Updated July 2026 · 7 min read

Thiamine (Vitamin B1): The ICU Nurse's Guide

Part of the ICU Emergencies Hub — browse every related guide in one place.

Thiamine looks like a throwaway order — a vitamin — but in the right patient it prevents permanent brain injury, and the timing of when you give it relative to glucose genuinely matters. It shows up in alcohol withdrawal, malnutrition, refeeding, and the sepsis metabolic-resuscitation debate. Here is why this humble vitamin earns real attention.

Why thiamine matters

Thiamine (vitamin B1) is a cofactor for enzymes central to carbohydrate metabolism — pyruvate dehydrogenase and others that feed the Krebs cycle. Without it, cells can't process glucose efficiently, and the tissues most dependent on that metabolism, especially the brain, suffer first. Body stores are small and deplete within weeks of poor intake, which is why chronic alcohol use, malnutrition, hyperemesis, bariatric surgery, and prolonged critical illness all set patients up for deficiency.

The glucose-before-thiamine trap

That said, in a truly hypoglycemic, obtunded patient you should not withhold life-saving glucose while hunting for thiamine — give both, with thiamine as close to first as feasible. See the dextrose/hypoglycemia guide for the acute-low context.

Dosing by indication

When Wernicke is genuinely suspected, guidelines favor generous high-dose IV thiamine rather than a token 100 mg — the downside of over-treating is negligible and the cost of under-treating is permanent. IV or IM is preferred in the acute setting because oral absorption is limited and unreliable in sick or malnourished patients.

Where thiamine shows up in the ICU

Alcohol withdrawal. Nearly universal supplementation, since chronic alcohol use is the classic deficiency setting. It runs alongside benzodiazepine therapy — see the lorazepam guide for the CIWA context.

Refeeding syndrome. As nutrition restarts in a starved patient, thiamine demand surges just as phosphate, potassium, and magnesium shift — thiamine is part of the refeeding-safety bundle.

Sepsis metabolic resuscitation. Thiamine featured in the "vitamin C, thiamine, and hydrocortisone" sepsis cocktail that generated intense interest. Later trials tempered the enthusiasm, and it is not standard care, but thiamine repletion in septic patients who may be deficient remains reasonable and low-risk.

Why CRNA students should know it

On the CRNA path, the thiamine-before-glucose rule is a classic exam and safety point, and understanding thiamine's role in glucose metabolism connects nutrition, neurology, and pharmacology. Recognizing Wernicke and the populations at risk is exactly the kind of quiet, high-stakes knowledge that separates a careful clinician from a checklist follower.

Bottom line

Thiamine is the cheap vitamin that prevents permanent brain injury: give it before or with glucose in at-risk patients, dose it generously when Wernicke is suspected, and remember it in alcohol withdrawal, refeeding, and malnourished critical illness. The risk of giving it is trivial; the cost of missing a deficiency is not. Learn the timing rule cold.

This article is general educational information for licensed clinicians and students, not medical advice or a substitute for your institution's protocols, pharmacy guidance, or a provider's orders. Always follow facility policy and verify every dose independently.