Anaesthesia Coffee Break Viva Practice with Mason - Fasting, Local Anaesthetics, Shunt and MAC
Sep 19, 2021
Mason dives deep into the metabolic differences between fasting and starvation, exploring hormonal responses like insulin and glucagon. The conversation shifts to local anesthetic pharmacology, detailing how lignocaine works and the benefits of combining it with adrenaline. He also tackles the complexities of shunt calculations and the effects of bronchial blocks on cardiovascular dynamics. Additionally, Mason explains MAC values and how they vary with age, offering study strategies while engaging listeners in an enlightening viva format.
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Choose Baricity To Control Spinal Spread
- 'Heavy' bupivacaine is hyperbaric due to added glucose and has greater cranial spread controlled by position.
- Plain bupivacaine is less position-dependent and often causes narrower block with less hemodynamic instability.
Main Bronchus Block Causes Large Shunt
- Blocking a main bronchus produces immediate shunt to that lung; without HPV this approximates a 50% shunt.
- Healthy patients often maintain sats due to hypoxic pulmonary vasoconstriction redirecting flow.
Shunt Lowers Sats Toward Venous Values
- If shunt remained 50% the arterial saturation would approximate mixed venous (~75%) and fall rapidly.
- Effective HPV and compensatory mechanisms often keep healthy patients' sats ~90–95%.