What is Acute Pain?
Acute pain is pain that happens suddenly, starts out sharp or intense, serves as a warning sign of disease or threat to the body, and generally subsides within weeks (typically 0–7 days, though definitions extend up to 3–6 months). 1
Core Definition and Characteristics
Acute pain should be viewed as the initiation phase of an extensive, persistent nociceptive and behavioral cascade triggered by tissue injury. 1 This cascade has the potential to span orders of magnitude of space and time, but generally subsides within weeks. 1
Key Distinguishing Features
Duration: Acute pain is limited in time, typically lasting 0–7 days, though clinical definitions may extend to 3–6 months past the acute onset and resolution of the insult (such as surgery for stricture or resolution of obstruction). 1
Biological purpose: Acute pain serves a useful biologic function as a protective mechanism, warning of actual or potential tissue damage. 2, 3
Self-limited nature: Unlike chronic pain, acute pain has a recognizable endpoint that corresponds with tissue healing. 2
Physiologic response: Acute pain is associated with skeletal muscle spasm and sympathetic nervous system activation (tachycardia, hypertension, diaphoresis). 1, 2
Underlying cause: Acute pain is provoked by a specific disease, injury, trauma, surgical procedure, or medical disorder with a clear, definable beginning. 1, 2
Pathophysiology
At the site of injury, inflammatory mediators (monoamines, cytokines, prostanoids, peptides), neurotransmitters (glutamate, substance P, CGRP), ATP, nitric oxide, and neurotrophins activate nociceptors in C and Aδ fibers, which convey nociceptive stimuli to the dorsal horn of the spinal cord. 1 From there, excitatory amino acids and neuropeptides transmit signals through ascending pathways to thalamic, limbic, and cortical structures responsible for the discriminative pain experience. 1
Inhibitory interneurons (cholinergic, opioidergic, GABAergic) and descending pathways from the brainstem (utilizing serotonin, noradrenaline, and dopamine) modulate nociceptive transmission at the spinal dorsal horn, limiting the flow of pain signals to supraspinal areas. 1
Clinical Context
Acute pain is a normal physiologic response to a noxious stimulus that can become pathologic if untreated or not treated effectively. 4 Examples of conditions associated with acute pain include fractured femur, appendicitis, burns, procedural pain (heel stick, suctioning, venepuncture, thoracic drainage), and postoperative pain. 1
Critical Distinction from Chronic Pain
Abdominal pain is considered chronic if it has persisted 3–6 months past its acute onset and resolution of the insult. 1 Chronic pain is experienced irrespective of the presence, intensity, or duration of peripheral stimuli, serves no biologic purpose, and has no recognizable endpoint. 1, 2 In animal models, inflammation-induced hyperalgesia often outlasts actual inflammation, demonstrating that the transition from acute to chronic pain involves sensitization of peripheral and central nervous systems, leading to neural plasticity at molecular, cellular, and synaptic levels. 1
Management Implications
Fortunately, acute pain in general can be easily controlled by clinically available medicines, and in most cases the problem can be resolved in parallel with the resolution of the injury and tissue healing, causing little suffering. 1 All current guidelines support using a multimodal approach to pain management and reserving use of opioids for patients with severe pain that cannot be managed with other agents. 4
Primary care practitioners who encounter patients with acute pain can help preserve function and quality of life and prevent progression to chronic pain by implementing appropriate management strategies. 4 The therapy of acute pain is aimed at treating the underlying cause and interrupting the nociceptive signals. 2