BACKGROUND

Total knee arthroplasty can be severely painful, and peripheral regional anesthesia is highly recommended as part of the perioperative pain treatment. Whether catheter-based techniques are better than single injection techniques are debatable. Furthermore, in catheter-based techniques, whether a low-dose automated, periodic infusion can produce similar analgesic effectiveness compared to a conventional, high dose, continuous infusion has never been explored.

AIM Comparison of the analgesic effectiveness of a low-dose automated, periodic infusion, a conventional continuous infusion and patient-controlled boluses only in catheter-based adductor canal blocks for patients undergoing total knee arthrplasty.

BACKGROUND

Total knee arthroplasty (TKA) is a very common procedure, with more than 600.000 being performed annually in the US alone. This number is expected to increase to more than 3 million by 2030. The procedure is associated with intense, early postoperative pain, and half of the patients report moderate to severe pain the first 2-3 postoperative days (POD). Peripheral regional anesthesia (PRA) using single injection nerve blocks is highly recommended as part of a multimodal, perioperative, analgesic treatment.

Patients who are expected to have postoperative, severe pain exceeding the duration of a single injection nerve block may benefit from a catheter-based nerve block (CBNB) using either a continuous infusion (CI) or intermittent infusions of local anesthetics (LA). Intermittent boluses can be either patient-controlled or prescribed in combination with a continuous infusion or as prespecified intermittent boluses. Whether a CBNB treatment is superior to a single injection nerve block after orthopedic surgery remains unanswered. There are several challenges when using a CBNB treatment: The dosing or delivery method may be either insufficient and thus not pain relieving or too powerful resulting in dense motor block and limb anesthesia which may compromise safety and rehabilitation. The peripheral nerve block catheter may also displace and therefore deposit LA too far from the targeted nerve(s) to produce an effective nerve block.

Previous studies suggest that an automated periodic infusion (API) regimen is superior to CI. It seems that an API produces better pain control, a lower analgesic consumption over time and less motor inhibition. This is welldescribed for epidural catheters for laboring women, but evidence is also apparent in PRA. Adding a PCA bolus option to a catheter-based nerve block treatment may even out the difference in pain scores between API and CI.

However, it seems that API groups require less LA via PCA function. Reducing LA consumption is of great importance for ambulatory patients whose LA reservoir is limited, but also for all other orthopedic patients whose motor block should be minimized in order to optimize rehabilitation.

OBJECTIVES

To investigate whether a low-dose API with patient-controlled bolus option can produce a similar analgesic effect compared to a conventional, high dose, CI with patient-controlled bolus option in catheter-based peripheral nerve blocks for patients undergoing total knee arthrplasty.

Analgesic effectiveness will be compared with a group only given the patient controlled bolus option.

HYPOTHESIS

Low dose API with supplemental patient-controlled bolus option will provide pain-relieving therapy not inferior to a conventional CI with supplemental patient-controlled bolus option. The intervention group receiving patient-controlled boluses only will experience more pain breakthrough.

Inclusion Criteria:

1. Age ≥ 18 years
2. American Society of Anesthesiologists Classification I-III
3. Normal cognitive function in order to sign written, informed consent and to understand trial protocol
4. Agreement to the trial protocol, including the randomized manner

Exclusion Criteria:

1. Allergy to LA
2. Infection in or near insertion site of the peripheral nerve catheter
3. Anatomical abnormalities preventing successful peripheral catheter insertion
4. Habitual use of opioids
5. Pregnancy or breastfeeding (disproved by a negative pregnancy test before trial inclusion)

All patients and outcome assessors will be blinded to the delivery administrations. Investigators will not be present while programming of the infusion pump is taking place. The display of the infusion pump will be concealed at all times after initiation. Furthermore, throughout the trial, the infusion pump will be concealed from the patient through a non-transparent bag. Trial interventions will not be visible in electronic patient charts. The infusion pump is making a discrete noise when administering medications. To make sure that the PCA group and the continuous infusion group is blinded to interventions, a sham administration is activated every 10th hour. This sham administration will be 0.1 mL of ropivacaine 0.2%. Such a small dose of LA will not have any anesthetic effect nor pose a risk for the patient.