How the Pain Scale Works

Doctors and researchers have always sought ways to measure pain. After all, judging pain based on self-reports -- whether from a scared child, a confused grandmother or even a perfectly capable adult -- isn't always reliable or helpful.
Doctors and researchers have always sought ways to measure pain. After all, judging pain based on self-reports -- whether from a scared child, a confused grandmother or even a perfectly capable adult -- isn't always reliable or helpful.
Iakov Filimonov/iStock/Thinkstock

Have you ever considered how difficult it is to measure pain? Probably not. But consider this: If you've got a fever, you grab a thermometer that gives you a temperature in degrees, and you can check blood pressure by slapping on a cuff and reading the millimeters of mercury (mmHg). But despite all the advances in modern medicine, there's no instrument to measure pain. That's where pain scales come in.

Pain scales are tools that doctors and nurses use to estimate the intensity of discomfort. Some rely on self-reporting, meaning patients are asked to assess their own pain. There are many ways to do this, but one familiar way is for a physician to ask those in their care to rate pain on a scale from 0 to 10. However, because such screenings are subjective and require communication, they aren't always reliable or even feasible. That's why doctors also use observation to make their own pain assessment. Some clues to a patient's discomfort level might be behavioral symptoms, like wincing and moaning, or physiological symptoms like increased heart rate and blood pressure.


So why measure pain? Whether determined through self-reporting or observation, pain levels are an important part of the medical diagnosis and treatment process. Say a patient comes in with chest pain, and they rate it at a 7 on the scale we mentioned above — that could indicate anything from a heart attack to a muscle strain. If the doctor then gives the patient some pain reliever and the pain goes down to a 2, that change in rating could help rule out the heart attack. Such measures can also aid doctors in tracking whether a patient's condition is improving or declining, as well as pinpointing the amount and type of pain medications needed to make the patient comfortable. In fact, measuring patient discomfort has become such an important part of medical practice that that the American Pain Society has declared pain "the fifth vital sign."

Despite their widespread use today, pain scales are a relatively new phenomenon. Read on to learn about their origins and one particularly misguided experiment conducted in an attempt to create the perfect pain scale.


Pain Scale History

Pain hasn't historically been well understood, but backrubs from nurses might help.
Pain hasn't historically been well understood, but backrubs from nurses might help.
Underwood Archives/Getty Images

Because pain is impossible to precisely measure or quantify, it remained poorly understood for many years. Well into the 20th century, doctors struggled to provide appropriate amounts of medication or anesthesia to patients experiencing traumalike injury, surgery or childbirth. Unfortunately, this lack of understanding led some doctors to test some pretty wacky theories.

One of the most infamous efforts to objectively measure pain occurred at New York Hospital in 1948. Two doctors, James Hardy and Carl Javert, fashioned a device called a dolorimeter, which literally means a "measure of pain," and connected it to a heat gun. Then they enlisted the assistance of 13 pregnant nurses or wives of doctors at the hospital. When the women went into labor, the physicians began applying heat of increasing intensity to the back of the ladies' hands in between contractions, asking them what intensity matched their pain. They used the resulting readings, given in "dols" (a pain unit they made up) to determine the level of pain experienced at a given length of time between contractions. Shockingly, one woman took the experiment so far that she received second-degree burns, maxing out the dolorimeter at 10.5 dols! Unfortunately for Hardy and Javert, not to mention the woman who was badly burned, their pain scale couldn't be reproduced by other doctors and, as a result, never caught on [sources: Hardy and Javert, RadioLab].


Meanwhile, other doctors were experimenting under a different assumption that now seems obvious: Pain is an experience that is best described by the person experiencing it. The same year Hardy and Javert were burning hands, cardiologist Kenneth Keele created an early pain scale in which patients were simply asked to rank their current pain as "0" for none, "1" for mild, "2" for moderate or "3" for severe. In 1964 a group of English psychiatrists devised a scale consisting of a 4-inch (10-centimeter) line with the words "no pain" on one side and "the pain is as much as I can bear" on the other. Then, beginning in the 1970s, the number of pain scales swelled, giving doctors today dozens from which to choose [source: Noble et al.].

Self-reporting Pain Scales

Adults typically use numerical pain-reporting scales, while children tend to be better off with pictures or colors.
Adults typically use numerical pain-reporting scales, while children tend to be better off with pictures or colors.

If a doctor or nurse has ever asked you to rate your pain, you've used a self-reporting scale. This can be done in many different ways: with numbers, pictures, descriptive words or even a simple mark drawn on a spectrum. One of the most important factors influencing a physician's choice of scale is age because people communicate differently depending on their stage of life.

Children can better conceptualize pain visually, so the scales commonly recommended for them use pictures or colors to represent different levels of discomfort. One popular scale is Wong-Baker FACES, which is recommended for children ages 3 and older. It consists of six faces that are lined up horizontally and drawn to convey increasing levels of pain. The face on the left is smiling, with the number "0" and the phrase "no hurt" written under it, while the face on the right is crying, with the number "10" and the phrase "hurts worst" written beneath it. The faces in the middle are similarly labeled. Children are asked to indicate which one is most like the pain they feel [source: Wong-Baker].


Another common scale is the color analog scale, which consists of a color spectrum that fades from dark red, which is labeled with the words "most pain," to white, which is labeled with the phrase "no pain." Children are asked to rate their pain on the scale using a sliding line, which corresponds with a number on the flip side of the tool so the ratings can be easily recorded and tracked [source: Bulloch et al.].

Adults, on the other hand, are much better at describing their pain with words or numbers. One common scale, the numerical rating scale, is often administered to patients by asking them to rate pain from 0 to 10, though some go as high as 20 or even 100. In this scenario, the "0" represents "no pain" while the high number represents "worst imaginable pain." The verbal scale, on the other hand, suggests adjectives of increasing intensity that patients can use to describe their pain. Common phrasing is "no pain," "mild pain," "moderate pain" and "severe pain." Finally, the visual analog scale consists of a 4-inch (10-centimeter) line with the phrase "no pain" on one end and "worst pain imaginable" on the other. Patients then mark their pain level on the line, which doctors measure with a millimeter ruler for recording purposes [source: Williamson and Hoggart].


Problems with Self-reporting Pain Scales

The reliability of self-reported pain goes out the window if the patient is a sick child who just wants to avoid getting another shot.
The reliability of self-reported pain goes out the window if the patient is a sick child who just wants to avoid getting another shot.

If the person experiencing pain is the only one who can feel it, and there's no tool to precisely measure it, then self-reporting must be the best way to go, right? Not necessarily. There are a number of factors that affect the viability and reliability of such scales, including the ability to communicate, age and honesty.

In order to use self-reporting pain scales, patients must understand how they work and be able to respond appropriately, but this isn't always possible. Patients can have all kinds of communication barriers, from emotional and cognitive impairments to cultural or educational differences that make the scales difficult to grasp. Speech, or a lack thereof, can also present an obstacle: Patients might speak a different language or have a breathing tube, both of which hinder their ability to communicate verbally. Sadly, some people are simply too sick to effectively communicate their pain [source: Berry et al.].


Perhaps the greatest influence on a patient's capacity to communicate pain is age. Infants aren't able to read or understand doctors' questions, so pain scales aren't likely to be much help until they're 3 or 4 [source: Kishner et al.]. Likewise, elderly people — perhaps because of dementia, poor vision or diminished hearing — may have trouble understanding pain scales to a point that the results become unreliable.

Self-reporting pain scales can also become unreliable when patients have some incentive to mislead doctors. An obvious example is an addict who lies about his or her pain in order to get certain medications. While this certainly a problem, there are other far less nefarious reasons why people might misreport their pain. Take children, for example. They might give doctors a low pain score in order to avoid an injection or other uncomfortable procedure, even if they are truly hurting. Elderly folks might underreport pain too, perhaps to cover up new disabilities or simply to avoid being a bother. Either way, doctors may have to use other measures to double-check a patient's self-report. But how?


Observational Measurements

Doctors have to rely on observations of pain-related behavior in patients -- like this upset baby -- who can't communicate their pain any other way.
Doctors have to rely on observations of pain-related behavior in patients -- like this upset baby -- who can't communicate their pain any other way.
Jose Luis Pelaez Inc/Blend Images/Thinkstock

If doctors can't rely on a patient to give them an accurate pain report — or any report at all — then they have to look at how the body is responding to pain. How? Think about the way you acted last time you were in pain. You probably made some sort of grimace and maybe groaned a little. If it was bad enough, perhaps you began sweating or your heartbeat increased. Those are exactly the kinds of things doctors are looking for.

The body's reactions to pain generally can be placed into two categories: behavioral and physiological. Behavioral responses are sometimes vocal, causing a person to talk about the pain or simply moan, whimper or cry. They can also manifest themselves in facial expressions like grimacing, which is characterized by movements like brow lowering, nose wrinkling and eye narrowing [source: Turk and Melzack]. Body language is a key indicator too: Movements like bracing, rocking, rubbing or guarding a specific area are all potential symptoms of pain. Physiological responses, on the other hand, have to do with changes in the normal function of your body and organs. This could mean an increase in heart rate, respiratory rate or blood pressure, in addition to sweating, nausea and pupil dilation.


Often doctors simply take these qualities into consideration when making a diagnosis, but sometimes they will score them using scales. Infant pain, for example, can be estimated using the CRIES tool, which takes into account crying, oxygen saturation, vital signs, facial expressions and sleep patterns. Each of these categories receives a rating between 0 and 2, and if the sum of the ratings is greater than four, the pain likely demands medication.

Other tools are specifically designed for use with elderly people exhibiting dementia. The Abbey Pain Scale, for instance, rates pain based on six categories, each rated between 0 and 3. These include vocalization, facial expression, change in body language, behavioral change, physiological change and physical changes. A score under 2 is considered "no pain," while one above 14 rates "severe pain." Still, these are only estimates, and the pain intensity of a patient who can't self-report is still considered unknown [source: Pasero and McCaffery].


Lots More Information

Author's Note: How the Pain Scale Works

My experience with pain scales stems from a short hospital stay for a collapsed lung. Aside from the tube in my side, there wasn't much to complain about, so my standard answer when asked to rate my pain from "0" to "10" was "2." But I was awake and able to communicate, so when it started to hurt a little more I said so and they gave me some medicine. While writing this article, however, I realized that a lot of hospital patients don't have the ability to speak up when they hurt. Doctors can only guess whether they're in pain and try to medicate accordingly. That's certainly a sobering thought. But thankfully there's a lot of research out there to help doctors estimate pain as best they can — at least until the day a Star Trek-y pain meter takes the mystery out of it.

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More Great Links

  • Abbey, J. et al. "Abbey Pain Scale." JH & JD Gunn Medical Research Foundation. (March 12, 2015)
  • Baker, Connie M. "FACES History." Wong-Baker FACES Foundation. (March 11, 2015)
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  • Bildner, Judy. "CRIES Instrument: Assessment Tool of Pain in Neonates." City of Hope Pain/Palliative Case Resource Center. 1997. (March 13, 2015)
  • Bulloch, Blake et al. "Reliability of the Color Analog Scale: Repeatability of Scores in Traumatic and Nontraumatic Injuries." Society for Academic Emergency Medicine. 2009. (March 12, 2015)
  • Hardy, James D. and Carl T. Javert. "Studies on Pain: Measurements of Pain Intensity in Childbirth." The Journal of Clinical Investigation. Jan. 28, 1949. (March 9, 2015)
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  • Wong-Baker FACES Foundation. "Instructions for Use." (March 12, 2015)