Chronic pain after childbirth - All About Epidural
chronic-pain

Chronic pain after childbirth

Date: July 13th, 2013

It was noticed some time ago that some patients developed pain after surgical operations that lasted considerably longer than expected: for months, years and sometimes even for the rest of their lives. The incidence ranges depending on the type of surgery, from around 10% after hernia repair to 30-50% after leg amputation and operations in the chest cavity. In 10 to 30% of these patients pain is severe and may lead to disability.

In order to understand how this happens, let’s run through a brief tutorial in pain physiology. Pain is caused by a variety of factors which may be divided into three basic groups: nociceptive, inflammatory and neuropathic.

Nociceptive factors refer to the direct trauma of the tissues. For instance, when the surgical knife moves through the skin it activates sensory receptors that send the signal through the ascending nerves to the brain. As soon as the trauma is stopped the signalling stops as well, and the sensation of pain fades.

After the injury the cells in the damaged area release chemicals – inflammatory mediators – that facilitate healing. These chemicals increase the sensitivity of the nerves in the damaged area, and the pain persists until the surgical wound has healed. This is the inflammatory component of pain.

Finally, neuropathic pain occurs as a result of damage to nerve endings. The physiology of this pain is complex and not completely understood. When the nerve fibers are damaged, the transmission of nerve impulses to the spinal cord and the brain stops. This leads to changes in the central nervous system and causes abnormal functioning of the nerves. In simplistic terms, the brain starts producing its own sensations. This, in combination with the inflammation at the site of the injury, produces new symptoms: the wound hurts at rest and becomes overly sensitive, so that even a light touch may cause significant pain, which lasts much longer than one would expect.

All these mechanisms serve one purpose, to protect the injured area and ensure proper healing. Once the injury is repaired by the body, the pain eventually disappears. However, in some instances the normal physiological processes get out of control, and the pain becomes chronic. This is the result of neuroplasticity.

Neuroplasticity

It has been known for many years that the nervous system – the brain and the peripheral nerves – is not a static system. On the contrary, it is adaptable and may change according to the physiological environment. One example of neuroplasticity is when a person loses their sight, his or her hearing and sensation of touch becomes sharper, to compensate for the loss. Another example: if an arm becomes paralyzed as the result of a stroke, the neurons (nerve cells) in the area of the brain adjacent to the affected area grow new neuronal endings and take over the function of dead cells, leading to the recovery of the function of the arm. In other words, the brain and the nerves change in response to radical changes.

Unfortunately, neuroplasticity may also be involved in pathological processes. (What does pathological mean?) One of these processes is central sensitization.

Central sensitization

Injury to the tissue produces a barrage of neural impulses to the areas of the brain involved in the perception of pain. If this stimulation is intense and lasts long enough it may lead to permanent changes in the central nervous system that lead to increased sensitivity to pain and other types of stimulation of the affected area. The neurons in the affected area become spontaneously activated, so that the pain signal in the brain is present even if the affected area is not stimulated. It is thought that the neuropathic component of pain plays an important role in central sensitization.

This physiology is confirmed by clinical experience. Two major risk factors for the development of persistent pain after surgery are preceding pain and the intensity of pain immediately after surgery. That is why treatment of surgical pain is important.

Because of pathological changes in pain physiology, the character of chronic pain that develops after surgery is often different from typical acute pain. Patients often report it as burning, getting worse when lightly touched, and the area is often sensitive to cold.

Chronic pain after cesarean section and vaginal birth

Chronic pain after cesarean section or vaginal delivery has not been extensively studied, though it has been coming under the spotlight in recent years. Incidence of this complication varies.

A study from Brazil, a country where cesarean section rates are high, points out that 67% of women with chronic pelvic pain had a cesarean section in the past, compared to 38% of those without symptoms. Another study showed that 12.3% of patients experienced pain more than 10 months after they had a caesarean section. No patients had constant pain, but 5.9% of women reported that they had pain every day. Patients whose caesarean was performed under general anesthesia had higher frequency of persistent pain than those who had a spinal.

A study from the USA published in 2008 compared the severity of pain after caesarean section or vaginal delivery. 10.9% of patients reported severe pain 36 hours and 9.8% 8 weeks postpartum. There was no difference between those who had vaginal delivery or caesarean. Women who had severe pain immediately after childbirth were 2.5 times as likely of developing persistent pain and a 3.0-fold risk of developing post-partum depression.

Another American study found that about 10% of women had persistent pain at 8 weeks after childbirth, with no difference occurring between caesarean and vaginal deliveries. About half of those patients reported that their daily activities were affected by the pain. Fewer patients experienced pain if spinal anesthesia was used. Among women who delivered vaginally, the severity of pain immediately after childbirth was associated with more pain 8 weeks later.

Finally, a study from Finland found that 18% of patients experienced pain a year after their caesarean section and 10% had pain after vaginal delivery. The pain was mild in 55% of women. The incidence of intense or unbearable chronic pain was slightly higher after vaginal birth (6 out of 209 after vaginal delivery versus 4 out of 229 after caesarean).

All studies found that the risk of developing persistent pain after caesarean or vaginal birth was considerably higher among women who had pain before childbirth and those who experienced severe immediately after giving birth or having surgery.

Potential advantage of labor epidural

According to current data, up to 18% of patients having caesarean section and up to 10% giving vaginal birth develop chronic pain. It has also been demonstrated that major risk factors leading to the development of such pain are the presence of pain before surgery and the intensity of pain immediately after it. Because the development of chronic pain is caused by changes in the central nervous system, controlling pain during and after surgery reduces the chances of developing this complication.

Caesarean section is a kind of surgery, and the fact that some patients develop chronic pain after it is not surprising. However, we tend to forget the fact that labor is also a highly traumatic process accompanied by considerable injury to the tissues and severe pain. In fact, labor pain is rated as one of the most serious kinds of acute pain known to humans. In view of these facts it is not surprising that some women develop chronic pain after giving vaginal birth, and that the risk factors are similar to those associated with surgery.

Regional anesthesia – epidural or spinal – is the most efficient way of controlling pain of childbirth. Spinal block reduces the incidence of chronic pain after caesarean. Therefore it is highly likely that labor epidural may prevent the development of chronic pain after vaginal delivery. At present there is simply no data assessing the influence of pain relief in labor on the development of persistent pain. However, existing evidence from other areas of surgery and physiology suggests it very well may do that. The barrage of painful stimuli during labor is capable of inducing neuroplasticity that may predispose to the development of chronic pain. By blocking these stimuli epidural anesthesia may prevent this from happening. This is another, potentially very important, advantage of labor epidural.

References.
1. Kehlet H, Jensen TS, Woolf CJ. Persistent postsurgical pain: risk factors and prevention. Lancet 2006; 367: 1618–25

2. Vermelis JM, Wassen MM, Fiddelers AA, Nijhuis JG, Marcus MA. Prevalence and predictors of chronic pain after labor and delivery. Curr Opin Anaesthesiol 23:295–299.

Image from: http://www.freedigitalphotos.net/images/view_photog.php?photogid=809

Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural

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