Anaesthesiauk.net

Ketamine in Anaesthetic Practice
Rachael Craven, Bristol Royal Infirmary, UK and Medecins sans Frontieres.
[email protected]
Raad Alkhafaji, Kirkuk Hospital, Iraq

Consider the following real life cases and how you might manage them:
Case 1
A 22 year old man has been admitted with a gunshot wound to the abdomen. He
is shocked from major internal bleeding and requires a laparotomy. You have a
very small supply of inotropes and want to try and not use them. What will you do
for induction and maintenance of anaesthesia?
Case 2
A 2 year old boy needs repair of his hernia. He is extremely frightened of the
hospital and its staff. You think that obtaining intravenous access will be very
difficult and that a gas induction will be difficult as well because of his agitation.
How will you anaesthetise this child.
Case 3
A 37 year old woman is recovering from 45% burns, she needs dressing changes
every two days which are very painful. She has very few sites left for i.v. access
and you don’t want to use them as she has further surgery to come. She is also
very scared of needles. How will you manage the sedation she requires for her
dressing changes?
Case 4
Your laparotomy patient (case 1) is back on the ward. He has severe
postoperative pain but you have been unable to get any morphine this month.
How can you manage his postoperative pain?
Case 5
A 25 year old man has had his leg amputated after a motorbike accident. He is
suffering from lots of problems with phantom limb pain. You have tried giving him
amitryptlline and carbamazepine but without effect. What could be your third line
option?
Case 6
An 18 year old girl has been admitted with severe asthma. You have been asked
to see her as she has not improved with subcutaneous injections of salbutamol
or intravenous aminophylline. She is getting tired and her oxygen saturation is
falling. Can you do anything to help?
Introduction
Ketamine is the only anaesthetic available which has analgesic (pain relieving),
hypnotic (sleep producing) and amnesic (short term memory loss) effects. When
used correctly it is a very useful and versatile drug.
Ketamine is available in three different concentrations 10mg/ml, 50mg/ml and
100mg/ml. 50mg/ml is most commonly stocked since it can be used for i.m.
administration or diluted for i.v. use.
Routes of Administration
Ketamine may be given intravenously (induction 1-2mg/kg, maintenance
0.5mg/kg) or intramuscularly (induction 5-10mg/kg, maintenance 3-5mg/kg) for
anaesthesia or orally (15mg/kg for a child to a maximum of 500mg for an adult)
for sedation.
Effects of Ketamine on the Body
Respiratory System
With ketamine the airway is usually well maintained it also preserves the
laryngeal and pharyngeal reflexes to some degree. This is not always
guaranteed however and standard techniques, where required, for prevention of
aspiration and maintenance of a patent airway must be used. When ketamine is
given slowly respiration is usually well maintained, after rapid i.v. injection the
breathing may stop for a short while but usually restarts within a minute. For this
reason ketamine is a very useful anaesthetic agent in areas where there is no
oxygen or only limited oxygen available. Ketamine is an effective bronchodilator.
Cardiovascular System
With ketamine there is an increase in both blood pressure and heart rate. This
usually reaches a maximum about 2 minutes after injection and settles over 15 –
20 minutes. There is wide variation in individual response and occasionally there
can be a large rise in blood pressure. The risk of this is not related to a
preoperative history of hypertension. This rise in blood pressure usually responds
to further doses of i.v. diazepam (1-2mg for an adult).
This increased workload for the heart means that ketamine should be avoided, if
possible, in those patients with ischaemic heart disease. Patients with diabetes
should have an ECG, if available, to rule out “silent” ischaemia (ischaemia
without chest pain), since this is a common feature of poorly controlled diabetes.
Central Nervous System
Ketamine produces dissociative anaesthesia (detached from surroundings). This
means that unlike with other anaesthetic agents the patient may have their eyes
open and make reflex movements during the operation. It has a slower onset
after an i.v. bolus (1-5 minutes). The duration of action depends on the route of
administration (20-30 minutes for i.m. and 10-15 minutes for iv).
Ketamine provides very good analgesia and may be used without any other
analgesics intraoperatively. Consideration does then have to be given however to
postoperative pain relief. Co-administration of opiates or tramadol
intraoperatively can reduce the amount of ketamine required for maintenance of
anaesthesia and therefore reduce the incidence and duration of postoperative
hallucinations. This does however increase the risk of the breathing stopping
during the operation.
In recovery the patient may be agitated – this is due to the frequent occurrence of
hallucinations after ketamine anaesthesia. These hallucinations can be reduced
by premedication with benzodiazepines (usually diazepam 0.15mg/kg orally 1
hour preoperatively or 0.1mg/kg) and by recovering the patient in a quiet area.
Ketamine increases the intracranial pressure and for this reason should be
avoided wherever possible in those patients with recent head injuries.
Gastrointestinal Tract
Ketamine increases salivation. This can lead to airway problems due to laryngeal
spasm or obstruction. It may also make the taping of endotracheal tubes more
difficult. To reduce this salivation atropine is usually given either as a premed
(20mcg/kg i.m.) 30 minutes preoperatively, or at the time of induction iv (10-
20mcg/kg).
Skeletal Muscle

Ketamine increases skeletal muscle tone. This is most prominent after the initial
iv bolus and gradually decreases. It is improved by administration of
benzodiazepines. It is rarely a problem intraoperatively.
Eyes
Ketamine increases intraocular pressure. The eyes also commonly move
continually during ketamine anaesthesia (nystagmus). This makes it an
unsuitable anaesthetic for eye surgery.
Placenta
Ketamine crosses the placenta. Newborn infants after caesarean section under
ketamine anaesthesia will therefore be partially anaesthetised and should be
cared for accordingly.
Some Practical Examples:
Case 1: IV ketamine for induction and maintenance
This gunshot victim is shocked and requires a laparotomy, you have limited
inotropes. Ketamine would be an ideal anaesthetic agent in this case due to its
cardiovascular effects of raising the blood pressure and heart rate, all other
anaesthetic agents tend to have a cardiac depressant effect.
Induction can be performed with iv ketamine (1-2mg/kg), atropine (10-20mcg/kg)
and diazepam (0.1mg/kg). It is still possible to perform a modified rapid sequence
intubation with ketamine, despite its slower onset time.
There are several options for maintenance:
1) intermittent boluses of iv ketamine (0.5mg/kg) given according to patient’s response - pupil size, heart rate, blood pressure, movement etc 2) ketamine infusion. Put 500mg of ketamine in a 500ml bag of saline or dextrose. Run this at 1-2mls/min (1-2mg/min). Some patients may require more and others less depending on what other drugs have been given and the type of surgery. Generally the ketamine will need to be discontinued 20-30 minutes before the end of the operation to avoid a long wait for the patient to wake up. This technique for laparotomy is best used with non-depolarising muscle relaxants (avoid pancuronium as combined with ketamine may have very high blood pressure increases). It is however possible, although more difficult, to
perform the laparotomy under ketamine alone.
Case 2: use of i.m. ketamine
This child is clearly going to be uncooperative and either i.v. access or gas
induction will be difficult. In these circumstances intramuscular ketamine is very
useful.
There are two possible options:
1) induce anaesthesia with i.m. ketamine (5-10mg/kg) + atropine (20mcg/kg) + diazepam (0.1mg/kg) these may all be mixed in the same syringe. Onset of anaesthesia will start about 5 minutes after injection. The disadvantage of this technique is that it requires a relatively large i.m. injection. While most textbooks quote 8-10mg/kg for induction it has been my experience that in many cases a much smaller dose (5mg/kg) is sufficient. 2) sedate with i.m. ketamine (2mg/kg) + atropine (20mcg/kg) + diazepam (0.1mg/kg). After 5 minutes you will have a docile child who can cooperate with either cannulations or a gas induction.
The author’s preference is for option 2 since the i.m. injection is smaller and it
can be performed safely in the waiting area on the mothers lap rather than in
theatre and is therefore less traumatic.
In either case iv access should then be obtained. If iv access is impossible
then anaesthesia can be maintained with i.m. ketamine (3-5mg/kg).
Case 3: oral ketamine sedation
This woman requires recurrent sedation for painful burns dressings. IV
ketamine is possible but in burns patients there are often limited sites for
cannulation and these are best saved for trips to theatre. IM ketamine is also
an option but requires relatively large painful i.m. injections. Instead the
intravenous preparation of ketamine can be given orally.
For an adult give 500mg of ketamine + diazepam 5mg.
For a child use 15mg/kg ketamine + 0.2mg/kg diazepam (you can use the i.v.
preparation but it tastes very bad and may have to be hidden in juice).
The dressing change can usually start after 20-30 minutes. Responses can
sometimes be unpredictable and onset time may be slower. There should
always be equipment for suction and face mask ventilation available and if
possible, oxygen and a pulse oximeter.

Case 4: ketamine for postoperative analgesia
Ketamine is a very good analgesic and can be a solution for severe pain
when morphine is not available. Its use postoperatively is limited by the
occurrence of hallucinations, however these are less of a problem when
relatively low doses are used. For adult patients in severe pain a loading dose
of 0.5-1 mg/kg i.m. may be given. This can then be followed by an infusion of
60-180mcg/kg/hr (4-12 mg/hr for a 70kg adult).
A reasonable regime is to put 50mg ketamine in a 500ml bag of saline or
dextrose (0.1mg/ml of ketamine) and run this at 40-120mls/hr (i.e. over 4-12
hours for a 70kg adult). This regime is relatively safe since even if the whole
infusion were to be given quickly by accident the patient is unlikely to become
deeply anaesthetised but the patient should still be closely monitored and
anaesthetic help should be available if needed.
Case 5: use of ketamine for patients with chronic pain

Many patients with amputations or patients with spinal cord injuries have
problems with chronic pain. The nature of this pain is often neuropathic (this
means originating from an injury to the nerves) and has an unpleasant
burning or shooting quality to it. When traditional first line treatments for
neuropathic pain such as amitriptyline or carbamazepine have failed ketamine
may also be added and has been shown to have success.
A standard dosing regime for an adult is 50mg orally (use the intravenous
preparation) three times per day. This may be increased to 100mg tds.
Problems with hallucinations and salivation are rare. The ketamine may be
discontinued after about 3 weeks of good pain control, reducing the dose
gradually to see if any pain symptoms reoccur. The authors have found this
regime useful in postoperative amputation patients to try and prevent the
onset of phantom limb pain. In this setting it seems the ketamine need only to
be taken for about a week.
Case 6: ketamine for the treatment of asthma
Ketamine is an effective bronchodilator and can be used for the patient who is
not responding to conventional bronchodilators such as salbutamol and
aminophylline. The doses of ketamine required are very low and problems
with hallucinations rare. A loading dose of 0.2 mg/kg iv is given initially
followed by an infusion of 0.5mg/kg/hr for 3 hours. This may be continued if
necessary. Close monitoring of the patient is required and an anaesthetist
should be available if necessary.

Source: http://anaesthesiauk.net/documents/Ketamine.pdf