Vital signs

Vital signs are a set of measurements that show how well the body's most basic functions are working. They are objective, meaning they are measured rather than assumed, and there are five: temperature, pulse, respiratory rate, blood pressure, and oxygen saturation.

Each one looks at something different. Body temperature is maintained by the hypothalamus, an area of the brain that works like a home thermostat and keeps it within a narrow range. Blood pressure speaks to circulation: it reflects what is called hemodynamic status, a bit like checking the water pressure in a home's pipes to see how the water is flowing. And pulse oximetry is not a direct measurement; it estimates how much oxygen the blood in the arteries is carrying, which is called arterial oxygen saturation.

But none of these measurements is read on its own. One reading is a snapshot; the trend over time is the movie. The way the numbers change often tells you more than a single reading, and those changes frequently appear several hours before cardiopulmonary deterioration becomes noticeable, that is, before it becomes apparent that the heart and lungs are getting worse.