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Newer techniques of drug delivery:

Trial of spinally administered opioid:

Before implanting a drug, it is essential and a decision to implant should be made only after a positive trial response. Spinal opioid sensitivity should be tested to define the patient's probable acute response to spinal infusions and to suggest the out come likely to be anticipated from long term administration. The daily epidural /intrathecal opioid consumption, the level of activity and sleep, subjective pain scores, the need for additional analgesics and side effects should be recorded. During the trial time, systemically administered opioid medications are needed for break through pain. During the trial, the response to spinal opioid, the need for the addition of local anesthetics or other drugs, the administered route and the success of method can be assessed.

"Which Delivery System"

In general, the delivery system is selected according to the life expectancy

Temporary epidural catheter:

Percutaneous or subcutaneously tunneled epidural and intrathecal catheters are selected for patients with a short life expectancy, inactive patients for whom occasional dislodgement and replacement are preferable to implantation, or patients with severe pain for whom the short-term catheter immediately provides quick access and rapid relief, with further device planning at a future date.

Permanently implanted catheters:

If improved, pain control and decreased side-effects warrant more prolonged therapy, temporary catheters are, usually replaced by permanent implanted catheters within days to weeks. These systems have advantages in terms of sterility, comfort and freedom of movement for the patient. This requires either a port for percutaneous access or an implanted, pump- driven, percutaneously refillable reservoir system. The port system has a resealable membrane capable of withstanding percutaneous injections, and a filter to prevent particulate matter being injected spinally. There are various injection ports available port-a-cath, Spinalgesic, Spinoplast, Periplant, celsite and pharmacia epidural port. Disadvantages of such systems include numerous skin punctures, blockage of the port outlet or catheter, greater expense, the risk of infection and surgical intervention being needed for system placement or removal.

Implantable infusion device:

Indicated in patients with long life expectancy. They are initially expensive but have the advantage of low costs over time. The device is implanted with in the subcutaneous tissues of the anterior abdominal wall or subpectorally, the catheter being sited in the intrathecal or epidural space. The only significant drawback of such a system is usually the low reservoir volume.

Implanted pumps consist of a reservoir system and a pump mechanism. The pump mechanism can be driven either internally (by a lithium battery), externally (by an induction device) or mechanically (being patient operated). Pumps offering continuous plus-on-demand infusion rates are preferable to those with fixed infusion rates because of greater flexibility as 'Tolerance' develops.

Complications: