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, ↓NAd release -> ↓NAd release

·   -/↓CO, ↓↓TPR

Volatile anaesthetic

Sevoflurane

·   ↓L-Ca2+ activity, ↓SNS output from medulla -> ↓NAd release

·   -/↓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

 

 

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