The efficiency of toxin clearance during extracorporeal therapies is determined by several interrelated factors that can be categorized into toxin-specific properties, treatment parameters, membrane characteristics, and patient factors.

The various toxin specific properties include Molecular weight as fundamental determinant of extracorporeal clearence. Small molecules (<500 Da) like glucose, urea, and electrolytes are easily cleared, while larger molecules encounter challenge. Standard hemodialysis effectively removes toxins up to 10,000-15,000 Da, while high-flux dialyzers can clear substances in the middle molecular weight range (<15,000 Da). Convective modalities such as hemofiltration and hemodiafiltration allow clearance of solutes approaching 25,000 Da, and newer high-cutoff membranes may remove poisons up to 50,000 Da. Another major determinant is Volume of distribution (VD) for extracorporeal removal of poisons. Substances with a low VD (<1-1.5 L/kg) are easily removed by extracorporeal treatment, while those with high VD (>2 L/kg) are poorly removed. Hydrophilic toxins distribute primarily in total body water, exhibit smaller VD, and are more readily removed, whereas lipophilic toxins distribute throughout extravascular tissues, especially adipose tissue, leading to large VD and poor clearance. Another factor which may affect the extracorporeal clearance of toxins is degree of plasma protein and tissue binding, which is inversely related to extracorporeal clearance because only unbound toxin (free fraction) is removed by most extracorporeal treatments. Poisons that are >80% protein bound are poorly removed by hemodialysis. However, some drugs like salicylates and valproic acid have high protein-binding ability at therapeutic concentrations but saturate at high plasma concentrations, increasing the free concentration and rendering them more easily removed. If endogenous clearance of the toxic substance is high, then extracorporeal treatment is unlikely to benefit unless there is impaired kidney function. The effectiveness of extracorporeal removal depends on whether it can significantly augment the body’s natural elimination pathways.

Treatment Parameters

Higher blood flow rates during extracorporeal therapies enhance toxin clearance efficiency. Common blood flow rate during haemodialysis ranges from 300-500 mL/min. However, excessively high blood flow rates can lead to vascular access complications. The other parameter is dialysate flow rate which maximizes the concentration gradient for toxin removal. Typical values range from 500-800 mL/min. Inadequate dialysate flow can result in suboptimal dialysis and poor clearance of dialyzable toxins. The solute clearance cannot exceed the lowest flow rate – plasma flow rate in hemodialysis or effluent flow rate in continuous renal replacement therapy. The duration of therapy should be tailored to the clinical situation rather than routine 4-hour treatments. Which can be increased for >10 hours as needed for some specific toxins such as dabigatran, ethylene glycol, and methanol. Precise estimation of duration to achieve target concentrations is possible using serial plasma concentrations and calculated elimination half-lives.

Larger surface area of filter and appropriate membrane flux enhance removal efficiency. A larger surface area enhances removal of larger molecules and middle molecules, providing more efficient clearance. Different membrane types (high-flux, high-cutoff, middle-cutoff) allow removal of different molecular weight ranges.

The choice between diffusive (hemodialysis) and convective (hemofiltration) modalities affects clearance efficiency. Convective transport is more effective for larger molecules (15,000-25,000 Da), while diffusive transport excels for smaller solutes. Combined techniques like hemodiafiltration utilize both mechanisms. Hemoperfusion help in removing high molecular weight toxin even with highly protein-bound characteristics. Whereas Plasma exchange can remove molecule with any size having any degree of protein binding.

Early preemptive initiation during absorption and distribution phases may promote removal of significant amounts of poisons with large VD. Initiation during the absorption phase is beneficial because a larger proportion of toxin in the intravascular compartment is available for removal.

Understanding these factors allows clinicians to optimize extracorporeal therapy selection and prescription parameters to maximize toxin clearance efficiency while considering patient safety and hemodynamic stability.

The decision to use extracorporeal therapies in severe poisoning requires a systematic approach considering both toxin characteristics and patient-specific factors. The selection of appropriate modality  involves evaluating the poison’s physicochemical properties, clinical severity, and available therapeutic alternatives.

Primary Determinants of Extracorporeal removal depends on several key poison characteristics:

• Molecular weight (MW): Lower MW compounds are more easily removed
• Volume of distribution (VD): Compounds with VD ≤1-2 L/kg are better candidates
• Protein binding: Highly protein-bound compounds (>80%) are poorly removed by most modalities
• Water solubility: Hydrophilic compounds are more readily eliminated
• Endogenous clearance: If natural clearance is high, extracorporeal therapy may not provide significant benefit

Key Decision Point: Extracorporeal elimination is generally considered worthwhile if it increases total body clearance by 30% or more.

Hemodialysis (HD)

Optimal Toxin Characteristics:

• Molecular weight: Up to 10,000-15,000 Da
• Volume of distribution: ≤1.5-2 L/kg
• Protein binding: ≤80%
• Water-soluble compounds

Primary Indications:

• Salicylates: Plasma concentration >500 mg/L or clinical toxicity with levels >300 mg/L
• Toxic alcohols (methanol, ethylene glycol): Plasma levels >50 mg/dL or severe acidosis
• Lithium: Levels >4 mEq/L with symptoms or >6 mEq/L regardless of symptoms

Advantages: High clearance rates for dialyzable compounds, widely available, well-established protocols, Cost effective

Continuous Renal Replacement Therapy (CRRT) – If both convective & diffusive therapy

Optimal Characteristics:

• Molecular weight: Up to 15,000-25,000 Da
• Volume of distribution: ≤1.5-2 L/kg
• Slower redistribution kinetics

Primary Indications:

• Hemodynamically unstable patients
• Compounds with slow redistribution (e.g., lithium in certain cases)
• When continuous removal is preferred over intermittent therapy

Limitations: Slower toxin clearance compared to intermittent HD, costly

Hemoperfusion/Hemadsorption

Optimal Characteristics:

• High protein binding (any level)
• Large molecular weight compounds
• Volume of distribution ≤1 L/kg
• Compounds with good charcoal adsorption properties

Primary Indications:

• Paraquet poisoning (If used within 4-5 hours of exposure)
• Valproic acid poisoning
• Carbamazepine overdose
• Theophylline toxicity
• Benzodiazepine poisoning in slow metabolizers
• Organophosphate poisoning (emerging evidence)

Advantages: Can remove highly protein-bound compounds that are poorly dialyzed

Limitations: Limited availability, risk of thrombocytopenia, hypocalcemia, and filter clotting

Plasmapheresis/Therapeutic Plasma Exchange (TPE)

Optimal Characteristics:

• Any molecular weight (no size limit)
• High protein binding
• Plasma-bound toxins
• Volume of distribution ≤1 L/kg

Primary Indications:

• Heavy metal poisoning (mercury, copper)^.
• Organophosphate poisoning (to replace cholinesterase)
• Monoclonal antibody toxicity
• Protein-bound drug overdoses (amitriptyline, propranolol, calcium channel blockers)

Mechanism: Removes toxin-bound plasma proteins and replaces with fresh plasma containing active enzymes

Extracorporeal Membrane Oxygenation (ECMO)

Primary Indications

• Cardiopulmonary failure unresponsive to conventional therapy
• Refractory cardiogenic shock from cardiotoxic poisoning
• Severe ARDS from pulmonary toxic exposure with inhalational agents or toxic fume
• Cardiac arrest with potential for recovery (ECPR)

Specific Poisoning Scenarios

• Aluminum phosphide poisoning with refractory shock
• Hydrocarbon aspiration with severe ARDS
• Cardiotoxic drug overdoses (calcium channel blockers, beta-blockers, tricyclic antidepressent)
• Cocain poisoning

ECMO Decision Criteria

• Mortality risk >50% (consider ECMO)
• Mortality risk >80% (strong indication for ECMO)
• Reversible toxicity expected
• Otherwise healthy patients

Clinical Decision Algorithm

Step 1: Assess Clinical Severity

• Severe poisoning with life-threatening complications
• Failure of conventional therapy including antidotes
• Predicted high mortality without intervention

Step 2: Evaluate Toxin Characteristics

• Identify the specific poison when possible
• Determine molecular weight, protein binding, and volume of distribution
• Assess endogenous clearance capacity

Step 3: Consider Patient Factors

• Hemodynamic stability (affects HD vs. CRRT choice)
• Kidney function (may influence clearance calculations)
• Age and comorbidities (especially for ECMO consideration)

Step 4: Select Appropriate Modality

For Small, Water-Soluble, Low-Protein-Bound Toxins

• First choice: Intermittent hemodialysis
• Alternative: CRRT if hemodynamically unstable

For Large or Highly Protein-Bound Toxins:

• First choice: Hemoperfusion/hemadsorption
• Alternative: Plasmapheresis for specific indications

For Cardiopulmonary Failure:

• ECMO as supportive therapy while other elimination methods are employed

Specific Contraindications

Consider Extracorporeal Therapy with specific goal:

• Tricyclic antidepressants: Risks outweigh benefits
• Digoxin poisoning: Use Fab fragments instead
• Compounds with very large VD (>5 L/kg): chloroquine, flecainide, paraquat, quinine

Combination Approaches

In severe cases, multiple modalities may be used sequentially or simultaneously:

• ECMO for cardiovascular support + HD/ CRRT for toxin removal & metabolic management
• Hemoperfusion followed by HD for comprehensive elimination
• Plasmapheresis + supportive ECMO in complex poisonings

Monitoring and Endpoints

Therapeutic Endpoints

• Clinical improvement in toxic symptoms
• Correction of surrogate parameters (pH, lactate, electrolytes)
• Reduction in toxin concentration below toxic thresholds
• Stabilization of organ function

The selection of extracorporeal therapy in severe poisoning requires individualized decision-making based on toxin characteristics, clinical severity, and resource availability. The EXTRIP workgroup recommendations provide evidence-based guidelines for specific poisons, emphasizing that intermittent hemodialysis remains the preferred first-line extracorporeal therapy when indicated. However, newer modalities like hemadsorption  and plasmapheresis should be used for elimination of those poisons which are not effectively dialyze with IHD. ECMO remain as supportive option in severe cardiovascular dysfunction or ARDS till the time poison is eliminated from the body.

Extracorporeal therapies have evolved significantly in their application to severe poisoning cases over the past decade. The evidence base, while still limited by the relative rarity of severe poisonings requiring these interventions, has been substantially strengthened by systematic reviews from the Extracorporeal Treatment in Poisoning (EXTRIP) workgroup and emerging clinical experience with newer modalities.

Overview of Extracorporeal Treatment Principles

Extracorporeal treatment (ECTR) represents a heterogeneous group of therapies that promote removal of endogenous or exogenous poisons while supporting or temporarily replacing vital organ function. These therapies are required in only 0.1% of intoxications, but can be life-saving in severe cases. The effectiveness of any extracorporeal therapy depends on several key toxin characteristics: molecular weight, volume of distribution, protein binding, and endogenous clearance.

The optimal dialyzable substance is a small molecule (<15,000 Da), has a low volume of distribution (≤1.5-2 L/kg), minimal protein binding (≤80%), and rapidly distributes from tissue to plasma. Only substances present in appreciable quantity in the intravascular space can be effectively cleared extracorporeally.

Hemodialysis: The Gold Standard

Intermittent hemodialysis (IHD) remains the extracorporeal treatment of choice for most poisonings amenable to removal. It is frequently available, least expensive with fewer complications, and quickest to implement compared to other modalities. The ability of IHD to treat concomitant metabolic disorders while providing significant clearance capacity for a wide spectrum of toxic substances makes it the preferred option.

High-efficiency dialyzers can clear poisons up to 15,000 Da, while newer high-cut off membranes may remove substances approaching 50,000 Da. Recent technological improvements have enhanced toxin removal efficiency, with clearances for small molecules like methanol exceeding 200 ml/min.

EXTRIP Recommendations

The EXTRIP workgroup has published evidence-based recommendations for specific toxins:

Strong recommendations for hemodialysis:

• Methanol: Severe poisoning with acidemia, seizures, vision deficits, or concentrations >70 mg/dl after fomepizole treatment
• Ethylene glycol: Severe acidosis (pH <7.25-7.30), renal failure, visual symptoms, or levels >50 mg/dl
• Salicylates: Concentrations >100 mg/dl, altered mental status, hypoxemia, or progressive toxicity despite appropriate medical treatment
• Lithium: Seizures, arrhythmias, coma, or levels >4.0 mEq/L with reduced kidney function

Conditional recommendations:

• Acetaminophen: Levels >900 mg/L with altered mental status and lactic acidosis while receiving N-acetylcysteine
• Metformin: Severe acidemia with lactate levels >20 mmol/L

Extracorporeal Membrane Oxygenation (ECMO)

Emerging Role in Poisoning

ECMO has gained increasing recognition as supportive therapy in severe poisoning cases, particularly when conventional treatments fail. Current evidence suggests ECMO should be considered when mortality risk reaches 50% and initiated at 80% mortality risk, similar to other clinical scenarios. (No separate recommendation for severely intoxicated patients)

Clinical Applications

Veno-venous ECMO (VV-ECMO) is recommended for:

• Respiratory failure when cardiac function is adequate or moderately depressed
• Risk of mortality ≥80% associated with PaO₂/FiO₂ <100 on FiO₂ >90%
• Murray score 3-4 despite optimal care for ≤6 hours

Veno-arterial ECMO (VA-ECMO) is indicated for:

• Refractory cardiogenic shock or cardiac arrest
• Acute Severe myocardial dysfunction (EF<20%)
• Life threatening arrhythmia
• Patients unresponsive to resuscitation, high-dose vasopressors, and intra-aortic balloon pump

Recent Evidence

Recent studies demonstrate successful ECMO applications in various poisoning scenarios. The western world have experience and data with severe intoxication due to cardiovascular medications while Asian countries have more experience with house hold chemicals with cardiotoxic potential.   A 2025 study found that VV-ECMO was infrequently utilized for poisoning-associated acute respiratory distress syndrome but showed promise in selected cases. ECMO has been successfully reported in aluminum phosphide poisoning, particularly for refractory hypoxemia and cardiovascular collapse.

However, there are no standardized guidelines for appropriate timing of ECMO initiation in severely poisoned patients, and decisions primarily depend on clinical judgment.

Hemofiltration and Continuous Renal Replacement Therapy

Limited Role in Acute Poisoning

Continuous renal replacement therapies (CRRT), including hemofiltration, have significantly limited utility in acute poisoning management. Poison clearance with CRRT is 50-80% less than intermittent modalities due to lower blood and effluent flow rates. However this is utilized as a modality to support metabolic management to break the vicious cycle of severe metabolic acidosis induced myocardial dysfunction.

Specific Applications

CRRT may be considered for:

• Lithium poisoning: Where slow redistribution from tissues makes continuous removal beneficial
• Hemodynamically unstable patients: When intermittent hemodialysis is not tolerated
• Bridge therapy: Following hemodialysis sessions to minimize toxin rebound

Recent evidence suggests CRRT use for poisoning has increased, likely due to procedural convenience, but should generally be avoided in favour of hemodialysis for rapid toxin removal.

Hemoadsorption

Expanding Applications

Hemoadsorption therapy has shown increasing promise in critically ill poisoned patients, particularly for removing inflammatory mediators and toxins through direct blood contact with sorbent materials.

Current Evidence

A 2023 systematic review and meta-analysis of hemoadsorption in critically ill patients with acute liver dysfunction showed:

• Significant reduction in total bilirubin levels (mean difference -4.79 mg/dL p=0.002)
• Reduction in aspartate transaminase levels and vasopressor requirements
• Trends toward improved liver function markers

Specific Poisoning Applications

Recent studies demonstrate effectiveness in:

• Paraquat poisoning: Early repeated hemoperfusion combined with hemodialysis significantly improved 90-day survival rates and acted as a protective factor.
• Organophosphorus poisoning: Combined plasma exchange and hemoperfusion showed reduced mortality (6.02% vs 23.08% in controls)

Plasmapheresis and Therapeutic Plasma Exchange

Limited but Specific Applications

Therapeutic plasma exchange (TPE) has utility for a small subset of poisonings, particularly those involving large molecular weight toxins or highly protein-bound substances.

Current Indications

TPE is recommended for:

• Monoclonal antibody poisonings: Where molecular size precludes other extracorporeal methods
• Arsine gas poisoning: For removal of protein-bound arsenic compounds
• Mushroom poisoning (Amanita phalloides): Though evidence remains limited

Recent Evidence in Organophosphorus Poisoning

A 2025 meta-analysis of 14 randomized controlled trials (1,034 participants) comparing plasma exchange combined with hemoperfusion versus hemoperfusion alone for organophosphorus poisoning showed

• Higher effective rate (RR = 1.20, 95% CI [1.11, 1.30])
• Lower fatality rate (RR = 0.28, 95% CI [0.15, 0.52])
• Reduced complications including pulmonary infection and intermediate syndrome

Limitations and Future Directions

Evidence Quality

The level of evidence for extracorporeal treatment in poisoning remains limited due to:

• Relative rarity of severe poisonings requiring these interventions
• Lack of large randomized controlled trials
• Heterogeneity in treatment protocols and patient populations

Emerging Technologies

New developments include:

• High-cutoff dialysis membranes: Capable of removing larger molecular weight substances
• Albumin dialysis: For protein-bound toxins, though typically inferior to standard hemodialysis
• Advanced hemoadsorption materials: Showing promise for cytokine and toxin removal

Clinical Decision-Making

Risk-Benefit Assessment

The decision to initiate extracorporeal therapy must balance:

• Severity and reversibility of toxicity
• Availability of alternative treatments
• Patient hemodynamic stability
• Risk of procedural complications^[2]

Multidisciplinary Approach

Optimal management requires collaboration between:

• Intensivists and emergency physicians
• Nephrologists for extracorporeal therapy expertise
• Medical toxicologists for poison-specific management
• ECMO specialists when mechanical circulatory support is needed^[3][5]

Conclusion

Current evidence supports a nuanced approach to extracorporeal therapies in severe poisoning. Intermittent hemodialysis remains the gold standard for most dialyzable toxins, with clear evidence-based guidelines from EXTRIP for specific substances. ECMO is emerging as valuable supportive therapy for cardiorespiratory failure in severe poisoning cases. Hemoadsorption shows promise for inflammatory mediator removal, while plasmapheresis has specific applications for large molecular weight or highly protein-bound toxins.

The evidence base continues to evolve, with recent studies demonstrating improved outcomes when these modalities are used appropriately and in combination. However, high-quality randomized controlled trials are still needed to strengthen recommendations and optimize treatment protocols for these complex clinical scenarios.

Extracorporeal membrane oxygenation (ECMO) has emerged as a life-saving intervention for patients with severe aluminium phosphide (AlP) poisoning, particularly those presenting with profound myocardial dysfunction and cardiogenic shock. This advanced support therapy has demonstrated remarkable effectiveness in reducing mortality rates in this traditionally fatal poisoning.

Mechanism of Action and Rationale

Aluminium phosphide poisoning causes severe systemic toxicity through the release of phosphine gas (PH3) when it comes into contact with moisture in the body after exposure. The toxic effects occur through multiple pathways, including inhibition of mitochondrial respiration and oxidative phosphorylation, generation of reactive oxygen species leading to oxidative stress, and direct cellular damage. This results in profound myocardial depression, precipitation of arrhythmia, severe acute respiratory distress syndrome, and multi-organ dysfunction.

ECMO provides crucial support in AlP poisoning through several mechanisms:

• Circulatory support: Provides mechanical cardiac support during severe myocardial depression and cardiogenic shock or arrhythmia
• Respiratory support: Manages severe hypoxemia and acute respiratory distress syndrome
• Metabolic stabilization: Helps correct severe metabolic acidosis by improving perfusion
• Toxin clearance: May potentially help remove circulating phosphine gas and other toxic metabolites^[2]

Clinical Evidence and Outcomes

Survival Benefit

The most compelling evidence comes from a landmark study that demonstrated dramatic improvements in survival rates. In high-risk AlP poisoning patients, ECMO reduced in-hospital mortality from 86.7% to 33.3% (p < 0.001). This represents a more than two-fold reduction in mortality compared to conventional treatment alone.

Recent real-world data from a large single-center study of 182 patients with AlP poisoning showed that among 78 patients who underwent veno-arterial ECMO, the overall survival rate was 67.9%. This contrasts starkly with the 100% mortality observed in patients who declined hospital admission.

Evidence

Multiple systematic reviews and meta-analyses have confirmed these findings:

• A meta-analysis of six studies involving 165 patients found ECMO was associated with a significantly higher survival rate (70.9%) compared to conventional therapy (30.8%) (p < 0.01)
• Another systematic review demonstrated that ECMO was associated with a significantly higher rate of survival compared to conventional management alone (RR 1.96, 95% CI 1.32-2.91, p = 0.001)

Patient Selection and Indications

ECMO is typically reserved for high-risk patients with AlP poisoning who present with:

• Severe left ventricular dysfunction (ejection fraction typically < 20%)
• Life threatening arrhythmia
• Refractory cardiogenic shock with systolic blood pressure < 90 mmHg despite vasopressor support
• Severe metabolic acidosis (pH < 7.0)
• Multiple organ dysfunction syndrome
• Refractory hypoxemia not responding to conventional ventilatory support

In the largest reported series, 76.9% of patients receiving ECMO presented with multiple organ dysfunction, and 94.9% showed electrocardiographic abnormalities.

Timing and Implementation

The timing of ECMO initiation is crucial for optimal outcomes. Studies show that:

• The median time from emergency department arrival to ECMO initiation should be early
• Interestingly, a slightly longer delay to ECMO initiation was observed among survivors, suggesting that extremely rapid deterioration may indicate a poorer prognosis
• ECMO was initiated in the emergency department for 87.2% of patients, highlighting the need for immediate availability
• The procedure was initiated during cardiopulmonary resuscitation in 10.3% of cases

Duration of Support and Recovery

The reversible nature of AlP-induced cardiac dysfunction makes ECMO particularly effective:

• Average duration of ECMO support ranges from 48-72 hours
• The half-life of phosphine gas is 5-24 hours, correlating with the temporary nature of cardio-respiratory failure
• At discharge, patients in both ECMO and conventional treatment groups had nearly normal left ventricular function, which completely normalized at follow-up
• At six-month follow-up, left ventricular ejection fraction recovered to 62% ± 2.4% in ECMO survivors

Complications and Considerations

While ECMO significantly improves survival, it is associated with substantial complications:

• Vascular access site complications requiring surgical correction
• Bleeding requiring multiple blood transfusions
• Profound thrombocytopenia
• Acute renal failure necessitating renal replacement therapy (required in 67.9% of patients)
• Overall complication rates of up to 80.8%, with 19.2% experiencing severe adverse events

Concurrent Therapies

ECMO is often used in conjunction with other organ support therapies:

• Renal replacement therapy: Required in approximately 68% of patients receiving ECMO
• Mechanical ventilation: For respiratory support
• Vasopressor support: Often continued despite ECMO support
• Standard supportive care: Including gastric lavage, activated charcoal, and symptomatic treatment

Predictors of Outcome

Several factors influence outcomes in patients receiving ECMO for AlP poisoning:

Poor prognostic factors:

• Lower baseline left ventricular ejection fraction (19.6% ± 1.7% in non-survivors vs. 26.2% ± 4.8% in survivors)
• Longer delay in hospital presentation
• Prolonged ECMO duration may be associated with additional complications

Future Directions

Current evidence suggests that ECMO should be considered as a standard intervention for severe AlP poisoning in appropriately selected patients. However, several areas require further investigation:

• Standardization of patient selection criteria
• Optimal timing of ECMO initiation
• Long-term neurological and cardiac outcomes
• Cost-effectiveness analyses
• Development of specialized protocols for this indication

Conclusion

ECMO represents a paradigm shift in the management of severe aluminium phosphide poisoning, transforming what was once considered a universally fatal condition into one with meaningful survival rates. The intervention is most effective when implemented early in carefully selected high-risk patients with severe myocardial dysfunction and cardiogenic shock. Given the reversible nature of AlP-induced cardiac toxicity and the temporary duration of phosphine gas effects, ECMO provides crucial “bridging” support during the most critical period, allowing time for recovery of native cardiac function. While associated with significant complications, the dramatic improvement in survival rates makes ECMO an essential consideration in the management of severe AlP poisoning cases.