What Is Acute Pain

Introduction

Definition of acute pain

Acute pain is short-lasting, lasting hours, days, or weeks and normally resolves when the body heals itself. It is commonly associated with tissue damage, inflammation or after a surgical procedure.¹  It is important to understand pain as it interferes with daily activities, so understanding and managing it can reduce the effects of pain and improve patient function. This article will highlight the function, causes and management of acute pain. 

Understanding pain

The general concept of pain

Pain is defined as an unpleasant sensory and emotional experience with actual or potential tissue damage. 

Types of pain (Acute vs. Chronic)

Acute pain lasts for a short duration, whereas chronic pain is when the pain becomes long-lasting, commonly longer than 6 months and may continue after the initial injury has been treated.

Functions of pain

The main function of pain is to alert the body; it is an indication of damage to the tissue or the presence of an injury.² This can be physical or chemical and may be visible or not. 

Another function of pain is that it can prevent further injury so the early stages of healing can occur. Once the pain lessens, the movement becomes easier, so you can return to doing normal everyday activities. When there is normal movement, the healing tissue becomes exposed to normal stresses again, allowing it to become stronger.

Characteristics of acute pain

Onset and duration

1. Sudden Onset

Acute pain usually starts abruptly, following straight from an incident that may cause injury. 

1. Short-Term Duration

Acute pain does not last long; the pain can last from a few minutes to a few weeks.

Location and severity

1. Localized Pain

Acute pain usually occurs in a specific area of the body and is not likely to spread to other areas of the body; this makes it easier to identify and treat. 

1. High Severity

This type of pain can be intense and may feel like a sharp, stabbing type of ache. The severity depends on factors such as the person's pain tolerance,  the location of the pain and the cause. 

Causes of acute pain

1. Injury and Trauma

The most common cause of acute pain is physical injury or trauma. This includes smaller injuries such as cuts or bruises or more serious injuries such as a fracture or burns.³

1. Surgery

It is likely that after a surgical procedure, a patient will experience acute pain at the site of surgery. This will be reduced by taking pain medications. 

1. Medical Procedures

Some medical procedures other than surgery include dental work or diagnostic tests, which may lead to acute pain. 

1. Infections

Acute pain is often an indication of an infection in the body. For example,  experiencing pain on the right side of the lower abdomen or around the navel or if pain occurs more when coughing  or  walking are often a sign of appendicitis, an infection causing the swelling of the appendix.

1. Inflammatory Conditions

Certain inflammatory conditions, such as arthritis, can lead to acute pain when the inflammation flares up.

Physiology of acute pain

Nervous system involvement

The peripheral nervous system (PNS) and the central nervous system (CNS) are both involved in the pain pathways. The PNS comprises nerves located outside of the brain and spinal cord and connects the CNS to other organs and limbs in the body. The CNS is made up of the brain and spinal cord, which interpret information from the PNS and coordinate the activities of the body.⁴

Pain pathways

There are different phases of the pain pathway:

1. Transduction 

When tissue damage or an injury such as cut or burn occurs, nociceptors are activated, this causes the conversion of the stimulus into electrical signals which are called action potentials.

1. Conduction 

The A-delta fibres transmit sharp, localised pain signals, while the C fibres transmit dull and poorly localised pain signals.⁵

1. Transmission of pain signals

Action potentials generated by nociceptors travel along the peripheral nerve fibres to convey the pain signal to the CNS. 

1. Modulation 

The brain can modulate the perception of pain. Endogenous pain leads to the release of neurotransmitters such as endorphins and serotonin, which are natural painkillers that can inhibit the transmission of pain signals.

1. Perception of pain

Perception of pain occurs when the stimulation of nociceptors is intense enough to activate such a feeling.

Neurotransmitters and pain modulation

1. Endorphins

The role of endorphins in the body is to help you survive. When the body feels pain, nerves in the body send pain signals to the brain. The brain releases endorphins to block the nerve cells that receive the pain signals, which turns off the feelings of pain.

1. Norepinephrine

If a person feels acute pain, the pain can cause the activation of norepinephrine; this involves a decrease in sensitivity to painful stimuli and pain relief. 

1. Serotonin

Serotonin is a neurotransmitter that functions in pain sensation, inflammation, and emotions such as depression. This neurotransmitter inhibits and promotes pain perceptions through different physiological mechanisms.

Symptoms and diagnosis

Subjective nature of pain

One main feature of pain is that it is a subjective experience, so it cannot be seen or felt by those who are not experiencing it. Therefore, it is important to conduct physical observations to assess the level of pain.

Patient's description of pain and physical examination

To assess the pain, a patient will be asked to describe factors such as the location, cause, duration, and intensity of the pain. This will be followed by a physical examination and diagnostic tests to identify the individual’s pain and help the healthcare provider identify ways to manage and treat the pain.

Diagnostic tests

1. Imaging 

In the diagnosis of pain, imaging is a useful tool to detect the precise location of where the person may be feeling the pain. An fMRI is used to measure acute pain where there are short periods of pain followed by a period that may be pain-free, which causes a change in hemodynamic response, which is the change in brain activity linked to changes in the blood flow.⁶

1. Blood Tests

Blood tests are also important to identify acute pain. Scientists in the US have developed blood tests that can tell doctors if a patient is in pain and the severity of the pain. This objective measure of pain is great for a clinician to identify the level of pain faced by the patient.⁷

1. Electromyography (EMG)

An EMG can help diagnose pain related to pinched nerves and provide an accurate assessment of muscle function.

Treatment of acute pain

Medications

1. Analgesics (Pain Relievers)

These are medications used to manage and treat pain. They include a range of medications such as anti-inflammatory drugs, antidepressants, and local anaesthetics.⁸

1. Anti-inflammatory Drugs

Anti-inflammatory drugs are commonly used to reduce inflammation and relieve pain symptoms; this includes drugs such as aspirin and ibuprofen. This can be used for a wide range of pain symptoms, such as headaches, period pains and sprains.⁹ The main mechanism of action of this is to inhibit the enzyme cyclooxygenase (COX) to reduce inflammation.⁹

Non-pharmacological approaches

In addition to medication, there are many methods of managing and reducing pain. 

1. Rest and Ice

It is very important to rest if feelings of pain occur as it prevents further injury and allows the body to be in a state to recover. Ice is also commonly used for injuries as the cold is effective in numbing the affected area, which reduces swelling and inflammation and reduces pain.

1. Physical Therapy

Physical therapy is a great way to reduce acute pain found in areas such as the lower back and knees. This method aims to reduce pain over time for a long term compared to other methods, which reduce pain quickly but temporarily. 

1. Heat Therapy

Heat therapy helps to soothe stiff joints and relax muscles so that they can move better. Heat in the area of pain allows the blood vessels to get bigger so that blood and oxygen can reach the injured tissues quickly and provide relaxation. 

1. Massage

Therapeutic massages are a great physical and mental way to reduce pain by relaxing painful muscles and tendons to improve stiffness and relieving stress. This is because the  massage increases blood circulation and releases endorphins. This method is commonly used for pain in the back or shoulders.

Complications and risks

Untreated acute pain

If acute pain is left untreated, it can lead to muscle and joint weakness and deteriorating health in the form of immunological and neural changes.¹⁰ If pain continues, this may also cause loss of some functions, leading to irritability, depression, and difficulty in eating and sleeping. For this reason, it is also possible for acute pain to transition to chronic pain, which will be longer lasting, so a person may find themselves feeling distressed for a longer period of time.

Side effects of pain medications

There are side effects associated with pain medications, although these are not serious. The most common side effects of pain medications are feeling sick or nauseous, drowsiness, and confusion.

Conclusion

Acute pain is a response to injury or illness and is key in providing protection to our bodies. This type of pain can be intense but usually lasts for a short duration and is easy to manage with the use of medicines and rest so a person can continue with their daily activities. However, if this is not treated on time it can cause the pain to worsen over time, so it is important for a healthcare professional to provide an assessment and management plan to relieve a person of the pain depending on their personal causes and levels of pain.