The evolution of nutrition in critical care: how much, how soon?

Critical care is a very recent advance in the history of human evolution. Prior to the existence of ICU care, when the saber-tooth tiger attacked you had but a few critical hours to recover or you died. Mother Nature, and her survival of the fittest mentality, would never have favored the survival of the modern ICU patient. We now support ICU patients for weeks, or even months. During this period, patients appear to undergo phases of critical illness. A simplification of this concept would include an acute phase, a chronic phase, and a recovery phase. Given this, our nutrition care should probably be different in each phase, and targeted to address the evolution of the metabolic response to injury. For example, as insulin resistance is maximal in the acute phase of critical illness, perhaps we have evolved to benefit from a more hypocaloric, high-protein intervention to minimize muscle catabolism. In the chronic phase, and especially in the recovery phase, more aggressive calorie delivery and perhaps proanabolic therapy may be needed. As the body has evolved limited stores of some key nutrients, adequate nutrition may hinge on more than just how many calories we provide. The provision of adequate protein and other key nutrients at the right time may also be vital. This review will attempt to utilize the fundamentals of our evolution as humans and the rapidly growing body of new clinical research to answer questions about how to administer the right nutrients, in the right amounts, at the right time.