Final answer:
Meperidine hydrochloride is an analgesic and narcotic that can cause respiratory depression, which is critical to monitor, along with other side effects such as nausea and vomiting.
Step-by-step explanation:
The medication in question, meperidine hydrochloride, is an analgesic and in higher doses can act as a narcotic. Among its side effects, the most critical to monitor for is respiratory depression. This occurs when the medication suppresses the body's urge to breathe, which can be life-threatening. Other common side effects of narcotics like meperidine can include nausea and vomiting, but these are less immediately dangerous than respiratory depression.