What is the diagnosis for a patient presenting with dizziness, fatigue, tachycardia, hypotension, and hyperthermia, who is diaphoretic and improves with intravenous (IV) fluids?

Heat Exhaustion

This patient has heat exhaustion, not heat stroke, based on the preserved mental status (oriented), presence of diaphoresis, moderate hyperthermia (101°F), and rapid improvement with IV fluids.

Diagnostic Reasoning

The clinical presentation clearly distinguishes between heat exhaustion and heat stroke through several key features:

Why Heat Exhaustion (Answer B):

• Preserved mental status: The patient is oriented, which is the critical distinguishing feature from heat stroke 1, 2, 3
• Temperature below critical threshold: Core temperature of 101°F (approximately 38.3°C) is well below the 104°F (40°C) threshold that defines heat stroke 2, 3, 4
• Diaphoresis present: Active sweating indicates intact thermoregulatory mechanisms, characteristic of heat exhaustion 1, 2, 5
• Rapid response to IV fluids: Heat exhaustion typically responds quickly to fluid resuscitation and cooling measures, as demonstrated in this case 6, 2
• Cardiovascular hypoperfusion: The tachycardia (HR 100/min) and hypotension (BP 90/60 mmHg) reflect volume depletion and cardiovascular strain typical of heat exhaustion 3, 4

Why NOT Heat Stroke (Answer A):

• Heat stroke requires: Core temperature ≥104-105°F (40-40.6°C) AND central nervous system dysfunction (altered mental status, confusion, seizures, coma) 2, 3, 4
• This patient lacks CNS dysfunction: Being oriented excludes heat stroke by definition 1, 3, 5
• Sweating may persist in exertional heat stroke: While 50% of exertional heat stroke cases have persistent sweating, the combination of preserved orientation and lower temperature rules this out 5

Why NOT Heat Syncope (Answer C):

• Heat syncope presents with: Brief loss of consciousness or near-syncope upon standing in hot environments due to peripheral vasodilation 6
• This patient has: Sustained symptoms of dizziness and fatigue during exercise, not a syncopal episode 6

Why NOT Heat Cramps (Answer D):

• Heat cramps are: Brief, intermittent, severe muscular cramps in fatigued muscles without systemic symptoms 2, 3, 5
• This patient has: Systemic manifestations including hypotension, tachycardia, and hyperthermia beyond isolated muscle cramping 3, 4

Clinical Pearls and Pitfalls

Critical distinction: The presence or absence of CNS dysfunction is the single most important factor differentiating heat exhaustion from heat stroke 3, 4. Heat exhaustion may present with minor mental status changes (poor judgment, irritability) but NOT disorientation or altered consciousness 5.

Temperature considerations: While heat stroke typically presents with temperatures ≥105°F, cellular damage begins at 104°F (40°C), so any patient with temperature approaching this threshold requires aggressive monitoring 4, 5.

Sweating is unreliable: The absence of sweating does NOT confirm heat stroke, and its presence does NOT exclude it—50% of exertional heat stroke cases maintain sweating 5. Always prioritize mental status assessment over sweating status.

Progression risk: Heat exhaustion can rapidly progress to heat stroke if left untreated, making early recognition and aggressive treatment essential 1, 2, 4.