Indirect calorimetry in critical care.

In critical care, particular attention is paid to disorders which lead to cerebral dysfunction. Hypoxia is the most common example and considerable effort is devoted to avoiding this problem. If the brain is deprived of fuel, as in hypoglycaemia, the outcome is similar yet far less attention is paid to maintaining an adequate and appropriate long-term fuel supply. Indirect calorimetry has been investigated for the past decade, focusing on its application to the clinical area. The only pathway to the effective clinical use of indirect calorimetry is via a meticulous research-precision approach with considerable attention to accuracy. Our institution played a key role in the development of parenteral nutrition. In the early days, patients were provided 12.6-20.9 MJ (3000-5000 kcal)/d with the ‘thought’ that ‘hyper’ alimentation was good. Energy requirements of sick patients were ill-defined and ‘guess-work‘ at best. Energy prescription often consisted of ‘three bottledd’ and such input often exceeded the capacity of the body’s disposal systems. Unfortunately serious adverse events accompanied overfeeding: hyperglycaemia, hyperosmolar states, steatosis, excessive carbon dioxide production , increased norepinephrine secretion and fluid overload. When any or all these events occurred the temptation for the clinician was to abandon forced feeding and blame total parenteral nutrition (TPN). TPN is not to blame, only its misuse. We must approach energy prescription much as we approach medication prescriptions with precision based on scientific objective information.