Pre-hospital Analgesia
Wollongong CGD
August 13th
Dr. Kent Robinson
Pain
• Pain is a common presentation.
• 78-86% of all presentations to the ED are for pain
related issues.
• Oligoanalgesia is common with the vast proportion of
our patients not receiving adequate analgesia.
• Minimal research done on the topic of pre-hospital
analgesia.
Summary
• Analgesia should be given early to patients in
acute severe pain.
• Intravenous analgesia should be aggressive
and titrated to effect
– Results in better analgesia
– Results in reduced dosages of medications
Summary
• Opiates should be the mainstay of analgesia
– Consider the use of titrated fentanyl
• Rapid onset of action
• Quicker time to effective analgesia
• Use ketamine as an opioid sparing agent
• Consider the use of targeted analgesia such as
local anaesthetic nerve blockade
Pain History
• Site of pain
– Location
– Radiation
• Circumstances associated with pain onset
• Character of pain
• Intensity of pain
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At rest
On movement
Duration of pain
Aggravating or relieving factors
Pain History
• Associated symptoms (nausea)
• Effect of pain on sleep and activities
• Treatment
– Current and previous medications (dose,
frequency, efficacy and side effects)
– Other treatments (TENS)
– Health professionals consulted
• Relevant past medical history
Pain History
• Factors influencing the patients symptomatic
treatment
– Belief concerning the cause of pain
– Knowledge, expectation and preferences for pain
management
– Expectations of pain treatment
– Reduction in pain required for patient satisfaction
– Typical coping response for stress or pain (past
history of psychiatric disorders)
Measurement of Pain
• Complex and difficult to measure
• Pain is an individual and subjective experience
• There are no objective measures for pain
– Hyperalgesia
– Stress response (cortisol levels)
– Behavioral response (facial expressions)
– Functional impairment
– Physiological responses (changes in heart rate)
Numerical Rating Score
Verbal Descriptor Scale
• Best choice in elderly patients including
patients with mild to moderate cognitive
impairment.
• This type of scale uses descriptor terms such
as none, mild, moderate, severe and
excruciating
General Principles of Pain Care
• Many factors can add to the pain
– Situation
– Movement of patient
– Procedures (cannulation, limb splintage, spinal care)
• Patients may be anxious or confused and not
think to ask for pain relief.
• Good analgesia facilitates patient care.
General Principles of Pain Care.
• Appropriate analgesia should be given via an
appropriate route in the shortest time frame
possible.
• Reassessment of pain should occur to
determine the effect of treatment. If pain is
severe this should happen every 5-15 minutes
(severe pain is defined as a pain score greater
than 7). Less severe pain should be reassessed
every 30-60 minutes.
General Principles of Pain Care
• Pain relief has medical benefits
– Reduction in pain related tachycardia
– Improved in lung function
– Reduction in PTSD
• Consider targeted analgesia
• Pain relief should be ongoing to avoid “wind-up” and
increased analgesia requirements
• If aggressive with analgesia, total requirements will be
lower.
General Principles of Pain Care
• Patients with severe injuries may require high
doses of analgesics which may depress their
level of consciousness.
– Cause hypoventilation and hypercarbia
– Necessitate intubation for analgesic control.
Methoxyflurane
• Halogenated ether
• Highly potent and lipid soluble
• Powerful analgesic
• Nephrotoxic and hepatotoxic - dose dependent effect
(anaesthetic dosages)
• Reduce pain sensitivity by altering tissue excitability
Methoxyflurane
• Extensively used in Australia and New Zealand in
the pre-hospital setting
• Inhaler – green whistle
• 3 ml dose – lasts approximately 30 minutes
• Maximum recommended dose is 6 ml per day
due to concerns about dose related
nephrotoxicity
• Pain relief takes effect after 6-8 breaths and
continues for several minutes after
discontinuation of the drug.
Morphine
• Naturally occurring alkaloid derived from opium
• Strongly lipophobic
• Onset time is 5 minutes
• Peak effect is 10 minutes
• Duration of action 1-4 hours
Morphine
• Dosage 0.05-0.1 mg/kg (repeat to effect)
• Moderate sedative effect
• Potent metabolites – analgesia and respiratory
depression
• Unlikely to cause apnea at therapeutic doses.
Morphine
• Gold standard for analgesia in severe pain
• Average dose to control acute severe pain is
0.4 mg/kg
Fentanyl
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•
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Synthetic opioid
Highly lipophilic
Onset time < 1 minute
Peak onset 2-3 minutes
Duration of action 30-45 minutes
Dosage 0.25-0.5 mcg/kg (repeat to effect),
maximum dose of 100 mcg (equivalent to 10
mg Morphine)
Fentanyl
• Causes minimal sedation
• No active metabolites
• High risk of apnea at therapeutic dosages
• High risk of chest wall rigidity syndrome
• Highly emetogenic compared to other opioids
Chest Wall Syndrome
• Muscle rigidity can occur with doses as low as
25 mcg in an adult.
• Often confused with apnea caused by mu-1
receptor agonism.
• Unable to resuscitate or ventilate patient
unless given naloxone or neuromuscular
blocking drug
Fentanyl
• Very efficacious
• Rapid onset of action
• Highly potent
• Probably the least safe of the opioids
available, but still has a very low side effect
profile.
Ketamine
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NMDA antagonist
Rapid acting GA
Profound analgesia
Normal airway reflexes
Increased skeletal muscle tone
Stimulation of cardiovascular and respiratory
system
Ketamine
• Contraindications
– Severe hypertension would result in a hazard
• Adverse Reactions
– Emergence reactions occur in 12% of patients
(lowest incidence in the young and elderly)
– BP and HR are frequently elevated
– Laryngospasm and bronchorrhoea
– Tonic / Clonic movements mimicking seizures
Ketamine
• Sub-dissociative dosage of drug – 0.25 mg/kg,
repeat every 30 minutes
• Some studies recommend lower dosages of 1-2
mg boluses (Make up the drug into 1 mg/ml)
• Paediatric dosage 0-4 mcg/kg/min
• Background infusion of 0.25-0.5 mg/kg/hr if
required.
Ketamine
The use of sub-dissociative doses of ketamine
reduces the dosages needed of opiates
Opiate sparing medication
Ketamine
• S+ ketamine is now becoming available
• Traditional ketamine contains equivalent
amounts of S+ and R- ketamine.
• S+ Ketamine has 4 times the affinity for the
NMDA receptor resulting in greater analgesic
efficacy.
Targeted Analgesia
• Femoral nerve block
– Indicated for injuries to thigh and knee
– Landmarks include the inguinal crease and the
femoral artery
– Can improve accuracy of infiltration with the use
of ultrasound
Targeted Analgesia
• Bupivacaine (Marcaine)
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0.25% or 0.5% strengths
Onset of action is 5 minutes
Duration of action is 2-4 hours
Duration of effect for nerve block is approximately 10
hours
– Maximum dose is 2 mg/kg up to 175 mg/dose (35 mL
0.5%, 70 mL 0.25%)
• For femoral nerve block, the volume of LA is
generally 20 mL or less
Summary
• Analgesia should be given early to patients in
acute severe pain.
• Intravenous analgesia should be aggressive
and titrated to effect
– Results in better analgesia
– Results in reduced dosages of medications
Summary
• Opiates should be the mainstay of analgesia
– Consider the use of titrated fentanyl
• Rapid onset of action
• Quicker time to effective analgesia
• Use ketamine as an opioid sparing agent
• Consider the use of targeted analgesia such as
local anaesthetic nerve blockade
References
• Kanowitz A et al. Safety and effectiveness of fentanyl
administration for prehospital pain management.
Prehospital Emergency Care. 2006; 10(1);1-7
• Galinski M et al. A randomized double-blind study
comparing morphine with fentanyl in prehospital analgesia.
Am J Emerg Med. 2005;23(2);114-119
• Borland et al. Options in prehospital analgesia. Emerg Med.
2002;14(1);77-84
• Prehospital analgesia in NSW, Australia. Prehospital &
Disaster Med. 2011;26(6);422-426