◊ BACKGROUND AND OBJECTIVES:
Interscalene brachial plexus block is associated with 100% incidence of hemidiaphragmatic paresis as a result of phrenic nerve block. We examined whether an ultrasound (US)-guided interscalene brachial plexus block performed at the level of root C7 versus a nerve stimulation interscalene brachial plexus block, both using 10 mL of ropivacaine 0.75%, resulted in a lower incidence of hemidiaphragmatic paresis.
◊ METHODS:
In a prospective randomized controlled trial, 30 patients scheduled for elective shoulder surgery under combined general anesthesia and interscalene brachial plexus block were included. Interscalene brachial plexus block using the same dose was performed using either US or nerve stimulation guidance of ropivacaine for both groups. General anesthesia was standardized. Ventilatory function was assessed using spirometry, and movement of the hemidiaphragm was assessed by US.
◊ RESULTS:
Two patients in the US group showed complete paresis of the hemidiaphragm, but in the nerve stimulation group, 12 patients showed complete and 2 patients had partial paresis of the hemidiaphragm (13% versus 93%, respectively; P < 0.0001). Ventilatory function (forced expiratory volume at 1 second, forced vital capacity, and peak expiratory flow) was significantly reduced in the nerve stimulation group compared with the US-guided group (P < 0.05). One block failure occurred in the nerve stimulation group compared with none in the US group. No adverse effects occurred in either group.
◊ CONCLUSIONS:
Ultrasound-guided interscalene brachial plexus block performed at the level of root C7 using 10 mL of ropivacaine 0.75% reduces the incidence of hemidiaphragmatic paresis. |
◊ BACKGROUND AND OBJECTIVES:
Supraclavicular brachial plexus block is associated with 50% to 67% incidence of hemidiaphragmatic paresis as a result of phrenic nerve block. We examined whether ultrasound-guided compared with nerve stimulation supraclavicular brachial plexus block using 0.75% ropivacaine results in a lower incidence of hemidiaphragmatic paresis.
◊ METHODS:
In a prospective randomized observer-blinded controlled trial, 60 patients scheduled for elective elbow, forearm, wrist, or hand surgery under supraclavicular brachial plexus block without sedation were included. Supraclavicular brachial plexus block was performed with 20 mL of 0.75% ropivacaine using either ultrasound or nerve stimulation guidance. Ventilatory function was assessed by ultrasound examination of hemidiaphragmatic movement and spirometry.
◊ RESULTS:
None of the 30 patients in the ultrasound group showed complete or partial paresis of the hemidiaphragm (95% confidence interval, 0.00-0.14), whereas in the nerve stimulation group, 15 patients showed complete paresis of the hemidiaphragm and 1 patient showed partial paresis of the hemidiaphragm (0% versus 53%, respectively; P < 0.0001). Ventilatory function (forced expiratory volume 1, forced vital capacity, peak expiratory flow) was significantly reduced in the nerve stimulation group compared with the ultrasound-guided group (P < 0.05). Two block failures occurred in the nerve stimulation group compared with none in the ultrasound group (P = 0.49). No adverse effects occurred in either group.
◊ CONCLUSIONS:
Ultrasound-guided supraclavicular brachial plexus block, using 20 mL of 0.75% ropivacaine with the described technique, is not associated with hemidiaphragmatic paresis.
◊ Reviewed by W. Urmey, M.D.
Associate Professor of Clinical Anesthesiology,
Hospital for Special Surgery, New York, USA
These were two well-designed studies. The authors successfully demonstrated that hemidiaphragmatic paresis could be avoided by US-guidance of low-volume local anesthetic (0.75% ropivacaine) injection posterior and lateral to the brachial plexus during either ISB or SCB. The authors pointed out that in previous studies incidences of hemidiaphragmatic paresis associated with ISB and SCB amounted 100% and 50-67%, respectively. Using a volume of 20 mL and directing the anesthetic distribution to the posterior lateral aspect of the brachial plexus, they were able to achieve good block success without detectable diaphragmatic paresis or significant alterations in pulmonary function during SCB. The C4 dermatome was not blocked in any of the SCB patients.
This has implications for the clinical performance of SCB and deepens our understanding of the mechanism underlying diaphragmatic paresis associated with the block. The findings may explain the variable incidences of hemidiaphragmatic paresis that were associated with SCB in previous studies. During conventional supraclavicular or subclavian perivascular block the needle direction is caudad and its orientation is not controlled, i.e. it may be at the anterior or posterior aspect of the plexus. Lower incidences may be related to a more posterior or lateral placement of the needle whereas larger volumes of local anesthetic may have resulted in higher incidences. By reducing the volume to 20 mL, and carefully targeting the drug to the posterior lateral aspect of the supraclavicular brachial plexus one can apparently avoid involvement of the C4 nerve root, which mainly contributes to the phrenic nerve. Since no patient had C4 dermatomal block, the mechanism of phrenic nerve blockade is most likely due to direct involvement of the phrenic nerve, regardless of the modality used for guidance. Higher volumes of local anesthetic may result in phrenic nerve paresis due to rostral spread and C4 involvement.
The interscalene block study has fewer clinical implications. In this study, the investigators used a very small local anesthetic volume (10 mL) and, most likely of necessity, combined it with general anesthesia. By placing a small volume of local anesthetic through US guidance in posterior lateral position at the level of the C7 nerve root, they were able to avoid the C4 nerve root and significant rostral spread in most, but not all patients. It is much more difficult to avoid diaphragmatic paresis during ISB because the mechanism of phrenic nerve paresis is secondary to rostral spread of local anesthetic to the cervical plexus. Reduction of the local anesthetic volume to 5 mL during US guided ISB still resulted in a 45% incidence of hemidiaphragmatic paresis in the study of Riazi et al. (2008) as referenced by the authors. This is due to the proximity of the interscalene injection point to the lower cervical plexus and the C4 nerve root. Despite the volume reduction of the local anesthetic to 10 mL, lowering the injection point to the C7 nerve root, and US guided targeting of local anesthetic posterior lateral to the nerve root hemidiaphragmatic paresis could not be avoided. As evidenced by the need for concomitant general anesthesia, a 10 mL injection volume is not sufficient for operative anesthesia. Importantly, one must conclude that diaphragmatic paresis cannot be avoided with certainty when performing interscalene brachial plexus block.
In conclusion, the investigators of these two studies were able to perform clinically successful SCB while eliminating meaningful hemidiaphragmatic paresis by carefully targeting the distribution of 20 mL of 0.75% ropivacaine. By contrast, ISB injections limited to 10 mL volume and combined with general anesthesia were still associated with incidences of hemidiaphragmatic paresis. The investigators’ strategy to position the needle below the classic C6 insertion point, to limit local anesthetic disposition through US guidance to the posterior aspect of the brachial plexus, and to reduce the dose to clinically questionable 10 mL was able to lower but not to eliminate the side effect of ipsilateral hemidiaphragmatic paresis. The mechanism of hemidiaphragmatic paresis during interscalene block is most likely linked to rostral spread of local anesthetic to the cervical plexus. By contrast, phrenic nerve paralysis during supraclavicular block may result from either spread to the cervical plexus or directly to the phrenic nerve at a lower point in the brachial plexus. Most importantly, as pointed out by the authors, these studies were insufficiently powered to rule out the possibility of hemidiaphragmatic paresis when performing either interscalene or supraclavicular block, with or without US guidance.
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