"Six Feet"

Six feet.

I’ve said it. You’ve said it. Fauci has said it. But why are we saying it?

Doesn’t that seem a bit… I don’t know, arbitrary? Random? Other synonyms?

Did you know that the World Health Organization actually recommends one meter?

Can’t germs travel seven feet? Or ten? What about the butterfly effect – if a butterfly sneezes in Taiwan, can’t it infect someone in Madagascar? (Something like that.)

Where did this number come from… (ominous ellipses)

Back in 1942, someone took a “high-speed camera” and photographed respiratory droplets to see if they could travel six feet. They found that most of the droplets fell within 3 feet, which became the party line for social distancing for decades. That’s right – we based social distancing on images from a 1940s camera that photographed spittle drops. 3 feet.

To try and further suss it out, a few bold (?crazy) scientists in the UK opened up the Common Cold Research Unit in 1946. They offered volunteers a 10-day getaway in Salisbury, UK, under one condition… volunteers agreed to be inoculated with the common cold. They suggested in 1947 that the safest distance was 30 feet, though the podcast referenced later here suggests 3ft for large droplets (again). Check out this original publication:

https://journals.sagepub.com/doi/pdf/10.1177/003591574704001104

And a video of their unit from the 50s: https://www.youtube.com/watch?v=SJfBU_MUpI0&feature=emb_logo

In the 1980s through the 2000s, more data (from studies and other outbreaks) came out to suggest not one, but two meters would likely be more effective. So that's where we've stayed...

Fast forward to this year, a systematic review that respiratory droplets often went farther than two meters – like, much farther. Like, 8 meters.

Not only that, but some suggest COVID stays in the air for 16hours! (Though the prevalence and infectivity of these particles is debatable.)

Lots of factors can increase the distance of droplet/particle transmission and it seems that 6 feet may be a bit of an outdated blanket statement. Consider maintaining as much distance as reasonably attainable in your various social situations. Wash your hands, wear a mask, and wear eye protection.

For all you auditory learners, check out this 20min podcast by Radiolab: https://www.wnycstudios.org/podcasts/radiolab/articles/dispatch-4-six-feet

For all you visual learners, below are some fascinating shots of simulated “violent respiratory events” with and without masks, from AIP Physics of Fluids.

(For all you kinesthetic learners, just wear a mask.) 

References:

WHO: who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-publi

CEBM: https://www.cebm.net/covid-19/what-is-the-evidence-to-support-the-2-metre-social-distancing-rule-to-reduce-covid-19-transmission/

Visualizing the Effectiveness of Face Masks in Obstructing Respiratoory Jets: https://aip.scitation.org/doi/10.1063/5.0016018

Radiolab: https://www.wnycstudios.org/podcasts/radiolab/articles/dispatch-4-six-feet

Other references embedded in the the above email

POTD: TPA in PE

POTD: TPA in PE

• Massive PE can lead to hemodynamic instability and death

• Smaller but clinically significant PEs can lead to pulmonary hypertension, RV dysfunction and subsequently poor quality of life (decreased exercise tolerance and even dyspnea at rest)

• TPA in PE is surrounded by controversy with various opinions on the matter

AHA:

• Massive: hemodynamic instability defined as SBP<90 (or 40 point drop from baseline) for >15 minutes=

• Thrombolysis indicated unless there are contraindications

• Sub-massive: hemodynamically stable but with signs of RV strain (elevated troponin/BNP, echo findings of RV dysfunction) = Thrombolysis may be considered (level IIb/C)

ACEP:

• Hemodynamically unstable patients: Thrombolysis indicated if benefits outweigh risks of bleeding

• Level B recommendation

• Hemodynamically stable patients: insufficient evidence to do thrombolysis

MOPETT (Moderate Pulmonary Embolism Treated with Thrombolysis):

If

• Symptomatic moderate defined as ≥2 signs/symptoms (7 total in inclusion criteria) in addition to CTPA involvement of >70% involvement of thrombus in ≥2 lobar, or left or right main pulmonary arteries

• Ventilation/perfusion scan showing mismatch in ≥2 lobes

• SBP<95 excluded

Then

• enoxaparin/heparin only vs enoxaparin/heparin + half dose tPA (10mg bolus then 40mg over 2 hours)

• primary end point: pulmonary HTN at 28 months

• rates in treatment group=16%, control group=57%

• combined end point: pulmonary HTN at 28 months + recurrent PE

• treatment group=16%, control group=63%

• no patients in either group bled

Conclusion:

• Studies suggest that half-dose thrombolysis is safe/effective in the treatment of moderate PE, with a significant immediate reduction in pulmonary artery pressure that was maintained at 28 months

• ”Thrombolytics have demonstrated faster improvements in RV function and pulmonary perfusion, but these benefits have not translated to improvements in mortality.”

• So the measured outcome is of questionable significance as opposed to actual measurements of quality-of-life

• Perhaps consider in your young patient in whom potential improvement in exercise tolerance in remaining lifetime may be more relevant than in older, immobile patients

Stay well,

TR Adam

POTD: Peripartum Cardiomyopathy

POTD: Peripartum Cardiomyopathy

Causes:

• Infectious (EBV, CMV, HSV)

• Genetics

• Pre-eclampsia

• Fetal cells present in the maternal system that elicit an inflammatory response

Clinical Findings (same as CHF findings):

• Tachycardia

• Decreased pulse oximetry (should be ≥ 97% at sea level).

• Blood pressure may be normal. (systolic >140 mm Hg and/or diastolic >90 mm Hghyperreflexia with clonus suggest preeclampsia).

• Elevated jugular venous pressure

• Third heart sound (turbulent ventricular filling secondary to poor wall relaxation from dilated ventricle)

• Loud pulmonic component of the second heart sound (increased right sided flow)

• Mitral or tricuspid regurgitation

• Pulmonary rales

• Peripheral edema

• Ascites

• Hepatomegaly

Management:

• CBC- to see if there is significant thrombocytopenia

• CMP- to see if there is any dysfunction in creatinine, LFTs, albumin

• Urine dipstick- to check if there is any proteinuria

• EKG

• Echocardiogram

• CXR

• Stress testing

• OBGYN, Cardiology consult in addition to reaching out to potential transplant hospitals

Treatment:

• Digoxin: first line in pregnancy

• Loop diuretics; Start with 10 mg of furosemide, as pregnant women have an increased glomerular filtration rate (GFR) that facilitates secretion of the drug into the loop of Henle.

• Hydralazine and nitrates: afterload and preload reduction

• B- Blockers (carvedilol or metoprolol): decrease all-cause mortality and hospitalization in those with systolic dysfunction.

• Heparin for EF<30% (high risk of venous and arterial thrombosis)

• LVAD

• May ultimately need heart transplant

• Delivery- Unless the mother is decompensating, you can manage her medically until delivery is possible. If the mother is not responding to medical therapy or if the fetus must be delivered for obstetric reasons, the best plan is to induce labor with the goal of a vaginal delivery. C-section can lead to a lot of dynamic fluid changes which can lead to maternal decompensation

Disposition: 

• ICU vs potential transfer to a center that offers tertiary care services for both the mother and the fetus.

Stay well,

TR Adam