INTRODUCTION AND AIMS: The fluid transfer from the interstitial compartment into the vasculature in response to ultrafiltration is known as plasma refill rate(PRR) and it is involved in intradialytic hypotension. Subcutaneous continuous glucose monitoring(CGM) devices measure glucose concentration in the interstitial fluid. We aimed to explore if this fluid transfer influences the accuracy of the CGM device when compared with the levels of serum glucose during haemodialysis(HD) and if these differences predict the refill rate. We also intended to assess the accuracy of Hemoscan measurements as well, since it is the most used tool in terms of relative plasma change measurements.
METHODS: Observational, prospective study of 13 HD sessions with consecutive paired determinations of GSM and serum glucose (before, during each hour and 20 minutes after). The plasma volume variation in the mentioned timepoints was calculated using 51Cr-labeled erythrocytes and hematocrit by the "isotope dilution technique". We calculated relative differences (RD) between CGM and serum glucose, and PRR by subtracting absolute plasma change to ultrafiltration rate. The strength of the correlation was determined by calculating the Spearman correlation coefficient (SCC).
RESULTS: Among the 13 HD sessions of 7 patients, the RD increased constantly from hour 2: -21.3%; -22.5% and -23.3% with a significant difference from the basal RD (p=0.043; 0.036 and 0.02 respectively). This statistical significant difference was lost in the first hour and post-desconnection. However, these differences between GSM and serum glucose were not explained by PRR (p>0.05) (Figure 1). The mean total ultrafiltration was of -2.5±0.82L. Refill rate was constant and did not increase along the HD session (mL): 1st hour: 436±259, 2nd: 582±299, 3rd:378±226, 4th: 481±248. Relative plasma variation measured with the Hemoscan device was compared with the isotopic method, and we found that Hemoscan underestimated the real plasma variation from hour 3 (at hour 3: -8,4% vs -19,3% and at 4 hour: -9,7% vs -24,3) (p<0.005).
CONCLUSIONS: We conclude that CGM underestimated plasma glucose during HD session. Statistically higher relative differences were found from the second hour of HD, and they were lost after 20 minutes of the end of the therapy. In our experience, this phenomenon can not be explained by the plasma refilling rate. On the other hand, we showed that in our population, hemoscan measurements underrate the real plasma variation at 3rd and 4th hours, as it has been cited in previous studies.
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