Vital Signs & Clinical Reasoning

Vital signs are often the first abnormal data point in critically ill patients. In Emergency Medicine, trend + context > single value.

Normal vital signs do NOT rule out life-threatening disease.

The core vital signs: think ABCs

• Heart rate (HR): perfusion and compensation.
• Blood pressure (BP): late marker of shock.
• Respiratory rate (RR): earliest marker of deterioration.
• Temperature: infection, inflammation, exposure.
• Pain and skin: physiologic stress, perfusion, shock type.

Tachycardia = compensation until proven otherwise.

Common ED causes: fever (↑ HR approximately 8–10 bpm per 1°F), pain, anxiety, hypovolemia, dehydration, sepsis, PE, and hemorrhage.

Dangerous causes: shock (all types), arrhythmias, toxicologic exposure (cocaine, meth, PCP), and thyrotoxicosis.

Hypotension is a late finding. A “normal” BP may still represent shock.

Adult BP: Normal <120/<80 · Pre-HTN 120–139/80–89 · HTN ≥140/≥90.

The most sensitive vital sign in the ED.

Tachypnea suggests metabolic acidosis (DKA, sepsis), PE, pneumonia, pain, or CNS pathology.

Normal temperature is a range and varies by measurement site (rectal > oral > axillary) and time of day (lowest early morning).

Fever may be benign or life-threatening. Absence of fever does NOT exclude infection.

Shock index

Shock index = HR ÷ SBP. Normal: 0.5–0.7. >0.9 = high risk and predicts the need for aggressive intervention.

Special pattern: neurogenic shock

Hypotension + bradycardia + warm, flushed skin.

ED mindset: consider multiple diagnoses simultaneously; vital signs rapidly shift probabilities.

The seven-step approach

1. History.
2. Focused questions.
3. Broad differentials.
4. Assign pre-test probabilities.
5. Targeted exam.
6. Hypothesis-driven testing.
7. Assessment and plan.

High-yield EM takeaways

• Always trend vital signs.
• HR and RR change before BP.
• Skin findings matter.
• Treat the patient, not the number.