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Crappy recommendations

October 7, 2010

Doctors should stop telling their patients with diverticular disease to avoid nuts, seeds, corn, and popcorn. Even though this has been our practice for nearly a century, there has never been any sound evidence that such dietary precautions would result in fewer complications from diverticula. In fact, we now have some fairly sound evidence that those recommendations are completely off course: a large study involving 47,228 men over an 18-year period demonstrated that higher rates of popcorn and nut consumption led to lower rates of diverticulitis. Yet large numbers of physicians and other health care providers still provide outdated recommendations for their patients.

The concept that nuts, seeds, and kernels could cause problems with diverticulosis came about in the early 1900s. Prior to that time, diverticular disease of the colon was a rare condition.  The Industrial Revolution greatly reduced the fiber content of the Western diet as a result of milling and refining grains on an increasing scale. After 20 or 30 years of this, diverticulosis rates started climbing dramatically. Surgeons saw more and more cases of diverticular perforation, one of the more critical complications of diverticular disease. They encountered these patients with an obvious intraabdominal catastrophe, and had to operate on them to try to save their lives.  At surgery, they identified a hole in the colon with a little outpouching, the diverticulum, often with a kernel or seed stuck in it.  This observation led surgeons to conclude that the wedged item was somehow responsible for the calamity.

So the word went out that patients with diverticular disease should avoid these food items like the plague. A low-residue diet became the standard recommendation for diverticulosis patients. This concept persisted through the 1960s and 1970s when investigators were determining that diverticula developed from increased intraluminal pressure which, in turn, was a major consequence of low fiber diet. The recommendations for a low-residue diet were 180 degrees in the wrong direction.

Even though there is now solid evidence that the previous recommendations were absolutely misguided, it would take a paradigm shift for everyone in medicine to start handing out the correct recommendations.

Overwhelming Infection and the Battle of New Market

October 5, 2010

The presence of an excess of immature white blood cells indicates the infectious process is overwhelming the immune system.

 In 1864, the Confederacy was losing the War Between the States (or, as the American Civil War was known in the South, the War of Northern Aggression).  Grant’s armies were moving into Virginia, so a stand was made by the Confederacy to hold the Union forces near the small northern Virginia town of New Market.  However, because the South’s forces were so severely depleted, additional troops were sought for fighting in the ensuing Battle of New Market in the form of cadets from the Virginia Military Institute out of Lexington, VA.  College boys aged 15-21 were sent to fight a man’s war.  Of the 257 cadets in the battle, 10 cadets died in the struggle, and 48 were wounded. 

This tragic circumstance is an analogy for what happens to the body’s defenses when it is overwhelmed by a severe bacterial infection.   White blood cells, primarily polymorphonuclear neutrophils (known as PMNs), rush toward the area of invasion, attempting to kill all the invading organisms.  As the PMNs  available become depleted, more and more are produced in the bone marrow.  Because of the demand, these developing cells start getting kicked out at earlier and earlier degrees of immaturity, which can be recognized under the microscope because their nuclei are distinctly different from those of mature PMNs.  The percentages of the various cell types are reported as a white blood cell differential count.  Traditionally, the appearance of more than usual numbers of immature forms is known as a “shift to the left,” based upon the system that was used to tally the various cell types in previous decades.

 Recognizing the desperation represented by a left shift, the astute clinician should ensure that his therapies are as aggressive as possible, lest his patient suffer the same consequences as those brave young boys at New Market.   Seeking to avoid this compensatory process by identifying and eliminating infections earlier and more effectively is our goal.  Understanding that a shift to the left represents a clinical failure to achieve our goal will be a paradigm shift in medicine.

Dehydration and Hypovolemia: Differences Can Be Important

September 29, 2010

We should be precise in our language, especially when discussing something as complex as human physiology.  Fuzzy language can lead to fuzzy logic, which can lead to problems we didn’t want.

One of the most misused terms in medicine is “dehydrated”.  We use that to indicate that someone’s overall fluid volume is low.  The more appropriate term is “hypovolemic”.  However, most people, including health care providers, do not understand the difference or its importance.

The Greek and Latin roots in the terms provide some distinction.  An understanding of physiology provides the rationale.

“Dehydration” means “loss of water”.  Water is the base fluid for all the body’s cells and their surrounding environment.  Over 60 percent of the body is water.  However, because water flows freely between the cells and their environment, when we are low on water – truly dehydrated – we see an increase in the concentration of the molecules dissolved in water.  In the cells, potassium levels increase, because potassium is the primary positively charged molecule (or cation) inside cells.  Outside cells, because sodium is the primary cation outside cells, sodium concentrations climb.  Because the molecules in the bloodstream exchange relatively freely with the fluid outside cells, a blood test showing a high serum sodium level confirms the diagnosis of dehydration.

“Hypovolemia” means “low blood volume”, which is not identical to dehydration because blood is not pure water.  Rather, blood is a solution of sodium and other salts, proteins, and various types of blood cells.  Low blood volume can only be detected by devices that can measure the volumes or pressures within blood vessels or heart chambers, such as central venous pressure, pulmonary capillary wedge pressures, or end-diastolic volume measurements.

Treatment of dehydration employs free water administration.  Treatment of hypovolemia requires salt-based so-called “crystalloid” infusions.  It should not be a major paradigm shift in medicine to know what we are talking about in order to treat the condition properly, yet all too often we’ve forgotten our roots.

Shock is what happens when the power goes out

September 27, 2010

Many definitions have tried to explain shock.  Unfortunately, some have left their mark too long.  For example, while most clinicians may claim they know otherwise, they still react to a low blood pressure (hypotension) as though it and shock are synonymous.  We’ve often seen patients’ blood pressures drop after a sedative or a narcotic are infused to keep them comfortable.  Physicians and nurses often respond with a fluid bolus, as though the patient is suffering from hypovolemic shock.  However, in most cases, the sedative and/or narcotic simply slowed down the patient’s metabolism so that their circulation didn’t need to work as much as it normally does.  The drop in blood pressure is simply a reflection of that.  The paradigm shift in medicine will be to fundamentally understand the nature of shock as well as the several mechanisms that can produce it.

Years ago, we lived in North Carolina when Hurricane Fran blew through.  It knocked out all the electricity for miles.  And it took days to weeks for it to be restored.  In our household, we couldn’t cook on our electric stove, so I bought a new gas grille.  We ate out of the refrigerator and freezer for a couple of days, but pretty soon, the food started to smell.  There were a few restaurants that had power, so we could go there to eat.  Our laundry piled up in the hallway outside the laundry room so that it was impassable.  I started to realize that if the power didn’t come on soon, we would have to move somewhere else to survive.

This was shock for our household.  Vital functions within our home were lost, such as nutrition and hygiene.  The circulation within our household corriders were blocked, which is analogous to diffuse intravascular coagulation, a syndrome often cited as responsible in part for the multiple organ failure that all-too-often follows an episode of severe shock.

Thus it is in the human body: when the power goes out, vital functions fail.  It can be an immediate process, occurring right before your eyes.  However, it can also be more drawn out, with a more chronic and subtle underperfused state leading to multiple organ failures down the road.  And once there are enough organ failures over a long enough period of time, death ensues.

Checklisting the Unnecessary

September 22, 2010

We shouldn’t need to make intubated patients “NPO” (“nil per os”, meaning nothing by mouth) prior to surgery.

In 1946, Mendelson described a syndrome wherein pregnant patients would develop severe pneumonitis when being placed under general anesthesia.  In order to place a breathing tube into the trachea (windpipe) for the administration of general anesthesia, chemical paralysis of the body’s muscles is produced by infusing specific paralyzing drugs into the bloodstream.  As a result, normal responses like the cough and gag reflexes are blocked.  If a patient strains or actively vomits during induction, stomach acid and food (if present) can regurgitate into the back of the mouth and be inhaled, causing severe lung damage.  However, with an empty stomach and some medication to counteract stomach acid, we can avoid this complication.  It is for this reason that patients are made NPO (nil per os, meaning “nothing by mouth”) the night prior to receiving a general anesthetic.  This checklist item is considered very important, and patients who were not made NPO after midnight prior to their operation can find their cases canceled in all except the most extreme emergencies.

Of course, the complication can also be avoided by already having a tube already in the trachea, because the endotracheal tube has a cuff near its tip that seals the tracheal channel, preventing fluid and air from going around the tube and allowing only air to go through the tube.  An interesting situation occurs when a previously intubated patient, such as an ICU patient receiving mechanical ventilation, is taken to the operating room to undergo a surgical procedure.  These patients are routinely made NPO as well, and their cases are canceled if an oversight failed to make them NPO.  Unfortunately, repeated cancellations can occasionally result in underfeeding or missed medications due to the NPO status.

Exactly why this is necessary in an already intubated patient is never made clear by those who enforce it, usually because they don’t understand why.  One of the paradigm shifts in medicine will be to understand conditional exceptions to every checklist.

Pressure and Gravity

September 19, 2010

Our blood pressure is an anti-gravity tool.  It actually doesn’t make sense for blood pressure to be the primary resuscitation goal for a supine patient.

The only animal with valves in its carotid arteries is the giraffe.  It’s head is 17 feet higher than the heart, so it needs valves to keep the blood flowing up there from falling back down.  And, to provide the oomph to push it up there, the giraffe’s blood pressure is over twice as high as our is.  Our systolic blood pressure is normally about 120 millimeters of mercury (mmHg), and we are considered to have high blood pressure (hypertension) when it is higher than 130 or 140 mmHg, depending on age.  Giraffes have systolic blood pressures well over 200 mmHg, and they have been recorded to be as high as 300 mmHg. 

Also, in order further to prevent the entire circulatory volume from pooling at the bottom of the giraffe’s towering anatomy, the blood vessel walls in its lower extremities (figure at right) are extremely thicker than those in its head (figure at left), preventing the former from stretching under the tremendous gravitational pull.  In addition, they have very thick connective tissues wrapping their thin legs to prevent fluid extravasation that would otherwise occur as a result of the extremely high blood pressure.

The pressure within our circulation’s microscopic capillaries has been determined to be about 25 mmHg, which is the pressure necessary to drive blood across the capillary network and into the venous system, nourishing cells on the way.  However, the mean arterial pressure within the aorta and major blood vessels is about 90 mmHg — a difference of 65 mmHg.  Why should the heart have to pump our pressure into the such a high level of 90 if it only takes 25 to get it through the circulation?  Doesn’t that make the heart work overtime?

It would, of course, if there weren’t any reason for the pressure discrepancy.  But, like most things in biology, there is a very good reason.  You see, we have the same problem as the giraffe, although not to the same degree.  Our head is also above our heart, so the heart needs to  be able to pump blood upwards against gravity.  But we’re not always upright, because we sleep lying down.  For about a third of the day, our heart is at the same level as our head and our legs. 

So our circulation has to adapt for changes in our position.  When we’re supine, our lower extremity vessels open up.  But when we stand, they must constrict.  Giraffes, having a less flexible circulation, have to sleep while standing.

The relationship of our physiology to our life on planet Earth (with its gravity) is most apparent when astronauts return after spending prolonged periods in space.  They have swollen, “puffy” faces and skinny, “bird-leg” legs as a result of having antigravity circulation exposed to zero gravity.

The paradigm shift in medicine will be to use precise, specific measures of circulatory performance to determine the nature and impact of our therapeutic interventions, rather than potentially misleading stand-ins such as blood pressure.

Layers

September 15, 2010

Intrinsic appreciation of the body’s layers facilitates paradigm shifts in medicine’s approach to health and disease management. 

Understanding how the human body works (and what is going on when it doesn’t work) requires an understanding of how it’s put together.  Not only do we need to know the locations of the various organs and tissues, we must also appreciate the elegant structure that provides the functional capabilities of the organs.

Many of the body’s tissues are built with a series of layers.  Each layer provides a specific function which has benefit to the organism.

  • Skin
    • Epidermis (meaning “above the dermis”):  dead flat (“squamous”) epithelial cells lying on top of each other in a growing pile that flakes off daily, expanding outward from its growth base.  It is this layer that makes skin water-tight and provides a barrier function against would-be microbial invaders. 
    • Dermis, made primarily of tough collagen providing tissue strength to the skin and also houses sensory nerves.  Glands extending from the epidermis penetrate into the dermis.
  • Intestine
    • Mucosa: The epithelium (mucosa) of the gastrointestinal tract  is continuous with the epithelium (epidermis) of the skin, joining it on either end at the mouth and the anus.  The type of cell changes however, where the esophagus (the “swallowing tube”) meets the stomach.  Instead of the flat squamous cells, the lining turns into columnar cells.  These cells, in addition to providing the barrier function, also possess many digestive, absorptive, and secretory functions. 
    • Lamina propria, which provides an immunologic defense layer. 
    • Muscularis externa, which propels food and waste through the intestinal tract.
    • Serosa: connective tissue covering, often fused with the peritoneum, whose smooth moist surface allows the intestines to contract freely within the peritoneal cavity.
  • Blood vessels
    • Intima: the inner surface providing a smooth surface.  If this surface is injured, blood clotting is stimulated by the underlying collagen and its negative charges
    • Media, containing collagen, elastic tissue, and, often, muscle fibers enabling changes in caliber of the blood vessel
    • Adventia, made up of connective tissue and housing nerves that control the blood vessel’s reactions

Below Our Radar

September 13, 2010

It is a huge paradigm shift in medicine to understand the difference between what we should know and what we actually can know.

 Rocket scientists are lucky.  When they fire off a missile into outer space, it seems that they can know and monitor just about anything.  In putting together that incredible electromechanical device, the engineers also built in sensors, detectors, and gauges all designed to sense whether any problems are developing.  This allows the astronauts, scientists, and engineers operating the missile to intervene and correct the problem before a catastrophe develops.

 Your doctor is not so lucky.  First of all, the human body comes to him already turned on; he doesn’t even get to do any error-checking during a boot-up sequence.  Once it has started, he can never do a reboot to correct any problems.  Most importantly, it is very difficult for him to know if anything is wrong until a real problem emerges.

 For example, when you get a cut on your hand, the doctor has a choice of 1) cleaning it up and suturing the wound shut or 2) letting it heal in from the base.  The former option is more likely to provide a less disfiguring scar; the latter option will reduce the chance of infection.  In most cases, closing the wound works out well.  In making this decision, the doctor can only hope that he’s cleaned the wound adequately prior to closing it.  Ideally, he would know exactly if any bacteria are still in the wound and in what concentration.  He would also know – again, ideally – which antibiotics are best at killing the specific bacteria in the wound.  With such knowledge, he would always be able to close a wound with complete confidence that an infection will not occur because there are no organisms left lurking in our tissues. 

 Yet, we don’t have that information because we did not invent, design, or build the human body.  If we had, we would have built in the sensors and detectors we would need for these and the trillion other decisions we make in health care.

LaPlace’s Law and Toothpaste

September 13, 2010

Enabling an intrinsic understanding of human structure and function is a paradigm shift for medical education.  We are taught so many things by rote, and fundamental concepts never seem to be conveyed.

For years, I struggled with understanding how colonic diverticula develop.  It seemed that what I’d been taught didn’t fit together enough for my mind to grasp.

We’d been taught that the origin of diverticula can be understood through the principle of LaPlace’s law:

T = Pr 

meaning the tension (T) on a cylindrical structure is equal to the product of the intraluminal pressure (P) and the radius (r) of the lumen.  This was a formula I could regurgitate on tests.  But it didn’t help me understand how diverticula form. 

Then one day, I was brushing my teeth, and I noticed how hard I had to squeeze the practically empty toothpaste tube to get out enough toothpaste to do the job.  I started to realize that, if it weren’t for the tube’s presence, squeezing that hard would cause toothpaste to ooze between my fingers.

 This, in fact, is exactly how diverticula develop.  When the human colon doesn’t have enough bulk due to poor fiber intake, it has to squeeze harder and harder to push waste further down toward the rectum.  That is, there is a higher tension (T) being generated in the muscle of its wall.  This produces smaller radius (r) due to the squeeze.  But to offset it, there must be a significantly higher pressure (P).  In the case of my hands squeezing, the higher pressure forces toothpaste between my fingers.  In the case of the colon, the higher pressure forces the inner lining of the intestine – the mucosa – to bulge through the muscle layer as an outpouching known as a diverticulum.

 To be a purist, these are known as false diverticula because the outpouchings do not contain all the normal layers of the intestinal wall.  True diverticula, which do contain all three layers of the intestinal wall, are almost always congenital – that is present since birth.  But these false diverticula are the ones that usually give us the most trouble.

The paradigm shift in medicine will be to ensure that our educational processes convey true understanding rather than rote memorization.

The Maker Did Not Provide a Dashboard

September 9, 2010

Here’s a paradigm shift in medicine: imagine you’ve got a critically injured trauma patient in the next decade or two.  You’re looking at a screen full of color-coded pixels representing every cell in your patient’s body.  Green pixels tell you that the cell has more than enough ATP for all its needs; red pixels tell you the cell needs more ATP than it has.

 All of the pixels – throughout the entire patient’s display – are green.

 Is the patient in shock?  Do  you need to know anything else (i.e., blood pressure, urine output, base deficit, etc.) to answer this?

 When you think about it, the tests we do in medicine are not the tests we’d like to do.  The things we monitor are only those which we can monitor, not what we’d like to know.

 There is no doubt that there is a great deal of testing in medicine: physiologic measurements and monitors, biochemical testing of various bodily fluids, microscopic inspection and testing of biopsied pieces of tissue, and various types of images of every single body part.  You name it, we’ve tried to inspect.

 Yet, in many cases, we’re not really evaluating what we’d like to evaluate.  For example, we can monitor a number of parameters that assess the circulation’s function: blood pressure, heart rate, central venous pressure, urine output, base deficit, serum lactate, pulmonary capillary wedge pressure, cardiac output, mixed venous saturation, ejection fraction, and end-diastolic volume, to name a few.  But none of these tell us what we really need to know.  If we could know that every single cell in the body had an adequate supply of ATP, we would know the patient is not in shock and the circulation was fulfilling its needs.  It wouldn’t matter what the blood pressure is (unless it’s too high); it’s clearly enough to provide the required energy supply.  Because the maker did not build a dashboard for us to use in managing the ailments of the human body, we have had to develop our own set of monitors to watch, and they’re far from perfect.