Central Nervous System Pain Management PDF

Analgesic Drugs - Medications that relieve pain without causing loss of consciousness - “Pain Killers” - Opioids - Adjuvants - i.e. NSAIDs, Antidepressants, Anticonvulsants, Corticosteroids, etc. — example: adjuvant drugs for neuropathic pain ——- Amitriptyline (antidepressant) ——-Gabapentin or preg...

Analgesic Drugs - Medications that relieve pain without causing loss of consciousness - “Pain Killers” - Opioids - Adjuvants - i.e. NSAIDs, Antidepressants, Anticonvulsants, Corticosteroids, etc. — example: adjuvant drugs for neuropathic pain ——- Amitriptyline (antidepressant) ——-Gabapentin or pregabalin (anticonvulsants) Classification of Pain Vascular: Vascular or perivascular tissues. Thought to account for vast majority of migraine headaches Referred: Visceral nerve fibres synapse at the spinal cord close to fibres from tissues in the body Neuropathic: Damage to nerve fibres Phantom: Occurs in body part that has been removed Cancer: Caused from pressure of tumours against nerves, organs, or tissues Central: Tumours, trauma, inflammation or disease affecting CNS tissues Onset and Duration of Pain Acute: Sudden, usually subsides once treated or less then 3 months Persistent/Chronic: Persistent or recurring, lasts 3-6 months or longer, often difficult to treat • Acute examples: • Persistent/Chronic examples: Gate Theory Pain transmission Gate theory 1. Transduction • The transformation of stimuli into electrochemical energy • Nociceptors detect depth/impact of harmful stimulus. Release of pain-medicating chemicals 2. Transmission • Pain impulses move along pain fibres to activate pain receptors up the spinal cord to brain • If no impulses are transmitted to higher centre’s in the brain, there is no pain perception 3. Perception • Subjective phenomenon of pain ; “How it is felt” • Complex behavioural psychological, and emotional factors 4. Modulation • Neural activity that controls pain transmission to neurons, both in CNS and PNS • descending nerve fibres release endogenous neurotransmitters to fight pain Pain Interpreted Pain threshold: • Level of stimulus needed to produce the perception of pain • Measure. Of the physiological response of the nervous system Pain Tolerance Amount of Pain a patient can endure without its interfering with normal function • Varies with each individual • Subjective response • Point beyond which pain becomes unbearable Treatment of Pain in special Situations • Patient-controlled analgesia (PCA) • Patient comfort versus fear of drug addiction • Opioid tolerance • Use of placebos • Recognizing patients who are opioid tolerant • Breakthrough Pain • Synergistic effects Mechanism of action: Opioid Analgesics • Opioid analgesics act by depressing pain impulse transmission at the spinal cord level by interacting with opioid receptors • Three classifications based on their ‘actions’ 1. Agonist = binds to a pain receptor in brain & produces analgesia (a reduction of pain sensation) • mild agonist - i.e. codeine, hydrocodone (more commonly used as an antitussive) • Strong agonist - i.e. morphine, hydromorphone, fentanyl, methadone ———Hydromorphone: very potent opioid analgesic ————- 1mg of IV or IM = 7mg of morphine 2. Agonist-Antagonist = binds to receptor causing a weaker pain response that full agonist • also called partial agonists or mixed agonists • i.e. Suboxone - buprenorphine with naloxone to enhance antagonist effect 3. Antagonist = non-analgesics that bind to pain receptors but do not reduce pain signals • Reverses the effects of these drugs on pain receptors • Also known as competitive antagonists • I.e. Naloxone Equianalgesia • Ability to provide equivalent pain relief by calculating dosages of different drugs or routes of administration that provide comparable analgesia Examples: morphine, hydromorphone, oxycodone, hydrocodone, bitartrate, fentanyl • continuous release vs. Immediate release formulations Opioid Analgesics: Indications • Mainly used to alleviate moderate to severe pain • Often first line analgesic in immediate post operative setting • Often given with analgesic drugs to assist primary drugs with pain relief Opioids are also used for: • cough centre suppression - codeine • Treatment of diarrhea Contraindications • Known drug allergy ——Often patient had side effect not true allergy (e.g. nausea) • Severe asthma • Use with extreme caution in patients with the following: — Respiratory insufficiency — Elevated intracranial pressure —Morbid obesity or sleep apnea — Paralytic ileus — Pregnancy Adverse effects • GI symptoms (most common) — Nausea, vomiting, constipation, and cramps • CNS depression — Leads to respiratory depression = Most serious adverse effect — Sedation • • • • Urinary retention Hypotension Itching, rash Pinpoint pupils indicating a possible overdose Opiate Tolerance • Common physiological result of chronic opioid treatment • State of adaptation • Once tolerance occurs, larger dose of opioids is required to maintain same level of analgesia Dependence to opiates Physical • Adaption of the body to the presence of an opioid • This is expected with long-term opioid treatment Psychological • A pattern of compulsive drug use characterized by a continued craving for an opioid and the need to use the opioid for effect other than pain relief Opioid Ceiling Effect • Drug reaches a maximum analgesic effect • Analgesia does not improve, even with higher doses *Tolerance and physical dependence should not be confused with psychological dependence (addiction) Addiction: A pattern of compulsive drug use characterized by a continued craving for an opioid and the need to use the opioid for effects other than pain relief. Assess for • #1 Respiratory dysfunction - resp depr