Disadvantage of ketamine is-

Ketamine increases all the pressures. i.e intracranial pressure, intraocular pressure, blood pressure, intragastric pressure. With the rise in CBF and the generalized increase in sympathetic nervous system response, ICP increases after ketamine use. The increase in CMRO2 and CBF can be blocked by the use of thiopental or diazepam. Ketamine increases aerial blood pressure, hea rate, and cardiac output, paicularly after rapid bolus injections. These indirect cardiovascular effects are due to the central stimulation of the sympathetic nervous system and inhibition of the reuptake of norepinephrine after release at nerve terminals. Ref: Miller's anesthesia 8th edition Ref: Morgan & Mikhail's clinical anesthesiology 6e