US articles: PTX in trauma, FAST for Thoracotomy, Pedi Hip Effusions

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Brown Ultrasound Tape Review:  10/15/15

Article 1: FAST Exam to Predict Survivors of ED Thoracotomy

Inabi, et al. FAST Ultrasound Examination as a Predictor of Outcomes After Resuscitative Thoracotomy. Annals of Surgery 262(3):512-518, 2015.

Fresh off the trauma surgical press last month, this study examined the utility of FAST exam (specifically parasternal and subxiphoid cardiac views) to predict positive outcomes (survival to discharge or organ donation) of ED resuscitative thoracotomy (RT).

This was a prospective cohort study at LA County/USC Medical Center. In 3.5 years, 187 patients arrived in traumatic arrest and underwent FAST and RT (that’s 4-5 thoracotomies a month – WOW!). They documented +/- pericardial fluid and +/-  cardiac motion. PGY2-4 EM residents performed the FAST exams after some formal training, and they were supervised by “faculty” – not clear if those were surgeons or EM attendings.

About ½ patients lost vitals at the scene and another ¼ both en route and in the ED. Overall survival – 6 patients (3.2%). Overall organ donation – 3 patients (1.6%). Cardiac motion on FAST was 100% sensitive for the identification of survivors and organ donors (and 73.7% specific).  While the tables and discussion include a lot on the presence or absence of pericardial fluid, this did not impact the sensitivity or specificity of FAST. If cardiac motion was absent, the likelihood of survival was 0.

Bottom line: Given that RT is such a high risk, low survival procedure, cardiac FAST can be used (with excellent sensitivity) to identify traumatic arrest patients with better odds of survival or organ donation from ED thoracotomy. No cardiac motion means pretty much no chance of survival or organ donation.


 

Article 2: Handheld E-FAST for Pneumothorax

Kirkpatrick, et al. Hand-Held Thoracic Sonography for Detecting Post-Traumatic Pneumothoraces: The Extended Focused Assessment With Sonography for Trauma (EFAST). Journal of Trauma 57:288-295, 2004.

This was another trauma surgery study out of Vancouver Hospital and Health Sciences Centre interested in the test characteristics of hand-held US to look for PTX in trauma patients. They compared EFAST examinations for PTX to:

(1) CXR results

(2) a “composite standard” of clinical information, which included some combination of CXR, CT if it happened, clinical course, and need for chest tubes/needle decompression

(3) CT alone (the gold standard for patients who had a CT).

This was a retrospective chart review on trauma patients (note – those who were in “physiologic extremis” with suspected PTX were excluded). All EFASTs were done by the attending trauma surgeon using a linear transducer. They looked for lung sliding or comet tail artifacts or color power Doppler evidence of pleural sliding in at least 3 rib spaces. PTX was diagnosed if neither sliding nor comet tail artifacts were seen.

Continue reading

When life gives you LEMONs- Predicting difficult intubations in the ED

Article:

Reed MJ, Dunn MJ, & McKeown DW. Can an Airway Assessment Score Predict Difficulty at Intubation in the Emergency Department? Emerg Med J 2005; 22(2): 99 – 102.

Main Points:

  1. Rapid assessment tools can be helpful in predicting difficult intubations in the emergency department
  1. Use of SOME elements of the LEMON (look, evaluate, mallampati, obstruction, neck mobility) approach to airway assessment MAY be helpful in predicting likely laryngoscopic view (Cormack- Lehane grade) as a proxy for difficulty of intubation. The following are more likely found in patients with high grade views (2-4).
  • large incisors
  • reduced inter-incisor distance
  • reduced thyroid to floor of mouth distance

Background:

Predicting difficult intubations is not always straightforward. At the time of publication (2005), little validation of rapid assessment of possible difficult intubations in the ED. The authors test the use of the LEMON approach as a predictor of difficult intubations, and suggest key parts of the assessment that are most helpful.

 

Details:

The study was a prospective, observational trial conducted in the UK at a teaching Emergency Department between June 2002 and September 2003.   156/177 patients intubated over that time were included in the study. Those excluded were done so because no LEMON assessment was completed. Of the remaining included, a modified LEMON assessment was completed including: LOOK- facial trauma, large incisors, large tongue, facial hair; EVALUATE- inter-incisor distance (<3 fingers), hyoid-mental distance (<3 fingers), thyroid to floor of mouth distance (<2 fingers); MALLAMPATI 1/2 versus 3/4 ; OBSTRUCTION; and NECK MOBILITY- cervical collar versus no collar. One point was assigned for each criterion that was found. If a criterion was though unassessable, a score of zero was given. Outcome was determined by laryngoscopic view as outlined by the Cormack-Lehane grading scale; grade 1 was considered an easy intubation, grades 2-4 were considered difficult. ALL intubations were successful, and if multiple attempts were used, the grade of view on the successful attempt was used. Authors used Fischer’s exact test to compare the categorical variables, Student’s t test to compare continuous data. Spearman rank sum test was used to assess correlation between categorical variables.

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Peds EM Follow Up 2015: Pediatric Osteomyelitis

2 Articles of Interest & An Excruciating, Detailed and Lengthy Guide to Diagnosis and Management

 

Dartnell J, Ramachandran M, Katchburian M. Haematogenous Acute and Subacute Paediatric Osteomyelitis: A Systematic Review of the Literature. J Bone Joint Surg Br. 2012 May;94(5):584-95.

  • A meta-analysis of 1854 papers, 132 of which were examined in detail
  • 40% of patients were afebrile
  • Tibia and femur were most common sites
  • Exam, labs, and imaging must be used in combination
  • S. aureus > Kingella > other
  • Typical treatment: start empiric IV abx, switch to PO when possible

Harris JC, et al. How Useful are Laboratory Investigations in the Emergency Department Evaluation of Possible Osteomyelitis? Emerg Med Australias. 2011 Jun;23(3):317-30. Epub 2011 Apr 4

  • A meta-analysis of 36 studies of adults and children
  • Recommended algorithm:
    • Adults and kids w/ low pretest probability: nL ESR and CRP<5 → done
    • Med/high pretest probability and puncture wounds: nL ESR and CRP<5 → LOW NPV
    • ESR >30 and/or CRP>10-30 → further investigation (imaging) required
    • WBC count is not especially helpful!

Osteo locations

 

PEDIATRIC OSTEOMYELITIS:

  • Definition: bacteria infecting bone
  • Usually hematogenous spread, but can be direct inoculation (surgery, open trauma, puncture, etc) or contiguous spread (skin, sinus, dental infections)

CLINICAL PRESENTATION

  • Constitutional symptoms, irritability, decreased PO
  • +/- fever
  • Localized pain, bony tenderness
  • Functional limitations, i.e. unwilling to crawl or walk
  • Time course: usually several days to >1 week
  • Risk factors: bacteremia, sepsis, immunocompromised, indwelling catheters/hardware, prematurity, skin infection, complicated delivery, GU abnormalities

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Orthopedic Review: Distal Radius Fracture Reduction

Case: 64 yo F presents to the Emergency Department after tripping over a curb and suffering a FOOSH (fall on outstretched hand) injury. There is obvious deformity about the wrist with associated swelling and tenderness. X-ray imaging reveals the following:

Her exam and imaging are consistent with a distal radius fracture. How do you treat this?

Page ortho?

Providing adequate analgesia, reduction of fracture, and proper splinting is well within the scope of EM practice, especially in the community setting. This post will review the technique of hematoma block for analgesia as well as the different techniques for reduction of distal radius fractures and application of splint.

Hematoma Block

  • Can be used alone or in combination with other analgesic modalities such as IV narcotics or benzodiazepines
  • Simple technique
  • Very few complications

 

But is hematoma block effective?

  • In 2011, prospective randomized controlled trial comparing hematoma block to conscious sedation with IV Propofol
  • 96 patients underwent randomization and researchers compared patients’ pain using VAS (visual analog scale) during the procedure and after the procedure
  • Patients who received Propofol had pain scores of 0 during the procedure compared to 0.97+/-0.7 in patients who received hematoma block
  • After the procedure, patients who received Propofol had pain scores of 2.72+/-0.7 compared to 2.25+/-0.2 in patients who received hematoma block
  • Patients who received hematoma block had significantly shorter ED stay times (0.9hrs vs 2.6 hrs)

Hematoma blocks result in similar analgesia as conscious sedation with IV Propofol AND leads to shorter ED stay times

Setting up for the procedure:

  • 10cc 1% Lidocaine
  • 10cc syringe with 2 large needles (one for drawing up Lidocaine, one for injecting)
  • Skin cleanser (betadine, Chloraprep, or alcohol wipe)

Procedure Technique:

  1. Identify the fracture site by palpating along the dorsal aspect of the forearm to feel for bony step-off. Cleanse this entire area thoroughly with skin cleanser.
  2. Insert needle attached to syringe filled with 10cc 1% Lidocaine at that site and advance needle along periosteum until needle falls into fracture site.
  3. Draw back on plunger to aspirate blood confirming the needle is in the fracture site.
  4. Inject 10cc Lidocaine into fracture site and remove needle.
  5. Allow 10-15min to pass to ensure full analgesic effect.

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CITW 7: A Swollen Elbow

Welcome back to another Clinical Image of the Week from the case files of the Brown EM Residency!

HPI: 6 year old male presents to the ED after falling about 4 feet off the monkey bars at his school playground, landing on his right arm. He’s had worsening pain and swelling of the right elbow since the fall, resulting in limited range of motion.  He denies numbness, tingling, or weakness. He sustained no other injuries.

Vitals: BP 107/72, HR 105, T 98.7 °F, RR 22, SpO2 100 % on RA

Notable PE: There is mild swelling of the right elbow, with limited active range of motion, but intact passive range of motion.  No obvious deformity. He is tender in the lateral supracondylar region. His right upper extremity is neurovascularly intact.

Plain films were obtained:

Rad Head 1

Rad Head 2

What’s the diagnosis?

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LBBB doesn’t have to block an MI diagnosis

What we are taking about:

Sgarbossa EM, et al. Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators. N Engl J Med. 1996 Feb 22;334(8):481-7.


Main Points:

In the presence of a left bundle branch block, suspect acute infarction when:

  1. ST-segment elevation ≥1 mm and concordant with QRS complex
  2. ST-segment depression ≥1 mm in lead V1, V2, or V3
  3. ST-segment elevation ≥5 mm and discordant with QRS complex

Background:

The presence of left bundle branch block on the electrocardiogram may conceal the changes of acute myocardial infarction, which can delay both its recognition and treatment. This study aimed to identify electrocardiographic criteria for the diagnosis of acute infarction in the presence of left bundle-branch block.


Methods:

This was a retrospective cohort study looking at electrocardiograms of North American patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial who presented with chest pain, had left bundle-branch block on baseline EKG, and acute myocardial infarction confirmed by enzyme studies (total of 131 patients). These EKGs were blindly compared with the electrocardiograms of control patients from the Duke Databank for Cardiovascular Disease who had chronic coronary artery disease and left bundle-branch block. The patients in the control group did not have acute chest pain at the time of the electrocardiographic recording.

Multivariate Analysis was used to determine independent predictors of acute myocardial infarction. These criteria were used to develop a scoring system to identify patients with acute myocardial infarction. Continue reading

Pigtail Catheter Placement for Pneumothorax

Traditionally, a pneumothorax has been treated with a large bore chest tube connected to suction, with inpatient observation until the chest tube can be pulled.   The patient, if stable, would then be discharged home.  Persistent discomfort, infection, and other complication rates are not insignificant.

More recently, there has been a push to treat stable small pneumothoraces with less invasive methods such as observation or small bore chest tubes. In cases of unstable patients or those with hemopneumothoraces, a large bore chest tube continues to be the most appropriate treatment.

Pigtail Catheter Indications

  • Drainage of air or thin simple fluid
  • Current teaching is for PTX usage only if <40%
  • How to know if fluid is simple? Lateral decub XR to see if fluid layers out onto the side

 

Hunting and Gathering

Find a workstation on wheels (WOW) with a functioning Topaz to obtain informed consent

Supplies

IMG_1946

  • Pigtail Catheter kits are currently not kept in clean utility rooms or in the critical care rooms. You will need to CALL SUPPLY and have them bring you a kit.
  • Extra 1% lidocaine
  • Sterile Gloves
  • Sterile Gown
  • Hat
  • Mask with eye shield
  • Sterile flush or 10cc of sterile saline

Setup

  • Patient Position: supine with arm above head, same as for a thoracostomy tube. Consider soft restraints to help the patient keep the arm in position.
  • Draw up your lidocaine into the provided syringe
  • Place the dilator all the way into the pigtail catheter
  • Prep the guidewire into the red applicator
  • Load the finder needle syringe with 3-4cc of sterile saline. Or take the sterile flush and discard 6-7cc of saline. Connect to the finder needle

The Procedure

Continue reading

EUS: Retinal Detachment & SSTIs

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Brown Ultrasound Tape Review:  9:24:2015

 

ARTICLE #1  –  Suddenly, painlessly blind?  Keep calm and get the Ultrasound.

Vrablik et al.  The Diagnostic Accuracy of Bedside Ocular Ultrasonography for the Diagnosis of Retinal Detachment: A Systematic Review and Meta-analysis.  Annals of Emergency Medicine 2014; 20: 1-6.

 In this systematic review, Vrablik et al assessed the diagnostic accuracy of ED Ocular US for retinal detachment.  They whittled 7771 unique citations down to 4 trials that included a total of 201 ED patients, where EUS Dx was compared to Ophthalmologic evaluation and/or Orbital CT.  Prevalence was 15-38%, sensitivity and specificity of EUS were 97-100% and 83-100%, respectively.

 This modality may be helpful because 1) vision-threatening complaints are time sensitive, 2) formal dilated fundoscopic exam may be impractical or impossible in the busy ED setting, and 3) formal Ophtho consultation may be limited or unavailable in some EDs.  These studies were small and participating physician training was variable, but results showed that we can reliably make this diagnosis in the ED with a linear array probe.

  We discussed distinguishing retinal detachment from vitreous hemorrhage or vitreous detachment (keeping in mind these are not mutually exclusive).  Retinal detachment classically presents as sudden, painless, monocular visual impairment, like “looking through a curtain.”  EUS will show the “sail sign”, a funnel shaped, sharply defined, reflective, linear membrane anchored to the optic disc and waving serpiginously as the patient moves their eyes.  In vitreous detachment the patient may describe “floaters” or “flashes of light” that move with eye movement, and EUS will show the “seaweed sign”: fine, granular, swirling echogenic debris in the posterior eye, with no tethering to the disc.

Retinal_detachment  Retinal Detachment  (www.foamem.com)

Vtreous_Detachment_main  Vitreous Detachment  (www.ultrasoundvillage.com)

 

 

ARTICLE #2  –  To incise, or not to incise, that is the question.

Squire et al.  ABSCESS: Applied Bedside Sonography for Convenient Evaluation of Superficial Soft Tissue Infections.  Academic Emergency Medicine 2005; 12(7): 6011-607.

 This study investigated the utility of EUS in detecting subcutaneous abscesses in 107 patients with presentations concerning for cellulitis vs abscess.  Residents and Attendings who had received a 30min training session were eligible, and their Clinical and EUS diagnoses for “+/- abscess” were compared to +/- pus with I&D, or +/- antibiotic failure at 7 day follow up (failure meaning most likely it was an abscess).

 

Sensitivity NPV Specificity PPV
Clinical Dx 86% 77% 70% 81%
EUS Dx 98% 97% 88% 93%

 

Interestingly, there were 18 cases where EUS and Clinical Dx disagreed, and EUS proved correct in 94% (n=17) of them: 9 of the negative Clinical Dx cases (23%) became positive with EUS, and 9 of the positive Clinical Dx cases (13%) became negative with EUS.  Many of the ED sonographers also discovered nerves and vessels, which changed management…most significantly for 4 of the falsely positive Clinical Dx patients, of whom 3 had hematomas and 1 had an aneurysm (#whoathatwasclose).  But while the investigators did prove that EUS can more accurately identify abscesses, they did not report any patient-centered outcomes, such as less antibiotic use, faster recovery, fewer complications, fewer return visits, or less recurrence.  So in summary, it remains to be seen whether the findings here should definitely change practice at this time.

 We also reviewed the EUS-for-abscess technique: with the linear probe placed on the skin, an abscess will appear as a hypoechoic heterogeneic mass, generally spherical with ill-defined borders, and with variable internal echoes (pus) that will “swirl” with compression.  Cellulitis is generally more hyperechoic and more uniform.

 

BROWNsound BONUS:   TAPE REVIEW RAPID FIRE!

– Achilles Tendon rupture: appears as a defect with surrounding hypoechoic hemorrhage

– B lines (lung US):

     1) must obliterate the A lines

     2) must be linear

     3) must go 18cm deep

     4) must be persistent

     5) must be more than 3 per zone

     6) must be more than 2 rib spaces per side to support HF

– Appendicitis:

     1) must be non-compressible

     2) must be a blind-ended pouch

     3) must be tender-to-palpation

     4) must be 6mm outside-to-outside to be “too big”

– Tamponade:  RV must collapse during diastole

– IUP:

     1) In the sagittal view the bladder apex correlates with the cervix, which may helps avoid confusion between the vagina and the endometrial stripe

     2) Key cutoff:  fluid tracking <2/3 up the uterus (in the caudal direction) may be physiologic; >2/3 is more likely pathologic

 

Horrid Local Envenomations

Below is the Hickory Tussock Moth caterpillar, which is quite prevalent in this region every fall (this particular one was photographed just outside my garage).  Despite the black-and-white warning coloration, children and adults often deliberately handle these insects and rapidly develop urticaria and pain at all points of contact.  This insect has multiple irritant spines, some of which may contain histamine, and while the reaction is rarely dangerous it is dramatic and very uncomfortable.

Hickory Tussock Moth caterpillar

Hickory Tussock Moth caterpillar

Treatment is supportive.  In particular, I recommend saturating gauze pads with 1% lidocaine with epinephrine and applying them over areas of irritated skin, and leave in place for at least 20 minutes.  This action will treat both the pain and urticaria.  With lidocaine, always be mindful of the total dose that the patient can tolerate (5-7mg/kg) even with topical application.  Antihistamines are also helpful, as well as brief lesson about warning coloration amongst our animal friends.

A clot in the lungs! And you are too nonspecific! You give D-dimers a bad name.

This is part of a recurring series examining landmark articles in Emergency Medicine, in the style of ALiEM’s 52 Articles.

Discussing: Wells, P., Anderson, D., & Rodger, M. (2001). Excluding Pulmonary Embolism at the Bedside Without Diagnostic Imaging: Management of Patients With Suspected Pulmonary Embolism Presenting To the Emergency Department By Using a Simple Clinical Model and D-dimer. Annals of Internal Medicine, 135(2), 98–107.

 

Main Points: Wells’ scoring system for risk of PE, when combined with a negative D-dimer, is useful to rule out patients unlikely to have significant illness from PE within the next 90 days.

  1. This scoring system combined with D-dimer measurement does not accurately identify patients who are likely to have PE at this encounter or subsequent encounters.

 

Background: Pulmonary embolism (PE) is a common disease (CDC estimates for 2015 are up to 1 in 1,000 persons) and half of patients with PE are not properly diagnosed in the ED due in part to non-diagnostic results of a V/Q scan. This reality presents a diagnostic challenge to ED physicians who are determining which patients should receive a CT scan, and risk stratifying patients for a PE. This study sought to validate the Wells’ Criteria  for determining pretest probability of pulmonary embolism in the ED population.

 

Methods: This was a prospective cohort study of consecutively recruited ED patients at four medical centers in Canada from September 1998 to September 1999. The authors excluded patients with upper extremity deep vein thromboses (DVTs) as the likely source of PE, patients who were symptom free for three days prior to presentation, those who had been on anticoagulation for 24-hours prior to presentation, patients who were not expected to live more than three months after presentation, or anyone who could not get IV contrast, was pregnant, lived too far away for follow-up, or was younger than 18 years of age.

Included patients were risk-stratified by ED physicians based upon the follow criteria:

  1. Objective clinical signs and symptoms of DVT (swelling and pain over deep vein region, 3 points)
  2. HR > 100 BPM (1.5 points)
  3. Immobilization (bed rest, except for using the bathroom, for more than 3 days) or surgery within the past fours weeks (1.5 points)
  4. Previously diagnosed DVT or PE (1.5 points)
  5. Hemoptysis (1 point)
  6. Malignancy (current diagnosis, diagnosis within the last six months, current chemo or palliative care. 1 point)
  7. PE as the most likely, or equally likely diagnosis (based upon clinical gestalt, 3 points)

A patient with a total score of less than 2 was considered low risk, 2-6 was moderate risk, more than 6 was considered high risk. Each patient’s D-dimer level was then measured, and he or she was evaluated for PE based upon an algorithm that can be found in the article (Figure 1). The evaluation included V/Q scan, bilateral lower extremity ultrasound, and/or pulmonary angiogram based upon risk stratification, D-dimer level, and imaging results.

All participants followed-up at 90 days via phone or in-person to recount events that occurred since the initial encounter.

 

Results: The data from 930 patients (average age of 50.5 years) were analysed, with prevalence of PE at 90 days found to be 9.5%. PE was diagnosed in 40.6% of patients with high pretest probability, 16.2% in moderate pretest probability group, and 1.3% in the low pretest probability group. These results indicate the negative predictive value of the d-dimer to be 97.3% in the entire cohort, and 99.5% in the low probability group, 93.9% in the moderate probability group, and 88.5% in the high probability group. In this study the Wells’ criteria/D-dimer model demonstrated poor positive predictive value because it only found PE in 16.9% of patients that were indicated to have any level of image testing (V/Q scan, DVT ultrasound, or angiography based upon the algorithm above). Seventeen patients (0.6%) who had PE and DVT ruled out based upon this model had suspicious events for PE or DVT on follow-up, with five of those events confirmed to be a PE or DVT.

 

While 17 people died during this study, none of the patients who had PE ruled out by the model died from a PE within 90 days of their initial presentation to the ED.

 

Points to consider:

  • Ten percent of the patients enrolled in the study did not have the protocol followed exactly, which limits the external validity of the study.
  • There were no imaging tests performed on the low-risk patients, so we cannot accurately say that they did not have a PE, only that they had a low risk of clinically meaningful event over the subsequent 90 days (either diagnosed PE or death).
  • This study used the more specific SimpliRED D-dimer rather than the traditional immunoassay linked D-dimer thus decreasing the sensitivity of this model compared to the traditional D-dimer assay.

 

Further Study: Only 17% of patients who ruled in for testing were found to have a PE, so there is clearly room to increase the positive predictive value of this tool. Fortunately there have been a number of subsequent studies that have tested methods to increase the specificity of this model, and we have included citations to a few of those studies in the related articles below.

 

Level of Evidence:

ACEP Clinical Policy Grading Level IIB

 

Surprises:

  1. V/Q scan was the test that was used to determine presence or absence of PE, and the current standard is CTPA as it is a more reliable test.
  2. SimpliRED D-dimer was used in this study, not the traditional immunoassay linked D-dimer, which may affect how this criteria applies to patients your department.
  3. Low risk patients got no V/Q scan, so we cannot be sure of actual incidence of PE in these patients, though they were followed up on so we do know there are few risks to not testing these patients for PE.

 

Relevant articles:

Simplification of the revised Geneva score for assessing clinical probability of pulmonary embolism: http://archinte.jamanetwork.com/article.aspx?articleid=414578

 

Performance of 4 Clinical Decision Rules in the Diagnostic Management of Acute Pulmonary Embolism: A Prospective Cohort Study: http://annals.org/article.aspx?articleid=746965

 

Diagnostic accuracy of D-dimer assay in suspected pulmonary embolism patients: http://ac.els-cdn.com/S0422763813003166/1-s2.0-S0422763813003166-main.pdf?_tid=4ce51214-6b05-11e5-9303-00000aacb35d&acdnat=1444010801_80598bd9006f6434671a010c02d76997

 

Source Articles:

Wells, P., Anderson, D., & Rodger, M. (2001). Bedside Without Diagnostic Imaging: Management of Patients With Suspected Pulmonary Embolism Presenting To the Emergency Department By Using a Simple Clinical. Annals of Internal Medicine, 135(2), 98–107.

ACEP Clinical Policy Committee. (2003). Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting With Suspected Pulmonary Embolism. Annals of Emergency Medicine, 41(2), 257–270.

Anderson, D. R., & Barnes, D. C. (2009). Computerized tomographic pulmonary angiography versus ventilation perfusion lung scanning for the diagnosis of pulmonary embolism. Current Opinion in Pulmonary Medicine, 15(5), 425–429.