Anaesthesia — Local and Regional Anaesthesia, NMC MBBS licence examination syllabus (Nepal Medical Council).
The patient who says their lips feel tingly is giving you the only warning you will get.
Local anaesthesia is the technique a newly qualified doctor uses most often and receives least teaching about. It is used for suturing, for drainage, for blocks and for procedures on wards where no anaesthetist is present — which is precisely why its complications have to be understood by the person holding the syringe.
The preoperative assessment, the airway, fasting and anaesthetic emergencies are covered in the perioperative chapter. This one is about the drugs themselves.
Local anaesthetics block sodium channels in the nerve membrane. Without sodium entry there is no action potential, so the nerve cannot transmit.
Small unmyelinated pain fibres are blocked first and large motor fibres last, which is why a patient may still be able to move a limb that has become numb to pain — a useful reassurance to offer, since patients often interpret retained movement as failed anaesthesia.
They work poorly in infected tissue, and the reason is worth knowing rather than merely remembering. Infected tissue is acidic, and the acidity keeps more of the drug in the ionised form that cannot cross the nerve membrane. So injecting into or around an abscess produces poor anaesthesia — and injecting more makes it worse, because it hurts, distends inflamed tissue and risks spreading infection. Block proximally instead, or use a field block away from the inflamed area.Adrenaline is added to some preparations to constrict local vessels. That slows absorption into the circulation, which prolongs the block, reduces bleeding in the surgical field, and permits a larger total dose.
Local anaesthetic reaching the systemic circulation in sufficient quantity produces a predictable sequence, and knowing the order is what allows you to stop before the serious part.
Systemic toxicity is usually not a dose calculation error. It is accidental injection into a blood vessel, which delivers the whole dose to the circulation at once.
Three habits prevent nearly all of it:
No maximum doses are given in this chapter, deliberately. They differ between agents, between preparations with and without adrenaline, and with the site injected — and a number remembered for one agent and applied to another is exactly how toxicity happens. Calculate from what is actually in your hand.
Lipid emulsion is the specific treatment for severe local anaesthetic toxicity, alongside standard resuscitation. The practical point for an exam and for practice is the same: know where it is kept in your department before you need it, because the moment you need it is not the moment to start looking.
Adrenaline's vasoconstriction is useful — until the tissue has no alternative blood supply. In areas supplied by end arteries, constriction can produce ischaemia and tissue loss.
The traditionally taught list is fingers, toes, nose, ears and penis. The teaching has been questioned in modern practice, particularly for digits, where large series suggest the risk with commercial preparations is lower than long assumed. That disagreement is worth knowing about — but follow your local protocol rather than a contested change.
For an examination, give the list and the reason: no collateral supply, so constriction risks the whole territory. The reason is what is being tested.
A small dose of local anaesthetic placed into the cerebrospinal fluid blocks an entire region of the body. It is widely used for caesarean section and lower limb surgery, and it has real advantages: the patient stays awake, the airway is not instrumented, and a mother can be present at her child's birth.
The physiological consequence follows directly from the anatomy: sympathetic fibres are blocked along with the sensory ones. Sympathetic block means vasodilatation, and vasodilatation means hypotension. This is expected and predictable rather than a complication — which is why blood pressure is monitored closely and treated proactively rather than being waited for.A block that rises too high is the serious risk. As the level climbs it affects the nerves supplying the chest wall and eventually the diaphragm. Warning features are numbness rising up the trunk, weakness or tingling in the arms, difficulty speaking, and a sense of not being able to breathe deeply. This needs immediate senior help.
Headache afterwards is characteristically postural — worse on sitting or standing, better lying flat. That posture-dependence distinguishes it from most other headaches and is the feature exam questions test.
No maximum doses, concentrations, volumes or lipid emulsion regimens appear here. Maxima differ by agent and preparation, and a remembered number applied to the wrong one is how toxicity happens. Calculate from what is in your hand and follow your local protocol.
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