Understanding Vital Signs: Purpose, Normal Ranges, and Patient Safety

What Are Vital Signs and Why Do They Matter?

Vital signs are a set of measurements that reflect the body's most basic life-sustaining functions. They give the nurse and the care team a quick, objective picture of how a patient's body is working at a given moment. Because vital signs can change rapidly, measuring them accurately and reporting abnormal findings promptly are among the most important tasks a Certified Nursing Assistant (CNA) performs every shift.

CNAs measure and record vital signs under the supervision of a licensed nurse. You do not interpret results, diagnose conditions, or change a care plan based on what you find. Your legal role is to measure accurately, document correctly, and report any value outside the normal range to the nurse immediately. Acting outside that boundary—for example, deciding on your own that a reading is "probably fine" and not reporting it—puts the patient in danger and places you outside your legal scope of practice.

The Five Vital Signs

Standard practice recognizes five vital signs measured by CNAs:

1. Temperature (T)

2. Pulse (P)

3. Respirations (R)

4. Blood Pressure (BP)

5. Oxygen Saturation (SpO₂)

Pain is sometimes called the "sixth vital sign" and is routinely assessed alongside the others, but the five listed above are the core measurements you will take and record.

Normal Adult Reference Ranges

The following ranges are widely accepted reference values for a healthy resting adult. Individual patients may have baseline readings that differ slightly; always compare today's reading to the patient's own baseline as well as to the standard range.

| Vital Sign | Unit | Normal Adult Range |

|---|---|---|

| Temperature | °F (or °C) | 97.8 °F – 99.1 °F (36.5 °C – 37.3 °C) |

| Pulse | beats per minute (bpm) | 60 – 100 bpm |

| Respirations | breaths per minute (breaths/min) | 12 – 20 breaths/min |

| Blood Pressure | mmHg (systolic/diastolic) | Less than 120/80 mmHg (systolic < 120, diastolic < 80) |

| Oxygen Saturation | percent (%) | 95% – 100% |

Source: Mosby's Textbook for Nursing Assistants, current edition.

Temperature

Body temperature is measured orally, rectally, in the axilla (armpit), or at the tympanic membrane (ear) or temporal artery (forehead), depending on the patient's condition and facility policy. Rectal temperatures run approximately 1 °F higher than oral; axillary temperatures run approximately 1 °F lower. Always document the route used (e.g., "99.0 °F oral").

Report immediately: temperature above 101 °F (38.3 °C) or below 96 °F (35.6 °C), or any reading your facility flags as critical.

Pulse

The pulse reflects the heart rate and rhythm. You count the beats felt at an artery—most commonly the radial artery at the wrist—for 30 seconds and multiply by 2, or count for a full 60 seconds if the rhythm feels irregular. Also note whether the pulse feels strong or weak, regular or irregular, and report those qualities to the nurse.

Report immediately: pulse below 60 bpm (bradycardia) or above 100 bpm (tachycardia), irregular rhythm, or a pulse that is very weak or bounding.

Respirations

Count the number of times the chest rises and falls in one minute. Because patients often change their breathing if they know it is being counted, observe respirations right after counting the pulse, while keeping your fingers on the wrist.

Report immediately: respirations below 12 (bradypnea) or above 20 (tachypnea), labored breathing, noisy breathing, or the patient using accessory muscles to breathe.

Blood Pressure

Blood pressure measures the force of blood against artery walls. The top number (systolic) is pressure during heart contraction; the bottom number (diastolic) is pressure when the heart relaxes. Use the correct cuff size—a cuff that is too small gives a falsely high reading; one that is too large gives a falsely low reading.

Report immediately: systolic at or above 140 mmHg or at or below 90 mmHg; diastolic at or above 90 mmHg; or any reading your facility designates as critical. Also report a significant drop from the patient's own baseline.

Oxygen Saturation

A pulse oximeter clips to the finger (or earlobe or toe) and uses light to estimate how much of the hemoglobin in the blood is carrying oxygen. The reading can be affected by cold hands, nail polish, poor circulation, or patient movement. If the waveform looks weak or the number seems inconsistent with how the patient looks and feels, reposition the probe or try a different finger and notify the nurse.

Report immediately: SpO₂ below 95%, or any reading below the patient's established baseline, especially if accompanied by shortness of breath, confusion, or color changes.

Scope of Practice: What the CNA Does and Does Not Do

| CNA Does | CNA Does NOT |

|---|---|

| Measure and record all five vital signs | Interpret results or make a diagnosis |

| Report abnormal findings to the nurse promptly and clearly | Decide whether an abnormal result is significant |

| Document accurately in the medical record per facility policy | Alter or delay documentation |

| Repeat a measurement if uncertain about accuracy | Change the care plan or withhold information from the nurse |

When you report, be specific. Say: "Mr. Rivera's blood pressure is 158 over 96, which is higher than his usual reading of 130 over 80. He also says he has a headache." Give the number, compare it to baseline if you know it, and include any symptoms the patient reports.

Safety First

• Never skip reporting an abnormal value because the patient appears comfortable. Serious conditions such as internal bleeding or early sepsis can produce dramatic vital-sign changes before visible symptoms appear.
• Document before you leave the room or move to the next patient. Delayed documentation increases the risk of error.
• If in doubt, report. Your scope of practice requires you to keep the nurse informed. It is never wrong to report a finding; it can be very wrong not to.