Abstract
BackgroundSepsis and infection are the leading cause of morbidity and mortality after surgery, but the inflammatory response to the trauma of surgery can make diagnosis challenging, and no biomarker with high diagnostic accuracy has been discovered or implemented in clinical practice. Carbon-13 breath delta value (BDV) is the ratio of the Carbon isotopes 12C and 13C in breath, where approximately 99% of universal carbon is 12C and 1% is 13C. Data suggests a shift in BDV during high metabolic states, for example sepsis, measured using infrared spectroscopy. 13C BDV has been shown to be discriminant as a novel diagnostic marker for sepsis and infection. This thesis assesses present putative biomarkers and novel breath and circulating biomarkers following major hepatopancreatobiliary (HPB) surgery and Liver Transplantation (LT) to diagnose postoperative infection/sepsis.
Methods
A meta-analysis of Procalcitonin (PCT) and Interleukin-6 (IL-6) was performed. A prospective cohort of 20 participants undergoing HPB surgery and 20 participants undergoing LT were recruited. Breath samples were collected from baseline preoperatively, and on postoperative days (POD) 1-9, with plasma and peripheral blood mononuclear cell (PBMC) samples preoperatively, POD1, 4 and 8 in the HPB group, and 2,5 and 8 in the LT group. Breath samples were analysed using infrared laser spectroscopy to generate BDV (per mil). Plasma was analysed for 9 proinflammatory cytokines using MesoScale Discovery (MSD) immunoassay, PCT using ELISA, and cell surface marker expression on monocytes was phenotyped using flow cytometry in the HPB group. Differences between groups who did and did not develop infective complications was analysed using two-way Analysis of Variance (ANOVA), Mann Whitney U test, and diagnostic accuracy.
Results
5/20 HPB participants developed infective complications, mean day of diagnosis POD5. There was no difference between BDV in patients with or without infection. Monocyte count was increased in infected participants at all timepoints, and monocyte expression of programme death-ligand 1 (PD-L1) on POD1, Cluster of differentiation 155 (CD155) and Human-leucocyte antigen - DR isotype (HLA-DR) on POD4 were upregulated, +13.09% (95%CI 1.59 to 24.61, p<0.05), +422.5 mean fluorescence index (MFI) (95% CI -770.9 to -73.68, p<0.05), and +19.02% (95% CI 37.58 to 0.45, p<0.05) respectively. 4/20 LT participants developed infective complications, mean day of diagnosis POD5. There was no difference in BDV, CRP or sequential organ failure (SOFA) score in patients with or without infection. Interleukin-12p70 (IL-12p70), Interleukin-2 (IL-2), Interleukin-4 (IL-4) and tumour necrosis factor α (TNFα) were upregulated and Interferon-γ (IFN-γ), Interleukin-6 (IL-6) and Interleukin-8 (IL-8) were downregulated on POD2 and 5 following surgery. Cytokines were not significantly different between participants with and without infection.
Discussion
In this prospective cohort, BDV was not significantly different between groups following HPB surgery or LT. Monocyte expression of PD-L1, HLA-DR and CD155 is associated with infection, +13.09% (p<0.05), +422.5 MFI (p<0.05), and +19.02% (p<0.05) respectively following HPB surgery. Proinflammatory cytokines were not significantly different between groups following HPB surgery or LT. All markers performed poorly as diagnostic markers.
The innate immune system is dysregulated in infection following major HPB surgery. In this cohort BDV did not predict infection. Further investigation of novel biomarkers including BDV and soluble monocyte markers in a higher-powered study is required.
| Date of Award | 1 Apr 2024 |
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| Original language | English |
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| Supervisor | Krishna Menon (Supervisor) & Mark McPhail (Supervisor) |