Is there a role for ketones as alternative fuel in critical illness?

Purpose of reviewThe evidence base advocating ketones as an alternative substrate for critically ill patients is expanding. We discuss the rationale for investigating alternatives to the traditional metabolic substrates (glucose, fatty acids and amino acids), consider evidence relating to ketone-based nutrition in a variety of contexts, and suggest the necessary future steps.Recent findingsHypoxia and inflammation inhibit pyruvate dehydrogenase, diverting glucose to lactate production. Skeletal muscle beta-oxidation activity falls, decreasing acetyl-CoA generation from fatty acids and subsequent ATP generation reduction.The benefits of induced ketosis are well established in epilepsy, whilst the evidence base for ketogenic diet therapy in other neurological pathology, such as traumatic brain injury and neurodegenerative diseases, is expanding. Evidence of upregulation of ketone metabolism in the hypertrophied and failing heart suggests that ketones may be utilized as an alternative fuel source to sustain myocardial function. Ketogenic diets stabilize immune cell homeostasis, promote cell survival following bacterial infection and inhibit the NLRP3 inflammasome, preventing the release of pro-inflammatory cytokines - interleukin (IL)-1 & beta; and IL-18.Whilst ketones provide an attractive nutritional option, further research is required to determine whether the proposed benefits are translatable to critically unwell patients.