Postoperative pain and analgesic treatment still remains a challenge in daily perioperative
medicine. Skin incisions, intraoperative tissue retraction and -dissection, intravasal
cannulations and drainages, sternotomy and pericardiotomy are the most important reasons for
postoperative pain. Poorly controlled pain can contribute directly or indirectly to
postoperative complications, such as myocardial ischemia, pulmonary dysfunction like
hypoventilation, pneumonia and atelectasis, a delayed return of gastrointestinal function and
decreased mobility. In addition, prolonged acute pain also results in chronic pain.
Opioids are internationally recognized as the golden standard in the treatment of acute
postoperative pain. On one side, the high potency of opioids in pain relief is clearly
undisputed, but on the other hand, the administration of opioids is associated with nausea,
vomiting, sedation and with the development of bowel dysfunction, which encompasses symptoms
including bloating, abdominal spasm, cramps and constipation. Opioid-induced constipation is
a frequently reported adverse effect and sometimes requires discontinuation of therapy, which
results in analgesic under-treatment, severely impairing quality of life. However, there are
many different regimes for the treatment of postoperative pain using opioids.
Patient-controlled analgesia (PCA) using morphine is widely used, but requires trained staff
and expensive equipment. Once patients are able to tolerate oral medications, the oral route
is preferred postoperatively because it is more convenient, noninvasive and less expensive.