2 year old child presented with sudden onset of altered sensorium on examination P was 200/100 –
This child is suffering from hypertensive crisis.
Hypertensive crisis 

In hypertensive crisis, BP is rapidly rising or a high BP level is associated with neurological manifestations, heart failure or pulmonary edema.
Hypertensive crisis may be divided : -


Hypertensive emergencies ---> Situations in which immediate reduction of BP is needed (within minutes), usually with parentral therapy.
Hypertensive urgencies     Situations in which reduction of BP is needed within hours, usually with oral agents.
Accelerated malignant hypertension ----> Situations in which papilledema, hemorrhage, and exudate are associated with markedly elevated BP. The diastolic pressure is usually greater than 140 mm. Hg.
Hypertensive encephalopathy --> Situations in which markedly elevated BP is associated with severe headache and various alteration in consciousness.


So, the child in question having hypertensive encephalopathy i.e., markedly elevated BP with impaired sensorium.
Hypertensive encephalopathy may develop in any cause of secondary hypertension if BP is markedly elevated.
Most common cause of secondary hypertension in a child is chronic glomerulonephritis.
Renal artery stenosis
Coarctation of Aorta
Glomerulonephritis
Essential hypertension