For long-time followers of the Nursing Show, you will be familiar with the inclusion of pain as part of the vital signs in our Vital Signs Review episode. True enough, even if the pulse rate, blood pressure, respiration, pulse ox, and temperature are all normal, if the patient is in pain then once couldn’t say that the patient is fine. Pain is the only vital sign that can not be measured quantitatively. If a person says he is in pain, then that person is in pain and there needs to be something done about it.
According to an journal article from the AACN, pain is the principal symptom causing patients to seek medical attention, affecting 1 in 5 Americans on any given day. With about 70 million pain-motivated health provider visits every year, there is an estimated cost of over $100 billion. Not does it take its toll financially, pain also takes its toll on an individual emotionally, physically and mentally. A person in pain will not be able to function normally affecting their comfort. In the long run, the individual may experience depression and withdraw from society. Overall, the quality of life is markedly decreased.
What is pain and how does it work?
From the AACN journal, pain has been described as a multifaceted and highly subjective experience that is unique to each person. Pain is not only influenced by physiological processes, but also influenced by psychological and emotional processes as well. It has been reported that the intensity of pain can be influenced by contextual cues. It is also said that the intensity of pain felt varies upon each individual’s tolerance to pain.
There two major types of pain- acute and chronic. Chronic pain and its mechanism will be discussed in a following article. For the meantime, acute pain is a physiological response that warns us of danger. The process of nociception describes the normal processing of pain and the responses to noxious stimuli that are damaging or potentially damaging to normal tissue. This process includes transduction, transmission, perception and modulation.
In transduction, nociceptors (free nerve endings) found in different parts of the body respond to noxious stimuli. The characteristic of pain felt depends on the type of neuron fiber affected. Noxious stimuli are categorized into mechanical (pressure,swelling, incision), thermal (burns), and chemical (excitatory neurotransmitter, toxic substance, ischaemia, infection).
Noxious stimulations may be internal or external and they cause the release of chemical mediators from damaged cells including prostaglandins, bradykinin, serotonin, potassium, and histamine. For the pain impulse to be generated, an exchange of sodium and potassium ions occurs at the cell membranes resulting in an action potential and generation of a pain impulse.
In pain transmission, three stages occur- from the site of transduction to the dorsal horn of the spinal cord, from the spinal cord to the brain stem, then lastly to the connections between the thalamus, cortex, and higher levels of the brain.
The C and A delta fibers (nociceptors) end at the spinal cord. There is a gap or synaptic cleft between the nerve ends and the nociceptive dorsal horn neurons (NDHN) and for the impulse to go through that gap neurotransmitters are released. Examples of these neurotransmitters are ATP, glutamate, bradykinin, and more. When the impulse arrives at the thalamus, it is then directed to different areas of the brain where it is processed.
Perception of pain is where transmission activities end and pain turns into an experience. Multiple cortical areas are activated which results to responses in different systems such as reticular (involves motor response to avoid the stimuli), somatosensory (perception and interpretation of sensation), and limbic (emotional and behavioral response).
Modulation of pain involves the inhibition of transmission of pain signals in the spinal cord. In this process, there are pathways called descending modulatory pain pathways (DMPP) which leads to either increase in transmission (excitatory) or decrease in transmission (inhibition). Neurotransmitters involved in pain inhibitioin are relased to produce analgesia. These include serotonin, GABA, endogenous opioids, acetylcholine, neurotensin and oxytocin.
This article is just an overview of the pain process in acute pain. For a more in-depth, detailed review, please refer to the resources provided below.
Anatomy and Physiology of Pain
The Physiology and Processing of Pain: A Review by Cynthia L. Renn, RN, PhD, ACNP; Susan G. Dorsey, RN, PhD. AACN Clinical Issues Volume 16, Number 3, pp. 277–29o, AACN 2005
