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Extracorporeal techniques in poisoning

Extracorporeal techniques in poisoning. Ben Creagh-Brown SHO Anaesthetics October 2003. Overview. Case report Haemodialysis, filtration, perfusion – what’s the difference? When is it necessary? Complications. Case report from Thorax 2000.

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Extracorporeal techniques in poisoning

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  1. Extracorporeal techniques in poisoning Ben Creagh-Brown SHO Anaesthetics October 2003

  2. Overview • Case report • Haemodialysis, filtration, perfusion – what’s the difference? • When is it necessary? • Complications

  3. Case report from Thorax 2000 • 53 year old woman was admitted to hospital with severe theophylline toxicity after taking 22.4 g (56 × 400 mg) of slow release theophylline tablets • Persistent sinus tachycardia (250 beats/min) resulting in left ventricular failure • Intractable vomiting with haematemesis • Hypokalaemia (K+ 2.6 mmol/l) • Tremor • Serum theophylline levels continued to increase during the first 24 hours after admission so she was transferred to the intensive care unit (ICU) where she had a tonic-clonic seizure, aspirated, and required intubation and ventilation

  4. Treatment on ITU • Haemofilter with a polyamide filter (1.4 m2) was used, with an average ultrafiltration rate of 25 ml/min. Primed with 5000 units heparin and clotting was subsequently prevented with 1000 units heparin per hour • Twelve hours after the onset of haemofiltration the patient's vomiting had settled and she was started on oral activated charcoal (50 g four hourly).

  5. Haemodialysis • Diffusion of solutes across a semi-permeable membrane down a concentration gradient • Rate of diffusion proportional to temperature, inversely proportional to viscosity and size of molecule • Increased flow through HD unit maintains concentration gradient and increases clearance, particularly of small molecules • High flux systems have thin membranes and large pores – more diffusion

  6. How HD works PUMP ARTERIAL WASTED DIALYSATE counter current a b DIALYSATE IN AIR TRAP VENOUS

  7. Drugs that can be eliminated

  8. HD

  9. Haemofiltration • Haemofiltration involves the passage of blood down one side of a semipermeable membrane which allows water and solutes with a molecular weight up to 40 000 to pass across the membrane by convective flow, as in glomerular filtration • The rate of removal of such a solute is proportional to its concentration in the blood and independent of its size • Can be performed for long periods in haemodynamically unstable patients

  10. Ultrafiltration • Is the process that HF uses to work • Convective flow of water and solutes down a pressure gradient. Pressure gradient caused by hydrostatic and osmotic forces. Water ‘drags’ solutes

  11. AIR TRAP How HF works PUMP ARTERIAL ULTRAPURE WATER a b VENOUS

  12. HF

  13. Haemoperfusion • Passage of blood through a circuit containing an adsorbent such as activated charcoal, carbon or polystyrene resin. • Some drugs bind to the adsorbent more effectively than they would be cleared by HD or HF • Eliminates protein-bound and lipophilic dugs and toxins

  14. CHARCOAL counter current a b DIALYSATE IN How HP works PUMP ARTERIAL WASTED DIALYSATE VENOUS

  15. HP

  16. Extracorporeal techniques in ITU • Enhance elimination of poison • Correct electrolyte and metabolic disturbance • Haemodialysis is only available in a limited number of hospitals and requires complex machines, equipment and trained staff • Haemofiltration can be done in most ITUs • Haemoperfusion can be done where HD or HF is done if a charcoal column is available

  17. Use in poisoning • 0.05% of all poisoning need extracorporeal techniques. • HD is used in 90% of cases. • HF not recommended as less effective but better than nothing.

  18. Which drugs need HD/HF?

  19. Which drugs need HP?

  20. Complications • Of HD/HF: • Disequilibrium syndrome • Hypophosphataemia (none in dialysate) • Hypokalaemia (little in dialysate) • Metabolic alkalosis (bicarb in dial.) • Extra ones of HP: • Charcoal emboli • Hypocalcaemia • Hypoglycaemia • Leucopenia and Thrombocytopenia

  21. Which one to use? • In general, if a compound is adsorbed by charcoal, the clearance by haemoperfusion will be higher than that achieved by haemodialysis. • Similarly, if a compound is amenable to removal by haemodialysis, its clearance will be greater than that achieved by haemofiltration • In practice, the compounds for which extracorporeal elimination is used most frequently are the alcohols, lithium and salicylate (haemodialysis) and theophylline (haemofiltration

  22. When should you use it? • Severe clinical intoxication • Clinical deterioration • Coma • Drugs with delayed actions or toxic metabolites • Impaired native clearance (liver/renal) • Known toxic levels of dialyzable drug

  23. Bibliography • Continuous venovenous haemofiltration for the treatment of theophylline toxicity J H Henderson, C A McKenzie, P J Hilton, R M Leach Department of Critical Care Medicine, St Thomas' Hospital, London SE1 7EH, UK • Oxford Handbook of dialysis • Oxford handbook of anaesthesia

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