Analgesia

Question 1

Pain Pathway

1: Transduction

Answer 1

• Beginning of the pain pathway, the exposure to a noxious stimulus is transformed by nociceptors (pain receptors) into an electrical signal (action potential)

Question 2

Pain Pathway

2: Transmission

Answer 2

• Once action potential is generated, the peripheral nerve fibres conduct the electrical impulses to the spinal cord

Question 3

Pain Pathway

3: Modulation

Answer 3

• Arriving at the spinal cord where the peripheral nerves terminate, the electrical impulse is further altered by neutrons which may amplify or suppress the signal

Question 4

Pain Pathway

4: Perception

Answer 4

• Once modified the electrical impluse is transmitted to the brain to be processed and recognised as pain

Question 5

Receptors and Drugs

Answer 5

• Different receptors are involved with each stage of the pain pathway, therefore different analgesics can target certain receptors

Question 6

Physiological Pain

Answer 6

• Sensation of pain when there is the possibility of, or actual tissue injury
• Classified as adaptive pain as it promotes survival through injury prevention and promotion of healing to injured tissue

Question 7

Pathological Pain

Answer 7

• Triggered by a malfunction or damage to the nervous system
• Typically develops from a noxious stimulus that activates peripheral neural receptors, however the pain extends beyond the actual duration of the stimulus
• Can be difficult to treat as it’s maladaptive pain (serves no protective function to the patient and causes further suffering)

Question 8

Inflammatory Pain

Answer 8

• When inflammatory mediators (prostaglandins and histamine) are released at the site of tissue injury, this is the type of pain that ensues
• Develops due to the alteration of the chemical environment around nociceptors, causing changes to their sensitivity and action potential threshold
• This pain usually resolves with healing of the injury as the inflammation and the presence of chemical mediators resides

Question 9

Neuropathic Pain

Answer 9

• Experiences when there is damage to the nervous system itself (i.e nerve damage)
• Injury to nerves results in multiple changes that can contribute to chronic neuropathic pain and hypersensitivity and allodynia (a normally non-painful stimuli feeling painful)

Question 10

Idiopathic Pain

Answer 10

• Pain where there is no identifiable cause

- Should be treated as real and significant

Question 11

Acute Pain

Answer 11

• Onset immediately after tissue injury and dissipates at the resolution of injury

Question 12

Chronic Pain

Answer 12

• Much longer in duration

- Can be difficult to treat as can persist during/after healing

Question 13

Physiological Signs of Pain

Answer 13

• Increased HR, RR, BP and temp
• Salivation
• Dilated pupils
• Peripheral vasoconstriction (Pale MM)
• Changes to respiratory effort and pattern

Question 14

Behavioural Signs of Pain

Answer 14

• Abnormal posture or gait
• Restlessness/agitation
• Vocalisation
• Depression
• Inappetence
• Aggression or timidity (changes in normal behaviour)
• Resentment of handling
• Grooming changes
• Reluctance to lie down/sleep

Question 15

Types of Analgesia: Opioids

Answer 15

• Block or depress pain signals
• Decrease the release of excitatory neurotransmitters as well as acting at the post-synaptic sites
• Analgesic of choice for moderate to severe pain

Question 16

Types of Analgesia: NSAIDs

Answer 16

• Best suited for inflammatory pain as they provide analgesia by decreasing production of inflammatory mediators at the site of tissue injury
• For mild pain

Question 17

Types of Analgesia: Ketamine

Answer 17

• Antagonism of NMDA receptors in the CNS or prevents sensitisation
• Not appropriate when used solely, works best with other analgesics
• For mild pain

Question 18

Types of Analgesia: Alpha-2-Adrenergic Agonists (Medetomidine, Xylazine)

Answer 18

• Mostly used with micro doses for sedation, can be reversed
• Activate both central and peripheral alpha-2 receptors and decrease the release of neurotransmitters
• Negatively affect cardiovascular system
• Mild visceral pain

Question 19

Multimodal Pain Relief

Answer 19

• Using multiple analgesic products in combination to provide a more thorough analgesia
• Allows the dose of each individual drug to be decreased and in doing so, the undesirable effects of each drug (compared to if being given in a large dose)
• Targets multiple locations in pain pathway

Question 20

Analgesic Considerations

Answer 20

• How much pain is the patient experiencing?
• What level of potency do we require?
• Is the patient painful now or will it be soon?
• Is the patient healthy or compromised?
• Will the pain change (improve/worsen)?