Sentinel Signs
We see toddlers everywhere. Toddlers seem to be doing everything, everywhere, all at once. They run, climb, creep, crawl and squat. This is all innocent play. But for approximately 1,600 children born each year, squatting is not innocent, nor are they playing. For toddlers with a serious heart disorder known as Tetralogy of Fallot, squatting is the only way they can catch their breath after exertion.
Tetralogy of Fallot represents a cluster of four different circulatory issues, but the end result is that breathing is labored for children with this disorder. When a toddler with Tetralogy of Fallot squats, the femoral arteries in their legs are pinched just enough to help their body reverse the negative hemodynamic effects of the disorder, increasing the flow of oxygenated blood. This position of relief is something they discover on their own. No one teaches it to them. And it suggests to a pediatrician that he or she take a closer look at the child’s heart. In this case, squatting in a toddler is considered a diagnostic clue, or a “sentinel sign.”
We don’t know for sure why or how this complex develops. Surgery at some point is necessary in individuals, usually male, who have Tetralogy of Fallot. And even though post-op life expectancy has improved, the individual will need to restrict vigorous physical activity and receive regular medical follow-up for the rest of their life.
In other cases, involving small children, the number, appearance, or location of hair whorls on a baby’s crown “may” portend specific neurological problems the infant may face. One whorl is the norm. Two whorls are not unusual, but beyond that a pediatrician “may” take note and watch for “potential” developmental issues.
Sentinel signs in nature
There are sentinel signs in nature. Meerkats, natural sentinels themselves but only as far as other meerkats are concerned, respond to alarm calls from other species — for example, birds such as drongos and starlings. These birds are primarily concerned with keeping their own relations safe from hawks, eagles, and falcons. But other animals have learned the wisdom of paying attention to their shrill screams.
Animals can also be trained to act as sentinels. Watchdogs, or police dogs that sniff out drugs or explosives, come to mind. But I’ve taught high school students in the past who occasionally had a service dog accompany them to class. These youngsters had diabetes-related problems, like hypoglycemia, and the dog would lick the student’s hand every few minutes. The dog was trained to alert the student whenever it perceived low blood sugar — or perhaps high blood sugar — in the child. At that point, the student would take a piece of candy, sugar paste, or insulin, as appropriate. Eventually, the child would learn the S/Sx of glucose monitoring and control, and the dog could stay home, which was just fine by me.
Can animals warn us in advance of natural disasters? Unusual activity in the animal kingdom may be related to future and potentially catastrophic events. Scientific studies involving goats indicated that they — and other animals — become alarmed hours, and possibly a day or more, before an event such as a volcanic eruption or an earthquake takes place. Animals may be sensitive to micro-vibrations, or to the trace release of gases such as sulfur dioxide, that people cannot perceive. Often, these sentinel variations cause the animals — geese, goats, elephants — to become increasingly vocal, restless, and alarmed, alerting people that some potentially catastrophic event is imminent.
And then there is the weather. Falling barometric pressure is generally a sentient sign of storms. There is also truth in the saying “Red skies in the morning, sailors take warning. Red skies at night, Sailor’s delight.”
What is a sentinel, and what do sentinels do?
A sentinel is someone who guards or keeps watch over another person, or perhaps something of value. Or, a sentinel can be something, like an intruder alarm or camera. Whether a person or a machine, a sentinel (sentry) sounds an alarm when something is amiss, or when danger is imminent. Some say that the word “sentinel” is derived from two Old Italian words: sentina, meaning “vigilance,” and sentire, “to hear or perceive.”
More on sentinel signs as far as our bodies are concerned
In medicine specifically, a sentinel sign is a symptom or event that suggests some sort of disease or disorder is present in a person. A sign is something that can be measured, like a pulse, blood pressure, or an elevated white blood cell count. A symptom is usually a subjective feeling — dizziness, sensitivity to light, a ringing in the ears, and so on. An event is the presence of variables that combine to cause an emergency, such as a heart attack, drug overdose, seizure, or attempted suicide, to name just a few possibilities. Hospitals abbreviate the term “signs and symptoms” as S/Sx.
It is possible that a squatting child — millions of squatting children, as a matter of fact — does not have a heart issue. In that case, squatting is not a warning. Sometimes we only know after the fact whether radiating pain in a person’s left arm was a sentinel sign of a heart attack, or whether it was nothing more than a pinched nerve. Sometimes we only discover the answer post-mortem. But generally, we must reasonably consider that when we have pain in the left arm, particularly along with shortness of breath, unexplained perspiration, or nausea, there may be a myocardial infarction in progress. We all need to find our “sweet spot” between ignoring something potentially life-threatening and obsessing over something that is not.
Types of sentinel events
Deena and I have been focusing on the word “sentinel” lately, in the context of her intracranial aneurysm. Until now, sentinel was a word that had largely escaped me, probably because we used the term “precursor” back in the day. Because of her aneurysm, I was introduced to a new word. One of the hallmarks of a teacher is the desire to share something new and interesting with the “class.” Hence, and without a teaching contract this semester, I am sharing this with you.
As far as intracranial aneurysms are concerned, there are several signs and symptoms worth mentioning briefly that can serve as sentinel indicators, abbreviated in medical notation as “S/Sx.” An aneurysm is a weakness in the wall of an artery that causes the arterial wall to “bulge” outward. Under certain circumstances, the bulge can leak or rupture. A ruptured aneurysm is serious wherever it occurs in your body, but particularly serious if it occurs in your brain, because while your ankle or elbow can swell, there is no room for expansion in your brain.
Sentinel signs of an intracranial aneurysm
Neurosurgeons will tell you that unless an intracranial — that is, a cerebral — aneurysm is fairly large (seven tenths of a centimeter or more), you will probably not have any indication that it is even there. However, sometimes an aneurysm can press on a nerve or adjacent structure, and in that case you may have unusual signs or symptoms. And if the aneurysm leaks or bursts, then there is an emergency.
Some people have terrible headaches for their whole life. That is something that may or may not respond to medication. But if a person who is 40 years old suddenly develops painful headaches, this needs to be evaluated. There are tension headaches, cluster headaches, sinus headaches, and, of course, migraines. But a tumor growing inside someone’s head — whether malignant or benign, it matters not — can cause headaches as well. Your doctor will likely order imaging, such as a CT or MR angiogram, if you have late-onset headaches, and this will in almost all cases determine whether you have an aneurysm.
The pain is a sentinel that can herald many different problems, and they are almost all serious. They include the following:
It’s important that you listen to your sentinel. And as far as Deena’s aneurysm goes, she had it successfully stented and you can read about it here.
