Situation: The nurse works in the high-risk pregnancy unit of a provincial hospital that receives referred pregnant clients from rural health units (RHUs). A client at 11 weeks' gestation with hyperemesis gravidarum has vomited for 3 weeks. Before a dextrose-containing intravenous infusion is started, which vitamin should be given to prevent Wernicke encephalopathy?

Prolonged vomiting depletes thiamine. Giving dextrose without thiamine increases thiamine use and can precipitate Wernicke encephalopathy (confusion, ataxia, abnormal eye movements). Thiamine is therefore given before, or together with, dextrose-containing fluids.

Clinical context
A client at 11 weeks' gestation with hyperemesis gravidarum has been vomiting for 3 weeks. Persistent vomiting produces both caloric deprivation and a sharp fall in thiamine stores, because thiamine is water-soluble, has limited body reserves, and is not consumed when oral intake is nearly impossible. In pregnancy, the demand for thiamine is already increased by maternal and fetal metabolism, so hyperemesis can deplete it rapidly ^[2][3].

Why thiamine must be given before dextrose
Thiamine, as thiamine pyrophosphate, is a required coenzyme for several steps in carbohydrate metabolism, including pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in the Krebs cycle. When a dextrose-containing infusion is started in a thiamine-depleted patient, the incoming glucose accelerates carbohydrate metabolism and sharply increases thiamine consumption. Administering dextrose without first replacing thiamine can therefore precipitate Wernicke encephalopathy rather than simply failing to prevent it. This is why thiamine is given before, or together with, the dextrose-containing intravenous fluid ^[1][3].

Recognizing Wernicke encephalopathy
Wernicke encephalopathy is the clinical syndrome of acute thiamine deficiency affecting the brain. The classic triad includes mental status change such as confusion, oculomotor abnormalities such as nystagmus, and motoric changes such as ataxia or postural instability ^[1][2]. In pregnancy, the presentation may be incomplete or atypical, so the diagnosis can be delayed. Key point! In a pregnant client with prolonged vomiting, any new confusion, abnormal eye movement, or unsteady gait should raise immediate concern for Wernicke encephalopathy.

Why the other vitamins are not the priority
Pyridoxine (vitamin B6) is important in pregnancy and is used for nausea and vomiting, but it does not prevent the specific neurological injury caused by thiamine deficiency. Folic acid (vitamin B9) is essential for neural tube development, and cyanocobalamin (vitamin B12) is needed for neurological and hematologic function, but neither addresses the immediate metabolic risk created by giving dextrose to a thiamine-depleted client. Watch out! The question asks which vitamin should be given before the dextrose infusion, not which vitamins are generally important in pregnancy.

Vitamin	Primary role in this scenario	Prevents Wernicke encephalopathy before dextrose?
Thiamine (B1)	Cofactor in glucose metabolism; depleted by prolonged vomiting	Yes — must be given before or with dextrose
Pyridoxine (B6)	Adjunct for nausea and vomiting in pregnancy	No
Folic acid (B9)	Neural tube defect prevention	No
Cyanocobalamin (B12)	Neurologic and hematologic function	No

Clinical application
For a client with hyperemesis gravidarum requiring intravenous fluids, the safe sequence is to administer thiamine before or with the dextrose-containing solution. The thiamine dose and route are determined by clinical severity; intravenous replacement is used when Wernicke encephalopathy is suspected or when gastrointestinal absorption is unreliable ^[1][3]. Delaying thiamine while dextrose is running increases the risk of permanent neurological injury, including progression to Korsakoff syndrome, so the timing of thiamine administration is a safety priority. In addition, prolonged starvation in hyperemesis can lead to refeeding syndrome when nutrition is restarted, and thiamine replacement is part of the preventive strategy in that setting as well .