Hon. Secretary (2016-17)
ACUTE POST OPERATIVE PAIN
“Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” Pain can be classified patho-physiologically as Nociceptive or Neuropathic. Acute postoperative pain is caused by noxious stimulation due to injury or disease process, or abnormal function of muscle or viscera. It is nearly always nociceptive.
Most patients fear surgery because of the pain one feels after awakening from anaesthesia. The success of a surgical procedure depends upon many factors which includes appropriate pain control, early ambulation and rehabilitation after surgery.
Although the mechanism of pain is fairly understood the level of postoperative pain relief in developed countries is still unsatisfactory. Inadequate pain relief can lead to many complications like immunosuppression ,poor wound healing, adrenergic activation leading to coronary events, decreased mobility causing thromboembolic events, untreated pain leading to chronic pain.
The multimodal concept of acute pain management
The development of postoperative pain is a complex process. During surgery the mediators of inflammation are released like histamine, leukotrienes, prostaglandins, cytokines, bradykinins and others, which intensify hyperalgesia at the surgical site and surrounding tissue. The pain is transmitted from the afferent neurons to spinal cord and higher centre where it is modulated.
The multimodal analgesia involves targeting each of the levels of pain transmission. Non steroidal anti inflammatory drugs and selective Cox 2 inhibitors affect the transduction of pain, regional nerve blocks affect the transmission, opiods, clonidine, ketamine and gabapentin reduce its perception and antidepressants impact the CNS reaction.
- Effective analgesia is an essential part of postoperative management.
- Important injectable drugs for pain are the opiate analgesics. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as diclofenac (1 mg/kg) and ibuprofen can also be given orally and rectally, as can paracetamol (15 mg/kg).
Non steroidal anti inflammatory group of drugs include Cox1 and Cox2 inhibitors which are used as first line of pain relief after surgeries. Paracetamol is a safer analgesic, antipyretic given intravenously 1gm/8hourly in an average built adult.
Generally, the preparation of paraceta¬mol for parenteral administration markedly increased its use as a perioperative analgesic that can be administered to patients who cannot take oral medications. Because the cost of parenteral administration is much higher than that of oral preparations, it is recommended to change the ad¬ministration route to oral as quickly as possible. Paracetamol taken in the therapeutic dose is well tolerated .Paraceta-mol is metabolised predominantly in the liver, and therefore caution should be exercised in patients with active liver disease and long-term alcohol abuse.
Diclofenac, Cox1 inhibitor, is a very good analgesic and anti-inflammatory for perioperative settings. But the severe gastrointestinal side effects and renal complications have limited its use.COX 2 have lesser side effects and have less effect on blood clotting.
Three types of opioid receptors are distinguished:
- MOR (formerly mi — μ)
- DOR (delta — δ) and
- KOR (kappa — κ).
Based on their methods of stimulation, opioids can be divided into: full agonists, characterised by relative selectivity for μ receptors, which reflects their similarity to morphine, partial agonists, which show partial agonism mainly for μ receptors, and opioids of mixed agonistic-antagonistic properties, which interact with more than one class of receptors and can therefore act as agonists for one receptor and as antagonists for the other. The most important opioids used in acute pain management include morphine, oxycodone, fentanyl, nalbuphine, buprenorphine and tramadol.
Morphine is an opioid used to treat severe pain and a standard to determine the action of other opioids administered orally or by injection. Morphine should be applied with caution in individuals with advanced kidney failure because of the possible accumulation of its active metabolite (morphine-6-glucuronide), which can cause respiratory failure.
There are three situations where an opiate might be given:
- intra-operatively and
- Opiate premedication is rarely indicated, although an injured patient in pain may have been given an opiate before coming to the operating room.
- Opiates given pre- or intraoperatively have important effects in the post-operative period since there may be delayed recovery and respiratory depression, even necessitating mechanical ventilation.
- Short acting opiate fentanyl is used intra-operatively to avoid this prolonged effect.
- Naloxone antagonizes (reverses) all opiates, but its effect quickly wears off.
- Commonly available inexpensive opiates are pethidine and morphine.
- Morphine has about ten times the potency and a longer duration of action than pethidine.
- Ideal way to give analgesia postoperatively is to:
- Give a small intravenous bolus of about a quarter or a third of the maximum dose (e.g. 25 mg pethidine or 2.5 mg morphine for an average adult)
- Wait for 5–10 minutes to observe the effect: the desired effect is analgesia, but retained consciousness
- Estimate the correct total dose (e.g. 75 mg pethidine or 7.5 mg morphine) and give the balance intramuscularly.
- With this method, the patient receives analgesia quickly and the correct dose is given.
- If opiate analgesia is needed on the ward, it is most usual to give an intramuscular regimen:
– Age 1 year to adult: 0.1–0.2 mg/kg
– Age 3 months to 1 year: 0.05–0.1 mg/kg
– give 7–10 times the above doses if using pethidine.
Fentanyl is a synthetic opioid whose action is 50– 80 times stronger than that of morphine. The onset of ac¬tion is quick (10 sec. after I.V. administration). The duration of action after the administration of 0.1 mg is 1–1.5 h. Fenta¬nyl is recommended when rapid, efficacious analgesia is required; however, owing to its short action, it should be used in continuous infusions or using PCA. Fentanyl can be used in patients with impaired renal functions because it is metabolised into inactive metabolites in the liver.
Tramadol, one of the weak agonist opioid receptors, is a synthetic analogue of codeine that acts centrally. It can be successfully used intravenously and parenterally for moder¬ate and severe pain. The analgesic potency of tramadol com¬pared with other opioids is as follows:
- tramadol:nalbuphine 5:1;
- tramadol:fentanyl 979:1;
- tramadol:oxycodone 8:1;
- tramadol:morphine 10:1.
Buprenorphine is a partial agonist and is similar to opioids of mixed agonistic-antagonistic properties, such as nalbuphine or butorphanol. The drugs in question are characterised by reduced ad¬dictive potential compared with that of full agonists. The parenteral form of buprenorphine, is rec¬ommended worldwide. In a dose of 5–15 μg /kg, parenteral buprenorphine provides analgesia comparable with that of IV morphine which lasts for upto 13hours.
Although the efficacy of opioids for post-operative pain therapy is undisputable, side effects and possible compli¬cations associated with their use should be considered. One study demonstrated that in 12% of patients who received post-operative opioids developed side effects that were strictly connected with their use and that di¬rectly prolonged their hospitalisations and increased their costs. The higher the doses of opioids, the higher the risk of complications. The complications were more common in certain groups of patients (the elderly, patients with COPD, sleep apnoea, and asthma and obese patients). The only correct strategy to eliminate complications is multimodal preventive analgesia to achieve the effect of reducing the opioid doses.
PERIPHERAL NERVE BLOCKS
The guidelines for post-operative pain management clearly emphasise the importance of multimodal analgesia, the essential element of which should be local anaesthesia (peripheral nerve blocks) whenever possible. The indica¬tions for continuous peripheral nerve blocks for relieving perioperative pain in hospitalised patients and those un¬dergoing ambulatory anaesthesia have expanded greatly. The techniques in question are used not only in patients undergoing upper and lower limb surgeries but also to provide perioperative analgesia in individuals undergoing abdominal plastic, thoracic, urological, gynaecological and trauma surgical procedures.
The protocols regarding local anaesthetics and their adjuvants should take into consideration the patient’s con¬dition before and after surgery, the nature and severity of surgery-related stress and the chances for quick recovery. The use of continuous peripheral nerve blocks allows for decreasing opioid consumption and reducing their adverse side effects, accelerating recovery and in many cases, de¬creasing the length of hospitalisation. Continuous periph¬eral nerve blocks were found to be a safer alternative to epidural anaesthesia in patients who were administered antithrombotic prophylaxis.
The indications for continuous peripheral nerve blocks include the relief of perioperative, trauma-induced, and chronic pain. Over a period of 12 years, the use of peripheral nerve blocks gained popularity for relieving acute post–operative pain after extensive orthopaedic and thoracic surgeries in adults and children, particularly in the context of the multimodal approach to post-operative pain manage¬ment. Moreover, an interest in peripheral nerve blocks is growing owing to their potential anti-inflammatory effects and out of fear of severe complications from using central blocks in patients who are receiving anticoagulants.
The use of continuous peripheral nerve blocks ensures better control of post-operative pain than does PCA and reduces opioid requirements and inci¬dences of opioid-associated complications, enabling earlier ambulation and rehabilitation, reducing hospitalisation lengths and decreasing total treatment costs . The majority of re¬searchers agree that the opioid consumption is reduced by 40–70% when continuous peripheral nerve blocks are used.
ADJUVANTS IN MULTIMODAL THERAPY
The adjuvants in acute pain therapy are the drugs pri¬marily used in monotherapy for other than acute pain indica¬tions but that have been demonstrated to be effective for acute pain relief. Their intravenous or enteral administration is recommended, combined with other analgesics, based on the concept of multimodal analgesia. This diverse group of adjuvants includes ketamine, clonidine, I.V. lidocaine and gabapentinoids.
Amongst NMDA antagonists, low perioperative doses of Ketamine provide effective pain prevention, showing a good safety and tolerance profile; however, continuous monitoring and meticulous post-operative surveillance are necessary.
Clonidine was demonstrated to have opioid sparing ef¬fects; however, its side effects, such as bradycardia and hypo¬tension, limit its use to the selected patients and necessitate widened monitoring and strict post-operative surveillance.
Lidocaine is an amide local anaesthetic characterised by antinociceptive, antiarrhythmic, anticoagulant, anti-in¬flammatory and wound healing properties. It deserves its place among adjuvants. Contrary to the mechanism of action of opioids, the analgesic efficacy of lidocaine appears to be independent of physiological pain transmission pathways and effects on sodium channels.
Pain Control in Children
- Ketamine anaesthesia is widely used for children in rural centres but is also good for pain control.
- Children suffer from pain as much as adults, but may show it in different ways.
- Make surgical procedures as painless as possible:
- Oral paracetamol can be given several hours prior to operation
- Local anaesthetics (bupivacaine 0.25%, not to exceed 1 ml/kg) administered in the operating room can decrease incisional pain
- Paracetamol (10–15 mg/kg every 4–6 hours) administered by mouth or rectally is a safe and effective method for controlling postoperative pain
- For more severe pain, use intravenous narcotics (morphine sulfate 0.05–0.1 mg/kg IV) every 2–4 hours
- Ibuprofen 10 mg/kg can be administered by mouth every 6–8 hours
- Codeine suspension 0.5–1 mg/kg can be administered by mouth every 6 hours, as needed.
The role of Epidural analgesia for postoperative pain relief cannot be over emphasized. It is a safe and effective method of providing post operative pain relief. It reduces the opioid requirements and provides excellent analgesia.
Epidural analgesia — recommended drugs and doses
|L 2-L 3; L 3-L 4
|1–2 ml per segment
|bupivacaine 0.125% or ropivacaine 0.2%
fentanyl 2 μg /ml or sufentanil 0.5–1 μg/ ml flow: 4−8 ml /h
|Abdominal and pelvic surgery
|T 8-T 10
|Titration 5 ml every 10 min
|Thoracic and epigastric surgery
|Centre of surgical incision T 4-T 8
|0.5 ml per segment Saturating dose 5 ml every 10 min
The anticoagulant and anti-thrombotic therapy given peri-operatively limits its use.
|Epidural catheter placement
|Continuous infusion into the epidural space
T 5-T 6
Th 6-T 7
T 7-T 8
|bupivacaine 0.1−0.25% ropivacaine 0.2% + adrenalin 2 μg/ ml combined with fentanyl, bolus 50-100 μg, 0.1−0.2 ml/ h (2−5 μg/ ml)
sufentanil, bolus 20−30 μg, 0.1−0.2 ml/ h (0.5−2 μg/ ml)
|Epigastric and intragastric surgery
T 10-T 11
T 12-L 1
|bupivacaine 0.1–0.25% + adrenalin 2 μg /ml ropivacaine 0.2%+ adrenalin 2 μg /ml combined with fentanyl, bolus 50–100 μg, 0.1−0.2 ml/ h (2−5 μg/ ml)
sufentanil, bolus 20−30 μg, 0.1−0.2 ml/ h (0.5−2 μg /ml)
|Hypogastric and lower limb surgery
|bupivacaine 0.1−0.25% + adrenalin 2 μg /ml ropivacaine 0.2%+ adrenalin 2 μg/ ml
fentanyl, bolus 50−100 μg, 0.1−0.2 ml/h (5 μg /ml)
sufentanil, bolus 20−30 μg, 0.1−0.2 ml/h (1−2 μg/ ml)
ACUTE PAIN SERVICE
There is a need for acute pain service in hospitals now. The APS is co-ordinated by the Anaesthesia department from the recovery and it provides optimal analgesia for the postoperative patients. The goal of the service is to appreciate each patient’s perception of pain and to apply different forms of analgesic therapy.
Role of the Pain squad:
- To improve the post operative analgesia in acute care setting.
- Daily review of patients with PCA epidurals and other acute pain problems.
- Provide education to the staff.
- Carry out quality improvement and collect data on pain relief and complications.
Acute postoperative pain management should target various levels of pain transmission from peripheral nociceptors to the central mechanism for successful analgesia. The better approach is multimodal analgesia which reduces the dependence on a single medication or mechanism and reduce the undesirable side effects of any one modality which was restricting its use.
NSAIDS, OPIODS and ADJUVANTS still form the first line of postoperative pain management. Peripheral nerve blocks and Epidural analgesia added to this armamentarium reduce the opioid requirements. It is beyond the scope of this article to cover different types of peripheral nerve blocks. The article is a brief overview of post operative pain management. Acute pain squad is the need of the hour.