Contributor: Aaron Lessen, MD

Educational Pearls:

• Point-of-care ultrasound (POCUS) is used to assess cardiac activity during cardiac arrest and can identify potential reversible causes such as pericardial tamponade

• Ultrasound could be beneficial in another way during cardiac arrest as well: pulse checks

• • Manual palpation for detecting pulses is imperfect, with false positives and negatives

  • Doppler ultrasound can be used as an adjunct or replacement to manual palpation for improved accuracy

• Options for Doppler ultrasound of carotid or femoral pulses during cardiac arrest:

• • Visualize arterial pulsation

  • Use color doppler

  • Numerically quantify the flow and correlate this to a BP reading - slightly more complex

• Doppler ultrasound is much faster than manual palpation for pulse check

• • Can provide information almost instantaneously without waiting the full 10 seconds for a manual pulse check

• The main priority during cardiac arrest resuscitation is to maintain quality compressions

• • If pulses are unable to be obtained through Doppler within the 10-second window, resume compressions and try again during the next pulse check

References

1. Cohen AL, Li T, Becker LB, Owens C, Singh N, Gold A, Nelson MJ, Jafari D, Haddad G, Nello AV, Rolston DM; Northwell Health Biostatistics Unit. Femoral artery Doppler ultrasound is more accurate than manual palpation for pulse detection in cardiac arrest. Resuscitation. 2022 Apr;173:156-165. doi: 10.1016/j.resuscitation.2022.01.030. Epub 2022 Feb 4. PMID: 35131404.

Summarized by Meg Joyce, MS1 | Edited by Meg Joyce & Jorge Chalit, OMS3

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Contributor: Travis Barlock, MD

Educational Pearls:

What is Hoover’s sign used to identify?

• This physical exam maneuver differentiates between organic vs. functional (previously known as psychogenic) leg weakness.

• Organic causes include disease processes such as stroke, MS, spinal cord compression, guillain-barre, ALS, and sciatica, among others

• In Functional Neurologic Disorder, the dysfunction is in brain signaling, and treatment relies on more of a psychiatric approach

How is Hoover's Sign performed?

• Place your hand under the heel of the unaffected leg and ask the patient to attempt to lift the paralyzed leg.

• If the paralysis is due to an organic cause, then you should feel the unaffected leg push down.

• This is due to the crossed-extensor reflex mechanism, an unconscious motor control function mediated by the corticospinal tract.

• If you don’t feel the opposite heel push down, that is a positive Hoover’s Sign.

How sensitive/specific is it?

• An unblinded cohort study in patients with suspected stroke found a sensitivity of 63% and a specificity of 100%

Fun Fact

• There’s also a pulmonary Hoover’s sign, named after the same doctor, Charles Franklin Hoover, which refers to paradoxical inward movement of the lower ribs during inspiration due to diaphragmatic flattening in COPD.

References

1. McWhirter L, Stone J, Sandercock P, Whiteley W. Hoover's sign for the diagnosis of functional weakness: a prospective unblinded cohort study in patients with suspected stroke. J Psychosom Res. 2011 Dec;71(6):384-6. doi: 10.1016/j.jpsychores.2011.09.003. Epub 2011 Oct 6. PMID: 22118379.

2. Stone J, Aybek S. Functional limb weakness and paralysis. Handb Clin Neurol. 2016;139:213-228. doi: 10.1016/B978-0-12-801772-2.00018-7. PMID: 27719840.

Summarized by Jeffrey Olson, MS3 | Edited by Jorge Chalit, OMS3

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Contributor: Jorge Chalit-Hernandez, OMS3

Educational Pearls:

• CYP enzymes are responsible for the metabolism of many medications, drugs, and other substances

• • CYP3A4 is responsible for the majority

  • Other common ones include CYP2D6 (antidepressants), CYP2E1 (alcohol), and CYP1A2 (cigarettes)

• CYP inducers lead to reduced concentrations of a particular medication

• CYP inhibitors effectively increase concentrations of certain medications in the body

• Examples of CYP inducers

• • Phenobarbital

  • Rifampin

  • Cigarettes

  • St. John’s Wort

• Examples of CYP inhibitors

• • -azole antifungals like itraconazole and ketoconazole

  • Bactrim (trimethoprim-sulfamethoxazole)

  • Ritonavir (found in Paxlovid)

  • Grapefruit juice

• Clinical relevance

• • Drug-drug interactions happen frequently and often go unrecognized or underrecognized in patients with significant polypharmacy

  • A study conducted on patients receiving Bactrim and other antibiotics found increased rates of anticoagulation in patients receiving Bactrim

  • Currently, Paxlovid is prescribed to patients with COVID-19, many of whom have multiple comorbidities and are on multiple medications

  • • Paxlovid contains ritonavir, a powerful CYP inhibitor that can increase concentrations of many other medications

• A complete list of clinically relevant CYP inhibitors can be found on the FDA website:

• • https://www.fda.gov/drugs/drug-interactions-labeling/drug-development-and-drug-interactions-table-substrates-inhibitors-and-inducers

References

1. Glasheen JJ, Fugit RV, Prochazka AV. The risk of overanticoagulation with antibiotic use in outpatients on stable warfarin regimens. J Gen Intern Med. 2005;20(7):653-656. doi:10.1111/j.1525-1497.2005.0136.x

2. Lynch T, Price A. The effect of cytochrome P450 metabolism on drug response, interactions, and adverse effects. Am Fam Physician. 2007;76(3):391-396.

3. PAXLOVID™. Drug interactions. PAXLOVIDHCP. Accessed March 16, 2025. https://www.paxlovidhcp.com/drug-interactions

Summarized & Edited by Jorge Chalit, OMS3

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