Narcotic Overdose Flashcards
How is pain transmitted?
Noxious stimuli is detected by nociceptors. Primary afferent nerves (A and C) transmit signal to the second-order neurons in the spinal cord. Signal is then carried through the spinal cord in the spinothalamic tract to the thalamus, for initial processing. The thalamus then sends the signal to the sensory cortex in the frontal lobe, allowing us to localise and feel the severity of the pain.
How does the body regulate pain?
You’re body has a natural analgesic response to pain via the production of endogenous opioids and the descending pain pathway.
The descending pathway usually remains inactive by the release of GABA. However when pain is detected by the brain, the descending pathway becomes active to provide some relief.
Endogenous opioids are released from a neuron within the brain, which binds to an opioid receptor (Mu, Delta, Kappa) on the inhibitory (GABA releasing) neuron on the descending pain pathway. This inactivates the Ca2+ channel on the inhibitory neuron, stopping the release of GABA. This means the post-synaptic neuron can release dopamine, and activate the descending pathway.
The descending pathway meets the ascending pathway in the spinal cord. Opioids bind to the ascending pathway neurons and prevent communication = pain relief.
How do opioids produce CNS depression?
Lots of different areas of the brain have opioid receptors, including the respiratory centres within the medulla, chemoreceptors in the carotid sinus and the locus coeruleus which is a part of the RAS.
The LC is an area within the brainstem which is responsible for controlling conscious levels and activating the fight or flight response (SNS). When inhibited through opioid receptor activation, it produces effects such as pupil constriction, drowsiness, sedation, decreased HR and decreased RR.
Similarly, when the respiratory centres and chemoreceptors are inhibited, the body loses it’s innervation to breathe and airway reflexes. This leads to apnoea, hypoxia and potentially death if untreated.
How do people become addicted to opioids?
The mesolimbic pathway in the brain, also known as the rewards centre, is responsible for causing addiction when combined with other genetic and social aspects.
This systems contains dopaminergic neurons, which are usually highly controlled by inhibitory neurons. However, these inhibitory neurons contain opioid receptors.
When opioids are circulating, they bind the the opioid receptors on the inhibitory neurons. This prevents GABA release and causes unopposed activation of the dopamingeric neurons and a constant release of dopamine. This activates the pleasure response, and after repeated use, a link is created within the brain between opioids and the pleasure feeling.
How does opioid tolerance occur?
Tolerance means that a person requires a higher dose of a certain drug to continue creating the same level of effect.
There are two theories as to why this occurs:
-Desensitisation of the opioid receptors, meaning they do not produce the same effect when an opioid binds.
-A homeostatic downregulation of opioid receptors
What are the different types of opioid receptors and the responses they produce?
- Mu: most widespread opioid receptor and responsible for most of the adverse effects including respiratory depression, desensitisation of chemoreceptors, sedation and bradycardia. Also mostly responsible for analgesic effects. Most exogenous opioids act on this receptor.
- Delta: mainly produces analgesic effects
- Kappa: produces analgesic effects, as well as the euphoria/dysphoric effects.
What are the signs and symptoms of an opioid overdose?
- decreased GCS/unconscious
- Apnoea or bradypnoea
- Hypoxia, cyanosis, low Sp02
- bradycardia, hypotension
- pinpoint pupils (opioid receptors on the occulomotor nerve)
What are the treatment priorities with an OD?
- Focus on airway and breathing - ensure a patent airway and oxygenation to reverse hypoxia
- can manage with good airway and breathing, naloxone can wait if need be
- Naloxone IV is preferred - reverse until they can maintain their own airway but be aware of full reversal for hypoxic agitation
- Paeds aim for complete reversal if possible
- Transport to hospital due to shorter half life of naloxone
What is the pharmacology of naloxone?
Drug type: competitive opioid receptor antagonist
Onset: 1-3 mins. Duration: approx. 60mins. Half life: 60m
MOA: Naloxone competitively antagonises opioid receptors, with an increased affinity for Mu receptors over kappa and delta. This means the naxolone causes the removal of anything already binded to the receptor, and ‘switches off’ or stops the action of the opioid receptor and effectively reversing it’s effects.
Contraindications: sensitivity or new born babies with an aquired opioid addiction.
Side effects: may induce withdrawal or cause pain to return
Precautions: be aware that the half life of naloxone is much less than that of opioid medication, once naloxone wears off the patient may return to an overdosed state.
