In a patient with Guillain-Barré Syndrome, which effect of succinylcholine is most expected?

Succinylcholine is a depolarizing neuromuscular blocker that can cause an increase in serum potassium levels. In patients with Guillain-Barré Syndrome, there is an autoimmune response that leads to demyelination of peripheral nerves, which can result in upregulation of extrajunctional acetylcholine receptors. The presence of these receptors increases the potential for hyperkalemia when succinylcholine is administered, as the drug continues to stimulate these receptors, leading to a significant release of potassium from the intracellular space into the bloodstream.

Thus, the most expected effect of succinylcholine in a patient with Guillain-Barré Syndrome is the possibility of life-threatening hyperkalemia. This is particularly important during anesthesia, as hyperkalemia can lead to dangerous cardiac arrhythmias and should be carefully managed.

Other effects like decreased efficacy or increased duration of action are not typical concerns with succinylcholine in this context, as succinylcholine's effects may actually differ due to the presence of extrajunctional receptors. Additionally, severe bradycardia is not a common result of succinylcholine administration, making hyperkalemia the most significant risk in these patients.