While you infiltrate local anaesthetic, the patient says his lips feel tingly and he can hear ringing. What is happening and what do you do? ANSWER: EARLY LOCAL ANAESTHETIC SYSTEMIC TOXICITY. STOP INJECTING. THE SEQUENCE, in order: EARLY perioral tingling, metallic taste, tinnitus, light-headedness — all REPORTED BY THE PATIENT, none visible to you THEN agitation, twitching, SEIZURES LATE arrhythmia and CARDIOVASCULAR COLLAPSE, which can be very difficult to resuscitate ACTIONS: stop injecting, call for help, give oxygen, monitor, and know where the LIPID EMULSION is kept. THE HABIT THIS TEACHES: talk to the patient while injecting. A conversation is a monitor — these features exist only in what the patient tells you.

Why does local anaesthetic work poorly when injected into infected tissue? ANSWER: infected tissue is ACIDIC. 1. Local anaesthetics must cross the nerve membrane in their un-ionised form to act. 2. Acidity keeps more of the drug IONISED. 3. The ionised form cannot cross the membrane. 4. So less drug reaches the sodium channels and the block fails. WHAT NOT TO DO: inject more. That hurts, distends inflamed tissue and risks spreading the infection, without improving the block. WHAT TO DO INSTEAD: block PROXIMALLY, or use a field block away from the inflamed area.

What is the commonest cause of local anaesthetic systemic toxicity, and how is it prevented? ANSWER: accidental INTRAVASCULAR INJECTION — not usually a dose calculation error. The whole dose reaches the circulation at once, so toxicity appears rapidly even when the total dose was within limits. THREE PREVENTIVE HABITS: 1. ASPIRATE before injecting, and again each time you reposition. Blood means move the needle. 2. INJECT SLOWLY in small increments — this limits how much reaches the circulation before symptoms appear, and gives the patient time to report them. 3. CALCULATE THE MAXIMUM before you start, from the agent, the actual preparation, whether it contains adrenaline, and the patient's WEIGHT. Point 3 matters most in CHILDREN, where a volume that is trivial in an adult is a large dose per kilogram.

Why is adrenaline traditionally avoided in local anaesthetic used on fingers, toes, nose, ears and penis? ANSWER: these tissues are supplied by END ARTERIES, with no collateral supply. 1. Adrenaline causes VASOCONSTRICTION. 2. Where an alternative supply exists, that is harmless and useful — it prolongs the block and reduces bleeding. 3. Where the tissue depends on a single artery, constriction risks ISCHAEMIA and tissue loss. A NOTE ON CURRENT PRACTICE: the teaching has been questioned, especially for digits, where large series suggest the risk with commercial preparations is lower than long assumed. Follow your LOCAL PROTOCOL rather than a contested change. FOR THE EXAM: give the list AND the reason. The reason — no collateral supply — is what is being tested.

A woman becomes hypotensive shortly after spinal anaesthesia for caesarean section. Is this a complication? ANSWER: it is EXPECTED PHYSIOLOGY, not an unexpected complication. MECHANISM: the spinal block does not affect only sensory fibres. SYMPATHETIC fibres are blocked as well. Sympathetic block → VASODILATATION → fall in systemic vascular resistance → HYPOTENSION. CONSEQUENCE FOR PRACTICE: blood pressure is monitored closely and treated PROACTIVELY rather than waited for. CONTRAST WITH THE GENUINE EMERGENCY: a block that RISES TOO HIGH. Warning features are numbness climbing the trunk, weakness or tingling in the ARMS, difficulty speaking, and a sense of being unable to breathe deeply. That threatens the diaphragm and needs immediate senior help.

A patient develops headache after spinal anaesthesia. Which feature suggests it is related to the procedure? A. Throbbing and unilateral B. Worse on sitting up, better lying flat C. Worse in the morning, improving through the day D. Associated with photophobia and neck stiffness ANSWER: B — POSTURAL headache, worse upright and relieved by lying flat. That posture-dependence is the characteristic feature and distinguishes it from most other headaches. A suggests migraine. C suggests raised intracranial pressure. D suggests meningitis — which after a spinal procedure must be taken seriously and excluded, not attributed to the anaesthetic. EXAM POINT: the postural nature is what is being tested. A headache after spinal anaesthesia that is NOT postural deserves a different differential.

A patient says he can still move his fingers after a local block and is worried the anaesthetic has not worked. What explains this, and what do you tell him? ANSWER: nerve fibres are blocked in ORDER OF SIZE. SMALL unmyelinated PAIN fibres are blocked FIRST. LARGE MOTOR fibres are blocked LAST. So a patient may retain movement in a limb that is already numb to pain. Retained movement does NOT mean the block has failed. WHAT TO TELL HIM: test the actual thing that matters — sensation to sharp touch in the area to be operated on — rather than movement. Explaining this in advance prevents the anxiety, and prevents the temptation to inject more anaesthetic that is not needed.