Reduction of circulating microemboli in the subclavian vein of patients undergoing haemodialysis using pre-filled instead of dry dialysers.

BACKGROUND: Chronic microembolization that can be demonstrated by pulsed Doppler ultrasound may give rise to pulmonary side-effects during haemodialysis by direct vessel obstruction, increased complement activation or platelet aggregation. The objective of the present investigation was to study whether the use of pre-filled instead of dry dialysers would help to minimize the number of microemboli. METHODS: The study cohort consisted of 23 patients undergoing maintenance haemodialysis. Using a 2 MHz pulsed ultrasound device, the subclavian vein downstream to the dialysis fistula was investigated for 10 min during the dialysis session. The ultrasound examination was performed twice during two successive dialysis sessions, using a pre-filled or a dry dialyser in randomized order. RESULTS: In all patients investigated, numerous microembolic signals (MES) could be observed in the subclavian vein. Treatment with pre-filled dialysers was associated with significantly less MES (82 +/- 94) as compared with dry dialysers (268 +/- 296; P = 0.002). CONCLUSIONS: In comparison to dry dialysers, the use of pre-filled dialysers leads to a significant reduction in microembolization, which may prevent repeated damage to the pulmonary vasculature and, thus, cause less pulmonary damage.     

Identification of microemboli during haemodialysis using Doppler ultrasound.

BACKGROUND: Doppler ultrasound methods were used during haemodialysis sessions for the detection of microemboli and determination of their origin. METHODS: A 2-MHz ultrasound probe (Multidop X(4) DWL((TM))) was used to assess the number of microembolic signals (MES) in the subclavian vein downstream from the arteriovenous fistula before the dialysis session and over two periods of 15 min at the beginning and end of haemodialysis sessions in 25 patients without previous cardiovascular disease. A similar probe was used during in vitro studies to detect MES at different sites in the dialysis machine (before and downstream from the blood pump, and before and downstream from the air trap). RESULTS: No MES were detected during in vivo studies before haemodialysis sessions. MES were registered in all patients (100%) at the beginning and end of the haemodialysis procedure at an average of 12.7+/-9 and 16. 7+/-11.5 signals/min respectively. The average intensity of MES was 19.2+/-5.0 dB and 19.4+/-3.9 dB respectively. No MES were detected on the arterial line during in vitro studies. In contrast, 19+/-6 MES/min were detected after the blood pump, 13+/-4.2 before the air trap, and 16.5+/-5.5 thereafter. CONCLUSIONS: In all patients, MES were recorded during haemodialysis sessions in the drainage vein from arteriovenous fistulae. The results of in vitro studies indicate that MES are formed by the blood pump of the haemodialysis machine. The intensity of the MES suggests that they correspond to synthetic particles or microbubbles, which are not detected by the air trap. The final destination of these microbubbles will be assessed in further studies.     

Patent foramen ovale, dialysis and microembolization

Background: Haemodialysis (HD) circuits are known to produce microemboli. Patent foramen ovale (PFO) may be important in HD patients by allowing right to left intracardiac shunting of microemboli (blood clots or microbubbles), which may pass into the cerebral circulation. Methods: We undertook bubble contrast transthoracic echocardiography to identify PFO in HD patients and in a control population of peritoneal dialysis patients. We interrogated draining arteriovenous fistulae to confirm that microemboli are created during HD. We then undertook transcranial Doppler scanning of the middle cerebral artery before and during dialysis, with and without Valsalva augmentation, to detect cerebral microemboli in HD patients and in the control group. Results: Eighty patients (age 60.4 ± 15.0 years) were recruited to the study. In 12 of 51 HD patients and five of 29 peritoneal dialysis patients a PFO was found (21.3%). Ultrasound scanning of draining arteriovenous fistulae showed a significant difference in the number of microemboli before (1.63 ± 3.47 hits per 5 min) and during (31.6 ± 28.9 hits per 5 min) HD (P = 0.012). However, there was no evidence of microembolization to the middle cerebral artery before or during HD in the study or control groups. Conclusions: Although microemboli are detectable in the draining arteriovenous fistulae of patients undergoing HD, there was no evidence of cerebral microembolization in the middle cerebral artery during HD in those with or without a PFO. The results contrast with previous reports demonstrating microemboli in the carotid circulation during HD.     

Effect of dialysis on serum/plasma levels of free immunoglobulin light chains in end-stage renal disease patients.

BACKGROUND: Free immunoglobulin light chains (FLCs) have previously been shown to be uraemic toxins. In this work we investigated the effect of haemodialysis and haemodiafiltration on the level of FLCs in serum/plasma of uraemic patients. METHODS: Serum/plasma proteins were separated by non-reducing SDS-PAGE and transferred to a nitro-cellulose membrane. FLCs were detected by specific antibodies and an enhanced chemiluminescence detection system. The FLC concentrations were calculated. We studied 15 healthy subjects, 10 patients with chronic renal failure, 71 patients undergoing haemodialysis treatment and 33 patients treated with haemodiafiltration. Different membranes were compared: low- and high-flux polysulfone membranes, low- and high-flux cellulose triacetate membranes, high-flux polymethylmethacrylate and polyacrylonitrile membranes. RESULTS: Chronic renal failure patients showed elevated FLC concentrations as compared with controls. In haemodialysis or haemodiafiltration patients these values were even higher. This was mainly due to an increased concentration of FLC of the lambda-type. The treatment modality per se did not influence the FLC concentrations. Only haemodialysis or haemodiafiltration with the polymethylmethacrylate membrane lead to a significant reduction in FLC concentrations; however, these did not reach control levels. We did not observe differences in FLC levels between patients with different underlying diseases, nor did we find a correlation between age or the duration of the dialysis treatment and FLC concentrations. We found a positive correlation between FLC concentrations at the beginning of dialysis treatment and the amount of IgLCs removed during treatment. However, the average FLC level after treatment did not reach control values. CONCLUSIONS: Currently available haemodialysis or haemodiafiltration treatments are unable to normalize the elevated serum/plasma levels of FLCs in end-stage renal disease patients.     

Broken piece in the lungs: A complication of haemodialysis via subclavian cannulation

For a total of 349 haemodialysis sessions in 35 patients, 50 special subclavian cannulations were performed. The catheters were implanted infraclavicularly by the Seldinger technique. The average duration of the cannulation period was 26.6 days (1–148) and the number of dialysis sessions per catheter was 7 (1–63). Aspects of subclavian cannulation together with indications and complications are described. In three chronically uraemic patients, after 1, 5, and 6 weeks of single-needle haemodialysis, it was noticed that the catheter tip (3–5 cm) inserted into the subclavian vein had broken off. The broken pieces, lodged in the segmental pulmonary arteries, never caused any complication during the observation periods as long as 6, 14 and 33 months. Therefore their removal, either open or transluminal, seemed unnecessary. To prevent complications of similar type it is advisable to avoid single-needle dialysis. Recommended instead is either the double-needle method or the use of a double-lumen catheter.     

Endotoxin transfer through dialysis membranes: small- versus large-pore membranes.

In this in-vivo study, dialysate and serum endotoxin was evaluated before and after haemodialysis with small-pore (PS400) and large-pore (PS600) polysulphone dialysers, and before and after haemodiafiltration with the PS600 filter. The source of the endotoxin was the presence in dialysate of Pseudomonads at a concentration of 10(3)-10(4) CFU/ml. Endotoxin was measured by a modified chromogenic limulus amoebocyte lysate (LAL) assay. In spite of dialysate endotoxin concentrations greater than 100 pg/ml, no changes in pre- versus posttreatment LAL reactivity were observed in PS400 dialysis and PS600 haemodiafiltration. In contrast, PS600 haemodialysis was related to an increase in serum LAL reactivity from 1.3 +/- 1.5 to 3.8 +/- 2.0 pg/ml (n = 15, P less than 0.01), and five patients (33.3%) showed a post-dialysis value in excess of 5 pg/ml. Our data are consistent with the absence of in-vivo endotoxin transfer during haemodialysis with small-pore dialyser membranes, and during haemodiafiltration with membranes with larger pores. An increase in LAL reactivity during haemodialysis with membranes with larger pores is, however, present, presumably due to the occurrence of backdiffusion/filtration with that specific strategy.     

Adequacy of haemodiafiltration

In this study we have evaluated the influence of blood and ultrafiltration flow rate on the performance of five different high-flux membrane dialysers during haemodiafiltration. On the basis of clearance data we optimised the haemodiafiltration schedule of six uraemic patients to maintain an adequate midweek blood urea nitrogen concentration, while reducing the treatment time from 285 +/- 23 min to 210 min. After a follow-up of 6 months, we observed no difference in the clinical tolerance or in the biochemical parameters, compared to those found during the preceding haemodialysis period. Our data confirm the suggestions of other authors that haemodiafiltration is an effective alternative to conventional haemodialysis.     

Solid and gaseous cerebral microembolization during off-pump, on-pump, and open cardiac surgery procedures

BACKGROUND: Neurocognitive dysfunction remains a limitation of cardiac surgery with cardiopulmonary bypass. Intraoperative cerebral microembolization is believed to be one of the most important etiologic factors. Using a new generation of transcranial Doppler ultrasonography, we compared the number and nature of intraoperative microemboli in patients undergoing on-pump and off-pump cardiac surgery procedures. METHODS: Bilateral continuous transcranial Doppler monitoring of the middle cerebral arteries was performed in 45 patients (15 off-pump coronary artery bypass grafting, 15 on-pump coronary artery bypass grafting, and 15 open cardiac procedures). All recordings were performed using a multi-range, multifrequency system to allow both measurement of the number and discrimination of the nature of microemboli in the 3 different groups. RESULTS: The median number (interquartile range) of microemboli in the off-pump coronary artery bypass grafting, on-pump coronary artery bypass grafting, and open procedure groups were 40 (28-80), 275 (199-472), and 860 (393-1321), respectively (P <.01). Twelve percent of microemboli in the off-pump coronary artery bypass grafting group were solid compared with 28% and 22% in the on-pump coronary artery bypass grafting and open procedure groups, respectively (P <.05). In the on-pump groups, 24% of microemboli occurred during cardiopulmonary bypass, and 56% occurred during aortic manipulation (cannulation, decannulation, application, and removal of crossclamp or sideclamp). CONCLUSIONS: Cerebral microembolization is significantly reduced with avoidance of cardiopulmonary bypass. The majority of microemboli occurring during cardiac surgery are gaseous, with a higher proportion of solid microemboli in the on-pump group, and may have a different significance for cerebral injury than solid microemboli. The ability to reliably discriminate gas and solid microemboli may have an important role in the implementation of neuroprotective strategies.     

Changes in pulmonary clearance of technetium labelled DTPA during haemodialysis.

An index of pulmonary epithelial permeability has been studied in 12 patients with chronic renal failure during haemodialysis. It was assessed by the half time clearance from lung to blood (t 1/2 LB) of a nebulised solution containing technetium labelled diethylene triamine pentacetic acid (99mTc DTPA). Six patients were cigarette smokers and six were non-smokers. The non-smokers had greater predialysis permeability (mean 37.7, range 24-54 min) than non-smokers without renal disease (mean 60.2, range 38-99 min; p less than 0.025). The t 1/2 LB was measured before dialysis and during the first half hour and the last half hour of dialysis in all 12 patients and also during other periods of dialysis in 10 of them. Dialysis lasted for five hours in 11 patients and four hours in one patient. There was no significant change in the t 1/2 LB of 99mTc DTPA during early dialysis; but as dialysis progressed there was a statistically significant increase in t 1/2 LB, suggesting a reduction of pulmonary epithelial permeability. These results show no increase in an index of pulmonary epithelial permeability in association with the pulmonary sequestration of neutrophils that occurs in early haemodialysis. They also suggest that in chronic renal failure the epithelial permeability is increased and that this can be modified by haemodialysis.     

Cerebral microemboli during minimally invasive and conventional mitral valve operations

BACKGROUND: Intraoperative cerebral microembolism may cause postoperative neurologic damage. The aim of this study was to determine the frequency of cerebral microembolic signals (MES) during minimally invasive surgery (MIS) and conventional (conv.) mitral valve operations and to determine the association of MES with various stages of the operation. METHODS: Intraoperative computer-aided transcranial Doppler measurements were performed to detect cerebral microemboli in 21 patients undergoing MIS and in 14 patients undergoing conv. mitral valve operation. We calculated the mean embolic rate for three time periods: P1, start of the operation until aortic clamping; P2, aortic clamping until clamp removal; and P3, declamping until end of surgery. RESULTS: There was no significant difference in the total number of detected cerebral MES between both patient groups (MIS 1,014+/-753, conv. 937+/-519; NS). In both groups, the highest number of MES were detected during the third time period when the heart regained effective ejection (MIS 875+/-746, conv. 680+/-462; p > 0.5). CONCLUSIONS: Transcranial Doppler was useful to detect cerebral microemboli in MIS and conv. mitral valve operation. We found no increased risk of cerebral microembolism during the minimally invasive method compared with the conventional technique.     

Successful use of single-lumen, urokinase immobilized femoral catheters as a temporary access for haemodialysis

Method: Placement of a femoral vein catheter as temporary vascular access for haemodialysis was conducted and the indications, catheter patency rate, and incidence of catheter-related infections were examined. A urokinase immobilized femoral vein catheter (UIFC) is a soft polyurethane single-lumen catheter 2.7 mm in diameter and 22 cm in length which needs no heparin infusion (Japan Shawood Co., Ltd., Tokyo; Unitica Co., Ltd., Hyogo, Japan). A soft silicon rubber was attached to the tip of the catheter in order to avoid excessive bleeding during insertion. Aseptic adhesive wound dressing was employed at the exit-site which was cleansed with popidone-iodine and renewed at each dialysis session. Results: Eighty-one UIFCs were used for haemodialysis in 64 patients (acute renal failure: 11; vascular access trouble: 53; initiation of chronic dialysis: 17). The average age of the patients was 58±13 years, ranging from 26 to 80 years. The mean duration of catheter indwelling was 22.4±13.1 days. An adequate blood flow of 180-200 ml/min was obtained through UIFC and returned to another peripheral vein punctured at each dialysis session. Unexplained fever occurred in four cases while the UIFC was in place (4.9%) but culture of either blood or the catheter tip was negative for bacteria. The catheter was removed immediately and fever subsided in all cases. The overall catheter survival rate was 84% at 34 days calculated using the Kaplan-Meier method. Catheter insertion was easy to perform and no serious complications such as pulmonary embolism or septicaemia occurred. Conclusion: Our modified type of UIFC is very useful as a temporary access for haemodialysis with a very low incidence of catheter-related infections and no need for heparinization. Excellent catheter patency was maintained with the plug system and careful dressing techniques without unnecessary bleeding during catheter care. Key words: femoral vein catheterization; haemodialysis; temporary vascular access; catheter survival rate      

Free serum leptin but not bound leptin concentrations are elevated in patients with end-stage renal disease.

BACKGROUND: Leptin is a 16-kDa protein that is thought to be a regulator of food intake and body weight. Although total serum leptin levels have been reported to be elevated in obese and normal weight patients with end-stage renal disease (ESRD), it is not known whether serum-free leptin concentrations are also increased in patients with ESRD with no apparent nutritional problems. Furthermore, there are no data on how different dialysis modes (high-flux haemodiafiltration and low-flux dialysis) influence serum leptin subfractions. METHODS: We measured fasting serum free and bound leptin levels in three groups of male subjects: patients on haemodiafiltration with high flux dialysers (n=11), patients on haemodialysis with low-flux dialysers (n=17) and healthy age (61+/-8 years) and BMI (23.8+/-3.1 kg/m(2)) matched control subjects (n=28). Both leptin components were determined before and after a single dialysis session. RESULTS: Body mass indices were correlated with serum free leptin levels in both patients (r=0.69, P<0.001) and controls (r=0.77, P<0.001). Mean (SD) serum free leptin levels were significantly higher in ESRD patients than in control subjects (91+/-33 vs 41+/- 21 pmol/l; P<0.01). Bound leptin levels did not differ in both groups (0.67+/-0.12 vs 0.56+/-0.11 nmol/l, NS). Elevated serum-free leptin levels in ESRD patients could be reduced by haemodiafiltration with high-flux membranes, but not with low-flux haemodialysis membranes.The former led to a reduction of initial serum free leptin values to 76+/-17% (P<0.01), whereas bound leptin remained unaffected. CONCLUSION: Serum-free leptin levels are elevated in ESRD without any apparent effect on body weight. In contrast, serum bound leptin levels remain stable, thus central feedback regulation via the bound form of the hormone may serve as an alternative explanation in the regulation of food intake and energy expenditure in chronic patients on haemodialysis with no apparent nutritional problems.     

Patent foramen ovale and brain microembolization during scoliosis surgery in adolescents

STUDY DESIGN: A case series is reported. OBJECTIVE: To improve understanding of the potential mechanisms associated with cerebral microemboli during scoliosis surgery in adolescents. SUMMARY OF BACKGROUND DATA: Paradoxical cerebral fat microembolization during scoliosis surgery has been associated with right-to-left shunting through an undetected patent foramen ovale. The prevalence of this cardiac defect in the adult population may be as high as 15% to 25%. Although the clinical relevance of this embolic phenomenon during scoliosis surgery has not been investigated, a few reports have documented its fatal consequences. It has been suspected in some patients with postoperative reduced visual function, particularly after complex instrumented fusions. METHODS: Bilateral transcranial Doppler (2 MHz) was used to monitor cerebral microemboli in the right and left middle cerebral arteries during spinal instrumentation and fusion in four patients. Additionally, transthoracic or transesophageal echocardiography incorporating pulse and color Doppler (3.5-5 MHz) and a contrast test was used in these patients to detect atrial shunts. RESULTS: Intraoperative transcranial Doppler monitoring detected high rates of cerebral microemboli associated with the presence of an atrial communication in two adolescents. In two additional patients with no detected brain microembolization, echocardiographic examination indicated the absence of an atrial shunt. CONCLUSION: The study findings suggest that unrecognized atrial communications in adolescents undergoing scoliosis surgery contribute to higher rates of Doppler-detected cerebral microemboli than those found in adolescents without this congenital defect.     

Comparison of high-efficiency and standard haemodialysis providing equal urea clearances by partial and total dialysate quantification

Background. Short-duration high-efficiency haemodialysis has been utilized increasingly in recent years to deliver adequate blood urea clearances per dialysis session. However, high-efficiency and standard-duration haemodialysis schedules, which achieve equal patient urea clearances, may not represent equivalent dialytic therapy due to solute differences in intercompartmental dysequilibrium during dialysis and differences in dialysis mechanics. Methods. To circumvent the effects of intercompartmental dysequilibrium and postdialysis rebound solute clearances were measured by direct dialysis quantification (total and partial dialysate collections) rather than blood clearances. High-efficiency haemodialysis (dialyser blood flow rate=400 ml/min; dialysis time=170.67 min) was compared with standard haemodialysis (dialyser blood flow rate=200 ml/min; dialysis time=240 min) performed in random order in six anuric patients using Fresenius F8 dialysers and the same haemodialysis machine. Such haemodialysis schedules were prescribed to provide equivalent urea clearances. Results. Patient plasma water urea clearances measured by direct quantification were equivalent, whereas high efficiency haemodialysis achieved significantly lower phosphate clearances (P=0.01), less net bicarbonate absorption (P=0.01), and {beta}2microglobulin removal (P<0.001) than standard haemodialysis. Estimated total dialysate effluent volumes with partial dialysate collection and total dialysate collection correlated closely (r=0.95) and there were no differences between patient urea, creatinine and phosphate clearances measured by partial and total dialysate quantification. Conclusions. The data indicate that even if high-efficiency and standard haemodialysis provide equal whole-body urea clearances, delivered dialysis therapy is not equivalent. The partial dialysate collection method is as accurate as the cumbersome total dialysate collection approach and may be applied to assess delivered dose by minor modification of current haemodialysis machines.     

Inferior vena cava diameter: a useful method for estimation of fluid status in children on haemodialysis.

BACKGROUND: An accurate assessment of fluid status in haemodialysis patients presents a significant challenge especially in growing children. Clinical parameters of hydration are not always reliable, and invasive methods such as measurement of central venous pressure cannot be used routinely. We evaluated the usefulness of inferior vena cava diameter (IVCD) measured by echocardiography in the estimation of hydration in children on haemodialysis. METHODS: Fifteen haemodialysis patients (mean age 14 years) were evaluated. Clinical assessment included patients' symptoms, weight, blood pressure, heart rate, presence of oedema and vascular congestion, before and after dialysis session. Dry weight was assessed based on the above parameters. Fifty-two echocardiographic studies immediately prior and 30-60 min following dialysis were performed. The anteroposterior IVCD was measured 1.5 cm below the diaphragm in the hepatic segment in supine position during normal inspiration and expiration. IVCD was expressed per body surface area. RESULTS: Following haemodialysis mean IVCD (average of expiration and inspiration) decreased from 1.12+/-0.38 to 0.75+/-0.26 cm/m(2) (P<0.0001). Changes in IVCD were significantly correlated with alterations in body weight following dialysis (P<0.0001). The collapse index (per cent of change in IVCD in expiration vs inspiration) increased significantly after dialysis (P=0.035). IVCD clearly reflected alterations in fluid status. It did not vary significantly with changes in dry weight in a given patient. CONCLUSIONS: Our findings support the applicability of VCD measurement in the estimation of hydration status in paediatric haemodialysis patients. The combination of clinical parameters and measurement of IVCD may enable more accurate evaluation of hydration of children on haemodialysis.     

The use of ultrasound for the placement of dialysis catheters

Background: The jugular vein should be preferred to the subclavian vein for the placement of dialysis catheters since subclavian catheters result in a high incidence (up to 50%) of subclavian-vein thromboses. Method: We conducted a prospective, randomized study between July 1996 and March 1997 to find out whether through the use of ultrasound, the rate of unsuccessful attempts in puncturing the internal jugular vein could be reduced. Seventy-three internal jugular vein cannulations were performed on 65 patients, using the guide-wire technique (according to Seldinger). Two groups were formed randomly by lot: in the first group the position of the internal jugular vein was marked on the skin by the use of ultrasound (Picker CS9100, Convex 3.5 MHZ) before disinfection and local anaesthesia took place. The puncture was performed according to this mark. In the second group, the internal jugular vein was cannulated with real-time ultrasound guidance on the monitor. Any withdrawal of the needle with a consecutive forward movement was judged as an unsuccessful attempt, whether or not a second skin puncture was performed. Result: Thirty-seven punctures of the internal jugular vein with a skin mark determined by ultrasound yielded 87 unsuccessful attempts. Thirty-six punctures with real-time ultrasound guidance resulted in 10 unsuccessful attempts (P<0.01). The time from the beginning of the local anaesthesia to successful puncture was 4.8±2.2 min in the first group compared to 3.4±0.9 min in the second group (P<0.01). The cross-section of the internal jugular vein in the first group was 1.7±0.8 cm² versus 1.5±0.8 cm² in the second group (not significant). Neither of the two methods caused any complications. Conclusion: The puncture of the internal jugular vein with real-time ultrasound guidance resulted in significantly fewer unsuccessful attempts of venepuncture without requiring additional time.     

Venography at insertion of tunnelled internal jugular vein dialysis catheters reveals significant occult stenosis.

BACKGROUND: Tunnelled catheters are widely used to provide vascular access for haemodialysis. Percutaneous insertion of these catheters requires large calibre tissue dilators with the potential to cause trauma to central veins, particularly if anatomical abnormalities are present. METHODS: We evaluated the use of venography to identify central vein anatomical abnormalities in 69 consecutive patients undergoing percutaneous placement of tunnelled right internal jugular vein catheters. The internal jugular vein was entered under ultrasound guidance and venography was performed prior to insertion of a guide-wire. Images were evaluated on-screen by the operator and a decision made regarding the need for additional fluoroscopy during insertion of the catheter. RESULTS: In 29 cases (42%), venography showed evidence of unexpected stenosis and/or angulation of the central veins of sufficient severity to warrant additional fluoroscopy during insertion of the dilators, or abandonment of the procedure. Patients who had previously had tunnelled internal jugular catheters had more than double the incidence of such abnormalities than those who had not [15/23 (65%) vs 14/46 (30%); P = 0.009]. In two patients the procedure was abandoned due to severe stenosis. No patient suffered central vein trauma or pneumothorax. There were no adverse reactions to contrast injection. CONCLUSIONS: Venography performed immediately prior to tunnelled internal jugular dialysis catheter insertion detects unexpected, clinically significant anatomical abnormalities of the central veins in a substantial proportion of patients, particularly those with a history of previous tunnelled catheter insertion. We suggest that the use of venography may help to minimize the risk of complications from this procedure.     

The right supraclavicular fossa ultrasound view for correct catheter tip positioning in right subclavian vein catheterisation: a prospective observational study

Central venous catheter misplacement is common (approximately 7%) after right subclavian vein catheterisation. To avoid it, ultrasound-guided tip navigation may be used during the catheterisation procedure to help direct the guidewire towards the lower superior vena cava. We aimed to determine the number of central venous catheter misplacements when using the right supraclavicular fossa ultrasound view to aid guidewire positioning in right infraclavicular subclavian vein catheterisation. We hypothesised that the incidence of catheter misplacements could be reduced to 1% when using this ultrasound technique. One -hundred and three adult patients were prospectively included. After vein puncture and guidewire insertion, we used the right supraclavicular fossa ultrasound view to confirm correct guidewire J-tip position in the lower superior vena cava and corrected the position of misplaced guidewires using real-time ultrasound guidance. Successful catheterisation of the right subclavian vein was achieved in all patients. The guidewire J-tip was initially misplaced in 15 patients, either in the ipsilateral internal jugular vein (n = 8) or in the left brachiocephalic vein (n = 7). In 12 patients it was possible to adjust the guidewire J-tip to a correct position in the lower superior vena cava. All ultrasound-determined final guidewire J-tip positions were consistent with the central venous catheter tip positions on chest X-ray. Three out of 103 catheters were misplaced, corresponding to an incidence (95%CI) of 2.9 (0.6–8.3) %. Although the hypothesis could not be confirmed, this study demonstrated the usefulness of the right supraclavicular fossa ultrasound view for real-time confirmation and correction of the guidewire position in right infraclavicular subclavian vein catheterisation.     

Prevention of clot formation during haemodialysis using the direct thrombin inhibitor melagatran in patients with chronic uraemia.

BACKGROUND: This study assessed the feasibility of replacing intravenous (i.v.) dalteparin with the direct thrombin inhibitor (DTI) melagatran administered via dialysis fluid in patients undergoing haemodialysis, and also examined the pharmacokinetics of melagatran with and without dialysis. METHODS: During two 4 h haemodialysis sessions, 10 adult patients were administered i.v. dalteparin. During two subsequent sessions, melagatran was administered as an i.v. bolus before dialysis, and in the dialysis fluid. The pharmacokinetics of melagatran administered as a bolus before dialysis, and of i.v. melagatran during a dialysis-free day, were studied. Dialysis performances were evaluated from clinical criteria including clot formation in the dialyzer and bloodlines, pre-post dialyzer pressures and iohexol clearance. Anticoagulant efficacy was evaluated from dialysis success. RESULTS: All dialysis sessions were successful, with no apparent difference in clot formation between the two treatments. Median iohexol clearance was similar with dalteparin (99-103 ml/min) and melagatran in the dialysis fluid (98-100 ml/min). There was no difference in pre- and post-dialyzer bloodline pressures between the two treatments. During dialysis sessions with melagatran in dialysis fluid, melagatran concentrations in plasma rapidly equilibrated to approximately 70% of those in dialysis fluid. While the clearance of melagatran was low in patients with renal failure (mean+/-SD, 0.93+/-0.36 l/h), haemodialysis provided efficient clearance of melagatran (7.20+/-0.76 l/h). Melagatran clearance by dialysis (104+/-10 ml/min) was comparable to iohexol clearance. CONCLUSIONS: The DTI melagatran administered via dialysis fluid may provide sufficient anticoagulation for haemodialysis. Melagatran is rapidly cleared from plasma by haemodialysis, suggesting that this method may be used to decrease drug levels in patients with renal impairment.     

Haemodialysis and cerebral oedema

BACKGROUND: Haemodialysis may cause neurological symptoms ranging from inconvenient feelings of disequilibrium to life-threatening neurological complications. There are animal data to suggest cerebral swelling may accompany haemodialysis and contribute symptomatically to dialysis disequilibrium. However, MR images acquired following haemodialysis often fail to demonstrate evidence of cerebral oedema. We wished to quantify any potential cerebral volume change which is caused by haemodialysis treatment. METHOD: Five renal patients and 5 control subjects had a two volumetric T1-weighted MRI scans on the same day. The patients were imaged immediately before and after haemodialysis. None were taking steroids. Precise positional matching (registration) was used to quantify cerebral volume change. RESULTS: Patients had an increase in cerebral volume following dialysis which averaged 32.8 ml (SE 7.4 ml, 3% brain volume). The change in the controls was 1.4 ml (SE 0.6 ml), p < 0.001. No patient had significant neurological symptoms. CONCLUSION: Cerebral oedema developed in the patients following dialysis. There is a good biological model for these observations. Modifications to dialysis may help. Common problems which increase cerebral volume, e.g. acute stroke, require careful appraisal in these patients. These observations need consideration when quantifying atrophy in dialysis patients.