4 Vital Signs: Measurement and Interpretation

Interpreting vital signs in context

Vital signs are a snapshot of physiologic status, not a diagnosis on their own. Interpret them alongside the patient’s symptoms, appearance, history, baseline, and trends. Reference ranges vary with age, health, activity, measurement method, and clinical context; a value outside a reference range does not by itself establish a diagnosis.

For a resting adult, common reference ranges are temperature $36.5\text{–}37.3\,^{\circ}\text{C}$ ($97.7\text{–}99.1\,^{\circ}\text{F}$), pulse $60\text{–}100$ beats per minute, respirations $12\text{–}18$ breaths per minute, and blood pressure roughly $\frac{90}{60}$ to $\frac{120}{80}\,\text{mm Hg}$. These are reference ranges, not stand-alone thresholds for diagnosing a condition.

Preparing for measurement

Before measuring, explain the procedure and ensure privacy and comfort. Use clean, functioning equipment that fits the patient, and let the patient rest beforehand when possible.

Note factors that may affect results, including recent activity, pain, anxiety, and medications. Compare each result with prior readings and the patient’s usual baseline.

Measuring temperature

Use an appropriate, functioning thermometer and a route suited to the patient and setting, such as oral, tympanic, axillary, or rectal. Follow the device instructions and infection-control procedures. Record the value, units, and route because routes can yield different readings; do not silently convert a reading from one route to another.

When assessing an unexpected oral reading, consider recent hot or cold drinks, smoking, oxygen use, and the patient’s symptoms.

Assessing the pulse

Palpate a peripheral pulse, commonly at the radial site, using the pads of the index and middle fingers rather than the thumb. Assess rate, rhythm, and strength. Count for $30$ seconds and double the result only if the rhythm is regular; count for a full $60$ seconds if the rhythm is irregular or the reading is unexpected.

If the pulse is difficult to feel or the rhythm is abnormal, confirm it with an appropriate method, such as an apical pulse, and report the finding as indicated.

Counting respirations

Observe chest or abdominal movement without drawing attention to breathing, because a person may consciously change their breathing pattern. One rise and fall counts as one breath. Count for $30$ seconds and double the result only when breathing is regular; count for a full minute if it is irregular or concerning.

Assess depth, rhythm, effort, and signs of distress as well as rate. Respiratory rate alone does not describe respiratory status.

Measuring blood pressure

Use a validated device and a cuff sized for the patient’s arm. For a routine seated measurement, have the patient rest quietly for about $5$ minutes, with the back supported, feet flat, legs uncrossed, and bare upper arm supported at heart level. Position the cuff as directed by the device, do not measure over clothing, and ask the patient not to talk during the measurement.

If a result is unexpected, check cuff size and position, posture, and recent activity. Correct any problems and repeat the measurement. For routine repeat readings, take $2$ measurements about $1$ minute apart and record them.

Checking oxygen saturation

Apply the pulse-oximeter sensor as instructed and wait for a stable reading. Check that the hand is still and adequately warm, and consider factors that may interfere with the signal, such as poor circulation, motion, or nail polish.

SpO₂ is an estimate, not a direct blood-gas measurement. Its accuracy can be affected by several factors, including skin pigmentation. Interpret the reading alongside breathing effort, symptoms, baseline, and any prescribed oxygen target. If the reading conflicts with the patient’s condition or seems implausible, reposition the sensor, allow the signal to stabilize, and repeat the measurement. Escalate persistent concern rather than relying on the number alone.

Responding to unexpected readings

A surprising value may reflect measurement technique, equipment, movement, poor positioning, an unsuitable cuff or sensor, or a genuine change in the patient. Do not dismiss an abnormal result as an artifact without checking it.

Reassess the patient first. If the patient appears seriously unwell, seek urgent help while verifying measurements as appropriate. Otherwise, correct likely technique or equipment problems, repeat the measurement, and compare it with other vital signs and the patient’s baseline. Follow local escalation criteria for concerning values or symptoms.

For example, if blood pressure seems unexpectedly high while the patient is talking with legs crossed, correct the position and repeat the measurement. If the repeat remains high, document both readings and the patient’s condition, then act according to clinical protocol.

Documenting and following up

Record the value, units, method or site, relevant conditions, repeat result, and any action taken. Continue reassessment at a frequency appropriate to the patient’s condition and response to care.

Use appropriate equipment and consistent technique, interpret readings in context, compare them with the patient’s baseline and trends, and repeat unexpected results after correcting possible sources of error. A concerning patient—not just a concerning number—requires timely reassessment and action.

• oxygen saturation (SpO₂)

• pulse oximeter