Department of Anesthesiology, Box 604, University of Rochester School of Medicine and Dentistry,Strong Memorial Hospital, 601 Elmwood Avenue, Rochester, NY 14642, USA E-mail: Paul_Bigeleisen@urmc.rochester.edu
Accepted for publication: May 4, 2003
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Abstract |
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Br J Anaesth 2003; 91: 916--17
Keywords: complications, anatomic variation; nerve, phrenic; neuromuscular block, supraclavicular
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Introduction |
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The patient was sedated with fentanyl 100 µg and midazolam 2 mg. His neck was then washed with alcohol and the nerve stimulator (B Braun, Bethlehem, PA) was set at a current of 0.5 mA, a frequency of 2 Hz and a prefixed pulse width of 0.1 ms. The patients head was turned toward the left and his sternocleidomastoid muscle was identified by having him lift his head off the pillow. The authors index finger was placed posterior to the clavicular head of the sternocleidomastoid muscle and rolled laterally into the groove between the anterior and middle scalene muscles. This groove was traced distally to a position inferior to the omohyoid muscle. After identifying the appropriate landmarks, a 50 mm, 22 gauge insulated needle (B Braun, Bethlehem, PA) was advanced in a coronal plane posterior to the subclavian artery until a motor reponse caused supination of the patients forearm. Simultaneously, the patient reported paraesthesia in his right thumb and the author noticed a motor response in the patients abdomen at 2 Hz.
The current was decreased to 0.2 mA. After this, the motor response in the patients forearm disappeared but the diaphragmatic twitch persisted. The latter was assumed to result from direct stimulation of the patients right phrenic nerve. It was assumed that the block needle was mistakenly placed anterior to the scalenius anticus muscle, and that the motor response in the patients forearm was from current leak across the plexus sheath rather than from direct stimulation of the plexus roots themselves. For this reason, the needle was removed. The landmarks in the patients neck were reassessed and the needle inserted several millimetres posterior to the original puncture site. The results were similar, a paraesthesia in the hand, supination of the forearm and motor response of the diaphragm. Convinced that the plexus had been properly located, the author injected 40 ml of bupivacaine (5 mg ml1) with epinephrine (1:300 000) in divided doses using an immobile needle technique. The intercostal brachial nerve was then anaesthetized with 5 ml of the same solution. The patient underwent an uneventful decompression without additional sedation or local anaesthetic.
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Discussion |
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However, further review clarifies the issue. The phrenic nerve usually arises from the root of C4 with contributions from C3 and C5. Because the nerve arises predominantly from C4, it is formally considered part of the cervical plexus.7 In most cases, it descends along the anterior surface of the scalenius anticus muscle and enters the thorax sandwiched between the subclavian artery and vein. Many variations of the phrenic nerve have been described. Rather than descending behind the subclavian vein, the phrenic nerve may also pass anterior to it. An accessory phrenic nerve may arise from roots C5 and C6 or from the nerve to the subclavius muscle. This variation is present in up to 75% of cadavers.8 The phrenic nerve may receive branches from the cervical or brachial plexus or arise entirely from the brachial plexus. Cranial nerves XI or XII may also contribute branches. These branches arise in close proximity to the site where supraclavicular block is performed. Thus, when one considers the relatively high frequency of an accessory phrenic nerve or a branch from the brachial plexus itself, there is a significant possibility of anaesthetizing only part of the phrenic nerve with a supraclavicular block. This may lead to a partial block of the ipsilateral hemidiaphragm and is consistent with the outcomes of the study by Neal and colleagues, particularly the preservation of FVC with supraclavicular block even in those patients who have evidence of hemiparesis.6
In this patient, the needle tip was likely placed near one of the posterior divisions of the plexus, which gives rise to the radial nerve and all or part of the phrenic nerve. Stimulation would have caused contraction of the supinator and brachioradialis muscles, a paresthesia in the thumb, and a motor response in the diaphragm. This is consistent with the phrenic nerve variations.
In the general population, we may assume that more distal blocks, such as a low interscalene or supraclavicular block, may also give rise to a partial phrenic nerve block, even if the phrenic nerve anatomy is standard. In this instance, less local anaesthetic might bathe the phrenic nerve roots resulting in a partial phrenic block. This scenario is also consistent with the work of Neal and colleagues.6
In summary, the author reports a case of simultaneous diaphragmatic and brachial plexus stimulation resulting in a successful nerve block. An explanation for the qualitative difference in phrenic nerve block between interscalene and supraclavicular block is postulated based on known anatomic variations. The case demonstrates the necessity of a thorough knowledge of anatomical variations and standard anatomy for the safe, efficient practice of regional anaesthesia.
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Acknowledgements |
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References |
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2 Farrar MD, Scheybani M, Nolte H. Upper extremity block, effectiveness and complications. Reg Anesth 1981; 6: 1334
3 Knoblanche GE. The incidence and aetiology of phrenic nerve blockade association with supraclavicular brachial plexus block. Anesth Intens Care 1979; 7: 346
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5 Urmey WF, Talts KH, Sharrock NE. One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography. Anesth Analg 1991; 72: 498503[Abstract]
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7 Clemente CD, ed. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1985; 12035
8 Bergman RA, Thompson SA, Afifi Ak, Saadeh FA. Compendium of Human Anatomic Variation. Baltimore: Urban & Schwarzenberg, 1988; 138139