The Relationship between Npo Duration and Fasting Blood Glucose:
A Preliminary Analysis
Jason Greenberg BA, Vivek Moitra MD, Melinda Drum PhD, Bobbi Jean Sweitzer MD
Department of Anesthesiology and Critical Care, University of Chicago Hospitals, Chicago, IL

Introduction
In order to minimize the risk of aspiration, all surgical patients are required to fast prior to a surgical procedure. This can be a particular challenge for diabetics taking insulin or oral hypoglycemics the morning of surgery as they are at risk for hypoglycemia2. Traditionally, diabetics have been scheduled for surgery in the morning in order to avoid this risk. The role of NPO duration on fasting blood glucose is unclear in type II diabetics who are not being treated with morning oral hypoglycemics or insulin. Our study examined the association of NPO duration to preoperative glucose values in this population of diabetics undergoing surgery.
Methods
The institutional review board approved this prospective observational study. Patients were recruited in the outpatient preoperative clinic, and the majority were scheduled for outpatient surgery. To date, 163 patients were evaluated in a preliminary analysis using multivariable linear regression with glucose level as the dependent variable and NPO duration as the primary explanatory variable, controlling for age, sex, race and BMI. NPO duration was based on the patient’s subjective history. This preliminary analysis excluded
patients who had taken morning insulin, steroids or hypoglycemic agents on the day of surgery, and those who had remained NPO for >24 hours.
Results
The estimated drop in blood glucose was 1.95mg/dL for every hour of NPO time in the unadjusted model and 2.24mg/dL in the model adjusted for patient characteristics. The confidence interval was –0.55 to 4.45 with a P value of 0.126 in the unadjusted model and -0.30 to 4.78 with a P value of 0.084 in the adjusted model.

Conclusions
While the relationship between the preoperative glucose value and NPO duration is not statistically significant in either the unadjusted or adjusted models, a trend toward an inverse relationship does seem to be apparent. When patient accrual is complete, the power to detect a relationship should be greater. Thus, in patients who are not taking morning hypoglycemics, a longer NPO status may be associated with lower blood glucose values. This association may be especially important for outpatient surgery when giving
patients NPO instructions based on their estimated surgery start time.

2 Jacober S, Sowers J. An update on perioperative management of diabetes. Arch Int Med. 1999; 159: 2405-2411.

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