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TPN: Novel energy substrates

Grimble, GK; Payne-James, JJ; Rees, RG; Silk, DBA; (1989) TPN: Novel energy substrates. Intensive Therapy and Clinical Monitoring , 10 (4) pp. 108-113.

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Abstract

Glucose is an attractive energy source in TPN. It is a natural fuel, is well metabolised and is also the cheapest substrate in TPN formulations. However, septic or traumatised patients may develop peripheral insulin resistance, limiting glucose utilisation. As a result, alternative carbohydrate energy sources have been considered. Of these, fructose, galactose, xylitol and sorbitol appear to be efficient non-insulin-dependent precursors for energy production in the sense that their metabolism bypasses control points in the glycolytic pathway. However, all carry a particular penalty for kinetic and metabolic reasons. The pathway of oxidation of fructose (and sorbitol which is converted to fructose) results in generation of large amounts of lactate. In the seriously ill patient, this extra load of lactate may be sufficient to precipitate lactic acidosis, especially when lactate/pyruvate ratios are significantly raised. A second feature of fructose administration is that rapid phosphorylation of fructose to fructose-6-phosphate may exceed the rate of generation of ATP and P(i), plus depleting both. This has a serious consequence in that inhibition of AMP deaminase by ATP and P(i) is reduced and purine nucleotide degradation increased. The consequent loss of intracellular ATP markedly affects all metabolic pathways requiring ATP. Thus, despite the promise that non-glucose carbohydrates hold for efficient energy metabolism, the net result may be the opposite to that expected. These substrates should not form the major part of the carbohydrate moiety of TPN solutions and their maximum recommended infusion rates are quite modest.

Type: Article
Title: TPN: Novel energy substrates
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Medical Sciences > Div of Medicine
URI: http://discovery.ucl.ac.uk/id/eprint/1403829
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