Acute Postop Pain Flashcards
Pain
5th vital sign
Unpleasant sensory & emotional experience associated w/ actual or potential tissue damage
Consistent w/ tissue injury degree
Acute Pain
Short duration <6 weeks Known cause Temporary & located in area trauma or damage Resolves spontaneously w/ healing
Chronic Pain
Persists beyond normal recovery duration from acute injury or disease
Cause not always identifiable
Affects patient self-image & well-being
Neuropathic Pain
Abnormal or unfamiliar pain
CNS or PNS dysfunction - injury or acquired abnormalities
Central pain d/t injury to brain or spinal cord (phantom pain)
Peripheral originates in nerve root, plexus, or nerve
Idiopathic Pain
Pain not attributable to identifiable physical or psychological cause
Perception - excessive pain
Psychogenic Pain
Sustained via psychological factors
Effective & behavioral disturbances
Nociceptive Pain
Appropriate response to identifiable tissue damage
Nociception
Noxious stimuli detection, transduction, & transmission
Transduction
Stimuli translated into electrical energy at the site
Transmission
Impulse propagation via the nervous system
Modulation
Stimuli alteration
Amplified or attenuation
Perception
Based on patient’s psychological framework
Somatic
Superficial arises from skin, subcutaneous tissues, & mucous membranes
- Sharp, pricking, throbbing, or burning
- Well localized
Deep arises from muscles, tendons, joints, or bones
- Dull, aching & less localized
Visceral
Internal organ disease process or abnormal function
Localized or referred
Allodynia
Ordinarily non-noxious stimulus perceived as pain
Analgesia
Absence pain perception
Anesthesia
Absence all sensation
Hyperalgesia
Exaggerated response to noxious stimuli
Neuralgia
Pain in nerve distribution
Paresthesia
Abnormal sensation perceived w/o stimulus
Radiculopathy
Functional abnormality 1+ nerve roots
Class A α
Peripheral afferent nerve fibers Large myelinated fibers Low activation threshold Diameter 1-20μm ALPHA Conduction impulse 60-120m/s Transmits motor & proprioceptive impulses
Class A β
Peripheral afferent nerve fibers Large myelinated fibers Low activation threshold Diameter 1-20μm BETA Conduction impulse 60-120m/s Cutaneous touch & pressure
Class A δ
Peripheral afferent nerve fibers Large myelinated fibers Low activation threshold Diameter 1-20μm DELTA Conduction impulse 5-25m/s Mediates pain sensation - Transmits fast or first pain - Sharp, stinging, pricking Glutamate binds to NMDA receptors
Class A γ
Peripheral afferent nerve fibers Large myelinated fibers Low activation threshold Diameter 1-20μm GAMMA Conduction impulse 5-25m/s Cutaneous touch & pressure
Class B
Peripheral afferent nerve fibers
Medium-sized myelinated fibers
Higher threshold (lower excitability) than Class A & lower threshold than Class C fibers
Diameter <3μm
Conduction speed 3-14m/s
Post-ganglionic sympathetic & visceral afferents
Class C
Peripheral afferent nerve fibers Un-myelinated or thin myelination Diameter 0.4-1.2μm Conduction speed 0.5-2m/s Pre-ganglionic autonomic & pain fibers - Transmits slow or second pain - Burning, persistent, aching, throbbing pain Substance P binds to NK-1 receptors
Pain Modulation
Descending dorsolateral spinal tract
Supraspinal Analgesia
Mu-1 receptors
Limbic system, hypothalamus, & thalamus
IV opioids
Spinal Analgesia
Mu-2 receptors
Periventricular/periaqueductal grey
IV & neuraxial opioids
Surgical Stress Response
CV ↑HR/CO ↑BP ↑SVR (angiotensin II) ↑MVO2
Resp ↑O2 consumption ↑CO2 production ↑minute ventilation ↑WOB ↓chest expansion d/t pain → atelectasis, intra-pulmonary shunting, hypoxemia, & hypoventilation
Endocrine ↑glucagon ↓insulin ↑epinephrine → vasoconstriction ↑myocardial contractility ↑cortisol & catecholamines → RAAS activation (Na+ & H2O retention)
GI ↑sphincter tone ↓VSMC tone → ileus or PONV
↑gastric acid production → stress ulcers
Immune - leukocytosis w/ lymphopenia ↓RAS → infection risk
Heme ↑platelet adhesiveness ↓fibrinolysis → hypercoagulable state
Opioid-Induced Hyperalgesia
Diminished pain threshold & enhanced pain sensitivity
Multi-Modal Approach
NSAIDs Ketamine Methadone Anticonvulsants Dexmedetomidine Clonidine Magnesium Glucocorticoids Local anesthetics Regional anesthesia
NSAIDs
Effective to treat mild to moderate pain
Adverse effects include GI bleeding, acute renal failure, & hepatotoxicity
Caution in elderly patients d/t ↑risk renal impairment
Ketamine
NMDA antagonist
Bolus 0.5mg/kg
Infusion 4mcg/kg/min
Methadone
D-isomer NMDA antagonist
0.2mg/kg
Anticonvulsants
Pregabalin & Gabapentin
Manage spontaneously firing sensory neurons associated w/ neuropathic pain
- Attenuate neuronal sensitization response
α2 Agonists
Dexmedetomidine
Clonidine
RISK BRADYCARDIA & HYPOTENSION
Acetaminophen
15mg/kg
Glucocorticoids
Anti-inflammatory + PONV
Regional Anesthesia
Peripheral nerve blocks - Lumbar plexus - Interscalene Central neuraxial blocks - Spinal - Epidural
Neuraxial Opioid Side Effects
Itching (most common) Nausea Urinary retention Respiratory depression (early & late) Sedation CNS excitation Neonatal morbidity
