Infusion pumps have been used for years to provide continuous, site-specific analgesia after surgery. Until recently, however, they were only used in the inpatient setting because the pumps were large, heavy and complex. Today, lightweight, user-friendly, portable pumps, in both reusable and disposable varieties, are letting us deliver safe, effective analgesia to our outpatients, even after they"re discharged.

Last year, 200 of our ambulatory surgery patients here at the University of Florida College of Medicine went home with a continuous peripheral nerve block. Here"s what we"ve learned about patient selection, catheter placement, pump and anesthetic selection, and post-op care. We"ll also discuss how portable infusion pumps have helped us convert typically inpatient orthopedic cases, such as total elbow and shoulder surgery, into outpatient procedures.

Many plusses of portable infusion pumps
We use continuous peripheral nerve blocks (administered by a perineural catheter connected to a portable infusion pump) to provide pain relief for a variety of procedures, particularly orthopedic cases, which result in moderate to severe pain that can"t be well controlled solely with oral analgesics.

The blocks offer many benefits.

• Faster discharge. They often let us discharge patients earlier, thereby minimizing the risks that come with remaining hospitalized and letting patients convalesce in the comfort of their own homes.
• Reduced pain. Patients who receive them have significantly lower resting and breakthrough pain scores compared with patients who use oral analgesics exclusively. While some patients may still require oral opioids, they require dramatically less medication to achieve an adequate level of pain relief. Fewer opioids result in fewer side effects, such as nausea, constipation, sedation and pruritis.
• Faster rehab. Patients also achieve target range of motion in their limbs much earlier, which allows for improved rehabilitation.

Home infusion not for everyone
Certain medical conditions make patients poor candidates for ambulatory continuous peripheral nerve blocks. We generally exclude patients with hepatic or renal problems to decrease the risk of local anesthetic toxicity. We also avoid placing interscalene or cervical paravertebral catheters in patients with heart or lung disease because these infusions may cause ipsilateral diaphragm paralysis and decreased ventilation and oxygenation.

There"s also a psychological component to patient selection. Not all patients want, or are capable of accepting, the responsibility that comes with an ambulatory infusion and portable pump. Patients must be comfortable with this equipment, and in many cases, they or their caretakers must be willing to remove the catheter when the infusion is complete (or return to the medical center for a healthcare provider to perform this procedure). We require all of our patients to have a caretaker for at least the first night; and for certain procedures, such as total hip or knee replacement, they must have a caretaker for the duration of the infusion.

Managing patient expectations is very important. We tell patients that the pump won"t relieve 100 percent of their pain, and at some point they may have to give themselves a bolus dose for breakthrough pain. Most patients aren"t intimidated by the pumps at all - they"re generally relieved that they"ll be getting out of the hospital earlier than they normally would, and they feel well-equipped to manage their pain.

Placing the catheter
Our anesthesiologists place the perineural catheters at the beginning of the surgical procedure to administer the surgical block; they"re left in place and connected to the portable infusion pump afterwards. It takes time and training to place these catheters accurately, and there are multiple techniques and equipment for doing so. Depending on the catheter site and clinical situation, we

• use a stimulating or nonstimulating catheter,
• place a bolus of local anesthetic via the needle or catheter, and
• tunnel or use Steristrips to maximize catheter retention.

However, in all cases we first remove any hair with a surgical razor, use copious amounts of benzoin or mastisol, cover the area with an occlusive dressing, and anchor the catheter with a Statlock device (Venetec International, San Diego, Calif.). The initial and any subsequent boluses of local anesthetic include epinephrine to help identify an intravascular catheter.

There"s an ongoing debate on whether stimulating catheters, which provide feedback on how close the catheter tip is to the target nerve, really help improve catheter placement and provide better postoperative analgesia or confer other benefits. To date, there are no published studies comparing stimulating and non-stimulating catheters.

What we look for in an infusion pump
There are many different kinds of portable infusion pumps; and the type we choose for a given situation depends on the clinical scenario. We use both disposable and reusable pumps; for the latter, we provide patients with a stamped, pre-addressed, padded envelope so they can easily return the pump. In general, we use pumps that

• allow for patient-controlled local anesthetic boluses,
• have an adjustable basal infusion rate,
• are easily reprogrammed and
• provide an adequate reservoir volume.

Other considerations include infusion rate accuracy and consistency, as well as reliability, battery life and temperature sensitivity (increased temperature can cause increased infusion rates in some models). Unfortunately, there"s no published data on the reliability of various pump models.

We"ve found that it"s critical to shop around because costs for similar models can vary widely. It"s also important to carefully consider the reusable vs. disposable issue - for a practice that provides ambulatory infusion to many patients, it"s often more cost-effective to invest in a reusable pump and purchase inexpensive disposable cassettes, even if discounted disposable pumps are readily available.

Anesthetic selection and dosing regimen
Bupivacaine and ropivacaine are the most common anesthetics used for continuous peripheral nerve blocks; levobupivacaine and shorter-acting drugs are sometimes used as well. We use 0.2% ropivacaine because it may result in less of a motor block than an equianalgesic infusion of bupivacaine.

The optimal dosing regimen depends on many factors, such as the location of the catheter and type of surgical procedure, but our typical dosing regimen is a basal rate of 5-8 mL/hour, a bolus volume of 2-5 mL and a lockout duration of 20 minutes to 60 minutes.

Post-op care
Patients are ready to go home when they meet all standard discharge criteria and are able to ambulate. We emphasize to patients with lower extremity regional blocks that they mustn"t put weight on the surgical limb. In addition, for all patients with a continuous peripheral nerve block, we ask them to keep any sling or brace on unless required to remove it for physical therapy.

All of our patients and their caretakers receive verbal and written instructions on a variety of issues, including

• infusion pump instructions;
• what to expect when the surgical block wears off;
• breakthrough pain treatment;
• specific instructions to not drive or operate machinery;
• catheter site care (patients must take sponge baths instead of showers)
• limb protection;
• what to do if anesthetic leaks from under the dressing;
• signs and symptoms of possible catheter- and local anesthetic-related complications, including catheter-site infection, catheter migration, local anesthetic toxicity and nerve injury; and
• a catheter removal plan.

All patients receive a prescription for oral opioids, which they must fill before arriving home. Some patients require supplemental pain medication even if the pump works perfectly - and if the catheter dislodges or a pump fails, patients must have back-up pain relief close at hand.

We call patients every day for the duration of their infusion, which usually last two days to five days. In most cases, patients or their caretakers remove the catheters themselves by removing the dressing and gently pulling the catheter out. In our 2003 study (see "Pain Pumps Please Patients"), only 4 percent of patients felt that they would have preferred to return to the surgical facility for catheter removal.

An added responsibility
Experience with perineural catheters, supportive surgeons and staff, and enthusiastic patients have all contributed to our success with continuous peripheral nerve blocks using portable infusion pumps. But success does come with a price - we"ve had to assume 24/7 responsibility for our patients during local anesthetic infusion. We believe, however, that the potential clinical benefits make portable infusion pumps an invaluable part of the comprehensive care we provide to our patients.