In-vitro and In-vivo spectrometric investigations on the behavior oflactate under conditions emulating septic shock

Abstract

Lactate is an inter- and intra-cellular product in the human body. In patients with life threatening illnesses, the secretion and excretion of lactate is impaired, which might cause the pH of blood to shift to be either acidic or basic. Lactic acidosis can be regarded as a useful biomarker for the onset of haemodynamic shock in patients. Lactate concentration levels are measured and monitored frequently in critical care by utilizing invasive blood sampling techniques. Such techniques, apart from their invasive nature, which is not desirable, are intermittent, time consuming and do not allow the continuous monitoring of lactate. Hence, there is a need for new innovative approaches in research which could lead to the development of non-invasive and continuous monitoring technologies for lactate. The motivation of this research is to explore rigorously the capability and potential of absorption spectroscopy as a technique which could enable the development of non-invasive lactate sensors. The focus of the research lies in unravelling the basic light lactate molecular interactions in different media, both in-vitro and in-vivo, utilizing a wide range of spectrometers. The research investigated lactate “signature peaks” in solution samples, including different concentrations of lactate, in various media (buffer, human serum and whole blood) across the UltraViolet (UV), Visible (Vis), Near Infrared (NIR) and Mid Infrared (MIR) parts of the EM. The results have shown that lactate has limited presence in the UV and Vis parts of the EM spectrum. For the first time, ’signature peaks’ for lactate in the NIR and MIR spectral regions have been identified, suggesting that these spectral regions could be used for lactate concentration predictions with 90 % accuracy. More uniquely, it has been shown that these ’signature peaks’ for lactate in the NIR spectral region are influenced by the change in physiological conditions and media; these are therefore, not consistent. Nevertheless, in the ’fingerprint region’ of the MIR spectral region, these ’signature peaks’ for lactate are not only consistent but they could be used inter changeably for different physiological conditions and media for lactate concentration prediction. The results from this suggests that the ’fingerprint region’ of the MIR spectral region is most preferred for lactate concentration determination in-vitro, for accuracy needed in critical care. Despite being the most preferred spectral region, the major disadvantage of MIR is the penetration depth and hence, it might not be suitable for in-vivo lactate measurements in blood through skin. Therefore, a pilot in-vivo study utilizing, a portable NIR spectrometer was conducted in order to evaluate the feasibility of measuring lactate concentrations in this region. The results from this study have shown for the first time that the NIR region could be suitable for measuring lactate concentrations using Absorption/ Reflectance portable Spectroscopy accurately and non-invasively. The output from this research could pave the way for the development of optical sensing point-of-car