2015A08 List the classes of drugs that may be used to manage an intra-operative hypertensive crisis,
and briefly outline the mechanisms of action.

Group	Example	Effect
IV anaesthetic	Propofol Quickest access	· ↓L-Ca²⁺ activity ↑Nitric oxide (NO) release ↓SNS output from medulla ↓CO, ↓↓TPR, ↑depth of anaes
IV opioid analgesic	Alfentanil	· ↓SNS output from medulla · ↔↓CO, ↓↓TPR
Volatile anaesthetic	Sevoflurane	· ↓L-Ca²⁺ activity, ↓SNS output from medulla · -/↓CO, ↓↓TPR, ↑depth anaes · But slower
Adrenergic drugs	Clonidine	· α₂ agonist · ↓NAd release -> ↓TPR
“”	Phentolamine	· α₁ and α₂ antagonist · ↓TPR, +/-↑HR (initial α₂ effect)
“”	Phenoxybenzamine	· α₁ and α₂ irreversible antagonist · Covalent bond
“”	Metoprolol	· β₁ antagonist · ↓CO -> ↓mAP · May precipitate acute LV failure if in setting of ↑↑SVR
“”	Labetalol	· α₁, β₁ and β₂ antagonist · IV 7:1 β:α · ↓CO, ↓TPR
Nitrate	Glyceryl trinitrate (GTN)	· React with ICF sulfhydryl group -> ↑NO -> activate GC -> ↑cGMP -> ↑MLCP activity, ↑Ca²⁺ reuptake, ↑K⁺ efflux · Venodilation -> ↓CO · Vasodilation -> ↓TPR
“”	NTP	· Release NO -> same
Calcium antagonist	Nifedipine	· Antagonist at L-Ca²⁺ · ↓TPR
“”	Magnesium	· Physiological antagonist at L-Ca²⁺ · ↓TPR