Ketamine (ketamine hydrochloride) has been approved for use in general anesthesia either alone or in combination with other medications. It is a superb drug for use in short-term medical procedures that do not require skeletal muscle relaxation, and it has approval for the induction of general anesthesia as a pre-anesthetic to other general anesthetic agents.
It also has indications for supplementing low-potency agents such as nitrous oxide. Ketamine is used for short-term procedural sedation, rapid sequence intubation, and is very useful in the emergency department setting for these conditions. It is the medication of choice for patients with bronchospasm because of its bronchodilatory properties. It can be utilized for procedures requiring short-term sedation/anesthesia, such as the reduction of fractures and dislocations, as well as in wound repair in uncooperative patients, especially children. It can be safely used in a wide age range, beginning at three months. Because children metabolize ketamine faster than adults, higher dosing is required than in the adult population. Elderly patients, on the other hand, need lower dosing since they are slow metabolizers of this agent.
There is a wealth of evidence indicating the value of ketamine in the treatment of severe pain, including conditions such as trauma, fractures, abdominal and flank pain, low back pain, and extremity pain. When used for pain management, sub-dissociative dosing, otherwise known as low dose ketamine (LDK) is used, either alone or as an adjunct to other medications for pain relief. It is safe and effective to use in combination with injectable nonsteroidal pain medications as well as opioids. It has gained greater acceptance as concern has grown regarding opioid use. Clinicians are also using ketamine to treat patients with depression and suicidal ideation successfully. It has been used recreationally as a drug of abuse. The street name for ketamine is "K" or "Special K."
Ketamine is FDA approved for use in anesthesia and procedural sedation. It has been used "off-label" and shown in numerous studies to be safe when used for pain management, as discussed above. Ketamine is not FDA approved for the treatment of depression and suicidal ideation, and such use is off label. FDA has recently approved the esketamine (the S enantiomer) form for use in treatment-resistant depression in conjunction with another oral antidepressant. Recreational use of ketamine is not FDA approved.
At doses below a certain threshold, ketamine produces analgesia and sedation. However, once the critical dosage threshold of roughly 1 to 1.5 mg/kg when given intravenously (IV) or 3 to 4 mg/kg when given intramuscularly (IM) is reached, the characteristic dissociative state abruptly appears. Because of this, the dissociative state is not consistent with the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) definitions of moderate sedation or deep sedation; therefore, ketamine must be considered from a different perspective than drugs with the classical sedation continuum.
Ketamine hydrochloride is a nonbarbiturate dissociative anesthetic. It is a cyclohexanone derivative that is rapidly acting and produces profound anesthesia and analgesia. Its chemical name is ±)-2-(o-Chlorophenyl)-2-(methylamino) cyclohexanone hydrochloride; its structural formula is CHClNO. Ketamine is a noncompetitive N-methyl-D-aspartate (NMDA) and glutamate receptor antagonist. It blocks HCN1 receptors. The unique dissociative action and partial agonism on opiate mu-receptors permit the performance of painful procedures in a consistent state of sedation and patient comfort.
Ketamine's effects in chronic pain, and as an antidepressant, far outlast the actual drug levels, and are probably mediated by a secondary increase in structural synaptic connectivity that is mediated by a neuronal response to the ketamine-induced hyper-glutamatergic state." (Sleigh 2014).
The N-methyl-D-aspartate (NMDA) receptor has a significant role in the etiology of depression. Ketamine, through its NMDA antagonistic action, works rapidly in controlling symptoms of depression and acute suicidal ideation. Ketamine may increase glutamate levels and lead to synaptogenesis and elevated levels of brain-derived neurotrophic factor (BDNF).
Ketamine may interact with the sigma receptors. It tends to work by decreasing central sensitization, wind-up phenomenon (development of ongoing, worsening or chronic pain), and pain memory. Cholinergic, aminergic, and opioid systems appear to play both a positive and negative modulatory role in both sedation and analgesia. Ketamine reverses tolerance to opioids. It is metabolized via the hepatic system by way of N-dealkylation, hydroxylation, conjugation, and dehydration. The half-life of ketamine is approximately 45 minutes.
Ketamine generally maintains normal pharyngeal and laryngeal reflexes and, therefore, permits spontaneous respiration. It slightly enhances or maintains normal skeletal muscle tone and is associated with cardiovascular and respiratory stimulation. These characteristics make it particularly useful in the emergency department setting for short-term procedures, especially, as is often the case when a patient has not been "prepped" for an emergency procedure. Since there is no guarantee of maintenance of the pharyngeal and laryngeal reflexes, there can be no assumption that they will "protect" the airway. Additionally, there may be transient minimal respiratory depression if the medication is administered too rapidly or in too high a dose. Therefore, the physician must be ready to perform emergency intubation.
Ketamine administration can be either IV or IM. The onset of action, when given IV, is within seconds. When administered IM, the onset of action is approximately 4 minutes with a duration of action from 15 to 30 minutes. Dosing needs to vary according to the desired effect, the patient's age, and underlying conditions. Children metabolize the drug more rapidly than adults and may require higher or additional dosing; elderly patients metabolize ketamine more slowly and may need lower dosing. When using larger total doses of ketamine, administering it more rapidly than normal, or when using ketamine with sedatives, barbiturates, or narcotics, exaggerated responses may occur, and prolonged recovery times should be expected.
The initial IV dose of ketamine ranges from 1 to 4.5 mg/kg (0.5 to 2 mg/lb) administered over 60 seconds for those 16 years old or older. A dose of 2 mg/kg (1 mg/lb) is the average amount required to produce approximately 5 to 10 minutes of anesthesia/dissociation with the onset of action in about 10 to 30 seconds and a duration of action approximately 5 to 15 minutes. For more prolonged anesthesia, additional doses can be administered IV or IM to maintain anesthesia without producing significant cumulative effects. One-half to full additional doses may be repeated as needed. Adjustments to dosing will be required if used in combination with other drugs such as IV benzodiazepines or narcotics. Maintenance when using diazepam in adults should be by slow infusion at 0.1 to 0.5 mg/minute of ketamine. Additional doses of diazepam in the amount of 2 to 5 mg are an option.
Illicit use of ketamine includes snorting or inhalation, and it is ingestable in food/drinks.
Tonic-clonic movements may present during the administration of ketamine. These movements do not mean that additional doses of the anesthetic are required.
The most common side effects associated with ketamine are nausea, vomiting, dizziness, diplopia, drowsiness, dysphoria, and confusion. There are reports of emergence phenomenon for approximately 6% to 12% of patients. Rarely, patients experience hallucinations.
A complete list of side effects follows:
Emergence delirium may be reduced by decreasing the recommended dose of ketamine, using it in conjunction with benzodiazepines, and/or reducing verbal and tactile stimulation during the administration of the drug. If "emergence" occurs, a small hypnotic dose of a short-acting barbiturate or benzodiazepine is the recommendation to terminate the reaction. Diazepam 2 to 5 mg IV push given over 1 minute (15 mg or less in most cases) can reduce emergence phenomena. "Emergence" is not typical in children younger than 15 years or elderly patients greater than 65 years. In a randomized controlled study of adult emergency department patients, Sener et al. found significant reduction of the incidence of agitation when coadministering midazolam with ketamine for procedural sedation.
Ketamine is contraindicated in those patients who have underlying conditions in which increased blood pressure would pose a risk of complications such as aortic dissection, uncontrolled hypertension, myocardial infarction, or aneurysms.
In patients with cerebrospinal fluid (CSF) elevations, the use of ketamine is controversial due to questionable elevations of the CSF caused by ketamine. Some studies indicate that the concern for CSF elevation with ketamine has been overstated. Kropf et al. found similar hemodynamic properties compared with etomidate. Newer research suggests that ketamine may improve cerebral perfusion pressure and may, in fact, have neuroprotective properties.
Monitor vital signs and cardiac function. Blood pressure, pulse, breathing, and oxygen saturation always need to be monitored when using ketamine.
Be prepared for intubation when administering ketamine.
Neuropsychiatric function always requires monitoring, and a patient must be at baseline before discharge from care. Even after a patient's return to baseline, the patient discharge should be under the supervision of another responsible adult. Patients should not drive, use heavy machinery, or perform other potentially hazardous activities for 24 hours following ketamine administration.
Ketamine is potentially fatal in chronic alcoholics and acutely alcohol-intoxicated patients.
*May increase CSF pressure (controversial-see above/contraindications)
Ketamine's primary use is by anesthesiologists, anesthesia nurses, dentists, emergency department physicians, pain specialists, and psychiatrists. It is an excellent drug for analgesia and sedation. At low doses, it does not produce a dissociative state. All healthcare workers who use ketamine should know the indications and contraindications. In addition, monitoring of the patient's vital signs is mandatory while infusing the drug. One should always have resuscitative equipment in the room in case intubation is required. Before discharge, the clinical team must record the patient's neuro-vitals. Patients should not drive, use heavy machinery, or perform other potentially hazardous activities for 24 hours after the administration of ketamine.
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