Q: Why would I give I.V. glucose to a patient being treated for hyperglycemia?-D.L., Conn.
A: Although this seems like a contradiction, it can be appropriate. The primary reason is to prevent hypoglycemia once the blood glucose level begins to return to normal.
Patients suffering from diabetic ketoacidosis (DKA), for example, can benefit from intravenous (I.V.) glucose. We'll explain why later, but first let's talk more about DKA.
On admission, patients with DKA usually have blood glucose levels between 250 mg/dl and 800 mg/dl. Because normal blood glucose is 70 to 120 mg/dl premeal, the blood glucose level is way too high.
To accurately diagnose a patient with DKA, we need to consider more than his blood glucose level. As the term DKA indicates, plasma or urine ketones must also be present. Ketones are weak acids, and when they accumulate, the blood pH drops to an average of 7.15. The normal blood pH range is from 7.35 to 7.45. As the pH falls, the plasma bicarbonate level drops as it tries to buffer the acids and restore a normal blood pH. An absence of ketosis or acidosis usually excludes a DKA diagnosis.
Put simply, the diagnostic parameters for DKA are: arterial pH of less than 7.2, plasma bicarbonate level less than 15 mg/dl, blood glucose level of greater than 250 mg/dl, and presence of serum and urine ketones.
Because patients with DKA have an absence of insulin, their cells can't use glucose properly. These patients usually have Type 1 diabetes. Treatment goals include fluids (fluids alone will help decrease the glucose concentrations), adequate insulin to restore normal glucose metabolism, and correction of the precipitating factor.
The most effective way to deliver the required insulin is through a continuous I.V. insulin infusion. Insulin is an anabolic hormone that prevents the formation of ketones. The insulin infusion (usually a dilution of 1 unit insulin to 1 ml of 0.9% sodium chloride) is piggybacked into a main line of 0.9% sodium chloride.
The goal of therapy is to decrease the blood glucose by 75 to 100 mg/dl of glucose each hour. Once the blood glucose level reaches 250 mg/dl, the main line should be changed from 0.9% sodium chloride to 5% dextrose in 0.45% sodium chloride.
If the patient with DKA achieves a normal blood glucose level but still has ketosis/acidosis, continue the I.V. insulin but provide a source of glucose to prevent hypoglycemia.
The other metabolic emergency associated with even higher blood glucose levels is hyperglycemic hyperosmolar nonketotic syndrome (HHNK). Treatment guidelines are the same as those prescribed for management of DKA, with one important difference. Patients with HHNK usually have Type 2 diabetes and produce insulin. But they may not produce enough to control blood glucose levels that can rise to levels as high as 600 to 2000 mg/dl.
With this scenario, HHNK patients don't produce ketones and aren't acidotic. They'll receive I.V. glucose with their insulin once the blood glucose level drops to 250 mg/dl. The I.V. infusion can be discontinued without concern for rebound ketosis as soon as the patient's blood glucose level is normal.
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