Regional Anesthesia Pain Management PDF

. Regional Anesthesia and pain management Yeneneh Negesse (BSc, MSc in anesthesia and critical care) Department of anesthesia and critical care, CMHS, Injibara University Ethiopia, 2...

. Regional Anesthesia and pain management Yeneneh Negesse (BSc, MSc in anesthesia and critical care) Department of anesthesia and critical care, CMHS, Injibara University Ethiopia, 2023 1 Pain and Pain pathways Pain IASP introduced a revised definition of pain. ‘’An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Pain is thus possible even without evidence of tissue damage. Also noted by this task force was that individuals through their life experiences learn the concept of pain and that the personal experience of pain is influenced to varying degrees by biologic and psychological factors Additional six key Notes and the etymology of the word pain for further valuable context: Con’t Pain is always a personal experience that is influenced to varying degrees by biological, psychological, and social factors. Pain and nociception are different phenomena. Pain cannot be inferred solely from activity in sensory neurons. Through their life experiences, individuals learn the concept of pain. A person’s report of an experience as pain should be respected. Con’t Verbal description is only one of several behaviors to express pain; inability to communicate does not negate the possibility that a human or a nonhuman animal experiences pain. Although pain usually serves an adaptive role, it may have adverse effects on function and social and psychological well- being. The statement that "pain cannot be inferred solely from activity in sensory neurons" emphasizes the complexity of pain perception, which involves more than just the activation of nociceptive sensory neurons.  Con’t Key Points Nociception vs. Pain: Nociception refers to the neurological processes that detect and transmit signals of potentially harmful stimuli to the central nervous system (CNS). However, pain is a subjective experience that may not always correlate directly with nociceptive activity. For instance, nociceptive signals can be present without the individual experiencing pain, and vice versa. Complex Processing: Pain perception involves multiple brain regions and processes, including emotional and cognitive components.  Con’t The brain integrates sensory information with past experiences, expectations, and contextual factors, which influence the perception of pain. This means that pain is not merely a sensory experience but also an emotional and psychological one. Cortical Involvement: The perception of pain is linked to various brain areas, including the somatosensory cortex, limbic system, and other regions involved in emotional processing. These areas contribute to the subjective experience of pain, highlighting that pain is a complex interplay of sensory inputs and higher cognitive functions. Con’t Subjective Experience: Pain is inherently subjective, and its perception can vary significantly among individuals based on psychological, cultural, and personal factors. This subjectivity means that even if nociceptive pathways are activated, the experience of pain can differ widely among individuals, making it impossible to infer pain solely from sensory neuron activity. In summary, while sensory neurons play a crucial role in detecting harmful stimuli, the experience of pain is a multifaceted phenomenon that requires consideration of emotional, cognitive, and contextual factors beyond mere neuronal activity. Pain pathways Understanding the anatomical pathways and key neurochemical mediators involved in noxious transmission and pain perception is fundamental to optimizing the management of patients with acute and chronic pain. Pain is conducted along three neuronal pathways that transmit noxious stimuli from the periphery to the cerebral cortex. (list of these pathways – somewhere in this ppt) Nociception Nociception refers to the physiological process by which the sensory nervous system detects and encodes noxious stimuli, which can cause harm or injury to tissues. This process involves specialized sensory receptors known as nociceptors, which respond to potentially damaging stimuli across three primary modalities: mechanical (e.g., cutting or crushing), thermal (e.g., extreme heat or cold), and chemical (e.g.,  Mechanism of Nociception When nociceptors are activated by intense stimuli, they generate electrical signals that travel along nerve fibers to the spinal cord and then to the brain. Types of Nociceptors Nociceptors can be classified based on their response to different types of stimuli: Thermal nociceptors: Respond to extreme temperatures. Mechanical nociceptors: Activated by intense mechanical pressure or deformation. Chemical nociceptors: Sensitive to harmful chemical agents. Con’t Some nociceptors are polymodal, meaning they can respond to multiple types of noxious stimuli. This adaptability is crucial for the organism's survival, as it allows for a broad range of protective responses. Clinical Significance Nociception plays a vital role in the experience of pain, particularly nociceptive pain, which arises from actual or potential damage to non-neural tissues. Understanding nociception is essential for managing pain effectively, particularly in clinical settings where Con’t It is important to differentiate nociception from pain perception, as nociception can occur without the conscious experience of pain, and vice versa. In summary, nociception is a critical biological process that enables organisms to detect and respond to harmful stimuli, thereby protecting them from injury and promoting survival. Nociception…con’t The conduction of pain does not simply involve conduction of impulses from the periphery to the cortical centers in the brain. Transmission of pain or nociception is a complex phenomenon and involves multiple stages that can be grouped broadly into three processes: (1) activation of specialized peripheral nerve endings; (2) conduction of noxious impulses to the spinal cord; and (3) transmission of impulses from the spinal cord to the supra-spinal and cortical centers.  CON’T The culmination of these processes results in the localization and perception of pain. At each of these stages, nociceptive impulses can be suppressed by local interneurons or by descending inhibitory fibers and modulated by a variety of neurotransmitters and neuromodulators. Any abnormality of peripheral and central pain pathways including pathological activation, or the imbalance of activation and inhibitory pathways, may increase the severity of acute pain and contribute to the development of persistent pain. Pain pathways The nociceptive pathway is an afferent three-neuron dual ascending system, with descending modulation from the cortex, thalamus, and brainstem. Nociceptors are free nerve endings located in skin,muscle, bone, and connective tissue with cell bodies located in the dorsal root ganglia. con’t The first-order neurons that make up the dual ascending system have their origins in the periphery as A-δ and polymodal C fibers. A-δ fibers transmit “first pain,” which is described as sharp or stinging in nature and is well localized. Polymodal C fibers (mechanical, thermal, and chemical) transmit “second pain,” which is more diffuse in nature and is associated with the affective and motivational aspects of pain. Con’t First-order neurons synapse on second-order neurons in the dorsal horn primarily within laminas I, II, and V, where they release excitatory amino acids and neuropeptides. Some fibers can ascend or descend in Lissauer tract prior to terminating on neurons that project to higher centers. Second-order neurons consist of nociceptive-specific and wide dynamic-range (WDR) neurons. Con’t Nociceptive-specific neurons are located primarily in lamina I, respond only to noxious stimuli, and are thought to be involved in the sensory-discriminative aspects of pain. WDR neurons are predominately located in laminae IV, V, and VI, respond to both nonnoxious and noxious input, and are involved with the affective– motivational component of pain. con’t Axons of both nociceptive-specific and WDR neurons ascend the spinal cord via the dorsal column–medial lemniscus and the anterior lateral spinothalamic tract to synapse on third-order neurons in the contralateral thalamus, which then project to the somatosensory Microsoft Edge cortex, where nociceptive input is perceived as pain. PDF Document Assending path way Activation of sensory end organs and/or nerve endings The nociception begins with the activation of peripheral sensory afferent receptors, also known as nociceptors, which are widely distributed throughout the body. Nociceptors are the peripheral endings of pseudo-unipolar neurons, whose cell bodies are located in the dorsal root ganglia Microsoft Edge PDF Document Microsoft Edge PDF Document (DRG). The nociceptor central ending terminates in the spinal cord and Con’t.. Nociceptors convey noxious sensation, either externally (i.e. skin, mucosa) or internally (i.e. joints, intestines).  They can be activated by any noxious insult.  Nociceptor activation is associated with a depolarizing Ca2+ current or a “generator potential”.  Once a certain threshold is met, the distal axonal segment depolarizes via an inward Na+ current, and an Microsoft Edge Con’t Noxious stimuli are conducted from peripheral nociceptors to the dorsal horn via both unmyelinated and myelinated fibers. Nociceptive nerve fibers are classified according to their degree of myelination, diameter, and conduction velocity. For instance, A-delta axons are myelinated and allow action potentials to travel at a very fast rate of approximately 6–30 meters/second towards the central nervous system. Con’t They are responsible for “first pain” or “fast pain”, a rapid (1 second) well localized, discriminative sensation (sharp, stinging) of short duration. Perception of first pain alerts the individual of actual or potential tissue injury and initiates the reflex withdrawal mechanism con’t The more slowly conducting non-myelinated C fiber axons conduct at speeds of about 2 meters/second. These unmyelinated C-fibers (termed polymodal-nociceptive fibers) respond to mechanical, thermal, and chemical injuries. C-fibers mediate the sensation of “second pain”, which has a delayed latency (seconds to minutes) and is described as a diffuse burning or stabbing sensation that persists for a prolonged period of time. Con’t Larger A-beta axons, which respond to maximally light touch and/or movement stimuli, typically do not produce pain, except in pathological conditions. Mediators A number of inflammatory and noxious mediators are involved in peripheral pain transduction. Peripheral noxious mediators are substances that play a crucial role in the process of nociception, which is the sensory perception of pain. These mediators are primarily released in response to tissue injury or inflammation and act on peripheral nociceptors to enhance their sensitivity and excitability. Con’t These are in part 1. Substance. P 4. Prostaglandins 2. Bradykinin 5. Serotonin or (5- hydroxytryptamine; 5-HT) 3. Histamine 6. Cytokines and interleukins Conduction Of Pain To The Spinal Cord And Medulla Nearly all sensory afferents, regardless of peripheral origin, terminate in the dorsal horns of the spinal cord and medulla. Unmyelinated C fiber nociceptors terminate principally in lamina II (substantia gelatinosa). Small myelinated A-delta nociceptors terminate lamina I of the dorsal horn. Con’t The terminal endings of the primary afferent neurons in the spinal cord transmit pain signals to second-order neurons via several neurotransmitters, including glutamate and substance P. The second-order neurons involved in the pain pathway are principally of two types; (1) nociceptor-specific neurons that respond exclusively to inputs from A- delta and C fibers, and (2) wide-dynamic-range (WDR) neurons that respond to both noxious and non-noxious stimuli. Con’t Higher-frequency stimulation leads to NMDA receptor activation, gradual increases in WDR neuronal discharge and a sustained burst of activity termed “wind-up”. In this situation, WDR neurons become sensitized and hyperresponsive and transmit normal tactile responses as painful stimuli. These central sensitizing changes are responsible for secondary hyperalgesia which increases the intensity of acute pain Con’t A number of neurotransmitters, neuromodulators and their respective receptors are involved in the neurotransmission at the dorsal horn. They can be broadly classified into two groups. 1. Excitatory transmitters that are released from the primary afferent nociceptors or interneurons within the spinal cord. 2. Inhibitory transmitters that are released by interneurons within the spinal cord or supraspinal sources Con’t Most often more than one neurotransmitter is released at the same time. Aspartate and glutamate are excitatory amino-acids (EAAs) involved in pain transmission. Glutamate is the main excitatory CNS neurotransmitter and mediates rapid, short-duration depolarization of second-order neurons. Peptides such as substance P and neurokinin are responsible for delayed long-lasting depolarization. Con’t Afferent impulses arriving in the dorsal horn are tempered and modulated by inhibitory mechanisms. Inhibition occurs through local inhibitory interneurons and descending pathways from the brain. Transmission of impulses from the spinal cord to the supraspinal structures - Several ascending tracts are responsible for transmitting nociceptive impulses from the dorsal horn to supraspinal targets. Con’t These include spinothalamic, spinoreticular, spinomesencephalic and spinolimbic tracts. Of these, the spinothalamic tract is considered the primary perception pathway. Axons traveling in the spinothalamic tract (STT) travel to several regions of the thalamus where pain signals diverge to broad areas of the cerebral cortex. Descending control of pain Descending neural pathways inhibit pain perception and efferent responses to pain. The cerebral cortex, hypothalamus, thalamus and brainstem centers send descending axons to the brainstem and spinal cord that modulate pain transmission in the dorsal horn. These axonal terminals either inhibit release of noxious neurotransmitters from primary afferents, or diminish the response of second-order neurons to the noxious input. Con’t Several neurotransmitters play critical roles in modulating pain transmission. Endogenous opioids (enkephalin, dynorphin), Gamma-aminobutyric acid (GABA), and norepinephrine. Con’t The PAG is an enkephalinergic brainstem nucleus responsible for both morphine- and stimulation-produced analgesia. Descending axons from the PAG project to nuclei in the reticular formation of the medulla, including NRM, and then descend to the dorsal horn where they synapse with and inhibit WDR and other neurons. Axon terminals from the NRM project to the dorsal horn, where key aspects of afferent pain signaling, cortical perception and efferent responses ref 1. “Regional Anesthesia - Acute Pain Medicine: Made for This Moment.” Made For This Moment | Anesthesia, Pain Management & Surgery, www.asahq.org/madeforthismoment/anesthesia-101/types-of-anesthesia/regional-anesthesia/. 2. Torpy JM, Lynm C, Golub RM. Regional Anesthesia. JAMA. 2011. 3. “Regional Anesthesia for Surgery.” ASRA Pain Medicine, www.asra.com/patient-information/regional-anesthesia.