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PROBLEM SPOT Mr. MacKinnon places an "iPACK" block, which can decrease posterior knee pain without masking a peroneal nerve injury.The problem spot for patients having total knee arthroplasty: the back of the knee. While regional nerve blocks have revolutionized pain control for total knees, until recently they've fallen short when it comes to easing pain in the back of the knee.
PROBLEM SPOT
What Is the 'iPACK' Block?
ON TARGET The goal of an "iPACK" block is to insert the block needle in a medial to lateral direction between the popliteal artery and the femur.The "iPACK" is an ultrasound-guided infiltration of the interspace between the popliteal artery and the capsule of the knee with a local anesthetic solution that provides an alternative analgesic when combined with a femoral nerve block. The new nerve block may provide an effective option for controlling posterior knee pain following knee replacement surgery.
Pain relief following knee replacement surgery has typically been concentrated in the anteromedial aspects of the knee, with little relief for the posterior. Femoral nerve blocks cover the femoral nerve and adductor canal blocks cover the saphenous nerve. Blocking the sciatic nerve, which is what provides innervation to the posterior of the knee, is dangerous, because it may cause foot drop and thus mask a surgically induced peroneal nerve injury caused during surgery. Thankfully, a new regional technique with a catchy name has proven to effectively control posterior knee pain.
Posterior pain
I augment each of my blocks with an "iPACK" (infiltration between popliteal artery and capsule of knee) block and have seen a significant reduction in post-op posterior pain.
As the name suggests, the local anesthetic is placed between the posterior capsule of the knee and the popliteal artery. Here, only the terminal sensory branches of the tibial nerve innervate the posterior knee joint. It is the posterior articular nerve of the tibial nerve that crosses the posterior capsule at the level of the oblique popliteal ligament and supplies the capsule and meniscal synovial junction, cruciate ligaments and the infrapatellar fat pad. This distribution makes it clear that if adequately blocked, the terminal sensory branches of the tibial nerve should significantly decrease posterior knee pain without potentially masking a peroneal nerve injury.
Step by step
Here's how to administer an iPACK block:
- Have the patient in the prone position.
- Scan with the ultrasound probe in the popliteal fossa, just proximal to the crease, so you find the femoral condyles.
- From there, move proximal until you can see the shaft of the femur and the popliteal artery. The goal is to insert the block needle in a medial to lateral direction between the artery and the femur.
- In this area, place 20 to 30 cc of local anesthetic (0.2% ropivacaine).
A previous problem spot
One study (osmag.net/QKu3qK) found that combining adductor canal and iPACK blocks improved physical therapy and reduced hospital length of stay for total knee patients. I now use both blocks for all of the total knees I work on, and patients who've previously had total knees with only femoral blocks say they're amazed by the improvement. OSM
Anesthesia News and Notes
- FDA Finally Approves Neuromuscular Blockade Reversal Drug. After a long uphill battle, the makers of sugammadex, which can be used to reverse neuromuscular blockade induced by rocuronium or vecuronium, finally have permission to sell their drug in the United States. Marketed as Bridion, the drug has been used in at least 70 other countries for years, but Merck and Co., which acquired it as part of a merger in 2009, has had to overcome numerous hurdles to gain FDA approval. The FDA first rejected Bridion in 2008, citing concerns about allergic reactions and increased risks of bleeding. A further series of setbacks followed in 2013, as the agency questioned clinical studies and expressed concern that the drug might trigger hypersensitivity. Hopes that the drug would be approved early in 2015 were dashed when the FDA announced that it wanted to conduct additional site inspections. Approval, which finally came in December, followed 3 clinical trials and a randomized, double-blind, parallel-group, repeat-dose trial. Of the 299 participants in the latter trial, one had an anaphylactic reaction. There have also been cases of marked bradycardia resulting in cardiac arrest. Patients should be closely monitored for hemodynamic changes during and after reversal of neuromuscular blockade, says the FDA (osmag.net/6oRgUH), and treatment with anticholinergic agents, such as atropine, should be administered if clinically significant bradycardia is observed.
- New substance a gift from above? An amino acid that literally fell from the sky shows promise as an alternative to opioids for anesthesia and procedural sedation, according to a new study published in Anesthesia & Analgesia (osmag.net/Bht6ZT). Isovaline, which was contained in a meteorite that landed in Australia in 1969, and which has since been synthesized, acts only on peripheral neuroreceptors outside the central nervous system and does not cross the blood-brain barrier. When administered to mice in combination with propofol — as an alternative to the combination of fentanyl and propofol — isovaline produced both general anesthesia and conscious sedation without increasing the risks of respiratory depression or other adverse events, leading researchers to conclude that its margin of safety may be considerably higher than that of fentanyl.
- Answers make for better questions. Do you give patients brochures about their anesthesia options? If so, they're likely to be more knowledgeable and engaged, finds a study presented at Anesthesiology 2015. A comparison of 59 patients who weren't given brochures and 67 patients who were, found that the latter group were significantly more likely to discuss their anesthesia choices and ask questions about regional anesthesia. Additionally, the brochures, which explained risks and benefits of different types of anesthesia, and which included space for questions and notes, did not increase anxiety and uncertainty.
"Clearly, more information is always helpful," says Karen L. Posner, PhD, of the Department of Anesthesiology and Pain Medicine at the University of Washington, who presented the findings. "Helping patients understand their choices allows them to feel fully prepared to discuss their options and make a mutually agreed upon decision in partnership with their physician anesthesiologist."
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