Podcast #268: Poiseuille’s Law

Author:  Dave Rosenberg, M.D.

Educational Pearls

  • Poiseuille’s Law addresses the flow of a fluid through a tube.
  • Many common ED presentations involve alterations in flow: asthma, MI, ischemic stroke, etc.
  • According to the law, flow increases with the 4th power of the radius. That is to say, doubling the radius of the tube will increase the flow by 16x.
  • Therefore, in situations that require re-opening of an anatomic tube (artery, airway), small changes in the size of the opening will result in dramatic effects.

References: https://www.openanesthesia.org/poiseuilles_law_iv_fluids/

Podcast #262: Pertussis

Author: Julian Orenstein, M.D.

Educational Pearls

  • Colorado has a high population of unvaccinated children, and is at increased risk for pertussis outbreaks.
  • The causative organism is Bordetella pertussis. It causes  causes respiratory epithelial necrosis leading to congestion of the bronchioles, leading to cough.
  • The cough is unique – it is usually a series of expiratory coughs followed by one deep inspiration
  • The clinical presentation is divided into 3 phases:
    • Catarrhal: cough and congestion with low-grade fever and coryza.
    • Whooping: characteristic cough.
    • Resolution: recovery with persistent cough.
  • Infants may not get this presentation, but may get apnea and nonspecific cough.  
  • Tongue depressor can be used to elicit cough for diagnosis.

References: Tozzi AE, Pastore Celentano L, Ciofi degli Atti ML, Salmaso S. Diagnosis and management of pertussis. CMAJ?: Canadian Medical Association Journal. 2005;172(4):509-515. doi:10.1503/cmaj.1040766.

Podcast #260: Preoxygenation

Author: David Rosenberg, M.D.

Educational Pearls

  • Preoxygenation is done before rapid sequence intubation, and should be done even if SaO2 is at 100%.
  • Preoxygenation is done to fill the lungs with oxygen rather than ambient air, which is only 20% O2. While the patient is paralyzed, the O2-filled lungs will continue to oxygenate venous blood, buying you more time for intubation.  
  • BiPAP is an effective tool for pre-oxygenation.

References: https://lifeinthefastlane.com/ccc/preoxygenation/

Podcast #247: D-Dimer

Author: Michael Hunt, M.D.

Educational Pearls

  • In the recent YEARS study, investigators checked every patient with suspicion for PE with a D-dimer, using a modified Wells score for risk stratification. The goal of the study was to show that CT scan usage could safely reduced using this screening method.
  • The Wells Criteria measures they used to stratify risk were: PE mostly likely dx, hemoptysis, and evidence of DVT. If the d-dimer was 1, but the patient had none of the Wells criteria, the patient did not get a CT. If the patient had any of the criteria, but the d-dimer was only 0.5, the patient did not get a CT scan.
  • The investigators reduced  CT usage by 14% using the new criteria, with no significant increase in morbidity and mortality.

References: van der Hulle et al. Simplified diagnostic management of suspected pulmonary embolism (the YEARS study): a prospective, multicentre, cohort study. The Lancet. 2017

Podcast #246: Patent Foramen Ovale

Author: Jared Scott, M.D.

Educational Pearls

  • The foramen ovale (FO) connects the left and right atria to allow oxygenated blood to bypass the developing lungs, it usually closes at birth but for some it remains patent (PFO).
  • A PFO allows clots to cross from the venous to arterial circulation, increasing the likelihood of stroke.
  • PFO is present in 25% of general population, present in 50% of those with stroke of unknown cause, and very common those with stroke under 50 years old.
  • Treat with anticoagulation or surgical correction.

References: http://www.heart.org/HEARTORG/Conditions/More/CardiovascularConditionsofChildhood/Patent-Foramen-Ovale-PFO_UCM_469590_Article.jsp#.WarsZZN95E

Podcast #232: HAPE

Author: Gretchen Hinson, M.D.

Educational Pearls

  • High-Altitude Pulmonary Edema (HAPE) is caused when hypoxemia due to low ambient pO2 leads to breakdown and constriction of the pulmonary vasculature leading to edema.
  • HAPE is very rare under 8000 ft, but common over 10000 ft (6%). Over 18,000 ft the incidence is very high (12-15%).
  • Symptoms include dyspnea, cough, weakness and chest tightness.
  • Signs include hypoxemia, crackles, wheezing, central cyanosis, tachypnea and tachycardia.
  • Drugs that reduce pulmonary resistance have been shown to help, but increased oxygenation and descent are the best treatments.

References: http://emedicine.medscape.com/article/300716-overview

Podcast #222: Wells Criteria for PE

 

Author: Michael Hunt, M.D.

Educational Pearls

  • Wells Criteria was initially designed to screen patients for further workup for PE.  
  • Aspects of the Wells Criteria include: signs and symptoms of DVT (3 points), PE most likely dia (3 points), HR > 100 (1.5 points), immobility for > 3 days or surgery in last 4 weeks (1.5 points), documented history of PE (1.5), hemoptysis (1), treatment for cancer in last 6 mo (1).
  • ACEP uses a score of less than or equal to 4 to define “low risk.” Greater than 4 is “high risk”.
  • Use Wells to guide clinical decisions about PE workup.

References: http://www.ebmedicine.net/media_library/files/1212%20Pulmonary%20Embolism

Podcast #208: Vocal Cord Dysfunction

Author: Martin O’Bryan M.D.

Educational Pearls:

  • Vocal cord dysfunction can mimic other causes of stridor, such as asthma and upper airway obstruction.
  • Patients are often very anxious because of the difficulty of inspiration.
  • The definitive diagnosis is laryngoscopy that must be done by a pulmonologist.
  • The treatment is general reassurance, asthma medications will not help. CPAP and heliox can be used to help with the stridor.
  • Benzodiazepines can be used to reduce the associated anxiety.

References: https://asthmarp.biomedcentral.com/articles/10.1186/s40733-015-0009-z

Podcast #182: Syncope and PE

Run Time: 3:44 minutes

Author: Aaron Lessen, MD

Educational Pearls:

  • A new Italian study has been released, which looks at the prevalence of Pulmonary Embolism (PE) in patients admitted for syncope.
  • This study examined all patients admitted with syncope, regardless of their clinical picture, and worked them up for PE, which included wells score, D-dimer, and CT
  • Study demonstrated 1 out of 6 pts admitted for syncope had a PE.
  • Despite the headlines this study is making in the news, it is difficult to make conclusions. The study was not perfect, and mainly looked at a sick population of patients (only those who warranted admission) who had many comorbidities.  Until further studies are conduction, current practice should be to only work up syncope patients for a PE if they are exhibiting related signs and symptoms.

Link to Podcast: http://medicalminute.madewithopinion.com/syncope-and-pe/

References: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/SymptomsDiagnosisMonitoringofArrhythmia/Syncope-Fainting_UCM_430006_Article.jsp