Specific antihypertensive drugs are shown in Fig 1. Other agents which can help by virtue of their hypotensive side effects are volatile anaesthesia, propofol infusion and remifentanil infusion.
Agents:
Esmolol
Esmolol is an ultra-short β-blocker, which is usually given by infusion due to its short half-life.
Start at 500 μg/kg/min for 1 min, followed by a 50–100 μg/kg/min infusion for 4 min. The dose should be titrated to a maximal dose of 300 μg/kg/min, though bradycardia may limit this maximum in reality.
Hydralazine
Hydralazine is a direct-acting smooth muscle relaxant which causes mainly arteriolar vasodilatation.
Boluses of 5-10 mg IV are given no more frequently than every 20 min (as the hypotensive effect takes some time). If required, an infusion may be commenced at 10 mg/h and titrated to effect.
Labetalol
Labetalol is a mixed α1- and β-blocker. It is commonly used in the treatment of pre-eclampsia and hypertension in the recovery room (once reversible causes have been excluded).
It can be given by intermittent bolus, starting with a slow bolus of 20 mg given over 2 min, then doubling the dose every 10 min until the desired response is achieved.
It may also be administered as an intravenous infusion, starting at 2 mg/min and titrated to response.
Glyceryl trinitrate
Glycerol trinitrate (GTN) vasodilates veins by the production of nitric oxide. By reducing preload, venous return and ventricular end-diastolic pressure and wall tension, it reduces myocardial oxygen demand and increases coronary blood flow. This makes it most useful in patients with cardiac failure and ischaemic heart disease.
Start an infusion at 5 μg/min initially, then titrate in 5 μg/min increments (can use 10 to 20 μg/min increments when doses are >20 μg/min) every 3–5 min until desired response or toxicity.
Nitroprusside
Sodium nitroprusside is primarily a venodilator, though it also relaxes arterioles. Its effects are mediated by nitric oxide. Toxic cyanide ions are produced on exposure to sunlight, so infusions must be covered in foil or use opaque syringes and giving sets.
Commence an infusion at 0.25–0.5 μg/kg/min, then titrate the dose every 1–2 min until desired response is obtained or to the maximum dose of 10 μg/kg/min.