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Prehospital analgesia 25
moderately effective (> 80% rates of pain relief in the prehospital setting), and
is recommended in prehospital reviews of analgesic methods for adults and
children. 12,21,34,35 There are some patient-based disadvantages. Nitrous oxide
use requires precautions (e.g. pneumothorax) attendant to administration of
any gas, and there is vomiting (and thus aspiration risk) in 10–15% of
patients. 32 It is the disadvantage of occupational risk (to ambulance providers)
that is the main barrier to more widespread EMS use of nitrous oxide.
Sufficient ventilation to keep nitrous oxide concentrations below acceptable
levels is difficult to achieve in the enclosed ambulance compartment.
In some settings (with physician-staffed EMS), ketamine is found useful as
a pain control adjunct for splinting, extrication, and transport of trauma
victims. 35,43 Particularly in areas outside the USA, ketamine has been useful
when given IV, IM, or intraosseously for a broad mix of patients including
those in shock; clinical series and discussions of its use are consistently
positive. 44–50 Ketamine’s near-100% efficacy is not surprising, given long
ED experience with the drug’s use in procedural sedation and analgesia.
The experience in acute care teaches another lesson: ketamine use requires
close familiarity with the agent’s pharmacology and adverse effect profile.
The problem is not vital signs depression, although there is some risk of
apnea with rapid IV administration. 51 Instead, hesitance to embrace ketamine
is related to other concerns (e.g. laryngospasm, hypersalivation,
emergence phenomena) that, while not unique to ketamine, are noted
more frequently with the dissociative agent than with alternatives such as
the opioids. Another (controversial) question is that of ketamine-mediated
(sympathomimetic) increases in intracranial pressure. The decades-old
assumption that ketamine’s sympathomimetic effects can exacerbate ICP
increases in head injury have been called into question, with recent reviews
of the evidence noting that data are mixed. 52 Detailed discussion of these
issues lies outside the scope of this chapter, but it is noteworthy that theorized
dangers of ketamine in head injury do not appear to materialize in
studies (including prospective trials in patients with ICP monitoring) of the
drug’s use in neurotrauma. 52–55 Clinical trials data are sparse for ketamine.
There are no data demonstrating ketamine’s risks, but there are also no
methodologically rigorous studies evaluating its risk-to-benefit profile in the