Toxicology – Part 1

Toxicology – Part 1

Jun 22, 2015 0
Addiction medicine & toxicology,onthepods

Toxicology assessment

In this first of a 2-part series, James talks to Associate Professor Andrew Dawson on the toxicology assessment of a patient presenting with a polypharmacy overdose in the Emergency Department. You can listen to Toxicology Part 2 – Treatment here, which focuses on how to manage a drug overdose and toxicology patients.

Summary Writer:  George McClintock

Editor:  James Edwards

Interviewee: Andrew Dawson

About Andrew Dawson

Associate Professor Andrew Dawson is a physician who has specialised in Clinical Pharmacology and Toxicology for the past 28 years. His experience ranges from working in primary rural hospitals and public health in Asia to large teaching hospitals in Australia. Andrew is currently a clinical toxicologist at Royal Prince Alfred Hospital and the Clinical Director of the NSW Poisons Information Centre. He is also a Clinical Professor of Medicine for Sydney Medical School, University of Sydney and Conjoint Professor for the Schools of Medicine at the University of Western Sydney and University of NSW. Additionally, Andrew is a Visiting Professor of Medicine at the University of Peradeniya, Sri Lanka.

Toxicology Part 1 – Assessment

With Professor Andrew Dawson, Toxicologist and Clinical Professor of Addiction Medicine at Sydney University, New South Wales, Australia

Most junior doctor’s main interaction with toxicology is in the Emergency Department.

Case

You are a junior doctor and asked to see a 22-year-old female who presents to the Emergency Department. The triage note documents a polypharmacy overdose. She is a little drowsy, but apart from a pulse of 110, her vital signs are within normal limits.

  • The first step is to try to perform an accurate risk assessment so that you can start to consider the likely things that will happen to them and their likely disposition
  • In toxicology, the initial assessment is based around the vital signs; checking them early to form a baseline is a good first step. Also check the GCS level and examine for hyperreflexia
    • Repeated physical examination over time can give a good idea prognostically about where the patient’s course is headed
  • The first step is to ask the patient; the vast majority of patients who come in following a self-poisoning do not want to die or to harm themselves. The ingestion is usually impulsive and they are willing to give information if they have it. In the minority of patients who are drunk, delirious or otherwise not reliable, other sources of information should be sought
  • Getting hold of the empty containers of tablets can be useful. Apart from obviously helping with confirming the substance, the quantity and dose it can also give you an idea who the prescriber is and who has dispensed it. This can provide you with a source of collateral history if the patient is unable to provide it
  • The ambulance reports or ambulance officers will often include useful information
  • The timing of the ingestion is important, if the patient has very recently ingested the toxins, it is more difficult to predict the outcome; if everything was ingested 5 hours ago they are likely to be survivors
  • If the patient is not sure of the time, you can ask what they were watching on television at the time, or check for any messages on social media posts they may have made
  • Important factors on history include
    • What medications?
    • How much?
    • Is the medication slow release?
  • Medications generally fall into two groups in terms of toxicity
    • Drugs causing respiratory depression
      • Most of these medications are psychiatric medications
      • Respiratory depression correlates very well with depressed level of consciousness
      • These patients may require respiratory support
      • Many of these medications also have cardiotoxicity, which should be assessed for by looking at the ECG
    • Drugs causing toxic damage to cells
      • A good example is paracetamol
      • These patients can be quite asymptomatic, so the question is not so much about supportive care, but more about do you have to administer specific treatment
  • Vital signs, as mentioned above, are the first and most important step
  • Much of the rest of the examination is focused on eliciting certain drug effects
    • Evidence of anticholinergic effects
      • Absent bowel sounds
      • Urinary retention
    • Reflexes
      • Brisk reflexes in a low GCS patient usually indicate one of two things
        • They have taken a drug that is pro-convulsant and they are twitchy
        • Patients on a serotonin re-uptake inhibitor will also give brisk reflexes, even at therapeutic doses
      • Clonus, especially more than 3 or 4 beats strongly suggests they have serotonin re-uptake inhibitor on board
  • Focal neurological signs generally indicate a cause that is not toxicological
    • It is important to keep an open differential such as encephalitis and intracerebral events
      • Amphetamines and cocaine can predispose patients to vascular complications
  • ECG
    • To screen for evidence of cardiotoxicity
    • Primary cardiac drugs are high risk for causing toxicity, but are relatively rare in overdose
    • More common is psychiatric drugs, in which two things generally happen to the ECG
      • Widening of the QRS complex, which reflects blockage of the fast sodium channels
        • Once you see a QRS > 100ms in the context of an overdose, you should consider a sodium channel blocking drug such as one of the older neuroleptic medications or tricyclic antidepressants
        • If the QRS is widened, look to the AVR lead, if you have an R wave more than 4-5mm, that raises your suspicion of a sodium channel blocking drug
        • In sodium channel blocking drugs, the ECG changes can be somewhat of a marker for how much of the drug they have on board, by this point they can often have quite depressed levels of consciousness
      • Lengthening of the Qt interval (start of Q to end of T wave) – you should read this yourself, the machine can often get this parameter wrong, especially when the baseline is wandering
    • If you see ECG abnormalities, you should check the potassium, calcium and magnesium and attempt to correct any abnormalities which may be responsible or contributing
  • Blood gas
    • It is common for patients to have some respiratory depression, which will manifest as a respiratory acidosis. This is a reasonably clear sign that something needs to be done about their breathing, reversal if possible or intubation if required
    • It is also common for patients to have lactataemia. This is usually related to tachycardia and vasodilation and is perfusion related and will often resolve with fluids. Very high lactates should raise concern that the patient has either fitted recently, or have taken some poison that is affecting the mitochondria
    • In toxicology, pH is often managed much more actively.Acidosis enhances the movement of many toxins into cells, so a primary manouvre in treatment is to correct the acidosis
  • Other investigations that can be done
    • Urine screen for recreational drugs – although this rarely changes management
    • Paracetamol level – paracetamol is a very common toxin, has delayed toxicity and can be treated. The test should be performed even if patients deny paracetamol use
    • Specific drug levels – there is a number of drugs where the drug levels can be useful in making decisions around intervening. These include theophylline, sodium valproate, carbamazepine and salicylate

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Tags: #addict,#addiction,#drug overdose,#drugs,#OD,#overdose,#polypharmacy,#respiratory depression,#toxic damage,#toxicology,#toxicology assessment

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