Finals Mcq/facts Miscellaneous Surgery

Front 1

SZ14a ANZCA version Q75
In the recovery room, following general anaesthesia for renal transplant surgery, your patient is found to have a serum potassium concentration of 6 mmol.l-1, despite having a normal potassium concentration pre-operatively. His oxygen saturation is 96% on approximately 40% oxygen via a Hudson mask. He is still unconscious, but breathing spontaneously at 8 breaths per minute. The most likely cause of his hyperkalaemia is

A. beta-blockers which he received peri-operatively

B. catabolic stress of surgery

C. opioid induced narcosis causing carbon dioxide retention

D. renal graft failure

E. washed red blood cell transfusion, which he received intraoperatively

Back 1

ANSWER C

All can cause hyperkalemia in this patient, but given the stem C is most likely

A. Beta blockers cause hyperkalemia through 2 mechanisms
1. blocking Ca/K channels, therefore Beta-adrenergic stimuli enhance potassium entry into cells is blocked
2. Reduced insulin activity

B. Increase in the catecholamine levels results in an increased uptake of K+ by the cells. This is mediated by B2- receptors. At the same time, renal secretion of K+ is decreased. The release of epinephrine during a stress response can acutely lower the plasma K+ by 0.5 - 0.6 mmol/L

C. 10 mmHg decrease in PaCO2 reduces plasma K+ concentration by about 0.5 mmol/L
K can increase by 0.5mmol/L for every 0.1 decrease in pH in patient with renal failure.

D. delayed caused of hyperkalemia

E. washed RBC transfusion has lower K