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Chronic Post Surgical Pain

Medico Legal

Dr Nigel Kellow MB BS FRCA MBA - Consultant in Pain Medicine

Surgery almost always involves some degree of cutting, burning, sawing, drilling or hammering of human tissue, either to fix a problem or to facilitate access into the body to get to it. This is inevitably going to hurt. Thankfully, modern anaesthesia permits surgery to be undertaken safely nowadays which could not have been contemplated in the past.

There are things we can do to minimise the amount of pain patients experience in the early post-operative period, such as local anaesthetic nerve blocks and the use of adequate amounts of strong painkillers, but it would be a rare patient indeed who gets through a whole peri-operative surgical period without some surgical pain.

But what is a “normal” level of pain? How long should it last? How should we manage it? When does post-surgical pain change from being expected to a problem? When it is recognised as a problem, is it the result of negligence or a recognised complication? Is there a clear binary distinction between negligence and a recognised complication?

Not surprisingly there aren’t simple answers to all of these questions but I hope you give you some idea of how you can get answers to some of them yourself, some of the time. However, chronic post-surgical pain (CPSP) is a significant problem in pain clinics with 22.5% of patients in one study citing surgery as the cause of their chronic pain.

There are problems around the definition of CPSP. For example, while an early research paper suggested pain persisting 2 months after surgery should be classified as CPSP, patients after some specific kinds of surgery, such as spinal fusions, can be expected to have some pain for six months or longer. This is further complicated by the amount of pain patients may have had before surgery, how long they had had it, and importantly, the doses and duration of any painkillers they had been taking.

There can also be some confusion over the specific symptoms a patient may be experiencing that taken together they call “pain.” This is a good point to introduce the definition of pain. Whilst it may seem obvious to you right now, it may not be in a few lines time.

What is the definition of pain?

The definition of pain that is in widespread accepted use by pain specialists around the world is that by the International Association for the Study of Pain (IASP). It is described here as:

“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

Pain is entirely subjective. It is what the patient says it is and can neither be more, nor less. If the patient says something is painful, then it is painful. If the patient says it is the worst pain they can imagine, then we have no objective diagnostic tests to tell them that it isn’t.

The problem of assessing pain

This is one of the criticisms levelled at the visual analogue pain score (VAS), which is the standard method used to quantify pain. In its purest form a 10cm line is drawn on a piece of paper and a patient is asked to indicate a point, by drawing a line across it, to indicate the amount of pain they have, ranging from 0, being no pain at all, to 10, being the worst pain they can possibly imagine. For the same painful stimulus one person’s 10 could be another person’s 3 because multiple subjective emotional, personality and additional factors contribute to the VAS indicated by the patient.

This can present problems to the medical expert asked to assess a patient in pain. In the personal injury claim setting there is probably an issue of compensation. The term “secondary gain” is used to describe benefits people may get from not overcoming a problem. For example if, during the meeting and clinical examination with the expert, they are able to persuade the expert that they have more pain and disability than they really do, they may be able to extract higher financial compensation.

While we have to accept what a patient tells us their pain is, we don’t have to rely entirely on the VAS. Fortunately, there are other well-known scoring systems that we commonly use in clinical practice to assess patients’ ability to do simple tasks such as washing or dressing, or the impact pain may have on their lives. But these aren’t fool proof either, so in practice, the examination of a patient in pain starts from the moment the expert first sees them as they call them from the waiting area into the consulting room.

Do they look as if they can sit comfortably in a chair? How easily can they stand up or walk? Are there any walking aids? Do they make eye contact? Are there any non-verbal indicators suggestive of pain? Are there any signs suggestive of exaggeration? If possible the expert should watch them after the consulta tion. This is a particularly important time, when they are normally relaxed and do not feel they are subject to examination. Can you see how they leave the clinic? Can you see them getting into a car?

Patients with CPSP may not describe symptoms or use words we would normally associate with our concept of pain, but to them feelings of tingling, numbness or increased sensitivity can be painful. Frequently patients describe a symptom as being something other than pain as either they or the doctor to whom they’re talking would normally understand, but they say that the sensations they feel are so unpleasant that they stop them from sleeping, concentrating or from having normal social interactions. Their symptoms then, are consistent with the IASP definition of pain.

How much pain, and for how long, is “normal”?

In terms of a “normal” level of pain there is no such thing, but for any operation, in any individual patient, or group of patients, a “normal distribution” – to use a statistical term – of the level and time course of pain exists in the post-operative period. To use an example of a knee replacement operation, these are notoriously painful operations that generally take several months to get over, and the early post-operative period can be very painful. A few patients get through a knee replacement without appearing to have much pain at all. These stand out as outliers. Most patients have severe pain in the first few days, which gradually and progressively reduces over the coming weeks, but a few patients are at the other end of the spectrum and have persistent pain in the knee for months or years after surgery.

Anaesthetists frequently use local anaesthetic techniques to make this period more comfortable – typically local anaesthetics injected around the major nerves that carry pain signals from the knee to the brain, or injections of local anaesthetics and strong opioid analgesics into the cerebrospinal fluid surrounding the spinal cord and nerve roots.

As soon as we do anything to the body we start to run the risk of procedural complications, and these attempts to alleviate early post-operative pain are no exception. Although uncommon there are risks associated with both of these procedures. The attempted injection of substances around large nerves can damage them if injected directly into them, because large nerves are collections of tens of thousands of nerve fibres held together by a membrane. Any kind of liquid injected into these nerves can damage them by increasing hydraulic pressure within them, reducing their blood supply below a critical level. It is also possible to damage these nerves through the action of inserting a needle into them, as most needles have a sharp cutting bevel, without which it would not be possible to pierce the skin. In order to reduce the incidence of damage to nerves by the bevelled cutting edge of a needle, skilled anaesthetists would frequently use a cutting needle to puncture the skin, and then a blunt needle to deliver the drugs around the target nerve.

If faced with a claim for a nerve injury related to attempted local anaesthetic blockade it would be important to consider in detail the conduct of the procedure. Similarly, sharp needles can cut the dura mater surrounding the spinal cord, allowing cerebrospinal fluid to leak out, resulting in what can be a whopping headache if patients attempt to stand up. This is known as a post-dural puncture headache (PDPH), and even with the pencil point needles that are most often used nowadays there can be an incidence of up to 1% even in skilled hands. This is a complication, but can it be the result of clinical negligence?

Patients undergoing knee replacement surgery are generally older and have degenerative spinal problems that distort the anatomy, making it harder for practitioners to find the necessary gap between vertebrae to insert a needle into the spine, increasing the risk of complications. But if one practitioner has a significantly higher incidence of PDPH or nerve injury after local anaesthetic blockade than another, so long as their patients and other circumstances are essentially similar, it may mean that one practitioner has more skilled hands than the other, but can this difference alone amount to negligence? Or do other factors have to be taken into consideration before such a judgment can be made?

If the blocks have been successfully performed patients should be comfortable for the first 24 hours after surgery but when they wear off the pain can be severe. The surgical and nursing teams doing these operations know the amount of pain patients are generally likely to have at any given stage of their care pathway but there are inevitably some outliers.

Normally post-operative pain would be at its worst immediately after surgery when the patient is in the recovery area, but the use of strong intra-operative analgesics and the increasing use of local anaesthetic nerve blocks has meant that the worst pain typically starts several hours, or in some case a day or more, after surgery. This is normally controlled with analgesics of steadily decreasing potency until patients have been fully mobilised and can be safely discharges home on mild to moderate strength painkillers.

Nerve injury is one of the most frequent causes of CPSP

CPSP can be so common after certain types of surgery as to be almost expected. One such example is after limb amputations where the incidence of phantom limb pain (unpleasant sensations envisioned in part or all of the newly absent amputated limb), or stump pain (typically pain and increased sensitivity within the stump and frequently located at the end of a cut nerve) occur in varying degrees in up to 9 out of 10 patients.

Fortunately, pain after amputations normally settles down over weeks or months, and if it persists one of the common causes of stump pain is a highly sensitive bulbous tip on the end of a cut nerve, known as a neuroma. Whilst falling under the definition of CPSP these can generally be sorted out quite easily with fairly simple treatments.

Neuromas are a type of nerve injury, and while they can be straightforward to treat, nerve injuries in general are amongst the most common, and in many cases, hardest to treat, causes of CPSP. There are nerves throughout the body from the brain and spinal cord, in and around most organs, to every square millimetre of skin. Damage to any one of these can in lead to the creation of long term painful problems.

Thoracotomies are operations inside the chest. They are normally undertaken through a skin incision that follows the line of the ribs, following which a retractor is inserted, which is wound open to push the ribs apart so the surgeon’s hands and instruments can get inside the chest cavity. They are a common cause of CPSP by two factors – mechanical disruption of the joints between the ribs and the spine at the back, or sternum and costal cartilages at the front, or by compression of intercostal nerves by surgical retractors.

Pain after hernia repairs

The tragic incidence of chronic pain and other problems after vaginal mesh surgery has been widely recognised but in terms of numbers the incidence of CPSP after groin hernia repair surgery is probably greater, with up to 35% of the 75,000 patients a year who have groin surgery suffering from CPSP. In common with all cases of CPSP there can be one or more causes in each patient, so it would not be uncommon for an individual patient to have a combination of nerve injury and an autoimmune mesh reaction as the causes for their pain. Both can be difficult to treat. The incidence of nerve injury after groin surgery may be higher than it should be, but it is not normally possible to anticipate before using mesh whether a patient will have a chronic sub-clinical autoimmune inflammatory reaction to it.

Pain after spinal surgery

Perhaps the single greatest cost of CPSP to the NHS, or indeed any advanced health system, is persistent pain after spinal surgery. One in twenty-five patients undergoing spinal surgery can get an infection at the surgical site, which, even if successfully treated can cause tissue damage resulting in CPSP. Around one in every twenty patients undergoing lumbar spinal surgery develops new numbness or weakness from damage to a spinal nerve or from the formation of scar tissue around it. And up to one patient in every three continues to have pain after surgery or develop problems again within a few years of surgery.

The incidence and cost of treating CPSP after spinal surgery, as well as the incidence of complications after it, are so high that the main medical indemnity societies, the Medical Protection Society and the Medical Defence Union, decided in 2017 to end their cover for spinal surgeons. This withdrawal of cover extended to spinal surgeons only operating in the NHS, meaning they had to rely on NHS indemnity. Spinal surgeons operating privately had to either abandon their private practice or find alternative arrangements.

It will come as no surprise to you that surgeons are not all created equal, and out of the recognition that surgeons differ in their levels of skill and experience grew niche insurance business offering indemnity to spinal surgeons on a personalised basis based on their specific work, experience and claims history. This has meant that some surgeons with a poor claims history have not been able to get cover and are therefore no longer able to operate privately. This is an example of the application of hard data to eliminate surgeons with a high complication rate from patient care. While there may be individual mitigating factors in each case, taken as a whole, is it such a bad thing? However, while they may have been excluded from operating on private patients they will still have NHS indemnity if they operate on patients in the NHS.

Persistent back and leg pain after spinal surgery is so common that it has its own syndrome – FBSS, which is the abbreviation for Failed Back Surgery Syndrome. The financial costs of FBSS in terms of lost income, compensation and treatment are huge. In one US study researchers estimated the cost of FBSS, in 1990 prices, to be $18,883 per year.

When is chronic pain after surgery the result of negligence?

Surgery is not an exact science. Performing operations on the body; making holes in it; putting one’s hands inside another person’s body; permanently changing the anatomy of another human being in order to try to help them is inherently fraught with risks, so it is inevitable that complications will occur. If every factor is the same – same surgeon, same anaesthetist, same patient, and so on – with only the day of the week different, it has been shown that there is a higher chance of death in operations carried out on the later days of the week than on Mondays or Tuesdays.

Looking at the example above of the different incidence of complications between different surgeons doing the same operations, does that mean that the surgeons who can no longer get insurance cover to perform spinal surgery are inherently negligent? Doctors all know who they would see for any particular problem, and conversely who they would avoid. It’s the same in any profession, or indeed any walk of life. Some people are just better at some things than others.

Based on the frequency with which he has won the Ballon d’Or, which for people who are not familiar with football, is the award for the male footballer judged by journalists to have been the best footballer over the previous year, Christiano Ronaldo is currently the best footballer in the world, having won it four times in the last five years. Like some surgeons, he has a set of skills that cannot be matched by rivals, all of whom try every time they go onto the pitch, or into the operating room, to do the best they can.

If, however, he was to pass the ball to his opponents or score an own goal, would that automatically make him reckless? Everything he does on the pitch is watched by hundreds of thousands, if not millions of people both in the stadium and on TV, so his every movement is subject to intense scrutiny. There are no CCTV cameras in operating theatres. Some have suggested there should be but there is no likelihood of that happening in the near future. So, if a patient develops CPSP after surgery it is often not possible for someone who wasn’t in the operating theatre at the time to confidently determine whether it was as the result of a complication that should be accepted, or negligence.

But what kind of complications should we consider acceptable, and at what incidence? Sometimes it is easy to tell if there is evidence of a surgeon or other doctor having knowingly done something reckless. But if one spinal surgeon has a 5% incidence of CPSP due to nerve root injury or scar tissue formation, while another has a 15% incidence, that can take a long time to get noticed. The people most likely to notice something different in the way the two surgeons operate are the surgeon’s assistant in the operating theatre or the scrub nurse, but as we have identified CPSP cannot be diagnosed until the patient has had it for two months or more, so it is only normally picked up at post-operative clinics.

Chronic pain after surgery is often the result of many factors

Unless the outcome from surgery is as binary as life or death after paediatric cardiac surgery, it can be difficult for an expert to determine whether there has been clinical negligence or a complication that should be accepted.

Cases resulting in permanent severe harm to a patient, where clinical negligence is suspected, are infrequently given the forensic microscopic analysis that is often needed to determine what actually went wrong. While attention is inevitably, and rightly, focussed on the surgeon, Contemporaneous environmental factors should also be taken into consideration. It would be wrong to excuse a surgeon if the scrub nurse had kept making errors, or if the ideal equipment had not been available, or if there was too much noise in the operating room so the surgeon was not able to keep concentration, but these factors should be borne in mind. It is of paramount importance that the surgeon be given the optimum conditions to ensure the highest likelihood of a good outcome and the lowest likelihood of a bad one, but as we have seen CPSP can occur as the result of an anaesthetic procedure. And if it arises as a long term consequence of infection it is rarely possible to identify the source.

Surgical site infection can occur as the result of bacteria from the patient’s own body become pathogenic in the wound, such as from organisms commonly found on the skin. When this occurs there could be many reasons for it. The skin wasn’t cleaned properly. The drapes became contaminated at some stage. Some bacteria entered the patient’s blood stream during intravenous cannulation before surgery. Bacteria were in advertently transferred by a member of the scrub team into the wound from an area of skin that had not been prepared. If infection does not come from the patient it could come from the surgical instruments, from a member of the scrub team, or indeed from anyone in the operating room.

The biggest problem with chronic post-surgical pain

One of the commonest complaints of pain specialists when seeing patients with CPSP is that it can take too long for patients to be referred to a specialist Pain Clinic, which means that it takes too long for the referring consultant to recognise CPSP as a problem. The longer a patient is in pain, the lower the likelihood of being able to rid the patient of it completely. Due in part to persistence of the pathology that initiated, and exacerbated by structural changes within the spinal cord, it is frequently the case that patients who have been in pain for months or years before diagnosis ,as is sometimes the case, can never be fully relieved of their pain. Some of these patients may have lost their jobs or relationships before getting to a Pain Clinic. They need multi-disciplinary specialist care from medical consultants, pain psychologists, specialist nurses, physiotherapists and occupational therapists. They need optimisation of their medications, sometimes advanced pain therapy techniques such as neuromodulation, and many are helped by pain management programs.

The most important factor about CPSP, by a wide margin, is to refer on to specialist care as soon as it is suspected, in order to give the patient the best chance of a good outcome.

Dr Nigel Kellow MB BS FRCA MBA

Consultant in Pain Medicine

The Wellington Hospital, London

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