For decades, Normal Saline (0.9% NaCl) has been the go-to fluid in trauma and head injury, it’s familiar, cheap, and easy to store. But there’s a problem, it’s not normal. And in patients with potential head injuries, it may actually make things worse. Normal saline contains a high chloride concentration (154 mmol/L), much higher than what’s in human plasma (~100 mmol/L). When we infuse large volumes, that excess chloride leads to hyperchloremic metabolic acidosis. Acidosis does three key things