Advances In The Postoperative Analgesia

Pain has been recognized as a problem of global proportions, and postoperative pain is one of the most common types of pain. Post-operative pain is a complex multidimensional conscious experience that incorporates sensory, cognitive, affective and behavioural components.,and that usually occurs in response to tissue trauma.Whereas responses to acute pain may be adaptive, they can have adversely physiologic and psychological consequences that are thought to contribute to organ dysfunction and postoperative morbidity. It has been assumed that sufficient pain relief will improve the surgical outcome with reduced the incidence of postoperative complications and morbidity, need for hospitalization and convalescence, and improve patients satisfaction. There is a common consensus that the optimal pain relief is a prerequisite for early postoperative recovery. So prompt and adequate treatment of acute pain is imperative. Successful pain management requires knowing:the mechanism of pain transmission, the mechanism and acting modes of analgetics, adverse reaction of analgetics,and the approaches of postoperative analgesia. .That is, improved clinical outcomes are dependent not only on the availability of effective drugs but also on theirappropriate utilization. Naturally,all of these above will be summarized below.Mechanism of pain transmission and analgesia: Peripheral nociceptive messages are conveyed by a mosaic of unmyelinated free fibres distributed throughout cutaneous, muscular and articular tissue, and within the visceral walls. They are then transmitted via various nerve endings (polymodal nociceptors) by small diameter A delta and C fibres, which are activated by mechanical, thermal and chemical stimuli,to a spinal level.At different stages of the pain pathway, thus,different control systems constantly modulate the transmission of nociceptive information. Consequently, at a spinal level, activation of the large diameter cutaneous fibres (A alpha et beta) blocks pain stimuli transmitted by the small diameter fibres. Knowledge of the "gate control' mechanism of the posterior horn of the spinal cord is put to practical application in treatments involving transcutaneous electrical nerve stimulation. Furthermore,the body has an endogenous analgesic system that prevents excess pain from interfering with the normal body functions. Depression of pain sensations occurs within the dorsal horn of the spinal cord where the primary pain fibers, which transmit pain sensations from the periphery, synapse with neurons that transmit pain to the higher centers.There appear to be two mechanisms by which the transmission of pain sensations are depressed; these include hyperpolarization of interneurons within the dorsal cord and depressing the release of the neurotransmitters associated with pain transmission.Analgetics: Pharmacologic management is the cornerstone of postoperative pain management. Highly effective analgesia can be provided from a repertoire of 5-10 agents. Opioids are the mainstay of postoperative pain therapy ,and nonopioids,in which there are non-steroidal anti-inflammatory drugs (NSAIDs), local anesthetics, the alpha 2-adrenergic agonists sucu as clonidine, noncompetitive, N-methyl-D-aspartate receptor antagonist ketamine and magnesium sulfate,L-type calcium channel blockers such as verapamil,neostigmine,tramadol and so on,take a adjuvant play in postoperative pain.Rational administration management is dependent on the understanding foranalgesic mechanisms. Activation of the analgesic mechanisms results from an interaction between specific neurotransmitters, such as enkephalin, serotonin, or norepinephrine, and specific receptors located on the neurons that transmit pain. The spinal analgesic mechanisms can be activated by either pain or nonpainful sensations arriving from the periphery or by supraspinal mechanisms. There are three systems associated with activation of the supraspinal mechanisms. These include the opioid system associated with the release of the endorphins, the adrenergic system with the release of norepinephrine, and the serotonergic system with the release of serotonin. The interaction between these systems activates the spinal analgesic system. When the endogenous analgesic systems fail to control pain, analgetics can be used to enhance the endogenous systems. Opiate drugs,for example, interact with opioid receptors and produce analgesia by the same mechanisms as enkephalin, i.e., hyperpolarization of interneurons and depressing the release of transmitters associated with transmission of pain. In addition, morphine can interact with opioid receptors located in the supraspinal structures and activate the supraspinal system. Under inflammatory conditions, furthermore,the anterograde axonal transport of opioid receptors from dorsal root ganglia toward the peripheral sensory nerve endings is augmented. The increased number of opioid receptors leads to improved analgesic effects of exogenously administered ligands and of endogenous leukocyte-derived opioid peptides. In a brief,various factors (e.g., preferred route of administration, time of onset, dosing frequency, side effect profile) influence the choice of individual agents in a drug class,and the concomitant use of other analgesics and nonpharmacologic methods can maximizes pain relief and minimizes the risk of treatment-limiting side effects.The approaches of administration of analgesics that are now available for postoperative pain control include intramuscular, subcutaneous, intravenous, oral, rectal, transdermal or transmuscular administration;regional or local analgesia such as:epidural or intrathecal block interpleural analgesia, peripheral nerves or plexuses block andintra-articular administration. Clearly, any technique that can be used for the surgical procedure will provide near perfect postoperative pain relief if it can be prolonged beyond the time of the surgery and /or can be continued into the postoperative period to provide effective pain relief. Also , commonly used physical agents such as Transcutaneous electrical nerve stimulation (TENS) is effective. Furthermore,patient-controlled analgesia is a more useful technique for the management of postoperative pain.The combination of a newly posed target-controlled technique with patient-controlled analgesia could be a far more prospective approach to postoperative analgesia. Also,there is a new concept in acute pain therapy known as Preemptive analgesia.It can minimize postoperative pain through preventing peripheral and central sensitization. Compelling evidence of the efficacy of preemptive analgesia exists in animal models, and human studies also have produced some promising results. A great deal of research has demonstrated that the modality of administration is far more important than the used type of drugs. Postoperative analgesia is better provided by a combination of two or more analgesic agents or techniques than by a single medication or administration route. This approach,which is known as "multimodal analgesia" or "balanced analgesia.", appears to be particularly valuable in obtaining additive beneficial effects, reducing side effects, or both when analgesia is produced by an action at two different sites or through different mechanisms of action, or when analgesic effects are synergistic.