Posts (18)

Sep 14, 2016 · How to succeed as a Teacher - New Skills (Episode 7)

Great posts. Keep the knowledge coming!

Oct 13, 2015 · Know Your Eye Medications

Know Your Eye Medications

By Damian Baalmann, MD and Margaret Reynolds, MD

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Emergency departments in the United States provide a large amount of eye care, the majority of which is for conditions other than trauma.[1] While emergency medicine physicians often are comfortable with eye pathology, there is a certain amount of discomfort with medications beyond anesthetics. This blog post attempts to outline/summarize the different classes of emergent ophthalmological medications.

Anesthetics

White Caps

Similar to local anesthetics, there are two types of anesthetics: esters and amides. The most common anesthetics are esters are proparacaine (0.5%) and tetracaine (0.5%). Tetracaine lasts about 30 minutes in comparison to proparacaine which lasts 15 minutes but is slightly more irritating and slower in onset.

MOA Sodium channel blocker–>decreased

depolarization–>decreased action potential

Indications ·         Used to facilitate eye exams and procedures

·         Used to help diagnose corneal causes of eye pain versus other causes[2]

·         Used to treat pain from corneal abrasions in outpatient setting [3]

Special Considerations Dogma is to never use topical anesthetics in outpatient use, but recent study RCT in 2014 by Waldman et al. demonstrates increased patient satisfaction with local anesthetics within 24 hour period and no evidence of difference in corneal healing

 

Mydriatics and Cycloplegics

Red Caps

Mydriatics and cycloplegics dilate the eye. Mydriatic agents accomplish this by paralyzing the iris sphincter only causing dilation without affecting accommodation while cycloplegics paralyze both the iris sphincter and the ciliary muscles (hence cycloplegia). Dare to dilate the eye.  A common mydriatic agent is phenylephrine (2.5%) which takes about 15 minutes to work and lasts for 3-4 hours. Cycloplegics are used for inflammation of the eye. Acute inflammation is often treated by agents with several hours of action. Common cycloplegics include:

  • Cyclopentolate: onset 30-60 minutes with duration of ~24 hours
  • Tropicamide: onset 15-20 minutes with duration of ~6 hours
  • Homatropine and atropine have days to week in duration and probably have no role in the emergency department
MOA Mydriatic: sympathomimetic agent that paralyzes the iris sphincter

Cycloplegic: parasympatholytic agent that paralyzes the iris sphincter and the ciliary muscles

Indications ·         Evaluation of painless monocular vision

·         Treatment of ciliary spasms in iritis and deep corneal abrasions

Special Considerations Contraindicated in patients with suspicion for increased IOP due to acute angle closure glaucoma, presence of shallow anterior chamber or concern for ruptured globe. Blue-eyed individuals are more sensitive than brown-eyed individuals to mydriatics and cycloplegics.

 

Miotics

Green Caps

In the setting of the emergency department, the most common use for miotic agents is acute angle closure glaucoma and the most common miotic is pilocarpine (2%) which facilitates drainage of the aqueous humor by pulling the iris back from its anterior position.

MOA Constricts the pupil, pulling the iris back from its anterior position
Indications ·         Acute Closure Glaucoma
Special Considerations Do not expect any effect until IOP<40

Also consider that if patients have had cataract surgery or have atypical causes of their acute angle closure glaucoma, it may be better to dilate the eye. Consider running it by your ophthalmologist.

 

Antimicrobials

Tan Caps

Topical antibiotics are indicated for a number of ophthalmic indications including bacterial conjunctivitis, corneal ulcers, and blepharitis. Antibiotics are administered as either drops (solutions) or ointments. Ointments have longer duration, require less frequent administration but do cause blurred vision when on the eye. Drops are rapidly absorbed and require frequent instillation.

Macrolides Erythromycin 0.5% ·         Only available as ointment

·         Gram-positive and Chlamydia trachomatis coverage

·         Safe in infants and newborns

Aminoglycosides Tobramycin 0.3%

Gentamicin 0.3%

·         Excellent gram-negative and Streptococcal coverage
Fluoroquinolones Ciprofloxacin 0.3%

Ofloxacin 0.3%

Levofloxacin 1.5%

4th Gen Quinolones

·         Early generation quinolones have high resistance

·         4th gen. quinolones (gatifloxacin, moxifloxacin, & besifloxacin) have gram-negative and pseudomonal coverage and poor Streptococci coverage

o    Very expensive

o    Often used in monotherapy for corneal ulcers

Other Sulfacetamide ·         Works by inhibiting folic acid production

·         Good for blepharitis

  Bacitracin ·         Gram-positive coverage
  Polymixin B/ trimethoprim ·         Good for pediatric population

·         Broad coverage including Haemophilus

 

Topical antivirals (vidarabine and trifluridine) are used for treatment of herpes simplex keratitis but should not be given without consultation with ophthalmologist.

Steroids

Pink Caps

Topic steroids (prednisolone acetate, fluorometholone, and dexamethasone) are indicated for iritis to reduce inflammation and contraindicated in herpes simplex keratoconjunctivitis. These too should not be given without ophthalmologist consultation.

Adrenergic Agents

Blue Caps

Topical adrenergic agents include beta-antagonists (timolol, betaxolol) and alpha2-agonists (apraclonidine, brimonidine).

MOA Reduce intraocular pressure by decreasing secretion of aqueous humor by the ciliary body
Indications ·         Acute Angle Closure Glaucoma
Special Considerations Be wary of cardiopulmonary effects including hypotension, syncope, heart block and worsening of asthma

 

Systemic Medications

  • Hyperosmotic agents
    • IV mannitol (20%)
    • Decrease intraocular pressure by decreasing the volume of fluid in the eye
    • Indicated in acute angle closure glaucoma
  • Carbonic anhydrase inhibitor
    • IV acetazolamide
    • Decrease intraocular pressure by decreasing secretion of aqueous humor by the ciliary body
    • Indicated in acute angle closure glaucoma and refractory retinal artery occlusion
    • Contraindications include sickle cell disease! pH change can increase sickling of RBCs in anterior chamber which decrease aqueous outflow and increases IOP. Use caution in chronic kidney disease as it may worsen.

 

Damian Baalmann is a PGY-3 resident at Mayo Clinic Emergency Medicine Program in Rochester, MN

Margaret Reynolds is a PGY-2 resident at Mayo Clinic Ophthalmology Program in Rochester, MN

 

  1. Nash, E.A. and C.E. Margo, Patterns of emergency department visits for disorders of the eye and ocular adnexa. Arch Ophthalmol, 1998. 116(9): p. 1222-6.
  2. Sklar, D.P., J.E. Lauth, and D.R. Johnson, Topical anesthesia of the eye as a diagnostic test. Annals of emergency medicine, 1989. 18(11): p. 1209-11.
  3. Waldman, N., I.K. Densie, and P. Herbison, Topical tetracaine used for 24 hours is safe and rated highly effective by patients for the treatment of pain caused by corneal abrasions: a double-blind, randomized clinical trial. Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 2014. 21(4): p. 374-82.

 

Sep 22, 2015 · The Role of Diagnostic Thoracentesis in the Emergency Department

The Role of Diagnostic Thoracentesis in the Emergency Department

Damian Baalmann

tor

What is the role of diagnostic thoracentesis in the emergency department? This is a question that I recently found myself asking.

The Undifferentiated Pleural Effusion

 

The space between the visceral and parietal pleurae is often described as a potential space but in reality –even in a healthy individual—is a space that is occupied by fluid. In a non-smoking, otherwise healthy individual, there is about 0.13-mL/kg of pleural fluid in each space.[1] Pleural effusions can occur when there is an increase in fluid entry into the pleural space or there is a decrease in the fluid removal but most commonly occurs because of both. Pleural effusions have traditionally been classified as transudative versus exudative and thoracentesis with application of Light’s Criteria is used to differentiate the two with 98% sensitivity and 83% specificity for exudative process.[2] Transudative effusions include CHF, nephrotic syndrome, malnutrition, cirrhosis and exudative effusions include infection/empyema, malignancy, infarction, rheumatological etiologies, and pancreatitis among others.[3] The most common causes of pleural effusion in the United States are congestive heart failure, pneumonia, and cancer with annual incidences of about 500,000, 300,000, and 200,000 respectively. [2]

 

Differentiation of Exudative and Transudative Pleural Effusions (Light’s Criteria)
Exudate Transudate
Ratio of Pleural:Serum Protein >0.5 <0.5
Pleural LDH >2/3 of the upper limit of normal <2/3 of the upper limit of normal
Ratio Pleural:Serum LDH >0.6 <0.6
Only one criteria in favor of exudative is needed

Adapted from Light et al.[3]

 

Often times with patients with pleural effusions, there is high pretest probability for a certain etiology and there is probably not a need for emergent diagnostic thoracentesis. For instance, an 89 year-old female with known cancer presenting with recurrent pleural effusion and symptoms consistent with previous pleural effusions may not require a thoracentesis in the emergency department for diagnostic purposes. Even a patient with new onset pleural effusions may not require diagnostic thoracentesis; for instance, a 58 year-old male with congestive heart failure and bilateral effusions of similar size, is afebrile, and has no chest pain may just need 48 hours of diuresis. In fact, in a series of 33 cases, clinicians were able to correctly identify all 17 transudates with clinical assessment alone (later confirmed by Light’s Criteria).[4]

 

However, it would seem there is a subset of pleural effusions that remain undifferentiated even after taking in the patient’s clinical scenario; especially if there is concern for exudative processes. Consider, for instance, the patient who presents with mild dyspnea, right pleuritic pain, temperature of 37.7 who has ‘atelectasis’ on x-ray and new 1.0-cm mass on CT without PE. Is this pleural effusion secondary to this mass or an infectious process? Knowing this information would greatly change the physician’s management of this patient. It is simply not appropriate to delegate this care to an inpatient team (at least not without a discussion). At many facilities, the patient with an undifferentiated pleural effusion who is admitted overnight may not have a thoracocentesis done until late morning for various reasons. Does this mean 14-hours of unnecessary antibiotic coverage? Does this mean no necessary antibiotic coverage? It is a little bit of comparing apples and oranges, but one would never subject the patient with concern for septic arthritis or spontaneous bacterial peritonitis to these conditions. Delays in treatment of parapneumonic effusions are not benign. What starts out as a small to moderate free flowing effusion that could be managed with antibiotics alone transforms into a more loculated picture with increasing risk of sepsis, poor outcome, need for drainage and possibly even surgical intervention.[5]

 

Diagnostic Thoracentesis: Indications and Contraindications

 

Indications for a diagnostic thoracentesis is the presence of a clinically significant pleural effusion (more than 10-mm thick on ultrasound or lateral decubitus radiography) with no known cause. [2] There are no absolute contraindications to diagnostic thoracentesis. Recently there have been studies that even those with coagulation abnormalities can be safely done under the guidance of ultrasound. [6]

 

Diagnostic Thoracentesis: Well within the emergency medicine physician’s scope of practice

 

There are several known complications of thoracentesis including pneumothorax (as high as 6%), cough, infection and less common complications including hemothorax, splenic rupture, reexpansion pulmonary edema (uncommon in general but especially so in diagnostic thoracentesis), and air embolism. [7] Pneumothoraces are known complications and can occur with even an experienced physician and are three times more likely in a patient with BMI<18, nearly four times more likely in large volume (>1500-mL), and three times more likely if a second pass is required.[8] There have been numerous studies demonstrating that the complications are reduced with the help of ultrasound.[9-11]

 

Barriers that currently exist to emergency medicine physicians preforming diagnostic thoracenteses are discomfort with the procedure and a need to facilitate departmental flow. Again, the emergency medicine physician need not be intimated by the thoracentesis. Especially as we are called to far more invasive procedures on a regular basis such as central venous catheters and lumbar punctures and we can emergently manage all complications of thoracentesis. While flow is important to a department, so is timely administration of appropriate antibiotics. So if you are an emergency medicine physician and not actively preforming diagnostic thoracenteses on undifferentiated pleural effusions, consider adding it your practice.

 

 

  1. Noppen, M., et al., Volume and cellular content of normal pleural fluid in humans examined by pleural lavage. American journal of respiratory and critical care medicine, 2000. 162(3 Pt 1): p. 1023-6.
  2. Light, R.W., Clinical practice. Pleural effusion. The New England journal of medicine, 2002. 346(25): p. 1971-7.
  3. Light, R.W., et al., Pleural effusions: the diagnostic separation of transudates and exudates. Annals of internal medicine, 1972. 77(4): p. 507-13.
  4. Scheurich, J.W., S.P. Keuer, and D.Y. Graham, Pleural effusion: comparison of clinical judgment and Light’s criteria in determining the cause. Southern medical journal, 1989. 82(12): p. 1487-91.
  5. Colice, G.L., et al., Medical and surgical treatment of parapneumonic effusions : an evidence-based guideline. Chest, 2000. 118(4): p. 1158-71.
  6. Patel, M.D. and S.D. Joshi, Abnormal preprocedural international normalized ratio and platelet counts are not associated with increased bleeding complications after ultrasound-guided thoracentesis. AJR. American journal of roentgenology, 2011. 197(1): p. W164-8.
  7. Roberts, J.R., J.R. Hedges, and A.S. Chanmugam, Clinical procedures in emergency medicine. 4th ed2004, Philadelphia, PA: W.B. Saunders. xiv, 1486 p.
  8. Ault, M.J., et al., Thoracentesis outcomes: a 12-year experience. Thorax, 2015. 70(2): p. 127-32.
  9. Koh, D.M., et al., Transthoracic US of the chest: clinical uses and applications. Radiographics : a review publication of the Radiological Society of North America, Inc, 2002. 22(1): p. e1.
  10. Barnes, T.W., et al., Sonographically guided thoracentesis and rate of pneumothorax. Journal of clinical ultrasound : JCU, 2005. 33(9): p. 442-6.
  11. Jones, P.W., et al., Ultrasound-guided thoracentesis: is it a safer method? Chest, 2003. 123(2): p. 418-23.

 

 

Sep 18, 2015 · A Learner’s Perspective on Social Media Medical Education versus Traditional Medical Education

Thank you for your comments! Definitely a lot of potential and excitement for the future of social media education.

Sep 16, 2015 · A Learner’s Perspective on Social Media Medical Education versus Traditional Medical Education

Thank you for your comments Damian. As a relatively new user of SoME and FOAMed, “Top 10 ways to reconcile social media and ‘traditional’ education in emergency care” was a great paper to dive into the topic.

I was more generalizing about social media medical education. I think there are definitely examples such as St. Emlyns. Great point that traditional medical education may not teach critical analysis well. I did a quick literature search and could find nothing to really support traditional medical education in this regard. Would be interesting to investigate further. Again, thank you for the comments!

Sep 16, 2015 · A Learner’s Perspective on Social Media Medical Education versus Traditional Medical Education

Author: Damian Baalmann

post-social

The following post is a learner’s response to “@SirBill: the power of social media to transform medical education”[1] and “Top 10 ways to reconcile social media and ‘traditional’ education in emergency care”[2]

 

Social media use in medical education is an emerging field of scholarship in emergency medicine that has the potential to enhance patient care, medical knowledge, and practice based-improvement. Social media is the social interaction among people in which they create, share or exchange information and ideas in virtual communities and networks[3]. These interactions in the medical community and medical education have exploded over the past several years, particularly in emergency medicine. Several papers and blog posts including the two listed above describe the strengths and weaknesses of social media in education from a teacher’s perspective particularly with regard and reference to traditional medical education. Although all physicians are both learners and teachers at some level, this article will approach the topic from a learner’s perspective. In doing so, the strengths and weaknesses of social media in medical education will be examined in four different features of learning: the purpose of medical education, the appearance of successful learning, the appearance of the successful learner, and the structure of successful learning.

 

The Purpose of Medical Education

 

As medical professionals, we both learn because we must and because we are curious. We must learn to provide appropriate, up-to-date patient care by identifying and managing pathology utilizing safe, evidence-based methods. Furthermore, we learn because we are curious about new, innovative approaches, ideas, and advances in medicine. For both of these reasons, the purpose of medical education cannot be solely the transfer of information. The purpose of medical education is that the learner should know more than the teacher. This is achieved by not merely learning information, but learning how to acquire information and appraise it. From a learner’s perspective, it would seem that social media falls short in medical education in this regard. Certainly the opportunities to acquire information are present, but the methodology on how to acquire it and appraise it is not well demonstrated. Roland and Brazil point out that this is very similar to traditional medical eduction in which one would use a journal article to answer a clinical question and be faced with the same obstacles in knowing where to look for the information and how to appraise it. However, in many medical schools and residency and faculty journal clubs, the learner is taught and practiced in this regard to journals, but not so with social media. As Roland and Brazil state, ‘the principles are the same, but the tools are not’ and from a learner’s perspective there remains work/education to be done in how to acquire and appraise social media medical education.

 

The Appearance of Successful Learning

 

The appearance of successful learning is probably more of networking and mapping information than it is of building a pyramid of knowledge. In either model, context is everything. Successful learning acknowledges that learners come from different contexts, need different things and probably the best judge of context is the learner themselves. This is probably where social media has advantages over traditional medical eduction. I entered medical school with a strong biochemical background a virtually no background in anatomy and pathophysiology where as some of my classmates were well versed in anatomy but knew little about the Kreb’s cycle. Regardless, we sat through the same lectures and while I napped my way through biochemistry, I struggled with anatomy. In medical education, context is everything. Sherbino and Frank speak of this with relation to the flipped classroom approach (which is often paired in the social media medical education discussion): social media provides many different resources/mediums and contexts for different learners. From a learner’s perspective, social media medical education takes on the appearance of successful learning by providing a network that the learner can grow and map out information based on their own context and needs.

 

The Appearance of the Successful Learner

 

The appearance of the successful learner is not one who can just spew back information without understanding it and is not one who determines limits for other learners.[4] The appearance of the successful learner is one who creates and gathers information for their own learning and does so seamlessly. Social media provides many avenues for this to occur. Rather than a governing body proposing limitations/clinical policies or a CME course providing a slew of facts, social media, through free open access medical education, allows for more innovation and freedom of thought by the learners. Unlike a traditional didactic series, the appearance of the learner is not one who is passive, but active and seeking out their learning material. Roland and Brazil acknowledge this by using the example of role modelling and personal reflections through social media and that the healthcare provider is more than a sum of their clinical knowledge and that social media provides the necessary feedback and comments that can facilitate this. Additionally, social media allows, from the learner’s perspective, the ability to made decisions for themselves. While in a traditional format, the learner may feel more pressure on what is taught as dogma, in social media, there exists more discussion of ideas without absolutes. The danger of this is when the learner does not take the time or is not experienced in making decisions and falls short and embraces or rejects something inappropriately.

 

The Structure of Successful Learning

 

If the appearance of successful learning is networks, the appearance of the structure of such a network would be a map demonstrating the collected pieces of information and how they relate. The learner is the cartographer, but how does one make sure the map is inclusive of the appropriate ideas? Despite the appearance of the successful learner being one who is more of innovation and freedom of thought, there is still a need for a curriculum. Despite the learner knowing his or her context, there is still a box of information that all providers must know. Traditionally, medical education curriculum has been manifested through the contents of a governing text book or a residency lecture syllabus or contested through board examinations. From a learner’s perspective, social media falls short here. Roland and Brazil speak of this specifically in their paper. They state, “Use social media as a medium, not a curriculum” and this is especially true for a learner. In my experience, there is a tendency for social media to rally around attractive topics in emergency medicine such as critical care and procedures and abstain from core topics that are less attractive like urinary tract infection microbial coverage. So, from a learner’s perspective, curricula should be held independent of social media education and possibly populated by social media education and completed with traditional sources. Finally, as a learner, one can see a lot of opportunity for improvement of the structure of social media medical education. As of now, so many varied sources and thoughts and ideas exist without connections, links or true networking. There certainly exist possibilities through Twitter and Reddit to engage and connect those ideas.

 

Conclusion

 

As an aspiring successful learner, there exists many opportunities to incorporate social media into my medical education. There is no place for replacement of traditional medical education but likely there can be coexistence and complementation. Social media medical education certainly has the capacity to meet the individual learner at their context and allows for more innovative and self-learning however may require some augmentation and further more work regards to methods on how to appraise it and how to successfully incorporate it into a learner’s curriculum.

 

 

  1. Sherbino, J. and J.R. Frank, @SirBill: the power of social media to transform medical education. Postgraduate medical journal, 2014. 90(1068): p. 545-6.
  2. Roland, D. and V. Brazil, Top 10 ways to reconcile social media and ‘traditional’ education in emergency care. Emergency medicine journal : EMJ, 2015.
  3. Contributors, W. Social Media. 5 September 2015 12:56 UTC; Available from: https://en.wikipedia.org/w/index.php?title=Social_media&oldid=679581145.
  4. Cormier, D. Workers, soldiers or nomads – what does the Gates Foundation want from our education system? 22 October 2011 08 September 2015]; Available from: http://davecormier.com/edblog/2011/10/22/workers-soldiers-or-nomads-%E2%80%93-what-does-the-gates-foundation-want-from-our-education-system/.

 

 

Image from JD Hancock via flickr used under CC BY 2.0

Sep 10, 2015 · Aortic Dissection and D-Dimer

D-dimer and Aortic Dissection

Damian Baalmann

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A 39 year-old, previously healthy, male presents to your emergency department with the chief complaint of chest pain. As the nursing staff gets the patient hooked up to the monitor, you learn from the patient that he experienced a sudden onset of  a constant, ‘tearing type’ 6/10 pain in the substernal part of the chest that radiates to his shoulders and his back about 6 hours ago without appreciable aggravation or alleviation. The patient denies shortness of breath, nausea, vomiting, fevers, chills, cough, history of cardiac disease, history of DVT/PE, unilateral leg swelling or posterior calf pain. Patient has no appreciable past medical or surgical history.  He takes no medication regularly. For social history, the patient is married, father of 3 children, works out regularly and denies history of smoking, illicit drugs or excessive alcohol use.

On exam you note a somewhat comfortable, normal heighted male with a blood pressure of 141/89, heart rate of 61, oxygen saturations of 100% and non-labored respirations at a rate of 16 breaths per minute. Exam is remarkable for clear lung sounds, regular rhythm with no murmurs, and equal 2+ radial pulses. There is no evidence of lower leg swelling or posterior calf pain. An electrocardiogram is handed to, as per your emergency department protocol, which demonstrates normal sinus rhythm without evidence of ischemia or arrhythmia. You quickly run through a differential diagnosis and consider, among other things, aortic dissection.

The Low Risk Patient

Aortic dissection is a longitudinal tearing of the wall of the aorta, which produces a false lumen that often propagates. Aortic dissection is a rare, but deadly pathologic process. The incidence is 3 in 100,000 people per year[1]. Of every 10,000 emergency department visits, aortic dissection is only seen about once.[2] Mortality for untreated proximal aortic dissection is about 25% by 24 hours of initial presentation and 80% at two weeks[3]. Furthermore, clinicians are not good at detecting aortic dissection. The diagnosis is missed in up to 38% of patients on their initial evaluation and unfortunately, 28% of the time, the first diagnosis of dissection is made on post mortem examination [1]. Although CT, TEE, and MRI are all common ways to evaluate for dissection, it would appear that spiral CT with contrast and appropriate electrocardiogram gating is the most sensitive imaging with sensitivity and specificity approaching 100%[4].

So how does one approach the patient in which aortic dissection is considered but has low risk or low pre-test probability? Furthermore, what constitutes low risk or low pre-test probability? The Aortic Dissection Detection (ADD) Risk Score was developed to address the latter question. The ADD Risk Score was put forth as part of a joint guidelines between 10 professional societies (emergency medicine not included) which is a total of 12 risk markers divided among 3 categories: predisposing conditions, pain features, and physical findings[5]. Risk score ranges from zero to greater than one depending on how many of the categories the patient has risk markers present in. A score of zero was found in 4.3% of aortic dissections in a retrospective analysis of analysis of the International Registry of Acute Aortic Dissection done by Rogers et al[2]. Further validation was performed by Nazerian et al with a prospective study with 1328 patients who aortic dissection was suspected in. In this study, if the ADD was 0 (or low risk), the prevalence was about 6%. The overall prevalence of dissection was very high in this study, however, at about 22%. [6] Is 4-6% an acceptable miss rate in aortic dissection? Probably not given that the outcome of dissection left untreated is such a devastating disease process. For comparison, a low-probability Well’s Score is associated with 2-4% prevalence of pulmonary embolism [7].

Aortic Dissection Detection Score
Predisposing Conditions Pain Features Physical Exam Findings
Marfan Syndrome

Family history of aortic disease

Known aortic valve disease

Recent aortic manipulation

Known thoracic aortic aneurysm

Abrupt Onset of Pain

Severe Pain Intensity

Ripping or tearing pain

Pulse deficit or SBP differential

Focal neurological deficit + pain

New Aortic Insufficiency murmur + pain

Hypotension/Shock State

If positive in any column, then add one point

Score=0; low risk (4.3%)

Score=1; intermediate risk (36.5%)

Score >1: high risk (59.2%)

Adapted from Rogers et al. [2]

 

 

The Role of D-dimer in Dissection

Before diving into the discussion on D-dimer and aortic dissection, it should be noted that there are many studies and even many meta-analyses regarding this topic. This is probably an indicator that there is no decisive study to define the role of D-dimer in aortic dissection.  That being said, there likely is a role for D-dimer, if somewhat limited, in the evaluation of aortic dissection.

Shimony et al conducted a meta-analysis of D-dimer in aortic dissection including 734 patients across seven studies which demonstrated plasma D-dimer less than 500 ng/mL was 97% sensitive with a negative LR of 0.06 [8]. There are at least four other meta-analyses and systematic reviews that demonstrate similar results [9-12]. Pitfalls of these meta-analyses and systematic reviews and Shimony et al are that the studies that are included are primarily retrospective cohorts sprinkled with case series and case-control studies and the studies lack any uniform analysis of D-dimer. Recently a meta-analysis was published in Annals of Emergency Medicine by Asha and Miers regarding D-dimer and aortic dissection. This paper included four prospective studies with a total 1,557 patients and a cutoff of 500 ng/mL for a negative D-dimer result and concluded a sensitivity of 98% and a negative LR of 0.05.[13] This paper also had pitfalls including an inherit selection bias, eliminating a third of the participants of the largest study because that particular study did not have D-dimers reported and all of the studies included in this meta-analysis had incidences of dissection between 23% to 48%.

Applying the D-dimer

How can this test be applied to the patient with concern for aortic dissection? If one uses the pre-test derived from the ADD scoring system and a negative LR of 0.05 derived from the discussed meta-analyses, it is easy to see that the D-dimer is probably only good enough for the low pre-test probability patients. So again, the question is who is low risk? Recalling the validation of the ADD Risk Score, low risk patients were defined as an ADD score of 0. The biggest issue with this is that likely any patient that one is considering dissection in, likely has one of the 12 risk factors in the ADD placing their risk score >0 automatically making them intermediate risk. For instance, the clinical vignette above describes a person if not for the characteristic of the pain; aortic dissection would not seriously be in the differential. There is a very small group of patients who there is concern for aortic dissection and who have an ADD scoring system of 0.

Gorla et al tackled this question with “Accuracy of a diagnostic strategy combining aortic dissection detection risk score and D-dimer levels in patients with suspected acute aortic syndrome”. In this paper, ‘low probability’ was defined as an ADD less than or equal to one. In this study, 376 patients were evaluated for dissection. Of these, 319 patients had an ADD score less than or equal to one and 57 patients had a ‘high probability’ with ADD score greater than one. Of those in the 319 patients in the ‘low probability’ group with D-dimers less than 500 ng/dL, none were found to have dissection but two were found to have aortic ulcers. This left the ‘low probability’ plus negative D-dimer with a sensitivity of 98.7% and NPV of 99.2%.[14] Probably the largest pitfall of this study was that there was an incidence of 23% for aortic pathology which is much higher than most literature suggests.

Pitfalls of D-dimer in Aortic Dissection

These factors in acute aortic dissection are known to cause a false negative D-dimer test:[15]

  • Chronic aortic dissection
  • Time from symptom onset > 48 hours
  • Presence of thrombosis or intramural hematoma
  • Short length of dissection
  • Young Age

Bottom Line

The bottom line is that D-dimer can likely be used in a select low pretest probability group for aortic dissection. The real question is who is low pretest probability? It is still up to the clinician and their gestalt as well as how comfortable they are deciding that a patient with an ADD score of 1 is low pretest probability. Furthermore, indiscriminate use of D-dimer for any chest pain will result in more unnecessary radiological testing.

Return to the Vignette

Decision is made that patient is not low probability for dissection given ADD score of 1 and CT scan was ordered which was negative for dissection. Patient dismissed after 3 hour troponin was negative, his pain had resolved, and lack of emergent pathology was discovered.

 

Currently, there is no good quality evidence to support the use of risk stratification models or to adopt the use of D-dimer in low-risk patients; as stated by the current ACEP clinical guideline in the topic[15]. (Editor’s Note)

 

  1. Meszaros, I., et al., Epidemiology and clinicopathology of aortic dissection. Chest, 2000. 117(5): p. 1271-8.
  2. Rogers, A.M., et al., Sensitivity of the aortic dissection detection risk score, a novel guideline-based tool for identification of acute aortic dissection at initial presentation: results from the international registry of acute aortic dissection. Circulation, 2011. 123(20): p. 2213-8.
  3. Khan, I.A. and C.K. Nair, Clinical, diagnostic, and management perspectives of aortic dissection. Chest, 2002. 122(1): p. 311-28.
  4. Sommer, T., et al., Aortic dissection: a comparative study of diagnosis with spiral CT, multiplanar transesophageal echocardiography, and MR imaging. Radiology, 1996. 199(2): p. 347-52.
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