Complex sentence: Inhaled agents are frequently supplemented by intravenous anaesthetics, such as opioids (usually fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam), though, for a propofol-based anaesthetic, supplementation by inhalation agents is not required.
Split into simpler sentences: Inhaled agents are frequently supplemented by intravenous anaesthetics, such as opioids (usually fentanyl or a fentanyl derivative) and sedative-hypnotics (usually propofol or midazolam). Though for a propofol-based anaesthetic, supplementation by inhalation agents is not required.