Estimations of Gestational Age

Emergency physicians most frequently use pelvic ultrasound to confirm intrauterine pregnancy (IUP) in the setting of  first trimester pregnancy complications. However estimation of gestational age is also described in ACEP’s ultrasound guidelines, and is worth discussing for a few reasons:

  1. Patients further along in their pregnancies are making their ways to Emergency Departments and it helps us guide pregnancy management (see I didn’t know I was pregnant)
  2. Emergency physicians are playing larger roles in Global Health/International Emergency care and are often among the first to volunteer in disaster situations.
  3. Accurate information on gestational age is helpful for the obstetricians who will follow up with these patients.

The type of measurement depends on the patient’s trimester with biometric data from the first trimester being the most accurate as there is very little biologic variation during this period.  Essentially, trust the dating from LMP if it is unequivocal and use ultrasonographic estimates if there is a discrepancy between the LMP & biometric estimates.

  • 1st Trimester:  >5 days
  • 2nd Trimester: >7 days

Basics of Obstetric Scanning

  • Ensure your ultrasound is on OB mode; this will provide access to all necessary calculations.
  • As with all obstetric ultrasounds, first attempt a transabdominal approach, then if needed use transvaginal.
  • All measurements should be taken at least three times and averaged.
  • Estimations of gestational age in the third trimester are unreliable due to biologic variation with errors in estimates up to three weeks or greater.

Scanning: 1st Trimester

  • Gestational Sac Measurement& Double Decidual sign:
    • These findings represent the presence of hCG.
    • Their presence is NOT definitive proof of an IUP.
  • Yolk sac:
    • ~5th week (earliest embryonic structure)
  • Fetal pole with fetal heart movement:
    • ~6th week

  • Crown-Rump Length (CRL):
    • Measurement can be performed after approximately 10 weeks gestation
    • Fetus should be imaged in the longitudinal plane
    • CRL is performed by placing the calipers at the the greatest embryonic length identified from the head to the rump.
    • Do not include the yolk sac
    • Accurate within 5 days.

 

 

Second & Third Trimester

  • Biparietal Diameter (BPD) & Head circumference (HC). HC is the most accurate single measurement to help determine gestational age.
    • Both are measuredthrough the same plane with the following landmarks:
      • Anterior: frontal horns of the lateral ventricle, cavum septum pellucidum
      • Central: thalami the third ventricle
      • Posterior: occipital horns , cisterna venae magnae cerebri and insula
    • BPD is measured with calipers placed at the outer margin of the proximal parietal bone to inner margin (to avoid overestimations due to posterior acoustic enhancement) of the distal parietal bone.
    • HC is measured by placing the ellipse on the outside margin of the skull and expanding.
  • Abdominal Circumference (AC)must be precisely measured at the following landmarks to avoid overestimations:
    • Stomach and bifurcation of the main portal vein to into the right and left portal veins
    • It should also be a perfectly round section
    • AC measurement is made by placing the ellipse on the outside margin of the abdomen
    • The smallest measurement obtained should be used
    • This measurement has a high degree of intra and inter-observer variability

  • Femur Length (FL):
    • FL is measured from the origin (greater trochanter) of the distal end of the shaft (lateral condyle)
    • The bone should be perpendicular to the beam
    • Can be measured from 10 weeks onward.

 

Pitfalls & Pearls:

  • This is not an exhaustive list of biometric measurements; others exist that are beyond the scope of this article, such as foot length, ear size, orbital diameter, cerebellum diameter etc.
  • It is better to use an alternative measurement than use a poorly visualized structure.
  • The first and earliest reliable measurements and estimates of gestational should be kept, and not changed on subsequent estimates.  However if there are discrepancies between the gestational ages of two examinations, it may represent Intrauterine Growth Retardation (IUGR).
  • In twin gestations, averages can be made between the measurements of twins
  • Are EM physicians good at these measurements? Yes (see last two references)

References:

  1. Obstetric ultrasound : artistry in practice, Hobbins, John C. Blackwell Pub. 2008.
  2. Sonographic Determination of Gestational Age.  Kalish RB, Chervenak F.  TMJ. 2009; 59:2.202-208.
  3. Ultrasound in Obstetrics and Gynaecology (First Edition), Wladimiroff, Juriy. Eik-Nes, Sturla. Elsevier. 2009.
  4. Shah S et al. Accuracy of emergency physicians using ultrasound to determine gestational age in pregnant women. Am J Emerg Med. 2010 Sep;28(7):834-8. Epub 2010 Mar 26.
  5. Bailey C et al. Accuracy of emergency physicians using ultrasound measurement of crown-rump length to estimate gestational age in pregnant females. Am J Emerg Med. 2012 Feb 3.

 

Straight Suture Safety

Hopefully you are using ultrasound to guide your insertion of central venous catheters. Once they are in, you still have to suture them at some point. Straight suture needles are often used to secure arterial and venous catheters to the skin. These types of suture needles have been demonstrated to be more dangerous than curved or blunt suture needles, with up to seven times higher rate of injury for health care workers. By utilizing the plastic needle sheath present in most central venous line kits as a “thimble,” counter pressure and skin puncture may be achieved without bringing the fingers near the sharp end of the suture. Here’s an image from Bret Nelson’s article on the technique.

Panel A shows counter-pressure being applied with the cap to direct the tip of the needle. Panel B shows the needle tip safely sheathed within the cap.

The video below demonstrates this technique in real time:

 

Safety technique for straight suture needle from Sinai EM Ultrasound on Vimeo.

 

Other authors have illustrated alternative techniques to reduce the risk of self-injury when using straight suture needles.  Steven Bauer uses a 5-mL syringe to ensconce the emerging straight needle. This can provide even more distance, and he also uses it to guide tying an ‘air knot’ when needed!

Haney Mallemat has just posted a video where he demonstrates using the paper envelope the suture is packaged in to distance the needle tip from your fingers.

Keep in mind NONE of these techniques has been studied- there is no evidence that they reduce needlesticks. We DO know that using curved, blunt-tip suture needles used with needle drivers and forceps is safer than using straight sutures. Whichever method you use please be careful!

References

  • Nelson BP. Making straight suture needles a little safer: a technique to keep fingers from harm’s way. J Emerg Med. 2008 Feb; 34(2):195-7. Epub 2007 Oct 1. (PMID: 18282537)
  • Bauer S, Tauferner D, Carlson D. Improving straight needle safety: an alternate method. J Emerg Med. 2011 Jul; 41(1):e19-20. Epub 2009 Sep 17. (PMID: 19765943)
  • Centers for Disease Control and Prevention. Evaluation of blunt suture needles in preventing percutaneous injuries among healthcare workers during gynecologic surgical procedures—New York City, March 1993–June 1994. MMWR Morb Mortal Wkly Rep 1997;46:25–9. (PMID: 9011779)
  • Edlich RF, Wind TC, Hill LG, Thacker JG, McGregor W. Reducing accidental injuries during surgery. J Long Term Eff Med Implants 2003;13:1–10. (PMID: 12825744)

 

Gallbladder wall thickening

The normal gallbladder wall should measure less than 3-4mm. It is recommended that this measurement be taken through the anterior wall of the gallbladder, since posterior acoustic enhancement will often make posterior measurements inaccurate. The image above was taken in a patient with cirrhosis, chronic ascites, and no acute complaints of upper abdominal pain. While a thickened gallbladder wall is one sign of cholecystitis, there are a number of normal and pathologic states which can lead to this finding as well.

  1. Normal contracted gallbladder
  2. Hypoalbuminemia
  3. Alcoholic liver disease
  4. Increased portal venous pressure
  5. Acute viral hepatitis
  6. Heart failure
  7. Renal disease
  8. Ascites

Why does this occur? A normal gallbladder can exhibit a thickened wall of 4-5mm due to contraction alone. Typically this will occur in the setting of a lower-than-normal gallbladder volume.

For the rest, hypoalbuminemia is a major culprit in gallbladder wall thickening; alone or as a secondary mechanism in patients with cirrhosis, heart failure or renal disease. Other speculated mechanisms of gallbladder wall thickening in the disease states above are increased portal venous pressure and generalized edema. Going back through radiology journal articles older than the ones below (1970s-80s), the same mechanisms are invoked repeatedly, and other older articles are referenced. There seems to be no definitive mechanism proven to cause the gallbladder wall thickening, though many articles demonstrate that it does in fact occur, and distinct from incomplete contraction of the gallbladder itself.

Gallbladder wall thickening is often evident in adenomyomatosis and gallbladder cancer as well. In these settings the gallbladder wall diameter is directly a part of the pathology, and not a side effect of some other process as in the cases above.

Thus, this finding is not specific to acute cholecystitis. It is present in many other disease states and may even signal the clinician that there is some other pathology at play.

References:

  • Wegener M, Borsch G, Schneider J et al. Gallbladder wall thickening: a frequent finding in various nonbiliary disorders–a prospective ultrasonographic study. J Clin Ultrasound 1987 Jun;15(5):307-12. (PMID: 3149957)
  • van Breda Vriesman AC, Engelbrecht MR, Smithuis RH et al. Diffuse gallbladder wall thickening: differential diagnosis. Am J Roentgenol 2007 Feb;188(2):495-501. (PMID: 17242260)

 

Effusion

Ultrasound is quite sensitive in detecting even very small pleural effusions; it has been demonstrated to perform better than chest x-ray and nearly as well as CT scan. In order to assess for pleural fluid, the transducer should be directed through the liver (Right side) or spleen (Left side) and diaphragm. In a normal thorax, a mirror image artifact will generally be seen above the diaphragm. When effusion is present, fluid eradicates this artifact, creating an anechoic appearance in the costophrenic angle.

The image above demonstrates a common pitfall in abdominal and thoracic ultrasound. The liver is visible in the near field, and a dark anechoic structure is evident just deep to the liver. Some see this fluid and may note a positive FAST examination or free intraperitoneal fluid. Others may see this appearance and diagnose pleural effusion or hemothorax. While it is true the anechoic area represents fluid, there is a more correct response.

The inferior vena cava can generally be seen posterior to the liver, towards the patient midline. As it is filled with blood it will appear anechoic. below the diaphragm it will course parallel and to the [patient’s] right of the Aorta. Just above the diaphragm it will quickly merge into the Right Atrium.

As with most scanning, fanning through multiple planes will generally sort out the true anatomy. In the clip below we see the IVC as the operator sweeps medially, and the the pleural effusion is more evident in the lateral portions of the sweep. One (of many) giveaways is that the hepatic veins drain into the IVC, and even in this brief sweep through the IVC a hepatic vein is visible anteriorly, draining into the IVC.

Pleural effusion and mimic from Sinai EM Ultrasound on Vimeo.

ACEP US Section Discussion Forums

If you aren’t a member of the Ultrasound Section or ACEP this is a great reason to become one.

 

 

Mike Stone with help from Phil Perera and no doubt others have built a forum where you can find all of the most pertinent discussions from the section list-serve. There are a few choice topics available for your perusal and comment right now, but I’m sure this will be built into an even better resource in the future. Great Job.

 

To find the forums, head to the acep ultrasound section page and look for “ultrasound forum”.

The FALLS-protocol

In critically ill septic shock patients, assessments of hemodynamic function, fluid status and improvement of clinical status are challenging.  As a consequence of critical illness and large volume administration of crystalloids as recommended by Early Goal-Directed Therapy, comes the potential of acute (respiratory distress/failure) and long-term sequelae  (ARDS, prolonged endotracheal intubation, anasarca, bedsores, poor IV access, increased resource utilization).

The FALLS-protocol, developed by Daniel Lichtenstein introduces novel clinical parameters useful in the assessment of fluid status dynamically.  It aims to define the critical point when fluid administration is becoming deleterious to the patient (lung saturation), and we must start considering the use of vasopressors as well as the potential for respiratory failure.

Review: Lung Ultrasound basics

Utilizing a decision tree that obligates several simple cognitive and sonographic steps in the evaluation of shock, the true protocol begins when septic shock remains the most likely etiology and resuscitation has already been initiated.  By evaluating the lung parenchyma at the Blue Points, we begin with the A-profile in healthy patients.  Patients with fluid overload however demonstrate a B-profile (lung rockets emanating from the pleural line) indicative of interstitial edema.  In combination with vital signs, as we are administering fluids, we can evaluate the profile in either intervals of time or fluid aliquots.  At any of these intervals, if the patient remains hypotensive but has an A profile, we can feel confident that we can continue to administer fluids with little risk for respiratory compromise.  However, if the profile transitions to B-profile, we must consider vasopressors and advanced airway management.

Fluid administration is often guided by clinical judgment, with no clearly defined end point other than a normalized blood pressure. However, blood pressures can be corrected by vasopressors and are often given as a last ditch effort.  With the current emphasis on sepsis management in the US, EDs are coming under scrutiny for our role.  Although the FALLS-protocol still requires exhaustive study, it has the potential to allow a more finessed management of acute circulatory failure.

Reference:

Lichtenstein, D.  (2010) Wholebody Ultrasonography in the Critically Ill.  London: Springer-Verlag Berlin Heidelberg

Fluid Administration limited by lung sonography: the place of lung ultrasound in assessment of acute circulatory failure (The FALLS-protocol).  Expert Rev Respir Med. 2012 Apr;6(2):155-62.

 

Sonocloud

On July First, while most of us were busy meeting new interns, Mike and Matt from the ultrasound podcast along with Mike Stone have released into the wild their newest creation, sonocloud.

 

Sonocloud Logo
Sonocloud is awesome.  It is a copyright free compendium of all the clips you wish you had in your ultrasound quiver.  So next time you are a) putting a talk together and you can’t find you old clip of biceps tendonitis, or b) you get a really cool high quality clip yourself, head over to sonocloud to a) download an open-source clip or b) upload your own for others to use…