Vital Signs Explained: Normal Ranges, Red Flags and What the Numbers Mean

Lachlan Baillie, Registered Paramedic

1 day ago

8 min read

Vital signs are the first numbers you learn as a student and some of the most powerful tools you will ever use. Respiratory rate, oxygen saturation, heart rate, blood pressure, temperature, level of consciousness and blood glucose can tell you whether a patient is stable, getting sicker or about to arrest, often before they look unwell. The trick is not just knowing the normal ranges. It is knowing what each number really measures, when it lies to you, and how the numbers fit together into a pattern. This guide covers all of that, with Australian units and ranges throughout.

The trend matters more than the number

A single set of observations is a snapshot. A patient with a heart rate of 98 might be perfectly well, or they might have been 72 an hour ago and be quietly bleeding. The direction a vital sign is moving is often more important than whether it sits inside a normal range.

Always compare with the patient's own baseline where you can. A systolic blood pressure of 110 mmHg is normal for many people, but in someone whose usual pressure is 170 mmHg, it may represent significant shock. Document every set clearly, with the time, so the next clinician can see the trend.

One normal set of observations does not make a patient well. Two worsening sets make them sick.

Respiratory rate

Respiratory rate has been called the neglected vital sign. It is the observation most often skipped or estimated, yet it is one of the best early predictors of serious deterioration. Research from Australian hospitals has shown that a respiratory rate above 24 breaths per minute is associated with serious adverse events, and that patients who later arrested often had a raised rate for hours beforehand.

How to measure it properly

Count for a full 30 seconds and double it, or count for a full minute if the breathing is irregular.
Try not to let the patient know you are counting, because people change their breathing when they know they are being watched. Many clinicians count while appearing to take the pulse.
Never estimate. A guessed "18" is one of the most common documentation errors in healthcare.

What the numbers mean

Normal adult range: about 12 to 20 breaths per minute.
Above 20: the patient is probably unwell. Look for a cause.
Above 24: suggests significant illness and warrants close monitoring and review.
Below 10: think about opioid toxicity, a head injury, exhaustion or impending respiratory arrest.

A rising respiratory rate is often the body's first response to almost anything: hypoxia, acidosis from sepsis or diabetic ketoacidosis, pain, anxiety, fever or shock. That is exactly why it is so useful.

Oxygen saturation

Pulse oximetry estimates the percentage of haemoglobin carrying oxygen. Healthy adults at sea level usually sit at 95 percent or above.

The Thoracic Society of Australia and New Zealand guideline recommends a target range of 92 to 96 percent for most acutely unwell adults who need oxygen, and 88 to 92 percent for patients at risk of hypercapnic respiratory failure, such as those with COPD, obesity hypoventilation syndrome, neuromuscular disease or severe chest wall deformity. Oxygen is treated as a drug, given to correct low oxygen levels rather than to treat breathlessness on its own.

When the oximeter can mislead you

Poor perfusion: cold hands, shock or vasoconstriction can give a poor trace or a falsely low reading.
Carbon monoxide poisoning: the oximeter can read carboxyhaemoglobin as oxygenated haemoglobin, giving a falsely normal saturation.
Movement and nail polish can interfere with the reading.
Skin pigmentation: studies have found pulse oximeters can overestimate saturation in people with darker skin, so a borderline reading deserves extra caution.

Most importantly, a normal saturation does not mean normal breathing. A patient breathing 36 times a minute can keep their saturation at 97 percent right up until they tire. Always pair the saturation with the respiratory rate and the work of breathing.

Heart rate

Feel the pulse as well as reading the monitor. You are assessing three things: the rate, the rhythm and the strength.

Normal adult range: about 60 to 100 beats per minute.
Tachycardia above 100: causes include pain, anxiety, fever, dehydration, blood loss, sepsis, hypoxia, arrhythmias and stimulant use.
Bradycardia below 60: can be normal in fit people and during sleep, but may also be caused by medications, heart block, hypothermia, hypoxia in children, or raised intracranial pressure.

Tachycardia is one of the earliest compensatory signs of shock, so an unexplained rising heart rate should always make you look harder. Remember that beta blockers and some calcium channel blockers can blunt this response, so an older patient on these medications may be in shock with a normal heart rate.

A weak, thready pulse suggests poor cardiac output. A bounding pulse may be seen in early sepsis or fever. An irregular pulse should prompt an ECG.

Blood pressure

Blood pressure tells you about the pressure driving blood to the organs, but it is a late sign of trouble in many patients.

A typical healthy adult systolic pressure sits roughly between 100 and 140 mmHg.
Hypotension is often described as a systolic pressure below 90 mmHg, or a significant drop from the patient's usual pressure.
Pulse pressure is the difference between the systolic and diastolic values. A narrowing pulse pressure can be an early sign of blood loss, while a widening pulse pressure is seen in sepsis and raised intracranial pressure.

Young adults and children compensate extremely well. They can maintain a near normal blood pressure while losing a large amount of blood by increasing their heart rate and constricting their blood vessels. When their blood pressure finally falls, they are often close to collapse. Do not let a normal blood pressure reassure you when every other sign says shock.

Older adults are different again. Many have high baseline pressures, stiffer vessels and medications that limit compensation, so a "normal" reading may be low for them.

Temperature

Normal adult range: roughly 36.0 to 37.5 degrees Celsius, with some variation between people and measurement sites.
Fever, often defined as 38.0 degrees or higher, suggests infection or inflammation.
Hypothermia, below 35.0 degrees, worsens bleeding and slows drug metabolism, and can occur in older adults even indoors.

A low temperature can be a sign of severe sepsis, particularly in older and frail patients, so do not rule out infection just because the patient has no fever.

Level of consciousness

Consciousness reflects how well the brain is being perfused and oxygenated, and whether something is directly affecting it.

AVPU (Alert, Voice, Pain, Unresponsive) is a quick screen.
ACVPU adds new Confusion, because new confusion is an important early sign of deterioration, particularly in sepsis and hypoxia.
The Glasgow Coma Scale gives a more detailed score from 3 to 15 and is the standard for tracking changes over time.

Any new confusion or drop in GCS needs an explanation. Always check a blood glucose level.

Blood glucose

In Australia, blood glucose is measured in mmol/L. A typical non fasting level in a person without diabetes sits roughly between 4 and 8 mmol/L. Hypoglycaemia is generally defined as a level below 4.0 mmol/L, which is easy to remember with the phrase "four is the floor".

Hypoglycaemia can look like a stroke, intoxication, a seizure or a psychiatric emergency. High readings may point to diabetic ketoacidosis or a hyperosmolar state, especially with dehydration and a raised respiratory rate.

Children are not small adults

Normal values change significantly with age. Babies breathe faster and have faster heart rates, and their blood pressure is lower. The Royal Children's Hospital Melbourne publishes acceptable ranges, which are approximately:

Newborn: respiratory rate 25 to 60, heart rate 120 to 170, systolic pressure 60 to 95.
1 year: respiratory rate 20 to 45, heart rate 105 to 150, systolic pressure 70 to 105.
4 years: respiratory rate 17 to 30, heart rate 80 to 150, systolic pressure 75 to 110.
8 years: respiratory rate 16 to 30, heart rate 70 to 130, systolic pressure 80 to 115.
12 years: respiratory rate 15 to 25, heart rate 65 to 120, systolic pressure 90 to 120.

Children compensate for shock very effectively and then decompensate quickly. Hypotension in a child is a late and ominous sign, and bradycardia in an unwell child is often caused by hypoxia.

Early warning scores

Hospitals use structured tools to turn vital signs into a single risk score that triggers a response. In the United Kingdom, the National Early Warning Score 2 combines respiratory rate, oxygen saturation, supplemental oxygen, systolic blood pressure, pulse, consciousness and temperature. A total of 5 or more, or a score of 3 in any single parameter, prompts urgent review.

In Australia, many hospitals use observation charts based on the Adult Deterioration Detection System developed with the Australian Commission on Safety and Quality in Health Care, often with colour coded zones that tell staff when to escalate. As a student on placement, learn the chart your ward uses and the escalation steps that go with it.

Putting it all together

The real skill is reading vital signs as a pattern rather than as separate numbers:

Shock from blood loss: rising heart rate and respiratory rate, pale cool skin, narrowing pulse pressure, then a falling blood pressure and consciousness.
Sepsis: raised respiratory rate, tachycardia, fever or low temperature, new confusion, and low blood pressure as it progresses.
Raised intracranial pressure: a falling GCS with rising blood pressure, a slowing heart rate and irregular breathing, known as Cushing's triad, which is a very late sign.
Respiratory failure: rising respiratory rate and work of breathing, falling saturation, then exhaustion with a slowing rate and drowsiness.
Opioid toxicity: slow, shallow breathing, pinpoint pupils and a reduced level of consciousness.

Common student mistakes

Estimating the respiratory rate instead of counting it.
Being reassured by a normal blood pressure in a young or paediatric patient.
Treating the saturation number without looking at the patient's breathing.
Forgetting a blood glucose level in a confused patient.
Recording a set of observations without comparing it with the last set.
Not escalating because "it is only one number".

Conclusion

Vital signs are simple to measure and easy to get wrong. Count the respiratory rate properly, treat saturation as one piece of the puzzle, remember that blood pressure falls late, and always look for the trend and the pattern. If you build these habits now, you will recognise the deteriorating patient long before they become obvious to everyone else in the room.

References

Cretikos MA, Bellomo R, Hillman K, Chen J, Finfer S, Flabouris A. Respiratory rate: the neglected vital sign. Med J Aust. 2008;188(11):657. https://www.mja.com.au/journal/2008/188/11/respiratory-rate-neglected-vital-sign

Beasley R, Chien J, Douglas J, et al. Thoracic Society of Australia and New Zealand oxygen guidelines for acute oxygen use in adults: "Swimming between the flags". Respirology. 2015;20(8):1182. https://doi.org/10.1111/resp.12620

Royal College of Physicians. National Early Warning Score (NEWS) 2: Standardising the assessment of acute illness severity in the NHS. London: RCP; 2017.

The Royal Children's Hospital Melbourne. Clinical Practice Guidelines: Acceptable ranges for physiological variables. https://www.rch.org.au/clinicalguide/guideline_index/Acceptable_ranges_for_physiological_variables/

Australian Commission on Safety and Quality in Health Care. Adult Deterioration Detection System (ADDS) chart resources. https://www.safetyandquality.gov.au

Sjoding MW, Dickson RP, Iwashyna TJ, Gay SE, Valley TS. Racial bias in pulse oximetry measurement. N Engl J Med. 2020;383(25):2477.

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