What is Ketamine? Ketamine as an Anesthetic
Ketamine is a Useful Human Anesthetic
What is Ketamine?
Ketamine is classified as a "dissociative anesthetic". It causes profound distortion of the perception of sensory input. In other words, it causes the recipient to have an "out of body" feeling, can cause hallucinations, causes significant pain relief, and makes purposeful movement difficult or unlikely. It is related to PCP, a hallucinogenic drug of abuse.
Most people associate the anesthetic use of ketamine with veterinary practice, but it is used fairly commonly in humans. Sometimes, it is the drug of choice in certain circumstances. Because ketamine produces many of the effects of general anesthesia without causing dangerous changes in breathing, it is often used by emergency medicine doctors. The impressive pain blockade produced by ketamine is very useful in children and adults during emergency procedures that would otherwise not be able to be performed in the ER setting. It is used more often in children for this purpose, as adults are more prone to emergence delirium and disturbing hallucinations than are children.
Ketamine acts in the brain at a specific site called the NMDA receptor. Blocking this receptor causes the characteristic effects of ketamine.
A patient who has received ketamine may have the following effects, dependent on the dose, the situation and other drugs administered at the same time. Not all of these effects occur in every person, every time.
- Eyes open, staring or with repetitive motion of eyeballs (nystagmus)
- Conscious-appearing, but not responding meaningfully to the environment
- Tense muscles with random movements that may seem purposeful, but likely are not
- Reflexes (cough, swallow, etc) intact, or at least mostly so
- Salivation or drooling
- Some pupil dilation
- No response to stimuli that would otherwise be painful (profound analgesia)
- Amnesia after the fact. Some memories are possible, but are usually incomplete and may not be specific
- Watery eyes, decreased blinking
- Potential emergence delirium, to be discussed below
From Clinical Practice
A 28 year old woman delivers a healthy newborn, vaginally. She is doing well, but needs to have a short procedure after the birth (sewing a tear and removal of retained placenta). The local anesthetic numbing medicine isn't working well, so the anesthesiologist gives ketamine to help her through.
The ketamine works well and she is unresponsive and seems comfortable during the procedure. Upon emergence, she is noted to be combative with elevated heart rate and blood pressure. During the short time it takes her to wake up, she appears to be frightened and does not respond to verbal reassurance. Another medication (midazolam, a benzodiazepine) is given to help her calm down.
Once fully awake, she acknowledged that she had no memory of the procedure and recalls no pain. However, she describes her emergence experience as "terrifying", "felt like she would die" and would never ever consent to the drug again.
A 60 year old man was having a spinal cord stimulator placed for relief of chronic pain. He would need to be comfortable during placement of the device, but fully awake and interactive during testing of the new stimulator. Midazolam was given for initial sedation, along with fentanyl. Because of his chronic lung disease, no further agents were deemed acceptable risk. Ketamine was used to relieve pain and maintain his spontaneous breathing. He had no significant changes in blood pressure, heart rate or oxygen level.
When the ketamine wore off, he reported no memory of the preceding 25 minutes. He had no pain and had no emergence delirium.
It is the practice of many anesthesiologists (this one included) to administer a benzodiazepine before ketamine to prevent emergence delirium.
He was thrilled with the anesthesia, as was the pain doctor placing and testing the device, and wondered if he could "always have that drug".
Ketamine Side Effects
Emergence delirium is the most common, unpleasant side effect of ketamine. Adults more than children, can have illusions/hallucinations, vivid and frightening dreams, excitability, combativeness and out-of-body experiences upon awakening from ketamine sedation or anesthesia.
The reaction can occur during the first hour of emergence from ketamine and vivid, unusual dreams can persist for several hours. Flashback phenomena have also been reported.
These reactions may be of little consequence or they may be quite frightening and unpleasant. Administration of a benzodiazepine medicine (like midazolam- in the same family as Ativan and Valium) has been shown to help prevent emergence delirium in adults.
Adults, women, those receiving higher doses and patients with pre-existing psychiatric disease are more prone to experience unpleasant emergence.
For the health care provider, there are several situations when ketamine should not be given. Ketamine increases pressure in both the eyeball and the brain, so should often be avoided if patients have severe glaucoma, an open-globe injury or brain swelling.
It may also be wise to avoid ketamine in patients where avoidance of increased heart rate or blood pressure is essential.
Ketamine as an Anesthetic
On the other hand, ketamine can (and probably should) be used in some of the sickest, most tenuous patients where use of other medications would worsen a life-threatening situation.
Ketamine stimulates the central nervous system and cardiovascular system. This allows heart rate and blood pressure to be maintained; this is the opposite effect of many other anesthesia drugs. In patients with certain types of heart disease, trauma with blood loss, shock and other situations where standard anesthesia drugs would cause further deterioration by depressing the cardiovascular system, ketamine is invaluable.
In addition, ketamine is often used in emergency rooms, especially for children. Ketamine can be given by intramuscular, intravenous and increasingly by oral or nasal routes. Because ketamine allows spontaneous breathing to be maintained and has a predictable duration of action, it's safety profile is very good in these situations.
Patients who are victims of burn injuries have to have frequent changing of their bandages. Ketamine provides excellent pain relief, without long-lasting effects or side-effects for this type of procedure.
PROCEDURAL SEDATION WITH KETAMINE ON A CHILD
You can see the child's eyes are open, but he is not responding at about the 3:30 mark. At about 4:50, the sewing starts. The medicine is redosed at 5:30. Don't watch the sewing if you are squeamish.
As used in the clinical setting, patients will not become addicted to ketamine. Unfortunately, ketamine has become a "club drug", especially when used with other drugs. Usually, the ketamine abuses is addicted to several recreational, illegal substances.
Special K, as it is known, has also been used as a rave and date-rape drug. Usually, the drug is obtained through theft of veterinary offices and sold illegally to distributers and users.
In the last few years as abuse has become even more common, more cases of urinary dysfunction have been reported from repeated ketamine use. Most patients report painful urination, bloody urine, frequent need to urinate and other symptoms. These symptoms all result from what seems like a dose-dependent bladder dysfunction.
Memory and psychiatric disorders also occur after repeated abuse of ketamine.
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