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.

[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.

[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.

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)).

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.

[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.

[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.

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.

[Steps for solutions and hindrances in progress in relation to an implantable bio-artificial hemofilter-intestine-hybrid kidney]. / Lösungsschritte und Hindernisse auf dem Wege zu einer implantierbaren bioartifiziellen Hämofilter-Darm-Hybridniere.

On the view of 1989 older and modern developments to a bioartificial implantable hybrid kidney are presented. To the realization proof of the implantable hemofilter-intestine-hybrid kidney the routes were described in an experimental rat model to the plasmakinetic simulation of the urea and sodium level as a marker of the hybrid kidney functions. The results of the bioartificial hemofilter-intestine-hybrid kidney development are presented, but significant detail problems must be solved, especially the hemofilter biocompatibility problem.

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.

[Hemorheological/hemodynamic study on miniaturized capillary filters in the concept of an implantable artificial kidney]. / Hämorheologische/hämodynamische Untersuchungen an miniaturisierten Kapillarfiltern im Entwicklungskonzept für eine implantierbare künstliche Niere.

The conception of an implantable kidney provides the substitute of the non-functioning kidney by a technical-biological system. The filtration function is to be performed by a capillary hemofilter. The results obtained in an open test circulation on 3 filters produced by optimum aspects were represented and compared with the physiological performance parameters of the kidney. The special importance of the construction of the flow conditions in the single capillary is accentuated as the fundamental aspect for additional optimization. An optimized capillary filter produced the necessary filtration rate for maintaining the homeostasis on condition of a low-protein diet and an increased level of blood urea. The changes of the hemorheologic parameters is to come up by an adequate absorption of fluid in the colon.

[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.

[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.

[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.

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.

[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.