Vital Signs — Normal Ranges and When to Act | Nursing Fundamentals

Before We Start

Why vital signs are called "vital"

The word vital means essential to life. Vital signs measure the most basic physiological functions — the ones that, when they fail, result in death. They are your first and fastest window into how a patient's body is actually functioning.

A single vital sign reading means less than a trend. A blood pressure of 100/60 in a patient whose baseline is 100/60 is fine. The same reading in a patient whose baseline is 160/90 represents a 60-point drop in systolic pressure — that's a potential emergency. Always compare to the patient's baseline.

💡 The Five Vital Signs

BP — Blood Pressure: normal <120/80 mmHg
HR — Heart Rate: normal 60–100 bpm
RR — Respiratory Rate: normal 12–20 breaths/min
Temp — Temperature: normal 36.1–37.2°C (97–99°F)
SpO₂ — Oxygen Saturation: normal 95–100%

Pain is often called the "5th vital sign" — it should be assessed with every set of vitals.

Blood Pressure

BP — what the numbers mean

Understanding the two numbers

Systolic (top number): The pressure in the arteries when the heart contracts and pumps blood out. The force of the beat.

Diastolic (bottom number): The pressure in the arteries when the heart relaxes between beats. The resting pressure.

Pulse pressure: Systolic minus diastolic. Normal = 40 mmHg. Widening pulse pressure (systolic rising, diastolic falling) = sign of increased intracranial pressure (Cushing's Triad).

Normal and Abnormal BP

Know every category — NCLEX uses all of them

Normal: Systolic <120 AND Diastolic <80
Elevated: Systolic 120–129 AND Diastolic <80
Stage 1 Hypertension: Systolic 130–139 OR Diastolic 80–89
Stage 2 Hypertension: Systolic ≥140 OR Diastolic ≥90
Hypertensive Crisis: Systolic >180 AND/OR Diastolic >120 → call provider immediately
Hypotension: Systolic <90 → assess for cause, notify provider

Orthostatic hypotension: Drop of ≥20 mmHg systolic or ≥10 mmHg diastolic when moving from lying to standing. Causes dizziness and falls — major fall risk assessment finding.

💊 BP 188/112 = hypertensive crisis. Do not leave the patient. Notify provider immediately. Keep patient calm and quiet. Dim lights. No exertion.

Heart Rate

HR — rate, rhythm, and quality

Normal: 60–100 bpm

When assessing pulse, document rate, rhythm (regular vs irregular), and quality (strong, weak, thready, bounding).

Tachycardia (>100 bpm): Common causes — pain, fever, anxiety, dehydration, blood loss, infection, hypoxia, medications (albuterol, atropine, caffeine). Tachycardia is often the FIRST vital sign to change in deteriorating patients.

Bradycardia (<60 bpm): Common causes — athletes (normal), beta-blockers, digoxin toxicity, increased intracranial pressure, hypothyroidism, vagal stimulation. Bradycardia with hypotension = hemodynamically significant — call provider.

Irregular rhythm: Always warrants assessment. New irregular rhythm in a patient not known to have A-fib = notify provider, obtain 12-lead EKG.

💊 Tachycardia is almost always a compensatory response — the heart is beating faster because something is wrong. Find the cause: pain? fever? blood loss? hypoxia? Don't just treat the rate.

Respiratory Rate

RR — the most neglected vital sign

Normal: 12–20 breaths/min

Respiratory rate is consistently the most poorly assessed vital sign in clinical practice — often estimated or not counted at all. This is a dangerous shortcut. RR is one of the earliest indicators of patient deterioration.

How to measure accurately: Count for a full 60 seconds. Do not tell the patient you're counting respirations — they will alter their rate unconsciously. Count while pretending to assess the pulse.

Tachypnea (>20 breaths/min): Pain, fever, anxiety, respiratory distress, metabolic acidosis (compensatory), sepsis (early sign), PE.

Bradypnea (<12 breaths/min): Opioid overdose (most common cause in hospitalized patients), CNS depression, severe hypothyroidism. RR <8 = hold opioids and notify provider. RR <6 = respiratory emergency, prepare for possible intubation.

RR as sepsis indicator: RR >22 is one of the qSOFA criteria for sepsis screening. An elevated RR in a febrile patient should trigger sepsis assessment.

💊 RR of 8 after opioid administration = hold further opioids, notify provider, have naloxone available. This is a pre-respiratory arrest warning sign.

Temperature

Temp — fever, hypothermia, and route differences

Normal: 36.1–37.2°C (97–99°F)

Fever: Temperature ≥38°C (100.4°F). Not all fevers need treatment — fever is a physiological response to infection. Treat the underlying cause, not just the number. However, fever increases oxygen demand and metabolic rate — patients with cardiac or pulmonary conditions need fever managed aggressively.

Hyperpyrexia: Temperature ≥41°C (105.8°F) — medical emergency. Risk of seizure, brain damage, death.

Hypothermia: Temperature <36°C (<96.8°F). Causes: cold exposure, post-op, sepsis. Hypothermia impairs coagulation and immune function.

Route differences (add to oral for comparison):
• Oral: baseline measurement
• Rectal: 0.5°C (1°F) HIGHER than oral — most accurate core temp
• Axillary: 0.5°C (1°F) LOWER than oral — least accurate
• Tympanic: approximately equal to oral
• Temporal artery: approximately equal to oral

💊 "Rectal is higher, axillary is lower" — if a patient has a rectal temp of 38.5°C, their true temp is consistent with fever. If axillary is 38.5°C, their actual temp is likely higher.

Oxygen Saturation

SpO₂ — what the number means and its limitations

Normal: 95–100%

SpO₂ measures the percentage of hemoglobin saturated with oxygen. It's measured non-invasively with a pulse oximeter on the finger, earlobe, or forehead.

Interpretation:
• 95–100%: Normal
• 91–94%: Mild hypoxia — monitor closely, consider supplemental oxygen
• 86–90%: Moderate hypoxia — supplemental oxygen required, notify provider
• <85%: Severe hypoxia — emergency

COPD exception: Patients with COPD often have chronically low SpO₂ (88–92%) and may have a hypoxic drive to breathe. Target SpO₂ for COPD patients is typically 88–92%, NOT 95–100%. Giving too much oxygen to a COPD patient can suppress their respiratory drive.

Limitations of pulse oximetry:
• Inaccurate with nail polish (especially dark colors — remove or use a different site)
• Inaccurate with poor perfusion (cold fingers, hypotension, vasoconstriction)
• Cannot detect carbon monoxide poisoning (CO-Hgb reads as oxygenated — SpO₂ appears normal while patient is being poisoned)
• Inaccurate with severe anemia (enough Hgb is saturated, but not enough total Hgb to carry adequate O₂)

💊 Carbon monoxide poisoning = normal-appearing SpO₂ but severe hypoxia. CO poisoning is diagnosed with co-oximetry (arterial blood), not pulse oximetry.

🏥 Clinical Scenario — Vital Sign Changes Over a Shift

Mr. Okafor, 71 years old, admitted for a hip fracture repair yesterday. You take his vitals at the start of your shift and again 4 hours later.

8am

0800 vitals: BP 118/72, HR 76, RR 16, Temp 37.0°C, SpO₂ 97%. Pain 3/10. Baseline: alert, oriented x4. → All within normal limits. Stable.

noon

1200 vitals: BP 96/58, HR 118, RR 24, Temp 38.9°C, SpO₂ 92% on room air. Pain 7/10. Patient confused, pulling at IV. → Multiple abnormal values — this patient is deteriorating.

→

Analysis: BP dropped 22 points systolic (hypotension). HR jumped 42 points (compensatory tachycardia). RR elevated (respiratory compensation for metabolic acidosis? sepsis?). Temp elevated (infection). SpO₂ dropped. New confusion.

This pattern — hypotension + tachycardia + fever + tachypnea + altered mental status — is sepsis until proven otherwise. Activate sepsis protocol immediately. Notify provider. Two large-bore IVs. Blood cultures x2 before antibiotics. Lactate level. IV fluid bolus per order. Continuous monitoring.

📌 NCLEX Application

Vital sign questions appear in almost every NCLEX category. Key facts to have memorized cold:

• Hypertensive crisis: systolic >180 or diastolic >120 → notify provider immediately
• Hypotension: systolic <90 → assess, notify provider
• Bradypnea from opioids: RR <12 → hold opioid, have naloxone ready. RR <8 = emergency
• Fever: ≥38°C (100.4°F)
• SpO₂ <90% = needs intervention NOW
• COPD target SpO₂: 88–92% (not 95–100%)
• Tachycardia is the FIRST vital sign to change in early shock
• RR is the earliest predictor of clinical deterioration (most often missed)

⚠️ The Trap — Treating Vital Signs in Isolation

No single vital sign should be interpreted alone. A heart rate of 110 in a patient who just walked back from physical therapy is expected. A heart rate of 110 in a patient who has been lying in bed all morning requires investigation.

Always interpret vital signs in context: What is the patient's baseline? What medications are they on? What procedure did they just have? What symptoms are they reporting?

The most dangerous nursing habit is charting vital signs without looking at them. Vital signs that don't match the patient's clinical picture — or that show a trend of worsening — require immediate action, not documentation and moving on.

✓ Quick Self-Test

What is the appropriate nursing response to each finding?

1. SpO₂ 87% on room air in a patient with pneumonia
2. BP 186/114 in a patient with no history of hypertension
3. HR 48 in a patient who just received their scheduled metoprolol
4. RR 8 in a patient who received IV morphine 30 minutes ago
5. Temp 38.2°C in a patient 24 hours post-op

Answers:
1. Apply supplemental oxygen, notify provider, reassess in 15 minutes
2. Notify provider immediately — hypertensive crisis threshold
3. Hold further beta-blocker doses, notify provider, monitor for symptoms
4. Hold further opioids, notify provider, have naloxone available at bedside
5. Notify provider, assess for source of infection, obtain cultures if ordered

Next Lesson

Pain Assessment — OLDCART

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