Solca M

Effects of heat and moisture exchangers on minute ventilation, ventilatory drive, and work of breathing during pressure-support ventilation in acute respiratory failure

OBJECTIVES To evaluate the effect of two commonly used heat and moisture exchangers on respiratory function and gas exchange in patients with acute respiratory failure during pressure-support ventilation. DESIGN Prospective, randomized trial. SETTING Intensive care unit of a university hospital. PATIENTS Fourteen patients with moderate acute respiratory failure, receiving pressure-support ventilation. INTERVENTIONS Patients were assigned randomly to two treatment groups, in which two different heat and moisture exchangers were used: Hygroster (DAR S.p.A., Mirandola, Italy) with higher deadspace and lower resistance (group 1, n = 7), and Hygrobac-S (DAR S.p.A.) with lower deadspace and higher resistance (group 2, n = 7). Patients were assessed at three pressure-support levels: a) baseline (10.3 +/- 2.4 cm H2O for group 1, 9.3 +/- 1.3 cm H2O for group 2); b) 5 cm H2O above baseline; and c) 5 cm H2O below baseline. Measurements obtained with the heat and moisture exchangers were compared with those values obtained using the standard heated hot water humidifier. MEASUREMENTS AND MAIN RESULTS At baseline pressure-support ventilation, the insertion of both heat and moisture exchangers induced in all patients a significant increase in the following parameters: minute ventilation (12.4 +/- 3.2 to 15.0 +/- 2.6 L/min for group 1, and 11.8 +/- 3.6 to 14.2 +/- 3.5 L/min for group 2); static intrinsic positive end-expiratory pressure (2.9 +/- 2.0 to 5.1 +/- 3.2 cm H2O for group 1, and 2.9 +/- 1.7 to 5.5 +/- 3.0 cm H2O for group 2); ventilatory drive, expressed as P41 (2.7 +/- 2.0 to 5.2 +/- 4.0 cm H2O for group 1, and 3.3 +/- 2.0 to 5.3 +/- 3.0 cm H2O for group 2); and work of breathing, expressed as either power (8.8 +/- 9.4 to 14.5 +/- 10.3 joule/ min for group 1, and 10.5 +/- 7.4 to 16.6 +/- 11.0 joule/min for group 2) or work per liter of ventilation (0.6 +/- 0.6 to 1.0 +/- 0.7 joule/L for group 1, and 0.8 +/- 0.4 to 1.1 +/- 0.5 joule/L. for group 2). These increases also occurred when pressure-support ventilation was both above and below the baseline level, although at high pressure support the increase in work of breathing with heat and moisture exchangers was less evident. Gas exchange was unaffected by heat and moisture exchangers, as minute ventilation increased to compensate for the higher deadspace produced in the circuit by the insertion of heat and moisture exchangers. CONCLUSIONS The tested heat and moisture exchangers should be used carefully in patients with acute respiratory failure during pressure-support ventilation, since these devices substantially increase minute ventilation, ventilatory drive, and work of breathing. However, an increase in pressure-support ventilation (5 to 10 cm H2O) may compensate for the increased work of breathing.

Protein sparing and protein replacement in acutely injured patients during TPN with and without amino acid supply

The metabolic effects of TPN were studied in a selected group of trauma patients. Nineteen patients were randomly divided into two groups: the first was treated with glucose and insulin, the second with glucose, insulin and amino acids. Each patient in both groups received TPN isocaloric with respect to daily energy output and the treatment lasted five days. Each group was further divided into two subsets (severe or moderate catabolism) according to fasting energy output with respect to the expected energy expenditure. During the acute flow phase, both in moderate as well as in severe catabolism, glucose and insulin were effective for protein sparing; the maximum protein sparing effect was reached when giving a caloric intake equal to 130% of daily energy output. Glucose, insulin and amino acids were effective in replacement of nitrogen losses. In moderately catabolic patients nitrogen balance was significantly better than in severely catabolic patients. This study shows that early and short-term TPN is effective in controlling the flow phase of trauma. Glucose and insulin appear to be the determinants of the protein sparing effect when given in amounts equal to those needed; amino acids provided protein replacement when given in amounts equal to about 20% of energy output. Energy supply higher than 120–130% of daily energy output does not increase protein sparing and protein replacement, the only effect being a further increase in metabolism, which is possibly dangerous in critically ill patients.

Influence of Total Parenteral Nutrition on Protein Metabolism following Acute Injury: Assessment by Urinary 3-Methylhistidine Excretion and Nitrogen Balance

The use of total parenteral nutrition after acute injury, either surgical or accidental, is widely accepted for its important benefits, although it is not yet completely understood whether a reduction of body protein catabolism can be effectively achieved. We applied total parenteral nutrition to 14 critically ill patients after either trauma or major surgery. Their daily nitrogen balance, urinary 3-methylhistidine and creatinine excretion, and molar 3-methylhistidine/creatinine ratio, during initial 24-hr fasting period, were respectively -0.19 +/- 0.01 (SEM) g kg-1, 5.46 +/- 0.47 mumol kg-1, 27 +/- 4 mg kg-1, and 0.030 +/- 0.005. Daily nonprotein calorie intake of 31.11 +/- 0.58 kcal kg-1, as glucose, and administration of nitrogen 0.350 +/- 0.004 g kg-1, as 10% crystalline L-aminoacids solution, and insulin 1 IU every 5.03 +/- 0.14 g of glucose, resulted in progressive decline of urinary 3-methylhistidine (4.21 +/- 0.43 mumol kg-1, p less than 0.001), creatinine (22 +/- 2 mg kg-1, NS), and their molar ratio (0.022 +/- 0.002, NS). Mean nitrogen balance resulted in 0.032 +/- 0.008 g kg-1. Since urinary 3-methylhistidine role as a marker of protein catabolism is well established, its decrease under total parenteral nutrition together with greatly improved nitrogen balance, demonstrates that our treatment can effectively quench protein catabolism, meanwhile enhancing protein synthesis.

The main determinants of nitrogen balance during total parenteral nutrition in critically ill injured patients

Factors influencing nitrogen balance during total parenteral nutrition have been investigated in 34 critically ill injured patients studied during the first 6 days after trauma. Basal nitrogen balance was severely negative (-0.26±0.12 (SD) g·kg-1), but improved consistently during treatment. Nitrogen intake proved to be the major determinant of a positive, or less negative, nitrogen balance, only secondarily followed by total energy intake corrected to predicted basal energy expenditure, according to multiple regression analysis. The amount of non-protein calories and the non-protein calorie to nitrogen ratio appeared to have little significance on nitrogen balance, when corrected for the two former variables.

Performance of a hydrophobic heat and moisture exchanger at different ambient temperatures

ObjectiveTo evaluate the effect of different room temperatures on hydrophobic heat and moisture exchangers (HME) humidifying capability and efficiency.MethodsStock HMEs were tested in vitro using an already described test model, with separation of inspiratory and expiratory gas. Absolute humidity (AH) was measured by means of dry-wet dual thermocouple, and HME efficiency was computed as the ratio between expired to inspired. AH, at room termperature of 20 and 26°C.ResultsInspired gas temperature and AH were significantly higher at 26 than at 20°C; since expired AH remained substantially unchanged, HME efficiency was also higher in warmer environment.ConclusionsHydrophobic HMEs appear to be affected by room temperature, increasing their humidifying ability and their efficiency with its rise.

Main nitrogen balance determinants in malnourished patients

Factors influencing nitrogen balance during total parenteral nutrition have been investigated in 38 malnourished patients studied for a cumulative period of 280 days. According to multiple regression analysis, nitrogen intake (0.213±0.004 g kg-1 day-1, mean ±SD) proved to be the major determinant of a positive nitrogen balance (0.018±0.004 g kg-1 day-1), followed by non-protein energy intake (43.3±0.5 kcal kg-1 day-1). Total calorie intake to predicted basal energy expenditure and non protein calorie to nitrogen ratios appeared to have little significance on nitrogen balance, when corrected for the two former variables.

Combined use of mask CPAP and minitracheotomy as an alternative to endotracheal intubation : preliminary observation

We describe the combined use of mask CPAP (continuous positive airway pressure) and minitracheotomy as an alternative to conventional endotracheal intubation in 3 patients requiring CPAP, secretion removal and diagnostic procedures such as bronchoalveolar lavage and bronchial cultures. These requirements were fulfilled with the combined technique approach, thus preserving glottic function and avoiding the disadvantages of endotracheal intubation or trachectomy. This approach seems particularly suitable in the treatment of immunocompromised patients because of its reduced invasiveness.

A new active model lung

A new model lung with the capacity for simulated spontaneous breathing is described. It consists of a modified commercial mechanical ventilator (Kontron ABT 4100), connected in parallel to a compliant system, a cylindric acrylic box with a latex thin membrane substituting for the top. Volume and compliance of the model are 2500 ml and 50 ml cmH2O-1, respectively. The modified ventilator simulates physiologic inspiratory flow at a rate of 10 to 30 min-1 and tidal volume up to 1000 ml, with an inspiratory to expiratory time ratio continuously variable between 1:4 and 4:1. The model has been tested under different respiratory assist techniques, connected either to continuous positive airway pressure proved to be reliable, versatile and bearing satisfactory resemblance to human ventilatory physiology.