In which group of patients is ketamine contraindicated?

Ketamine is an NMDA antagonist that is frequently used as an anesthetic and for pain management. One of its effects is to increase intracranial pressure (ICP), which can be particularly problematic in patients with head injuries. This is largely due to the potential for ketamine to induce dissociative anesthesia, which may lead to increases in ICP. For patients with existing head injuries, managing ICP is critical, making the use of ketamine contraindicated in this population to avoid exacerbating potential neurological damage or complications.

In contrast, while ketamine does have cardiovascular effects, particularly in increasing heart rate and blood pressure, it can sometimes be used in patients with cardiovascular disease under careful monitoring. The considerations for renal failure are more related to dosing and risk of accumulation rather than absolute contraindication. Substance abuse issues may raise concerns regarding the potential for misuse, but do not constitute a formal contraindication from a pharmacological standpoint, allowing for its possible use in medically supervised environments.

Therefore, its contraindication in patients with head injury is clear and justified based on its effects on intracranial dynamics.