Lit Matters #2: Balanced fluids or Normal Saline for TBI?

Fluid choice in critical care is not one-size-fits-all. In traumatic brain injury, balanced crystalloids may worsen outcomes compared with normal saline, while in non-TBI ICU patients the mortality signal leans the other way.

Fluids for TBI and Critical Illness

• TBI mortality signal: In brain-injured ICU patients, balanced crystalloids were associated with higher mortality than normal saline, reinforcing the concern that relative hypotonicity may worsen cerebral edema.
• Non-TBI mortality trend: In critically ill patients without TBI, balanced crystalloids were associated with lower mortality, consistent with the physiologic appeal of avoiding chloride-heavy saline.
• Pathophysiology tradeoff: Normal saline is slightly hypertonic to plasma but can drive hyperchloremic acidosis, whereas balanced fluids are closer to plasma composition yet carry theoretical edema risk in TBI.
• Aggregate result caution: When TBI and non-TBI patients were pooled, the mortality difference disappeared, a reminder that mixed populations can hide clinically important subgroup effects.
• Secondary outcomes stability: Acute kidney injury, renal replacement therapy, ICU length of stay, and other secondary outcomes were similar between fluids. We get into why mortality may still move when these outcomes do not in the episode.
• Practical bedside nuance: Lactated Ringer's brings familiar caveats beyond osmolality, including calcium compatibility issues and potential disadvantages in severe hepatic dysfunction; the fluid-specific exceptions are worth hearing in the chapter.