Massage application to decrease anesthetic spread in brachial plexus blocks: A cadaveric study
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Introduction: Peripheral nerve blocks of the brachial plexus have become increasingly popular for upper limb surgery due to the benefits of using regional anesthesia. However, anesthetic from supraclavicular nerve blocks can spread medially and anesthetize the phrenic nerve, leading to partial paralysis of the diaphragm, also known as hemidiaphragmatic paresis. The addition of ultrasound guidance has reduced the incidence of phrenic nerve involvement due to the ability to see the spread of anesthetic in real time. There has been little research focused on whether or not ultrasound massage could manipulate anesthetic distally down the arm and away from the phrenic nerve. The aim of this study is to determine if ultrasound massage can be used to minimize the spread of anesthesia medially. Methods: Four fresh frozen cadavers were injected with 15 mls of a 25:75 mixture of methylene blue and 2% lidocaine. The specimens were divided into control (n=4) and massage (n=4) groups. A nurse anesthetist used ultrasound guidance to perform a supraclavicular block. Immediately following injection, the massage group received 5 distally directed massage strokes with the ultrasound transducer. After 15 minutes, both groups were dissected and measurements of anesthetic spread were taken. The medial spread was measured in all four cadavers and distal spread was measured in three out of the four. Results: Spread of anesthetic medially was not reduced in the massage group when compared to the control group. Distal spread of the anesthetic was increased in the massage group when compared to the control group (p< 0.05). Conclusions: The similarity of medial spread between the two groups implies ultrasound massage application will not prevent phrenic nerve palsy any more than a traditional supraclavicular block. The increased distal spread of the anesthetic suggests this technique can improve anesthesia to the brachial plexus by increasing the area the anesthetic travels. Significance: The incidence of phrenic nerve palsy during a supraclavicular block has decreased since the introduction of ultrasound, but some reservations persist when using the technique in non-healthy patients. Phrenic nerve palsy can cause respiratory distress in patients with pre-existing respiratory condition. Given the small sample size, continued study of this method is needed to further evaluate if this method could be used to reduce incidence of phrenic nerve palsy.