What is the preferred analgesic when SBP is less than 90 mmHg?

In cases where the systolic blood pressure (SBP) is less than 90 mmHg, the preferred analgesic is ketamine at a dosage of 0.2 mg/kg. Ketamine is favored in this scenario because it not only provides effective analgesia but also has the added benefit of being a dissociative anesthetic, which can provide sedation without significantly lowering blood pressure. This is crucial considering the hemodynamic instability often associated with low SBP.

Fentanyl, while an effective analgesic, can cause respiratory depression and may lead to further hypotension in patients with an already compromised cardiovascular status. Morphine shares similar drawbacks, as it can cause vasodilation and may exacerbate hypotension. Acetaminophen, although safe in many scenarios, is less effective for immediate and severe pain management compared to ketamine in an emergency setting where rapid action is required.

Therefore, in a patient with low blood pressure, ketamine provides a suitable balance of analgesia and hemodynamic stability, making it the preferred choice.