What IV fluid is recommended for an individual experiencing weakness, dizziness, and fatigue after running a marathon?

IV Fluid Management for Post-Marathon Symptoms

Do not administer IV fluids routinely to this patient without first determining their sodium status, as exercise-associated hyponatremia (EAH) is a life-threatening condition that can be worsened by IV fluid administration and must be ruled out before giving any intravenous fluids. 1

Critical First Step: Rule Out Exercise-Associated Hyponatremia

• EAH occurs in 3-22% of marathon runners and is defined as serum sodium <135 mmol/L during or up to 24 hours after prolonged physical activity. 1
• The primary risk factors present in this scenario include: race time >4 hours (this patient has had symptoms for 4 hours post-race), and the classic presentation of weakness, dizziness, and fatigue. 1
• EAH is a dilutional hyponatremia caused by excessive fluid consumption relative to total body fluid losses, not primarily from sodium loss. 1
• Administering standard IV fluids to a patient with undiagnosed EAH can precipitate acute cerebral edema, seizures, coma, and death. 1

Diagnostic Approach

Point-of-care sodium testing must be performed immediately if available, or the patient should be transferred to a facility with fluid restriction en route. 1

If Sodium Testing Shows EAH (Na+ <135 mmol/L):

• For mild symptoms without confusion: provide oral hypertonic solutions and monitor closely - 16 runners with EAH recovered within 30 minutes using this approach. 1
• For severe symptoms (confusion, seizures, altered mental status): administer up to three 100 mL boluses of 3% sodium chloride solution spaced at 10-minute intervals. 1
• Absolutely restrict all hypotonic and isotonic IV fluids in confirmed EAH. 1

If Sodium Testing Shows Normal or Elevated Sodium (True Dehydration):

Administer balanced crystalloids (lactated Ringer's solution or Plasma-Lyte) as first-line IV fluid therapy rather than 0.9% saline. 1

Rationale for Balanced Crystalloids:

• Balanced crystalloids have electrolyte composition closer to plasma (sodium 130-145 mmol/L, chloride 98-127 mmol/L) compared to 0.9% saline (sodium 154 mmol/L, chloride 154 mmol/L). 1
• Large randomized trials involving over 15,000 critically ill patients demonstrated that balanced crystalloids reduce major adverse kidney events compared to saline (14.3% vs 15.4%, P=0.04). 2
• Balanced crystalloids prevent hyperchloremic metabolic acidosis that occurs with large-volume saline administration. 3, 4
• The potassium content in balanced solutions (4-5 mmol/L) does not cause clinically significant hyperkalemia even in high-risk patients. 1

Common Pitfalls to Avoid

• Never assume all post-marathon symptoms represent simple dehydration - EAH can present identically and requires opposite treatment. 1
• Do not rely on weight loss to exclude EAH - the condition has been documented even in athletes who lost weight during the event. 1
• Avoid Ringer's lactate specifically if the patient has any head trauma (osmolarity 273-277 mOsm/L makes it hypotonic and can worsen cerebral edema). 1, 5
• Female sex and low BMI are additional risk factors for EAH that should heighten suspicion. 1

Practical Algorithm

1. Assess mental status immediately - confusion, seizures, or altered consciousness indicate potential severe EAH requiring emergent hypertonic saline. 1
2. Obtain point-of-care sodium level - this single test determines whether IV fluids will help or harm. 1
3. If Na+ <135 mmol/L: Give 3% hypertonic saline (100 mL boluses) for severe symptoms or oral hypertonic solution for mild symptoms; restrict all other IV fluids. 1
4. If Na+ ≥135 mmol/L: Administer balanced crystalloids (lactated Ringer's or Plasma-Lyte) for volume resuscitation. 1, 2
5. If sodium testing unavailable: Restrict IV fluids during transport and obtain testing at receiving facility. 1