Management of postoperative pain relieves suffering and leads to earlier mobilization, shortened hospital stay, reduced hospital costs, and increased patient satisfaction .Pain control regimens should not be standardized; rather, they are tailored to the needs of the individual patient, taking into account medical, psychological, and physical condition; age; level of fear or anxiety; surgical procedure; personal preference; and response to agents given. The major goal in the management of postoperative pain is minimizing the dose of medications to lessen side effects while still providing adequate analgesia. This goal is best accomplished with multimodal and preemptive analgesia
A multidisciplinary team approach (e.g. acute pain service) is useful for formulating a plan for pain relief, particularly in complicated patients, such as those who have undergone extensive surgery, chronically use narcotics, or have medical co morbidities that could increase their risk of analgesia-related complications or side effects..The preoperative consultation is also an opportunity to discuss pain relief options including invasive techniques such as  epidural , spinal  opioid  and peripheral nerve blocks.Postoperative pain management is an important but undervalued aspect of perioperative care.
Surgical pain is due to inflammation from tissue trauma , patient senses through the afferent pathway, tissue trauma releases local inflammatory mediators that can produce sensitivity to stimuli in the area surrounding an injury ( hyperalgesia )or misperception of pain to non- noxius stimuli ( allodynia). Other mechanisms contributing to hyperalgesia and allodynia include sensitization of the peripheral pain receptors ( primary hyperalgesia  ) and increased excitability of central nervous system neurons ( secondary  hyperalgesia )
Analgesic therapy has  traditionally   targeted central mechanism involved in the perception of pain using opioids, pain receptor can be directly blocked by local anesthetics or NSAID can be used to diminish the local hormonal response to injury, thus indirectly decreasing pain receptor activation. Some analgesics  agents target the activity of neurotransmitters by inhibiting or augmenting their activity ( eg.ketamine, clonidine,paracetamol, garbapentin) Opioids are the corner stone options for the treatment of post operative pain, act on mu receptors  and no anlagesic ceiling,. Nausea ,vomiting, sedation and respiratory depression and pruritus are the disadvantages.
The effect of post operative pain involve all organs ,reduce cough, sputum retention, hypoxemia ,increase myocardial oxygen consumption, ischemia ,delay gastric emptying, reduce gastric motility, constipation, urinary retention, hyperglycemia, protein catabolism, sodium retention, reduce motility , pressure sores, increased risk of DVT and  anxiety and fatigue Persistent noxious input may result in relatively rapid neuronal sensitization and possibly chronic pain Preventing central sensitization preemptive analgesia may reduce acute and chronic pain .
Post operative analgesia includes  Opioids( PCA,PCEA)  ,Neuraxial blocks  (epidural  ,Peripheral nerve blocks  ) Local anesthetic wound infiltration, Continuous wound infusions,  Paracetamol , NSAID including cyclo oxygenase inhibitors,Tramadol/ Tapentadol  ,Alpha 2 agonists ( clonidine, dexomedetomidine ,Garbapentin and pregabalin and Ketamine    .
 Monitoring  includes  level of consciousness,  respiratory rate and depth, standard sedation score, spo2/etco2. All patients with epidurals should be examined daily by a clinician, adequacy of pain releief , level of activity tolerated, any motor blockade, nausea , vomiting , pruritus, hypotension ( assessment of fluid balance ), signs of infection (erythema, swelling,tenderness , discharge ) at the site of epidural catheter placement .
Preemptive analgesia is the administration of analgesics prior to onset of noxious stimuli. Effective preemptive analgesic techniques  use pharmacological  agents to reduce  nociceptor  activation by blocking or decreasing receptor activation and inhibiting the production or activity of neurotransmitters. A metanalysis of randomized trials found significantly Preemptive analgesia reduces postoperative opioid use and opioid side effects. some randomized trials have shown that local anaesthetic  injection around small incision sites reduces post operative somatic pain , but is inadequate for visceral pain.
Neuraxial (regional  analgesia )
For major abdominal surgeries with extensive incision , epidural infusions with local anesthetic provide superior pain relief as compared with conventional parenteral  narcotics.  with less extensive surgery, however, intrathecal  narcotics alone can be used post operative analgesia. A single dose of intrathecally administered narcotic can provide substantial pain relief up to 18 hours after a hydrophilic agent Morphine is injected. The onset of analgesia and its duration depend upon whether the drug is hydrophilic or lipophilic and how it is transported within the cerebrospinal fluid. Intrathecal dose Morphine 0.1 -0.2 mg., Fentanyl 10-20 mics.opioids administered in spinal act through Mu receptors in substantia gelatinosa and suppress the release of neuropeptides from nerve fibres. The combination of PCA and intrathecal opioids  does not increase the risk of respiratory depression over that with either modality alone .
Epidural injection- The dose of morphine is 3 mg for lumbar and lower thoracic epidural ; however , for less painful surgery or high risk patients ,lower doses can provide adequate analgesia with fewer side effects. Epidural morphine 1.5 mg  was as effective as 3 mg for post cesarean delivery pain and was associated with a 60 % reduction in pruritus.
A combination of a local anesthetic and opioid is administered via a Patient controlled epidural pump PCEA,  combination lowers requirement of the dose of each drug as well as the frequency of side effects. Common drugs- bupivacaine 0.125%  or Ropivacaine 0.2 % plus fentanyl 2mcg/ml or hydromorphine 20 mcg/ml.  sufentanyl  has also been used, but expensive without proving any anesthetic or analgesic advantage. A meta analysis randomized trials comparing the efficacy of epidural with local anesthetic alone versus epidural with local anesthetic and opioid concluded that combination therapy was associated with a significant reduction in VAS pain score s on the first post operative day. usually epidural infusions are started prior to completion of surgery to obtain pain relief at the conclusion of surgery.Less commonly , epidurally aministered alpha 2 agonists ( clonidine ) ,NMDA receptor antagonists ((ketamine )and choline esterase inhibitors ( neostigmine ) are used. They are opioid sparing and provide preemptive analgesia that improves postoperative analgesia.
Peripheral nerve blocks , Local anesthetics can also be administered in a selective manner, perineurally, single shot or continuous infusion. Surgical anesthesia 20-30ml of 0.5 % ropivacaine for surgical anesthesia , continuous infusion 0.2 % ropivacaine at a rate of 10ml /hour commonly used.
For post operative chest wall and abdominal pain, paravertebral block can be utilized, multiple spinal levels to be blocked individually to provide effective pain relief.
Patient Controlled Analgesia       PCA empowers patients to take a proactive role in the management of their pain . A sedated patient will not press the button to deliver more opiates  thus avoiding toxicity. Proxy PCA has resulted in over sedation , respiratory depression and even death. Misprogramming of PCA is by far the most frequently reported practice related issue. Even at therapeutic doses, opiates can depress respiration, heart rate, blood pressure , caregivers typically monitor patients at frequent intervals while they are using PCA.
Studies have shown that the use of PCA alleviates anxiety and fear surrounding postoperative pain management; offers slightly better pain control; is associated with greater patient satisfaction; and possibly may alleviate the detrimental physiological responses due to pain
The principles behind PCA involve initially achieving a minimum effective analgesic concentration using a loading dose followed by maintaining a constant plasma concentration, thereby avoiding peaks and troughs. The purpose of the initial loading dose is to achieve a minimal level of analgesia such that pain assessment scores—i.e. scores on a visual analogue scale—are ≤4 (range 0-10); this may be started while the patient is still in the recovery room.
A background infusion is thought to bypass the inherent safety measure that a sedated patient is unlikely to continue ordering bolus doses. It is best to avoid administration of a background infusion because of the concern over respiratory depression.
Among the advantages of PCA over traditional administration of analgesics, either orally or via intramuscular (IM) injection, include improved pain relief, greater patient satisfaction, less sedation, and possibly fewer postoperative complications.
Improper patient selection, inadequate patient monitoring, programming errors, lack of knowledge by the team administering the PCA, drug-interactions, patients’ use of their own home medications,technical problems are some of the issues that complicate PCA therapy.  One of the greatest human factors associated with adverse effects is unauthorized administration of IV bolus doses of an analgesic by well-meaning family, friends, or hospital staff, which is known as PCA by proxy. Family members of patients receiving PCA must be educated about this risk. PCA is not a “one size fits all” or “set it and forget it” intervention.The PCA pump was developed and introduced by Philip H. Sechzer in the late 1960s and described in 1971
PCEA   For PCEA, a typical bolus dose of a local anesthetic is 2 to 5 mL with a lockout interval of 10 to30 minutes. For nonelderly patients, a typical continuous infusion rate is 3 to 10 mL/h, with a slower rate and smaller boluses utilized in older adults.
When comparing IV PCA with an opioid versus PCEA with a local anesthetic and opioid, research has shown that the latter offers superior pain relief .The majority of studies show that the use of a mixture of LA and opioid is associated with significantly better dynamic pain relief after lower or upper abdominal, orthopaedic  and thoracic  surgery than the components of the mixture infused alone.
Additional benefits of PCEA include promotion of early mobilization, improvement of bowel function, shortening of the duration of hospitalization, less sedation, less nausea, and a reduction in cardiovascular morbidity compared with IV PCA. Another possible advantage of PCEA over IV PCA is that PCEA may provide for a more rapid recovery of mental status in older surgical patients with delirium.
Newer version of involving patient activated electrically facilitated delivery of transdermal fentanyl has been introduced for use in  hospitalized  adult patients. Use of single dose hydrophilic opioid may be especially helpful in providing postoperative epidural analgesia when the epidural catheter location is not congruent with surgical incision  (e.g. lumbar epidural catheter for thoracic surgery )- morphine, hydromorphine. An extended release formulation of ( single –dose ) epidural morphine encapsulated within liposomes that results in up to 48 hours of analgesia has recently been introduced.
The use of peripheral regional analgesic techniques as a single injection or continuous infusion can provide superior analgesia to that with systemic opioids.
Ketamine – increasing interest in the use of low dose ketamine for postoperative analgesia (NMDA antagonistic properties ), attenuating central sensitization , reduce morphine 24 hour consumption  and less adverse effects . Low dose ketamine does not appear to cause hallucination and cognitive impairment .  Racemic mixure of ketamine is neurotoxic and it is discouraged for epidural or intrathecal. Surveillance study- ketoroloc didn’t increase in operative bleeding.
Acute Pain Service ( APS )  Analgesia is part of package care. Not only good pain relief is humanitarian imperative, it may also both improve clinical outcomes for patients and save money for health care system. Multi professional education including hospital managerial cadre. Education is key factor in the provision of effective and safe acute pain management The introduction of acute pain services is associated with a decrease in pain scores, the effect of APS on the incidence of analgesic related side effects (nausea  vomiting ), satisfaction and overall costs is uncertain.APS needs dedicated team and provide valuable service at the individual , institutional and societal levels .
Procedure specific analgesia  There is a need for the development of an evidence based approach to reliable , comprehensive individualized analgesic plans for specific surgical procedures.
In ambulatory surgical patients, routine use of acetaminophen , especially when an NSAID is added to the regimen , is recommended to maximize post operative analgesia. The future of post operative pain control in ambulatory surgical patients may include post discharge home use of continuous infusion of local anesthetics or even use of long acting sustained release local anesthetics.
In pediatric patients, use of intramuscular injection is discouraged because fear of  needles., regional anesthetics useful, PCA is useful above 4 years of age , continuous or intermittent intravenous administration of opioids is effective .
In obesity and OSA patients , avoid  the respiratory depressants by optimizing the use of NSAID and epidural analgesia with local anesthetics – based regimen.
Summary
We know that there is no single way to relieve pain ,  Current trend of treating this vital sign is using multimodal management,  It is not permissible to give an excellent anesthesia and neglect post operative analgesia. According to declaration of Montrel, access to pain management is such a fundamental   human right. Use of regional  technique prevent the development of post surgical pain Opioids are considered gold standard for the management of postoperative pain despite its adverse effects.With many advances in pain management for the surgical  patient , surgeons and pain care providers have myriad choices of analgesic pharmacotherapy and analgesic techniques to choose from to provide adequate postoperative pain control for the surgical patient in 21 st century.
However , many factors must be considered before deciding on the type of pain therapy to be provided to the surgical patients. These include the patients co morbid conditions, psychological status, exposure to analgesic therapies and the type of surgical procedure
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3.Patient controlled analgesia and the older patient  US pharm 2013;38(3);HS2-HS6
4.Pain Management after surgery – Anaesthesia and Pain Medicine , 2012;1(3);184-6
5.Recent advances in Post operative Pain Management  Yale Journal of Biology and Medicine   
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6. Miller 7th edition 2010 
7.Safety issues with PCA- Institute of Safe Medication Practices July 2003 March ;83(1);11-2