So, it can be used in severe congestive heart failure where this combination of effects can act to increase cardiac output. In situations where cardiac output is normal, the effect is to reduce blood pressure. It is sometimes also used to induce hypotension (to reduce bleeding) for surgical procedures (for which it is also FDA, TGA, and MHRA labelled).The medication is extremely beneficial for use in medical patients because the effects of the medication will directly stop the second that it stops being infused. This is due to the metabolism of the drug, and the rapid inactivation to thiocyanin once conversion of the drug stops. This compound has also been used as a treatment for aortic valve stenosis, oesophageal varices, myocardial infarction, pulmonary hypertension, respiratory distress syndrome in the newborn, shock, and ergot toxicity. Adverse effects
Adverse effects by incidence and severityCommon

Unknown frequency

Serious

Ileus
Reduced platelet aggregation
Haemorrhage
Increased intracranial pressure
Metabolic acidosis
Methaemoglobinaemia
Cyanide poisoning
Thiocyanate toxicity

Contraindications
Sodium nitroprusside should not be used for compensatory hypertension (e.g. due to an arteriovenous stent or coarctation of the aorta). It should not be used in patients with inadequate cerebral circulation or in patients who are near death. It should not be used in patients with vitamin B12 deficiency, anaemia, severe renal disease, or hypovolaemia. Patients with conditions associated with a higher cyanide/thiocyanate ratio (e.g. congenital (Lebers) optic atrophy, tobacco amblyopia) should only be treated with sodium nitroprusside with great caution. Its use in patients with acute congestive heart failure associated with reduced peripheral resistance is also not recommended.
Sodium nitroprusside crystals are also of interest for optical storage. For this application, sodium nitroprusside can be reversibly promoted to a metastable excited state by blue-green light, and de-excited by heat or red light.In physiology research, sodium nitroprusside is frequently used to test endothelium-independent vasodilation. Iontophoresis, for example, allows local administration of the drug, preventing the systemic effects listed above but still inducing local microvascular vasodilation. Sodium nitroprusside is also used in microbiology, where it has been linked with the dispersal of Pseudomonas aeruginosa biofilms by acting as a nitric oxide donor. Analytical reagent
Sodium nitroprusside is also used as an analytical reagent under the name sodium nitroferricyanide for the detection of methyl ketones, amines, and thiols. It is also used as a catalyst in the quantitative determination of Ammonia in water samples via the Phenate Method. Ketones
The nitroprusside reaction is used for the identification of ketones in urine testing. Sodium nitroprusside was found to give a reaction with acetone or creatine under basic conditions in 1882. Rothera refined this method by the use of ammonia in place of sodium or potassium hydroxide. The reaction was now specific for methyl ketones. Addition of ammonium salts (e.g. ammonium sulfate) improved the sensitivity of the test, too.In this test, known as Rotheras test, methyl ketones (CH3C(=O)-) under alkaline conditions give bright red coloration (see also iodoform test). Rotheras test was initially applied to detecting ketonuria (a symptom of diabetes) in urine samples. This reaction is now exploited in the form of urine test strips (e.g. "Ketostix").