. In more recent years, sonography has moved from the radiology suite to the bedside and is used by a variety of practitioners to improve the safety and success of potentially dangerous procedures.

Central Venous Catheterization

Central venous catheterization is a procedure that is often required for critically ill ED patients. Although this is generally a safe procedure, the complication rate has been reported to vary from 3% to as high as 20% in some studies.119-121 Complications range from minimal to life-threatening and include arterial cannulation, pneumothorax, cardiac tamponade, air embolus, hematoma formation, and injury to adjacent neurovascular structures. The goal of real-time ultrasound is to enable the operator to visualize the target vessel and surrounding structures before and during needle insertion. (See Figure 16.) While the traditional landmark technique is successful in many cases, factors such as patient body habitus, prior cannulation, the presence of scar tissue or thrombus, and variant anatomy can all make the landmark approach to vascular access more difficult.



There is ample literature supporting the use of ultrasound for the placement of central venous catheters. Leung et al in a randomized prospective trial demonstrated the superiority of sonographic guidance compared with landmark methods in the rate of successful internal jugular venous catheterization and the rate of complications, even when performed by inexperienced operators (as defined by those with less than 25 previous central venous catheterizations).119 Various other authors have demonstrated decreased time for cannulation and the need for fewer attempts, even with minimal training in the use of ultrasound.120-124 Miller and colleagues showed a significantly reduced time for central venous catheter placement in their study, with operators having minimal ultrasound training (1 hr) prior to participation.125 Of note, the greatest reduction in time to successful line placement in this study was seen in patients considered to have difficult access, as defined by coagulopathy, obesity, abnormal anatomy, or a history of intravenous drug use.

It should be mentioned that there are concerns with the routine use of ultrasound for central line placement. Potential disadvantages include a timeconsuming learning process, an initial delay due to set-up, the need to prepare the machine and the transducer (applying a sterile probe cover) for use, and the initial cost of an actual ultrasound machine for use in the clinical setting. In addition, more clinical trials may be needed to prove the utility of sonographic guidance for sites other than the internal jugular vein, since there are limited data on subclavian, axillary, and femoral approaches.126-129 A recent case series reported 6 accidental arterial cannulations despite ultrasound guidence.130 The authors report that the short-axis approach can lead to a false sense of security and that the long-axis approach should also be used to verify the position of the needle or guidewire in the vein.

The potential limitations of ultrasound are outweighed, however, by the evidence supporting its routine use for central line placement. The role of real-time ultrasonographic guidance has become so well-established in the medical literature that it is now recommended by multiple societies, including the Agency for Healthcare Research and Quality,131 the American College of Emergency Physicians,1 the American College of Chest Physicians,132 and the British National Institute for Clinical Excellence.133 Given this overwhelming support and the potential for error reduction as compared with traditional landmark techniques for line placement, ultrasound guidance for central venous catheterization should be used whenever possible and is considered by many to be the standard of care.

Paracentesis

Paracentesis, thoracentesis, and pericardiocentesis are all commonly performed procedures with potentially severe complications. The use of BUS has been advocated as a means to decrease the incidence of complications as well as to improve procedure success.

As early as 1970, clinicians realized that ascites and abdominal fluid could be detected by ultrasonography.134 Many authors consider this the “gold-standard” test for the diagnosis of ascites, since it can detect as little as 100 mL of fluid in the abdomen.135,136

Although paracentesis is generally safe when performed by the conventional method of blind-needle entry, it can be aided by the use of BUS, especially in patients with small or moderate amounts of abdominal fluid or with abnormal anatomy. The first clinicians to study the use of ultrasound for procedural guidance in paracentesis noted that loops of bowel were often present between the abdominal wall and the expected location of ascitic fluid based on physical examination.137 They concluded that the distribution of ascites was too variable in most patients to identify a single ideal site for blind-needle puncture and that patients with minimal fluid in the abdomen were more difficult to drain without sonography.

Recent authors have examined the benefits of real-time procedural guidance during paracentesis. In a prospective randomized study comparing ultrasound guidance versus the traditional technique of needle entry, Nazeer and colleagues noted that ultrasound guidance improved the success rate of paracentesis and, moreover, identified a number of patients in whom the procedure could not be performed owing to the presence of too little fluid or the presence of another disease process that had been mislabeled as ascites based on physical examination.138 Another interesting finding of this study was the ability of novice operators (emergency medicine residents given a 1-hour didactic course) to perform ultrasound guidance after minimal training.

Thoracentesis

The ability of ultrasound to detect disease processes in the thorax has been well established.139 In the critically ill patient, the presence of pleural effusions can be easily detected on BUS and with greater accuracy than with portable chest radiography.140,141 In patients with respiratory insufficiency due to pleural effusions, therapeutic thoracentesis may be indicated, with drainage of significant amounts of fluid. Patients with undifferentiated pleural effusions require diagnostic thoracentesis as a part of their medical work-up. Because both physical examination findings and the presence of a density on a chest radiograph can be misleading, ultrasound-guided thoracentesis offers a safer alternative to thoracentesis with blind-needle entry. Ultrasound allows for direct visualization of surrounding anatomic structures such as the liver, spleen, diaphragm, and lung parenchyma. In a prospective study of 26 patients referred for ultrasound-guided thoracentesis after failed attempts with blind-needle passage, Weingardt et al found that when the puncture sites from these previous attempts were examined, errors in needle placement were noted, including insertion below the hemidiaphragm, above the fluid collection, into consolidated lung, or into multiple solid organs.142

Thoracentesis is recognized as one of the most common causes of iatrogenic pneumothorax, and this is the most common major complication of this procedure.143,144 It is noted to occur in 4% to 30% of cases performed without sonographic guidance, and of these, up to 50% of patients require tube thoracostomy.145,146 A number of authors have noted that ultrasound-guided thoracentesis significantly decreases the rate of iatrogenic pneumothorax and the subsequent need for tube thoracostomy.145,147-150 Ultrasound-guided thoracentesis has also been shown to decrease the incidence of other common minor complications, including cough and bleeding at the puncture site.147 To decrease pain and improve patient comfort, BUS can be used in real time to visualize and anesthetize the pleural lining prior to puncture. An additional benefit of bedside sonography in this setting is post-procedure evaluation of the thorax for both pneumothorax and re-expansion pulmonary edema.

Pericardiocentesis

A number of diseases can lead to the development of a pericardial effusion. Typically, traumatic injury leads to the rapid accumulation of pericardial blood and cardiac tamponade, whereas chronic processes such as malignancy, infection, connective tissue disorders, and renal failure result in a more gradual accumulation of pericardial fluid. The ability to detect pericardial effusions and tamponade is important to the emergency clinician, since rapid decompensation or frank arrest can result from the hemodynamic effects of cardiac tamponade physiology.

Emergency echocardiography is rapid and noninvasive and can be performed at the bedside to detect pericardial effusions. (See the section on Emergent Echocardiography) Once a pericardial effusion has been noted, management will vary according to patient status. The patient with cardiac tamponade and hemodynamic compromise may need emergent pericardiocentesis.151

For years, clinicians have been instructed to carry out emergent pericardiocentesis using a blind subxiphoid approach, with a complication rate reported to be near 50%.152 Complications include ventricular puncture, coronary vascular laceration, pneumothorax, visceral abdominal puncture, and diaphragmatic injury. Bedside cardiac ultrasound guidance during this procedure has been shown by multiple authors to decrease the risk of these complications.153-157 (See Figure 17.) The largest of these studies examined a series of 1127 patients over a period of 21 years and noted a complication rate below 5%, well below the rate reported for standard pericardiocentesis using the landmark-based approach. The same group published a study of pericardiocentesis in pediatric patients in which the use of ultrasound guidance not only resulted in a lower complication rate but also reduced the need for repeat drainage and surgical intervention, probably owing to more accurate catheter placement and increased drainage made possible by direct ultrasound visualization.158 Interestingly, most authors note that the subxiphoid approach may not be the optimal approach, and that with ultrasound guidance, the parasternal or apical approach may provide more direct access to pericardial fluid.



One potential criticism of these studies is that they were carried out by cardiologists in a cardiology laboratory using large, cumbersome diagnostic echocardiography machines, which are not readily available in the ED. Despite this, the same basic principle of increased safety with direct visualization should apply in emergency situations. In addition, one group has looked at the utility of hand-carried ultrasound for procedural guidance during pericardiocentesis and thoracentesis. Although a small study, their results indicate that this is not only feasible but also increases patient safety.159

Conclusions

Sonographic guidance has resulted in improved success, more rapid completion, and decreased incidence of iatrogenic injury for a variety of procedures. Whether using the static or dynamic technique, needle-guidance should be performed with ultrasound, whenever possible. In particular, the use of ultrasound guidance for central venous catheterization is nearly uniformly recommended by professional societies and healthcare quality agencies around the globe.

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