Postoperative Pain Management

Perioperative pain relief or postoperative pain management or postoperative analgesia deals with the treatment of pain that occurs after the surgery.

Postoperative pain can be acute that occurs immediately after the surgery or chronic that occurs and continues over a period.

This article mainly concentrates on acute postoperative pain and the term postoperative pain here means acute postoperative pain.

Optimal management of acute postoperative pain requires planning, patient and staff education, and tailoring to the type of surgery and the needs of the individual patient.

Individuals differ in their requirement for analgesia, even after identical surgical procedures and the difference could be eightfold.

Untreated pain or undertreated pain not only gives immense discomfort to the patient but also causes secondary effects of pain like pain with tachycardia, hypertension, vasoconstriction and guarding which could lead to their own list of complications.

For example, uncontrolled tachycardia in an old person could lead to myocardial ischemia and subsequent effects.

Painful abdominal and thoracic wounds restrict inspiration, leading to tachypnea, small tidal volumes, and inhibition of the patient from effective coughing and mobilization. This predisposes to the chest infection, delayed mobilization, deep venous thrombosis etc.

But on the other side, the administration of analgesics beyond the tolerance of patient could increase the risks of side and if greatly in excess, severe central effects like depressed consciousness and respiration.

Opioids were once standard drugs for postoperative analgesia. But the availability of more drugs and increased used of blocks has reduced that reliance on opioids.

Today, postoperative pain relief is multimodal including local anesthetic blocks, spinal opioids, NSAIDs along with other drugs.

A well managed postoperative pain relieves suffering and helps to achieve early mobilization. This has a greater effect on patients’s well being and also reduces the length of hospital stay.

Mechanism of Perioperative pain

Pain results from inflammation caused by tissue trauma. The trauma is caused by surgical incision and dissection or direct nerve injury as in nerve transaction/compression.

The pain is mediated by

• The release of local inflammatory mediators results in
  • Augmented sensitivity to stimuli (hyperalgesia)
  • Misperception of pain to non-noxious stimuli (allodynia)
• Sensitization of the peripheral pain receptors (primary hyperalgesia)
• Increased excitability of central nervous system neurons (secondary hyperalgesia)

Different drugs attack the pain at different sites and thus the role of multimodal anesthesia.

Assessment & Evaluation

This includes preoperative patient evaluation and planning  and includes

• A directed pain history
• Physical examination
• Pain control plan

Quantification of the pain can be done by a pain scoring system like a 10-point pain assessment scale

When Should Analgesia Start?

The pain control drugs should be given before the painful stimulus occurs as it can  prevent or substantially reduce subsequent pain or analgesic requirements [though the unequivocal evidence has not been achieved yet.]

Different Analgesic Drugs Uses in Postoperative Pain Management

Opioids

The mainstay of postoperative pain therapy in many settings is still opioids. Opioids carry their effect by binding to receptors in the central nervous system and peripheral tissues. In the immediate postoperative period, they can be given by transdermal, parenteral, neuraxial, and rectal routes.

Morphine, hydromorphone, and fentanyl are most commonly used drugs.

Butorphanol has also been used with substantial success.

Morphine is the standard choice for because it has a rapid onset of action with peak effect occurring in 1 to 2 hours. Fentanyl and hydromorphone are synthetic derivatives of morphine and are more potent, have a shorter onset of action, and shorter half-lives compared with morphine.

The most important side effect is respiratory depression that could result in hypoxia and respiratory arrest. Hence, regular monitoring of respiration and oxygen saturation is essential in patients on opioids postoperatively.

In addition, nausea, vomiting, pruritus, and reduction in bowel motility leading to ileus and constipation are also common side effects of these medications.

Once the patient is able to tolerate oral intake, oral opioids can be initiated and continued.

Intravenous Patient-Controlled Analgesia {PCA}

This involves morphine, hydromorphone, and fentanyl being administered through the PCA pump. This method of analgesia requires special equipment, which allows the patient to administer the drug as per the requirement. It gives the patient better autonomy and control over the amount of medication used. However, both patients, as well as staff setting up the equipment, require training for proper use. It provides the patient a great satisfaction as the control is with the patient.

Epidural and Spinal Analgesia

Epidural and spinal analgesia act as neuraxial regional blocks and are used extensively in thoracic, abdominal, and pelvic surgery.

In epidural analgesia, a catheter is inserted into the epidural space in the thoracic or lumbar spine and continuous infusion of local anesthetic agent along with opioids results in postoperative analgesia.

A combination of local anesthetic and opioid can be administered via a patient-controlled epidural pump too. this would lower the dose requirements for each individual drug as well as the frequency of side effects.

Insertion of epidural catheters is a specialized procedure and failure of analgesia has been reported in 27-32% cases of lumbar and thoracic analgesia respectively.

Hypotension is quite a frequent problem, necessitating administration of additional IV fluids.

Intrathecal administration of opioid and local anesthetic (0.5% bupivacaine) at induction of anesthesia results in good postoperative analgesia for up to 24 hours. Administration of intrathecal analgesia takes the same time as epidural analgesia during the anesthetic process before surgery but does not need the skilled postoperative care required for the epidural.

NSAIDs

Nonsteroidal anti-inflammatory agents (NSAIDS) form mainstay of non-opioid analgesia.

They are useful in mild to moderate levels of pain. NSAIDs act by inhibiting the enzyme cyclooxygenase (COX) thereby blocking the production of prostaglandins resulting in an anti-inflammatory response.

Ketorolac is an injectable NSAID which reduces narcotic consumption by 25 to 45%.

Ibuprofen, Diclofenac, and paracetamol are other commonly used drugs.

Acetaminophen or paracetamol’s major advantages over NSAIDs are its lack of interference with platelet function and safe administration in patients with a history of peptic ulcers or asthma. Opioid-sparing effects have been associated with paracetamol administered intravenously.

Local Anesthetics

Peripheral Nerve Blocks

The peripheral nerve blocks are effective for postoperative pain control. A nerve block is especially very useful for extremities. The drugs used are local anesthetics and long-acting like bupivacaine can provide analgesia for as long as 12 hours effectively. Lignocaine is the shorter acting drug.

In most of the cases, the peripheral nerve block is given preoperatively and is effective enough for surgical anesthesia too and in the postop period, same takes care of the postoperative pain.

Local Infiltration

This means deep infiltration of the wound edges by a long-acting anesthetic agent like bupivacaine. It is very common in colon and rectal surgeries but now increasingly being used in extremities too.

It reduces the need for other drugs for analgesia for the time it acts. Lysosomal bupivacaine is a very long acting drug and is used in local infiltration particularly.

Drugs Reducing Secondary Hyperalgesia

Ketamine

Ketamine is mainly used as the anesthetic agent. Ketamine is a noncompetitive antagonist of the NMDA receptor when used in subanaesthetic doses. Use of perioperative IV infusions of low-dose ketamine [0.1 mg/kg/hour] with results in improved analgesia and is able to spare opioid, especially in patients after major surgeries that are suffering severe pain.

Pregabalin and gabapentin

These are the alpha-2-delta ligands which were developed for the treatment of neuropathic pain but are effective in postoperative periods in reducing opioid consumption. This beneficial effect can be achieved with a single preoperative dose. In addition, the anxiolytic effect of these drugs should be taken into consideration and might be an additional beneficial factor.

Clonidine and Dexmedetomidine

These are alpha-2 agonists. These, when used in perioperative period decrease pain intensity, opioid consumption, and nausea.

Hypotension and bradycardia are dose-dependent side effects.

References

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