Pre-hospital Analgesia

Wollongong CGDAugust 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– 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

• 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

• 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)– 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