Aorte Flashcards
Type de sonde à utiliser?
curvilinéaire
PRéparation machine et position du pt préscan de l’aorte?
Dive the depth to centre relevant anatomy.
Recommended starting depth for beginners: 30 cm or machine maximum in adults.
Beginners should always set the initial depth deep enough to avoid missing relevant anatomy. With experience, initial depth should be adjusted to account for patient body habitus.
Gain = mid-range.
System preset(s) = aorta / abdominal.
Position/orientation et prise de la sonde?
Probe orientation:
Probe held perpendicular to the floor / stretcher with the beam directed towards the patient’s back and the probe marker oriented towards patient right.
Probe grip:
Forceps/Pencil grip – thumb, index finger and 3rd finger holding probe close to the probe face, with at least one finger or some part of the ulnar aspect of the hand in contact with the patient to enhance proprioception.
repère externe?
processus xyphoide
repère interne?
vertèbres
anatomie pertinente de cette région?
aorte, VCI, spine (acoustic shadow)
Zone d’intérêt
paroi externe de l’aorte (pas la mesure de la lumière)
technique EDU aorte?
Technique
To assess the caliber of the abdominal aorta, a CPoCUS-IP must place a finger on the xiphoid process and then position the probe in true transverse so it contacts both the finger and the xiphoid process. This position is maintained until the internal landmark (spine with acoustic shadow) is visible on the screen.
The aorta is identified by its location immediately anterior to the spine, its thick echogenic wall and its non-compressibility with the application of pressure.
Non-compressibility of the aorta often cannot be assessed at the level of the xiphoid process due to the costal margin. This criterion for aortic identification may be utilized more distally provided the operator has seen the structure they believed to be the aorta from the xiphoid on down. If they choose to start caudal to the xiphoid, the operator must slide cephalad until the probe and a finger placed on the xiphoid come into contact with each other to ensure that the aorta is visible at this level.
The area of interest (outer wall of the aorta) is visualized while sliding the probe towards the umbilicus until the aorta bifurcates into the two iliac vessels.
The diameter of the aorta must be continuously estimated by comparing its size to the centimeter marks on the ultrasound screen. If there appears to be dilation at any point, the image should be frozen and the ultrasound calipers used to measure the largest diameter.
During the aortic scan, an IP must always:
Maintain a true transverse orientation with respect to the aorta.
Keep the aorta centered on the screen from side to side and top to bottom.
Stop at any areas where the aorta and spine are obscured by gas and secure a view (see troubleshooting) of the aorta at these locations.
4 trucs pour contourner les gaz?
Gas:
1. Use firm probe pressure and hold (up to 30 seconds) to displace / dissipate bowel gas. If an adequate view of the aorta is obtained, HOLD this pressure and slide distally towards to bifurcation.
- Ask the patient to take a deep breath in and hold it. This should move loop(s) of bowel caudally and may uncover the aorta. While maintaining good probe pressure, slide distally as the patient holds their breath until the view of the aorta becomes obscured from the same bowel loop(s). Ask the patient to exhale and this should move the bowel cephalad, uncovering the aorta once again. Continue scanning, with good probe pressure, towards the umbilicus. Please note that this maneuver usually only works for the first half of the aorta from the xiphoid process.
- Slide laterally and heel medially to move around loop(s) of bowel.
- Flex hips / bend knees to allow deeper probe pressure.
comment diminuer l’effet du tissu adipeux?
- Lower probe frequency. This will increase beam penetration, potentially improving clarity of the aorta through dense adipose tissue.
Pièges à éviter ds l’interprétation?
Pitfalls (Image interpretation)
Failure to properly identify the wall of the aorta. Remember that the aortic diameter is measured from outer wall to outer wall of the aorta. When we see an atheroma within the aorta, the inner edge of the atheroma is sometimes mistaken for the wall of the aorta. This can lead to an underestimation of the aortic diameter and a false negative scan.
Mistaking other circular / fluid filled structures (IVC, other vessels, para-aortic lymph nodes) for aorta.
Underestimating the size of the aorta when using maximal depth by not comparing it to the centimeter markers on the screen / not freezing and using calipers.
Scanning past the bifurcation (implies poor screen awareness).
Piège à éviter ds la génération d’image?
Pitfalls (Image generation)
Scanning too fast.
Poor probe control / grip. This could include holding the probe too tightly thus limiting proprioceptive feedback to the hand, not contacting the patient with the hand / fingers or not using the fingertips to contact the probe. All of these pitfalls make it more difficult to keep the probe in true transverse.
Not scanning in true transverse.
Not starting at the xiphoid process. Risks missing a suprarenal AAA.
Sliding down the scaphoid abdomen before looking at the screen, potentially missing a suprarenal AAA.
Overestimating size of aorta by creating an oblique cut of the aorta (i.e., not being in true transverse).
Not visualizing a centimeter or more of the aorta due to bowel gas.
Piège ds l’intrégration clinique?
Pitfalls (Image interpretation)
Failure to properly identify the wall of the aorta. Remember that the aortic diameter is measured from outer wall to outer wall of the aorta. When we see an atheroma within the aorta, the inner edge of the atheroma is sometimes mistaken for the wall of the aorta. This can lead to an underestimation of the aortic diameter and a false negative scan.
Mistaking other circular / fluid filled structures (IVC, other vessels, para-aortic lymph nodes) for aorta.
Underestimating the size of the aorta when using maximal depth by not comparing it to the centimeter markers on the screen / not freezing and using calipers.
Scanning past the bifurcation (implies poor screen awareness).
Pitfalls (Image generation)
Scanning too fast.
Poor probe control / grip. This could include holding the probe too tightly thus limiting proprioceptive feedback to the hand, not contacting the patient with the hand / fingers or not using the fingertips to contact the probe. All of these pitfalls make it more difficult to keep the probe in true transverse.
Not scanning in true transverse.
Not starting at the xiphoid process. Risks missing a suprarenal AAA.
Sliding down the scaphoid abdomen before looking at the screen, potentially missing a suprarenal AAA.
Overestimating size of aorta by creating an oblique cut of the aorta (i.e., not being in true transverse).
Not visualizing a centimeter or more of the aorta due to bowel gas.
Pitfalls (Clinical integration)
Assuming that a AAA less than 5 cm cannot rupture. While a AAA greater than 5 cm is more likely to rupture, any dilated abdominal aorta greater than 3 cm has the potential to rupture. The clinical suspicion of the treating physician always supersedes a PoCUS finding.
Assuming that debris inside a AAA represents thrombus and therefore means acute rupture. Acute thrombus and chronic atheroma appear identical using PoCUS. Debris within the lumen of the abdominal aorta does not make rupture any more likely. Suspicion of aortic rupture is always a clinical impression.
Declaring a negative scan (i.e., no AAA) when the entire aorta from crux of diaphragm (at xiphoid process) to iliac bifurcation has not been imaged clearly.
autres trucs?
Tips and tricks
Please see the troubleshooting section for primary maneuvers to improve an aortic image.
Hold the probe like a pencil/forceps, not like a hammer.
Always scan in true transverse.
Adjust the “knobology” while scanning: center the image from near field to far field with the depth and adjust the gain during the scan. The gain often needs to be decreased when the depth decreases.
Center the image from side to side by moving the probe from side to side rather than heeling / toeing the probe.
Push, push, push to get through gas. This might involve having an assistant help you push.
You can also use your opposite hand (i.e., the hand not holding the probe) to push gas out of the way while you slide towards the umbilicus. This is done by spreading the fingers of this hand and placing one or two fingers on either side of probe and pushing while scanning.
If the clinical status of the patient allows, the scan can be delayed 15-30 minutes and then reattempted. This delay may allow some bowel gas to dissipate.
For patients with a strong clinical suspicion of a AAA, a “quick look” of the aorta can be attempted to save time. The probe is placed in the epigastrium in true transverse and the probe is slid rapidly toward the umbilicus. If a AAA is identified, the scan is positive and complete. If no AAA is seen, the scan should be re-started from the xiphoid process using standard technique to image the entire aorta.
The iliac bifurcation does not need to be visualized in true transverse as it is just a marker to identify the distal part of the aorta and confirm scan completion.
Trucs pour imager la bifurcation?
Tips for imaging the iliac bifurcation include:
Sweeping the probe above or below the umbilicus.
Filling the umbilicus with ultrasound gel.
Moving the probe to either side of the umbilicus and heeling the probe back to identify the bifurcation.
