Maintaining blood flow in the extracorporeal circuit: haemostasis and anticoagulation

The Hematological Effects of Extracorporeal Membrane Oxygenator Exchange

Membrane oxygenator failure during venovenous (V-V) extracorporeal membrane oxygenation (ECMO) can lead to life-threatening hypoxia, high replacement costs, and may be associated with a hyperfibrinolytic state and bleeding. The current understanding of the underlying mechanisms that drive this is limited. The primary aim of this study therefore is to investigate the hematological changes that occur before and after membrane oxygenator and circuit exchanges (ECMO circuit exchange) in patients with severe respiratory failure managed on V-V ECMO. We analyzed 100 consecutive V-V ECMO patients using linear mixed-effects modeling to evaluate hematological markers in the 72 hours before and 72 hours after ECMO circuit exchange. A total of 44 ECMO circuit exchanges occurred in 31 of 100 patients. The greatest change from baseline to peak were seen in plasma-free hemoglobin (42-fold increase p < 0.01) and the D-dimer:fibrinogen ratio (1.6-fold increase p = 0.03). Bilirubin, carboxyhemoglobin, D-dimer, fibrinogen, and platelets also showed statistically significant changes ( p < 0.01), whereas lactate dehydrogenase did not ( p = 0.93). Progressively deranged hematological markers normalize more than 72 hours after ECMO circuit exchange, with an associated reduction in membrane oxygenator resistance. This supports the biologic plausibility that ECMO circuit exchange may prevent further complications such as hyperfibrinolysis, membrane failure, and clinical bleeding.

Integration of transcriptomics and metabolomics reveals the molecular mechanisms underlying the effect of nafamostat mesylate on rhabdomyolysis-induced acute kidney injury

Objective: To investigate the role and mechanisms of action of nafamostat mesylate (NM) in rhabdomyolysis-induced acute kidney injury (RIAKI). Methods: RIAKI rats were assigned into control group (CN), RIAKI group (RM), and NM intervention group (NM). Inflammatory cytokines and proenkephalin a 119-159 (PENKID) were assessed. Cell apoptosis and glutathione peroxidase-4 (GPX4) were detected using TUNEL assay and immunohistochemical staining. Mitochondrial membrane potential (MMP) was detected by JC-1 dye. The expression of genes and metabolites after NM intervention was profiled using transcriptomic and metabolomic analysis. The differentially expressed genes (DEGs) were validated using qPCR. The KEGG and conjoint analysis of transcriptome and metabolome were used to analyze the enriched pathways and differential metabolites. The transcription factors were identified based on the animal TFDB 3.0 database. Results: Serum creatinine, blood urea nitrogen, and PENKID were remarkably higher in the RM group and lower in the NM group compared to the CN group. Pro-inflammatory cytokines increased in the RM group and notably decreased following NM treatment compared to the CN group. Tubular pathological damages were markedly attenuated and renal cell apoptosis was reduced significantly in the NM group compared to the RM group. The expression of GPX4 was lower in the RM group compared to the CN group, and it increased significantly after NM treatment. A total of 294 DEGs were identified in the RM group compared with the NM group, of which 192 signaling pathways were enriched, and glutathione metabolism, IL-17 signaling, and ferroptosis-related pathways were the top-ranking pathways. The transcriptional levels of Anpep, Gclc, Ggt1, Mgst2, Cxcl13, Rgn, and Akr1c1 were significantly different between the NM and RM group. Gclc was the key gene contributing to NM-mediated renal protection in RIAKI. Five hundred and five DEGs were annotated. Compared with the RM group, most of the upregulated DEGs in the NM group belonged to Glutathione metabolism, whereas most of the downregulated DEGs were related to the transcription factor Cytokine-cytokine receptor interaction. Conclusion: NM protects the kidneys against RIAKI, which is mainly associated with NM mediated regulation of glutathione metabolism, inflammatory response, ferroptosis-related pathways, and the related key DEGs. Targeting these DEGs might emerge as a potential molecular therapy for RIAKI.

Segmental citrate anticoagulation for double-filtration plasmapheresis: A case report and literature review

Regional citrate anticoagulation (RCA) has been widely used in patients with high-risk bleeding for anticoagulation in renal replacement therapy. However, scientific reports on the use of RCA in double-filtration plasmapheresis (DFPP) are limited. In the available reports, anticoagulation was not performed in the plasma component separator. However, as demonstrated in the present study, during the treatment of a patient with anti-neutrophil cytoplasmic antibody-associated vasculitis, although RCA was used for DFPP, coagulation occurred in the plasma component separator, resulting in the interruption of treatment. Thus, segmental citrate anticoagulation (SCA) was used and the filter was successfully prevented from clotting again. The present study demonstrates that SCA can more effectively prevent the clogging of the plasma separator and the plasma component separator, thereby maintaining the continuity of treatment and avoiding treatment interruption.

Hemostatic effects of therapeutic plasma exchange: A concise review

Therapeutic plasma exchange (TPE) alters the hemostatic balance. Contributing to TPE's hemostatic effects is the mechanical processing of blood in the extracorporeal circuit, circuit anticoagulant, type of replacement fluid, TPE schedule and number of procedures, TPE timing relative to invasive procedures, and removal of nontargeted components such as platelets, coagulation proteins, and cytokines. Although TPE's hemostatic effects are well established, how it impacts the bleeding risk is not clearly understood. In this concise review, we describe the effects of the above TPE-related factors on hemostatic balance, present data on the effects of TPE on blood hemostasis, including its effects on platelet counts and clotting assays, and review the literature on the impact of TPE-induced hemostatic changes on TPE-associated bleeding events. Finally, we discuss risk factors associated with bleeding during TPE and review the literature on TPE-associated hemostatic effects in the pediatric population.

Ex Vivo Testing of Heparin-Coated Extracorporeal Circuits: Bovine Experiments

In this study the intrinsic thrombogenicity of the extracorporeal circuits and the benefit of heparin-bonded circuits in an extracorporeal life support system without full systemic heparinization and with minimal interference of the so called material-independent factors was tested in four calves. In two circuits (group A) all blood-contacting surfaces were coated with end-point-attached heparin and the other two were non-coated (group B). Under standardized conditions the calves were perfused at a blood flow rate of 2 L/min. After only one bolus injection of heparin (250 IU/kg body weight) before cannulation, plasma heparin activity rapidly decreased in both groups: half life of about 55 minutes. This decrease of the heparin activity was accompanied by a fall of the activated clotting time (ACT) level to baseline values. The experiments using a heparin-coated circuit, had a runtime of more than 360 minutes, whereas the experiments using a non-coated circuit had to be terminated after a runtime of 255 minutes, because massive fibrin formation was noticed in the circuit. This formation was accompanied by a rapid increase in the line pressure, measured just before the inlet of the oxygenator. The macroscopic inspections after terminating the experiments and rinsing the circuit showed a clean circuit in group A. The fibrinopeptide A (FPA) level increased faster during perfusion with the non-coated circuit than in the heparin coated circuit. Lung histopathological examinations of the lungs of the animals in group A showed no fibrin deposition, whereas most of the blood vessels of the lung preparations of the animals in group B were partially or completely occluded with fibrin. These results suggest that heparin-bonding greatly reduces the thrombogenicity of the extracorporeal circuit, and therefore it can reduce the need for systemic heparinization in an extracorporeal life support system.

Global and Extended Coagulation Monitoring during Extracorporeal Lung Assist with Heparin-Coated Systems in ARDS Patients

Heparin-coated systems for extracorporeal lung-assist (ECLA) were developed to reduce hemorrhagic risk by lowering the systemic heparinization, monitored by global tests, e.g. activated coagulation time (ACT) and activated partial thromboplastin time (APTT). Since this strategy gives no insight into procoagulant states, five ARDS patients receiving ECLA with heparin-coated systems were investivated for changes in coagulation using both global and extended tests. During ECLA onset the APTT and ACT were within or near normal ranges, platelets decreased 76.5% within 48h, fibrinogen decreased 28.7%, thrombin-antithrombin-III complexes were elevated before ECLA (53 μg/L), but demonstrated an additional peak (238 μg/L), plasminogen-activator-inhibitor-1 increased 12-fold, and the C1-inhibitor dropped 14.1%. In conclusion, after the onset of ECLA from a previous prethrombotic state, the precoagulant, anticoagulant, fibrinolytic and complement systems were activated in a similar way to that reported for non-heparinized systems with high-dose heparin. This was however only monitored by an extended test panel which was unable to predict thromboembolic events during ECLA.

Activation of the Clotting System: Heparin-Coated versus Non Coated Systems for Extracorporeal Circulation

The purpose of this experimental study was to compare heparin-coated versus non-coated systems for extracorporeal membrane oxygenation (ECMO), to investigate the dynamic course of clotting activation in both groups.

Methods.

Eight pigs weighing 19.7 (± 1.3) kg, each underwent ECMO for 24 hours. Two groups were formed: in group 1, heparin-coated circuits were used with low dose heparinization (10 IU/kg/hr), whereas in group 2 non-coated circuits with high dose heparinization (60 IU/kg/hr) were used. Coagulation was monitored by measuring prothrombin time, partial thromboplastin time, fibrinogen, antithrombin III (AT III) and specific markers of clotting activation (thrombin-antithrombin III complexes (TAT) and D-dimer). Furthermore, platelet count, hematocrit, activated clotting time (ACT), and plasma heparin concentration were determined regularly.

Results.

The dynamic course of the specific coagulation activation markers showed some differences: whereas TAT and D-dimer increased quickly in group 2, the increase in group 1 was delayed. Activation marker values tended to be lower in group 1 during the first six hours, after which no more differences between the groups were seen. After 24 hours of ECMO, TAT and D-dimer had nearly returned to baseline values. Platelets showed a continuous decrease throughout the experiment, which was very similar in both groups.

Conclusions.

The heparin coated system showed a distinct delay in clotting activation during the first six hours of ECMO. After six hours there were no more differences between the groups.

Soluble fibrin is a useful marker for predicting extracorporeal membrane oxygenation circuit exchange because of circuit clots

A circuit clot is one of the most frequent complications during extracorporeal membrane oxygenation (ECMO) support. We identify coagulation/fibrinolysis markers for predicting ECMO circuit exchange because of circuit clots during ECMO support. Ten patients with acute pulmonary failure who underwent veno-venous ECMO were enrolled between January 2014 and December 2016. ECMO support lasted 106 days. The 6 days on which the ECMO circuits were exchanged were considered as circuit clot (+) group, while the remaining 100 days were considered as circuit clot (-) group. The predictors of ECMO circuit exchange because of circuit clots were identified. The mean duration of ECMO support was 10 ± 13 days, and the mean number of ECMO circuit exchange was 0.6 ± 1.1 times per patient. Thrombin-antithrombin complex (TAT) and soluble fibrin (SF) were higher in the circuit clot (+) group than in the circuit clot (-) group (both P < 0.01). According to a multivariate analysis, SF was the only independent predictor of ECMO circuit exchange (P < 0.01). The odds ratio (confidence intervals) for SF (10 µg/ml) was 1.20 (1.06-1.36). The area under the curve and optimal cut-off value were 0.95 and 101 ng/ml for SF (sensitivity, 100%; specificity, 89%). SF may be useful in predicting ECMO circuit exchange because of circuit clots.

Preoperative Platelet Count Predicts Lower Extremity Free Flap Thrombosis: A Multi-Institutional Experience

BACKGROUND

Thrombocytosis in patients undergoing lower extremity free tissue transfer may be associated with increased risk of microvascular complications. This study assessed whether preoperative platelet counts predict lower extremity free flap thrombosis.

METHODS

All patients undergoing lower extremity free tissue transfer at Duke University from 1997 to 2013 and at the University of Pennsylvania from 2002 to 2013 were retrospectively identified. Logistic regression was used to assess whether preoperative platelet counts independently predict flap thrombosis, controlling for baseline and operative factors.

RESULTS

A total of 565 patients underwent lower extremity free tissue transfer, with an overall flap thrombosis rate of 16 percent (n = 91). Elevated preoperative platelet counts were independently associated with both intraoperative thrombosis (500 ± 120 versus 316 ± 144 × 10/liter; p < 0.001) and postoperative thrombosis (410 ± 183 versus 320 ± 143 × 10/liter; p = 0.040) in 215 patients who sustained acute lower extremity trauma within 30 days before reconstruction. In acute trauma patients, preoperative platelet counts predicted a four-fold increased risk of intraoperative thrombosis (cutoff value, 403 × 10/liter; OR, 4.08; p < 0.001) and a two-fold increased risk of postoperative thrombosis (cutoff value, 361 × 10/liter; OR, 2.16; p = 0.005). In patients who did not sustain acute trauma, preoperative platelet counts predicted a four-fold increased risk of intraoperative thrombosis (cutoff value, 352 × 10/liter; OR, 3.82; p = 0.002).

CONCLUSIONS

Acute trauma patients with elevated preoperative platelet counts are at increased risk for lower extremity free flap complications. Prospective evaluation is warranted for guiding risk stratification and targeted treatment strategies.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

The effect of specialized continuous renal replacement therapy team in acute kidney injury patients treatment

PURPOSE

Continuous renal replacement therapy (CRRT) has been established for critically ill acute kidney injury (AKI) patients. In addition, some centers consist of a specialized CRRT team (SCT) with physicians and nurses. To our best knowledge, however, ona a few studies have yet been carried out on the superiority of SCT management.

MATERIALS AND METHODS

A total of 551 patients, who received CRRT between January 2008 and March 2009, were divided into two groups based on the controller of CRRT. The impact of the CRRT management on 28-day mortality was compared between two groups by Kaplan-Meier curve and Cox analysis.

RESULTS

During the study period, the number of filters used, down-time per day, and intensive care unit length of day were significantly higher in non-SCT group than in SCT group (6.2 hrs vs. 5.0 hrs, p=0.042; 5.0 hrs vs. 3.8 hrs, p<0.001; 27.5 days vs. 21.1 days, p=0.027, respectively), while net ultrafiltration rate was significantly lower in non-SCT group than SCT group (28.0 mL/kg/hr vs. 29.5 mL/kg/hr, p=0.043, respectively). In addition, 28-day mortality rate was significantly lower in SCT group than with non-SCT group (p=0.031). Moreover, Cox regression analysis showed that 28-day mortality rate was significantly lower in SCT control group, even after adjusting for age, gender, severity scores, biomarkers, risk, injury, failure, loss, and end-stage renal disease, and contributing factors (hazard ratio 0.91, p=0.046).

CONCLUSION

A well-trained CRRT team could be beneficial for mortality improvement of AKI patients requiring CRRT.

The benefit of specialized team approaches in patients with acute kidney injury undergoing continuous renal replacement therapy: propensity score matched analysis

Introduction

Continuous renal replacement therapy (CRRT) has been widely used in critically ill acute kidney injury (AKI) patients. Moreover, some centers operate a specialized CRRT team (SCT) composed of physicians and nurses, but few studies have yet determined the superiority of SCT control.

Methods

A total of 334 among 534 patients in the original cohort, who started CRRT for severe AKI between August 2007 and September 2009 in Yonsei University Health System and were matched with a propensity score (PS), were divided into two groups based on SCT application. Moreover, we compared CRRT-related outcomes including down-time per day and lost time per filter-exchange between the two groups. The primary outcomes were 28- and 90-day all-cause mortality, and the secondary outcomes were the rates of renal function recovery at 28- and 90-day.

Results

The down-time per day, lost time per filter-exchange, and red blood cell-transfused numbers during CRRT treatment were significantly lower after SCT approach compared with the group before SCT, while net ultrafiltration rate in the after SCT group was significantly higher compared to the before SCT group. During the study period, the 28- and 90-day all-cause mortality rates were significantly decreased after SCT application. Cox regression analysis revealed that 28- and 90-day all-cause mortality rates were significantly lower under SCT control, after adjusting for primary diagnosis, emergent surgical cases, Charlson Comorbidity Index and biochemical parameters. However, there were no significant differences in the rate of renal function recovery before and after SCT approach in CRRT.

Conclusions

A well-organized CRRT team could be beneficial for clinical outcomes through improving quality of care in AKI patients requiring CRRT treatment in the ICU.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0454-8) contains supplementary material, which is available to authorized users.

Bubble chamber clotting during continuous renal replacement therapy: vertical versus horizontal blood flow entry

BACKGROUND

The continuous renal replacement therapy (CRRT) bubble trap chamber is a frequent site of clotting.

AIMS

To assess clot formation when comparing our standard 'vertical' blood entry chamber (BEC) with a new 'horizontal' BEC.

METHODS

Adult ICU patients requiring CRRT were treated with the vertical BEC and then a similar subsequent cohort with the horizontal BEC in continuous veno-venous haemofiltration mode.

RESULTS

40 chambers were assessed for each design. Circuit life was 13.9 ± 9.5 h for the vertical and 17.7 ± 15.9 h for the horizontal BEC (p = 0.33). APTT, however, was higher for the horizontal BEC (55.7 ± 34.7 vs. 37.4 ± 9.0, p < 0.002) and no difference in circuit life was found after multivariable analysis. A clotting score ≥3 was observed in 85% of all chambers. There was no difference in chamber clotting score (vertical 3.6 ± 1.03 vs. horizontal 3.8 ± 1.0, p = 0.5). In addition, no difference was found when scores were divided into two groups using a 'likelihood' to clot analysis (p = 1.0).

CONCLUSION

CRRT horizontal BEC were not associated with less clotting compared to our standard vertical BEC.

Specific glycosaminoglycans promote unseeded amyloid formation from β2-microglobulin under physiological conditions

Dialysis-related amyloidosis (DRA) is a complication of hemodialysis where beta2-microglobulin (beta2m) forms plaques mainly in cartilaginous tissues. The tissue-specific deposition, along with a known intransigence of pure beta2m to form fibrils in vitro at neutral pH in the absence of preformed fibrillar seeds, suggests a role for factors within cartilage in enhancing amyloid formation from this protein. To identify these factors, we determined the ability of a derivative lacking the N-terminal six amino acids found in ex vivo beta2m amyloid deposits to form amyloid fibrils at pH 7.4 in the absence of fibrillar seeds. We show that the addition of the glycosaminoglycans (GAGs) chrondroitin-4 or 6-sulfate to fibril growth assays results in the spontaneous generation of amyloid-like fibrils. By contrast, no fibrils are observed over the same time course in the presence of hyaluronic acid, a nonsulfated GAG that is abundant in cartilaginous joints. Based on the observation that hyaluronic acid has no effect on fibril stability, while chrondroitin-6-sulfate decreases the rate of fibril disassembly, we propose that the latter GAG enhances amyloid formation by stabilizing the rare fibrils that form spontaneously. This leads to the accumulation of beta2m in fibrillar deposits. Our data rationalize the joint-specific deposition of beta2m amyloid in DRA, suggesting mechanisms by which amyloid formation may be promoted.

Anticoagulation in CRRT: Agents and strategies in Australian ICUs

BACKGROUND

Continuous Renal Replacement Therapy (CRRT) should ideally operate with as little interruption as possible. The majority of circuit terminations occur due to clotting. The Longevity of CRRT is able to be improved when the extracorporeal circuit is anticoagulated.

AIMS

This article willt focus attention on anticoagulant agents used in Australian intensive care units (ICU) to prevent clotting in the CRRT circuit.

DISCUSSION

Anticoagulants reviewed include unfractionated or standard heparin, regional heparinisation, low-molecular weight heparins and heparinoids, regional citrate, platelet-inhibiting agents (prostacyclin), thrombin antagonists (recombinant hirudin) and therapy with no anticoagulant use. Each type of anticoagulant was reviewed for mode of action, the method of delivery and how the effect is monitored. Circuit life and the incidence of bleeding were considered as the principle end points in selecting therapy, as well as side-effects with administration such as metabolic disturbances, contraindications to use including allergy and ease of use in the clinical environment.

CONCLUSION

No approach to anticoagulation has yet been reported to be as successful in extending circuit life, whilst remaining inexpensive, easy to manage and easy to reverse, as unfractionated heparin. Certain patient conditions may preclude the use of heparin, such as heparin-induced thrombocytopenia (HIT); then heparinoids, thrombin antagonists and sodium citrate are suggested as alternatives. Regional citrate reduces haemorrhagic complications in patients who have coagulation disorders or are at risk of bleeding. Clinical experience with various agents and strategies should also influence choice. The option of no anticoagulant may be appropriate in selected patients rather than more expensive and less familiar drugs.

Anticoagulation strategies in continuous renal replacement therapy: can the choice be evidence based?

OBJECTIVES

Critical illness increases the tendency to both coagulation and bleeding, complicating anticoagulation for continuous renal replacement therapy (CRRT). We analyzed strategies for anticoagulation in CRRT concerning implementation, efficacy and safety to provide evidence-based recommendations for clinical practice.

METHODS

We carried out a systematic review of the literature published before June 2005. Studies were rated at five levels to create recommendation grades from A to E, A being the highest. Grades are labeled with minus if the study design was limited by size or comparability of groups. Data extracted were those on implementation, efficacy (circuit survival), safety (bleeding) and monitoring of anticoagulation.

RESULTS

Due to the quality of the studies recommendation grades are low. If bleeding risk is not increased, unfractionated heparin (activated partial thromboplastin time, APTT, 1-1.4 times normal) or low molecular weight heparin (anti-Xa 0.25-0.35 IU/l) are recommended (grade E). If facilities are adequate, regional anticoagulation with citrate may be preferred (grade C). If bleeding risk is increased, anticoagulation with citrate is recommended (grade D(-)). CRRT without anticoagulation can be considered when coagulopathy is present (grade D(-)). If clotting tendency is increased predilution or the addition of prostaglandins to heparin may be helpful (grade C(-)).

CONCLUSION

Anticoagulation for CRRT must be tailored to patient characteristics and local facilities. The implementation of regional anticoagulation with citrate is worthwhile to reduce bleeding risk. Future trials should be randomized and should have sufficient power and well defined endpoints to compensate for the complexity of critical illness-related pro- and anticoagulant forces. An international consensus to define clinical endpoints is advocated.

Assessment of the Heparin-Binding AN69 ST Hemodialysis Membrane: II. Clinical Studies without Heparin Administration

Binding polyanionic unfractionated heparin over the modified AN69 polyacrylonitrile membrane, the surface electronegativity of which has been neutralized by polyethyleneimine (AN69-ST), renders the membrane more hemocompatible. This property was tested in two groups of long-term hemodialysis patients. Results were rated as massive or partial clotting of a dialyzer at the end of the session. Group I patients were included in a prospective, cross-over study comparing standard dialysis with hemodialysis without systemic administration of unfractionated heparin (n = 12, 123 sessions). In all instances, priming was made with 2 I saline containing 5,000 IU/l heparin. Only patchy or partial clotting was observed in 11% and 39% of the sessions with standard and heparin-free administration, respectively. Group II patients were included in an open, observational pilot study testing the effects of the heparin-coated membrane, without systemic administration of heparin, in patients at high risk of bleeding (n = 68, 331 sessions). Massive clotting was observed in six sessions only (less than 2%) and normal or slightly patchy dialyzers were found in 88% of the sessions. It is concluded that the dialysis AN69 ST membrane, after adequate priming at bedside, can be used without systemic administration of heparin for hemodialysis in patients at high risk of bleeding.

Renal replacement therapy in the intensive care unit

Acute renal failure is a common complication in the intensive care unit (ICU). Over the last 25 years, there have been significant technological advances in the delivery of renal replacement therapy, particularly as it pertains to the critically ill patient population. Despite these advances, acute renal failure in critically ill patients continues to carry a poor prognosis. In this article, we review the current literature about timing and initiation of renal replacement therapy in the ICU as well as practical considerations regarding the prescription and delivery of dialysis.

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.

Citrate anticoagulation in a piglet model of pediatric continuous renal replacement therapy

OBJECTIVE

To develop pediatric guidelines for the use of citrate as a regional anticoagulant for continuous renal replacement therapy (CRRT) using a neonatal piglet model.

DESIGN

Prospective observational study.

SETTING

Animal laboratory in the research center of a tertiary-level children's hospital.

SUBJECTS

Ten neonatal piglets.

INTERVENTIONS AND MEASUREMENTS

Using a venovenous CRRT circuit and filter, we randomly altered the filter blood flow rate, replacement flow rate, and citrate flow rate over conventional pediatric ranges. Measured end points were prefilter serum ionized calcium and citrate levels.

MAIN RESULTS

A prefilter serum citrate concentration of 6 mmol/L is required to maintain the prefilter ionized calcium < or =0.4 mmol/L. Using multiple regression analysis on collected data, we derived a formula to predict prefilter serum citrate for combinations of replacement flow rate, blood flow rate, and citrate flow rate.

CONCLUSIONS

The available literature and our past experience indicate that a prefilter ionized calcium < or =0.4 mmol/L is required to anticoagulate a CRRT circuit; a prefilter serum citrate concentration of 6 mmol/L is required to achieve this. Our multiple regression analysis can be expressed graphically to allow easy calculation of the required citrate flow rate, given the knowledge of the replacement flow rate and blood flow rate. Our results provide the first guidelines for the use of citrate as a regional anticoagulant in a pediatric-size model of CRRT.

Changes of haemostasis in patients undergoing major abdominal surgery--is there a difference between elderly and younger patients?

Many physiological functions are altered in the elderly. It is not clear whether this applies to haemostatic mechanisms in patients undergoing major surgery. Twenty-five consecutive patients <60 yr and 25 consecutive patients >70 yr scheduled for abdominal surgery for malignancies were included in our study. Various standard coagulation variables and specific markers of coagulation were serially measured before surgery (baseline), at arrival on the intensive care unit (ICU), 4 h after arrival on ICU, and on the morning of the first postoperative day. Platelet function was assessed using the Platelet Function Analyser PFA-100 with adenosine diphosphate (ADP) as an inductor. Anaesthesia and surgery were similar between the elderly (76(3) years) and younger (53(5) years) groups. Baseline plasma levels of prothrombin fragments F1+2, thrombin-antithrombin III (TAT) complex, and D-dimers were significantly different between the two groups, indicating thrombin activation and fibrin formation in the elderly. Postoperatively, only F1+2 plasma levels were significantly higher in the elderly (4.0(0.8) nmol/l) than in the younger patients (2.2(0.9) nmol/l), whereas the course of D-dimer and TAT did not differ significantly between the two groups. Endothelial-derived markers of coagulation (von Willebrand factor, collagen-binding activity of von Willebrand factor) were not different between the groups throughout the study period. Platelet function was impaired in the elderly compared with the younger patients. It is concluded that elderly patients showed more prothrombin activation/thrombin generation and increased fibrinolytic activity prior to surgery than younger patients. However, perioperative changes of coagulation in the elderly were similar to those seen in younger patients.

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 x 10(3)/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.

Changes of the hemostatic network in critically ill patients--is there a difference between sepsis, trauma, and neurosurgery patients?

OBJECTIVE

To study the time course of coagulation data in intensive care patients.

DESIGN

Prospective, descriptive study.

SETTING

Clinical investigation on a surgical and neurosurgical intensive care unit of a university hospital.

PATIENTS

Fifteen patients with severe trauma (injury severity score, 15 to 25), 15 sepsis patients secondary to major surgery, and 15 neurosurgery patients (cancer surgery) were studied.

INTERVENTIONS

Standardized intensive care therapy.

MEASUREMENTS AND MAIN RESULTS

Standard coagulation data and molecular markers of coagulation activation and fibrinolytic activity (soluble thrombomodulin, protein C, free protein S, thrombin/antithrombin III complex, plasmin-alpha 2-antiplasmin complex, tissue plasminogen activator, platelet factor 4, beta-thromboglobulin were measured from arterial blood samples on the day of admission to the intensive care unit (trauma/neurosurgery patients) or on the day of diagnosis of sepsis (baseline value) and serially during the next 5 days. Antithrombin III, fibrinogen, and platelet counts were highest in neurosurgery patients but without significant differences between sepsis and trauma patients. Thrombin/antithrombin III complex increased in the sepsis patients (from 22.6+/-4.2 microg/L to 39.9+/-6.8 microg/L), but decreased in trauma (from 40.2+/-5.1 microg/L to 17.6+/-4.0 microg/L) and neurosurgery patients (from 28.2+/-4.2 microg/L to 16.2+/-3.8 microg/L). Tissue plasminogen activator increased in the sepsis patients (from 14.4+/-3.9 microg/L to 20.7+/-3.8 microg/mL) and remained almost unchanged in the other two groups. Soluble thrombomodulin plasma concentration increased significantly in the sepsis group (max, 131.8+/-22.5 ng/mL), while it remained elevated in the trauma (max, 75.5+/-5.9 ng/mL) and was almost normal in the neurosurgery patients. Protein C and free protein S remained decreased only in the sepsis group.

CONCLUSIONS

Alterations of the hemostatic network were seen in all three groups of critically ill patients. Hemostasis normalized in the neurosurgery patients and posttraumatic hypercoagulability recovered within the study period. By contrast, monitoring of molecular markers of the coagulation process demonstrated abnormal hemostasis in the sepsis patients during the entire study period indicating ongoing coagulation disorders and abnormalities in fibrinolysis in these patients.

Anticoagulation in continuous renal replacement therapy

Continuous renal replacement therapies (CRRTs) allow for gradual solute and fluid removal. In very sick patients with acute renal failure, they may be better tolerated than hemodialysis. The major drawback to CRRTs is the need for anticoagulation to maintain filter patency. The patients who are likely to benefit from CRRTs are also at higher risk for bleeding from systemic anticoagulation. The most commonly used form of anticoagulation for CRRTs, low-dose heparin, causes bleeding in 10-50% of patients. Regional anticoagulation using protamine may reduce the risk of bleeding, but it is difficult to use. Low molecular weight heparin and prostacyclin both may partially reduce bleeding, but are difficult to dose. Regional anticoagulation with citrate is easy to use and has been shown to prolong filter life without systemic anticoagulation. It is the anticoagulant of choice for most patients on CRRT.

Nitric oxide diffusion across membrane lungs protects platelets during simulated extracorporeal circulation

BACKGROUND

The absence of a protective endothelial surface on membrane oxygenators during extracorporeal circulation (ECC) promotes platelet trapping and damage, leading to increased bleeding complications. We investigated the effects of transmembranous diffusion of gaseous nitric oxide (NO) on platelets during simulated ECC.

MATERIAL AND METHODS

Two paired circuits were run in parallel with fresh, heparinized (1 U mL-1) blood from healthy human donors for 240 min. To one of the paired circuits, 20 ppm NO was added transmembranously.

RESULTS

NO significantly attenuated platelet trapping and reduced intracircuit platelet activation evaluated by the release of beta-thromboglobulin, platelet factor 4 and soluble P-selectin. Furthermore, NO significantly preserved platelet reactivity to stimulating agents (ADP and adrenaline), evaluated as the ability to expose P-selectins and activate glycoprotein (GP)-IIb-IIIa. Nevertheless, circulating activated platelets expressing P-selectin or activated GPIIb-IIIa were not different and were not significantly increased. The mean fluorescence intensity of GPIb and GPIIb-IIIa decreased in both circuits equally.

CONCLUSIONS

Transmembranous diffusion of gaseous NO revealed protective effects on platelets by reducing thrombocytopenia/pathia and preserving platelet reactivity.

Peripheral circulatory effects of pump perfusion on cat skeletal muscle with and without prostacyclin

The present study analyses the peripheral circulatory effects of pump perfusion on a sympathectomized cat skeletal muscle in terms of effects on segmental vascular resistances (large-bore arterial vessels, arterioles and veins), hydrostatic capillary pressure, capillary filtration coefficient, transcapillary filtration and autoregulation of blood flow. The effect of prostacyclin during pump perfusion was analysed to evaluate whether it interferes with the pump-induced vascular alterations, especially if it reduces transcapillary filtration through its capillary permeability decreasing effect. Pump perfusion initiates a marked vasodilation (from 17.3 to 10.1 PRU), an increase in hydrostatic capillary pressure, and a marked inhibition of myogenic reactivity and of autoregulation of blood flow. There was a slow restoration of vascular tone reaching a steady-state level somewhat below the autoperfusion value within 2 h. Pump perfusion did not change the capillary filtration coefficient, indicating that the capillary permeability was not increased. This implies that short-term pump-induced capillary leakage is more an effect of increase in hydrostatic capillary pressure, perhaps in combination with increased number of open capillaries, than of an increase in capillary permeability. Prostacyclin decreased capillary permeability by at least 22% but simultaneously increased hydrostatic capillary pressure, resulting in an unchanged filtration compared with the situation just after the starting of the pump. The results obtained show that experiments using pump perfusion should be interpreted with care due to the interference with normal peripheral vascular control. The results give reasonable explanations of the lowered blood pressure and transcapillary fluid loss during the clinical use of a heart-lung machine.

Activation of the clotting system during extracorporeal membrane oxygenation in term newborn infants

OBJECTIVES

To determine the degree of clotting activation that occurs with the usual anticoagulation regimen with systemic heparinization.

METHODS

To allow a standardized comparison of the patients, this study focused on the first 48 hours of extracorporeal membrane oxygenation (ECMO) in term newborn infants. The ECMO perfusion circuit consisted of a roller pump, silicone membrane lungs, and silicone rubber tubing. Coagulation was controlled routinely by measuring prothrombin time, fibrinogen, antithrombin III, and reptilase time. Platelet counts, activated clotting time, and heparin concentration were controlled regularly. The following specific activation markers of the clotting system were measured: prothrombin activation fragment 1 + 2(F1+2), thrombin-antithrombin III complexes, and D-dimer. Measurements were done before the start of ECMO, after 5 minutes, and at hours 1, 2, 3, 4, 6, 12, 24 and 48.

RESULTS

All seven term infants had excessively high levels of clotting activation markers within the first 2 hours of ECMO: F1+2, 11.6(+/- O.9) nmol/L (mean +/- SEM); thrombin-antithrombin, 920(+/- 2.2) microg/L; D-dimer, 15.522(+/- 3.689) ng/L. During the next 46 hours of ECMO, F1+2 and thrombin-antithrombin III complexes decreased from those high values, whereas D-dimer did not. The increase of activation markers was accompanied by low fibrinogen, low platelet counts. and prolongation of reptilase time.

CONCLUSIONS

These findings fit the pattern of consumptive coagulopathy during neonatal ECMO, especially in the first 24 hours.

Influence of long-term continuous intravenous administration of pentoxifylline on endothelial-related coagulation in critically ill patients

OBJECTIVE

To determine the influence of pentoxifylline on endothelial-associated coagulation.

DESIGN

Prospective, randomized, placebo-controlled study.

SETTING

A surgical intensive care unit of a university hospital.

PATIENTS

Consecutive patients (n = 60) with trauma or sepsis secondary to major (nontrauma) surgery. All patients received controlled mechanical ventilation.

INTERVENTIONS

According to a randomized sequence, the patients either received pentoxifylline continuously over 5 days (1.5 mg/kg/hr iv) (trauma-pentoxifylline group [n = 15], sepsis-pentoxifylline group [n=15] or saline solution as placebo (trauma-control group [n = 15], sepsis-control group [n = 15].

MEASUREMENTS AND MAIN RESULTS

In addition to the standard coagulation screen, thrombomodulin, protein C, (free) protein S, and thrombin-antithrombin plasma concentrations were measured by enzyme-linked immunosorbent assays. Intensive care therapy, hemodynamics, and changes of Acute Physiology and Chronic Health Evaluation II score were comparable for pentoxifylline-treated and nontreated patients. An average dose of 2.5 g/day of pentoxifylline (range 2.2 to 2.9) was infused into the pentoxifylline-treated patients. At baseline, plasma thrombomodulin concentrations were higher in the septic patients than in the trauma patients. Thrombomodulin plasma concentrations increased significantly more in the control patients (trauma: from 38.9 +/- 10.5 to 59.9 +/- 10.1 ng/mL; sepsis: from 49.7 +/- 12.1 to 72.3 +/- 11.2 ng/mL) than in the pentoxifylline-treated patients (trauma: from 37.9 +/- 11.9 to 50.2 +/- 9.2 ng/mL; sepsis from 51.9 +/- 10.1 to 63.3 +/- 10.2). Starting from similar baseline values, protein C concentration increased significantly more in the sepsis-pentoxifylline patients (from 52.0 +/- 11.1% to 69.1 +/- 11.1%) than in the untreated septic patients (from 50.1 +/- 10.0% to 52.5 +/- 9.5%). There were no significant differences between the pentoxifylline-treated and nontreated groups for protein S and thrombin-antithrombin concentrations. Standard coagulation parameters (fibrinogen, activated partial thromboplastin time, antithrombin III) did not differ between these groups either.

CONCLUSIONS

Continuous intravenous administration of pentoxifylline for 5 days beneficially influenced the thrombomodulin/protein C/protein S system in both the trauma and septic patients.