ASRA Pain Medicine Update

A 71-year-old male with past medical history of coronary artery disease, hypertension, severe chronic obstructive pulmonary disease (COPD) on home oxygen 2 L/min, and sleep apnea with nightly continuous positive airway pressure (CPAP) use is admitted for right total shoulder arthroplasty due to severe primary osteoarthritis. Upon chart review, you note a past surgical history of 3-vessel coronary artery bypass grafting two years ago with a recent cardiology report stating that the patient is stable from a cardiovascular standpoint and requires no further optimization for surgery. His pulmonary function test shows forced expiratory volume at 1 second/forced vital capacity (FEV1/FVC) of 35% of predictable. You meet this patient in the preoperative area on the day of surgery, where he has the following vital signs: heart rate 74 in normal sinus rhythm, blood pressure 154/76, respiratory rate 18, peripheral capillary oxygen saturation 93% on 2 L nasal cannula. 

1. Which roots form the brachial plexus and which nerves should be blocked to get appropriate coverage for shoulder surgery? Why?

The brachial plexus is formed by the ventral rami of C5 to T1 roots with variable contributions from C4 and T2. These nerve routes unite to form 3 trunks: superior, middle, and inferior.¹ The shoulder joint innervation is very complex and involves multiple nerves originating from the brachial plexus, but the axillary and suprascapular nerves (SNs) cover most of the shoulder joint innervation.² The SN originates from the superior trunk (C5-C6), and the axillary nerve is a terminal branch of the posterior cord and receives its contribution from C5 and C6. Other nerve contributions include the lateral pectoral nerve and subscapular.³

2. Is this patient a candidate for an interscalene nerve block? Why or why not?

No. Even though the interscalene brachial plexus block provides excellent coverage for surgery involving the shoulder, upper arm, and lateral two-thirds of clavicle (as it targets primarily C5-C6 at the root level), this approach will also result in ipsilateral phrenic nerve blockade 100% of the time.^2,4 This leads to hemidiaphragmatic paresis (HDP), and subsequently decreases pulmonary function by around 25%.⁴ This decrease is not clinically significant in healthy patients, but it can lead to respiratory distress in patients with ventilatory problems.^3,4

3. What is the origin of the phrenic nerve, and what is its trajectory?

The phrenic nerve is formed by junctions of fibers from C3 to C5 and innervates the diaphragm. The phrenic nerve descends through the neck on the anterior surface of the anterior scalene muscle, passing through the superior thoracic aperture, and descending on the walls of the mediastinum to the diaphragm. All approaches to the block of the brachial plexus above the clavicle with high volumes results in phrenic nerve blockade.⁵

4. For which patient population would you consider a phrenic-sparing nerve block?

A phrenic nerve sparing approach should be considered in patients who are unable to tolerate a 25% reduction in pulmonary function. These may include patients with moderate-to-severe obstructive disease, obstructive sleep apnea, morbid obesity, and preexisting contralateral phrenic nerve palsy.⁴

Patients who are also unable to recruit intercostal or accessory muscles are also at risk for ventilatory failure after HDP, such as those with ankylosing spondylitis.⁴

5. To prevent HDP, your medical student suggests performing an interscalene block with a lower volume, such as 10mL or Ropi 0.5%. How would you respond?

Using lower volumes of local anesthetic has not been shown to decrease the risk of HDP in comparison to standard volumes when performing an interscalene nerve block.⁶

Performing an interscalene block with 0.5% ropivacaine using 20 mL in comparison to 10 mL does not reduce the incidence of HDP or impairment in pulmonary function.⁶ Significant reduction of spirometric values (FEV1/FVC) occurs to a similar degree in both groups after an interscalene block.⁶  

A reduction in the incidence of HD paresis is only seen in reductions of volume below 5 mL. The estimated volume that does not cause HD paresis is 4.29 mL.⁷

6. Which peripheral nerve block would you offer this patient? Would you do a single shot or continuous catheter?

A single shot, phrenic-sparing nerve block would be the best course of action for this patient. This can be achieved in the following ways:

• A superior trunk block targets the fusion of C5 and C6 nerve roots (superior trunk of the brachial plexus) and allows for local anesthetic to be deposited further away from the phrenic nerve. It’s found that this block provides noninferior analgesia for shoulder surgery, with less incidence of HDP.⁸
  
• The combination of infraclavicular and SN block can provide similar analgesia after 30 minutes of injection when compared to an interscalene block, with significantly decreased risk of HDP (0%-6% depending on the approach and volume).³ A combination suprascapular-axillary nerve block omits the contributions of the lateral pectoral and subscapular nerves; it is not routinely used because it provides inferior analgesia for a total shoulder arthroplasty.⁹ 
• A supraclavicular nerve block, where local anesthetic is deposited posterolateral the neural cluster and not within, can provide an equianalgesic effect when compared to an interscalene nerve block, with an incidence of 9% HDP. An incidence of up to 60% HDP is seen when local anesthetic is deposited within the neural cluster.³
  
• A costoclavicular nerve block is an approach that targets the three cords within the proximal infraclavicular fossa and allows for local anesthetic to migrate proximally toward the supraclavicular brachial plexus and SN. This can provide equal analgesia to the interscalene block with a 0% risk of HDP. However, more data is required in a larger population size to ensure validity.¹⁰

7. You decide to proceed with a single shot infraclavicular block and a suprascapular block. Where can the SN be blocked?

The SN is composed of fibers from the 5th and 6th cervical roots and branches from the superior trunk of the brachial plexus. As it branches, the SN travels through the suprascapular notch and under the suprascapular ligament. The SN can be blocked (with high efficacy) in two locations: 

• Blocking the SN using the anterior approach involves targeting the nerve at a proximal location, close to its brachial plexus branching point. Using a linear transducer and in-plane needle technique, the SN is identified with ultrasound (US) probe cephalad to the clavicle in the supraclavicular fossa, typically less than 1 cm below the skin. The SN is typically identified at the most lateral and posterior aspect of the brachial plexus. Once identified, local anesthetic is deposited around the nerve.¹¹ An important consideration is volume of injectate as 5-10 ml can spread proximally and block the phrenic nerve 20% of the time.³
  
• The SN can alternatively be blocked through a posterior approach.¹² With a linear US probe, the SN is identified along the floor of the suprascapular spine between the suprascapular notch and spinoglenoid notch. Blocking of the SN with this approach can be done in a direct manner with US or indirectly by using landmarks. This approach nearly eliminates the risk of pneumothorax. To achieve adequate SN blockage, only 5-8 ml of local anesthesia is typically required with the spread outside of the region minima.¹³ As such, blocking the SN through this posterior approach results in 0% HDP.³

8. Prior to proceeding, your attending anesthesiologist suggests a selective superior trunk block instead for this patient. Does it minimize the risk of complete HDP?

The superior trunk is formed by the junction of C5 and C6 roots, providing complete anesthesia of the shoulder. The incidence of complete HDP significantly decreases to 5% when compared to an interscalene block.⁸ In comparison to an infraclavicular with posterior SN block, which has a 0% incidence of HDP,³ the superior trunk block does present a higher risk for this patient.

References

1. Johnson, RL, Kopp, SL, Kessler, J, et al. Peripheral nerve blocks and ultrasound guidance for regional anesthesia. In Gropper MA. Miller's Anesthesia. New York: Elsevier, 2020.
2. Hadzic, A. Shoulder block. In Compendium of Regional Anesthesia. https://nysoralms.com/courses/nysora-compendium-of-regional-anesthesia/. Accessed Feb. 28,2022.
3. Tran DQ, Layera S, Bravo D, et al. Diaphragm-sparing nerve blocks for shoulder surgery, revisited. Reg Anesth Pain Med 2019;45:73-8. https://doi.org/10.1136/rapm-2019-100908.  
4. Urmey WF, McDonald M. Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics. Anesth Analg 1992;74(3):352-7. https://doi.org/10.1213/00000539-199203000-00006.  
5. ​​Carrera, A, Lopez, AM, Sala-Blanch, X, et al. Functional regional anesthesia anatomy. In Hadzic A: Hadzic's Textbook of Regional Anesthesia and Acute Pain Medicine. New York: McGraw-Hill Education, 2017.
6. Sinha SK, Abrams JH, Barnett JT, et al. Decreasing the local anesthetic volume from 20 to 10 mL for ultrasound-guided interscalene block at the cricoid level does not reduce the incidence of hemidiaphragmatic paresis. Reg Anesth Pain Med 2011;36(1):17-20. https://doi.org/10.1097/aap.0b013e3182030648.   
7. Falcão LFR, Perez MV, de Castro I, et al. Minimum effective volume of 0.5% bupivacaine with epinephrine in ultrasound-guided interscalene brachial plexus block. Brit J Anaesth, 2013;110(3): 450-5.
8. Kang R, Jeong JS, Chin KJ, et al. Superior trunk block provides noninferior analgesia compared with interscalene brachial plexus block in arthroscopic shoulder surgery. Anesthesiology 2019;131(6):1316-26. http://doi.org/10.1097/ALN.0000000000002919.
9. Price D. Optimizing the combined suprascapular and axillary nerve (SSAX) block. Reg Anesth Pain Med 2017;42(1):122. http://doi.org/10.1097/AAP.0000000000000518.  
10. Aliste J, Bravo D, Layera S, et al. Randomized comparison between interscalene and costoclavicular blocks for arthroscopic shoulder surgery. Reg Anesth Pain Med 2019;44:472-7. https://doi.org/10.1136/rapm-2018-100055.  
11. Grant S, Auyong D. (Eds.), Ultrasound Guided Regional Anesthesia. Oxford, UK: Oxford University Press. Retrieved Mar. 8, 2022, from https://oxfordmedicine.com/view/10.1093/med/9780190231804.001.0001/med-9780190231804.
12. Moore DC. Block of the suprascapular nerve. In: Thomas CC, ed: Regional nerve block. Springfield, IL: Charles C Thomas Publisher LTD; 1979.
13. Feigl GC, Anderhuber F, Dorn C, et al. Modified lateral block of the suprascapular nerve: a safe approach and how much to inject? A morphological study. Reg Anesth Pain Med 2007;32:488-94. https://doi.org/10.1016/j.rapm.2007.06.394.