Ketamine

Ketamine is a phencyclidine (PCP) derivative that acts as a dissociative sedative or anaesthetic through binding of the N-methyl-D-aspartate (NMDA) receptor. It has anxiolytic, analgesic, amnesic and dissociative properties with a wide safety margin. It is commonly used to facilitate short painful procedures, such as suturing or brief orthopaedic manipulations, and for paediatric anaesthesia.


Ketamine causes less hypotension than thiopental sodium and propofol during induction. Recovery is relatively slow and there is a high incidence of extraneous muscle movements. The main disadvantage of ketamine is the high incidence of hallucinations, nightmares, and other transient psychotic effects (though these can be reduced by administering a benzodiazepine e.g. diazepam).

Properties of ketamine

Ketamine typically causes the following:

• Increased blood pressure
• Increased heart rate
• Increased cardiac output
• Bronchodilation
• Respiratory stimulation
• Normal pharyngeal-laryngeal reflexes

These properties make ketamine useful in patients who are hypovolaemic or those with severe asthma or other forms of reactive airway disease.


Contraindications to ketamine sedation

• Acute porphyrias
• Eclampsia and pre-eclampsia
• Head trauma
• Raised intracranial pressure
• Hypertension
• Severe cardiac disease
• Stroke

Common side effects

• Anxiety
• Abnormal behaviour
• Confusion
• Diplopia & nystagmus
• Hallucination, nightmares and emergence phenomena
• Muscle tone increased
• Nausea & vomiting
• Skin reactions
• Sleep disorders
• Tonic clonic movements

Rare but serious side effects

• Apnoea
• Laryngospasm

Management of complications

Laryngospasm

Laryngospasm is a sudden contraction of the vocal cords that results in partially obstructed inspiration characterised by stridor. It is a rare transient complication of ketamine sedation occurring in approximately 0.3% of cases. Management involves:

• Attempt airway repositioning
• Attempt gentle suctioning of secretions and apply a high flow oxygen mask with reservoir bag
• If child is saturating appropriately continue the procedure
• If the stridor gets worse or the child starts de-saturating let the child breathe oxygen via a bag-valve-mask. Stop the procedure & seek help
• If SPO2 drops below 92% start gentle bag-valve-mask ventilation.
• Apply PEEP, if necessary
• Prepare for RSI.
• If the stridor worsens further, seek help and prepare relevant anaesthetic agent (e.g. suxamethonium) and proceed to RSI.

Apnoea
Apnoea is another rare (0.3%) complication of ketamine sedation that is more commonly seen of a rapid IV bolus is given. Management involves:

• Airway repositioning or brief bag-valve-mask ventilation.
• Prevention by using slow IV administration over 60 seconds

Emergence phenomena
Ketamine is known to induce agitation and hallucinations in adults and children as the dissociative effects wear off (more common in older children and adults). Management involves:

• Positive psychology prior to drug administration e.g. advise child they will have a happy dream
• Mitigated by giving benzodiazepines in recovery period if it occurs (prophylactic administration is NOT advised)

Vomiting
Intractable vomiting post procedure may be managed with IV ondansetron in a dose of 0.1mg/kg (maximum of 4mg) by slow intravenous injection

Discharge instructions

Typically patients will be alert, talkative and walking by 90 minutes post sedation. Discharge advice should include the following:

• Patients should be closely supervised for the first 8 hours following discharge
• Allow the patient to sleep
• No eating or drinking for 2 hours post procedure then only eat and drink small amounts to minimise the risk of vomiting which may occur.

For 24 hours following discharge they should not do the following due to risk of ataxia and falls:

• Do any strenuous or sporting activities.
• Use play equipment where there is higher risk from falls such as monkey bars, climbing frames, trampolines etc.