Time for part 4️⃣ of my comparative physiology series:
Case 1
You are called about an elevated blood alcohol level in an inpatient.
"That’s impossible," the tech says, "he’s been admitted to the ICU for a month!"
It’s totally normal, you say, because the sample came from a __
1/
Answer: 🐠
Under anoxic conditions vertebrates produce lactate. This accumulates causing acidosis.
Goldfish & carp are unique b/c they can convert lactate to ethanol, which diffuses out of their gills into the water. They can survive w/o O2 for months! nature.com/articles/s4159… 2/
Other answers
Bats & primates are good ethanol metabolizers by necessity due to a diet that includes fermented fruit.
The Pen Tailed Shrew is an especially fast ethanol metabolizer: adjusted for size, it consumes the equivalent of 9 beers/day! 3/
In contrast to the shrew, the 🐘 is a very slow EtOH metabolizer due to a loss of the AHD7 gene. Despite their size, elephants can get drunk easily if they eat fermented fruit…which they do.
Clinical 🥡:
Rarely, humans produce EtOH too. Unlike goldfish (who do it endogenously) in humans it occurs due to abnormalities in gut flora, which ferment sugars into EtOH. This is called auto-brewery syndrome (ABS) & cam occur after a high carb meal. bmjopengastro.bmj.com/content/6/1/e0…
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Case 2:
Which of these patients would be *MOST* likely to need to visit an oncologist:
6/
Answer: Tazmanian Devil
Devils face extinction from a transmissible cancer called Devil Facial Tumor Disease (DFTD)
When one Devil bites another (as they often do) it can transmit tumor cells directly to the other animal
In 2 decades (1995-2015) over 95% of Devils died of DFTD 7/
A transmissible cancer means that cells from one organism *directly* invade another.
DFTD occurs b/c the Devil's immune systems can’t recognize the tumor as foreign: limited MHC diversity/expression, constricted T-cell repertoire, & PDL1 upregulation. pubmed.ncbi.nlm.nih.gov/30225648/
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Clinical 🥡:
Normally the our immune system prevents non-viral clonally transmissible cancers. Normally.
There is a case of a surgeon who cut himself while resecting a sarcoma & went to to develop a genetically identical sarcoma in his finger later. nejm.org/doi/full/10.10… 9/
Case 3:
Which of these patients would be *LEAST* likely to need to visit an oncologist:
10/
Answer: 🐀Naked Mole rat
The naked mole rat is remarkable: a cold blooded mammal that is insensitive to cutaneous pain & can live in as little as 5% FiO2 or as much as 80% CO2.
It’s also the longest lived rodent & it probably *NEVER* develops cancer! nature.com/articles/s4156… 11/
We could (& maybe should) have a whole tweetorial about the naked mole rat, but on the topic of cancer resistance & longevity, there are several mechanisms: a unique ECM matrix & contact inhibition pathways, highly accurate ribosomes, & a low metabolic rate. 12/
Other answers:
Elephants & bowhead whales are both exceptionally long-lived and highly cancer resistant.
The elephant (lifespan up to 70 years) has 19 additional copies of the p53 tumor suppressor, which makes it highly cancer resistant. pubmed.ncbi.nlm.nih.gov/26447779/ 13/
The bowhead whale (lifespan >200 years) has enhanced DNA repair mechanisms & upregulates uncoupling protein 1. It likely has novel mechanisms of longevity and cancer resistance that we still don’t comprehend.
ASIDE: There may be bowhead whales that are older than America! 14/
in 1975 Richard Peto observed that despite the fact that humans have 1000x more cells than mice and live 30x longer our risk of cancer is lower. Despite more cells dividing more often, our cancer risk is somehow lower. This is called “Peto’s paradox” pnas.org/content/116/6/… 15/
Clinical 🥡:
There are advantages to having 40 alleles of p53 like elephants do.
Recall that in humans, who have just two copies of p53 (one each from mom & dad), the germline loss of one allele (in Li-Fraumeni syndrome) increases the lifetime risk of cancer to almost 100%.
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Case 4:
You are called by respiratory therapy about some very weird ventilator settings you ordered:
Tv 55 ml/kg PBW, RR 2, PEEP +5, FiO2 30%
(Yes that really says 55 ml/kg not 5.5!)
You say, it’s OK because the patient is a ___.
17/
Answer: Dolphin 🐬
Almost every animal has a tidal volume of ~6 cc/kg PBW.
*The exception is cetaceans (dolphins, whales, porpoises) who need to take much larger breaths more infrequently in order to dive underwater. 18/
But *why* is tidal volume constant across (almost) all species?
VO2 increases with size, so alveolar surface area must increase too. Lungs remain about 1% of body weight.
Pressure volume curves are similar across species (the exception is the cat; 🐈s have very stiff lungs!) 19/
This detail about cat lungs is a bit ironic since this figure (from a 1929 paper by Kurt von Neergaard) is *ALWAYS* used to demonstrate the effect of surfactant on lung compliance, even if it was obtained from “Cat #27”.
H/T to @derangedphys for this. derangedphysiology.com/main/cicm-prim… 20/
Also, if you want to learn a lot more about comparative lung physiology I *HIGHLY* recommend this excellent page from McGill. All the graphs, allometric equations, and lung physiology you could possibly want! medicine.mcgill.ca/physio/resp-we…
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Clinical🥡:
That fact that every animal has a TV of 6 cc/kg PBW is a great physiologic basis for “low” tidal volume ventilation, as we use in lung protective ventilation (LPV)
I say “low” b/c a TV of 6 ml/kg PBW really ought to be considered "normal"! pubmed.ncbi.nlm.nih.gov/24714700/ 22/
I hope you’ve enjoyed part 4️⃣ of my comparative physiology series.
Thanks to those who suggested topics, the years I spent doing cancer research, & my google news alert about naked mole rats.
If you want more, you can find links to parts 1-3 below:
23/23
#HurricaneHelene damaged the factory responsible for manufacturing over 60% of all IV fluids used in the US, leading to a major national shortage.
As clinicians what can we do to about the #IVFluidShortage and how can we prevent this crisis from happening again?
A thread 🧵 1/
There are many things we can do as clinicians to improve ICU care & reduce IVF use.
1️⃣Don't order Maintenance IV Fluid!
Almost no patient actually needs continuous IV fluids.
Most either need resuscitation (e.g. boluses) or can take fluid other ways (PO, feeding tube, TPN).
2/
Frequently if someone is NPO overnight for a procedure, MIVF are ordered.
This is wrong for two reasons.
We are all NPO while asleep & don't need salt water infusions!
We should be letting people drink clears up to TWO HOURS before surgery, per ASA.
New favorite physiology paper: Central Venous Pressure in Space.
So much space & cardio physiology to unpack here including:
- effects of posture, 3g shuttle launch, & microgravity on CVP
- change in the relationship between filling pressure (CVP) & LV size
- Guyton curves! 1/
To measure CVP in space they needed two things:
📼 an instrument/recorder that could accurately measure pressure despite g-force, vibration, & changes in pressure. They built & tested one!
🧑🚀👩🚀👨🚀 an astronaut willing to fly into space with a central line! 3 volunteered! 2/
The night before launch they placed a 4Fr central line in the median cubital vein & advanced under fluoro.
🚀The astronauts wore the data recorder under their flight suit during launch.
🌍The collected data from launch up to 48 hrs in orbit. 3/
Did he have a head CT? What did it show?
Did he have stitches? Tetanus shot?
The NYT ran nonstop stories about Biden’s health after the debate but can’t be bothered to report on the health of someone who was literally shot in the head?
To the people in the replies who say it’s impossible because of “HIPPA” 1. I assume you mean HIPAA 2. A normal presidential candidate would allow his doctors to release the info. This is exactly what happened when Reagan survived an assassination attempt. washingtonpost.com/obituaries/202…
My advice to journalists is to lookup tangential gunshot wounds (TGSW).
Ask questions like:
- what imaging has he had?
- what cognitive assessments?
- has he seen a neurosurgeon or neurologist?
- he’s previously had symptoms like slurred speech, abnormal gait - are these worse?
If you intubate you need to read the #PREOXI trial!
-n=1301 people requiring intubation in ED/ ICU were randomized to preoxygenation with oxygen mask vs non-invasive ventilation (NIV)
-NIV HALVED the risk of hypoxemia: 9 vs 18%
-NIV reduced mortality: 0.2% vs 1.1%
#CCR24
🧵 1/
Hypoxemia (SpO2 <85%) occurs in 10-20% of ED & ICU intubations.
1-2% of intubations performed in ED/ICU result in cardiac arrest!
This is an exceptionally dangerous procedure and preoxygenation is essential to keep patients safe.
But what’s the *BEST* way to preoxygenate? 2/
Most people use a non-rebreather oxygen mask, but because of its loose fit it often delivers much less than 100% FiO2.
NIV (“BiPAP”) delivers a higher FiO2 because of its tight fit. It also delivers PEEP & achieves a higher mean airway pressure which is theoretically helpful! 3/
Results from #PROTECTION presented #CCR24 & published @NEJM.
- DB RCT of amino acid infusion vs placebo in n=3511 people undergoing cardiac surgery w/ bypass.
- Reduced incidence of AKI (26.9% vs 31.7% NNT=20) & need for RRT (1.4% vs 1.9% NNT=200)
Potential game changer!
🧵 1/
I work in a busy CVICU & I often see AKI following cardiac surgery.
Despite risk stratification & hemodynamic optimization, AKI remains one of the most common complications after cardiac surgery with bypass.
Even a modest reduction in AKI/CRRT would be great for my patients. 2/
During cardiac surgery w/ bypass, renal blood flow (RBF) is reduced dramatically. This causes injury, especially in susceptible individuals.
But what if we could use physiology to protect the kidneys?
Renal blood vessels dilate after a high protein meal increasing RBF & GFR! 3/