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RENAL REPLACEMENT THERAPY IN THE ICU
Dr. Kondamudi Sai Kiran Internal Medicine & Critical Care 20th April, 2016
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INTRODUCTION One third of patients admitted to ICU have acute kidney injury. Five to ten percent of those require some form of renal replacement therapy. Mortality for patients with AKI needing RRT is as high as 60%.
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INITIAL MANAGEMENT Treat underlying cause Stop nephrotoxic drugs
Maintain euvolemia Maintain adequate MAP
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INDICATIONS Acute Kidney Injury with : No universally accepted levels
Fluid overload (refractory to diuretics) Hyperkalemia (K+ > 6.5) Severe metabolic acidosis (pH < 7.1) Rapidly climbing urea/creatinine (or urea > 30 mmol/L) Symptomatic uremia: encephalopathy, pericarditis, bleeding, nausea, pruritus Oliguria / anuria No universally accepted levels Rate of change of renal parameters and overall clinical status
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INDICATIONS (cont.) 2. Overdose with a dialyzable drug or toxin
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Rimmelé and Kellum Critical Care 2011, 15:205
INDICATIONS (cont.) 3. Sepsis: High Volume Ultrafiltration Hemadsorption Plasmapheresis Coupled Plasma Filtration Adsorption High adsorption Hemofiltration and high cut-off membranes Rimmelé and Kellum Critical Care 2011, 15:205
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“In the IVOIRE trial, there was no evidence that HVHF at 70 mL/kg/h, when compared with contemporary SVHF at 35 mL/kg/h, leads to a reduction of 28-day mortality or contributes to early improvements in haemodynamic profile or organ function. HVHF, as applied in this trial, cannot be recommended for treatment of septic shock complicated by AKI”.
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Major Renal Replacement Techniques
Intermittent Hybrid Continuous IHD Intermittent haemodialysis SLEDD Sustained (or slow) low efficiency daily dialysis CVVH Continuous veno-venous haemofiltration IUF Isolated Ultrafiltration CVVHD Continuous veno-venous haemodialysis SLEDD-F Sustained (or slow) low efficiency daily dialysis with filtration CVVHDF Continuous veno-venous haemodiafiltration SCUF Slow continuous ultrafiltration
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Intermittent Therapies - PRO
(Relatively) Inexpensive Flexible timing allows for mobility/transport Rapid correction of fluid overload Rapid removal of dialyzable drugs Rapid correction of acidosis & electrolyte abnormality Minimises anticoagulant exposure
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Intermittent Therapies - CON
Hypotension 30-60% Cerebral oedema Limited therapy duration Renal injury & ischaemia Gut/coronary ischaemia
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Continuous Therapies - PRO
Haemodynamic stability => ??? better renal recovery Stable and predictable volume control Stable and predictable control of chemistry Stable intracranial pressure Disease modification by cytokine removal (CVVH)?
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Continuous Therapies - CON
Anticoagulation requirements Higher potential for filter clotting Expense – fluids etc. Immobility & Transport issues Increased bleeding risk High heparin exposure
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SLED(D) & SLED(D)-F : Hybrid therapy
Conventional dialysis equipment Online dialysis fluid preparation Excellent small molecule detoxification Cardiovascular stability as good as CRRT Reduced anticoagulation requirement 11 hrs SLED comparable to 23 hrs CVVH Decreased costs compared to CRRT Phosphate supplementation required Fliser, T & Kielstein JT. Nature Clin Practice Neph 2006; 2: 32-39 Berbece, AN & Richardson, RMA. Kidney International 2006; 70:
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SOLUTE CLEARANCE - DIFFUSION
Small (< 500d) molecules cleared efficiently Concentration gradient critical Gradient achieved by countercurrent flow Principal clearance mode of dialysis techniques
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SOLUTE CLEARANCE - ULTRAFILTRATION
Water movement “drags” solute across membrane At high UF rates (> 1L/hour) enough solute is dragged to produce significant clearance Convective clearance dehydrates the blood passing through the filter If filtration fraction > 30% there is high risk of filter clotting* Also clears larger molecular weight substances (e.g. B12, TNF, inulin) * In post-dilution haemofiltration
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“ These data suggest that, provided strict guidelines to improve tolerance and metabolic control are used, almost all patients with acute renal failure as part of multiple-organ dysfunction syndrome can be treated with intermittent haemodialysis.”
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ACCESS FOR HD Venovenous RRT requires a double lumen vascular catheter placed in a central vein. IVC for femoral lines, SVC from IJV/SC Catheter made of polyurethane or silicone Each lumen at least 11 french gauge Good flow through catheter is crucial to prevent stasis of blood in circuit and clotting of filter.
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SITE OF ACCESS
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TIMING OF INITIATION Based on clinical assessment
“In critically-ill patients, the dilution of sCr by fluid accumulation may lead to underestimation of the severity of AKI and increases the time required to identify a 50% relative increase in sCr. A simple formula to correct sCr for fluid balance can improve staging of AKI and provide a better parameter for earlier recognition of severity progression”
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“In this study, planned early initiation of dialysis in patients with stage V chronic kidney disease was not associated with an improvement in survival or clinical outcomes”
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WHICH FORM OF RRT Aim of removal Cardiovascular status
Available resources Clinician’s experience Other specific considerations CRRT can aid feeding regimens CRRT may be associated with better cerebral perfusion
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AIM OF REMOVAL
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OPTIMAL FLOW RATE / DOSE OF RRT
Flow rate refers to the ultrafiltrate produced by the filtration process as well as any effluent dialysis flow. Marker of solute clearance Urea kinetic modelling (URR , Kt/V) Solute removal index
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“In critically ill patients with acute kidney injury, treatment with higher intensity (40 ml/kg/hr) continuous renal replacement therapy did not reduce mortality at 90 days”
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“Intensive renal support in critically ill patients with acute kidney injury did not decrease mortality, improve recovery of kidney function or reduce the rate of non-renal organ failure as compared with less-intensive therapy involving a defined dose of intermittent hemodialysis three times per week and crrt at 20 ml/kg/hour”
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ANTICOAGULATION Extracorporeal circuit will activate coagulation pathways Premature clotting off of a filter is a common problem May result in significant blood loss
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ANTICOAGULATION (cont.)
Unfractionated heparin – 40 to 70 IU/kg bolus f/b pre-filter infusion at 5 to 10 IU/Kg/Hr. Monitor aPTT. Reversed by protamine sulfate. LMWH – Dose adjustment guided by anti factor Xa levels ( IU/ml). Longer half life. Partial reversibility with protamine. Prostaglandins – Inhibit platelet function. Synergistic effect. Short half life. Hypoxemia. Expensive. Regional citrate anticoagulation – Sodium citrate infused into circuit pre-filter which chelates calcium and inhibits clot formation. Calcium infusion post filter. Metabolic derangements.
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FILTERS Cellulose based or synthetic (polysulphone and polyamide)
Biocompatibility – patient’s inflammatory and coagulation pathways Flux – permeability Adsorption – clears mid sized molecules Thickness – thin membranes allow greater movement Surface area – greater the area, more diffusion and ultrafiltration CRRT: synthetic, high flux membranes with surface area of m2 and a pore size allowing the passage of molecules up to 50,000 Daltons
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REPLACEMENT FLUID Balanced salt solutions with either lactate or bicarbonate buffer Lactate based solutions are stable, cheaper and more practical. But may not be favourable in certain conditions. Bicarbonate based replacement solutions have a more reliable buffering capacity but need to be prepared just prior to use. No evidence to suggest one better over the other. Can be added pre or post filter
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PHARMACOKINETICS Associated factors – Protein binding
Size of drug molecule and mode of RRT Timing of RRT Dose of RRT Membrane permeability Residual GFR
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COMPLICATIONS OF HD Related to catheter Haemodynamic instability
Air emboli Platelet consumption Blood loss Electrolyte imbalances Hypothermia Effects of anticoagulation
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Managing Intra-dialytic Hypotension
Dialysate temperature modelling Low temperature dialysate / 0.5 degrees C below pt’s Dialysate sodium profiling Hypertonic Na at start decreasing to 135 by end Prevents plasma volume decrease Dosing Anti-hypertensives Avoid oral food or glucose Midodrine if not on pressors UF profiling Colloid/crystalloid boluses Sertraline (longer term HD) 2005 National Kidney Foundation K/DOQI GUIDELINES
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DIALYSIS DISEQUILIBRIUM SYNDROME
Set of systemic and neurologic symptoms Associated with characteristic EEG findings Can occur during or after dialysis Early – Nausea, vomiting, restlessness, headache Serious – seizures, obtundation, coma Cause – acute increase in brain water content, changes in pH of CSF Minor – treat symptomatically Major – stop HD. AED. Mannitol. Recovers in 24 hours Prevention – URR < 40%, adjust dialysate sodium
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THE FUTURE REDY (Recycled Dialysis System) Alliant HD system WAKPD
RAD (Renal Assist Device)
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THANK YOU !
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