Metabolic consequences of hypercaloric glucose infusions.

Recent studies have demonstrated that an altered pattern of substrate mobilization and fuel utilization exists in patients who are acutely ill secondary to either injury or infection. These studies have important implications regarding the nutritional support of these patients. This review addresses some of the metabolic sequelae of total parenteral nutrition with hypertonic glucose as the primary source of non-protein calories. The consequences of administering glucose calories in excess of energy requirements are considered. The patterns of gas exchange, fuel utilization and fuel storage in nutritionally depleted and hypermetabolic patients are discussed with specific reference to fat metabolism. Administration of glucose in hypercaloric quantities may produce a respiratory as well as a metabolic stress. The former appears to be related to a ventilatory stimulus associated with an increased rate of carbon dioxide production. In acutely ill patients, this response is magnified and there is also a considerable rise in oxygen consumption and free norepinephrine excretion. It is this group of patients which shows the most profound elevation in minute ventilation. The metabolic pathways and regulatory mechanisms which may be involved are discussed. A scientific approach to substrate administration in acutely ill patients can be taken only after these patterns of metabolic responses have been fully elucidated.