Moderate Suction Research Articles

Experimental Investigation of Hydro-Mechanical Soil Properties of a Slope Failure

A sudden slope failure occurred in Manisa possibly due to the effect of water infiltration because of a slightly damaged sewage pipe. Considering that there was no other evidence such as rainfall or any loading conditions to trigger the slope failure, a laboratory investigation on the soil’s unsaturated hydro-mechanical properties was initiated. Slopes are naturally unsaturated soils, and they may lose their stability with increased saturation degrees with water infiltration. Thus, for a proper investigation, the unsaturated hydro-mechanical properties of soils should be determined. The results presented in this study are focused on determining the key parameters to evaluate the slope failure for unsaturated soil conditions. In this regard, hydraulic conductivity and suction characteristics and the shear strength parameters were determined as well as the classical geotechnical properties of the soil. Classification of soil was determined as silty sand which is known to have slight to moderate suction stresses and mostly affected suddenly by water infiltration. A flexible-wall permeability test was run with a falling head procedure and the saturated hydraulic conductivity of the soil sample was measured as 1x10-7 m/s. Suction characteristics were detected by filter paper method, besides, the soil water retention curve of the soil was constructed. The maximum matric suction of the soil was measured as 2887 kPa for an air-dried sample. Following, the shear strength parameters were measured by conventional direct shear test for both dry and soaked conditions. Finally, the friction angle due to suction was calculated to be 1.7 degrees from the results of dry and saturated shear strength parameters.

653 Capillary Suction Device-a Novel Approach to Negative Pressure Wound Therapy

Abstract Introduction Negative Pressure Wound Therapy (NPWT) is a well-established procedure used for non-healing wounds including burn wounds. In NPWT, a special sealed dressing of large cell foam (>400 µm) or gauze is connected to a pump. The sealed dressing acts as a conduit to pressure transfer and aids in the passive flow of fluid. Most commonly, negative pressures between -10 and -125 millimeters of mercury (mm Hg) are used. The mechanism of healing is unknown but maybe due to removal of the exudate and bacteria, and the stimulation of tissue repair through micro deformation. Reticulated foams with micron-size open cells (100 to 5µm) exerts capillary suction between 10 and 60 mm of Hg with a multilayered foam dressing. The negative pressures produced are within the range of suction by mechanical pumps. Therefore, the long-term goal our research is to examine effectiveness of Capillary Suction Devices (CSD) as a topical device in both preventing and healing complicated wounds, burn and donor site wounds. Our hypothesis is that CSD is an effective, safe and lower cost alternative to vacuum-assisted NPWT. Methods Yorkshire pigs received 4 surgical posterior excision wounds, measuring 2 in. by 2 in. The wounds were covered with a NPWT dressing (110 mm Hg negative pressure by a pump), CSD with capillary suctions of 30 mm Hg (CSD-30) and 60+ mm Hg (CSD-60), and a conventional gauze dressing. The wounds were measured on 2 day and then every 4 to 5 days until wounds closed. We also measured and compared the total fluids collected with each dressing. Results By post-wound day 20, the wounds treated with CSD-60 and NPWT were 100% closed while the wounds treated with CSD-30 and gauze were 65 and 45%, respectively. This indicated comparable wound closure efficacies for CSD-60 and NPWT. The CSD-30 product was superior to gauze, but less efficacious than the tested NPWT protocol. The average total fluid uptake measured in grams dry weight were similar for CSD-60 and NPWT, 36 and 38g., respectively while the values were 24g for CSD-30 and 12g for gauze. However, the maximum fluid uptake observed at day 2 indicated that CSD-60 and CSD 30, 24 and 14g respectively, were superior to NPWT and gauze 12 and 7g respectively. Conclusions This data indicates comparable wound closure efficacies for CSD-60 capillary suction and NPWT. The CSD product with 30 mmHg suction was superior to gauze, but less efficacious than NPWT or CSD-60 protocol. The study results provide impetus for further research on the use of high suction CSD for replacement of pump mediated NPWT and the moderate suction CSD for preventing progression of high-risk wounds to an ulcerous stage. Applicability of Research to Practice This small study suggests that CSD maybe alternative in to NPWT. CSD provides a significant cost and weight advantage to the patient, as well is allowing for increased mobility.

Field‐Obtained Soil‐Water Characteristic Curves of KPK Expansive Soil and Their Prediction Correlations

Expansive clays are found worldwide in arid and semiarid regions. Such soils are considered a natural hazard for civil engineering infrastructures especially when they are lightly loaded. Expansive soils are often unsaturated due to the high absorption capacity of moisture. The damaging effect of expansive soils is intimately related to the distinctive soil‐water characteristic in the surficial soil layers subjected to wetting‐drying cycles. The soil‐water characteristic curve (SWCC) also known as the water‐retention curve shows the fluctuation of suction with the moisture content. It is one of the key parameters that have been developed and used by soil engineers for studying the properties of partially saturated soils. Currently, the SWCCs produced by most of the researchers are grounded on lab testing which is quite different from the field‐obtained curves. In the current study, the SWCCs for Karak expansive soil have been obtained from in situ testing (field). For this purpose, three sites were selected at Amberi Village (Karak) for instrumentation. An open trench of six‐foot depth was excavated in each site and instrumented. Electrical resistivity sensors (G‐blocks) and tensiometers were used for matric suction measurements. The gravimetric moisture content was measured with the help of moisture sensors calibrated with a speedy moisture meter. To check the fluctuation of moisture and suction, these instruments were installed at three different depths, that is, 0–2, 2–4, and 4–6 feet. Based on results, the maximum suction of 705.79 kPa was observed in the site “A” in 0–2‐foot depth (near the ground surface) with a moisture content of 15 percent. The variations in suction and moisture content follow the almost same trend at low suction; however, the trend was slightly different at the moderate suction range. The measured suction showed a strong correlation with the free swell index (FSI) and moisture content. It was found that the upper layers of expansive soil have high suction than lower layers due to more exposure to the environmental agencies and low density.

An improved reservoir for the flushing test to diagnose shunt insufficiency.

OBJECTIVE Reservoirs integrated into hydrocephalus shunts are commonly used for the removal of CSF and for intra-ventricular pressure measurement. Pumping with the reservoir to diagnose shunt sufficiency is still a matter of controversy. The authors describe an improved flushing device and its characteristic features in vitro and in vivo. METHODS The flushing reservoir is constructed with a sapphire ball in a cage as a nonresistance valve to also enable the detection of distal occlusions. The most important reservoir parameters were investigated in vitro, simulating total and partial proximal and distal shunt occlusions. Then the expected advantages were assessed in vivo by evaluating the pump test data of 360 implanted reservoirs. The results were compared with those found in the literature. RESULTS The optimization of the technical parameters of the device, such as the high stroke volume in combination with moderate suction force, are obvious advantages compared with other flushing devices. Total occlusion of the ventricular catheter and the valve could be assessed with high certainty. The detection of a total obstruction of the peritoneal catheter or any partial obstruction is also possible, depending on its exact grade and location. CONCLUSIONS Shunt obstructions can be assessed using the pumping test. The reservoir construction presented here provides a clear enhancement of that diagnostic test.

Alcohol ablation of pericardial cysts under pericardioscopical control

Pericardial cysts are rare. They are often asymptomatic mediastinal abnormalities, which are usually congenital. If symptomatic differential diagnosis can pose a diagnostic challenge since it has to consider the different causes of pericardial effusion including malignant forms. In 2 symptomatic female patients (aged 51 and 58years) pericardiocentesis, pericardioscopy and pericardial fluid analysis confirmed the diagnosis of "spring water cysts." Pericardioscopy excluded protrusions, petechial bleeding, neovascularization or inflammation. Application of contrast media into the cyst confirmed by radiological control that no communication to the true pericardial sac was present. So after aspiration of the entire fluid, subsequent instillation of 10ml ethanol for a few minutes was carried out to prevent recurrence of the cystic formation. The aspiration of the residual fluid under moderate suction demonstrated and 24-h clinical observation at the ICU completed the short intervention. All symptoms were relieved immediately in both patients. Recurrence was not observed in the follow-up.

Turbulent asymptotic suction boundary layers studied by simulation

The turbulent asymptotic suction boundary layer (ASBL) is studied using numerical simulations. Uniform suction is applied on the wall in order to compensate for the momentum loss inflicted by the wall friction. Four Reynolds numbers, defined as the ratio of free-stream velocity and suction rate, Re = 333, 400 and 500, are considered, whereas Re = 280 relaminarised. In agreement with previous studies, suction causes the fluctuation intensities to decrease, and the near-wall anisotropy to increase. The shape of the mean velocity profile is considerably changed yielding a decreased slope in the overlap region. It is shown that even for moderate suction rates large values for the friction Reynolds number Reτ = δ99+ are obtained; at Re = 333 a value of Reτ = 1900 is reached and Re = 400 yields Reτ = 5700. Artificially using smaller computational domains, limiting the size of the largest turbulent structures, gives unexpected results: The mean velocity profile starts to show a distinct wake region which only disappears for large enough domains. Moreover, the boundary layer thickness δ99 strongly depends on the chosen domain size. Spectral maps of the flow are analysed, showing an outer peak appearing at a spanwise size of about 0.6δ99, albeit with considerably lower amplitude compared to cases without suction. Visualisations of the flow are also discussed.

Application of boundary layer suction for reducing hydrophone sensing noise

One of the leading noise sources for hydrophone arrays on moving vessels is hydrodynamic noise which results from the presence of turbulent boundary layers. This ongoing experimental study explores the impact boundary layer suction has on reducing the hydrodynamic pressure fluctuations and thereby increasing the signal to noise ratio for sensing. A custom hydrophone array is used to capture the pressure signatures with and without boundary layer suction under 2D fully developed turbulent boundary layers with momentum thickness Reynolds numbers ranging from 2000–4000. The first generation suction device shows a reduction in noise of up to 50% with moderate suction intensities. The current focus is on observing the effect suction has on the boundary layer velocity field using both single point laser Doppler anemometry and 2D particle image velocimetry. This information will provide insight into how the hydrodynamic structures are being removed and will provide a basis for the development of future optimized suction devices.

Asymptotic analysis of the small-scale structure of the laminar boundary layer with suction

Unwanted regimes of boundary layer suction when organized vortex structures known from experience arise have been determined. To this end, we performed an inspection analysis of the three-scale problem of the flow past a perforated boundary on the assumption that the inner scale equal to the perforation period is small compared to the outer scale characterizing the global problem. An asymptotic classification of suction regimes is given. The classical boundary layer problem — moderate suction — has been investigated in detail.

Mechanical Suction: An Effective and Safe Method to Remove Large and Tenacious Clots From the Urinary Bladder

To describe an alternative technique for removing tenacious and chronic clots by applying stronger suction pressure through the cystoscope sheath in patients who had failed clot evacuation using the traditional Ellik evacuator. In this method, either the 25-F cystoscope sheath or 26-F resectoscope sheath was directly attached with the tubing from centralized suction source, and moderate negative pressure (up to 250 mm Hg) was applied. This technique was used in 15 adult patients with clot retention. Average duration for clot retention was 36.5 hours (range 22-60 hours). All patients were rendered clot free in an average operative period of 88 minutes (range 60-120 minutes). At the end of the procedure, apart from punctuate hemorrhagic spots on the bladder mucosa, no complications were encountered. Clots that are old, large, and tenacious can be effectively and safely evacuated by applying moderate suction pressure from central suction source directly through the cystoscope sheath.

A Control System for Rotary Blood Pumps Based on Suction Detection

A control system for rotary ventricular assist devices was developed to automatically regulate the pumping speed of the device to avoid ventricular suction. The control system comprises a suction detector and a fuzzy logic controller (FLC). The suction detector can correctly classify pump flow patterns, using a discriminant analysis (DA) model that combines several indices derived from the pump flow signal, to classify the pump status as one of the following: no suction (NS), moderate suction (MS), and severe suction (SS). The discriminant scores, which are the output of the suction detector, were used as inputs to the FLC. Based on this information, the controller updates pump speed, providing adequate flow and pressure perfusion to the patient. The performance of the control system was tested in simulations over a wide range of physiological conditions, including hypertension, exercise, and strenuous exercising for healthy, sick, and very sick hearts, using a lumped parameter model of the circulatory system coupled with a left ventricular assist device. The controller was able to maintain cardiac output and mean arterial pressure within acceptable physiologic ranges, while avoiding suction, demonstrating the feasibility of the proposed control system.

Mechanosensitive channel properties and membrane mechanics in mouse dystrophic myotubes

Muscular dystrophy is associated with increased activity of mechanosensitive channels (MSCs) and increased cell calcium levels. MSCs in patches from mdx mouse myotubes have higher levels of resting activity, compared to patches from wild-type mice, and a pronounced latency of activation and deactivation. Measurements of patch capacitance and geometry reveal that the differences are linked to cortical membrane mechanics rather than to differences in channel gating. We found unexpectedly that patches from mdx mice are strongly curved towards the pipette tip by actin pulling normal to the membrane. This force produces a substantial tension (approximately 5 mN m(-1)) that can activate MSCs in the absence of overt stimulation. The inward curvature of patches from mdx mice is eliminated by actin inhibitors. Applying moderate suction to the pipette flattens the membrane, reducing tension, and making the response appear to be stretch inactivated. The pronounced latency to activation in patches from mdx mice is caused by the mechanical relaxation time required to reorganize the cortex from inward to outward curvature. The increased latency is equivalent to a three-fold increase in cortical viscosity. Disruption of the cytoskeleton by chemical or mechanical means eliminates the differences in kinetics and curvature between patches from wild-type and mdx mice. The stretch-induced increase in specific capacitance of the patch, approximately 80 fF microm(-2), far exceeds the specific capacitance of bilayers, suggesting the presence of stress-sensitive access to large pools of membrane, possibly caveoli, T-tubules or portions of the gigaseal. In mdx mouse cells the intrinsic gating property of fast voltage-sensitive inactivation is lost. It is robust in wild-type mouse cells (observed in 50% of outside-out patches), but never observed in mdx cells. This link between dystrophin and inactivation may lead to increased background cation currents and Ca2+ influx. Spontaneous Ca2+ transients in mdx mouse cells are sensitive to depolarization and are inhibited by the specific MSC inhibitor GsMTx4, in both the D and L forms.

Drainage after total knee replacement

AbstractA simple lumped hydraulic model of knee drainage following arthroplasty is developed incorporating a pressure-volume equation of state for the knee capsule and a wound healing rate dynamically retarded by the blood flow-induced shear stress. The resulting second-order nonlinear ordinary differential system is examined numerically and qualitatively to map the parameter space. In the model, moderate suction or a slight back-pressure promotes gradual drainage and healing whereas excessive suction can lead to a bifurcation in which healing is retarded or even prevented. Guided, then, by the model, the literature, and experience, continuous drainage with a small constant back-pressure appeared beneficial so we prospectively evaluated a series of ten patients. The results are consistent with the model and promising.

Invited commentary

Dr Brunelli and colleagues have presented another important study on the common problem of air leaks. This trial is well designed, performed, analyzed, and written. On the surface, their findings seem to be contrary to the ones Marshall and we have reported. However careful scrutiny of Brunelli's data actually shows that it may support the findings in those previous prospective studies. The management of chest tubes is only one way to manage air leaks. Intra-operative preventative measures rather than post-operative management are always more important for any post-operative complication. Some intra-operative techniques include: fissure-less surgery, sealants, buttressing of staple lines, pneumoperitoneum, and pleural tents. Although chest tube management is important in patients with an air leak, the advantage of one chest tube setting over another becomes weakened when air leaks are small. In this study the authors have nicely shown that when a pleural tent is used, the setting of the chest tube makes little difference. This is of little surprise. Unfortunately, the previously reported classification of air leaks and an air leak meter were not used in this study, but the natural history of the leaks in this series suggests that many were small. When one eliminates the patients who had pleural tents, which the authors essentially do for us in Table 4, their own data begin to show the advantages of water seal. The numbers may be too small to show a statistically significant difference but the air leak duration was 5.4 days compared with 7.0 days and the “air leak days/cm of staple line” was only 0.08 compared with 0.12, both favoring the water seal group. Thus, perhaps a better title for this paper may be “Pleural Tents After Upper Lobectomy Negate the Advantages of Placing Chest Tubes on Water Seal.” This finding is also not unexpected because this group has already shown the advantage of a pleural tent after upper lobectomy in a very well done prospective randomized study that was recently published. Finally, why do the authors choose to use water seal in patients who had no air leak and were excluded in this study? We prefer suction in these patients since water seal seems to offer no real advantage. Furthermore, I am perplexed as to why they conclude the paper with the statement: “Based on the results of this analysis our current practice is to use moderate suction (−10 cm H2O) overnight and water seal during the day.” The authors never even studied −10 cm of suction and found no advantage to water seal and potential harm. Why is this now their preferred protocol? We are indebted to Dr Brunelli and colleagues for once again heightening our awareness of the problem of air leaks and for a well-done prospective randomized study. Perhaps more studies are needed to examine patients who undergo lobectomy only. Their finding that water seal may lead to increased complications is provocative. It would be easy to do a prospective randomized trial that only studied patients who underwent lobectomy and to recruit enough patients in the study so one could generate the statistical power needed to fully assess the advantages and disadvantages of water seal versus suction [1Marshall M.B Deeb M.E Bleier J.I.S Suction versus water seal after pulmonary resection, a randomized prospective study.Chest. 2002; 121: 831-835Crossref PubMed Scopus (139) Google Scholar, 2Cerfolio R.J Bass C Katholi C.R A prospective randomized trial compares suction versus water seal for air leaks.Ann Thorac Surg. 2001; 71: 1613-1617Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar, 3Brunelli A Al Rafai M Monteverde M Borri A Salati M Pleural tent after upper lobectomy a randomized study of efficacy and duration of effect.Ann Thorac Surg. 2002; 74: 1958-1962Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar].

Normalization based on the active motion in a turbulent boundary layer

A comparison between the inner regions of self-preserving turbulent boundary layers over an impervious wall and a porous surface with a uniform moderate suction rate indicates that, in each case, the relevant velocity and length scales are those of the ‘‘active’’ motion. There is close agreement between the two flows for velocity and temperature variances and longitudinal heat fluxes when the measurements are conditioned on only the negative part of the Reynolds shear stress and are normalized by the scales of the active motion

Chloride channels activated by osmotic stress in T lymphocytes.

We have used whole-cell and perforated-patch recording techniques to characterize volume-sensitive Cl- channels in T and B lymphocytes. Positive transmembrane osmotic pressure (intracellular osmolality > extracellular osmolality) triggers the slow induction of a Cl- conductance. Membrane stretch caused by cellular swelling may underlie the activation mechanism, as moderate suction applied to the pipette interior can reversibly oppose the induction of Cl- current by an osmotic stimulus. Intracellular ATP is required for sustaining the Cl- current. With ATP-free internal solutions, the inducibility of Cl- current declines within minutes of whole-cell recording, while in whole-cell recordings with ATP or in perforated-patch experiments, the current can be activated for at least 30 min. The channels are anion selective with a permeability sequence of I- > SCN- > NO3-, Br- > Cl- > MeSO3- > acetate, propionate > ascorbate > aspartate and gluconate. GCl does not show voltage- and time-dependent gating behavior at potentials between -100 and +100 mV, but exhibits moderate outward rectification in symmetrical Cl- solutions. Fluctuation analysis indicates a unitary chord conductance of approximately 2 pS at -80 mV in the presence of symmetrical 160 mM Cl-. The relationship of mean current to current variance during the osmotic activation of Cl- current implies that each cell contains on the order of 10(4) activatable Cl- channels, making it the most abundant ion channel in lymphocytes yet described. The current is blocked in a voltage-dependent manner by DIDS and SITS (Ki = 17 and 89 microM, respectively, at +40 mV), the degree of blockade increasing with membrane depolarization. The biophysical and pharmacological properties of this Cl- channel are consistent with a role in triggering volume regulation in lymphocytes exposed to hyposmotic conditions.

Mechanosensory calcium‐selective cation channels in epidermal cells

This paper explores the properties and likely functions of an epidermal Ca(2+)-selective cation channel complex activated by tension. As many as eight or nine linked or linkable equivalent conductance units or co-channels can open together. Open time for co-channel quadruplets and quintuplets tends to be relatively long with millimolar Mg2+ (but not millimolar Ca2+) at the cytosolic face of excised plasma membrane. Sensitivity to tension is regulated by transmembrane voltage and temperature. Under some circumstances channel activity is synchronized in rhythmic pulses. Certain lanthanides and a cytoskeleton-disturbing herbicide that inhibit gravitropic reception act on the channel system at low concentrations. Specifically, ethyl-N-phenylcarbamate promotes tension-dependent activity at micromolar levels. With moderate suction, Gd3+ provided at about 0.5 microM at the extracellular face of the membrane promotes for several seconds but may then become inhibitory. Provision at 1-2 microM promotes and subsequently inhibits more vigorously (often abruptly and totally), and at high levels inhibits immediately. La3+, a poor gravitropic inhibitor, acts similarly but much more gradually and only at much higher concentrations. These properties, particularly these susceptibilities to modulation, indicate that in vivo the mechanosensitive channel must be mechanosensory and mechanoregulatory. It could serve to transduce the shear forces generated in the integrated wall-membrane-cytoskeleton system during turgor changes and cell expansion as well as transducing the stresses induced by gravity, touch and flexure. In so far as such transduction is modulated by voltage and temperature, the channels would also be sensors for these modalities as long as the wall-membrane-cytoskeleton system experiences mechanical stress.

Mechanosensory calcium-selective cation channels in epidermal cells.

This paper explores the properties and likely functions of an epidermal Ca(2+)-selective cation channel complex activated by tension. As many as eight or nine linked or linkable equivalent conductance units or co-channels can open together. Open time for co-channel quadruplets and quintuplets tends to be relatively long with millimolar Mg2+ (but not millimolar Ca2+) at the cytosolic face of excised plasma membrane. Sensitivity to tension is regulated by transmembrane voltage and temperature. Under some circumstances channel activity is sychronized in rhythmic pulses. Certain lanthanides and a cytoskeleton-disturbing herbicide that inhibit gravitropic reception act on the channel system at low concentrations. Specifically, ethyl-N-phenylcarbamate promotes tension-dependent activity at micromolar levels. With moderate suction, Gd3+ provided at about 0.5 micromole at the extracellular face of the membrane promotes for several seconds but may then become inhibitory. Provision at 1-2 micromoles promotes and subsequently inhibits more vigorously (often abruptly and totally), and at high levels inhibits immediately. La3+, a poor gravitropic inhibitor, acts similarly but much more gradually and only at much higher concentrations. These properties, particularly these susceptibilities to modulation, indicate that in vivo the mechanosensitive channel must be mechanosensory and mechanoregulatory. It could serve to transduce the shear forces generated in the integrated wall-membrane-cytoskeleton system during turgor changes and cell expansion as well as transducing the stresses induced by gravity, touch and flexure. In so far as such transduction is modulated by voltage and temperature, the channels would also be sensors for these modalities as long as the wall-membrane-cytoskeleton system experiences mechanical stress.

Rapid adaptation of single mechanosensitive channels in Xenopus oocytes.

Mechanosensitive (MS) channels are expressed in a wide range of cell types and have been implicated in diverse functions, including osmoregulation and mechanoreception. The majority of previous studies on single MS channels have been carried out on nonsensory cells and have dealt with the steady-state properties of the channel. Here we measure the dynamic or nonstationary properties of the MS channel in Xenopus laevis oocytes. MS channels open transiently in response to a step change in suction applied to the membrane patch. This adaptive behavior occurs because of a reduction in open channel probability rather than a decrease in channel conductance. Double-step suction protocols indicate that adapted MS channels can be reactivated by application of stronger stimulation, consistent with a change in gating sensitivity rather than channel inactivation. Adaptation is highly voltage dependent, being most evident at resting or hyperpolarized potentials and absent at strongly positive potentials. Neither adaptation nor its voltage sensitivity requires the presence of extracellular Ca2+. Adaptation is fragile, dependent on patch history, and can be irreversibly abolished by moderate suction applied to the patch while MS channel activity is retained. Further suction can abolish MS channel activity without compromising the seal. We propose that the selective loss of adaptation and MS channel activity is due to different stages of membrane-cytoskeleton decoupling caused by the mechanical stresses associated with patch clamp recording.

Normalization for a turbulent boundary layer with wall suction

When a moderate suction rate is applied at the wall of a turbulent boundary layer, the normalized distributions of the Reynolds stresses, temperature variance, and heat fluxes in the inner region are analogous to those obtained without suction, provided the normalization is based on local maxima of the Reynolds shear stress and turbulent heat flux instead of the wall shear stress and the wall heat flux.

Continuous Arteriovenous Haemofiltration and Haemodiafiltration in Acute Renal Failure

Continuous arteriovenous haemofiltration (CAVH) was employed in ten patients with acute renal failure using an AN-69 plate filter. Special measures were taken to improve the efficiency of the technique, including the use of short, large-bore catheters for vascular access, predilution infusion of the substitution fluid, and moderate vacuum suction to the ultrafiltrate compartment. In five patients continuous arteriovenous haemodiafiltration was performed by the addition of slow dialysis at a dialysate flow of 1 litre per hour. This technically simple manoeuvre enhanced solute clearances up to 20 ml/min and obviated the need for standard intermittent dialysis sessions in all cases. Repeated measurements of transmembrane pressure and ultrafiltration rate permitted calculation of the in vivo membrane permeability index, which showed a reproducible decline with time. With relatively low heparin requirements an adequate filter performance could be maintained for over 48 h. The encouraging clinical results indicate that CAVHD, in spite of the invasive nature of this technique, may be considered a first-choice treatment for patients with acute renal failure in the intensive care unit.