Final answer:
Bradycardia is the least frequent adverse reaction to Fentanyl, Remifentanil, and Sufentanil compared to nausea and vomiting, respiratory depression, and hypotension.
Step-by-step explanation:
The least frequent adverse reactions to Fentanyl, Remifentanil, and Sufentanil are most likely to be 4) Bradycardia. These drugs are potent opioids that can cause a range of adverse reactions, however, issues like nausea and vomiting, respiratory depression, and hypotension are relatively more common. Nausea and vomiting (option 1) are well-known side-effects of opioids but are often prevented or treated with antiemetic medications.
Respiratory depression (option 2) is the most serious side effect and can be life-threatening, which is why vigilant monitoring is crucial during opioid administration. Hypotension (option 3) can also occur, especially in patients with other risk factors or when opioids are combined with other medications that lower blood pressure. In contrast, bradycardia is a less frequent side effect but can still present in certain patients, particularly when opioids are used in higher doses or with other medications that affect heart rate.