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Biomedical subjects

Ian Baldwin

Publications and source records attributed to Ian Baldwin.

17 recordsLinked to original sources
PubMed2005

Myoglobin clearance by super high-flux hemofiltration in a case of severe rhabdomyolysis: a case report.

OBJECTIVE: To test the ability of a novel super high-flux (SHF) membrane with a larger pore size to clear myoglobin from serum. SETTING: The intensive care unit of a university teaching hospital. SUBJECT: A patient with serotonin syndrome complicated by severe rhabodomyolysis and oliguric acute renal failure. METHOD: Initially continuous veno-venous hemofiltration was performed at 2 l/hour ultrafiltration (UF) with a standard polysulphone 1.4 m2 membrane (cutoff point, 20 kDa), followed by continuous veno-venous hemofiltration with a SHF membrane (cutoff point, 100 kDa) at 2 l/hour UF, then at 3 l/hour UF and then at 4 l/hour UF, in an attempt to clear myoglobin. RESULTS: The myoglobin concentration in the ultrafiltrate at 2 l/hour exchange was at least five times greater with the SHF membrane than with the conventional membrane (>100,000 microg/l versus 23,003 microg/l). The sieving coefficients with the SHF membrane at 3 l/hour UF and 4 l/hour UF were 72.2% and 68.8%, respectively. The amount of myoglobin removed with the conventional membrane was 1.1 g/day compared with 4.4-5.1 g/day for the SHF membrane. The SHF membrane achieved a clearance of up to 56.4 l/day, and achieved a reduction in serum myoglobin concentration from >100,000 microg/l to 16,542 microg/l in 48 hours. CONCLUSIONS: SHF hemofiltration achieved a much greater clearance of myoglobin than conventional hemofiltration, and it may provide a potential modality for the treatment of myoglobinuric acute renal failure.

Acute Kidney Injury↗
PubMed2005

Renal replacement therapy and the kidney: minimizing the impact of renal replacement therapy on recovery of acute renal failure.

PURPOSE OF REVIEW: Although renal replacement therapy is the mainstay of supportive care in patients with severe acute renal failure, its performance can have untoward effects that contribute to the prolongation of renal failure or impede the ultimate recovery of renal function. In this review, we categorize the major complications associated with renal replacement therapy and assess their impact on recovery of renal function. RECENT FINDINGS: The major mechanisms by which renal replacement therapy is postulated to delay renal recovery include treatment-associated hemodynamic instability, vascular catheter-related bacteremia and sepsis, and cytokine activation by bioincompatible membranes. Clinical data regarding the role of dialysis catheter infections in delay of renal recovery are lacking. The data regarding the role of membrane biocompatibility and the modality and dose of renal replacement therapy are limited and conflicting. SUMMARY: Clinical recommendations must be limited to the broad admonishment that complications during renal replacement therapy, including hemodynamic instability and catheter-related bacteremia, be minimized by using best clinical practices, while recognizing that the impact of specific practices on recovery of renal function have not been evaluated. The data do not support recommendations regarding utilization of specific membranes or the modality or dose of renal replacement therapy on the basis of their impact on recovery of renal function.

Acute Kidney Injury↗
PubMed2004

Blood flow reductions during continuous renal replacement therapy and circuit life.

OBJECTIVE: Reductions in blood flow rate may occur undetected during peristaltic pumping of blood through continuous renal replacement therapy circuits. We investigated whether undetected reductions in blood flow rate occur during continuous veno-venous haemofiltration, and whether they are correlated with filter life. PATIENTS: Twelve patients receiving continuous veno-venous haemofiltration in the intensive care unit of a tertiary hospital. METHODS: Extracorporeal circuit blood flow during haemofiltration was continuously monitored utilizing a miniature ultrasound Doppler device. Otherwise undetected blood flow reductions were identified at severity levels of between 20% and 100% less than the set diastolic flow rate (83 ml/min). Information on anticoagulation status was simultaneously obtained. The frequency and severity of blood flow reductions were recorded, and the correlation with filter life was determined. MEASUREMENTS AND RESULTS: The duration of filter life ranged from 1.5 to 53 h, with a mean functional life of 19.62+/-16.32 h. There were 314 episodes of blood flow reduction during the 525 h of monitoring (0.59 episodes/h). There was a significant inverse relationship between the number of medium-level blood flow reductions and filter life. This correlation was much stronger than that between APTT and filter life. CONCLUSIONS: Undetected blood flow reductions occur during continuous veno-venous haemofiltration. Such reductions are frequent, and when sufficiently severe appear to be correlated with filter life more strongly than the blood coagulation variables typically used to monitor adequacy of anticoagulation and promote filter longevity.

Adult↗
PubMed2003

The impact of lactate-buffered high-volume hemofiltration on acid-base balance.

OBJECTIVE: To evaluate the effect of high-volume hemofiltration (HVHF) with lactate-buffered replacement fluids on acid-base balance. DESIGN: Randomized crossover study. SETTING: Intensive Care Unit of Tertiary Medical Center PARTICIPANTS: Ten patients with septic shock and acute renal failure. INTERVENTIONS: Random allocation to 8 h of isovolemic high-volume hemofiltration (ultrafiltration rate: 6 l/h) or 8 h of isovolemic continuous venovenous hemofiltration (ultrafiltration rate: 1 l/h) with lactate-buffered replacement fluid with subsequent crossover. MEASUREMENTS AND RESULTS: We measured blood gases, electrolytes, albumin, and lactate concentrations and completed quantitative biophysical analysis of acid-base balance changes. Before high-volume hemofiltration, patients had a slight metabolic alkalosis [pH: 7.42; base excess (BE) 2.4 mEq/l] despite hyperlactatemia (lactate: 2.51 mmol/l). After 2 h of high-volume hemofiltration, the mean lactate concentration increased to 7.30 mmol/l ( p=0.0001). However, a decrease in chloride, strong ion difference effective, and strong ion gap (SIG) compensated for the effect of iatrogenic hyperlactatemia so that the pH only decreased to 7.39 ( p=0.05) and the BE to -0.15 ( p=0.001). After 6 h, despite persistent hyperlactatemia (7 mmol/l), the pH had returned to 7.42 and the BE to 2.45 mEq/l. These changes remained essentially stable at 8 h. Similar but less intense changes occurred during continuous venovenous hemofiltration. CONCLUSIONS: HVHF with lactate-buffered replacement fluids induces iatrogenic hyperlactatemia. However, such hyperlactatemia only has a mild and transient acidifying effect. A decrease in chloride and strong ion difference effective and the removal of unmeasured anions all rapidly compensate for this effect.

Acid-Base Equilibrium↗
PubMed2003

Continuous is not continuous: the incidence and impact of circuit "down-time" on uraemic control during continuous veno-venous haemofiltration.

OBJECTIVE: There is little information on the duration of time that patients spend off therapy (down-time) during continuous veno-venous haemofiltration (CVVH) and the effect of this treatment free time on azotaemic control. DESIGN AND SETTING: Prospective observational study in the ICU of tertiary hospital. PATIENTS AND PARTICIPANTS: 48 critically ill patients treated with CVVH at 2 l/h of ultrafiltration. INTERVENTIONS: Prospective collection of demographic and biochemical data. MEASUREMENTS AND RESULTS: Two hundred and sixty-six filters were observed. Start and end times were collected for each filter. Creatinine and urea were measured daily and percentage of reduction of these two solutes was calculated (%Delta creatinine and urea). The median period when CVVH was not applied to a patient (down-time) was 3 h per day. There was a significant inverse correlation between down-time and %Delta creatinine and urea over each 24-h time cycle. On average at least 16 h per day of CVVH was required to maintain creatinine and urea concentration for each 24-h cycle. CONCLUSIONS: "Continuous" therapy is not truly continuous. Down-time adversely affects azotaemic control. Physicians prescribing CRRT should be aware of the consequences of such down-time on the quality and quantity of renal replacement therapy delivered.

Aged↗
PubMed2003

Pre-dilution vs. post-dilution during continuous veno-venous hemofiltration: impact on filter life and azotemic control.

BACKGROUND/AIMS: To determine the impact of replacement fluid infusion site on filter life and azotemic control during continuous veno-venous hemofiltration (CVVH). METHODS: Pre-dilution CVVH was conducted from February 2001 to December 2001 and then practice was changed to post-dilution (from January 2002 to July 2002). Filter life was prospectively observed and the following data obtained for each filter: starting date and time, ending date and time, heparin use, heparin dose and protamine use. Daily creatinine, urea, INR, APTT and platelet count were also collected. RESULTS: Forty-eight patients were studied (33 in pre-dilution and 15 in post-dilution) for a total of 309 filters (202 in pre-dilution and 107 in post-dilution). The median filter life was significantly shorter in the post-dilution period (18.0 vs. 13.0 h, p = 0.021). Multivariate linear regression analysis showed that pre-dilution was a significant independent predictor of increased filter life (p = 0.029), together with platelet count (p = 0.0035) and heparin dose (p = 0.046). There was no significant improvement in daily creatinine and/or urea reduction in the post-dilution period (% Delta creatinine: 7.9 vs. 10.2%/day, p = 0.99, urea: 5.4 vs. 9.7%/ day, p = 0.78). CONCLUSIONS: Post-dilution was associated with reduced filter life without any beneficial effect on daily changes in urea and creatinine levels. Pre-dilution appears a preferable technical approach to CVVH.

Acute Kidney Injury↗
PubMed2002

A technique for the monitoring of blood flow during continuous haemofiltration.

OBJECTIVE: To establish a technique for the monitoring and graphic display of blood flow during continuous renal replacement therapy (CRRT). DESIGN AND SETTING: Technique assessment study in a tertiary intensive care unit. PATIENTS: Six ICU patients receiving CRRT. INTERVENTIONS: A technique was devised to monitor and graphically display blood flow during CRRT. This technique used a mini-ultrasound Doppler probe attached to the blood tubing with link to a lap top computer for quantitative graphic display. Blood flow was measured and displayed during routine treatment using this method in six patients. MEASUREMENTS AND RESULTS: Blood flow wave data were monitored and successfully displayed as a real-time wave form and analysed using Windaq data analysis software. This initial analysis over a 6-h period revealed the following facts: (a) blood flow was not the same as set by the machine roller pump on nine occasions, (b) blood flow reductions defined as a drop in the 'diastolic' were 20% (seven) and 30% (two) less than set flow, (c) flow reductions frequently failed to trigger machine alarms, and (d) the blood flow wave displayed had unique characteristics. Complete flow monitoring was then undertaken for the functional life of one haemofilter over 24.5 h. There were 27 blood flow reductions, and blood flow was less than set for a total of 463.9 min or 31.5% of operating time. CONCLUSIONS: Blood flow during CRRT can be monitored by an ultrasound Doppler probe and displayed graphically. Preliminary data using this technique suggest potentially serious and undetected problems with blood flow during routine CRRT.

Australia↗
PubMed2002

Introduction to an alternate view of acid/base balance: the strong ion difference or Stewart approach.

The carbonic acid/bicarbonate system, as defined by the Henderson-Hasselbach (H-H) equation, has traditionally formed the centrepiece of the presentation of acid/base physiology in nursing education. However, an alternative approach to describe acid/base physiology was proposed by Peter Stewart in 1983. Stewart determined, using the physiochemical principles of dissociation equilibrium, electroneutrality and conservation of mass, that hydrogen ion concentration [H+] was dependent upon the difference between the concentrations of strong cations and strong anions in a solution (the strong ion difference or SID), concentration of weak acid anions, and the partial pressure of carbon dioxide in plasma. Therefore, a change in pH (the [H+] expressed as its negative log) indicates that there must be a change in one of these independent variables, and not simply explained by movement of hydrogen ions or bicarbonate into or out of the body fluids. An analysis of the complex acid/base derangements commonly seen in the critically ill can be achieved using this approach. The acid/base consequences of vomiting, gastric aspiration, diarrhoea, diuretic therapy, the infusion of large volumes of normal saline, the contribution of lactate, and the effects of methanol and ethylene glycol poisoning can all be more readily understood considering Stewart's explanation of acid/base balance. This paper outlines this alternative approach and provides some examples for the intensive care setting.

Acid-Base Equilibrium↗
PubMed2002

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 degrees C were pumped using a standard Prisma M60 circuit through several hemofiltration catheters. Blood pump speed was increased and decreased in steps of 30mL/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.

Blood Flow Velocity↗
PubMed2002

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 +/- 2.8h 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 CWH. The bubble trap chamber is a frequent site of circuit clotting.

Acute Kidney Injury↗
PubMed2002

Continuous renal replacement therapy. Keeping pace with changes in technology and technique.

The rapidly changing nature of new technologies and techniques in acute health care means it can be difficult keeping pace. Most facilities, large or small, are usually in continuous evaluation of a new technology. Published reviews and professional group guidelines can assist the process of change for continuous renal replacement therapy (CRRT) technologies and techniques. The current techniques and technologies are a mixed application of old and new technologies providing a combination of convective and diffusive solute clearance methods. There are a variety of anticoagulation approaches. New, purpose-built CRRT machines offer many advantages over old technology but their costs can be prohibitive and users do not always meet them with rapid behavioral change. Reading journal publications and texts, scientific meetings, education and training, Internet web site review/participation, quality improvement activities and an accurate local data base are the keys to keeping pace with changes and identifying whether a benefit can be anticipated and demonstrated. Possible changes for the future of techniques and technologies may be in the areas of modified approaches to continuous therapy with tailored approaches for specific patient care settings. Improved membrane characteristics for wider indications and the bio-artificial kidney are emerging along with blood pump and circuit design improvements, with new machine/operator interfaces.

Equipment and Supplies↗
PubMedDate not supplied

Cytokine dialysis: an ex vivo study.

To test the hypothesis that dialysis using a new large pore membrane would achieve effective cytokine removal, blood from six volunteers was incubated with endotoxin (1 mg) and then circulated through a closed circuit with a polyamide membrane (nominal cut-off: 100 kDa). Hemodialysis was conducted at 1 or 9 L/hr of dialysate flow at the start of circulation and after 2 and 4 hours. The peak dialysate/plasma concentration ratios were 0.92 for interleukin (IL)-1beta, 0.67 for IL-6, 0.94 for IL-8, 0.33 for tumor necrosis factor (TNF)-a, and 0.11 for albumin. The dialysate/plasma ratios for all cytokines and albumin were decreased with increased dialysate flow from 1 to 9 L/hr (p < 0.05). Clearances for IL-1beta, IL-6, and IL-8, however, were significantly improved with increased dialysate flow (p < 0.01). There was no increase in TNF-a clearance (not significant) and a decrease in albumin clearance (p < 0.01). The peak clearance at 9 L/hr was 33 ml/min for IL-1beta, 19 for IL-6, 51 for IL-8, 11 for TNF-alpha, and 1.2 for albumin. No adsorption of cytokines was observed. We conclude that cytokine dialysis is achievable through a membrane with a high cut-off point with negligible albumin loss. These findings support the technical feasibility of this new approach to blood purification in sepsis.

Blood Flow Velocity↗
PubMedDate not supplied

Continuous venovenous hemofiltration without anticoagulation.

We conducted a prospective observational study to assess the efficacy of continuous venovenous hemofiltration (CVVH) with no anticoagulation. A standard anticoagulation protocol for CVVH, which prescribed no anticoagulation for patients at risk of bleeding, was applied to 48 critically ill patients treated with CVVH. Circuit life was prospectively observed, and the following data were obtained for each circuit: heparin use and dose, protamine use, daily prothrombin time-international normalized ratio, activated partial thromboplastin time, and platelet count. Out of 300 consecutive circuits, 143 (47.6%) received no anticoagulation, 31 (10.3%) received regional anticoagulation, and 126 received low dose heparin. No patients experienced bleeding complications secondary to CVVH. Platelet count was significantly lower in the no anticoagulation group (73 x 10(3)/microl) compared with the low dose heparin group (119 x 10(3)/microl) and the protamine group (104 x 10(3)/microl) (p < 0.01 for both comparisons). There was no significant difference in mean circuit life among the three groups (heparin, 20.9 hours; no anticoagulation, 19.3 hours; protamine, 21.2 hours; not significant). In conclusion, for a group of patients deemed to be at risk of bleeding, CVVH without anticoagulation achieved an acceptable circuit life, which was similar to that obtained in other patients with low dose heparin anticoagulation or regional anticoagulation with heparin/protamine.

Acute Kidney Injury↗