Blood glucose can be lowered via insulin and/or fluid administration. Insulin, although efficacious, can cause hypoglycemia and hypokalemia. Fluids do not cause hypoglycemia or hypokalemia, but the most effective route of fluid administration has not been well described. This study compared the efficacy and safety of oral versus intravenous fluids for reducing blood glucose in patients with hyperglycemia.

We conducted a prospective, nonblinded, randomized, controlled trial. Inclusion criteria were blood glucose > 13.9 mmol/L, age > 18 years, and ability to tolerate oral fluids. Subjects were excluded for critical illness, contraindication to fluids, and/or hyperglycemia therapy prior to enrolment. Subjects were randomized to receive oral bottled water or intravenous normal saline (maximum 2 L) over 2 hours. The primary outcome of interest was a change in blood glucose at 2 hours across treatment arms.

The 48 subjects were randomized. Baseline blood glucose levels and total amount of fluid received were similar between the two groups. The mean decrease in blood glucose at 2 hours was similar for both treatment arms: a mean decrease of 3.4 mmol/L (20.2 mmol/L to 16.8 mmol/L) in the oral fluid group versus a mean decrease of 4.0 mmol/L (19.7 mmol/L to 15.7 mmol/L) in the intravenous fluid group. The mean difference between groups was −0.6 mmol/L (95% confidence interval −2.3–1.2; p = 0.51). No adverse events were observed in either group.

In this unblinded randomized trial, oral and intravenous fluids were equally efficacious in lowering blood glucose levels in stable hyperglycemic patients and no adverse events were noted. Physicians should be mindful that, although similar, the reduction in blood glucose was modest in both groups.