SELECTING FACTORS Age alone is not an exclusion criterion, but the patient should be able to understand and follow through on block-related education about post-op care.

Who's a candidate for continuous peripheral nerve blocks? The real question is who isn't? Anatomy and age are rarely limiting factors. Your anesthesia provider can insert a perineural catheter adjacent to nearly any nerve identifiable by ultrasound. And perineural infusion isn't limited to a specific age group. There have been reports of at-home CPNB use in infants and patients approaching 100 years old.

But the ability of patients and their caregivers to be educated about post-op care is absolutely critical. And because of their intrinsic risks, you should reserve continuous blocks for

• surgical procedures that you expect to result in pain not easily controlled by less-invasive analgesic techniques, such as oral analgesics and cooling or heating pads; and

• patients who'll benefit from CPNBs or who are intolerant to alternative analgesics (for example, they experience opioid-induced nausea).

There are few contraindications to in-facility CPNBs, such as infection at the catheter insertion site. But because patients are rarely directly monitored outside of the hospital — and not all patients desire or are capable of accepting the additional responsibility of caring for the catheter and pump system — patient selection criteria must be more stringent for ambulatory CPNBs.

To avoid local anesthetic toxicity, exclude patients with renal or hepatic insufficiency from outpatient perineural infusion. For infusions possibly affecting the phrenic nerve and weakening the ipsilateral diaphragm (interscalene and paravertebral catheters, for example), use caution among patients with heart or lung disease and in obese patients who may not be able to compensate for mild hypoxia or hypercarbia.

Limited evidence indicates that the risk of nerve injury from prolonged local anesthetic exposure may be increased in patients with diabetes or preexisting neuropathy — something to keep in mind, though not a deciding factor, when selecting CPNB candidates.

HIDE AND SEEK Ultrasound-guided catheter insertion has been demonstrated to greatly reduce catheter insertion times, compared with older insertion modalities.

The case for CPNBs
Benefits may include decreased supplemental opioid requirements, opioid-related side effects and sleep disturbances, thus decreasing required nursing interventions. In addition, time until discharge may be decreased with ambulatory infusion, reducing facility and personnel costs, freeing additional post-op beds and permitting an increased surgical volume.

Providing analgesia is the primary indication for post-operative CPNB, and most CPNB benefits appear to hinge on successfully improving pain control. Potent analgesia is most dramatic for surgical sites that are completely innervated by nerves affected by the perineural infusion, as is often the case for shoulder and foot procedures (interscalene and sciatic perineural catheters, respectively).

Drawbacks include increased expense (if paying out-of-pocket), additional equipment to carry (infusion pump and local anesthetic reservoir) and — for ambulatory patients — catheter removal at home. Fortunately, infusion-related serious and lasting injuries are uncommon, and relatively minor complications occur at a frequency similar to single-injection peripheral nerve blocks. Still, it's necessary to be knowledgeable about these potential complications.

During the perineural infusion, more-common (and benign) complications include catheter dislodgement or obstruction and fluid leakage at the catheter site. Additional possible complications include infusion pump malfunction, undesired pause or disconnection, skin irritation or allergic reactions to the catheter dressing and liquid adhesive, and catheter-induced brachial plexus irritation.

In addition, a CPNB-induced insensate extremity may prove disconcerting to patients. It may impede physical therapy or ambulation, and is considered a risk factor for injury by some investigators. You can also pause the infusion pump until sensory perception begins to return, then restart the infusion at a lower basal rate. Conversely, inadequate analgesia or breakthrough pain may occur. They are often treated by increasing the basal infusion and providing patient-controlled bolus doses. Give patients clear post-op instructions on these topics, and have a contact person and plan in place to handle either of these occurrences.

Perineural infusions affecting the femoral nerve correlate with patient falls after hip and knee arthroplasty, possibly due to CPNB-induced sensory, proprioception or quadriceps weakness. Consider interventions that may decrease the risk of falls, such as limiting the local anesthetic dose or mass; providing crutches or walker and a knee immobilizer during ambulation; and educating surgeons, nurses, and physical therapists about possible CPNB-induced deficits and fall precautions.

Implementing your program
Without surgeon buy-in, perineural infusion is a non-starter. Surgeons must understand and accept that there will be drawbacks in addition to the benefits to their patients. Just as there are risks associated with every surgical procedure, there are risks associated with CPNBs. If the CPNB program is terminated after the first CPNB-related complication, there's no point in even starting the program.

The surgeon should introduce patients to CPNBs during the initial discussion of the surgical procedure and perioperative period. Details of the specific risks and benefits should be introduced in the anesthesia pre-op clinic to provide informed consent and prevent delay of the surgical start on the day of surgery. The person checking patients in should have a list of the patients expected to have CPNBs so that these individuals can receive priority upon check-in, allowing for perineural catheter insertion without surgical delays.

If there is a healthcare provider who can insert perineural catheters before entering the OR, the procedure will not delay surgical start times. Regard-less, ultrasound-guided catheter insertion has been demonstrated to greatly reduce catheter insertion times, compared with older insertion modalities.

The recovery room nurses should be trained to prepare and program infusion pumps and initiate infusions, as well as to provide patients or caretakers with instructions regarding the catheter and pump. A healthcare provider — often one of the recovery room nurses — should call ambulatory patients daily (typically in the morning, before the busy midday and afternoon) until catheter removal, which may be done by patients or caretakers following written or oral (during post-op phone calls) instructions.

Knowledge is power
Patients must understand the potential risks and benefits of CPNBs, and act on post-op instructions to prevent untoward outcomes. For lower-extremity infusions, warn patients of the risk of falling. Make sure patients have a thorough grasp of the following:

• how to pause the infusion pump if their toes or fingers become completely numb (and how to restart the pump at half the basal rate when they regain feeling in those extremities),
• how and when to adjust the basal infusion rate,
• how and when to administer a patient-controlled bolus dose, and
• how and when to remove the perineural catheter (and dispose of the portable infusion pump).

Always provide patients with oral instructions, written instructions, and — most critically — the ability to contact a healthcare professional at any time for catheter- or pump-related questions and concerns. This support structure is vital to a safe and successful ambulatory CPNB program.