11. Pain management Flashcards
Algogenic (pain producing) substances
- K+ from damaged cells
- Serotonin from active platelets
- Histamine from mast cells
- Badikinin from tissue kallikrein
Sensitizing agents in pain
- PGs, LTs from damaged cells
- Primary polymodal afferents: Substance P, Calcitonin Gene Related Peptide (CGRP)
Unimodal receptors
Mechanical
Bimodal receptors
Mechanical + thermal (> 45 degrees)
Polymodal receptors
Mechanical + thermal + chemical
Pain receptor fibres
1) Fiber Aδ - fast, sharp pain, easy to localize
2) Fiber C - slow, blunt/burning pain, harder to localize
CNS components of pain
Spinothalamic - spinoreticular - spinomesencephalic tracts
- Complex association between many brain regions*
- Somatosensory cortex (feeling, localization)
- Hypothalamus (vegetative, humoral)
- Limbic (mood, behaviour)
- Frontal cortex (socialization)
- Amygdala (cognitive reactions)
- Hippocampus (pain memory)
- Ant. Cingular cortex (emotional)
Gate-control theory of pain
Ascending inhibitory pathways of brain and ascending Abeta fibers can inhibit spread of incoming pain in SUbstantia Gelatinosa
Opioid and NMDA antagonists action
Inhibit inhibitory GABAerg cells which inhibit descending pathways (noradrenaline, serotonin)
Inhibition of inhibition reduces pain sensation
Endogenous opioids
Released by stimulation of periaqueductal grey stock (serotonin, noradrenaline)
Pain classifications
1) By duration
2) By etiology
3) By associated social/cognitive effects
Pain duration
Acute (< 6 weeks/3 months)
- No cognitive-emotional, socializing effects!
Chronic
- Often psychosomatic etc
Nociceptive pain
Released mediators activate pain receptors
- Somatic
- Visceral
Neuralgia
Direct irritation of nerves by mechanic or metabolic disturbance
Deafferentation pain
Hyperexcitability of spinal nerves after sensory deafferentation
Special pain syndrome
Migraine
Psychosomatic pain
Somatic symptoms caused by psychological stress
Afferentation of visceral pain
- Thoracic / abdominal => sympathetic nerves
- Pelvic viscera => parasympathetic nerves
- Esophagus, trachea, pharynx => vagus + glossoph. nn
Visceral pain
- Difficult to localize (C fiber)
- Radiating pain
- Accompanied by nausea and vegetative signs
- Can be large pain
- Reflex contraction of surrounding muscles
Etiology of abdominal pain + quadrants
Se internal
Pain radiation visceral pain
CNS cannot distinguish between somatic and visceral stimuli, so visceral pain radiates to skin (head zones)
- Dermatoma rule - to same emrbyonic dermatome
Radiation GERD
To the back
DDx chest pain that I don’t think of
- Pleuritis sicca
- Boerhaave SY
- Tietze SY
- Herpes zoster
IPAT, BPI, McGill questionaire
Pain scales:
- Initial pain assessment tool
- Brief pain inventory
- McGill questionaire
Pain assessment in ICU
- Behvioural pain scale (BPS) - face, upper limb, ventilation compliance
- Critical-care observation tool (CPOT) - face, body, muscle tension, ventilation compliance
- The most valid pain assessment tools*
WHO guidelines for cancer pain
- Mild pain: NOA (non-opoid analgetics)
- Moderate: Low-potential opioids
- Strong: High potential opioids
Pain management in ICU
- Routinely performed
- BPS and CPOT pain assessment
- Opioids as first line therapy
- Gabapentine or carbamazepine in addition - for neuropathic pain
- Thoracic epidural anesthesia in rib fractures
Effects of NOA drugs
COX-1
- Kidney function, gastric mucosa
- ASA, Indomethacine, Piroxicam
COX-2
- Inflammatory augmentation, fever
Current first-line NOA drugs
- Ibuprophen, naproxen?
- Acetaminophen (paracetamol)
- Litterature: diclophenac (MOA)
NOA drugs with the best analgetic potential
High - low:
1) ASA, oxicam, acetic acid derivatives
2) Ibuprophen ++
3) Paracetamol
Most immportant SEs of mainetance of opoids
- Obstipation
- Sedation
- Xerostomia
- Pruritus
Cannabinoid effects and indications
Effects: antiemetic, analgesic, appetite up, anti-tumorgenetic
Indications: Tumor, AIDS, Multiple Sclerosis
Peripheral nerve block types + some advantages/disadvantages
Brachial plexus blockade and Femoral blockade
Advantages
- Less cardiovascular effect
- Enhanced bowel motility
- No sedation
Disadvantages
- Needs post-op observation
- Needs intra-op supervision
Neuroaxial blocks types + some advantages and disadvantages
SPA (spinal) and EDA (epidural)
Advantages
- Pain stimulus does not enter CNS - no sympathetic stimulation
Disadvantages
- Parasympathetic tone enhancement
- Circulatory and respiratory effects
- Delayed mobilization
Types of blockade in EDA
- Sensory
- Motoric
- Vegetative
Indications os EDA
- Efficient anesthesia per se (abdominal, special ind: COPD)
- Combined anesthesia
- Obstetric anesthesia
- Permanent anesthesia (acute pancreatitis, cancer?)
Absolute CI of EDA
- Hemophilias and/or coagulation disturbances
- Inflammation/wound on skin
Relative CI of EDA
- Hypovolemia/shock
- Severe cardiovascular disease
- Lack of informed consent
EDA techniques
1) LOR: Loss of resistance technique
- CI: Narrow dura-myelon distance
2) Hanging Drop (hypobaric pressure of epidural space)
- Indication: Narrow epidural space
Complications of EDA
- Dural punction and Headache (lying position)
- Dural punction and myelon punction
- Epidural hematome
- CNS infection
- Cannule disruption
- Intrathecal drug misadministration
Where to put SPA in adults?
Under L2
Effects SPA
- Sensory
- Motoric
- Vegetative (hypotension, urinary stop)
Solution used in SPA
2-4 ml (hyperbaric) bupivacaine 0,5 % solution
Complications SPA
- Headache (posture irrelevant)
- Infection (sterility)
- Backache
- Epidural hematome (hemophilias, anticoag, TAG)
Local anesthetics
- Weak bases (pH 8-9)
- Less effective in inflammatory environment! (pH decreases)
LA - esters
- Cocaine
- Benzocaine
- Procaine
- Chlorprocaine
- Tetracaine
LA - Amides
- Lidocaine
- Mepivacaine
- Bupivacaine
- Ropivacaine
- Articaine
Cocaine effects
- Less psychostimulating than amphetamine
- Sympathetic effects (vasoconstr, HT, tachyc, mydriasis)
- Lethal dose per os 1 g, subcut 0,2-0,4 g
Benzocaine
Powder and ointment for painful wounds
Procaine
Infiltration anesthesia
- Rapid elimination in liver and by serum esterase
Chlorprocaine
Infiltration and regional anesthesia
Twice as effective and less toxic than procaine
Tetracaine
Topical anesthesia
Ten times more effective, but also more toxic than procaine
Accumulates easily in brain (lipid-soluble)
Lidocaine
Topical anesthesia
Sudden onset and prolonged effect (Dur: 1,5-2 hours)
Hypersensitivity common
Single max dose ca. 500 mg
Mepivacaine
Faster and last longer than lidocaine
Bupivacaine
Very effective, but some cardiotoxic - cannot be used i.v!
Ropivacaine (S-isomer)
Dissociative anesthesia
Articaine
Short-acting, fast metabolism
Used in dentistry
Used in many ways (iv, spinal, epidural, ocular etc)
