Suppose Kevin’s pre-op blood work indicates that his extracellular potassium concentration is much ...

Hi,

Elevated potassium levels would increase the amount of potassium in the extracecellular fluid. This would alter the membrane potential of the cells. The normal resting membrane potential of a cell is around -70 mV.  Increasing the potassium concentration would cause the extracellular matrix to become more positive, which would increase the cell's resting membrane potential.

Normally to reach threshold, the membrane potential of a cell must increase from about -70 mV to -55 mV. Reaching this voltage triggers an action potential, leading to a muscle contraction. If the membrane potential of the cell is more positive as a result of more extracellular potassium (let's say it brought the resting membrane potential from -70 mV -> -60 mV), it will take less of a depolarization to bring the cell's membrane potential to -55 mV (the level needed to trigger a muscle contraction).

~CooperS

By the end of Action potential, the all Sodium ion channels would have been deactivated, but Potassium ions will remain open which will cause continued outflux of K+ ions out of the cell. At this time, the voltage drops even below the resting potential, which is called hyperpolarization.

But this hyperpolarization does not last more than 2-3 mSec. Consider a prolonged hyperpolarization (due to high K+ ions already), and the situation aggravated by anesthesia. This will cause abnormal heart beat and a life threatening condition. As a surgery usually follows an anesthesia, it is necessary to correct the hyperkalemic condition.