On March 22, 2012 the Division of Emergency Ultrasound will host its annual hands-on CME course at Mount Sinai. Targeted at clinicians in emergency and critical care settings, the course consists of presentations by national faculty and plenty of hands-on scanning with live models.
Basic to advanced topics covered
Organ system-based approach to bedside ultrasound use
Faculty with international experience in ultrasound education
Diagnostic applications as well as procedure guidance covered
Both experienced sonographers and neophytes will benefit from small group sizes and an interactive course design.
One of the major indications for bedside cardiac ultrasound is the detection of pericardial effusion and its extreme form, cardiac tamponade. You may remember that Beck’s Triad (hypotension, jugular venous distension, and muffled or distant heart sounds) isÂ pathognomonic for cardiac tamponade. You should also remember (to say to your colleagues who recite that tamponade is a clinical diagnosis) that the triad is present in about one-third of cases.
If you can spot tamponade clinically in a hypotensive, tachycardic patient with muffled heart tones and JVD, congratulations! You may pass your boards, save a simulated patient, or impress a junior medical student. But how does one diagnose this condition a bit earlier in its natural history?
Pulsus parodoxus is not as hard to assess as it sounds- inflate a blood pressure cuff as you normally would. Slowly deflate the cuff and listen for Korotkoff sounds. If they are present during inspiration and expiration, there is no pulsus parodoxus and you are done. If you only hear Korotkoff sounds during expiration, note the pressure reading and keep slowly deflating until they are present throughout the respiratory cycle. What is the pressure difference between sounds during expiration only and sounds throughout the entire cycle? If it is greater than 10 mmHg, pulsus paradoxus is present.
But you read this far down because you want to know how to find tamponade using ultrasound, right? There are some earlier findings of cardiac tamponade which are detectable with ultrasound before hemodynamic instability ensues. They are:
Hard to have tamponade without this
Diastolic collapse of right atrium and right ventricle
Ideally diastole can be recognized with EKG monitoring on ultrasound, or using M-Mode
Inferior Vena cava plethora
Dilated IVC with loss of respiratory variation
Atrio-ventricular valve Doppler inflow velocities
If these words are unfamilar, use the first three findings instead! Respiratory variation in inflow across the atrioventricular valves (like a valvular pulsus parodoxus) can be a sign of early tamponade physiology. However this is an advanced technique.
The video below shows the first three findings nicely:
We’ve all seen ultrasound augment the physical examination and even allow for assessments we could not otherwise accomplish at the bedside. One great example is the use of ultrasound to check the pupillary light reflex. If you are wondering why a pen light would not suffice for this physical examination standby, you have never encountered a patient with facial trauma whose eyes were swollen shut.
We already know what to look for without ultrasound (thanks to Greyson Orlando and Wikipedia for the GIF):
By directing the beam of a high-frequency linear array transducer through the plane of the iris, you can obtain the following image (while shining a light through the closed eyelid of the same or contralateral eye):
It takes a bit of practice to align both planes, and not worth the trouble if the patient can open their eyes.
Placing a Tegaderm over the closed eye prior to applying gel can make cleanup much easier afterwards (a useful tip for any type of ocular ultrasound).
Sargsyan AE, Hamilton DR, Melton SL, et al. Ultrasonic evaluation of pupillary light reflex. Critical Ultrasound Journal. 2009 1(2): 53-57.
Harries A, Shah S, Teismann N, Price D, Nagdev A. Ultrasound assessment of extraocular movements and pupillary light reflex in ocular trauma. Am J Emerg Med. 2010 Oct; 28(8):956-9.
For some reason, most clinicians seem to grasp x-ray and CT scan imaging reasonably well. Denser structures are white, less dense are black, water dense structures are grey.
Thus, when novice ultrasound users attempt to discern images created with sound, it can be confusing that bone and air both create bright white signal as well as shadow. The purpose of this brief post is to describe very subjectively how sound behaves as it crosses media of different densities. In the real world of physics this would be referred to as Snell’s Law (unless you want to give more credit to Ibn Sahl or Descartes).
For a very concise and well-animated description of Snell’s Law please see Dr. Dan Russells’ excellent website. The basic premise is thatÂ sound (like light) will bend depending on the density of the medium it is traveling in. The greater the change in density from one medium to another, the greater the bend. For our purposes, that also means the more scattering of ultrasound waves back towards the transducer and less acoustic energy propagating forwards.
For practical purposes, we always start with liquid density in clinical sonography. That is because the transducer and acoustic gel are roughly water-dense, and so is the skin (bear with this oversimplification a moment).Â Thus, we really only have three scenarios to think about. Going from liquid to air, liquid to liquid, and liquid to bone.
As illustrated above, the great density differences from liquid to air or bone create lots of scatter (and therefore bright white signal on the screen), and leave little or no acoustic energy to travel deeper into the tissue (thus the distal shadowing). When liquid-dense structures are encountered, relatively little energy is lost (attenuated), and the beam continues to send signal deeper into the body. Thus, liquid structures such as liver, spleen, kidney, bladder make good acoustic windows. They allow lots of ultrasound energy to propagate into the body. Bone and air make poor windows, as it is difficult to see past them.
Fellows Leila PoSaw and Gene Chan attended the NYSORA (New York School of Regional Anesthesia) Winter Symposium held on December 17-18, 2011 at the Marriott Marquis Hotel on Broadway.
In addition to the expected excellent lectures and educational sessions, there was a new needle guidance system being demonstrated which may be of benefit to clinicians performing ultrasound-guided procedures.
The SonixGPS system by Ultrasonix uses a sensor in the ultrasound transducer and another in the needle to track the needle’s trajectory and tip placement. The system can work in any direction: in-plane or out-of-plane. Needle trajectory is displayed as a graphic on the main screen, and orientation with respect to the transducer is modeled in the lower right. The system promises the ability to plan out their trajectory before needle placement as well, thus facilitating decisions regarding optimal entry points.
Please note that no members of our ultrasound division have a financial relationship with Ultrasonix.