Canopy Hood Research Articles

Effect of the energy source on changes in energy expenditure and respiratory quotient during total parenteral nutrition.

It has been suggested that malnourished patients respond to glucose intake in excess of energy needs by a rise in respiratory quotient (RQ) above 1.0, indicating net fat synthesis. This would represent inefficient utilization of glucose as an energy source. It is unclear, however, whether this also occurs when some of the energy source is provided as a fat emulsion.Energy expenditure was measured by indirect calorimetry using a canopy hood and RQ, calculated from the analysis of 2 X 5 minute collections of expired air, were measured every 3rd day in two groups of surgical patients who received a 14‐day course of intravenous nutrition [total parenteral nutrition (TPN)]. Group I (mean ± 1 S.D. 57.4 ± 15.4 yers, 9 females, 3 males) received glucose as the only source (46.6 ± 9.2 kilocalories per kilogram per day and group II (55.8 ± 14.2 years, 5 males, 3 females) 60% of their calories as fat (44.0 ± 7.5 kilocalories per kilogram per day). Both groups were given similar amounts of crystalline amino acid solution (0.34 ± 0.007, 0.32 ± 0.005 gram nitrogen per kilogram per day, respectively) and no other intake. There was no significant difference between the groups mean values of body weight (52.3 ± 7.9 versus 57.9 ± 12.5 kilograms) or energy expenditure before TPN commenced (31.3 ± 6.5, 32.3 ± 3.0 kilocalories per square meter per hour). In group I there was a persistent elevation (p < 0.001) of mean RQ above 1.0 from the 9th day of TPN, together with a significant increase (p < 0.001) in mean energy expenditure which attained the value of 38.0 ± 4.8 kilocalories per square meter per hour on the 14th day. In group II, the mean RQ never exceeded 1.0. The rise in the mean expenditure in group II was significantly less (p < 0.02) than that observed in group I.This study shows that the use of glucose as the only energy source during TPN is associated with a greater rise in energy expenditure than is observed with a glucose‐fat regime and a persistent elevation of RQ above 1, indicating net lipogenesis. These results suggest, therefore, that complete oxidation of glucose occurs when it is the only source of nonprotein calories given during TPN.

The relative significance of thermal and metabolic demands on burn hypermetabolism.

To evaluate the claim that burn hypermetabolism can be eliminated by making patients warm and comfortable, respiratory gas exchange was measured, using a canopy hood system, in 20 burn patients and five normal controls resting in a 30°C ambient environment. Metabolic rates of burn patients determined by the canopy hood system were comparable to previous values obtained using Douglas bag techniques. In another study, the effects of induced hyperthermia were evaluated in seven febrile, hypermetabolic burn patients. External heating elevated rectal temperatures from 38.6 ± 0.3 to 39.4 ± 0.2 (mean ± S.E.M., p < 0.001) but did not significantly reduce metabolic rate (76.5 ± 3.7 kcal/m2± hr vs. 73.9 ± 3.5). When five normals and seven burn patients adjusted room temperature until they were comfortable, the “preferred‘’ environmental temperature selected by the burn patients was 31.5 ± 0.7°C, significantly warmer than the 28.6 ± 0.7°C selected by the controls. In this comfortable environment the sleeping, febrile burn patients remained hypermetabolic (63.9 ± 5.7) and the Q10 effect of the hyperpyrexia accounted for only 20 to 30% of the hypermetabolism observed. These studies demonstrate that the hypermetabolic response to burn injury is not significantly reduced in comfortable patients resting or sleeping in a warm environment, and the increased oxygen consumption cannot be accounted for by the elevated body temperature. This evidence does not support the contention that burn hypermetabolism is primarily the result of thermoregulatory drives. The increased heat production following injury is the consequence of an elevated metabolic state.

CONTROLLING VAPOURS FROM OPEN SURFACE VESSELS

Tests are described on four ventilation extraction systems—canopy hood, ‘push-pun’, rim and central slot—for removing toxic vapours from open surface vessels. As access was an important consideration, the central slot proved to be the most practical system. Initial design details for the central slot were obtained from Industrial Ventilation. A Manual of Recommended Practice. The rates of air flow were varied to establish the most efficient volume required to control the vapours effectively under all operating conditions. The reults indicate that lower volumes of air can be used for ‘undisturbed’ locations than those recommended by Industrial Ventilation. However, the volume flow rates required for ‘disturbed’ locations, i.e. those subject to cross draughts or similar conditions, are comparable to those outlined in Industrial Ventilation for ‘undisturbed’ locations. The paper provides design criteria for the central slot extraction system.