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Approach to The Toxicology Patient

Overview

This section will give a brief overview to the toxicology patient covering initial approach, risk assessment, examination, investigations and treamtents.

Links are provided to more in depth discussion of some topics patricualrly treatment modalities.

Toxicoepidemiology

Some knowledge of the epidemiology of poisoning (toxicoepidemiology), preferably from your area, is useful as an aid to diagnosis when the history of ingestion is unclear. Common poisonings occur commonly. The poisons ingested vary substantially between countries and between urban and rural areas (where pesticides and herbicides are more common). They are also different for adults, adolescents and children.

Medications ingested to some extent reflect what is prescribed in the community, with patients being far more likely to ingest some types of drugs per prescription than others.

A combination of knowledge of the possible toxic effects of drugs, the frequency with which these effects occur and the frequency with which these drugs are taken in overdose is a sensible approach to diagnosis.

Approach to the Toxicology Patient

The following paper gives a summary of factors that need to be considered when assessing and manging to toxicology patient.

Daly FF, Little M, Murray L. A risk assessment based approach to the management of acute poisoning. Emerg Med J. 2006 May;23(5):396-9. doi: 10.1136/emj.2005.030312. PMID: 16627846; PMCID: PMC2564094. PDF

Risk Assessment

Toxicology covers a wide range of presentations including deliberate self-poisoning, recreational drug misuse and abuse, accidental poisoning, occupational exposure and envenomation. Central to the management of the toxicology patient is risk assessment, as it will anticipate the poisoning severity and help guide treatment.

A thorough risk assessment is crucial in the approach to the toxicology patient and includes:

agent/s taken
dose
time of ingestion
any co-ingestions
clinical manifestations since the exposure
regular medications
relevant co-morbidities

If the exposure is a deliberate self-poisoning, a mental health risk assessment should also be undertaken.

Patients are usually reliable when giving a risk assessment. In some scenarios – patient in custody, highly suicidal, using illicit drugs – there may be less willingness to divulge what was taken. In this instance, or if the patient is too sedated to give a history a collateral history can be taken from paramedics, family and friends. Empty pill packets on scene can be helpful to estimate a worst-case scenario. Sometimes contacting the patient’s regular doctor or getting a dispensing history from the patient’s chemist can be helpful to know what medications they may have access too. Access to electronic medical records can make this process easier.

Examination

Examination should be focussed on the expected toxicity given the risk assessment. In the patient where the risk assessment is unclear, examination for specific toxidromes may be helpful in determining likely agents involved in the poisoning. The below table summaries the examination findings of common toxidromes.

Specific complications of poisoning should also be considered and sought on examination:

Aspiration
Pressure areas
Neuropraxia
Rhabdomyolysis
DVT/PE

Investigations

The following investigations may be useful to perform:

Blood gas analysis to assess gas exchange and metabolic disturbance particularly in patients with altered level of consciousness
Paracetamol concentration is often tested routinely when a patient is not alert enough to give a reliable risk assessment
ECG assessing for QT prolongation or evidence of sodium channel blockade
Electrolytes, renal function, liver function tests
CK if rhabdomyolysis is suspected on risk assessment, particularly following long lie
Specific drug concentrations (eg valproate, carbamazepine, lithium) may be helpful if results are available in a clinically useful timeframe
Urinary drug screens have limited utility in a toxicology patient, they confirm the presence of some drug classes which are commonly misused, however false positives and negatives occur.
CXR if evidence of aspiration
Bedside echo in patients with haemodynamic instability to determine the contribution of negative inotropy versus vasodilation
CT head if concerns for concurrent trauma or hypoxic brain injury

More in depth description of some investigations can be found in appropriate sections (e.g. Bloods Gases , ECG) or in specific drug monographs.

Treatment

Resuscitation

Resuscitation should occur along standard lines with attention to a patient’s airway, breathing and ventilation.

Bedside echo may be helpful to delineate negative inotropy from vasodilation to better guide inotropic and vasopressor therapy.

Seizures if they occur should receive benzodiazepines in the first instance. Second line therapy is barbiturates.

Hypoglycaemia should be corrected with glucose.

Severe hyperthermia (> 39oC) should be corrected with cooling techniques.

In the event of cardio-respiratory arrest advanced life support protocols should be provided. Prolonged resuscitation attempts are often advised as patients with poisonings are typically healthy before the exposure and the toxicity is likely to be reversible once peak toxicity has passed. Extracorporeal membrane oxygenation may have a role in refractory cardiac arrest due to poisoning and should be considered early where available.

Decontamination

Decontamination refers to techniques that reduce the exposure to a drug or toxin by reducing absorption.
The use of decontamination methods should be based on a risk/benefit assessment. In those cases where the risk of toxicity is high decontamination should be given if the poisoning is amenable to it. Decontamination should always be a lower priority than resuscitation.
Methods of decontamination include:

• Activated charcoal
• Other binding resins
• Whole bowel irrigation
• Washing skin after dermal exposure

In general, decontamination can only be performed on a consenting patient. If it is felt the risk of the poisoning is so high that good supportive care or antidote therapy won’t result in a safe outcome it may be necessary to perform decontamination procedures even without consent. This would require intubation and ventilation in most cases.

Further information regarding decontamination techniques can be found here.

Enhanced Elimination

Enhanced elimination aims to reduce the severity and duration of an intoxication. As with decontamination, the decision to proceed with enhanced elimination techniques requires a thorough risk/benefit analysis and shouldn’t interfere with resuscitation or good supportive care. It is only available for ingestions with the toxicokinetics amenable to elimination, in particular the volume of distribution and clearance of the drug in question needs to be considered.

Methods of Enhanced Elimination include:

Multi Dose Activated Charcoal
Urinary Alkalinisation
Extracorporeal Techniques

More in depth discussion of enhanced elimination techniques can be found here

Antidotes

Antidotes for poisonings have existed for thousands of years and the term refers to a wide range of substances that ameliorate poisonings. Broad mechanisms of action of antidotes include reducing absorption, restoring function, or treating effects of poisoning. Examples of antidotes used currently are supplied in the following table (click to enlarge).

Supportive Treatment

Good supportive care is the mainstay of managing the poisoned patient. It involves;

Maintaining hydration with IV fluids
Placing a urinary catheter if there is urinary retention
Treating agitation with sedation (eg benzodiazepines)
Adequate thromboprophylaxis
Prevent of pressure areas
Treating nausea with antiemetics

The Toxicology Patient