Tachycardia sodium nitroprusside

Nitroprusside [nye troe PRUSS ide] is administered intravenously, and causes prompt vasodilation, with reflex tachycardia. It is capable of reducing blood pressure in all patients, regardless of the cause of hypertension. The drug has little effect outside the vascular system, acting equally on arterial and venous smooth muscle. [Note Because nitroprusside also acts on the veins, it can reduce cardiac preload.] Nitroprusside is metabolized rapidly (t1/2 of minutes) and requires continuous infusion to maintain its hypotensive action. Sodium nitroprusside exerts few adverse effects except for those of hypotension caused by overdose. Nitroprusside metabolism results in cyanide ion production, although cyanide toxicity is rare and can be effectively treated with an infusion of sodium thiosulfate to produce thiocyanate, which is less toxic and is eliminated by the kidneys (Figure 19.14). [Note Nitroprusside is poisonous if given orally because of its hydrolysis to cyanide.]... 

A 21-year-old Canadian man presented with severe headache, nausea and vomiting, hypertension (220/ 120 mmHg), and a sinus tachycardia of about 120/minute with frequent multifocal ventricular extra beats. He was treated with intravenous sodium nitroprusside and lidocaine and recovered fully within 24 hours. 

The infusion of sodium nitroprusside has an almost immediate hypotensive effect which will last only for few minutes after withdrawal of the infusion. The powerful vasodilatation causing the hypotension also leads to reflex tachycardia and to an increase in the cardiac output. 

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