Introduction Brachial plexus block by injection above the clavicle for shoulder surgery has been associated with phrenic nerve paralysis resulting in unilateral hemidiaphragmatic paresis. Incidences of phrenic nerve paralysis of up to 100% have been reported following interscalene block. Incidence of phrenic nerve paresis can be influenced by the injection site, position of the block needle tip, and the volume and/or concentration of local anesthetic used. the use of ultrasound-guided injection has resulted in targeted injections to the brachial plexus as well as peripheral nerves to the upper extremity that provide effective analgesia to the shoulder while decreasing or eliminating phrenic paralysis. Various strategies for providing regional anesthesia and analgesia for shoulder surgery and the resulting effects will be discussed below.
Phrenic Nerve Paresis and Brachial Plexus Block above the Clavicle Shaw first recognized that brachial plexus anesthesia could result in paralysis of the phrenic nerve.1 He published his findings in 1949. the modern interscalene block was first described by Winnie in 1970.2 This block was performed at the level of the nerve roots identified by a paresthesia in response to the advance of the block needle. a 100% incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus block was described by Urmey in 1991.3 Although not initially readily accepted upon publication, several follow-up studies from multiple investigators confirmed the 100% incidence of phrenic nerve paresis caused by interscalene block.3–9 the 100% incidence of phrenic paralysis was not reduced by the use of bupivacaine or ropivacaine, two agents with relative motor-sparing effects.10 11 Reduction of local anesthetic injection volumes to 20 or 10 mL did not result in a reduction of phrenic nerve paresis. To achieve surgical anesthesia by interscalene block for surgical procedures on the shoulder, it is a necessity to block the C-4 and C-5 nerve roots which contribute to the formation of the phrenic nerve(C-3 is usually blocked as well). C-4 is the main contributor to the phrenic nerve. Blocking C-3 through C-5 results in paralysis of the nerve roots that form the phrenic nerve prior to its formation. Phrenic nerve paralysis is therefore unavoidable if brachial plexus block is to be used as the sole anesthetic for shoulder surgery.
Many investigators have studied techniques that provide analgesia of the brachial plexus or supplement general anesthesia for shoulder surgery. These techniques involve strategies that limit local anesthetic spread to the cervical plexus. Riazi et al. compared interscalene block with 20 vs. 5 mL local anesthetic volume and found that reduction in local anesthetic volume to 5 mL still resulted in a 45% incidence of diaphragmatic paresis.12 Among the first investigators to use portable ultrasound guidance to target an area of the brachial plexus, Renes, et al., used ultrasound guidance to target the brachial plexus at the C-7 level. a 10 mL volume of ropivacaine reduced the incidence of phrenic nerve paresis to 13% compared to 93% when peripheral nerve stimulation was used to identify the brachial plexus.13
Reductions in concentration of bupivacaine from 0.75% to 0.125% did not affect the incidence of phrenic nerve paralysis during conventional interscalene block. However, targeted interscalene block with 20 mL 0.125% (vs 0.25%) bupivacaine resulted in a decrease in diaphragmatic paresis diagnosed by ultrasonography from 78% to 21%, without decreasing analgesia.14 However, as is often the case with such studies, general anesthesia with endotracheal intubation was used for surgery and significant amounts opiates were used during and after surgery. Continuous interscalene block prolongs the duration of hemidiaphragmatic paresis.15
Hemidiaphragmatic paresis resulting from interscalene block results in significant diminutions in routine pulmonary function tests. Reductions in FVC in the range of 27–29% have been reported.4 These results are consistent with the 30% reduction in FVC resulting from complete surgical sectioning of the phrenic nerve.16 Although usually well tolerated, respiratory failure has been reported secondary to interscalene block.17 Convention supraclavicular block has been associated with a 50–70% incidence of phrenic nerve block.18–20
Diaphragm-Sparing Blocks for Shoulder Surgery Interscalene block is still regarded as the gold standard for analgesia for shoulder surgery. Ultrasound-guidance used to target a specific block needle endpoint, in conjunction with lowered local anesthetic volume or concentration, has not been able to decrease the incidence of phrenic nerve paralysis below 20%.21
Ultrasound guided supraclavicular block reduces the incidence of phrenic nerve paresis but has not been shown to eliminate it. Ultrasound guided supraclavicular block for shoulder surgery has been associated with a reduction in incidence of hemidiaphragmatic paresis to 34%.22 Recently, Bao, et al., studied diaphragm compound muscle action potentials and pulmonary function after 20–30 mL 0.375% ropivacaine injections for supraclavicular block.23 Reduction in FVC was only 8.0% following 20 mL injection. Block success and diaphragm function were lower when 20 mL was compared to 30 mL indicating that more local anesthetic spread to the cervical nerve roots in the higher volume group. a recent study that compared low volume interscalene to supraclavicular block found equivalent postoperative analgesia but a higher incidence of hemidiaphragmatic paresis in the interscalene group (95% vs 9%).24 However, fentanyl was used before block placement, intraoperatively, and intravenous morphine patient-controlled analgesia was used postoperatively.
Auyong et al. recently studied anterior supraclavicular block performed more distally than supraclavicular block. Anterior supraclavicular block, but not supraclavicular block, was shown to provide noninferior analgesia compared to interscalene block, with better preservation of FVC.25
Injecting local anesthetic extrafascially reduced hemidiaphragmatic paresis and respiratory complications compared to convention intrafascial needle tip placement for injection.26 27
It is difficult to impossible to eliminate diaphragmatic paresis with any brachial plexus block above the clavicle. Although originally thought to result from spread to the cervical plexus and anesthesia of the C-3 through C-5 nerve roots, a recent study by Stundner et al. utilizing contrast magnetic resonance imaging (MRI) showed that 5 mL interscalene block resulted in a 27% incidence of diaphragmatic paresis.28 MRI showed a high incidence of spread to the peripheral phrenic nerve.
One method of regional analgesia that completely avoids diaphragmatic paresis involves blocking one or more peripheral nerves to the shoulder. Ultrasound guided peripheral nerve blocks have been used for postoperative analgesia following shoulder surgery while completely avoiding phrenic nerve block. Shoulder innervation is provided by four nerves that arise from the brachial plexus. These nerves are the subscapular, axillary, lateral pectoral, and suprascapular nerves.29 Suprascapular/axillary nerve blocks have been found to result in adequate analgesia following shoulder surgery.30 31 Weigel et al. concluded that suprascapular nerve block ‘seems preferable to interscalene block’ for outpatients undergoing rotator cuff repair.32 Closer examination of their results show that the suprascapular nerve was not clearly visualized in 17.7% of their study patients. the anesthetic used was a general anesthetic using a sufentanil-based technique. Another recent study found that interscalene block resulted in superior analgesia compared to suprascapular block.33 Interscalene was shown to provide better analgesia than the combination of suprascapular/axillary nerve blocks in two additional studies.34 35
Conclusions Interscalene block provides optimal anesthesia and analgesia for shoulder surgery. Interscalene block that is sufficient as the sole anesthetic for shoulder surgery is associated with and unavoidable incidence of phrenic nerve paresis, up to 100%. Other brachial plexus blocks may provide adequate postoperative analgesia and may be used to supplement general anesthesia decrease the overall incidence of phrenic nerve block, but do not completely eliminate it. Peripheral nerve blocks are less reliable than brachial plexus blocks, but completely eliminate diaphragmatic paralysis. However, these blocks have been associated with diminutions in standard pulmonary function tests in the postoperative period.
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