Opioids for Use in Postoperative Pain Management

Postoperative pain is a good example of acute nociceptive pain, which demands immediate therapy. Aside from peripheral nociceptor activation of the skin and the muscles, by means of traction at the peritoneum and muscles during the operation, also visceral and spastic painful afferences are triggered. Therefore, any sufficient postoperative pain strategy should consider all these origins of nociception. The most simple and effective way to reduce postoperative pain is the installation of local anesthetics at the site of incision [144]. Although not being confirmed in a controlled study, such intervention has been claimed to result in a delay of healing process [145]. In general, however, the expected pain in the postoperative period depends on:

1. The site of the incision,

2. The type of anesthetic being used during operation.

About 74% of all patients following a thoracotomy are in need of an analgesic. After upper abdominal operations 63% and after lower abdominal operations 51% ask for some kind of pain relief. The figure even drops further to 27% when an operation is done on the upper or lower extremities, and following an urological or general surgical intervention up to 36% and 49% respectively will need no analgesic at all [146]. According to Ferrari and coworkers, aside from the site and the size of operation, the type of anesthesia has a major impact on the incidence of postoperative pain. Following anesthesia with the volatile anesthetic methoxyflurane 90% and after halothane, 85% need some kind of postoperative pain management. However, after neuroleptanesthesia, when using the opioid fentanyl, only 50% were in need of an additional analgesic within the first 8 postoperative hours [147]. Especially when using the more potent opioid sufentanil as the main anesthetic intraoperatively, in contrast to fentanyl, the duration of postoperative pain relief is significantly prolonged [148].

In spite of the vast number of potent opioid analgesics available for postoperative pain therapy, over the past decade there has been little improvement in reducing the incidence of postoperative pain. Similar as in 1980 where Cohen and coworkers described an unsatisfactory pain relief in about 75% of all patients having undergone a surgical procedure [145], there has been little improvement in its management over the past years. This is underlined by data from the year 1983 where in spite of all the knowledge on pain transmission and upload receptors being involved in its alleviation, still 41% of all patients complained of insufficient postoperative pain relief [149]. Even in 1990 no improvement in overall pain therapy in the PACU was noted and even today, in 2008 it is suggested that around 40% of all patients unnecessarily still have to undergo pain in the immediate postoperative period [150]. This is supported by data in the literature, which demonstrate insufficient pain relief and its therapy in up to 21%-43% of all patients [151, 152, 153]. Such data should not lead to the conclusion of non-existing potent analgesics for postoperative pain management; it rather implies that other aspects have an effect on the quality of pain management (Figure III-48):

• First and most of all there is insufficient knowledge of the medical personnel in handling potent opioid analgesics.

• There is a non-justified fear of potential side effects from potent opioid analgesics, especially the development of addiction and respiratory depression.

• In addition, there is insufficient knowledge on the duration of action of the different analgesics.

• Lack of use of a non-rating scale (NRS) for determining individual pain intensity results in insufficient monitoring the efficacy of pain strategy.

• No additional alternative therapeutic strategies such as epidural analgesia, regional blocks etc. are integrated in pain management.

• Lack in co-administration of peripheral non-opioid analgesics (e.g. cyclooxy-genase inhibitors) would result in an opioid-sparing effect.

Figure III-48. Hours of despair in the postoperative anesthesia care unit (PACU), a nightmare if not given the proper pain treatment

Although the anesthesiologist, due to his knowledge on the pharmacology of potent analgesics, the type of drugs being used intraoperatively, the patients individual reaction to a specific agent, very likely is the most experienced person to deal with postoperative pain, he no longer is responsible for postoperative pain therapy on the ward (Figure III-49). It is therefore that often in a patient's file recommendations for postoperative pain therapy simply consists of an analgesic given "pro re nata (PRN)". Finally, it is the nurse on the ward who, according to her knowledge and her past experiences, decides when and which analgesic should be given. Common thinking like

• the potential of addiction liability by an opioid analgesic

• the potential of side effects such as ° respiratory depression o urinary retention o extreme sedation

• constipation often results in underdosing the opioid rather than resulting in sufficient pain relief [154, 155].

Figure III-49. The way it should be in the PACU - a care-taker educated in opioid use results in a satisfied patient with no pain
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