Effect of unidirectional airflow ventilation on surgical site infection in cardiac surgery: environmental impact as a factor in the choice for turbulent mixed air flow.

BACKGROUND: Surgical site infection (SSI) in the form of postoperative deep sternal wound infection (DSWI) after cardiac surgery is a rare, but potentially fatal, complication. In addressing this, the focus is on preventive measures, as most risk factors for SSI are not controllable. Therefore, operating rooms are equipped with heating, ventilation and air conditioning (HVAC) systems to prevent airborne contamination of the wound, either through turbulent mixed air flow (TMA) or unidirectional air flow (UDAF). AIM: To investigate if the risk for SSI after cardiac surgery was decreased after changing from TMA to UDAF. METHODS: This observational retrospective single-centre cohort study collected data from 1288 patients who underwent open heart surgery over 2 years. During the two study periods, institutional SSI preventive measures remained the same, with the exception of the type of HVAC system that was used. FINDINGS: Using multi-variable logistic regression analysis that considered confounding factors (diabetes, obesity, duration of surgery, and re-operation), the hypothesis that TMA is an independent risk factor for SSI was rejected (odds ratio 0.9, 95% confidence interval 0.4-1.8; P>0.05). It was not possible to demonstrate the preventive effect of UDAF on the incidence of SSI in patients undergoing open heart surgery when compared with TMA. CONCLUSION: Based on these results, the use of UDAF in open heart surgery should be weighed against its low cost-effectiveness and negative environmental impact due to high electricity consumption. Reducing energy overuse by utilizing TMA for cardiac surgery can diminish the carbon footprint of operating rooms, and their contribution to climate-related health hazards.

Methods in clinical hemorheology: the continuous measurement of arterial blood density and blood sound speed in man.

Both blood density and sound speed are closely related to total protein concentration in blood and, as a consequence, to rheologically important parameters of blood. Two methods that permit continuous measurement of these properties, the mechanical oscillator technique and the new ultrasonic technique, were used for measuring blood protein concentration over a continuous period of time in a group of hemodialysis patients and in volunteers. It was seen that the concentration of the components of blood varies considerably. This variability is related to transport phenomena within as well as to the flow of masses across the cardiovascular compartment. From the continuous measurement of concentrations during hemodialysis treatment, relative changes in blood volume can be recorded in order to control the fluid balance of the patient. Rapid fluctuations at the macroscopic scale with periods of 5 to 30 seconds are due to heterogeneities at the microscopic scale and to the particular rheological behaviour of the red blood cells at the level of the capillaries and the small blood vessels. The amplitude of rapid oscillations increased up to 1.2% in terms of hematocrit values when there was rhythmic, spontaneous breathing at various frequencies. The measurement of concentrations at an accessible measuring site may be used to investigate the rheology of blood in the human microvasculature.

The measurement of blood density to investigate protein deposition at the blood/hollow fiber membrane interface during ultrafiltration.

Concentration polarization and secondary membrane formation change the membrane hydraulic permeability of capillary filters during hemofiltration reducing initial value filtration rates up to 50%. This leads to a significant loss of filter efficiency which must be taken into consideration when designing filters for long-term application such as in implantable artificial kidneys. By measuring blood density uninterrupted over a period of time using the mechanical oscillatory technique it is possible to follow the dynamics of protein deposition at the interface between the blood and capillary walls. The resulting picture of the deposition behaviour can lead to a better understanding of time-dependent filtration where flow and pressure conditions change. Protein deposition (Pt) with polysulfone membranes in relation to the effective capillary surface was in the range of 2.2. mg/(h x cm2) according to a logarithmic function (Pt = a + b x log(t)).

Experiments with continuous hemofiltration and hemofiltrate regeneration in the rat.

Experimental studies were made with continuous hemofiltration treatment for bilaterally nephrectomized rats and initial observations regarding the effects of such treatment on leukocyte and thrombocyte counts are reported. Hemofiltration of unanesthetized rats able to move freely within their cage could be continued for up to 30 h using a pump-driven ECC system. Blood parameters recorded during this treatment indicate that the detoxification was effective. In another series of experiments the water and electrolyte reabsorption capacity of the colon ascendens of healthy rats was tested by continuously supplying NaCl solution into the colon via a fistula. A large proportion, if not all, of the hemofiltrate can be discharged into the colon without diarrhoea. A final series of experiments showed that the three-stage operation (implantation of permanent catheters, connection of a permanent intestinal fistula and bilateral nephrectomy) is possible with the rat.

[Differentiated characterization of pulmonary diffusion]. / Zur differenzierten Charakterisierung der pulmonalen Diffusion.

The results of Single-Breath-Test with carbon monoxide offers only a rough estimation of the gas exchange situation in the lung as concerns pulmonary diffusion capacity. This statement is related to overestimation of diffusion capacity and reduced possibility to characterize disturbances of pulmonary diffusion function on the basis of values assessed. The proposed six-array-diagram offers the possibility to characterize the disturbances of diffusion more exactly and to differentiate them simultaneously regarding the values determined. So it is possible, to characterize better structural changes of the blood-gas barrier of the lung and to demonstrate compensatory mechanisms.

[Relationship between respiratory reserve in the flow-volume curve and the expected ergometric capacity]. / Zusammenhang zwischen der Atmungsreserve in der Fluss-Volumen-Kurve und der zu erwartenden Ergometrieleistung.

To evaluate the physical work capacity in patients with chronic obstructive lung disease (COLD) it was checked, if determination of breathing reserve can replace the exercise test with blood gas analysis. In 28 patients with lung disease and 7 healthy subjects the flow-volume-curve under resting conditions and during the forced breathing maneuver to measure the breathing reserve and the exercise test with blood gas analysis were examined. A correlation was found between both. Therefore, in patients with COLD the determination of breathing reserve is a practicable method for estimating the physical work capacity, especially in cases with absent breathing reserve. Nevertheless, for medical opinion exercise testing is necessary.

[Functional differentiation of residual volume changes and problems of evaluation from the physiopathologic viewpoint]. / Funktionsdiagnostische Differenzierung der Residual-volumenveränderung und Befundungsprobleme aus pathophysiologischer Sicht.

The ascertainment of the residual volume is a very important method for pulmonary emphysema diagnosis. But there are problems of estimation on the basis of this residual volume. The usual relation (RV/TLC) greater than 0,35 as measure for an emphysema will be considered critically. In this way functional relations will be given which allow a more secure emphysema diagnosis. They use as measure comparisons between RV and fit reference volumes, such as normal values of RV, VC or TLC. These equations make it possible to differentiate between structural and functional disturbances.

[Lower oesophageal sphincter pressure and gastrooesophageal reflux (author's transl)]. / Verschlussdruck des unteren Osophagussphinkters und gastroösophagealer Reflux.

On consecutive days sphincter pressure (pull-through-perfusion manometry) and gastrooesophageal reflux (continuous pH measurements) were determined under basal conditions and after application of pentagastrin (6 microgram/kg b.w.s.c.) in 44 patients. In the half of patients with reflux disturbances of sphincter pressure were not evident under basal conditions and under pentagastrin. In patients with lowered sphincter pressure reflux frequency was found to be higher and single reflux duration was found to be lower than in patients with normal or elevated sphincter pressure.

[Comparative methodologic studies of closing volume and increase in airway resistance volumes]. / Vergleichende methodologische Untersuchungen über das Closing Volume und das Strömungswiderstandsanstiegsvolumen.

The early recognition of obstructive lung diseases plays an important role in the subsequent therapy; the closing volume, determined by means of single-breath oxygen test has been established as a suitable parameter. This technique, however, has not succeeded as a routine method due to prohibitive costs. In a clinical study the closing volume and the easier estimatable so-called flow-resistance elevation volume (Ros-volume-curve parameter obtained from oscilloresistometry/volumetry) were compared and a correlation sought. It could be concluded, that for characterization of small airways diseases the closing volume is a more suitable parameter than the flow-resistance elevation volume.

[Hypoxia, acidosis and nephrology]. / Hypoxie, Azidose und Nephrologie.

In a survey the correlations between hypoxia, acidosis and nephrology are presented. In chronic oxygen deficiency the individual aspects concern the uncertainties of erythropoietin and the carotid-sinusoidal natriuresis stimulated by chemoreceptors. The effects of acute ischaemic hypoxic reactions are described with regard to the acute renal failure. The regulatory renal function of acidification and its disturbance in chronic renal insufficiency as well as the renotubular acidosis are discussed. Finally the authors enter the influence on the renal function during positive pressure respiration (e.g. for the purpose of the normalisation of the pulmonary gas exchange in acute respiratory insufficiency) as well as on reactions of the haemodialysis (bicarbonate and acetate dialysis) to the blood gas and acid-base metabolism, taking into consideration the pulmonary function.

[Effects of the hemodialyzer on blood gases and acid-base equilibrium]. / Einflüsse des Hämodialysators auf Blutgase und Säure-Basen-Haushalt.

During bicarbonate and acetate dialysis the blood gas parameters and the acid-base balance values were measured before and after the dialyzer. Significant changes of these values are revealed after the dialyzer passage of the blood. This result constrains to a decoupled approach of the entire system organism-extracorporeal circulation, when the interpretation of values measured in the arterial part of this system and the judgment of the haemodialysis system following from this are concerned.

[Modelling and simulation of urea balance in a rat model on the condition of large intestine infusion analogous to the ultrafiltrate as a contribution to the development of an implantable intestinal hybrid kidney]. / Modellierung und Simulierung des Harnstoffhaushaltes im Rattentiermodell unter den Bedingungen der ultrafiltratanalogen Dickdarminfusion als Beitrag zur Entwicklung einer implantierbaren Darmhybridniere.

The urea kinetics in blood plasma is discussed for the animal model in rats in the development conception of an implantable artificial kidney, in which the filtration process is received energetically endogenically by a technical hemofilter whereas the ultrafiltrate procedure takes place by intestinal reabsorption and elimination of the end-products. The underlying monocompartment model contains the elements plasma, hemofilter, intestine including their urea turnover rates. Further on a special model conception is developed for the animal experimental designation of the selective urea reflecting power of the intestinal mucosa. The hemofilter-intestine-hybrid kidney-system has chanced to be in order if the experimentally ascertained quantities of the preliminary experiments will be inserted simultaneously for essential parameters in the model experiment.

[Methodologic references for clinical function diagnosis of glomerular permeability selectivity by molecular wight related protein analysis and additional para-aminohippuric acid load]. / Methodologische Hinweise zur klinischen Funktionsdiagnostik der glomerulären Permselektivität durch molekulargewichtsbezogene Proteinanalyse und zusätzlicher Paraamonohippursäure-Belastung.

Glomerular perm selectivity can be approximately estimated from the apparent glomerular protein clearance in terms of molecular weight since the relative protein clearance is approximately identical with the corresponding screen coefficient relation. Systematic relativization of individual protein clearances by reference to albumin (or transferrin) clearance requires the application of special calculations to find out the regression coefficients relevant to functional diagnosis. A PAH load influences tubular protein reabsorption so that the clearance of higher-molecular proteins (IgA alpha 2-macroglobuli, IgM) rises. Taking the changes in protein clearance under renotubular PAH load into account allows a more precise estimation of glomerular permeability to be made, in comparison with protein analyses not using PAH load.

Changes in rheology and red blood cell function under recombinant human erythropoietin therapy.

The rh-EPO is a potent drug to treat renal anaemia. RBC aggregation is not influenced by the rh-EPO therapy. Membrane elasticity and RBC deformability improve remarkably after rh-EPO which might benefit microcirculation. Rh-EPO therapy can not prolong RBC life span. Obviously uremic milieu alone determines RBC life time. Rh-EPO treatment corrects renal anemia by increasing the number of RBC and the RBC volume.

Optimization of hemofilters for the development of implantable artificial kidneys.

The concept of developing an implantable artificial kidney demands, in addition to the regeneration of endogenous filtrate, a small hemofilter with a high filtration rate. Conventional capillary filters are limited in their capacity to yield adequate filtrate, even if the number of capillaries is increased. To improve filter design so as to modify flow conditions for filtration rate augmentation, it is necessary to consider such factors as blood flow through a single capillary, wall shear rate, and transmembrane pressure (ptm) in in vivo applications, where such biological considerations as blood pressure, blood flow, and flow characteristics of blood are important. These requirements lead to a completely new filter type, the "curl filter," characterized by a large effective filtration surface in a relatively small number of hollow fibers in which optimal flow conditions prevail.

[What is the current outlook for an implantable artificial kidney?]. / Welche Aussichten gibt es gegenwärtig für eine implantierbare künstliche Niere?

Considering the homeostatic demands made by the organism on an artificial eliminating substitute kidney system, it seems that the haemofiltrative principle for transporting matter is the most suitable for simulating the natural glomerular kidney function in an implantable artificial kidney. Biophysical laws can be used to influence long-term filtrative efficiency and the blood-flow in the haemofilter system can be controlled by technical feedback regulation. Endogenically, the filtration process is, in terms of energy, driven by the aterial blood pressure (specifically, by the trans-membrane pressure thus generated). The definitive ultrafiltrate treatment takes place by intestinal reabsorption and elimination of the end products, whereby these functions may be assisted by the use of sorbents etc. or an adequate substitution therapy if reabsorption is insufficient. These processes can reasonably be triggered by neurohormonal feedback regulation if the homeostasis situation is greatly disturbed by the haemofiltration process. The implantable artificial kidney is thus a biochemical hybrid kidney.

[The selective elimination function of the colon in a rat model for the substances water and urea in long-term experiments as a contribution to the development of an implantable hemofilter-intestine-hybrid kidney]. / Untersuchungen zur selektiven Eliminationsfunktion des Kolons im Rattenmodell für die Substanzen Wasser und Harnstoff im Langzeitversuch als Beitrag zur Entwicklung einer implantierbaren Hämofilter-Darm-Hybridniere.

The investigations on the selective elimination and preservation function of the colon represented one of the numerous problems in the development of an implantable hemofilter-intestine-hybrid kidney. The assumption of an ideal reflection of urea on the intestinal mucosa and the ability of water absorption of the colon had to be checked. A fluid which is nearly analogous to the ultrafiltrate with different urea concentrations was infused into the colon of rats by a cecocutaneous catheter fistula during two-phasic long-term experiments. The renal and enteral urea elimination rates were defined. The apparent reflection coefficient for urea of the colon amounted 0.5 to 0.6 in an infusion rate of 80 ml/day. The ability of water absorption of the colon in rats of nearly 300 g of weight could be increased up to 200 ml/day during slow and continuous adaptation in the infusion quantity.

[Ergometric results of r-erythropoietin treatment of hemodialysis patients]. / Ergometrische Ergebnisse bei r-Erythropoietin-Behandlung von Hämodialysepatienten.

To investigate the effect of partial correction of anemia in patients maintained by chronic intermittent hemodialysis on exercise capacity, patients underwent a bicycle acido-ergometry before and after treatment with recombinant human erythropoietin. The results demonstrate a (subjective) improvement of exercise capacity without any evidence for that in the pH values.