Continuous brachial plexus nerve blocks offer improved postoperative outcomes for patients undergoing shoulder surgery. These outcomes include decreased opioid consumption and improved readiness for hospital discharge.1 Brachial plexus blocks, however, also can cause phrenic nerve paralysis,2 leading to clinically significant dyspnea in up to 10% of patients.3 Because obesity causes a restrictive lung disease pattern, postoperative analgesia in obese patients can be particularly challenging because of the increased risks of block-related respiratory dysfunction. In addition, obese patients are at greater risk of having obstructive or central sleep apnea, a condition that may be exacerbated with the use of systemic opioids.4–6 Perioperative analgesia, preserved respiratory function, and patient safety must be reconciled while caring for those patients most at-risk. We present a novel approach for perioperative nerve catheter management by using a short-acting local anesthetic for a clinical test dose of diaphragm paralysis and demand-only continuous nerve block dosing in a patient with extreme obesity.
A 53-year-old woman of 219 kg (body mass index = 82 kg/m2) was scheduled for open reduction and internal fixation of a proximal humerus fracture with rotator cuff repair after suffering a fall at home. Her medical history included extreme obesity and obstructive sleep apnea that required treatment with continuous positive airway pressure. She admitted to shortness of breath while performing simple tasks at home, but she did not require the use of supplemental oxygen. The patient also reported chronic low back pain and generalized arthralgia that she rated at a baseline numeric rating score of 6 of 10 and was treated with oral oxycodone, acetaminophen, tramadol, and cyclobenzaprine.
After a lengthy discussion regarding her anesthetic options, the patient elected for general endotracheal anesthesia with a continuous supraclavicular brachial plexus catheter to manage her postoperative pain. In the preoperative holding area, she was placed in a semirecumbent position with continuous electrocardiogram, peripheral capillary oxygen saturation (SpO2), and noninvasive blood pressure monitors in place. Her baseline SpO2 on room air was 95%. A standard facemask was placed with 6 L/min oxygen administered. Sedation was achieved with 1 mg midazolam intravenously (IV) and 50 μg fentanyl IV. A supraclavicular brachial plexus nerve catheter was placed by the use of an in-plane ultrasound-guided technique (Sonosite, M-Turbo, 6–15 MHz, Bothell, WA) with a 17G Tuohy needle and a 19G flexible catheter (FlexTip, Teleflex–Arrow International, Morrisville, NC). A 10-mL bolus of 2% chloroprocaine was given through the needle and demonstrated excellent local anesthetic spread around the brachial plexus. The catheter was secured with a clear bandage, and an additional 5 mL of 2% chloroprocaine were injected through the catheter.
Approximately 5 minutes after local anesthetic injection, SpO2 values slowly began decreasing from 95% to 91%. Ten minutes later, the patient reported symptomatic shortness of breath. She was taken to the operating room, where the SpO2 values reached a nadir of 88%. A rapid sequence induction with propofol and succinylcholine was initiated, and endotracheal intubation with video laryngoscopy was achieved without complication. General anesthesia was maintained with sevoflurane and cisatracurium. Total intraoperative opioid dose was limited to 50 μg fentanyl IV. The supraclavicular nerve catheter was not used in the operating room. At the end of the 3-hour procedure, the patient was extubated fully awake in the sitting position. She was taken to the postoperative anesthesia care unit (PACU) in stable condition on 8 L/min of oxygen through facemask. She reported no dyspnea in PACU, and her initial pain numeric rating score was 8 of 10.
The patient’s pain numeric rating score increased to 10 of 10 shortly after her admission to PACU. Hydromorphone 1 mg IV and 2 mg orally provided only mild analgesic improvement. A 2-mL bolus of 0.2% ropivacaine through the perineural catheter was delivered as an alternative to the escalation of postoperative opioids. Diaphragmatic excursion was assessed 45 minutes later with the patient in the supine position using a 2- to 5-MHz curvilinear ultrasound transducer. The cephalad border of the zone of apposition of the diaphragm to the costal margin at the midclavicular line was identified at baseline end-expiration and full end-inspiration.7 The distance between each point was measured and found to be symmetrical and >6 cm bilaterally (Figure).
Sixty minutes after the ropivacaine bolus, the patient reported a pain numeric rating score of 6 of 10, a reasonable pain level similar to her baseline pain score. Her SpO2 remained at >92% on 3 L/min of oxygen through nasal cannula. She was transferred to the hospital floor in a stable condition. During the next 18 hours, she received 2 additional 2-mL boluses of 0.2% ropivacaine, consistent with the pharmacodynamics of ropivacaine in nerve blocks.8 In addition, she received a total of 2 mg hydromorphone IV, 18 mg hydromorphone orally, scheduled acetaminophen orally, and scheduled ketorolac IV. This multimodal pain regimen allowed the patient to spend several hours sleeping on the first postoperative night without any respiratory compromise.
By early morning on postoperative day (POD) 1, the patient no longer required the use of supplemental oxygen and reported a pain numeric rating score of 4 of 10 at rest, a number below her preoperative baseline. Scheduled acetaminophen 650 mg every 6 hours and 4 mg hydromorphone orally every 4 hours, as needed, were continued through the rest of her hospital stay. The perineural infusate was changed to a 1% chloroprocaine solution with a patient-controlled bolus of 2 mL every 30 minutes as needed through the continuous supraclavicular catheter. A diaphragmatic excursion measurement was again assessed 20 minutes after the first 2-mL bolus of 1% chloroprocaine. Again, there was no difference between either diaphragm measurement (>5 cm bilaterally). On this regimen, we hypothesized that any phrenic nerve paralysis might resolve quickly, given the pharmacokinetics of chloroprocaine metabolism. After the demand-only continuous nerve block regimen for 24 hours was used, the patient was discharged home on POD 2 with the supraclavicular catheter intact. It is a standard practice at our institution to allow patients to take their perineural catheter and continuous infusion pump home at discharge.9 We continued to follow-up the patient at home with daily telephone calls until the catheter was removed. She required intermittent, patient-controlled boluses of chloroprocaine through the catheter and pump and never complained of dyspnea. She also continued to use 4 mg hydromorphone orally, as needed. By POD 5, the patient was no longer using the perineural catheter, and she removed it without difficulty. We have obtained written, signed consent from the patient to publish this case report.
This case highlights several important management decisions in the care of a patient with extreme obesity having shoulder surgery. Nerve blocks for upper extremity surgery are clearly beneficial for postoperative analgesia, but the potential for phrenic nerve paralysis remains a significant concern. Despite adaptations in single-injection techniques including low local anesthetic volumes and blocks placed distally located along the brachial plexus, phrenic nerve paralysis still persists.7,10 Also, patients with extreme obesity may benefit more from the opioid-sparing effects of a brachial plexus block compared with their nonobese counterparts. In the absence of phrenic nerve paralysis, this subset of patients may show dramatic improvement in outcomes with a nerve block because of decreased opioid consumption.
Several adaptations in this patient’s care were made in the attempt to provide non-opioid analgesia while minimizing the risks associated with phrenic nerve paralysis. First, we chose to use chloroprocaine in our initial bolus for its rapid onset and short duration of action. The rapid onset allowed us the ability to assess the patient’s clinical response to phrenic nerve paralysis. The short duration of action facilitated safe tracheal extubation at the conclusion of the 3-hour surgical procedure as the phrenic nerve paralysis had resolved by this point. If the patient had tolerated the initial local anesthetic bolus, we could have prolonged the nerve block with a standard continuous infusion of 0.2% ropivacaine during her surgery and into the recovery room.
Second, we chose an initial bolus dose volume of 15 mL as a “test dose” to evaluate our patient’s clinical response to phrenic nerve blockade. With this test dose, the actual pulmonary deterioration happened rapidly, but still while the patient was under our direct care, with access to advanced airway equipment. Smaller bolus volumes may have avoided acute phrenic nerve paralysis, but a continuous infusion may have led eventually to phrenic nerve paralysis in an unmonitored setting. We are effectively suggesting a brachial plexus test dose to evaluate the effect of phrenic nerve paralysis in high-risk individuals. By using a short acting, fast-onset local anesthetic such as chloroprocaine or lidocaine will result in a rapid but temporary assessment of the patient’s ability to tolerate phrenic nerve paralysis. If no clinical sequelae are detected, dosing through the continuous catheter may then prolong the nerve block providing extended analgesia. The use of a test dose is not a novel concept in the placement of epidural continuous catheters11 but has not yet been described for brachial plexus blocks to assess for phrenic nerve paralysis.
Third, we chose to place a supraclavicular catheter rather than the more standard interscalene catheter. The interscalene block is the most common block performed for shoulder surgery but is also associated with up to 100% phrenic nerve paralysis.12,13 Complete paralysis of the ipsilateral hemidiaphragm occurs after a supraclavicular block in about 50% of patients.14
Finally, because of our patient’s profound dyspnea after the initial bolus, we altered not only the type of local anesthetic to be infused through the continuous perineural catheter but also adjusted the dosing regimen itself. We avoided continuous-infusion, large-volume boluses, and high concentration local anesthetic to avoid phrenic nerve paralysis. We started overnight with small volume (2 mL) boluses of 0.2% ropivacaine delivered every 6 hours. A brachial plexus continuous infusion of 0.2% ropivacaine is a standard local anesthetic concentration with even higher concentrations of up to 0.75% ropivacaine being reported in the literature1,15–17 Only 3 boluses were required postoperatively in the first 24 hours, consistent with the pharmacodynamics of dilute ropivacaine dosing. To plan for discharge home, we switched to chloroprocaine through the continuous catheter on POD 1. We hypothesized that at the same volume, 1% chloroprocaine may have a lesser effect on phrenic nerve paralysis than a standard nerve block concentration of 2% or 3% chloroprocaine solution. Also, if any respiratory complications arose, these side effects would resolve much more quickly than a standard long-acting local anesthetic such as ropivacaine. Because the nerve block pump did not have a continuous infusion rate and was set at patient-controlled bolus only, the nerve block would only be used when necessary, decreasing the chance of local anesthetic spread to the phrenic nerve. Therefore, a low-volume, demand-only regimen with a short-acting anesthetic through a perineural catheter proved to be safe and effective for this patient. She had no diaphragmatic or pulmonary sequelae from our unique catheter regimen and was able to discontinue supplemental oxygen the morning of POD 1. In addition, she was likely spared from the use of much larger doses of opioids in an unmonitored setting at home.
In conclusion, this case illustrates how continuous brachial plexus nerve catheters can be used to safely provide appropriate postoperative analgesia for obese patients at high risk for respiratory dysfunction. The use of a brachial plexus test dose with short-acting local anesthetic should prove useful in determining the ability of a patient to clinically tolerate phrenic nerve paralysis. An intermittent, patient-controlled, demand-only regimen using a short-acting, low-concentration local anesthetic may have less effect on phrenic nerve paralysis than traditional continuous infusion regimens. Further studies investigating analgesic efficacy and respiratory dysfunction in different block locations and infusion regimens along the brachial plexus will help corroborate this report.
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