Transport and demand of oxygen in severe burns.

The balance equation or oxygen-conservation equation in which oxygen consumption is equal to cardiac output times the maximal oxygen binding capacity times the oxygen saturation difference between arterial and mixed venous blood shows the three factors by which the oxygen supply to the tissues can be regulated according to the need. The release of oxygen to the tissues is regulated directly through the venous oxygen tension and indirectly through cardiac output, the 2,3-DPG system, and erythropoietin. Of these indirect regulation mechanisms, cardiac output has the most rapid response and erythropoietin the slowest. As the pool of oxygen in the tissues is comparatively small, the transport and the demand of oxygen under normal conditions are approximately equal over a longer period of time. The tissue oxygen tension (Fig. 21) is thus directly a result of the flows (Fig. 21), solid lines) and indirectly a result of the regulation mechanisms (Fig. 21, broken lines). Hypermetabolism, weight loss, and severe protein wasting characterize the metabolic response to thermal injury. The increased adrenergic activity following severe burns signifies a shift of flow of body substrate from storage to utilization and an increase in energy requirements. The greater the stress, the greater the response. All systems operate at maximal or near maximal levels. The critically injured patients have an accelerated glucose turnover and increased nitrogen loss; the main source of catabolized protein seems to be from skeletal muscle. The metabolic wheel has a tremendous speed. It is thus essential to feed the patient. Energy support with heat supply and nutrition must equal energy demand to avoid weight loss. Most important is to avoid loss of "lean body tissue." No hypermetabolism was found in burned patients when the patients themselves controlled the heat supply from infrared heaters. The metabolic rate corrected for rectal temperature was independent of the total body surface burned. The energy expenditure of patients with burns was studied during the daily treatment routine and showed that it is important to avoid hypovolemia, underhydration, pain, fear, and anxiety, all of which increase the metabolic demands. To prevent hypermetabolism, infrared radiation is a practical way of distributing energy from the environment to the patient. Weight loss can be essentially prevented as energy support equals energy demand (Fig. 20). Furthermore, the method has the advantages that many patients can be treated individually, the method is inexpensive, and the ambient air temperature can be kept normal. From the results of the present investigation, it may be concluded that in patients with burns treated with infrared heaters the energy intake can be predicted in an appropriate way from the calculated basal metabolism, the rectal temperature, and the activity of the patient. The effect of storage of blood on oxygen, proton, and carbon dioxide transport is mainly mediated over the concentration of 2,3-DPG...