Opiate Overdose

Introduction

Opioids work by inhibition of synaptic neurotransmission in both the peripheral and central nervous systems. They most commonly affect mu, kappa and delta receptors leading to analgesia, euphoria, CNS depression and respiratory depression with miosis(constricted pupils). The most serious and life-threatening sequel of opioid use (especially intravenous heroin) is the drugs effect on central responsiveness to levels of carbon dioxide and hypoxia leading to reduced respiratory drive. Respiratory arrest is the main cause of death in people who inject heroin.

Risk Factors

Opiate addiction can occur in many forms from heroin use, to addiction to prescription opiates to over the counter analgesics containing codeine which can also be addictive. Risk factors for opiate addiction include;

Adverse socioeconomic factors
Male gender
Younger age
Lack of fixed address - however its difficult to establish if opioid abuse is more common among homeless youth or do they become homeless as a result of their drug use

Clinical Features

In undifferentiated patients with the triad of CNS depression, respiratory depression and miosis opiate toxicity should be suspected. This triad can also be referred to as an opiate toxidrome. Signs of opiate overdose include;

CNS

Low GCS
Respiratory Depression
Seizures (rare)
Respiratory arrest - severe overdose

Respiratory

Bronchospasm
Non-cardiogenic pulmonary oedema

Gastrointestinal

Nausea
Vomiting
Biliary Colic

Differential Diagnosis

There is a wide differential for a patient who presents with altered consciousness. The opiate toxidrome can point you in the right direction however, patients may not be displaying all of the features depending on the time since ingestion / injeciton of the opiate and the presence of other co-ingestants. It is important to consider potential other diagnoses and rule them out as required. Differentials include but are not limited to;

Ingestion / co-ingestion other drugs

Alcohol intoxication

Head Trauma

Intracerebral haemorrhage

Hypoglycaemia

Hyponatraemia

Hypothermia

Hypoxaemia

Hepatic Encephalopathy

CNS infection

Seratonin Syndrome

Investigations

Bedside

Capillary blood glucose - essential for ruling out severe hypoglycaemia as the cause of reduced consciousness
Urine toxicology is available in most EDs, beware that some synthetic opioids i.e. fentanyl opioids are not detected and neither are most co-ingested recreational drugs
ECG - if QRSs are widened or QT is prolonged consider ingestion of other substances
ABG - looking for hypoxemia and respiratory acidosis (high CO2 and low pH)

Laboratory

Lab investigations are generally not helpful in the diagnosis of simple opiate overdose however in certain cases they may be necessary to;

FBC / CRP - rule out infectious causes
U&E - rule out electrolyte abnormalities
Paracetamol levels - if any suspicion of intentional overdose +/- salicylate levels as appropriate

Radiology

Radiology investigations are not required in simple opiate overdose however in some patients they may be required

Cxr - concerned for aspiration / pulmonary oedema
Ct Brain if concerned about
- Head injury
- Spontaneous intra-cerebral haemorrhage
- CNS infections
Abdominal x-ray if body packing is suspected

Management

Naloxone

Naloxone – is the antidote to opiates. It has a short half-life and the therapeutic effect lasts around 20 to 40 min. There is therefore a risk of repeated respiratory and CNS depression with longer acting opiates (ie; methadone) or larger doses of heroin.
Rapid and over-reversal of opiates is also dangerous because;
Patients may become agitated, leave and take a second dose of opiate. The Naloxone then wears off and they have the effect of both doses which may be fatal
Over reversal can lead to nausea, vomiting, severe hypertension, tachyarrhythmias and ventricular fibrillation
As such Naloxone dosing should follow the principles of start low and go slow. Naloxone infusions are generally safer than stat dosing, especially for overdose of long acting opiates.
If IV access is unavailable there are many other routes of administration - intramuscular, subcutaneous and intranasal (rememeber wont work in respiratory arrest)
Always follow your local hospitals prescribing guidelines for opiate reversal
Patient may require respiratory support until the naloxone takes effect, depending on your breathing and airway assessment patients might need respiratory support with bag-valve-mask or C-circuit, they can also benefit from oropharyngeal or nasopharyngeal airway adjuncts.
Once patients respiratory effort improves patient should be nursed on high observation bed with non-invasive capnography

Other Measures

Hypotension – might require IV fluids
Hypothermia – some patients require active rewarming
Hypoglycaemia – should be corrected with PO intake if awake patient and IV dextrose in patient with reduced GCS
Seizures – IV or buccal benzodiazepines

Disposition

Asymptomatic patients who have taken a short activing agent and do not require treatment could be discharge following a period of observation
Patients who require Naloxone treatment either prehospitally or in ED require a period of observation prior to discharge to ensure they are respiring adequately and not going to become worse again due to the short half-life of Naloxone
Patients who require repeated doses of Naloxone or Naloxone infusion are likely to require admission to the hospital
If there is a suspicion of intentional overdose or suicide attempt patients require psychiatry assessment prior to discharge