Status Asthmaticus or Severe Bronchiolitis: The patient's symptoms of URTI for 3 days, altered sensorium, bilateral wheezes, low SpO2 (75%), and hypertension suggest a severe respiratory condition. The age and presentation are consistent with bronchiolitis, but the presence of wheezes could also indicate asthma. The altered sensorium could be due to hypoxia.

Pneumonia: Given the URTI symptoms progressing to altered sensorium and respiratory distress (indicated by low SpO2 and bilateral wheezes), pneumonia is a plausible diagnosis. The clinical presentation and the need for immediate intervention make this a strong consideration.
Acute Respiratory Distress Syndrome (ARDS): Although less common in this age group without a clear predisposing factor, the severe hypoxemia and respiratory distress could suggest ARDS, especially if there's an underlying viral or bacterial infection.

Meningitis or Sepsis: Altered sensorium in a child can be a sign of central nervous system infection or sepsis. Although the primary symptoms suggest a respiratory issue, the possibility of meningitis or sepsis cannot be overlooked due to the potential for rapid deterioration and high mortality if not promptly treated.
Congenital Heart Disease with Acute Decompensation: Hypertension and severe respiratory distress could be indicative of a congenital heart disease decompensating, especially if there's an issue with pulmonary blood flow or systemic vascular resistance.

Cystic Fibrosis: While less likely given the acute presentation, cystic fibrosis could present with recurrent or severe respiratory infections and should be considered in the differential for chronic or recurrent cases.
Inborn Errors of Metabolism: Certain metabolic disorders can present with acute respiratory distress or altered mental status, especially during periods of stress like infection. However, these are rare and typically have other associated findings.