G. Damia

The role of total static lung compliance in the management of severe ARDS unresponsive to conventional treatment

A group of 36 patients with severe adult respiratory distress syndrome (ARDS) meeting previously established blood gas criteria (mortality rate 90%) became candidates for possible extracorporeal respiratory support [low frequency positive pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCO2R)]. Before connecting the patients to bypass we first switched the patients from conventional mechanical ventilation with positive end expiratory pressure (PEEP) to pressure controlled inverted ratio ventilation (PC-IRV), and then when feasible, to spontaneous breathing with continuous positive airways pressure (CPAP). Forty eight hours after the patients had entered the treatment protocol, only 19 out of the 36 patients in fact required LFPPV-ECCO2R, while 5 were still on PC-IRV, and 12 were on CPAP. The overall mortality rate of the entire population was 23%. The only predictive value of success or failure of a particular treatment mode was total static lung compliance (TSLC). No patients with a TSLC lower than 25 ml (cm H2O)-1 tolerated either PC-IRV or CPAP, while all patients with a TSLC higher than 30 ml (cm H2O)-1 were successfully treated with CPAP. Borderline patients (TSLC between 25 and 30 ml (cm H2O)-1) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if Paco2 rose prohibitively. We conclude that TSLC is a most useful measurement in deciding on the best management of patients with severe ARDS, unresponsive to conventional treatment.

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.

Hemodynamics and renal function during low frequency positive pressure ventilation with extracorporeal CO2 removal. A comparison with continuous positive pressure ventilation.

Six lambs were anesthetized and connected in venouvenous mode to a Membrane Lung for Extracorporeal CO2 removal. The animals underwent several hours periods of continuous positive pressure ventilation (CPPV), at 5 cmH2O positive end expiratory pressure (PEEP), alternated with several hours periods of low frequency positive pressure ventilation (5 cmH2O PEEP, 2 b.p.m.) with extracorporeal CO2 removal (LFPPV-ECCO2R). During LFPPV-ECCO2R compared with CPPV, cardiac output increased by 26%, pulmonary vascular resistances and systemic vascular resistances decreased by 28% and 22% respectively. The renal function improved significantly during LFPPV-ECCO2R compared with CPPV, i.e. urinary flow, creatinine clearance and osmolar clearance increased by 50%, 37% and 52% respectively. In these experiments LFPPV-ECCO2R, a form of completely artificial ventilation, seems to prevent hemodynamic and renal complications of CPPV.

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.

Influence of parenteral nutrition on leg nitrogen exchange in injured patients.

Body N balance, 3-methylhistidine (MEH) excretion, amino acid (AA) plasma concentration, and fluxes across the leg were investigated both during fasting and during parenteral nutrition of injured patients in order to better understand protein-sparing mechanisms induced by metabolic support in the whole body and in skeletal muscle. Patients were randomized to receive 15 or 30 kcal/kg·day coupled with 0.30 g of N either with standard or branch-chain (BC)-enriched AA solutions. During fasting, patients were highly catabolic (N balance −14.7 ± 1.2 g N/m2·day, MEH excretion 422 ± 25 μmol/m2 · day) and showed a high efflux of AA N from the leg (5.08 ± 2.1 g N/m2 · day) without difference between the groups. During treatment, body N balance (-5.55 ± 0.88, p < .001) and MEH excretion (284 ± 20, p < .001) were significantly reduced without difference among the groups; also, AA N leg efflux (2.64 ± 0.47, p < .001) was reduced. Moreover, considering the effect of calorie load, patients receiving 30 kcal/kg · day showed a lower efflux of total AA N and of some AA considered as markers of muscle protein catabolism, such as phe, lys, met, and glu. The main difference between solutions was in the efflux of BCAA; particularly, val and leu efflux was turned into uptake in the BCAA group. No significant difference among the groups was found in N balance and MEH excretion during treatment. In brief, muscle catabolism was reduced in an amount dependent on glucose and insulin load, but it was not influenced by BCAA supply. Whole body net protein catabolism was reduced through different mechanisms, either an increased visceral N retention or a decreased muscle N loss. However, muscle N loss was never abolished even in the high calorie groups.

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.

Comment on the paper “The importance of the circuit capacity in the administration of CPAP”

The difference between the slope in the straight portion of the V/P curve and the TSLC was lower in group A 14.0 + 9.7 (data from the 7 pts presenting an inflection point) and in group B 15.0_+ 7 than in group C 21.96 _+ 8.4. Noting that 4 patients in group A did not present any inflection point and that the remaining 7 presented a lower slope TSLC it seems possible to suggest that patients in group A (undergoing LFPPV-ECCO2R ) presented not only a lower TSLC but also a straighter curve. Further studies are required in a larger number of patients to clarify this point. The number of patients appears too low to draw any conclusion about differences in terms of V/P curves, among survivors and non-survivors, in patients treated with LFPPV-ECCO2R. However, of 4 patients who did not present an inflection point in group A, 2 survived and 2 did not survive. The slope in the straight part of the V/P curve was slightly higher in survivors (38 _+ 13 ml cm H20-I) than in non-survivors (31 _+12 ml cm H2 Oi ) as was TSLC (28_+4; 25_+9), but in both cases the difference was not statistically significant.