The late response to injury is characterised by an early and late anabolic phase. The transition from catabolism to anabolism is marked by a decrease in nitrogen loss, diuresis of retained water and an improvement in the patient's overall condition. The early anabolic phase occurs over a period of several months and the nitrogen gain gradually equals the nitrogen lost in the catabolic phase. Nitrogen balance is achieved in the late anabolic phase, as the body's protein structures are repleted. Fat stores will be restored if the caloric intake is greater than caloric expenditure.
Unfortunately, in many patients who have sustained severe trauma, an overload of inflammatory cytokines and an overactive vascular endothelial response lead to an increase in metabolism and the inability of the cardiac output to maintain a hyperdynamic circulation. These in turn lead to anaerobic metabolism, organ failure and death and prompt resuscitation and treatment of injuries is one way to try to limit this.
A significant catabolic phase is observed in critically ill patients as part of the stress response. The advantages of instigating early enteral feeding are thought to include maintenance of the mucosal barrier of the gut, limiting the alteration of commensal flora in the gut, minimising the catabolic response, and boosting the immune system. Enteral feeds, particularly those supplemented by L-arginine, omega-3 fatty acids, L-glutamine (the entero-cyte's primary energy source) or branched amino acids, have been shown to decrease infective complications and intensive care unit (ICU) stay after major trauma.
An interesting avenue of research is into bacterial translocation and the development of sepsis. Glutamine enteral nutrition has been shown to decrease this phenomenon, but isolation of specific protein involved in bacterial translocation, and their antagonism, may be possible future therapeutic options. In the future, care of the severely injured patient is likely to undergo some exciting changes, with the emergence of combination antioxidant therapy, activated protein-C trials, and blood substitutes, which may improve outcome and ultimately survival.
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