Emergency Medical Minute

Contributor: Travis Barlock, MD
Educational Pearls:
 
Caffeine Geography and Types:
Caffeine is found throughout the world and has evolved independently in various plants that are not evolutionarily related through direct lineage, but rather demonstrate convergent evolution (i.e. different species evolve the same traits). 

These plants use caffeine as an insecticide. 

Examples of caffeine sources include coffee, tea, yerba-mate, guaraná, cacao, and yaupon holly.

Roughly 85% of Americans are estimated to consume caffeine daily.  

Caffeine Pharmacology in Humans: 
In humans, caffeine is a nonselective competitive antagonist (blocker) of adenosine receptors (A1 and A2A). 

During waking hours, neuronal metabolic activity consumes ATP, and a byproduct of ATP hydrolysis is created: adenosine. 

Adenosine proceeds to build a "sleep pressure". 

Acting on A1 and A2A adenosine receptors to induce sleep (on A1, it suppresses neuronal "wakefulness" and on A2A it is believed to be an inducer of sleep). 

Caffeine, by blocking those receptors, blunts sleep induction and feelings of being tired. 

Caffeine has a half-life of around 6 hours, and a quarter life of approximately 12 hours, which is when the caffeine will off-load and adenosine can once again occupy those receptors, potentially causing a "crash". 

Thus, for shift-workers, it is important to time caffeine intake roughly 10 hours before target bed time. 

Caffeine exerts other effects on the body. 

It is methylxanthine similar to theophylline, which works as a bronchodilator (via phosphodiesterase and adenosine pathways). Caffeine has clinical use to promote bronchodilation in pre-term infants. 

Caffeine exerts diuretic effects as well (blocking proximal renal tubule reabsorption). 

Recent ingestion of caffeine may blunt therapeutic use of adenosine in patients with SVT. 

Key Takeaway?
Caffeine exerts a wide variety of effects beyond making us feel more awake. It has cardiovascular, pulmonary, and renal implications in its pharmacodynamics.

 
References 
 
Benarroch EE. Adenosine and its receptors: multiple modulatory functions and potential therapeutic targets for neurologic disease. Neurology. 2008;70(3):231-236. doi:10.1212/01.wnl.0000297939.18236.ec

Mitchell DC, Knight CA, Hockenberry J, Teplansky R, Hartman TJ. Beverage caffeine intakes in the U.S. Food Chem Toxicol. 2014;63:136-142. doi:10.1016/j.fct.2013.10.042

Bruschettini M, Brattström P, Russo C, Onland W, Davis PG, Soll R. Caffeine dosing regimens in preterm infants with or at risk for apnea of prematurity - Bruschettini, M - 2023 | Cochrane Library. Accessed May 23, 2026. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD013873.pub2/full?cookiesEnabled

Huang R, O'Donnell AJ, Barboline JJ, Barkman TJ. Convergent evolution of caffeine in plants by co-option of exapted ancestral enzymes. Proc Natl Acad Sci U S A. 2016;113(38):10613-10618. doi:10.1073/pnas.1602575113

Cabalag MS, Taylor DM, Knott JC, Buntine P, Smit D, Meyer A. Recent caffeine ingestion reduces adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia. Acad Emerg Med. 2010;17(1):44-49. doi:10.1111/j.1553-2712.2009.00616.x 

Summarized by Dan Orbidan, OMS2 | Edited by Dan Orbidan & Ahmed Abdel-Hafiz, NREMT-P
 
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Contributor: Travis Barlock, MD
Educational Pearls:
 
Endocannabinoid System: THC binds CB1 and CB2 receptors in neurons and immune cells
Δ9-Tetrahydrocannabinol (THC) is the main psychoactive compound in cannabis

CB1 and CB2 receptors typically bind endogenously-produced 2-arachidonoylglycerol (2-AG) and anandamide (AEA) to regulate pain, stress, and inflammation

THC similarly binds CB1 and CB2, leading to the cannabinoid high: euphoria, paranoia, anxiety, analgesia, anti-inflammation, and appetite, among a variety of others

Ingestion via edibles, vice inhalation via smoking, leads to chemical modification of Δ9-THC to 11-hydroxy-Δ9-THC, which more easily crosses the blood-brain barrier and binds CB1 with higher affinity, leading to increased psychoactivity

 
Cannabinoid Hyperemesis Syndrome (CHS): Chronic THC use leading to the classic presentation of persistent nausea and intense, frequent vomiting
Chronic activation of CB1 receptors in brain builds a tolerance and dependence on THC, in addition to chronic activation of the capsaicin and vanilloid receptor TRPV1, which binds capsaicin or is activated by heat

Treatment by warm showers works due to TRPV1 activation by heat

Treated with benzodiazepines, fluids, and gastro-intestinal or central nervous system agents according to patient presentation

 
Over 200 synthetic cannabinoids have been created (K2, spice, black mamba, mojo, etc), which are more dangerous and can lead to a variety of etiologies
 
Acetaminophen binds CB1 receptors to reduce inflammatory pain
 
References
Loganathan P, Gajendran M, Goyal H. A Comprehensive Review and Update on Cannabis Hyperemesis Syndrome. Pharmaceuticals (Basel). 2024;17(11):1549. Published 2024 Nov 18. doi:10.3390/ph17111549 

Wall ME, Sadler BM, Brine D, Taylor H, Perez-Reyes M. Metabolism, disposition, and kinetics of delta-9-tetrahydrocannabinol in men and women. Clin Pharmacol Ther. 1983 Sep;34(3):352-63. doi: 10.1038/clpt.1983.179. PMID: 6309462. 

Mills B, Yepes A, Nugent K. Synthetic Cannabinoids. Am J Med Sci. 2015 Jul;350(1):59-62. doi: 10.1097/MAJ.0000000000000466. PMID: 26132518.

Klinger-Gratz PP, Ralvenius WT, Neumann E, et al. Acetaminophen Relieves Inflammatory Pain through CB1 Cannabinoid Receptors in the Rostral Ventromedial Medulla. J Neurosci. 2018;38(2):322-334. doi:10.1523/JNEUROSCI.1945-17.2017

 
Summarized by Sam Pahl | Edited by Sam Pahl & Ahmed Abdel-Hafiz, NREMT-P
 
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Contributor: Aaron Lessen, MD
Educational Pearls:
There has long been many questions about which IV fluid is best for ED resuscitation

Multiple adult studies have shown no clear benefit of balanced fluid vs normal saline

A large pediatric randomized clinical trial published in April compared balanced fluid vs normal saline in children with septic shock 

The study included about 9,000 patients from 47 emergency departments in five countries

Patients with septic shock were randomized to receive either balanced fluid or normal saline

The primary outcome was adverse kidney event (death, dialysis, or persistent kidney dysfunction) at 30 days or hospital discharge

Results showed no difference in any safety outcomes and no adverse events occurred

The key takeaway is that early fluid resuscitation matters more than which crystalloid you choose

 
References
Balamuth F, Weiss SL, Long E, et al. Balanced Fluid or 0.9% Saline in Children Treated for Septic Shock. New England Journal of Medicine. Published online April 23, 2026. doi:https://doi.org/10.1056/nejmoa2601969

 
Summarized by Meg Joyce, MS3 | Edited by Meg Joyce & Ahmed Abdel-Hafiz, NREMT-P

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Carepoint Journal Club is a quarterly series with discussions about a medical topic, brought to you by Carepoint's Emergency Physicians.

Contributor: Taylor Lynch, MD
Educational Pearls: 
 
Conduction abnormalities are a common and clinically significant complication in patients who undergo transcatheter aortic valve replacement (TAVR)
 
Clinical Features
The most common abnormalities include high grade AV block and new onset LBBB 

Due to the close proximity of the aortic annulus to the AV node and His-Purkinje system

More common in males, the elderly, and those with pre-existing conduction disease (RBBB or LBBB)

Sinus pauses and sinus arrest are a rare post-TAVR rhythm disturbances

Temporary failure of sinus node firing with absent P waves, followed by return of sinus rhythm

Sinus Pauses: Typically last Sinus Arrest: Typically last > 3 seconds

Not due to direct mechanical injury from the valve, but may occur in patients as a result of pre-existing disease or other external factors:

Medications

Beta blockers, calcium channel blockers, digoxin

Pre-existing damage to the SA node

Fibrosis from a previous MI

 
Treatment
If the patient is asymptomatic, provide ongoing surveillance

If the patient is symptomatic, treatment should be aimed at the underlying cause:

For medication-induced abnormalities, stop the offending medication

For acute, unstable bradycardia:

Medications: Atropine, Dopamine Infusion, Epinephrine Infusion

If cardiology is not immediately available, initiate transcutaneous pacing or insert a temporary transvenous pacemaker

Definitive treatment: Pacemaker

~10–15% of patients may develop a bradyarrhythmia post TAVR, with ~8-15% later requiring a pacemaker

 
Due to the risk of conduction abnormalities post TAVR, many patients are discharged with ambulatory rhythm monitoring such as a ZioPatch or Holter monitor, and may present to the emergency department for evaluation of rhythm disturbances.
 
References:
Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Heart Rhythm. 2019;16(9):e128-e226.

Lilly, S, Deshmukh, A, Epstein, A. et al. 2020 ACC Expert Consensus Decision Pathway on Management of Conduction Disturbances in Patients Undergoing Transcatheter Aortic Valve Replacement: A Report of the American College of Cardiology Solution Set Oversight Committee. JACC. 2020 Nov, 76 (20) 2391–2411.

https://doi.org/10.1016/j.jacc.2020.08.050
Sammour, Y, Krishnaswamy, A, Kumar, A. et al. Incidence, Predictors, and Implications of Permanent Pacemaker Requirement After Transcatheter Aortic Valve Replacement. J Am Coll Cardiol Intv. 2021 Jan, 14 (2) 115–134.

https://doi.org/10.1016/j.jcin.2020.09.063
Tarakji KG, Patel D, Krishnaswamy A, et al. Bradyarrhythmias detected by extended rhythm recording in patients undergoing transcatheter aortic valve replacement (Brady-TAVR Study). Heart Rhythm. 2022;19(3):381-388.

 
Summarized by Ashley Lyons, OMS3 | Edited by Ashley Lyons & Ahmed Abdel-Hafiz, NREMT-P
 
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