Pain Management Chronic Pain Adverse Effects Of Analgesic Medications Notes

Pain Management  Introduction

• Pain is a sensation of discomfort associated with injury. It can be acute or chronic. Acute pain (nociception) is associated with tissue damage and an inflammatory response, it is self-limiting and of short duration. Often it does not involve neural tissue.
• Chronic pain, however, persists long after the tissue damage is treated. Chronic pain, on the other hand, is the pain which persists even after 3 months of surgical illness. In surgical patients, it can be due to postoperative pain, malignancies, or diseases such as chronic pancreatitis.

Read And Learn More: Basic Principles Of Surgery Notes

Principles Of Providing Postoperative Pain Relief

• One of the main fears patients have about surgery is the postoperative pain and it is only humane that this is relieved. In addition, pain has adverse effects on various systems of the body such as tachycardia, hypertension, arrhythmias, and rarely even myocardial ischemia and infarction.
• The patients may not breathe properly leading to retained secretions because of inadequate cough, atelectasis, pneumonia, and respiratory failure. Hypertension can precipitate bleeding, e.g. after thyroidectomy.
• Pain relief can be given in many ways but it must be tailored to the patient since pain medications have adverse effects and hence, safety must be ensured at all times.
• The pain prescription must contain clear instructions regarding the name of the drug, dose, route, frequency, monitoring required, treatment for known side effects such as for nausea and vomiting, and when to call the duty doctor.

The Pain Pathway

• Postoperative pain varies with the patient’s tolerance to pain, type of surgery, anaesthetic and site, and extent of incisions given. The pain may be somatic, visceral, or both. It is important to understand how pain is transmitted and appreciated by the body to treat it effectively.
• Pain is produced in the injured tissue due to the release of prostaglandins, serotonin, substance P, and acetylcholine which stimulate the peripheral nociceptors (transduction).
• These stimulate the peripheral nerve supplying the area and the impulses are transmitted through it to the dorsal horn of the spinal cord (transmission). These impulses then travel through the ascending tracts to the thalamus (transmission) and the sensory cortex where the pain is perceived (perception).
• The perception of pain can be inhibited by stimulating the descending inhibitory pathway and release of inhibitory neurotransmitters such as GABA, glycine, opioid peptides, and norepinephrine (modulation). Generally, acute postsurgical pain can be controlled by addressing each component of this pain pathway and hence it is called multimodal approach to pain control.
• Transduction is reduced by local anaesthetic infiltration (e.g. bupivacaine) and the use of nonsteroidal anti-inflammatory drugs. Transmission through peripheral nerves can be blocked by nerve blocks (transverse abdominis pain block for abdominal surgery). Transmission through the spinal cord to

Pain Mechanisms and Medications:

1. Mechanism Medications
2. Transduction Local anaesthetic infiltration, NSAIDs
3. Transmission Local anaesthetics (nerve blocks, epidural)
4. Perception Opioids, alpha2 agonists
5. Modulation Opioids, alpha2 agonists, NMDA receptor antagonists

ascending pathways can be inhibited using epidural analgesia. Opioids (morphine, fentanyl, tramadol, nalbuphine) reduce perception.

• They also have a modulating effect on pain perception through their effects on the µ receptors in the brain as well as spinal cord.

Assessment Of Pain

• Pain is totally a subjective phenomenon. The patient knows by his experience about nature of the pain and other related features. Example: Any severe pain in the abdomen results in vomiting. Thus, one can deduce that the pain is severe.
• Each person may respond differently to the pain. When a patient says he has pain, he probably has pain and must be believed. He can simply rate it as none, mild, moderate or severe.

Assessment Of Pain Numerical rating score (NRS):

In this, whenever the patient has pain, he can be asked to rate the pain on a scale numbering from 0 to 10, where 0 means no

pain and 10 represents the most severe pain they can imagine. The patient can then be followed up using the same scale to gauge whether severity of the pain has changed or whether the analgesia provided is sufficient.

• Pain score <3 is acceptable. NRS of 10: Very severe pain: Ureteric colic, mesenteric ischaemia or dissecting aneurysms, etc.
• NRS 4–6 Moderate pain, e.g. acute cholecystitis or appendicitis
• NRS 2–3: Dull aching pain, e.g. hepatomegaly or splenomegaly

Assessment Of Pain Visual Analogue Scale (VAS):

• In this, the patient is shown a 10 cm long scale, where one end represents no pain and the other end (10 cm) represents very severe pain.
• However, unlike the NRS, the patient is not shown any number in between and the patient slides a rider across the scale to point out the level of his pain.
• The numbers are present on a continuous scale on the side facing the investigator and can be in fractions.

Assessment Of Pain Wong-Baker FACES scale:

This scale consists of a series of faces, where one end has a happy face representing no pain and the other end, a face depicting severe pain. This is particularly useful for older children.

Routes Of Administration Of Analgesia

Pain medications can be given by various routes.

Routes Of Administration Of Analgesia Oral route:

• This route is a common method of providing postoperative analgesia for day care surgeries. A combination of a mild opioid such as codeine or tramadol along with paracetamol gives good pain relief for superficial surgeries such as hernia repair or breast lumpectomy.
• The oral route can be used only after the patient is able to take orally after surgery and thus would not be feasible in the immediate postoperative period after surgery on the bowel, etc.
• It is also not suitable for patients who are still sedated, not regained their ability to swallow and are at risk of aspiration. They may also have postoperative nausea and vomiting.

Routes Of Administration Of Analgesia Intramuscular route:

• Regular injections of intramuscular opioids used to be given for postoperative pain relief. Although the analgesia might last longer than intermittent intravenous opioids, repeated intramuscular injections are not pleasant and must be avoided.
• Subcutaneous route: To avoid the pain of repeated intramuscular injections, a cannula can be inserted subcutaneously, usually in the deltoid region and intermittent injections can be given subcutaneously through this cannula. However, absorption of the medications can be unreliable.

Routes Of Administration Of Analgesia Intravenous route:

• For patients who have undergone major surgery and are in-patients, postoperative analgesia is given very commonly by the intravenous route. This may be given intermittently on a regular and ‘as required’ basis by the nurse.
• A continuous infusion is better for the immediate postoperative period for a patient who has undergone major surgeries. These patients must be closely observed for any complications including respiratory depression and hypotension.

Routes Of Administration Of Analgesia Epidural analgesia:

This involves insertion of a thin plastic catheter into the epidural space before surgery. Infusion of dilute solution of local anaesthetic (0.25% bupivacaine or 0.2% ropivacaine) either alone or in combination with an opioid (usually fentanyl at 2 µg/ cc) provides excellent analgesia. The patient is not drowsy, is more comfortable and outcomes are better.

Routes Of Administration Of Analgesia Patient-controlled analgesia (PCA):

• This method is by far the most preferred and safest of the different approaches. By definition, the patient himself/herself administers the medication when he/she thinks pain

 

relief is required. This can be used for either intravenous route or the epidural route, although the drugs and dosages will differ with the route.

• This requires an electronic pump which can be programmed by the pain nurse or the anaesthetist. They can set the amount of bolus of the drug to be delivered, the minimum mandatory interval before which another bolus cannot be given (lock-out period), and the hourly maximum dose.
• The pump is fitted with a trigger button, which when pressed will deliver the drug to the patient. To ensure safety, only the patient is allowed to press the button, and no one else (nurse, parent, relative, etc. not allowed).
• Thus, if a patient has been administered a bolus unless he is awake enough to press the button, he would not get another dose. This increases safety.

Adverse Effects Of Analgesic Medications

• Provision of analgesia after surgery is humane and a necessity. However, it has to be titrated to the patient. The type of analgesia given to a patient will vary with the surgical procedure, patient consent, presence of comorbidities, and facilities available at the hospital.
• Superficial and keyhole surgeries are associated with less pain compared to open major body cavity surgeries. A multimodal approach helps in reducing the amount of each medication and adds safety and efficacy to the treatment.
• The patient must be monitored closely for any adverse effects due to these medications. Common adverse effects attributable to opioids are respiratory depression, hypotension, and bradycardia. Epidural narcotics can produce pruritus as well.
• Local anaesthetics when given epidurally can cause hypotension and urinary retention. The patients must be monitored closely postoperatively and documented.

Chronic Pain

• When pain persists beyond three months of injury, it is termed chronic pain. While, in acute pain, the injured tissue is the source of pain; in chronic pain, the injured tissue might have ‘healed’ but the pain persists. This is due to plasticity of the spinal neurons and a phenomenon called wind-up.
• In this situation, an impulse that is normally painless also can become painful. Features of chronic pain include hyperaesthesia, hyperalgesia (increased sensitivity to touch and pain), and allodynia (stimuli that are not normally painful are sensed as painful). It can be debilitating and can affect healthrelated quality of life.

Types of Chronic Pain

Chronic Pain Neuropathic pain:

• This type of pain is burning or shooting in nature. It can occur due to irritation of a nerve or due to entrapment of nerves. Diabetic neuropathy in the foot can produce neuropathic pain with tingling and numbness. Chronic groin pain after inguinal hernioplasty and mesh repair is not uncommon (10 to 15%). It may be due to ilioinguinal or genitofemoral nerve irritation or entrapment by mesh fibrosis or sutures.
• Thus, when performing mesh removal after a previous Lichtenstein repair, it is recommended to remove as much of the mesh as possible (preferably all mesh material) together with triple neurectomy anterior to the annulus, i.e. outside of the abdominal cavity without dissection behind the transversalis fascia.

Chronic Pain Nociceptive pain:

• A nociceptor (pain receptor) is a sensory neuron that sends pain signals to the spinal cord and the brain as a result of damaging or potentially damaging stimuli. This pain occurs due to actual tissue injury, example. burns or bruises.
• These receptors are present in the skin and in the central nervous system. As a result of stimuli, the cutaneous nociceptors are activated leading to exaggerated response in the dorsal horn of the spinal cord.

Chronic Pain Psychogenic pain:

This is due to depression. This depression will add to any illness resulting in chronic pain.

Chronic Pain Musculoskeletal pain: This occurs due to excessive activity of muscles or consequent to injury to muscles or ligaments, e.g. back pain, myofascial pain.

Chronic Pain Inflammatory pain: Autoimmune disorders such as rheumatoid arthritis or gout can be associated with joint pains as they get involved due to the disease.

Chronic Pain Mechanical pain: Pain experienced by patients with malignant conditions is often due to expanding malignancy and involves stretch or compression of surrounding tissues, nerves, blood vessels, or bone.

Management of Chronic Pain

 Patient evaluation:

• A thorough history must be taken regarding the onset, characteristics, site, side, severity, etc. of the pain and associated symptoms.
• Unlike acute pain, it is important to also note how much this pain is interfering with the patient’s daily activities.
• Structured questionnaires (McGill Pain Questionnaire) are available to document all aspects of this assessment. A detailed physical examination, especially neurologic examination must be done.

Chronic Pain Treatment

This includes pharmacologic, nonpharmacologic, adjunct therapies, and interventional treatments when they do not respond adequately to these.

Pharmacologic Treatment of Chronic Pain

The WHO has advised Step-Ladder pattern for the use of medications to treat chronic pain.

The WHO three-step analgesic ladder states as follows:

1. Step 1 (mild pain with NRS 1–4): Treated with acetaminophen and adjuvants as required.
2. Step 2 (moderate pain with NRS 5–6): Milder analgesics such as hydrocodone, oxycodone, tramadol, nonopioid analgesics, and adjuvants can be used.
3. Step 3 In patients with severe pain (NRS 7–10), strong opioids such as morphine and fentanyl can be used in addition to those mentioned above.
   1. Morphine is usually given in the form of tablets or liquid every 4 or 6 hours. Slow release-enteric coated morphine is also available.
   2. Nausea and constipation are common complications. Morphine can also be given subcutaneously if pain is severe.

First-line Therapy:

• For musculoskeletal pain includes nonsteroidal anti-inflammatory drugs and paracetamol. NSAIDs act by inhibiting the enzyme cyclooxygenase (COX), thereby blocking the production of prostaglandins.
• They may be contraindicated in patients with stomach ulcers and renal dysfunction. Adjunctive therapy includes capsaicin cream or lignocaine.
• First-line drug for neuropathic pain is gabapentin or pregabalin. They prevent the reabsorption of neurotransmitters called serotonin and norepinephrine.
• They also reduce spontaneous neuronal activity. The addition of antidepressants such as amitriptyline can be helpful. Carbamazepine may be especially helpful in trigeminal neuralgia.

Second-line drugs

• Include opioids. In more severe cases—example: Pain of chronic pancreatitis—oral preparations of morphine can be used. Fentanyl and buprenorphine cutaneous patches are also available.
• When patients have neuropathic and nociceptive elements, tapentadol can be used. It is an opioid with norepinephrine reuptake inhibition.
• Side effects of opioids such as constipation are less with this drug. However, the benefit of pain relief must be weighed against the possible side effects such as dependence, constipation, respiratory depression, etc.
• For this reason, adjunctive therapies must be tried first and opioids must be used with caution in patients, particularly with nonmalignant conditions.

Nonpharmacological

• Options include heat and cold therapy, relaxation therapy, ultrasound stimulation, acupuncture, physical therapy, occupational therapy, and TENS units.
• Interventional techniques such as epidural steroid injections, radiofrequency nerve ablations, nerve blocks, and trigger point injections can be used to treat chronic pain.
• Transcutaneous nerve stimulators and acupuncture increase the levels of endorphin production in the central nervous system.
• In trigeminal neuralgia, nerve decompression is a better option by doing craniotomy than percutaneous coagulation of the ganglion.

Adjuncts

Adjuncts Neurolysis:

• It refers to division of neural fibres, e.g. coeliac plexus blocks with alcohol in pancreatic cancer and gastric cancer.
• Anti-oestrogen drug such as tamoxifen 20 mg tablet in carcinoma breast and anti-androgen cyproterone 50/100 mg tablets in carcinoma prostate for disseminated metastasis are used.
• They also relieve bony pain. Both these drugs are antipituitary, avoiding pituitary ablation surgery.

Adjuncts Infusion of diamorphine:

• Various routes can be used: Intravenous, subcutaneous, intrathecal, or epidural. Pain is a symptom when acute and borders on to disease when chronic.
• If acute pain is well-addressed, the likelihood of chronic pain is much reduced. If chronic pain occurs, prompt treatment may be sought so that healing can be faster. Good pain relief will be taken as a blessing.