16 October 2023

Good Inside Evil; Evil Inside Good

This story happened a long time ago. I think I've written it online before, perhaps as a Twitter thread that is now long gone. I've rewritten the story here because I think of it often and wanted to be able to share it.

When I was an ICU fellow there was a night shift where I'd been out of the ICU for a week or two and wasn't overly familiar with all the patients. I came in and got sign out and checked in on everyone. Handled things as they went along. Sometime near midnight when there wasn't anything actively requiring my attention I did what I always did and went around and checked in with each nurse.

Discussing one of the patients, an infant with a severe congenital problem whose solution was failing, the nurse expressed to me her sorrow that we were keeping the child alive just to keep the parents out of jail. I knew this nurse well and it was such a bizarre, jarring thing to hear from her I asked what she meant. She was shocked I didn't already know the context. When I asked what it was she told me to just google the child's last name. The conversation got stilted and I moved on to my other patients.

After finishing rounds I had time to lay down, but I had taken a nap before my shift and wasn't tired so sitting at my computer I googled the family's name. The first couple results were all about the child abuse allegations and impending trial against my patient's parents, but the allegations didn't include my patient, but another of their children. I don't have words for the feelings those allegations engendered in me but the closest are enraging, infuriating, wrathful.

I spent the rest of the night mad that the world could let children be so mistreated and furious with the perpetrators and enablers. I also spent the rest of the night extremely angry with myself.

When I was young(er) and dumb(er) and a medical student I had done a rotation at the hospital that served a large prison complex of both state and federal prisoners. The state prisoners were on a different floor with a different medical service, but the federal prisoners were on the general med/surg floor and cared for by our team. One day an intern and I were idly speculating about what crime a particular patient had committed. Our attending overheard us and angrily interrupted us telling us both, in a tone that brooked no argument, "Never ask that question. The answer to it will never help you take better care of your patient."

I had remembered that lesson and mostly abided by it; being a pediatrician helped. My patients were rarely the barbarous ones, it was usually someone around them. Another attending, during another tragedy, had taught me to, when caring for abused or mistreated children, focus on creating the most caring and loving environment that I could rather than on the terrible things that happened outside it. The frameshift helped me immensely through the subsequent tragedies that came into my care. I still teach that re-framing now that I am the attending.

Back to my night in the ICU though. I was angry with myself because I had known that my google search wouldn't help my patient in any way and in fact it may harm my ability to care for the child and family with compassion. I'd given in to my own morbid curiosity for nothing except a sense of righteous anger that helped no one. Truly the definition of a negative-sum endeavor.

The rest of the night shift went by and there was enough that happened that I never got any sleep but I wasn't busy enough to stop thinking about the google search. I went home and eventually managed to get some sleep before going back to the ICU for the next night. It went by much the same except that when I did my late night rounds the same nurse had the same child and she asked if I'd looked it up. I admitted I had. 

She expressed how wrong it was that we were keeping the child alive just so that the parents could push the trial off longer. I expressed how mad I was at myself for having read about the allegations and how upset I was that people were presuming the only reason the family hadn't let their child die was to forestall justice. Our impressions of what was happening and why were so wildly different it was hard to recognize that they grew from the same set of facts.

The nurse's perspective that I did not adequately consider then was her hour-to-hour, day-to-day experience trying to manifest that impulse of love and compassion that I talked about earlier. In her care was a child whose life was supported by all the implements of modern medicine, lines and tubes and drains, none of which are comfortable to endure. Her job was to palliate suffering, but for this child there was no therapy sufficient to that end.

Across our philosophical divide I couldn't believe that the grief I saw and heard from the child's parents was not genuine. Perhaps it's naïve but if I see grief like those parents showed and disbelieve its authenticity I will know it is time for me to retire from caring for patients. Within those parents I saw people who were terribly, terribly flawed but I also saw that despite their flaws they felt tremendous love and grief for their dying child.

I don't know what the moral of this story is. I know that I think about it whenever I get the sense that a person, or a group of people, are being portrayed as not deserving our compassion.

20 August 2023

Respiratory Physiology for Climbers and Mountaineers

*in progress*

With intermittent frequency I read trip reports, articles, social media comment threads or whatever from mountaineers and climbers who go to altitude and say many partially correct things about oxygen and altitude with a smaller number of completely wrong things mixed in.

Every so often my frustration boils over and I write a comment or reply or DM to someone and try to explain things and correct their misapprehensions. It's happened enough times that I figured I should write down the most salient aspects of respiratory physiology at altitude in a way that (hopefully) makes sense to mountaineers and climbers.

Background
As background, I'm a pediatric critical care physician and an amateur mountaineer. The former gives me a lot of expertise in respiratory physiology; as to the latter, I haven't done anything noteworthy but I've done enough rapid ascents from sea level to 4000 meters to have experienced AMS and have spent a lot of time cavorting the mountains.

I can't promise that anything in this writeup will help you climb a mountain but I hope that it will help you understand what's going on in your own body at altitude and maybe help you make plans and sound decisions.

Also, I'm a barbarian American and our weird meteorological pressure measurements have found their way into our physiology, so my apologies if you've stumbled upon this writeup from the enlightened world. There are plenty of calculators to turn mmHg into kPa if you wish. I will probably also switch randomly between feet and meters when referring to altitude as different domains (climbing, meteorology, etc) have different norms for me.

For the most part I'm going to write this without putting in a ton of references because, as anyone who's ever done academic writing can attest, it's an exorbitant amount of work and I trust that all of my readers can operate a search engine. For things that are esoteric, hard to dig up, or from whence I've borrowed images I'll try and put in a link. Much of the primary literature on this stuff pre-dates digital publication so has been retroactively scanned or is otherwise a pain to get ahold of beyond abstracts.

With that throat clearing aside, one law of physics that will come up over and over again throughout this discussion that is very important (and thankfully simply and intuitive):

Dalton's Law says that in any mixture of gasses the pressure that each exerts is proportional to its concentration and all of the proportions add up to the total. Putting this into layman's terms is really easy: all of the parts make up the whole and all of the parts take up as much space as their proportion.

Ambient Air and Barometric Pressure:
Below the tropopause (~36,000 ft) air is well mixed by a bunch of different physical phenomena and its composition is the same over the whole surface of the earth (local pollution notwithstanding) and 20.947% of the molecules in that air are oxygen molecules. Just round it to 21% for your own and everyone else's sanity.

As we ascend in altitude the barometric pressure decreases. This is because the atmosphere above us has substance and mass and as we go up, there is less of it above us. Less stuff above getting pulled down by gravity means less pressure. There are a couple of mathematical models that explain how much the pressure decreases as the altitude increases, if you find yourself worrying about this: choose the model atmosphere equation (not the standard atmosphere equation) as its output matches measured data much better.

As this barometric pressure decreases it doesn't change the composition of the atmospheric air (20.947% of the molecules in the air are still oxygen) but it does mean there are fewer molecules in the air -- including oxygen. This means that there are fewer oxygen molecules inside of our lungs (since the volume of our lungs doesn't change as we ascend in altitude) available for our body to absorb.




While altitude is, by far, the largest factor in barometric pressure changes that a climber may encounter, there are others which bear mentioning.

Latitude, Temperature, Weather
For a bunch of complicated physics reasons there is a bulge in the atmosphere over the equator which has the effect of increasing the barometric pressure the closer one gets to the equator (when compared to the same altitude nearer the poles) because the troposphere is about twice as thick (5km vs 10km).



Anyone with a passing familiarity with meteorology will recognize that it is usually discussed in terms of high and low pressure regions -- the interaction between them being what gives us weather. Depending on where you live and its usual weather patterns a "strong" high or low pressure system will usually deviate from normal by about 25 millibars (domain specific units are very annoying in this sort of cross discipline discussion… 25 millibar ≈ 19 mmHg). As we'll see later a 20 mmHg change in barometric pressure can have dramatic effects on our body's ability to absorb oxygen.

Pressure Map (via windy.com on 20 August 2023). Numbers are mmHg. Note the tropical storm and its low pressure center off the coast of California compared to the high pressure center south of Alaska.

There is also a diurnal (ie day-night) fluctuation to barometric pressure which varies by latitude but is generally small enough to be ignored (the shift is +/- 2.5 millibar (≈1.9 mmHg) at most).

Source

A lot of work has been done developing (for example) mathematical models for the interaction of temperature, latitude, and altitude to determine the difference between physical height and pressure height of a variety of summits. This work builds upon experimental data that has confirmed similar effects. In general the further away a peak is from the equator the more dramatic the difference between physical and pressure heights will be; though, these effects rarely lead to a difference of more than 200-300m to; moreover, since the great ranges mostly lie near the equator this effect usually serves to lower a summit (in pressure terms) rather than raise it. Denali is the big exception with winter conditions generally making the summit ~600m taller in pressure height vs physical height. I'm not aware of any data for Mount Vinson (calculations exist -- though these particular ones use the standard atmosphere rather than the model atmosphere) or other more polar peaks, but I'm also not aware of winter ascents of those peaks.

Physical altitude vs pressure altitude values calculated (from the standard atmosphere model) and extrapolated from distant temperature measurements. (Source)


Respiratory Physiology
Now we need to move on to how these pressure differences affect our respiratory physiology and why very small differences in barometric pressure can make such enormous differences to human physiology.

Our breathing serves two purposes: 1) to move oxygen molecules from the atmosphere into our lungs (the alveoli within the lung is where gas exchange happens but mostly I will just use the term lung to refer to the part of the lung where gas exchange occurs) and 2) to move carbon dioxide molecules produced by our metabolism out into the atmosphere. Per the title of this article we're talking about oxygen physiology, but it turns out that carbon dioxide matters as well since there's a lot more of it in the air we breathe out than in the atmosphere and it takes up space, so it'll come up later.

Respiratory system overview (pressures in individuals at rest, at sea level and healthy).


Oxygen Absorption and Carrying
The main way that our body gets and transports oxygen from the lung is by using hemoglobin which is an oxygen transporter molecule that lives within our red blood cells. Without hemoglobin we wouldn't be able to deliver enough oxygen to our brain or organs. There's even an equation that tells us how many mL of oxygen is in each dL of blood:
Arterial Oxygen Content = (1.34 x Hemoglobin x Percent Arterial Oxygen Saturation) + (Pressure of dissolved oxygen in arterial blood * 0.003)

Note that almost all oxygen is carried on hemoglobin molecules. (source)

Whether or not hemoglobin molecules with carry or release oxygen molecules is determined (mainly) by the pressure of oxygen in your blood. This effect is not linear and very non-intuitive. Very small changes in oxygen pressure can make comparatively large changes in the amount of hemoglobin that is carrying oxygen. More on this later.

Standard oxyhemoglobin dissociation curve under usual physiologic conditions.

When we breathe our nose, mouth, throat, and trachea heat and saturate the air we breathe with water before it reaches our lungs. This is necessary because the tissue in our lungs is very fragile and cold, arid air is quite irritating to the body. It's a problem for people at altitude because of Dalton's law though -- all of that water vapor in the air displaces other gasses, including oxygen.


Similar to the calculation we can do to determine how much oxygen is in someone's blood we can also calculate the amount of oxygen in a person's lung that is available for the body to absorb and use:
Oxygen pressure in the lung = [(Barometric Pressure - Water Vapor Pressure) * Oxygen %] - [Blood CO2 level / O2-CO2 exchange constant]



I promise that the important concepts in this equation are much more straightforward than the complexity of the equation would make it seem. Let's take the terms one at a time and combine them with things already laid out above to bring some important considerations forward.

Before we move on to breaking down the components of the equation, we need to note that its output tells us the maximum amount of oxygen pressure inside the air sacs of our lung. For a variety of physics and physiology reasons we cannot achieve arterial oxygen amounts that are equivalent; there will always be at least a small decrement between this equations's output and our blood's oxygen pressure.

Discussing the first half of the equation: the FiO2 is the same for everywhere on Earth (~21%). The atmospheric (aka barometric) pressure is what we've talked about at length above that will fluctuate with altitude, season, weather, time of day, and so forth. The water vapor pressure inside our lung will always be the same (47 mmHg) because we heat all our inspired air to our body temperature and fully saturate it with water, thus it represents a fixed loss of available atmospheric pressure. Looking at this equation it becomes clear why supplemental oxygen can make such a big difference when climbing at very high altitudes. Anything that moves the 21% number upward will result in a much larger amount of oxygen pressure within the lung (ie able to be absorbed into the blood stream).

As to the second half of the equation we'll start with RQ. Conceptually RQ represents the ratio of carbon dioxide molecules we release to oxygen molecules that we absorb. For nearly all humans (though not infants) eating normal diets (including what people generally consume at high altitudes) it is generally approximated at 0.8 (a variety of studies using direct measurement of human subjects at pressures below 350 mmHg have found a mean value of 0.82). If you want further information Wikipedia's explanation is sound.

Carbon Dioxide (ie Ventilation)
A language note before we dive in: the process of moving oxygen into our body is referred to by physiologists as oxygenation which is simple enough; but the process of getting rid of carbon dioxide from our body is referred to as ventilation. Thus when we someone is discussed as hyperventilating it means they are breathing their carbon dioxide levels down below normal; someone who is hypoventilating is allowing their carbon dioxide levels to accumulate or rise beyond where the body wants them to be.

As mentioned conceptually and now mathematically, the amount of carbon dioxide in our blood (and subsequently in our exhaled breath) takes up space that could otherwise be occupied by oxygen. Our body regulates its carbon dioxide pressure within a very narrow range (the normal pressure of CO2 in our arterial blood is 40 mmHg +/- 5) because it is tied to many aspects of our physiology such as: the blood pressure within our lungs, the amount of blood flow to our brain, and the ability of muscles to contract and relax normally are all intricately linked to our carbon dioxide concentration directly or indirectly.

As a brief aside, carbon dioxide is the reason you cannot hold your breath very long. At sea level most healthy adults can go 4-6 minutes without breathing before their oxygen levels (measured by hemoglobin saturation) will start to fall, yet most people can only hold their breath for 1-2 minutes. The reason for this is the build up of carbon dioxide which directly stimulates our brain to start breathing. In fact, if one holds their breath long enough, through the excruciating discomfort, the brainstem will force the diaphragm to start contracting despite a person willing it not to.

Perhaps obvious, but worth stating clearly: as holding our breath causes carbon dioxide to accumulate, breathing more rapidly (or more deeply, or both) causes our carbon dioxide level to decrease from normal. If you do this long enough a variety of things related to the physiological connections I mentioned above will start to occur (you'll feel tingly, your fingers and toes may spasm, you'll get a headache, you might get nauseous).

I've avoided doing math as much as I can in this article (despite the presence of many equations), but working through the alveolar gas equation will illustrate the importance of carbon dioxide at extreme altitudes in a way that words cannot (recall that the result of these calculations is the oxygen pressure available to our body):

The alveolar gas equation at sea level (all pressures in mmHg): 



On the summit of Mt. Everest (8849 meters):



On the summit of Mt. Rainier (4392 meters):



Put another way: if humans do not hyperventilate on the summit of Mt. Everest, there cannot be any oxygen in their lungs (though this is sort of a paradox, since if there's no oxygen in their lung they'd be dead and they wouldn't be producing carbon dioxide…). Even on the summit of Mt. Rainier an oxygen pressure of 32.5 mmHg without hyperventilation would mean a climber has a hemoglobin saturation of only ~60% (see the oxyhemoglobin chart above)!

Now that we've worked through the math we can talk about acclimatization, or to put it another way: how our body can fiddle with some things to overcome these unalterable constraints of physics.

14 November 2011

The Vets Are Alright (The Rest of Us Are the Problem)

This post is cross posted over at the wonderful Gunpowder & Lead blog. They're the same post.

As I read through recent stories about military veterans one thing has crystallized for me: the relentless focus on injuries, PTSD, TBI and the soldier's and veteran's general distress.

Based solely on the media's portrayal of returning soldiers and veterans one would believe them all to be fragile individuals whose lives may shatter at the slightest additional trauma. However, the vast majority of soldiers return healthy and capable, even if they are forever changed by their experience serving. That is to say, we seem to live in a world where the afflictions of soldiers are covered in the media like airplane crashes, rather than car accidents:
Page-one coverage of airplane accidents was sixty times greater than reporting on HIV/AIDs; fifteen hundred times greater than auto hazards; and six thousand times greater than cancer, the second leading killer in America after heart disease.
To be sure, PTSD, TBI, amputations, automobile accidents, plane crashes, and cancer deaths are all very real and very tragic but it's long past due that we consider the consequences of our relentless focus on the those afflicted by war because they are real as well.

While the media's predilection for rare and extraordinary stories has been well documented what's more important than the coverage itself is the nature of the coverage. For example: this October 2010 Washington Post article, Traumatic brain injury leaves an often-invisible, life-altering wound. This article is typical for its genre, coming in at nearly 3,000 words, yet devoting only a few sentences to any sort of wider context. We are told the raw number of diagnoses of TBI since 2000, then given another, larger, number from a RAND corporation study. Completely missing is any sense of scale. Do those 180,000 (or is it 300,000?) soldiers represent 1%, 10%, or 90% of individuals at-risk for TBI?

03 October 2011

Misdirection by euphemism

As I watched the news a few weeks ago waiting to see if, and then when, the state of Georgia would execute Troy Davis—a man wrongly convicted at worst, or unjustly sentenced at best—something about the images from outside the prison struck me: The innocuous and anodyne name of the prison, the Georgia Diagnostic and Classification Prison.

Naming the prison this way asserts that the public should know that this facility is where diagnosing and classifying occur. While it's undeniably true that those terms do accurately convey some of the actions that the Georgia Department of Corrections carries out there, it begs the question: Why are these functions of this prison so vital as to claim space in its very name?

George Orwell, in his famous 1946 essay Politics and the English Language said, "In our time, political speech and writing are largely the defense of the indefensible." It is a coincidence of history that only a year later the United States would consolidate the belligerently named Departments of War and Navy into the comparatively docile Department of Defense.

The labels a culture applies to its institutions serve a purpose beyond mere identification: they signal the purpose and expectations by which we should judge them. This is why those two superfluous words in the Georgia prison's name are so important. They were not chosen lightly, nor were they included in the prison's title carelessly.

Let's examine the word diagnostic closely (classification's particulars ought to be self evident afterward). Beyond its definition, the verb diagnose is notable because it is overwhelmingly used to indicates a label applied by an authority. To wit: the OED's first usage example for diagnose is, "doctors diagnosed a rare and fatal liver disease." One can easily construct other common usages, e.g., "the mechanic diagnosed the problem with the car."

No matter the usage example, they all refer to situations where higher-information individuals (or professions, or institutions) apply a label to something. To put it more simply, diagnosis is an act of profound authoritarianism. While the authoritarian implications of both diagnosis and classification are important, the more subtle endorsement is toward the medical usage. It is no accident that diagnose's usage example invokes the medical profession.

10 March 2011

Hospitals are not like airports; patients are not like airplanes

In writing blog posts that are critical of other writing one of my goals is not to point to the specific flaws of any particular article. No one has time to discredit all of the specious and nonsensical things that get posted, even by reputable outlets, to the internet each day. One of the things I try, and you can let me know if I'm failing, is to point out some of the tricks used to manipulate and/or mislead readers.

Which brings me to the false dichotomies. For an excellent example there's this piece in the Washington Monthly. You don't even have to read past the subhead to find the comparison:
Last year there wasn’t a single fatal airline accident in the developed world. So why is the U.S. health care system still accidentally killing hundreds of thousands? The answer is a lack of transparency.
I've added emphasis on a particularly important part here, and I'll get back to it in a bit.

14 February 2011

How problems in WTUs are like drug interaction deaths

Medical issues in the military seem to be getting a lot of press attention these days, so I feel it's important to take a look at the genesis of these problems, specifically the polypharmacy issue and the troubles with Warrior Transition Units (WTUs). The policies leading to these problems have been well intentioned, yet there seems to be little thought or care for how and why they've gone so far astray, although there is plenty that they have gone astray.

Before delving into the issues I mentioned above, let's use a more well known example of these "second order effects." During the toughening of drug sentences in the late 1980s the Anti-Drug Abuse Act made prison sentences proportional to the quantity of illicit substance that a dealer was holding when arrested. The thinking behind such laws is straightforward: stiffer sentences for bigger time drug dealers. At first blush this sounds like a solid enforcement strategy; however, both in theory and in practice these laws had the unintended consequence of incentivizing dealers to hold smaller quantities while still being able to meet demand. Dealers responded to this by placing a new premium on purity. If they could sell their customers half the weight for the same price, they faced a lighter sentence if/when they were arrested. In this way drug laws that were designed to curtail large scale drug dealing had the perverse effect of increasing drug purity, which itself has many second order consequences (higher overdose rates, increased addiction potential, etc).

20 January 2011

Breaking down the Army's suicide data

Part I: What does the data say?

There's a lot of grist to Wednesday's news briefing with Gen. Chiarelli on the 2010 Army suicide statistics. As usual, everything I write is my own opinion, unvarnished.

Looking past the headlines telling you some suicides were up and some where down I want to point out an underemphasized point that Gen. Chiarelli made during his briefing:
So the numbers [...] have really only focused on this group, both the Army Reserve and the Army National Guard, to collect this data for about five years.