Background & Indications Probe Selection

Transcription

1 Teresa S. Wu, MD, FACEP Director, EM Ultrasound Program & Fellowship Co-Director, Simulation Based Training Program & Fellowship Associate Program Director, EM Residency Program Maricopa Medical Center Associate Professor, Emergency Medicine University of Arizona, College of Medicine-Phoenix Background & Indications When patients are suspected of having a life-threatening pericardial effusion and cardiac tamponade, prompt diagnosis and treatment is imperative to improve chances of survival. Making the diagnosis of a pericardial effusion is often difficult based on clinical findings alone. Clinical ultrasound can be used to determine if a pericardial effusion is present, to estimate the size of the fluid collection, to assess for cardiac tamponade and to help guide an emergent pericardiocentesis. If a pericardial effusion is noted on ultrasound, the heart should be assessed for any evidence of right atrial or right ventricular collapse. Diastolic collapse of the right atrium is the first sonographic sign encountered with increased pericardial pressures from a growing effusion. Once intrapericardial pressures exceed right ventricular pressures, enddiastolic right ventricular collapse is noted and cardiac output is compromised. Right atrial and right ventricular collapse are best seen in the apical 4- chamber view of the heart. An ultrasound-guided pericardiocentesis minimizes the chances of accidental puncture or laceration of the cardiac chambers and surrounding structures. Probe Selection Use the low frequency (3-5 MHz) phased array transducer to assess the heart and to evaluate for evidence of cardiac tamponade (Image 1). The high frequency linear transducer can be used to guide the pericardiocentesis if a parasternal or apical approach is used (Image 2).

2 Page 2 of 10 Image 1: Low frequency phased array transducer. Image 2: High frequency linear array transducer. Performing the Exam Time permitting, prep and drape the patient and the ultrasound transducer in a sterile fashion. In an emergent resuscitation situation, the ultrasound-guided pericardiocentesis may need to be performed in a non-sterile fashion. Obtain subxiphoid, parasternal and apical views of the pericardial space and adjacent structures to determine the best site for performing a pericardiocentesis. Determine which site provides direct access to the maximum amount of pericardial fluid, while minimizing the risk of puncturing adjacent organs. Traditionally, a subxiphoid view of the heart is the easiest window to obtain and typically provides the best view of all four chambers of the heart because the liver serves as an excellent acoustic window (Image 3). If the subxiphoid approach is utilized, recognize that there is a high chance of liver puncture during the pericardiocentesis.

3 Page 3 of 10 Image 3: Subxiphoid view of a pericardial effusion. Note the liver parenchyma at the top of the screen. If a subxiphoid approach is taken to perform the pericardiocentesis, the liver will be punctured by the needle en route to the pericardial sac. The parasternal view of the heart can also be utilized to guide the emergent pericardiocentesis via an intercostal approach (Image 4). Utilizing the parasternal approach puts the patient at risk for puncture of the left anterior descending artery or the internal mammary artery. Image 4: Parasternal long axis view of a pericardial effusion. The apical view of the heart can be more difficult to obtain during a bedside scan but often provides unobstructed access to the pericardial sac (Image 5). Once the heart is adequately visualized along the 6 th -7 th intercostal space at the anterior-axillary line, the apical approach for a pericardiocentesis allows the practitioner to enter the pericardial sac with reduced risk of injuring adjacent organs. Note that the apical approach can put patients at higher risk for accidental pleural puncture and subsequent pneumothorax.

4 Page 4 of 10 Image 5: Apical view of a pericardial effusion with right ventricular collapse from tamponade. Use the depth markers on the side of the ultrasound image to determine the needle length required to enter the pericardial space (Image 6). Image 6: Depth markers on the side of the ultrasound screen can be used to determine the needle length required to enter the pericardial sac. In this image each line represents 1 cm. To perform the procedure, grab a pericardiocentesis kit, a triple lumen central venous access kit, or a long, large gauge needle (5-10 cm, gauge) attached to a 3-way stopcock and saline-filled syringe. Under ultrasound guidance, insert the needle and aim towards the pericardial sac (Images 7 and 8). Gently aspirate back on the syringe as you slowly advance the needle. Monitor the needle trajectory as you aim towards the pericardial effusion. Continue applying negative pressure on the syringe until the parietal pericardium is penetrated and pericardial fluid or blood is noted in the syringe.

5 Image 7: Pericardiocentesis via the parasternal approach. US Guided Pericardiocentesis Page 5 of 10 Image 8: Pericardiocentesis via the peri-apical approach. Once the needle tip is clearly in the pericardial space, attach a cc syringe to the 3-way stopcock and continue fluid aspiration until the patient s blood pressure improves or until there is resolution of tamponade on ultrasound (Images 9 and 10). Image 9: Ultrasound visualization of the needle in the pericardial sac via a parasternal approach using a linear array transducer.

6 Page 6 of 10 Image 10: Ultrasound visualization of the needle in the pericardial sac via a peri-apical approach using a phased array transducer. Inject 1-2 ml of normal saline under direct ultrasound visualization to flush the needle and to confirm needle tip location. If the needle tip is in the pericardial space, bubbling from saline injection will be noted within the pericardial sac. Insert a catheter into the pericardial space via the Seldinger technique to allow for continuous aspiration. If a commercial pericardiocentesis tray is not readily available, a central venous access catheter can be used as a substitute. Normal Sonographic Anatomy Image 11: Subxiphoid view of a normal heart. RV=right ventricle; RA=right atrium; LV=left ventricle; LA=left atrium.

7 Page 7 of 10 Image 12: Parasternal long axis view of a normal heart. RV=right ventricle; LV=left ventricle; LA=left atrium; Ao=aortic outflow tract. Image 13: Apical 4-chamber view of a normal heart. RV=right ventricle; RA=right atrium; LV=left ventricle; LA=left atrium. Notable Pathology Image 14: Subxiphoid view of a large, circumferential pericardial effusion.

8 Page 8 of 10 Image 15: Parasternal view of a large, circumferential pericardial effusion. Image 16: Apical 4-Chamber view of a large pericardial effusion with right ventricular collapse indicating cardiac tamponade. Pearls & Pitfalls in Performing an US-Guided Pericardiocentesis Do not mistake a large pleural effusion for a pericardial effusion in the subxiphoid view. Always locate the circular descending aorta. Pleural effusions will course posterior to the descending aorta, whereas pericardial effusions will be seen nearfield to the descending aorta (Image 17).

9 Page 9 of 10 Image 17: Parasternal long-axis view of the heart with the descending aorta (Ao) visualized posteriorly. The pericardial effusion is seen anterior to the descending aorta, whereas the pleural effusion is coursing more posteriorly to the descending aorta. Although the phased array (5-1 MHz) transducer is the most common probe used during an ultrasound guided pericardiocentesis, note that a high frequency linear transducer (10-5 MHz) may give you optimal needle visualization during the apical approach (Image 10). Use the phased array transducer to locate the largest collection of unobstructed pericardial fluid and then switch over to the linear transducer to guide your needle during the pericardiocentesis if the fluid collection lies superficially. If a phased array transducer is not readily available, a low frequency curvilinear transducer (5-2 MHz) can be manipulated in between the ribs or under the xiphoid process to visualize the heart and surrounding structures. In general, obtaining a view of your needle in the long-axis plane will optimize visualization of the needle and its trajectory throughout the entire procedure. If you have not mastered the long-axis approach, aim your ultrasound beams so they bisect your needle tip as it punctures the skin and enters the subcutaneous tissue. Utilize tissue movement and artifacts, such as ring down, to help you visualize the needle trajectory. You may need to fan or slide the probe away from the puncture site to maintain visualization of the needle tip as you advance the needle deeper into the patient. Stroke volume of the collapsed RV typically increases 77% with the removal of the first 200 ml of the pericardial effusion. Remember that rapid fluid removal can cause significant hemodynamic changes from the sudden increase in left ventricular (LV) preload. These changes can result in sudden pulmonary edema, circulatory collapse, profound bradycardia, and rebound hypertension.

10 Page 10 of 10 Remove enough fluid to achieve return of spontaneous circulation and an adequate perfusing blood pressure. If there is time, utilize ultrasound to locate and visualize surrounding vascular structures. During the pericardiocentesis, attempt to avoid local vascular structures such as the intermammary artery, which lies 3-5 cm lateral to the sternal border, and the intercostal arteries that run along the lower rib margin. During the procedure, reconfirm needle or catheter placement by examining the bloody aspirate for clot. Remember that intracardiac blood will clot, whereas blood that has transmigrated into the pericardial sac will not clot because it is defibrinated. Note that traumatic effusions will have blood in the pericardial sac that originated from the ventricles. In these situations, blood in the pericardiac sac will clot. When in doubt, inject a small amount of normal saline and visualize the anatomic distribution of the saline bubbles on bedside ultrasound. For more bedside ultrasound tips and tricks, check out the ultrasound app SonoSupport.