Vital Signs and Pain Assessment

Temperature

Body temperature is regulated and maintained by the hypothalamus. When pathogens invade the body, exogenous pyrogens—endotoxins produced by the pathogen—are released and travel to the hypothalamus. Pyrogenic cytokines are produced when phagocytic cells destroy microorganisms, leading to production of prostaglandin E ₂ . The hypothalamus raises the body’s temperature set point, stimulating heat production and a fever (pyrexia). Release of epinephrine and norepinephrine increases heat production by raising the basal metabolic rate ( Huether and Rodway, 2019 ). Increased muscle tone and shivering, a rapid contraction and relaxation of the skeletal muscles, also produce heat. The body conserves heat by vasoconstriction, which reduces heat loss through the skin. Body cooling occurs through the skin by radiation, vasodilation, conduction, convection, evaporation, decreased muscle tone, and an increased respiratory rate.

Pulse Rate

The arterial pulse results when the ventricular heart contraction pushes a pressure wave of blood throughout the arterial system.

Respiratory Rate

The primary muscles of respiration are the diaphragm and the intercostal muscles. The diaphragm is the dominant muscle. It contracts and moves downward during inspiration to increase the intrathoracic space. The external intercostal muscles increase the anteroposterior chest diameter during inspiration, and the internal intercostal muscles decrease the lateral diameter during expiration. Air is drawn into the lungs during inspiration and expelled during expiration when the intercostal muscles and diaphragm relax, allowing the chest wall to recoil.

Blood Pressure

The arterial blood pressure is the force of the blood against the wall of an artery as the ventricles of the heart contract and relax. Systolic pressure—the force exerted when the ventricles contract—is largely the result of cardiac output, blood volume, and compliance of the arteries. Diastolic pressure is the force exerted by peripheral vascular resistance when the heart is in the filling or relaxed state. Blood pressure is highest during systole and falls to the lowest point during diastole. The pulse pressure is the difference between the systolic and diastolic pressures.

Pain

Pain is an uncomfortable sensation and emotional experience associated with actual or potential tissue damage. Acute pain is of short duration and has a sudden onset in association with injury, surgery, or an acute illness episode. Inflammation helps sustain the pain response. Persistent (chronic) pain lasts several months or longer and is often sustained by a pathophysiologic process (e.g., joint Disease, chronic inflammation, headache, or cancer). Neuropathic pain is long-term pain associated with damage or dysfunction of the central or peripheral nervous system (e.g., amputation, complex regional pain syndrome, diabetic neuropathy).

Nociceptors are free nerve endings in the peripheral nervous system activated by tissue damage from injury or inflammation. Biochemical mediators such as bradykinin, prostaglandins, serotonin, glutamate, and substance P facilitate the transmission of pain impulses from the nerve endings along nerve pathways. Pain impulses travel from the site of tissue damage to the dorsal horn of the spinal cord through the ascending spinal tracts to the thalamus and cerebral cortex. Two specialized nerve fibers transmit pain impulses (nociception) to the dorsal horn of the spinal cord. Sharp, well-localized pain is quickly transmitted by the large, myelinated A-delta fibers. Dull, burning, diffuse, and chronic pain is slowly transmitted by the small, unmyelinated C fibers ( Fig. 6.1 ). Specific spinal tracts transmit the pain signals to the brain where perception occurs.

After the pain impulses reach the spinal cord’s dorsal horn, the pain signal may be modified when other stimuli are present from either the brain or the periphery. Substances such as endorphins (endogenous opioids), and gamma-aminobutyric acid (GABA) can change or inhibit the pain perceived. Pain impulse transmission may be reduced when non-pain impulses (e.g., ice, massage) compete to transmit sensations along the same spinal pathways to the brain.

Response to pain is individualized because it is a physiologic, behavioral, and emotional phenomenon. Individuals have different thresholds at which pain is perceived and different pain tolerance levels. Emotions, cultural background, sleep deprivation, previous pain experience, and age are some factors that have an impact on a person’s perception and interpretation of pain.