Side Effects and Contraindications

The common psychological emergence reactions were discussed earlier. Contraindications to ketamine relate to specific pharmacologic actions and patient diseases. Patients with increased ICP and with intracranial mass lesions should not receive ketamine because it can increase ICP and has been reported to cause apnea on this basis.^[570] The S-(+)-enantiomer also increases CBF and is probably similarly contraindicated.^[571] Additionally, ketamine is contraindicated in patients with an open eye injury or other ophthalmologic disorder, in whom a ketamine-induced increase in intraocular pressure would be detrimental. Because ketamine has a propensity to cause hypertension and tachycardia with a commensurate increase in myocardial oxygen consumption, it is contraindicated as the sole anesthetic in patients with ischemic heart disease. ^[515] Likewise, it is unwise to give ketamine to patients with vascular aneurysms because of the possible sudden change in arterial pressure. Psychiatric disease such as schizophrenia or a history of adverse reactions to ketamine or one of its congeners also constitutes a contraindication.^[285] In addition, one should be cautious in using ketamine when there is a possibility of postoperative delirium from other causes (e.g., delirium tremens, possibility of head trauma) and a ketamine-induced psychomimetic effect would cloud the differential diagnosis.

Other side effects include potentiation of nondepolarizing neuromuscular blockade by an undefined mechanism.^{[572] [573]} Finally, because ketamine's preservative, chlorobutanol, has been demonstrated to be neurotoxic, subarachnoid administration is contraindicated.^[573] It is probably unwise to administer the drug epidurally for this reason. S-(+)-ketamine is available in a preservative-free solution. The Food and Drug Administration has not approved the use of intrathecal or epidural ketamine.