Simultaneous monitoring of potassium, glucose and lactate during spreading depolarization in the injured human brain – Proof of principle of a novel real-time neurochemical analysis system, continuous online microdialysis

Figures

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  Figure 1.. Continuous online microdialysis analysis system for bedside monitoring using microfluidic chips containing biosensors for glucose and lactate and a potassium ion selective electrode. (a) shows the overall setup. (b) Raw traces from glucose (red), potassium (purple) and lactate (green) during a computer-controlled three-point automatic calibration run. Concentrations indicated by legend. (c) Sequential analysis of sensor performance over 12 h using automatic calibration. (d) Raw data for microdialysate brain lactate levels collected at the bedside with three automatic calibrations. The green boxes indicate sections of clinical data and the grey boxes indicate calibrations. Clinical data were collected from patient 2.

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  Figure 2.. Spreading depolarization recorded in patient 5 confirmed by ECoG. The increase in potassium indicates the depolarization of the cells surrounding the microdialysis probe. The fall in the local concentrations of glucose and the rise in the level of lactate indicates that the demand for energy is outstripping the supply, thus creating a mismatch that is potentially harmful to the local tissue area.

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  Figure 3.. Microdialysate changes during spreading depolarizations. SDs that are confirmed using ECoG are seen in patients 1, 3 and 5a, as indicated by the blue-shaded box. In patients 4, 5b and 6, the events have not been confirmed as SDs, either as there was no ECoG data recorded at that time or due to problems time-aligning the two datasets. This is indicated by the orange-shaded box. In patient 6, there is no lactate data available at the time of the event. Significance of the change from baseline to peak was tested using a Wilcoxon signed-rank test, p = 0.01.

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  Figure 4.. ECoG and microdialysate data of repetitive spreading depolarizations collected from patient 3. (a) Image of probe placement on the brain taken during craniotomy. The numbers relate to the ECoG channels and the arrows to the potential paths of two SD waves. (b) Data showing a total of four SD waves. Top six traces show the large slow potential change in the near-direct current (DC) ECoG data, a hallmark characteristic of SD. The bottom three traces show the tissue response from the microdialysate data: potassium (purple), glucose (red) and lactate (green). The arrows indicate the SD waves in the ECoG data. There are two waves repeating with cycles of 38 and 35 min.

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  Figure 5.. Spreading depolarizations occurring over 4 h apart within the same patient dataset (patient 3). (a) Data of an SD occurring at 5:15 am. The table shows levels of potassium, glucose and lactate before and after the event and the traces show the data. Note that only three traces of the near-DC ECoG are shown for simplicity. The grey box represents an electrical artefact in the baseline potassium level that was not included in the baseline measurement. (b) Data of an SD occurring over 4 h later at 9:26 am. The table shows levels of potassium, glucose and lactate before and 10 min after the event and the traces show the data. Note that only three channels of the near-DC ECoG data are shown for simplicity.