Extracorporeal Therapies In Poisoning

Toxins in Which Extracorporeal Therapy is Tried

Common Indications: ethylene glycol, lithium, and salicylate poisoning. 

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Factors Determining Toxin Removal

• Generally activated charcoal is given to cleanse the gut
• Absorption is prevented
• Specific chemical therapy provided
• Some toxins require extracorporeal removal, they depend upon :-

Protein Binding

• Toxins bound to proteins can't be removed by dialysis
• Plasmapheresis is used.
• Salicylates are exception
• Can be removed easily- Intermittent hemodialysis is done.
• Though salicylates have high protein binding

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Techniques Used in Extracorporeal Removal

Intermittent Hemodialysis

• Maximize Qb and dialyzer membrane surface area
• Aim for Qb/Qd ratio of >/= 2.5:1 (although diminishing benefits gained from increasing Qd beyond -600 ml/min)
• Maximize treatment times to at least 4 hours
• Use high-flux (kuf), high- efficiency (KoA) dialyzer, particularly if middle molecular weight solutes (>1000 Da) are to be cleared

Intermittent Hemofiltration/Filtrative Component of Intermittent hemofiltration:

• Aim for post-dilution fluid replacement to maximize efficiency with high-flux membrane
• Maximize Quf according to filtration fraction

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CRRT (Continuous renal replacement therapies)

Aim for high convective clearance (i.e., post-dilution CVVH with high flux membrane) for larger solutes (> 1000 Da). Aim for high diffusive clearances (i.e., CVVHD) for small solutes (<=1000 Da). For CVVH, maximize Quf according to the filtration fraction. For CVVHD, CVVHDF, maximize Qd up to at least 2.5 L/h for small solutes; For larger solutes (e.g., of an equivalent size to ꞵ2- microglobulin; MVV 11,800) there may be little gain from a Qd > 1.5 L/h

Hemoperfusion

limit Qb to -100 to 250 ml/min. Change cartridge every 3 to 4 hours. Consider the benefits of charcoal vs resin cartridges depending on the poison

Plasma exchange

• Aim for two plasma volume exchanges per day
• Modify replacement fluid according to poison

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Extracorporeal Therapy in Alcohol Poisoning

Ethylene glycol and methanol used in - antifreeze, de-icing solution cause poisoning

Toxicity is from ethylene glycol→ glycolic acid because of alcohol dehydrogenase

• Methanol→ formic acid
  • Presentation
  • Nausea
  • Vomiting
  • Abdominal pain
  • AKI
• Early treatment
  • Fomepizole/ ethanol to prevent alcohol dehydrogenase
  • To prevent the formation of glycolic acid and formic acid
• Indication of fomepizole
  • osmolal gap > 10 mosm/kg
  • Ethylene glycol/ methanol blood level > 20 msg/dl
• Alcohol poisoning
• Ideal to be removed by extracorporeal therapy
  • Immediate HD when levels > 50 mg/dl
  • HD should be continued till pH normalizes and blood level of toxin < 25 mg/dl

Extracorporeal Therapy in Salicylate Poisoning

• Salicylate poisoning presents as
  • Fever
  • Sweating
  • Tinnitus
  • Vertigo
• Severe poisoning leads
  • Depression of mental state
  • Non-cardiogenic pulmonary edema
  • Death
• Mixed respiratory alkalosis + metabolic acidosis seen
• IV sodium bicarbonate is given to reduce tissue penetration
• Salicylates are 90% protein bound
• Saturation of binding site → significant free level
• Extracorporeal therapy in severe poisoning, level > 100 mg/dl
• Intermittent HD-rapid correction of acidemia and electrolytes

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High Yield Questions

Q. Molecular weight of substance/protein binding of substance?

Ans.

Q. Level of alcohol at which extracorporeal therapy should be used?

Ans. > 50 mg/dl

Q. What level of salicylate at which extracorporeal therapy should be used?

Ans. > 100 mg/dl

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