Dr Andy Tomlinson,
City General Hospital, Newcastle Rd, Stoke on Trent, Staffs ST4 6QG.

Introduction		Premedication
Actions on the Body		Intramuscular Ketamine
Routes of Administration		Intravenous Ketamine
Indications for Use		Case History

Ketamine is frequently described as a "unique drug" because it has hypnotic (sleep producing), analgesic (pain relieving) and amnesic (short term memory loss) effects - no other drug used in clinical practice combines these three important features. It was first used clinically in 1970, and because of these combined effects it was thought that it might be the perfect anaesthetic agent. This is not quite the case, but its continued use in all parts of the world demonstrates that for certain situations, when used appropriately, it is a very valuable drug.

Ketamine is available in three different concentrations - 10mg/ml, 50 mg/ml and 100 mg/ml. The 10 mg/ml is for intravenous use; the 50 mg/ml and 100 mg/ml preparations are for intramuscular use. If only one strength is to be kept in a hospital, the 50 mg/ml ampoule is the best compromise as this may be diluted down to 10 mg/ml for intravenous injections.

 
Actions of Ketamine on the Body

The duration of action depends on the route of administration (see later), and in contrast to the smooth induction of anaesthesia, the patient may be agitated on recovery from ketamine. This is often called "emergence delirium", during which the patient may be disorientated, restless, and crying. Patients may continue to experience unpleasant dreams up to 24 hours after the drug has been given. The use of benzodiazepines (ie. diazepam) as premedication, as well as allowing the patient an undisturbed recovery helps to reduce these unpleasant side effects.

Ketamine causes a rise in intracranial pressure and should not be used in patients who have sustained a recent head injury.

Cardiovascular System (CVS)
Ketamine causes mild stimulation of the CVS. The blood pressure rises by about 25% (on average the systolic pressure rises by 20-30 mmHg) and the heart rate is increased by about 20% - the overall effect is therefore to increase the workload of the heart.

In the majority of patients the blood pressure rises steadily over 3-5 minutes and then returns to normal 10-20 minutes after injection. There is wide individual variation in cardiovascular responses, and occasionally alarming increases in blood pressure can occur. These increases do not seem to be dose-related when more than 1 mg/kg is given and larger doses do not necessarily cause a greater increase in pressure. There is no evidence to suggest that patients with a high preoperative blood pressure are at greater risk of developing a rise in blood pressure following ketamine administration when compared with normotensive patients.

Premedication with diazepam reduces this rise in blood pressure. If the blood pressure rises excessively after induction, a further small intravenous dose of diazepam (2mg to the average 60-70 kg adult) may help to decrease the pressure. As the cardiovascular stimulation following ketamine is mediated through the sympathetic nervous system it would seem appropriate to give alpha or beta blockers to patients who develop excessively high blood pressures. However, the effects of these drugs are unpredictable, and they are probably best avoided in otherwise normal patients as there is no evidence of damage occurring from these short episodes of elevated blood pressure.

Respiratory system
If ketamine is administered rapidly by intravenous injection it often causes the patient to stop breathing for a short time (up to one minute). After a slow intravenous induction, breathing is well maintained and may even increase slightly. The airway is usually well maintained during ketamine anaesthesia and there is some preservation of pharyngeal and laryngeal reflexes in comparison with other intravenous agents. However this cannot be guaranteed, and normal airway care must be maintained to prevent obstruction or aspiration.

Recent research in Kenya using a pulse oximeter has shown that following an intravenous induction with ketamine (2 mg/kg) the oxygen saturation falls in a significant number of people (eight out of twenty three patients studied). Nevertheless, there were no untoward events even though this study took place at an elevation of 5000 feet where an increased incidence of hypoxia would be anticipated. The overall message is to observe the patient closely, and if oxygen is available give some during anaesthesia. A simple ward oxygen mask or nasal cannulae may be used.

Ketamine produces some bronchodilation making it a useful anaesthetic drug for patients with asthma.

Gastrointestinal tract
Salivation is increased.

Skeletal muscle
Muscle tone is often increased. Spontaneous movements may occur during anaesthesia but reflex response to surgery is uncommon if the patient is adequately anaesthetised.

Uterus and Placenta
Ketamine crosses the placenta easily and concentrations in the fetus are approximately the same as those in the mother.

The Eyes
The pressure within the eyeball (intra-ocular pressure) rises for a short time following administration. Eye movements may continue throughout surgery. It is not suitable for use in patients with a perforated eye injury or for ophthalmic surgery where a still eye is required.

 
Routes of Administration

Ketamine can be given by either the intravenous or intramuscular routes to provide surgical anaesthesia. Excellent analgesia and sedation can be obtained with smaller intravenous doses. (It has also been used orally or rectally as a form of premedication. However, this only produces sedation, not surgical anaesthesia and is unpredictable in its effect).

 
Indications for Use

Ketamine may be used as the sole anaesthetic agent for a large number of superficial operations and procedures in both adults and children. Common procedures undertaken with ketamine anaesthesia include minor to intermediate orthopaedic surgery (especially distal arm or lower leg surgery including manipulation of fractures), gynaecological surgery (eg. dilatation and curettage and other minor surgical procedures), drainage of abscesses, debridement of burns, change of dressings and minor dental procedures, as well as a variety of examinations under anaesthesia.

(Continued...)

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