J. De Castro

Pharmacokinetics of opioids

All the opioids have a common chemical structure (Fig. 16): a basic amino group of different length an aromatic moiety a basophilic centre.

Equipment and drug delivery systems

The technical data and illustrations of special regional opioid analgesia equipment mentioned in this chapter, as well as the Tab. 79 to 89 and Fig. 89 to 122 are arranged in groups in Chapter 20. In Chapter 8 are only reported the clinical problems and results due to the equipment and drug delivery systems.

Chronic non-malignant pain

The analgesia obtained with epidural opioid infusion is very helpful for pain control in cancer patients, but the results are far less satisfactory for patients with non-cancer related chronic pain (Harbaugh 1983). This is generally the case if social and psychological factors (anxiety, opioid abuse, insecurity, etc.) play a greater role in pain perception than ongoing tissue injury.

Clinical applications, generalities

Since the first reports on the successful administration of spinal opioids for pain treatment, the literature has given access to a wide variance of clinical situations, where the new method has been investigated. One of the great dangers of a fascinating method is the extreme extent to which it possibly may be used. Post-tonsillectomy pain, sexual dysfunction, postspinal headache are some of the strange indications seen off and on in the literature. Situations, where spinal opioids may act, other methods act as well and are perhaps less dangerous. We have to realize that spinal opioids are not the treatment of choice for all clinical cases with severe pain.

Micropharmacology of antinociceptive substances in the spinal cord

Opioid receptors are distributed through the entire body primarily not to act with injected morphine but to act with endogenous substances which have nociceptive stimuli modulating activity. Those endogenous drugs belong to the group of about 30 neuropeptides, whose members are, among others, endorphins and substance P.

Pharmacodynamics of opioids

Nearly all effects of the opioids (analgesia, sedation, respiratory depression) result from an interaction with a specific opioid receptor. The desired interactions of spinal opioids are those with the spinal receptors. But rostral distribution and effect on brain receptors as a source of undesired actions can neither be completely prevented nor completely excluded.

Other applications in acute pain situations

In ventilated patients with multiple injuries haemodynamic instability is not unusual and each injection of a sedative analgesic combination may be associated with a fall in blood pressure. This effect can be prevented by the use of intraspinal opioids since this technique has a well-established haemodynamic stability (Rawal 1986). The pain treatment of polytraumatised patients by the epidural administration of opioids has real advantages: Compared to the epidural injection of a local anaesthetic, opioids do not produce hypotension with the result that a more objective supervision of the blood pressure values can be made. Contrary to epidural anaesthesia with local anaesthetics the epidural opioid analgesia has the advantage that in most cases a lumbar catheter is sufficient even for thoracic pain treatment (Fromme et al. 1985 b; Hojkjaer et al. 1985; Shulman et al. 1983). Compared to parenteral use of opioids the epidural route does not so much modify the vigilance of the patients. The result is that the clinical changes can be followed more easily.

Technical data of equipment for spinal opioid therapy

In many situations the anaesthesiologist will have the task to select and adapt the already existing equipment in his clinic to the special requirements of the patients, the treatment and the financial costs involved in spinal opioid therapy. That is the reason why we have compiled in this chapter an overview of the equipment, mainly on an objective informative basis. The technical data do not provide any commercial promotion, they are certainly incomplete and the authors decline any responsibility for incomplete or inaccurate information.

Comparative evaluation of the risk/benefit ratio

During the last years there has been very substantial progress in obtaining key pharmacokinetic and pharmacodynamic data to permit rational decisions concerning the safe and effective use of spinal opioid and non-opioid drugs and to decide upon the relative merits of this route of administration, compared with other options for the control of acute and chronic pain (Cousins 1988).

Developments, advantages and drawbacks of regional opioid analgesia

Centuries ago as well as today, opioids have been and still are the cornerstone of severe pain treatment. High specificity of the compounds and possibility of administration by all the classical medication routes provide an explanation for their success (Fig.1a).