Nagelhout Ch 56 Acute Pain: Physiology & Management

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Questions and Answers

Which type of neurons receives input from Aδ, C, and Aβ fibers?

Second-order neurons

Wide-dynamic-range (WDR) neurons (correct)

Primary afferent neurons

Nociceptive neurons

Where do the second-order neurons synapse with third-order neurons?

Lateral thalamus and intralaminar nuclei (correct)

Substantia gelatinosa

Anterior commissure

Rexed laminae I, II, and V

What is the primary function of the tract of Lissauer?

To ascend pain signals to the thalamus

To segregate and ascending/descending pain signals (correct)

To transmit pain signals from the trunk and lower extremities

To synapse with second-order neurons

What happens to substance P release when enkephalin binds to opiate receptors?

It decreases Signup and view all the answers

Which structure is involved in the descending efferent pathway that suppresses pain transmission?

All of the above Signup and view all the answers

What is the consequence of poorly controlled acute pain?

Chronic pain states Signup and view all the answers

Where are the cell bodies of primary afferent neurons located?

Dorsal root ganglia of the spinal cord Signup and view all the answers

What is necessary for the perception of pain?

Recognition by various areas of the brain Signup and view all the answers

What is the classification of pain based on?

Both longevity and underlying pathophysiology Signup and view all the answers

Which type of pain is associated with stimulation of specific nociceptors?

Nociceptive pain Signup and view all the answers

What is the characteristic of somatic pain?

Well localized, sharp, and hurts at point of stimulus Signup and view all the answers

What is the characteristic of visceral pain?

Diffuse, dull, and cramping Signup and view all the answers

What is the result of sensitization of nociceptive pathway from mx mediators released at site of tissue inflammation?

Inflammatory pain Signup and view all the answers

What is the process of transformation of noxious stimuli into an action potential?

Transduction Signup and view all the answers

What type of pain is caused by damage to peripheral or central neural structures?

Neuropathic pain Signup and view all the answers

What type of nociceptors elicit fast-sharp pain?

Myelinated Aδ fibers Signup and view all the answers

Which of the following neurotransmitters is released from peripheral afferent nociceptor C fibers and involved in slow, chronic pain?

Substance P Signup and view all the answers

What is the primary effect of bradykinin on peripheral nociceptors?

Direct stimulation Signup and view all the answers

Which of the following chemical mediators is released from mast cells, basophils, and platelets via substance P?

Histamine Signup and view all the answers

What is the primary effect of prostaglandins on peripheral nociceptors?

Sensitization Signup and view all the answers

Which of the following chemical mediators is released from platelets after tissue injury?

Serotonin Signup and view all the answers

What is the primary effect of calcitonin gene-related peptide (CGRP) on peripheral nociceptors?

Local cutaneous vasodilation Signup and view all the answers

What is the primary effect of cytokines on prostaglandin production?

Increase Signup and view all the answers

What is the sequence of events that occurs when chemical mediators and neurotransmitters stimulate peripheral nociceptors?

Na influx, K efflux, AP Signup and view all the answers

What is a contraindication for the use of SNRIs?

History of recent MI Signup and view all the answers

What is the primary use of SSRIs?

Treatment of depression Signup and view all the answers

What is a characteristic of serotonin syndrome?

Hyperthermia and hyperreflexia Signup and view all the answers

What is the mechanism of action of corticosteroids in pain management?

Inhibition of PLA2 on cell membranes Signup and view all the answers

What is a potential side effect of corticosteroids?

Suppression of the hypothalamic-pituitary-adrenal axis Signup and view all the answers

What is the mechanism of action of methadone's D-isomer?

Antagonism of NMDA receptors Signup and view all the answers

What is a characteristic of methadone?

High lipophilicity and long half-life Signup and view all the answers

What is a potential benefit of methadone in chronic pain management?

Useful for chronic nonmalignant pain management Signup and view all the answers

Why may opioids need to be increased by 30-100% in intraoperative anesthesia?

Because of receptor downregulation and/or tolerance Signup and view all the answers

What is a useful indicator for estimating adequate analgesia with general anesthesia?

Pupil size and heart rate response Signup and view all the answers

What is a recommendation for postoperative pain management in elderly patients?

Use regional anesthesia with local anesthetics and opioids whenever possible Signup and view all the answers

What is a characteristic of pain processing in aging adults?

Decreased neurotransmitters in the CNS Signup and view all the answers

What is a consequence of repeated exposure to untreated painful stimuli in premature and full-term infants?

Central sensitization and increased free radicals Signup and view all the answers

What is the primary reason for using opioid analgesics as first-line therapy in elderly patients?

To provide effective pain relief at the lowest dose possible Signup and view all the answers

What is a characteristic of pain perception in pediatric patients?

Exaggerated pain perception and stress response Signup and view all the answers

What is a consideration for postoperative pain management in elderly patients?

Increased risk of adverse effects due to polypharmacy Signup and view all the answers

Study Notes

Pain Classification and Physiology

Pain can be classified based on longevity (acute vs. chronic) and underlying pathophysiology (nociceptive or non-nociceptive)
Nociceptive pain is associated with stimulation of specific nociceptors and can be either somatic or visceral
Somatic pain has an identifiable locus and is well localized, sharp, and hurts at the point/area of stimulus
Visceral pain is often associated with distension of organ capsules or obstruction of hollow viscus, and is diffuse, dull, cramping, squeezing, or vague in nature
Non-nociceptive pain is caused by damage to peripheral or central neural structures, resulting in abnormal processing of painful stimuli
Inflammatory pain results from sensitization of the nociceptive pathway from mediators released at the site of tissue inflammation without neural injury

Somatic Nociceptive Pain Pathway

Transduction: transformation of noxious stimuli into an action potential
Peripheral nociceptors are categorized according to morphology:
- Myelinated Aδ elicit fast-sharp pain
- Nonmyelinated C fibers elicit slow-dull, burning, throbbing, and aching pain
Biochemical events take place, including:
- Release of chemical mediators from inflammatory response and neurotransmitters from nociceptive nerve endings
- Substance P release from peripheral afferent nociceptor C fibers, involved in slow, chronic pain
- Glutamate release from Aδ and C primary afferent fibers, causing initial, fast, sharp pain
- Bradykinin release during inflammatory process, directly stimulating peripheral nociceptors
- Histamine release from mast cells, basophils, and platelets, acting on various histamine receptors
- Serotonin release from platelets, acting on multiple receptors and nociceptors
- Prostaglandins synthesized from COX-1 and COX-2, sensitizing peripheral nociceptors
- Cytokines released in response to tissue injury, leading to increased PG production
- Calcitonin gene-related peptide release from peripheral afferent nociceptor C fibers, producing local cutaneous vasodilation and plasma extravasation

Transmission and Modulation

Transmission: action potential conducted from periphery to CNS
Primary afferent neurons Aδ and C fibers cell bodies located in dorsal root ganglia of spinal cord
2 types of 2nd-order neurons:
- Nociceptive neurons receive input from Aδ and C fibers
- Wide-dynamic-range (WDR) neurons receive input from Aδ, C, and Aβ fibers
Modulation: involves altering neural afferent activity along the pain pathway
Suppression occurs through local inhibitory interneurons and descending efferent pathways
Descending axons from cerebral cortex, hypothalamus, thalamus, periaqueductal gray area, nucleus raphe magnus, and locus coeruleus synapse with and suppress pain transmission to brainstem and spinal cord dorsal horn

Perception

Occurs once the signal is recognized by various areas of the brain, including amygdala, somatosensory areas of cortex, hypothalamus, and anterior cingulate cortex

Physiologic Consequences

Acute pain is responsive to pharmacotherapy and treatment of the precipitating cause
Poorly controlled acute pain may lead to chronic pain states
Contraindications for certain medications, such as recent MI, prolonged QTi, cardiac dysrhythmias, and unstable CHF

Pharmacological Management

SNRIs (duloxetine, venlafaxine) lack affinity for cholinergic, histaminergic, and adrenergic receptors
SSRIs primarily used for treatment of depression, with relatively weak analgesic effects
Corticosteroids used as adjuncts for management of acute onset and chronic pain syndromes
Methadone: a synthetic opioid with a racemic mixture of two enantiomers, D-isomer (S-methadone) and L-isomer (R-methadone)
Intraoperative management: opioids may need to be increased by 30-100% compared to opioid-naïve patients
Postoperative management: consider IV PCA if unable to do RA/CPNB

Special Populations

Elderly: alterations in pain processing and perception, with decreased nociceptive processing and neurotransmitters in CNS
Pediatric: nociceptive pathways are well developed in premature and full-term infants, but maturation of descending pathway precedes ascending neural pathway

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Description

This quiz covers the classification, physiology, and management of acute pain, including nociceptive and non-nociceptive pain, somatic and visceral pain, and the underlying pathophysiology. Learn about the characteristics of acute pain and its differences from chronic pain.