Ketamine - Medicinal Use

Medicinal Use

Indications for use as an anaesthetic:

• Pediatric anesthesia (as the sole anesthetic for minor procedures or as an induction agent followed by muscle relaxant and endotracheal intubation);
• Asthmatics or patients with chronic obstructive airway disease;
• As part of a cream, gel, or liquid for topical application for nerve pain — the most common mixture is 10% ketoprofen, 5% Lidocaine, and 10% ketamine. Other ingredients found useful by pain specialists and their patients as well as the compounding pharmacists who make the topical mixtures include amitriptyline, cyclobenzaprine, clonidine, tramadol, and mepivicaine and other longer-acting local anaesthetics.
• In emergency medicine if entrapped patient is suffering severe trauma;
• Emergency surgery in field conditions in war zones;
• To supplement spinal / epidural anesthesia / analgesia utilizing low doses;

In medical settings, ketamine is usually injected intravenously or intramuscularly. Since it suppresses breathing much less than most other available anaesthetics, ketamine is still used in human medicine as an anesthetic; however, due to the hallucinations which may be caused by ketamine, it is not typically used as a primary anesthetic, although it is the anaesthetic of choice when reliable ventilation equipment is not available. Ketamine tends to increase heart rate and blood pressure. Because ketamine tends to increase or maintain cardiac output, it is sometimes used in anesthesia for emergency surgery when the patient's fluid volume status is unknown (e.g., from traffic accidents). Ketamine can be used in podiatry and other minor surgery, and occasionally for the treatment of migraine. There is ongoing research in France, the Netherlands, Russia, Australia and the US into the drug's usefulness in pain therapy, depression, and for the treatment of alcoholism and heroin addiction.

In veterinary anesthesia, ketamine is often used for its anesthetic and analgesic effects on cats, dogs, rabbits, rats, and other small animals. Veterinarians often use ketamine with sedative drugs to produce balanced anesthesia and analgesia, and as a constant rate infusion to help prevent pain wind-up. Ketamine is used to manage pain among large animals, though it has less effect on bovines. It is the primary intravenous anesthetic agent used in equine surgery, often in conjunction with detomidine and thiopental, or sometimes guaifenesin.

Ketamine may be used in small doses (0.1–0.5 mg/kg·h) as a local anesthetic, particularly for the treatment of pain associated with movement and neuropathic pain. It may also be used as an intravenous co-analgesic together with opiates to manage otherwise intractable pain, particularly if this pain is neuropathic (pain due to vascular insufficiency or shingles are good examples). It has the added benefit of counter-acting spinal sensitization or wind-up phenomena experienced with chronic pain. At these doses, the psychotropic side effects are less apparent and well managed with benzodiazepines. Ketamine is a co-analgesic, and so is most effective when used alongside a low-dose opioid; while it does have analgesic effects by itself, the higher doses required can cause disorienting side effects. The combination of ketamine with an opioid is, however, particularly useful for pain caused by cancer.

The effect of ketamine on the respiratory and circulatory systems is different from that of other anesthetics. When used at anesthetic doses, it will usually stimulate rather than depress the circulatory system. It is sometimes possible to perform ketamine anesthesia without protective measures to the airways. Ketamine is also a potent analgesic and can be used in sub-anesthetic doses to relieve acute pain; however, its psychotropic properties must be taken into account. Patients have reported vivid hallucinations, "going into other worlds" or "seeing God" while anesthetized, and these unwanted psychological side-effects have reduced the use of ketamine in human medicine. They can, however, usually be avoided by concomitant application of a sedative such as a benzodiazepine.

Low-dose ketamine is recognized for its potential effectiveness in the treatment of complex regional pain syndrome (CRPS), according to a retrospective review published in the October 2004 issue of Pain Medicine. Although low-dose ketamine therapy is established as a generally safe procedure, reported side effects in some patients have included hallucinations, dizziness, lightheadedness and nausea. Therefore nurses administering ketamine to patients with CRPS should do so only in a setting where a trained physician is available if needed to assess potential adverse effects on patients.

In some neurological ICUs, ketamine has been used in cases of prolonged seizures. There has been some evidence that the NMDA-blocking effect of the drug protects neurons from glutamatergic damage during prolonged seizures.

Pain Management

The dissociative anesthetic effects of ketamine have also been applied within the realm of postoperative pain management. Low doses of ketamine have been found to significantly reduce morphine consumption as well as reports of nausea following abdominal surgery.

Oral ketamine

• Ketamine can be started using the oral route or patients may be changed from a subcutaneous infusion when pain is controlled.

• Starting dose: 5-10mg four times daily.

• Increase dose in 5-10mg increments.

• Usual dose range: 10mg-60mg four times daily.

Subcutaneous ketamine infusion

• Starting dose: 50-150mg/24 hours.

• Review daily; increase dose in 50-100mg increments.

• Usual dose range: 50mg- 600mg/24 hours

Converting from a 24 hour SC ketamine infusion to oral ketamine

• Oral ketamine is more potent than SC ketamine (due to liver metabolism). Many patients require a dose reduction of 25-50% when changing to oral ketamine.

• Titrate dose in 5-10mg increments.

• Some specialists stop the SC infusion when the first dose of oral ketamine is given. Others gradually reduce the infusion dose as the oral dose is increased.