Han Khim Tan

Early and intensive continuous hemofiltration for severe renal failure after cardiac surgery

BACKGROUND The aim of this study was to test whether early and intensive use of continuous venovenous hemofiltration (CVVH) achieved a better than predicted outcome in patients with severe acute renal failure undergoing cardiac operations, and whether a simple and yet accurate model could be developed to predict their outcome before starting CVVH. METHODS Medical record analysis with collection of demographic, clinical, and outcome information was used. RESULTS Sixty-five consecutive patients were treated with early and intensive CVVH (mean operation to CVVH time, 2.38 days; pump-controlled ultrafiltration rate, 2 L/h) after coronary artery bypass grafting (56.9%), single valve procedure (16.9%), or combined operations (26.2%). In 32.3% of patients, intraaortic balloon counterpulsation was required and 20% of patients were emergencies. Sustained hypotension despite inotropic and vasopressor support occurred in 40% of patients and prolonged mechanical ventilation in 58.5%. Using an outcome prediction score specific for acute renal failure, the predicted risk of death was 66%. Actual mortality was 40% (p = 0.003). Using multivariate logistic regression analysis and neural network analysis, patient outcome could be predicted with good levels of accuracy (receiver operating characteristic 0.89 and 0.9, respectively). CONCLUSIONS Early and aggressive CVVH is associated with better than predicted survival in severe acute renal failure after cardiac operations. Using readily available clinical data, the outcome of such patients can be predicted before the implementation of CVVH.

High Protein Intake during Continuous Hemodiafiltration: Impact on Amino Acids and Nitrogen Balance:

Aims To study the effect of combined continuous veno-venous hemodiafiltration (CVVHDF) and high (2.5 g/kg/day) parenteral amino acid supplementation on nitrogen balance, amino acid losses and azotemic control in a cohort of patients with severe acute renal failure (ARF). Methods We administered 2.5 grams/kg/day of amino acids intravenously to seven critically ill patients with ARF. We obtained paired blood and ultrafiltrate (UF) samples (n=20) and calculated amino acid clearances and losses, nitrogen balance, protein catabolic rate and total nitrogen losses. Results The median total serum amino acid concentration was high at 5.2 mmol/L with particularly high concentrations of ornithine, lysine, and phenylalanine, but a low level of histidine. The median overall amino acid clearance was 18.6 ml/min (range: 12 to 29 ml/min). UF losses as percentage of administered dose were high for tyrosine (53.6 %) but low for methionine (3.0 %) and arginine (2.3 %). A positive nitrogen balance was achieved in 7 (35%) of the 20 study days with an overall median nitrogen balance of -1.8 g/day. Urea levels were maintained at a median of 26.6 mmol/L. Conclusions High protein intake increases the serum concentrations of most amino acids. Such protein supplementation, when coupled with CVVHDF, achieves a slightly negative overall nitrogen balance in extremely catabolic patients while still allowing adequate azotemic control.

Phosphatemic control during acute renal failure: intermittent hemodialysis versus continuous hemodiafiltration.

Background Achieving “adequacy of dialysis” includes the maintenance of normal serum phosphate concentrations and is an important therapeutic goal in the treatment of acute renal failure (ARF). It is unknown whether this goal is best achieved with intermittent or continuous renal replacement therapy. Methods We compared the effects of continuous veno-venous hemodiafiltration (CVVHDF) and intermittent hemodialysis (IHD) on serum phosphate concentrations using daily morning blood tests in 88 consecutive intensive care patients half of which were treated with IHD and half with CRRT. Results Mean patient age was 54 ± 14 years for IHD and 60 ± 14 years for CVVHDF (NS). However, patients who received CVVHDF were more critically ill (mean APACHE II scores: 24.4 ± 5.1 for IHD vs. 29.2 ± 5.7 for CVVHDF, p<0.003). Before treatment, the serum phosphate concentration was 2.04 ± 0.16 mmoll L for IHD and 1.96 ± 0.17 mmoll L for CVVHDF (NS), with abnormal values in 79.4% of IHD patients and in 64.8% of CVVHDF patients (NS). During treatment, CVVHDF induced a greater reduction in serum phosphate (p=0.02) during the first 48 hours and conferred superior subsequent control of hyperphosphatemia (achieved in 64.6% of observations during CVVHDF vs. 41.8% during IHD; p<0.0001). The serum phosphate concentration was also more likely to be within the normal range during CVVHDF (55.3% vs.36.2%; p<0.0001). There was a trend toward more frequent hypophosphatemia (9.3% vs. 5.6%; P<0.1) during CVVHDF. Conclusions Abnormal serum phosphate concentrations are frequent in ARF patients before and during renal replacement, however, normalization of phosphatemia is achieved more frequently with CVVHDF.

POSSIBLE STRATEGIES TO PROLONG CIRCUIT LIFE DURING HEMOFILTRATION: THREE CONTROLLED STUDIES

Background and Aims: The prevention of filter clotting is an important goal in the management of continuous renal replacement therapy (CRRT). Anticoagulation is the mainstay of such prevention. However, other strategies might prolong filter life without increasing the risk of bleeding. We tested the effectiveness of three strategies (use of flat plate configuration, heparin administration into the air chamber and use of a larger membrane surface) aimed at prolonging circuit life without increasing the dose of anticoagulation. Methods: Thirty-one critically ill patients with acute renal failure (ARF) managed with continuous venovenous hemofiltration (CVVH) were studied. Filters were randomized in a crossover design to three consecutive studies: (1) filtration with either hollow-fiber or flat-plate hemofilters, (2) administration of heparin dose pre-filter or divided into pre-filter and directly into the bubble trap chamber and (3) use of two different surface areas with Filtral 8 (surface area 0.75 m2) vs. Filtral 12 (surface area 1.30 m2) hemofilters. Results: Mean circuit life for flat-plate and hollow-fiber hemofilters (cohort 1) was 14.7 ± 4.7 h and 17.1 ± 2.8 h respectively (NS). Mean circuit life for single heparin administration site vs. double site administration (cohort 2) was 17 ± 3.2 h and 18 ± 3.1 h respectively (NS). Mean circuit lifespan for 0.75 m2 and 1.30 m2 hemofilters was 16 ± 12.2 h and 15.7 ± 14.3 h respectively (NS) (cohort 3). Visible clot formation in the bubble trap chamber was a frequent cause of circuit failure. Conclusion: Neither flat plate membrane configuration nor increasing membrane surface area, nor heparin administration in the air chamber prolong circuit life during CVVH. The bubble trap chamber is a frequent site of circuit clotting.

Electrolyte Mass Balance During CVVH: Lactate vs. Bicarbonate-Buffered Replacement Fluids

Objective: To compare the effect of lactate vs. bicarbonate‐buffered replacement fluids on electrolyte mass balance during isovolemic continuous veno‐venous hemofiltration (CVVH). Design: Randomized controlled study with double cross over. Setting: Intensive care unit of a tertiary university hospital. Patients and participants: Eight patients with acute renal failure (ARF). Interventions: Isovolemic CVVH (2L/hr of replacement fluid) was performed in random order with either bicarbonate or lactate‐buffered replacement fluid delivered pre‐filter. Measurements and Results: Sodium, potassium, chloride, magnesium, and phosphate, were measured in each sample. There was a mass gain of sodium, which was similar under both conditions (bicarbonate: 23.3 ± 4.9 mmol/hr, lactate: 22.7 ± 3.5 mmol/hr). Mass chloride gains occurred with bicarbonate‐buffered replacement fluid only (12.8 ± 5.3 mmol/hr), while there was an overall net loss of chloride with lactate fluids (− 2.5 ± 5.2 mmol/hr), resulting in a significant difference in chloride mass balance (p < 0.0001). Magnesium mass balance was negative with bicarbonate buffer only (− 0.6 ± 0.2 mmol/hr) and also differed significantly from that obtained with lactate fluids (− 0.1 ± 0.2 mmol/hr, p < 0.0001). Phosphate losses (bicarbonate: − 1.7 ± 0.7 mmol/hr, lactate: − 1.7 ± 0.5 mmol/hr) were equivalent with both buffers. Potassium mass balance was neutral. Conclusions: Mass balance during isovolemic CVVH is significantly affected by the type of replacement fluid administered pre‐filter. Isovolemic CVVH is not isonatremic and the use of bicarbonate‐buffered fluid results in a significant accumulation of chloride and a loss of magnesium.

IONIZED SERUM CALCIUM LEVELS DURING ACUTE RENAL FAILURE: INTERMITTENT HEMODIALYSIS VS. CONTINUOUS HEMODIAFILTRATION

Background: Achieving “adequacy of dialysis” includes the maintenance of normal serum ionized calcium concentrations and is an important therapeutic goal in the treatment of acute renal failure (ARF). It is unknown whether this goal is best achieved with intermittent or continuous renal replacement therapy. Methods: We compared the effects of continuous veno–venous hemodiafiltration (CVVHDF) and intermittent hemodialysis (IHD) on serum ionized calcium concentrations using daily morning blood tests in 88 consecutive intensive care patients of which half were treated with IHD and half with CRRT. Results: Mean patient age was 54 ± 14 years for IHD and 60 ± 14 years for CVVHDF (NS). However, patients who received CVVHDF were significantly more critically ill (mean APACHE II scores: 24.4 ± 5.1 for IHD vs. 29.2 ± 5.7 for CVVHDF, p<0.003). Before treatment, the mean ionized calcium concentration was 1.177 ± 0.03 mmol/l for IHD and 1.172 ± 0.04 mmol/l for CVVHDF (NS), with abnormal values in 51.6% of IHD patients and in 68% of CVVHDF patients (NS). During treatment, hypocalcemia was significantly more common among CVVHDF patients (24.5% vs. 14.9%; p<0.011) while hypercalcemia was more frequent during IHD (36.1% vs. 25.6%; p<0.019). Conclusions: Abnormal serum ionized calcium concentrations are frequent in ARF patients before and during renal replacement. Once dialytic therapy is applied, CVVHDF is more likely to lower serum calcium concentrations, while IHD is more likely to induce hypercalcemia. Appreciation of these different biochemical effects may assist clinicians in adjusting dialytic therapy in selected patients.

The effect of continuous hemofiltration on acid-base physiology

Continuous hemofiltration techniques have a powerful effect on acid-base physiology. In patients with metabolic acidosis, hemofiltration techniques replace plasma water, which is low in bicarbonate concentration, with a solution, which contains either an above-normal bicarbonate concentration or a h

An ex-vivo evaluation of vascular catheters for continuous hemofiltration.

Objectives: To measure outflow and inflow hydraulic resistance in double-lumen catheters used for hemofiltration under standardized laboratory conditions. Setting: ICU Laboratory of tertiary unit. Methods: Heparinized spent red cells diluted in polygeline solution to a constant hematocrit of 32% at 37°C were pumped using a standard Prisma M60 circuit through several hemofiltration catheters. Blood pump speed was increased and decreased in steps of 30 mL/min (30, 60, 90, 120, 150, and 180 mL/min) and catheter outflow and inflow pressures recorded and used to define the pressure flow relationship (line of hydraulic resistance) for each. Results: Double-lumen catheters posed different resistances to outflow or inflow. Among the <15 cm long catheters, the 11.5 Fr Quinton-Mahurkar (0.56 mmHg/mL/min) catheter offered the least resistance to outflow, while the Medcomp 11.5 Fr catheter offered the least resistance to inflow (0.78 mmHg/mL/min). Among the >19 cm long catheters, the 13.5 Fr Vascath Niagara catheter showed the lowest blood flow resistance to both outflow (0.63 mmHg/mL/min) and inflow (0.83 mmHg/mL/min). Longer catheters did not pose statistically greater resistance to both outflow and inflow. Resistance to inflow was consistently greater than resistance to outflow (p = 0.003). Overall, the Prisma M60 blood circuit alone accounted for 40% of the total extracorporeal circuit blood flow resistance. Conclusions: Proprietary hemofiltration catheters have variable resistance to blood flow under standard ex-vivo conditions. This ex-vivo information might be useful to clinicians in guiding their choice of catheters for clinical use.

A PROSPECTIVE STUDY OF THROMBOELASTOGRAPHY (TEG) AND FILTER LIFE DURING CONTINUOUS VENO-VENOUS HEMOFILTRATION

Anticoagulants are commonly used to prolong circuit life during continuous hemofiltration. However, a clear correlation between routinely performed blood coagulability tests and circuit life has not been demonstrated. This lack of correlation may derive from the limited ability of such tests to describe the likelihood of in vivo clotting. We hypothesized that thromboelastography (TEG), which derives its variables from a closer reproduction of in vivo coagulation, would significantly correlate with filter life. Accordingly, we conducted a prospective pilot study of the correlation between filter life and TEG-derived variables in 21 hemofilters used in 6 critically ill patients admitted to a tertiary intensive care unit. It involved the performance of TEG during steady state anticoagulation, measurement of circuit life, and of routine coagulation variables. The results showed that the mean circuit life was 20.7 ± 4.0 h despite an average aPTT of 67.7 ± 12.8 s and a mean heparin dose of 472.5 ± 96.2 IU / h. The mean INR was 1.4 ± 1 and the mean platelet count was 118 ± 16 × 103 / mm3. Although several TEG variables correlated with heparin dose (p < 0.03), no correlation was found between any of the routine coagulation variables or any of the TEG variables and circuit life. In conclusion, no significant correlation between TEG derived variables or routinely measured coagulation variables and circuit life could be demonstrated. These findings suggest that such tests are not useful indicators of circuit anticoagulation adequacy and that factors other than blood coagulability may play a role in circuit failure.