What feature is least consistent with a Phase II block after succinylcholine?

What feature is least consistent with a Phase II block after succinylcholine?

• A. Fade with tetanic stimulation
• B. Post-tetanic potentiation
• C. Train-of-four ratio of 1.0
• D. Total dose of succinylcholine >4 mg/kg

Answer: (C)

A train-of-four ratio of 1.0 is indicative of a complete neuromuscular block, which typically occurs during a Phase I block, where you would expect a consistent effect of succinylcholine without fade in response to stimulation. In contrast, a Phase II block may present with some fade during stimulation, although it can initially appear similar to a Phase I block. Therefore, a train-of-four ratio of 1.0 suggests that the neuromuscular transmission is intact, which is not characteristic of a Phase II block. In a Phase II block, you might observe a fade with tetanic stimulation, reflecting some degree of neuromuscular dysfunction. Post-tetanic potentiation can also be a feature associated with Phase II blocks, as it indicates that the nerve is still able to respond, albeit at a diminished level. The total dose of succinylcholine exceeding 4 mg/kg is usually associated with a higher likelihood of experiencing a Phase II block, as prolonged exposure to the agent can shift the response from a Phase I to a Phase II block due to receptor desensitization. Thus, the train-of-four ratio being at 1.0 aligns least with the expected features of a Phase II block.

A train-of-four ratio of 1.0 is indicative of a complete neuromuscular block, which typically occurs during a Phase I block, where you would expect a consistent effect of succinylcholine without fade in response to stimulation. In contrast, a Phase II block may present with some fade during stimulation, although it can initially appear similar to a Phase I block. Therefore, a train-of-four ratio of 1.0 suggests that the neuromuscular transmission is intact, which is not characteristic of a Phase II block.

In a Phase II block, you might observe a fade with tetanic stimulation, reflecting some degree of neuromuscular dysfunction. Post-tetanic potentiation can also be a feature associated with Phase II blocks, as it indicates that the nerve is still able to respond, albeit at a diminished level. The total dose of succinylcholine exceeding 4 mg/kg is usually associated with a higher likelihood of experiencing a Phase II block, as prolonged exposure to the agent can shift the response from a Phase I to a Phase II block due to receptor desensitization. Thus, the train-of-four ratio being at 1.0 aligns least with the expected features of a Phase II block.