Use of a continuous glucose sensor in an extracorporeal life support circuit

Abstract

Background: Standard care for infants on extracorporeal life support (ECLS) relies on intermittent measurement of blood glucose (BG); however, this can lead to significant changes in BG that go unrecognized for several hours. The present study was designed to assess performance and clinical applicability of a subcutaneous glucose sensor technology modified for use as a blood-contacting sensor within the ECLS circuit.

Methods: Twelve children, aged 3 years or less, requiring ECLS support were studied. Three continuous glucose sensors (Medtronic MiniMed) were inserted into hubs placed in line with the ECLS circuit. Blood glucose was assessed with a laboratory analyzer (BG(LAB); Bayer Rapidlab 860) approximately every 5 h (mean 4.9 ± 3.3 h) with more frequent samples obtained with a bedside monitor (HemoCue) as needed. Sensor current (I(SIG)) was transmitted to a laptop computer and retrospectively calibrated using BGLAB. Sensor performance was assessed by mean absolute relative difference (MARD), linear regression slope and intercept, and correlation, all with BGLAB as reference.

Results: The BGLAB averaged 107.6 ± 36.4 mg/dl (mean ± standard deviation) ranging from 58 to 366 mg/dl. The MARD was 11.4%, with linear regression slope (0.86 ± 0.030) and intercept (9.0 ± 3.2 mg/dl) different from 1 and 0, respectively (p < .05), and correlation (r² = 0.76; p < .001). The system was not associated with any adverse events, and placement and removal into the hubs was easily accomplished. Instances in which more frequent BG values were obtained using a bedside HemoCue (BGHEMO) monitor showed the sensor to respond rapidly to changes.

Conclusions: We conclude that continuous sensors can be adapted for use in an ECLS circuit with accuracy similar to or better than that achieved with the subcutaneous site. Continuous glucose monitoring in this population can rapidly detect changes in BG that would not otherwise be observed. Further studies will be needed to assess the benefit of continuous glucose monitoring in this population.

Figure 1

(A) Pre-inserted hub with glucose sensor; (B) transmitter; (C) afferent circuit showing placement of redundant sensors. Sensor signals were transmitted to a bedside laptop computer and retrospectively calibrated.

Figure 2

Regression showing paired sensor (SG) and reference glucose (BG) values. Regression slopes were not different using TX1 and TX2 (not shown), and the data were combined to form a single regression line (solid line), which was determined to have slope and offset different from the unbiased BG = SG line (dashed line).

Figure 3

(A) Triplicate SG profiles obtained in one subject requiring repeat glucose boluses (marked as upward-pointing arrows) to maintain euglycemia. Sensors were calibrated using laboratory glucose values and the one-point calibration algorithm but are shown here with the more frequent bedside BG_HEMO measurements. (B) Recalibration using linear regression of BG_HEMO and sensor current, with sensor OS current identified as ~7.8 nA for all 3 sensors. (C) Recalibrated SG signals with OS removed.

Figure 4

(A) Current in two sensors recorded with transmitter 1 (unmodified) compared to BG assessed with a HemoCue. (B) Sensor current obtained in two sensors connected to transmitter 2 (modified for rapid run in) compared with BG assessed with a laboratory analyzer.