Trialing

SECTION 2

UPDATES ON IMPLANTATION ISSUES

Catheter Location

The traditional understanding of CSF circulation has evolved to a more complex model involving oscillatory and pulsatile movements influenced by cardiac and respiratory cycles^80,81. Drug distribution in the CSF is limited to a few centimeters from the administration site, making the placement of the catheter tip critical for therapy success^60,64.

Pharmacokinetic Factors

• Hydrophilic Drugs: Display broader rostrocaudal movement in the CSF, resulting in lower systemic uptake and prolonged spinal analgesia⁶⁵.
• Lipophilic Drugs: Have limited spread in the CSF and are quickly reabsorbed in systemic circulation⁶⁵. Catheter placement near the targeted spinal segments is essential for these agents.

Bupivacaine has a limited distribution at low flow rates and should be administered with a dermatomal approach. For head and neck cancer pain or neuropathic facial pain, in combination with an opioid, catheter advancement as high as the C1 level has been reported^84,85.

For lumbar and leg pain, a classic lumbar approach with catheter tip placement around T9-T10 can minimize migration risks. Retrograde placement may be effective for pelvic cancer pain⁸³, and placement as high as C1 may be appropriate for head and neck pain.

Consensus Point 10: Intrathecal catheter placement should be targeted to the optimal vertebral level to cover spinal segments involved in the neuronal transmission of pain. USPSTF grade A; level of certainty moderate; evidence level IB.

CSF Dynamics and Infusion Strategies

Several studies failed to show any improvement in pain relief when increasing the continuous flow rate of drugs without changing the daily dose and switching from continuous to intermittent bolus administration has shown unpredictable results^94,95,96. This suggests that merely adjusting pump programming does not sufficiently improve drug distribution. Cardiovascular changes, such as heart rate and stroke volume, impact drug distribution in ways that are difficult to predict in clinical settings⁶². A slower infusion rate may reduce cardiovascular effects on drug spread.

There are fewer reported complications when using bolus administration compared to continuous flow at comparable total daily doses⁹⁷. However, bolus administration increases localized concentration (near the infusion site), but not overall spread.

Consensus Point 11: Switching modes of intrathecal catheter delivery from continuous to intermittent bolus may not produce improved outcomes. Impact on safety and efficacy both remain undetermined. USPSTF grade B; level of certainty moderate; evidence level IB.

Pump implantation sites

The standard practice involves placing the pump in the abdominal wall, as it avoids being in contact with clothing or daily movements^98,99. Improper implantation, such as placing the pump too superficially, can result in complications like skin erosion, pump malfunction, or damage from daily activities. Special considerations are necessary for patients with a lower or higher body mass index (BMI), who may face difficulty with placement.

Several studies have explored alternative implantation sites for patients where abdominal placement is not feasible, such as in those with high BMI or complex anatomy. Alternative locations like the flank or anterior thigh have been examined, but these sites are associated with their own set of challenges, including body posture affecting pump positioning and difficulty in maintaining consistent placement^100,101. It is also important to ensure that tubing is properly placed to avoid kinks or other issues, which could interfere with the functionality of the pump.

Consensus Point 12: The traditional implantation site for intrathecal pump placement remains in the abdominal wall. The PACC recognizes that the practice pattern is evolving and that for many practitioners, the buttock/posterior sites and other sites may be applicable and should be considered on a case-by-case basis. USPSTF grade B; level of certainty moderate; evidence level II.