Unless you have an unbelievably high pain threshold, I think we can all appreciate anaesthetics for preventing patients from:
- Allowing patients to undergo invasive procedures in an unconscious state
- Preventing the patient from attacking the surgical team
This form is used for more extensive procedures which take longer to complete, both during and after surgery to relieve pain.
This is an antimuscarinic agent which competes with acetylcholine on muscarinic receptors:
On the post ganglionic receptors of the parasympathetic nervous system; PNS –
- Decrease bronchial secretion for clear airway ventilation
- Decrease salivary gland activity
- Decrease gut motility
- Decrease bladder emptying via smooth muscle relaxation
- Increased heart rate – monitor for tachycardia
In the sympathetic nervous system; SNS –
- Decrease sweating
Remember to always check for any allergies the patient may have and also drug history for potential interactions.
Did you know? Patients with myasthenia gravis require a lower dose as they have fewer nicotinic type II receptors.
NOTE: Atropine does not affect ganglia at the neuromuscular junction as they are nicotinic receptors for acetylcholine.
Route of administration:
Intramuscular (IM) injection
This drug has a half life of around 3 hours and the metabolised product via the liver is excreted through urine.
This is used for less invasive procedures such as cannulation which take a shorter amount of time to complete. The mechanism of action involves blocking the sodium channels involved in propagating the nerve impulse; reducing action potentials travelling to the site of treatment.
Example: Lidocaine with adrenaline
Lidocaine acts on voltage-gated sodium channels, preventing depolarisation of the membrane for the action potential to transmit the impulse through peripheral neurons.
Adrenaline is an alpha I adrenoceptor agonist which acts on the sympathetic nervous system; SNS. Ultimately, this causes vasoconstriction for the localising effect and minimises bleeding as alpha 1 receptors are found within the smooth muscles of blood vessels.
So lidocaine acts as the protectors, shielding the gates of the voltage-gated sodium channels to prevent the patient from feeling pain at the site. The adrenaline kicks in with its parenting skills to prevent lidocaine travelling further than necessary. Together, they make a great team in allowing the patient to undergo procedures without taking over their consciousness.
Route of administration:
- Percutaneous and intravenous for peripheral nerve block for the brachial plexus and intercostal nerves
- Central neural techniques for epidural blocks for delivering babies via Caesarean section
Lidocaine has a shorter half-life of around 90 to 120 minutes in most patients, whereas adrenaline has a much shorter half-life of around 5 minutes. This allows systemic circulation of lidocaine for metabolism to allow excretion and can also account for some discomfort felt following the procedure. Metabolism of both drugs are initially by the liver which makes the drug more soluble, more viable for excretion by the kidneys to be released in the urine.
NOTE: Local anaesthesia should be avoided in peripheral sites with end-arterial supply due to the lack of alternative circulation in the area in case of emergency.
You’ll come around…eventually – we hope?!
Overall, both of these techniques show how far we have come in adjusting the level of consciousness of a patient with regards to the type of procedures they require for treatment. More and more, we are forming more localised and less invasive ways to treat patients because sleep is for the weak, right?
Remember, sedation can also be achieved with anaesthesia, which is simply a sleep-like state but the patient remains conscious!
Written by Tasnim
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