The relief of pain is an essential component of prehospital care and, when required is usually administered on completion of the primary survey. For simple analgesia morphine sulphate titrated to the clinical response and preceded by an antiemetic is usually effective, for example, in the relief of pain in chest trauma or myocardial infarction. For patients with multiple injuries and for those patients requiring manipulation and splintage of fractures and for entrapments and difficult extrications ketamine is a safe and effective option, which avoids the potential decrease in blood pressure and respiratory depression that is associated with opioid analgesia. This paper reports the personal experience in the prehospital administration of ketamine by a non-anaesthetist working as an immediate care practitioner as part of a British Association for Immediate Care (BASICS) Scheme.
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The author is a medical responder predominantly for the West Midlands Ambulance Service NHS Trust and also less frequently for Hereford and Worcester Ambulance Service NHS Trust and Warwickshire Ambulance Service NHS Trust. Call out is normally by pager and may be in response to information given to the call taker, for example, entrapped patients, multiple casualties, or at the request of the ambulance crews in attendance at the scene.
This paper reports the relevant clinical data on all patients who received ketamine as the sole intravenous analgesic/anaesthetic agent attended by a single immediate care practitioner. Ketamine was administered in most cases in sub-anaesthetic doses for its analgesic affect and additional supplements given as required.
Thirty two patients were treated between 1992 and 2002. Nineteen were male with a mean age of 36 (range 16–75). Thirteen patients were female with a mean age of 38 (range 9–87). Table 1 shows the mechanism of injury, predominant injuries, drugs administered, and the reasons for their use.
Ketamine produces dissociative anaesthesia in which the limbic system is selectively anaesthetised. Sensory stimuli are therefore prevented from reaching the cerebral cortex producing general anaesthesia and analgesia with a cerebral cortex that is minimally depressed. The brain stem functions normally.
Ketamine is presented as a colourless liquid for single use in glass vials in concentrations of 10 mg/ml (20 ml vial), 50 mg/ml (10 ml vial), and 100 mg/ml (10 ml vial). It is stable at room temperature and does not require any special storage conditions. Administered intravenously at a dose of 2 mg/kg it will produce general anaesthesia within 30–60 seconds, which will persist for 10 to 15 minutes. Anaesthesia can be maintained by repeated bolus injections usually 1–3 mg/min.
Ketamine is metabolised in the liver with an elimination half life of 180 minutes. The two main metabolites norketamine and hydroxynorketamine are both active and analgesia will persist after awakening.1 Therefore, ketamine can be used in sub-anaesthetic doses for analgesia alone.
In this series the initial bolus dose seems comparatively small compared with the recommended 2 mg/kg for anaesthesia (table 1). Despite this small dose all patients had a period of initial unconsciousness. Where required, additional increments of ketamine were given after the initial bolus to maintain an analgesic effect. (Table 1 case numbers 8, 19, 23, 29). Ketamine was administered either as a single bolus to facilitate manipulation and splintage of fractures and extrication if necessary or by an initial bolus and incremental doses in patients with significant pain at the outset and to maintain pain relief.
To avoid confusion by carrying more than one preparation of ketamine and to facilitate the administration of small incremental doses only the 10 mg/ml vials were carried. This is an important safety issue particularly because many of these patients were treated in difficult, poorly lit environments where there is the potential for an increased risk of drug error.
Ketamine produces dissociative anaesthesia with profound analgesia however; airway, tone, and reflexes are usually maintained. While aspiration during the use of ketamine has been recorded, the drug, however, promotes gut motility and vomiting after administration is unusual. Ketamine produces a sympathomimetic effect due to brain stem stimulation, which leads to catecholamine release and an inhibition of noradrenaline reuptake. As a consequence it increases the pulse rate and volume, and leads to an increase in the mean blood pressure. The patient therefore continues to breathe spontaneously and blood pressure is normal or increased.2
In this series there were no significant airway problems after the administration of ketamine or ketamine and midazolam. In those patients hypotensive at the outset (table 1 case 1 and 24) blood pressure was maintained. Importantly neither developed an increased systolic blood pressure that could have lead to increased bleeding. It should be noted that after standard anaesthetic doses, increased hypotension can occur in the shocked patient.
Hypersalivation may also occur and is more commonly seen in children. In this series it occurred in case number 26, a 9 year old child and was not a clinical problem.
Historically the use of ketamine in patients with a changed level of consciousness has been questioned. It has been reported that ketamine increases cerebral blood flow and intracranial pressure in spontaneously breathing patients,3 a scenario that is worsened in the presence of hypercapnia.4,5 It has subsequently been reported that ketamine confers a direct neuroprotective role,6 where in the presence of normocapnia it does not increase intracranial pressure and confers haemodynamic stability superior to other analgesics and sedatives.7–9 In this series ketamine was only prescribed in those patients with head injuries who had a normal respiratory rate and pattern of breathing. While this does not necessarily equate to normocapnia no patients obviously suffered as a consequence of ketamine administration. This has to be a judgement call, particularly as the only other effective alternative may be rapid sequence induction of anaesthesia.
Recovery from ketamine administration can in some cases lead to visual and auditory hallucinations and delirium. These undesirable effects can be minimised by giving benzodiazepines.10,11 Simultaneous administration of ketamine and midazolam can produce respiratory compromise and in this series midazolam was administered in 12 of the 32 cases when the patients were recovering from their ketamine administration (table 1). In this series the indication for the administration of midazolam when wakening from ketamine administration was aggression or agitation.
Patients given ketamine have a typical catatonic appearance. They are unconscious and amnesic but their eyes commonly remain open and exhibit nystagmus. It is important to warn members of the emergency services, friends, and relatives present as this can be particularly distressing to onlookers and reassurance is necessary that this is a normal occurrence and that the patient is amnesic and unaware of these events. This was particularly a problem with case 13 (table 1) who was a fireman and had to be rescued by his colleague.
Ketamine can be used to facilitate surgical procedures, in this series an above knee amputation (case 27, table 1). Although an unusual necessity in prehospital civilian practice in the United Kingdom ketamine is commonly used in military surgery.11
It must be recognised that ketamine is an anaesthetic agent, therefore the user must be competent in airway maintenance and have training and confidence in managing airway compromise. All patients should have ECG and pulse oximetry monitoring applied. Suction devices and equipment for advance airway interventions should be immediately to hand. In the case of the author, who is a consultant trauma surgeon and who is not trained in rapid sequence induction, to facilitate endotracheal intubation the fallback position includes the administration of midazolam and ketamine to facilitate the passage of a laryngeal mask airway or a surgical airway. As a surgeon frequent airway management practice and skill retention is provided through anaesthetic colleagues.
In conclusion, ketamine has provided safe and effective anaesthesia/analgesia for this cohort of trauma patients that includes adults and children, polytrauma, patients with a changed level of consciousness, and patients who are hypotensive due to hypovolaemia. For the non-anaesthetist it is essential that the immediate care practitioner maintains their knowledge and skill base to be able to confidently manage any airway compromise that may occur.
Conflicts of interest: none declared.