Collapse at the Finish Line With a Normal-ish Rectal Temperature

Working diagnosis: exercise-associated hyponatremia (EAH), with exertional heat stroke still requiring active exclusion.

The reasoning is a convergence of four findings that point the same direction:

1. Rectal temperature 38.6 C. Rectal temperature is the gold standard, and EHS is defined by hyperthermia - typically above roughly 40–40.5 C - plus CNS dysfunction. A rectal temperature this low substantially reduces, though does not eliminate, the probability of EHS.
2. Weight gain of about 1 kg. This is the strongest single clue. Athletes do not gain weight during a race unless intake exceeded losses. Combined with 6 L of fluid, this is a dilutional picture.
3. Cool, clammy skin and muscle twitching. Consistent with hyponatremic encephalopathy; EHS more often presents with hot skin, though cutaneous vasoconstriction can occur in severe cases.
4. Mild ambient temperature and high humidity. A cool-weather collapse with fluid overload argues against classic heat stroke and toward a dilutional cause.

The confounder is that confusion and combativeness are common to both, so mental status cannot discriminate. The temperature and the weight data do.

Evidence that would flip the diagnosis back to EHS: rectal temperature at or above 40 C on repeat measurement, absence of fluid overload or weight loss rather than gain, or persistent encephalopathy despite fluid restriction and correction.

Immediate management:

• Remove him from further oral intake and restrict fluids. Do not let well-meaning bystanders hand him bottles.
• Move him to a controlled area with supervision; a combative, confused athlete needs continuous observation and should not be left alone.
• Check point-of-care glucose and, if available, point-of-care sodium. Treat hypoglycemia if present.
• Monitor mental status, vital signs, and airway continuously; have suction and airway equipment ready.
• Activate EMS transport - symptomatic hyponatremic encephalopathy is a hospital-level problem regardless of how quickly he seems to settle.
• If severe symptoms are present or develop - seizure, decreasing consciousness, respiratory distress - give hypertonic saline (3%) as a small bolus (about 100 mL) per protocol and transport urgently. This is the specific treatment; isotonic saline is not.

What the medic should not do:

• Do not run normal saline wide open. Large-volume isotonic fluid in a dilutionally hyponatremic athlete worsens the sodium and can precipitate cerebral edema.
• Do not use a fluid bolus as a reflex before the sodium question is addressed.
• Do not assume heat stroke and immerse him on the basis of confusion alone; with a rectal temperature of 38.6 C, immersion adds hypothermia risk and treats nothing.
• Do not discharge him to family because he 'calms down' - improvement can be transient and delayed deterioration is described.

Switch to the EHS pathway if any of the following is present:

• Rectal temperature at or above 40 C on a properly placed, repeated measurement (recheck rather than relying on a single low reading, especially if the probe was shallow).
• Hot skin with absent or minimal sweating rather than cool and clammy.
• Weight loss rather than gain, or a history of modest fluid intake.
• No improvement in mental status after fluid restriction and a short period of observation, or deterioration (seizure, coma, respiratory compromise) - which may indicate either severe hyponatremia or unrecognized heat stroke.
• Evidence of end-organ involvement: dark urine, profound weakness, markedly elevated creatine kinase, or abnormal liver enzymes later.

How management changes:

• Cold-water immersion becomes the priority and should begin immediately; target cooling to approximately 38.5 C and stop there to avoid overshoot.
• IV fluids are appropriate - cool isotonic fluids support the circulation and do not carry the same hazard they do in hyponatremia.
• Transport remains mandatory, with labs (electrolytes, CK, renal and hepatic function, coagulation) to assess rhabdomyolysis and organ injury.

Where the two conditions cannot be separated at the point of care, err toward cooling - cold-water immersion is not dangerous for a hyponatremic athlete with a core temperature that is genuinely elevated, whereas withholding cooling from an unrecognized heat stroke is potentially fatal.