It is believed that acute pain transforms into chronic pain when continuous nerve stimulation alters pain pathways, leading to an impaired Central Nervous System (CNS). It is also believed that genetics and circuity in the part of the brain controlling emotions impact the transition of acute pain into chronic pain.
Acute pain alerts you to the fact the body has undergone some kind of injury, like a broken bone or strained muscle. Chronic pain is more complex due to the fact it can involve the interaction of psychosocial, biological, injury or illness and trauma factors. Sometimes, there is no identified specific cause of the chronic pain.
Acute pain is a continuum, ranging from a symptom to a disease process, a nidus for a host of chronic conditions, similar to the model of progression of inflammation to sepsis.
Medical researchers continue to research neurotransmitters, impact of inflammation, the spinal cord and brain activity to explain the medical reason for moving from acute to chronic pain. University of Utah’s Professor Emeritus of Anesthesiology Prof Richard Chapman, said, “The question of the transition from acute to chronic pain is one of the most fundamental and enduring challenges in the field.”
Some of the common identified causes of chronic pain include:
- Nerve damage caused by injury, illness or medications
- Damaged tissue
- Inflammation from a condition like trigeminal neuralgia
- Pain from the cause of the acute pain that is prolonged by psychological factors such as fear and anxiety.
Types of acute pain
Acute pain can vary significantly and may be categorised into two main types: spontaneous insult or trauma and elective or planned procedures, according to Krat et al, 2019.
Spontaneous insult or trauma
Mildly painful spontaneous conditions include headache, upper respiratory infection, or a sore back from doing gardening, and may be self-treated with rest-ice-compression-elevation (RICE) therapy and over-the-counter analgesics.
Moderately painful conditions include a sprained ankle, strained ligament, deep laceration, or simple bone fracture. These may require interventions such as minor outpatient surgery or splinting, but are generally managed with nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, and RICE.
Severely painful conditions include trauma such as a motor vehicle accident, traumatic amputation, or burn, and will likely involve surgery and a protracted hospital stay. A stronger combination of analgesics, including opioids, may be required. Of course, the pain level for each case must be individually determined.
Elective or planned procedures
Nearly all cases of chronic pain begin as acute pain. Many models suggest that prolonged exposure to acute pain leads to structural changes within the central nervous system that transform this condition into a chronic pain syndrome. Depending upon the type of surgery, as many as 50% to 70% of patients may experience surgical-site pain at least 6 months after surgery, with approximately 10% rating their pain as severe in intensity. Established risk factors for the transition of acute to chronic pain in the surgical setting include younger age, female gender, catastrophizing, low socioeconomic status, preoperative pain, impaired diffuse noxious inhibitory control, type and duration of surgery, injury to specific nerves, severity of acute pain, and, possibly, prior exposure to radiation therapy and chemotherapy.
Office procedures, including immunisations, phlebotomy, or catheter placement, tend to result in mild acute pain that is usually eased with application of topical lidocaine/prilocaine (EMLA), lidocaine, ice, or devices that combine the application of ice and vibration.
Moderately painful procedures include same-day dental, arthroscopic, laparoscopic, or podiatric surgeries. This type of pain may be managed with simple analgesics, such as NSAIDs and acetaminophen. At most, a total of 6 to 8 doses of an opioid and acetaminophen combination might be needed if the patient’s discomfort is not controlled with simple analgesics.
Severely painful procedures include surgeries requiring inpatient stays, such as orthopedic joint replacement, spine surgery, or colorectal surgery. These will require a combination of analgesics and stronger opioids, possibly starting preoperatively.
Intense, acute pain afflicts millions of patients each year. Despite the recently increased focus on the importance of pain control, management of acute pain has remained suboptimal. The objective of a study by Sinatra (2010) was to identify through a literature review the barriers to effective treatment of acute pain and the potential consequences of inadequate pain management.
His studies examining the use of multiple analgesics with different mechanisms of action suggest that multimodal therapies may offer an improved efficacy/tolerability balance over single agent regimens. The use of multimodal therapy has demonstrated increasing promise and is supported by current practice guidelines.
Subject to the cause of the pain as well as other patient and external factors, a traditional stepwise approach includes commencing treatment with paracetamol, adding a NSAID and thereafter, co-prescribing a weak opioid such as codeine or tramadol (Outhoff et al, 2015).
This rational practice facilitates additive or even synergistic efficacy and furthermore results in a reduction of the use of the more potent opioids. The strong opioid-sparing effects of these compounds may lead to reduced nausea, vomiting, constipation, urinary retention, respiratory depression and sedation, which are important factors particularly when considering pain associated with ambulatory surgery and the increasing need to facilitate an earlier hospital discharge.
According to Krat et al, 2019, multimodal treatment is crucial for optimising pain relief. Because different modalities may be additive or synergistic, this approach can also reduce the potential for side effects. The cornerstones of multimodal treatment include nerve blocks or epidurals, opioids or other analgesics, adjunctive medications, physical modalities (RICE), and rehabilitation. Psychosocial interventions, including distraction, meditation, and deep breathing, are also central components. Providers and patients are often too focused on the pharmacologic options, which are only a small part of the solution.
Consensus indicates that a comprehensive, multimodal, holistic approach is foundational to the practice of acute pain medicine (APM), but lack of uniform, evidence-based clinical pathways leads to undesirable variability throughout US healthcare systems.
According to Krat et al, 2019, “Acute pain studies are inconsistently synthesised to guide educational programs. Advanced practice techniques involving regional anesthesia assume the presence of a physician-led, multidisciplinary acute pain service, which is often unavailable or inconsistently applied. This heterogeneity of educational and organisational standards may result in unnecessary patient pain and escalation of healthcare costs.”
A multidisciplinary panel was nominated through the Acute Pain Medicine Shared Interest Group (APMSIG) of the American Academy of Pain Medicine (AAPM). The panel met in Chicago, 2014, to identify gaps and set priorities in APM research and education.
The panel identified three areas of critical need:
1. An open-source acute pain data registry and clinical support tool to inform clinical decision making and resource allocation and to enhance research efforts
2. A strong professional APM identity as an accredited subspecialty
3. Educational goals targeted toward third-party payers, hospital administrators, and other key stakeholders to convey the importance of APM.
The ultimate goal is to reduce the conversion of acute pain to the debilitating disease of chronic pain.
Unimodal vs multimodal pain management
Acute pain control is an essential component of current clinical pathways and enhanced recovery protocols after surgery. Ever-improving multimodal regimens have brought everyday acute pain control to a level of effectiveness previously seen only in intensive research protocols.
Unfortunately, unimodal reliance on systemic opioids for aggressive pain control is fraught with serious and sometimes fatal side effects, mandating the need for progress in delivering effective opioid-sparing analgesia.
Acute pain medicine requires dedicated providers with the knowledge and training to avoid pain chronification. An acute pain service that is multidisciplinary and practices multimodal analgesia is generally accepted as best for achieving effective acute pain care. Multimodal analgesia typically refers to the use of 2 or more analgesic medications that work through different mechanisms, additively or synergistically, thereby reducing the dose and side effects of any one pain medication. An additional benefit of multimodal analgesia is a reduction in opioid use with its associated side effects and potential for mortality.
Analgesic and anxiolytic efficacy and tolerability of multimodal pain management
Successful treatment of moderate to severe acute pain often necessitates several analgesics that target different sites of the nociceptive pathway. Fixed-dose combination analgesics facilitate a reduction in dose of individual components, increased compliance and strong-opioid sparing.
Carefully designed oral fixed-dose combination analgesics have potential advantages over monotherapy, which include a reduction in dose of each of the components, theoretically resulting in improved tolerability and safety. The simplified oral regimens of combination analgesics may also be invaluable in promoting compliance.
For instance, paracetamol/codeine/meprobamate, a combination analgesic widely prescribed in South Africa, contains relatively small doses of 320mg paracetamol and 8mg codeine, which are usually prescribed individually in increments of 500mg and 30mg respectively in acute pain management.
Low-dose meprobamate (150mg) is also included in this preparation. Pain is often accompanied by anxiety, and in the past it was therefore considered beneficial to add this sedative to analgesic regimens specifically for its anxiolytic properties. Yet it appears that meprobamate also possesses intrinsic analgesic properties, which may further complement the overall analgesic efficacy of the multimodal therapy.
Outhoff et al (2015) compared the analgesic and anxiolytic efficacy and tolerability of two widely prescribed combination analgesics, paracetamol/codeine/meprobamate and paracetamol/tramadol in a randomised clinical trial.
A prospective randomised parallel group phase IV clinical trial was conducted in 100 patients experiencing moderate to severe pain after third molar extraction at the Oral and Dental Hospital, University of Pretoria.
Pain intensity and pain relief were assessed using Likert and visual analogue scales. Medication efficacy, time to perceptible pain relief and meaningful pain relief were also assessed. Primary variables included the Pain Intensity Difference (PID) between baseline and scheduled visits, and hourly pain relief (PAR). The Summed Pain Intensity Difference (SPID), Sum of hourly PAR, hourly PIDs from baseline (SPRID) and Total Pain Relief (TOTPAR) were calculated according to standard methods. Beck Anxiety Questionnaire assessed anxiety. Tolerability was assessed chiefly by the reporting of adverse events.
Paracetamol/codeine/meprobamate and paracetamol/tramadol were equally effective at relieving moderate to severe acute pain. No differences in anxiolytic efficacy were found between the two treatment arms and differences in tolerability failed to reach statistical significance. Despite their distinctive compositions and mechanisms of action, they were equally effective and well-tolerated combination analgesics in patients experiencing moderate to severe acute pain.
Acute pain is disabling and common, and while it may be inevitable, treatment with effective analgesics may alleviate the suffering. Aggressive control of acute pain may also reduce the risk of developing chronic or even lifelong pain. Successful treatment of moderate to severe acute pain often necessitates several analgesics that target different sites of the nociceptive pathway.
Opioids are a key part of pharmacotherapy for acute pain. They are quite effective, particularly when used in combination with other analgesics, and are essential for both planned and unplanned severe acute pain situations. However, opioids must be used judiciously, for the shortest duration possible, and while giving the proper respect to risks of adverse effects, misuse, and abuse.
Tighe P, Buckenmaier CC 3rd, Boezaart AP, et al. Acute Pain Medicine in the United States: A Status Report. Pain Med. 2015;16:1806-26. doi: 10.1111/pme.12760. Epub 2015 Jun 10. PMID: 26535424; PMCID: PMC4634553.
Outhoff K, Dippenaar JM, Nell M et al. A randomised clinical trial comparing the analgesic and anxiolytic efficacy and tolerability of Stilpane® and Tramacet® after third molar extraction. Southern African Journal of Anaesthesia and Analgesia 2015;21:40-45.
Kral L, Singh T. Medical Management of Acute Pain. Practical Pain Management. 2019. Site visited 21 April, 2021.
Sinatra R. (2010). Causes and Consequences of Inadequate Management of Acute Pain. Pain medicine (Malden, Mass.). 11. 1859-71. 10.1111/j.1526-4637.2010.00983.x.
Ghauri M. Can You Prevent Acute Pain from Becoming Chronic? 2019. Spine & Pain North America. www.sapnamed.com. Site visited 21 April, 2021.