CHAPTER 9 Pain Management
I. PAIN OVERVIEW
Despite research that has increased the understanding of pain management and broadened knowledge of effective methods to assess and manage pain, health professionals have not adequately used this knowledge to improve the care of patients experiencing pain.1,2 Multiple studies have shown that the undertreatment of pain often occurs in emergency department settings.3–5
II. DEFINITIONS
These definitions originate from the Agency for Healthcare Policy and Research and the International Association for the Study of Pain.6,7
III. PAIN PHYSIOLOGY
A. Neuroanatomy
4) Transmit impulses to the midbrain via the neospinothalamic tract (acute pain) and to the limbic system via the paleospinothalamic tract (dull and burning pain)
2. Central nervous system (CNS)
b. Arousal, discrimination and localization of pain; coping response; release of corticosteroids; cardiovascular responses; modulation of spinal pain transmission
a. Fibers connecting the reticular formation, midbrain, and substantia gelatinosa in the dorsal horn of the spinal cord
b. Afferent fibers stimulate the periaqueductal gray mater in the midbrain, which then stimulates the efferent pathway
5) Opiate receptors: mu (μ) receptors on the membrane of afferent neurons, inhibit the release of excitatory neurotransmitters; beta (β) receptors react with enkephalins to modulate pain transmission; kappa (κ) receptors produce sedation and some analgesia; sigma (σ) receptors cause pupil dilation and dysphoria
B. Effect of Medications on Modulating Pain9,10
1. Stimulation of afferent pathways results in activation of circuits in supraspinal and spinal cord levels. Each synaptic link is subject to modulation
b. Nonsteroidal anti-inflammatory drugs (NSAIDs): inhibit prostaglandin synthesis, which reduces hyperalgesia
c. Opiates: interact with mu and kappa receptors; powerful effect on the brainstem and the periphery
C. Pain Theories
a. A specific sensation that is independent of other sensations. Experiments on animals provided clinical evidence of separate spots for heat, cold, and touch
1) The pain impulse is transmitted via nociceptor fibers in the periphery to the substantia gelatinosa through large A-delta and small C fibers
2) At the terminus of the nociceptive fibers, neurotransmitters such as substance P, adenosine triphosphate, and glutamate carry the impulse across the synapse to the dorsal horn
3) A gating mechanism regulates transmission from the spinal cord to the brain, where pain is perceived
4) Stimulation of large fibers closes the gate and thus decreases transmission of impulses unless persistent
3) Descending fibers release endogenous opioids that bind to opioid receptor sites and thereby prevent release of neurotransmitters such as substance P, thus inhibiting transmission of pain impulses and producing analgesia
a. A widespread network of neurons consists of loops between the thalamus and cortex and between the cortex and limbic systems; neural processes are modulated by stimuli from the body but can also act in the absence of stimuli
2) Cyclic processing of impulses produces a characteristic pattern in the entire matrix that leaves a neurosignature
3) Signature patterns are converted to awareness of the experience and activation of spinal cord neurons to produce muscle patterns for action
b. Neural inputs modulate the continuous output of the neuromatrix to produce a wide variety of experiences felt by the individual
1) Awareness of the experience involves multiple dimensions (e.g., sensory, affective, and evaluative) simultaneously
D. Types of Pain7,11
b. Generally associated with trauma, acute illness, surgery, burns, or other conditions that are of limited duration; generally relieved when healing takes place (Table 9-1)
b. May be perpetuated by factors remote from the original cause and extend beyond the expected healing time; generally lasts longer than 3 months (seeTable 9-1)
a. Elicited by noxious stimuli that damages tissues or has the potential to do so if the stimuli are prolonged
1) Somatic pain: arises from skin, muscle, joint, connective tissue, or bone; generally well localized and described as aching or throbbing
2) Visceral pain: arises from internal organs such as the bladder or intestine; poorly localized and described as cramping
