Part of the ICU Emergencies Hub — browse every related guide in one place.
| Vital Sign | Normal Adult Range | Definition of Abnormal |
|---|---|---|
| Temperature (oral) | 36.1–37.2°C (97–99°F) | Fever: >38.0°C (100.4°F). Hyperthermia: >40°C (104°F). Hypothermia: <35°C (95°F) |
| Heart rate (HR) | 60–100 bpm at rest | Tachycardia: >100 bpm. Bradycardia: <60 bpm. Clinical significance depends on symptoms and baseline |
| Blood pressure (BP) | Systolic 90–120 mmHg; Diastolic 60–80 mmHg; MAP 70–100 mmHg | Hypertension: SBP ≥130 or DBP ≥80 (AHA 2017 guidelines). Hypotension: SBP <90 or MAP <65. Hypertensive crisis: SBP >180 and/or DBP >120 |
| Respiratory rate (RR) | 12–20 breaths/minute at rest | Tachypnea: >20 breaths/min. Bradypnea: <12 breaths/min. RR is the most sensitive early indicator of physiological deterioration |
| Oxygen saturation (SpO2) | 95–100% on room air | Mild hypoxemia: 90–94%. Significant hypoxemia: <90%. Critical: <85%. Note: COPD patients may have lower baseline SpO2 (88–92%) |
| Pain (5th vital sign) | 0 (no pain) — patient-defined acceptable level | Patient-reported; no universal threshold. Assess with NRS 0–10 or appropriate tool for patient population |
| Route | Normal Range | Add/Subtract to Get Oral Equivalent | Notes |
|---|---|---|---|
| Oral | 36.1–37.2°C | Reference standard | Affected by recent eating, drinking, or smoking — wait 15–30 minutes after |
| Rectal | 36.6–37.6°C | Subtract 0.5°C to get oral equivalent (rectal is ~0.5°C higher) | Most accurate; not used routinely; appropriate for patients who cannot maintain oral measurement |
| Axillary | 35.5–36.5°C | Add 0.5°C to get oral equivalent (axillary is ~0.5°C lower) | Least accurate; used in neonates and when other routes unavailable |
| Tympanic | 36.1–37.2°C | Generally equivalent to oral when properly positioned | Requires proper probe placement; cerumen impaction affects accuracy |
| Temporal (forehead) | 36.1–37.2°C | Generally equivalent to oral | Non-invasive; may be affected by diaphoresis; useful for screening |
Low-grade fever (38.0–38.5°C / 100.4–101.3°F) in a post-operative patient in the first 24–48 hours is common and typically represents the normal inflammatory response — not infection. The classic mnemonic for post-operative fever by day: Wind (day 1–2, atelectasis — most common cause), Water (day 3–5, UTI), Wound (day 5–7, surgical site infection), Walking (day 5+, DVT/PE), Wonder drugs (any time, drug fever).
High fever (above 39.4°C / 103°F) or fever accompanied by rigors, hypotension, tachycardia, or altered mental status requires urgent assessment and provider notification — this is the sepsis presentation pattern. Hyperthermia above 40°C (104°F) is life-threatening: risk of seizure, rhabdomyolysis, and end-organ damage.
Tachycardia (>100 bpm): Always find the cause — tachycardia is a response, not a primary diagnosis in most cases. Common causes: pain, anxiety, fever (every 1°C temperature increase → ~10 bpm HR increase), hypovolemia (early compensatory response to volume loss), anemia, hypoxia, sepsis, hyperthyroidism, stimulant medications (albuterol, decongestants), caffeine, alcohol withdrawal, arrhythmia (atrial fibrillation, SVT).
Bradycardia (<60 bpm): In a symptomatic patient (dizziness, syncope, hypotension, altered mental status, chest pain) — notify provider immediately. In an asymptomatic athletic patient — often normal. Causes: sinus bradycardia (vagal tone, trained athletes, sleep), heart block, beta-blockers, digoxin, calcium channel blockers, hypothyroidism, hypothermia, increased intracranial pressure (Cushing's response: bradycardia + hypertension + irregular respirations = impending herniation).
Patient seated, arm at heart level, back supported, legs uncrossed, no talking for 5 minutes before measurement. Cuff bladder should encircle at least 80% of the arm circumference — too small a cuff reads high; too large reads low. Confirm initial readings with a second measurement 1–2 minutes apart; use the average. For new patients, measure both arms — persistent difference greater than 15 mmHg between arms may indicate subclavian stenosis or aortic dissection.
Pulse pressure = Systolic − Diastolic. Normal: 40 mmHg. Wide pulse pressure (>60) suggests aortic regurgitation, severe anemia, fever, or sepsis (hyperdynamic circulation). Narrow pulse pressure (<25 mmHg) suggests decreased stroke volume — cardiogenic shock, cardiac tamponade, hypovolemic shock.
MAP (Mean Arterial Pressure) = DBP + 1/3 (SBP − DBP). Normal: 70–100 mmHg. MAP ≥65 mmHg is the widely used hemodynamic target in sepsis management — the minimum required to perfuse the kidneys, brain, and gut. MAP below 60 for more than a few minutes risks ischemia to vital organs.
Research on rapid response team activations consistently shows that elevated respiratory rate precedes clinical deterioration by hours — often before any other vital sign changes. A patient with a respiratory rate of 24–26 at rest who is not receiving supplemental oxygen for a known condition should be assessed immediately and escalated if the RR cannot be explained by a benign cause (anxiety, pain, recent exertion).
Common errors in respiratory rate measurement: counting for only 15 seconds and multiplying (inaccurate); documenting "18" as a default when not actually counted; telling the patient you are counting their respirations (patients unconsciously alter their breathing rate when aware). Count over a full 60 seconds, ideally without the patient's awareness — continue holding the wrist after "checking the pulse" and count respirations.
Pulse oximetry measures the percentage of hemoglobin saturated with oxygen. Limitations nurses must know: Carbon monoxide poisoning — carboxyhemoglobin reads as oxyhemoglobin; SpO2 may be normal or high despite severe poisoning. Peripheral vasoconstriction — cold extremities, hypoperfusion, nail polish, or dark skin pigmentation can reduce accuracy. Anemia — SpO2 may be normal even if oxygen delivery to tissues is severely compromised (the hemoglobin present is fully saturated, but there is not enough of it). Methemoglobinemia — SpO2 reads approximately 85% regardless of true saturation.
When SpO2 readings seem inconsistent with the patient's clinical presentation, correlate with clinical appearance and obtain ABG (arterial blood gas) for authoritative PaO2 measurement.
Related guides: Respiratory assessment | Shock recognition | Prioritization | Acid-base balance
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