[Comparison of 2 devices to measure spinal fluid glucose concentration in hyperbaric spinal anesthesia]

To compare spinal fluid glucose measurements recorded by the laboratory analyzer Synchron LX20 Pro and the glucometer Ascensia Elite XL during continuous spinal anesthesia after injection of 10 mg of hyperbaric bupivacaine, in order to assess the reliability and speed of the 2 devices for monitoring changes in glucose concentration.

Prospective study of 34 patients under continuous spinal anesthesia administered through a 22-gauge catheter; 9 samples of spinal fluid were extracted from each patient for glucose level measurement. The first extraction was before administration of the anesthetic and the remaining ones were during spinal anesthesia until the end of complete motor block. Correlation was assessed with the Pearson test and agreement with the Bland-Altman method.

A total of 241 pairs of measurements were obtained. The correlation was r = 0.96 (P < .01). The mean (SD) difference in measurements from the 2 devices was -1.06 (34.82 mg x dL(-1)). The percentage of variation (systematic error) was -1.9% (11.8%), placing the 95% confidence interval between -25% and 21.2%.

Measurements from the 2 devices are highly correlated. The absolute and percentage systematic error (bias) is negligible. Finding that 95% of measurements are within 23% of the mean seems a fair percentage of error to us. We therefore believe the percentage variation, or systematic error, is clinically acceptable and that either device can be used.