Ketamine is frequently used in severely injured people and appears to be safe in this group. It has been widely used for emergency surgery in field conditions in war zones, for example, during the Vietnam War. A 2011 clinical practice guideline supports the use of ketamine as a sedative in emergency medicine, including during physically painful procedures. It is the drug of choice for people in traumatic shock who are at risk of hypotension. Low blood pressure is harmful in people with severe head injury, and ketamine is least likely to cause low blood pressure and often even able to prevent it.