Evaluation of the end-expiratory pressure by multiple linear regression and Fourier analysis in humans.

This study was designed to compare the end-expiratory pressure (EEP) during mechanical ventilation (MV) measured dynamically (EEPdyn), by multiple linear regression (MLR) of the airway pressure (Pao) vs volume (V) and flow (V') and after Fourier analysis (FA) of the Pao and V'. Pao and V' were recorded from 32 ICU patients (II without respiratory disease, 10 COPD, II ARDS) under MV, at three levels of PEEPe (0, 5 and 10 hPa). Volume was calculated by numerical integration of V'. Data were analysed by MLR and FA, while the actual value of EEPdyn was recognised on the Pao signal at zero V' and V. EEPdyn, EEPMLR and EEPFA were compared for all patients, for each group of patients and for every level of applied PEEPe. Despite the different evaluation of respiratory mechanics between MLR and FA, the EEP values were always not significantly different between the three applied methods (P > 0.05). A high degree of correlation was found between them, taken two at a time (r > 0.99, P < 0.001). Two non-invasive analytical methods for the evaluation of respiratory mechanics during MV, MLR and FA offer a reliable and clinically useful estimation of EEP during MV.

Sulfur hexafluoride (SF6): global environmental effects and toxic byproduct formation.

This work provides information concerning possible global environmental implications and personnel safety aspects that should be considered during the commercial uses of sulfur hexafluoride (SF6). SF6 is an anthropogenically produced compound, mainly used as a gaseous dielectric in gas insulated switchgear power installations. It is a potent greenhouse gas with a high global warming potential, and its concentration in the earth atmosphere is rapidly increasing. During its working cycle, SF6 decomposes under electrical stress, forming toxic byproducts that are a health threat for working personnel in the event of exposure. Several precautions are recommended to avoid personnel exposure to toxic byproducts: oxyfluoride levels or other byproduct concentrations in the operating gas matrix should be traced to predetermine the overall gas toxicity; contaminants should be systematically considered during maintenance, chamber evacuation and system opening process; small SF6 quantities leaking into air or stagnated pollutant concentrations in the operating field should be analyzed and compared to the threshold limit values and permissible exposure levels. New system design rules (i.e., hermetically sealed gas compartments, gas recycling or disposal in the field area) and different handling policies--both during maintenance and final disposal--now should be considered globally to provide for environmental and personnel safety.

Long chain versus medium chain lipids in patients with ARDS: effects on pulmonary haemodynamics and gas exchange.

OBJECTIVE: To compare pulmonary haemodynamic and gas exchange alterations in septic patients with ARDS receiving long-chain triglycerides (LCT) versus medium-chain triglycerides (MCT). DESIGN: Prospective, randomised, clinical study. SETTING: Surgical ICU patients in a University Hospital. PATIENTS: Twenty-one septic patients with ARDS were randomly assigned to receive 50 % of their non-protein caloric requirements as either 20 % LCT (group 1, n = 10) or 20% 1:1 mixture of LCT/MCT (group 2, n = 11). INTERVENTION: Intravenous infusion of LCT and LCT/MCT combinations at a rate of 12 g x h(-1). MEASUREMENTS AND RESULTS: The LCT infusion was associated with an increase of pulmonary venous admixture (Qva/Qt) from 24 % +/- 5 % to 37 % +/- 6 %, an increase of mean pulmonary artery pressure (MPAP) from 25 +/- 5 to 33 +/- 4 mmHg and decrease of PaO2/FIO2 from 240 +/- 30 to 180 +/- 35. LCT/MCT administration was only associated with an elevation of oxygen consumption (VO2) from 329 +/- 14 to 396 +/- 12 ml/ min. During lipid infusion group 1 patients presented higher Qva/Qt (37% +/- 6% vs 25% +/- 4%), MPAP (33 +/- 4 vs 27 +/- 3 mmHg) and VO2 (359 +/- 11 vs 396 +/- 12 ml/min) and lower PaO2/FIO2 (180 +/- 35 vs 235 +/- 30) values compared to group 2. CONCLUSION: In conclusion, we have shown that, in septic patients with respiratory failure, LCT administration was associated with more significant changes of Qva/Qt, MPAP and PaO2/FIO2 compared to infusion of an LCT/MCT 1:1 emulsion. Clinically, these transient alterations might cause serious problems in patients with marginal arterial oxygenation and cardio-respiratory impairment.

A modified per os double contrast examination of the colon in the elderly.

A modified per os double contrast examination of the colon was used in 62 elderly patients in whom conventional barium enema had been unsuccessful. We created endogenous gas generation instead of air insufflation by per os administration of a special mixture containing barium sulfate, lactulose and gastrografin. Good quality double contrast images of the colon were obtained after 12 hours in 59 of the 62 patients. The sensitivity of the method was 100% in 6 patients suffering from carcinoma and in 15 patients suffering from diverticular disease. However, the method failed to demonstrate small solitary polyps in 5 patients and it was also negative in another 27 patients. 7 of these had negative endoscopy and in the remaining a definite diagnosis was not established by any other method. It seems that this method may become an alternative for investigation of suspected colonic pathology in the elderly patients with difficulty in retaining the barium enema.

The inhibitory action of oxygen radical scavengers on proteinuria and glomerular heparan sulphate loss in the isolated perfused kidney.

The perfused isolated kidney is a partial ischemic system that is characterised by glomerular proteinuria and release of glomerular heparan sulfate. Metabolic changes associated with the levels of glutathione, xanthine oxidase and glyceraldehyde 3-dehydrogenase indicated that oxygen radical metabolites were being produced during the perfusion. We have demonstrated that a mixture of oxygen metabolite scavengers containing mannitol, superoxide dismutase and catalase included in the perfusion medium significantly reduced protein excretion. Similar results were obtained with the administration of allopurinol to the rat 24h prior to kidney removal and allopurinol in the perfusion medium. [35S]Heparan sulfate loss from the glomerulus was totally inhibited by the scavenger mixture. These results suggest that reactive oxygen metabolites may be involved in damage to renal capillaries, specifically to heparan sulfate proteoglycan, which leads to proteinuria as a result of partial ischemia produced during perfusion.

Partial ischemia and proteinuria during isolated kidney perfusion is accompanied by the release of vascular [35S]heparan sulfate.

The isolated kidney perfused with modified Krebs-Henseleit buffer with amino acids yields heavy proteinuria associated with reduced ATP levels characteristic of partial ischemia. These conditions are associated with a similar perfusion time dependent release of degraded vascular [35S]heparan sulfate proteoglycan into the perfusate solution which included a 60% loss of [35S]macromolecular material from the glomerulus after 2h of perfusion. Small amounts of [35S]macromolecular material were found in the urine and lymph. These results demonstrate that partial ischemia promotes a specific response in the overall renal vasculature, probably involving oxygen reactive metabolites, that results in the preferential release of heparan sulphate from the basement membrane and endothelial cells on the luminal side of the capillary wall.