Neil Goldsack,
respiratory specialist registrar
Chest Clinic,
North Middlesex Hospital,
London
David Howell,
Medical Research Council fellow
Richard Marshall,
Wellcome fellow
Hugh Montgomery, cardiology specialist registrar
University College and Middlesex Hospital,
London

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In the fifth part of our emergency series, Neil Goldsack, Hugh Montgomery, Richard Marshall, and David Howell tell you how to treat patients who have taken a drug overdose

Introduction

Drug overdoses, both accidental and deliberate, are common. As a house officer, you will see patients who have taken overdoses on a regular basis. Usually, overdoses are deliberate efforts at self harm. In most cases these attempts are not severe, and the drug taken is mild. Those who do this may, however, often take substances that are potentially life threatening. Even those who are "crying for help" may take life threatening medication. If you can elucidate what they have taken, either from the patients themselves or from a witness, this is valuable. If the patient is semiconscious, then you won't get a history. Even if the patient is conscious, however, you may be little better off. The people you are dealing with are likely to be dishonest. If they were really trying to kill themselves, they won't want you to know the truth. If they weren't, and they were misusing drugs, they won't want you to know the truth either. The same goes if they were "just" crying for help. Additionally, the drugs taken may actually confuse the patient. You should never fully trust patients who have taken an overdose. Doing so may kill them. Never assume they have taken only what they say. Often drug overdoses are washed down with alcohol, and the patient may deny this. In the case of paracetamol, for example, alcohol can induce the metabolism of the drug with the production of more toxic metabolites that will eventually contribute to hepatic failure.

Treating people who have taken an overdose requires quick decisions
Photo: ROY MORSCH/THE STOCK MARKET

Why do patients die after taking an overdose?
There are several reason why people may die after taking an overdose. These include the following.

(1) Cerebral depression. This leads to drowsiness and then coma. Either breathing will stop (followed by the heart), or the patient will vomit and aspirate (and then die of hypoxia).

(2) The effects of the drugs themselves - for example, the metabolic effects of aspirin, or the cardiotoxic effects of tricyclic antidepressants.

(3) Repeat overdose or suicide attempt - for example, an attempt to jump from the hospital window.

Your job, therefore, is to prevent these happening. This will entail a few basic principles.

(i) Management of the unconscious patient

(ii ) Getting any tablets out of the patient's system

(iii) Identifying what the patient has taken

(iv) Providing specific treatment.

Management of the patient who has taken an overdose (and exam answer)

(1) This is a medical emergency. Go immediately to the casualty department.

(2) Assess the need for immediate resuscitation - ABC - and call help if necessary:

Airway - ensure that the airway is open.

Breathing - check that the patient is making adequate respiratory efforts. Remember that opiates can cause a decreased respiratory rate and that salicylates in the early stages can cause an increased respiratory rate.

Circulation - check that the patient has an adequate circulation

(3) Give oxygen.

(4) If the patient is not fully conscious you will have to manage appropriately. If the patient has a Glasgow coma score of less then 8 (sBMJ 1999;7:10.[Table.]) then you should call for the immediate help of an anaesthetist. Turn the patient into the recovery position, place a guidal airway into their mouth, and give them high flow oxygen. Remember, in particular, not to assume that the cause is (or is only) a drug overdose. Head injury and infection are common in people addicted to alcohol and drugs. Don't make assumptions! If in any doubt as to the cause of coma then intravenous glucose (50 ml of 50% dextrose), naloxone (400 µg), or thiamine can all be safely given. None will do any harm.

(5) Establish venous access. Always check the blood sugar concentration at this stage. Take blood samples and send them off. If the patient has taken an overdose, then analysis should routinely include paracetamol and salicylates, even if the patient denies having taken them. You should also ask the lab to save the serum for a later toxicological analysis, if required. You may also wish to do this with a urine sample in a complicated (or possibly medicolegal) situation. Send off an arterial blood gas specimen to ensure that there is no unexpected acid-base disturbance.

(6) Treat shock. These patients may be hypotensive; this is particularly common with phenothiazines and tricyclic antidepressants. In this case give crystalloids or colloids to maintain a good circulating blood pressure.

(7) History and examination. The physical examination may give you a clue to the agent that has been taken. Opiates are among the most commonly taken drugs and result in drowsiness, decreasing conscious level, a reduced respiratory rate, and small pinpoint pupils. Most cerebral depressants, such as alcohol and benzo- diazepines, will cause drowsiness and dilated pupils. Sympathomimetic agents, such as amphetamines and cocaine, may cause dilated pupils and agitation. Always check the arms of the patient for injection marks. Patients who continuously use intravenous drugs will develop thick tracks where the veins have become clotted; this is known as "tracking." In addition, certain agents, including tricyclics or barbiturates, may result in skin blistering. A golden rule is not to put your hands into the pockets of drug addicts. Your keenness in this situation to ascertain if they have other drugs on them may result in a potentially life threatening needlestick injury.

(8) All overdoses should be discussed with a local poisons unit, which can give up to date advice on the current management. Their phone numbers are found in every casualty department.

(9) All patients should be given activated charcoal regularly (every four hours), either orally or through a nasogastric tube. This uses the gut as a dialysis membrane, binding drugs that are drawn out from the circulation. It causes no harm and works for most drugs. Even if unnecessary, it is cheap and safe.

(10) Gastric lavage. This has been the subject of some controversy recently. Previously most patients, except those with a reduced conscious level or known to have taken a caustic substance, were washed out. There is, however, no certain evidence that it improves clinical outcome, and it is therefore recommended only in patients who present within 60 minutes of ingestion of a known non-caustic substance that may be potentially life threatening. If you are unsure as to whether to use gastric lavage, your local poisons unit will be pleased to help. Note also that vomiting induced with ipecacuanha is also no longer routinely recommended.

(11) Treat the overdose with the antidote if appropriate (see below)

(12) Measure creatinine kinase concentrations in any patient who has been unconscious or asleep for a long time on a hard surface. If the concentration is elevated this can result in rhabdomyolysis. The muscle proteins accumulate in the renal tubules, resulting in renal failure. These patients need to be transferred to the intensive care unit as they can rapidly develop severe acute renal failure. Remember, patients who have taken ecstasy will often have danced the night away vigorously, and this can itself result in severe muscle trauma and rhabdomyolysis.

(13) All overdose patients should be monitored very carefully, with regular monitoring of vital signs. If they have taken a drug that could reduce their Glasgow coma score then they should also have regular neurological observations performed.

(14) All patients should be assessed by a psychiatrist before discharge.

Summary
Patients who have taken overdoses can easily die if the appropriate care is not taken. Ensure that they are fully assessed and that the relevant blood tests are sent off. We would recommend sending off arterial blood samples to be analysed for gases in most cases of overdose. As these patients may not be telling the whole truth, it is possible that they have taken additional drugs, such as aspirin or tricyclic antidepressants, that may result in severe unexpected acid-base imbalance.

Overdose can induce cerebral depression and cardiotoxic effects
Photo: SCIENCE PH0TO LIBRARY

 

Table 1 Effects of common drugs used in overdoses   Drug Signs Aspirin*   Often very few Hyperventilation, sweating, flushing, tinnitus, confusion Paracetamol*   Often very few Nausea, late - jaundice and confusion Opiates   Depressed conscious level Reduced respiratory rate, hypotension, small pinpoint pupils, injection tracks on the arms Barbiturates   Depressed conscious level Reduced respiratory rate, hypotension, hypothermia, peripheral vasodilation Benzodiazepines   Depressed conscious level Reduced respiratory rate Tricyclic antidepressants   Depressed conscious level Dilated unequal pupils (responding poorly to light), tachycardia, respiratory depression, hypotension, increased muscle tone, convulsions, increased tendon reflexes, upgoing plantar response * Note: People who have taken an overdose of aspirin or paracetamol may show very few signs.

Special cases

Alcohol
Calculating the amount of alcohol in the blood
It is often important to have a rough idea as to how much a person's acute alcohol consumption is contributing to their sleepy state. The patients often lie, but you can actually easily work it out for yourself. Most hospital labs won't tell you at night. Send blood for the usual full biochemical screen (urea, electrolytes, liver function tests, and glucose), but also ask for the osmolality to be checked.

(1) Calculate what osmolality should be. This is 2(Na+K)+glucose+urea. Let's assume that the figures are Na+=140 mmol/l, K+=3.5 mmol/l, urea=4.0 mmol/l, and glucose=5.0 mmol/l. This gives a calculated osmolality of 296 mosmol/l.

(2) Subtract this from the measured osmolality. Let's assume that this was 396 mosmol/l. Thus, the difference between the two is 396-296=100 mosmol.

(3) If you suspect heavy boozing, then you are about to assume that the osmotically active substance that you haven't measured is all alcohol. So how much alcohol exerts an osmolality of 100 mosmol? Answer: 100 mmol. So there are 100 mmol of alcohol per litre of blood. The rapid micromedia method of alcohol is easily calculated from the masses of each atom (alcohol is C2H5OH). Two carbon atoms (at an atomic weight of 12 g each), six hydrogen atoms (at an atomic weight of 1 g each), and an oxygen atom (at an atomic weight of 16g) means the rapid micromedia method of alcohol is 46 (1 mol of alcohol weighs 46 g). Thus 1 mmol weighs 46 mg.

(4) Now do some calculations. The patient has 100 mmol of alcohol per litre of blood. He or she thus has 100 x 46 mg alcohol per litre of blood, which means they have 4600 mg alcohol per litre of blood, or 460 mg alcohol per 100 mg blood. This is seriously plastered! Given that in many European countries you can't drive when you have above 60 mg alcohol per 100 ml blood, this patient is nearly eight times over the limit! As the saying goes: "He or she may also have some blood left in his or her alcohol stream."

Paracetamol
This is the commonest overdose in this country, but it does result in severe morbidity and often death. Paracetamol is unfortunately widely available without prescription and can be bought in large amounts across the pharmacy counter. Each tablet contains 0.5 g of paracetamol, and a 20 g overdose can easily prove fatal. The same principles as above apply.

(1) Go immediately to casualty.

(2) Establish venous access.

(3) If a patient admits to taking paracetamol then an urgent request for paracetamol level should be sent (remember to check salicylate concentrations as well). Most hospitals have a normogram for the calculation of the toxic dose of paracetamol; the first time point at which this can be accurately calculated is four hours. Remember that there is no safe concentration for paracetamol. If the patient does have a toxic concentration, or if you are in any doubt about the timing of the overdose, then the patient should be treated, and he or she should receive intravenous N-acetylcysteine. This should be given at an initial high rate and then reduced over the next 16 hours. It is sometimes worth continuing this for 48 hours in those who have taken a severe overdose.

On the first morning after the patient has been admitted you should do liver function tests and a clotting screen. If these are deteriorating then you should seek advice from the nearest liver unit. However, in most cases, even with very high international normalised ratios, these patients can survive. If you are in any doubt, seek an expert opinion.

Aspirin
An overdose of aspirin can be life threatening as a result of the major acid-base disturbance that occurs. The same principles once again apply.

(1) These patients should all have regular four hourly doses of activated charcoal. This is particularly good for aspirin and will often be life saving.

(2) The acid-base status of the patient should be reviewed on a regular basis, as should repeat salicylate concentrations (every 4 hours), until two successive concentrations are falling. If these patients are deteriorating then your registrar needs to be informed as they may need an alkaline diuresis or, in severe cases, haemodialysis. Patients with severe acid-base disturbance should ideally be managed on an intensive care unit. They may require subsequent transfer to a renal unit for consideration of haemofiltration.

(3) Speak to your local poisons unit about whether they recommend gastric lavage. Aspirin delays gastric emptying, and gastric lavage may be appropriate, even after four hours.

Opiates
Overdoses of opiates are, again, very common. Patients are usually very drowsy with small pupils (see above). They should be managed with naloxone 400 µg, given intravenously. If you are unable to get venous access it can be given intramuscularly. This should be repeated as necessary. Remember that the effect of this will wear off before all the heroin is out the patient's system. They should therefore be strongly advised to remain in hospital. If a patient insists on leaving despite all your explanations then make sure that this is recorded in the medical notes and that the patient signs a self discharge form. This is helpful if the case goes to the coroner's court.

 

Things to be aware of (1) If the patient has taken an opiate overdose, and is given naloxone, he or she usually comes round with a bang! Stand clear, as the patient can often be violent at this point. There is nothing more annoying, when you have saved a patient's life, than being smacked with a right hook to the chin. An experience you won't forget, and one you won't want to repeat! (2) I can well remember a patient admitting to taking only an overdose of antibiotic tablets but becoming increasingly unwell after admission. A severe metabolic acidosis was diagnosed, and the patient finally admitted to having taken aspirin, just as ventilation was about to start. (3) Most overdose patients have also consumed alcohol. This can confuse the situation as they may be drowsy and have tachycardia as a result.

Benzodiazepines
For benzodiazepines there is a specific antidote known as flumazenil (very short duration of action). This agent should, however, be reserved for iatrogenic overdoses of benzodiazepines, as seen after endoscopy or bronchoscopy. If an overdose patient has a deteriorating conscious level or a reduced respiratory rate then he or she should be intubated rather than be given flumazenil. This is because this complication usually occurs as a result of the ingestion of a second drug. Most of these other drugs are epileptogenic, and the administration of flumazenil will result in a lowering of the seizure threshold. Clearly an epileptic unconscious patient with a low respiratory rate has a greatly increased chance of aspirating his or her stomach contents. As discussed previously, this results in very high mortality.

Tricyclic antidepressants
Tricyclic antidepressants are unfortunately often taken in overdose. These can result in collapse, cardiac arrhythmias, and severe acid-base disturbances. You should seek expert help at an early stage in these patients. Make sure that they are connected to a cardiac monitor and that the arterial blood gases are taken at regular intervals. You should ensure that they have a normal potassium concentration as a low concentration can further predispose to arrhythmias. You should ensure that your seniors are contacted when you have to deal with these patients. Arrhythmias should usually be managed with bicarbonate.

Conclusion
Overdoses are a common medical emergency that will often frustrate you, but most cases are easily treated with simple measures. The adherence to these simple measures will save you a lot of time in the long run. In all cases it is important to contact the local poisons unit on admission and to ensure that these patients are properly assessed by a psychiatrist before discharge.

Next month - how to treat oliguria