Anesthesiology

Rotator cuff repair

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What the Anesthesiologist Should Know before the Operative Procedure

Patients may present for rotator cuff repair (RCR) after a relatively acute injury, or the injury may have occurred in the distant past. As such, a thorough history of the events surrounding the injury and associated injuries should be elicited. The spectrum of patient comorbidities is reflective of a diverse patient population from teenagers to elderly adults, and from athletic to inactive. Postoperative pain control with interscalene block (ISB) is highly recommended when appropriate.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

RCR is always an elective procedure. There is no risk associated with delaying the case to obtain additional preoperative information and/or medical optimization.

Elective: RCR is always an elective procedure. There is no risk associated with delaying the case to obtain additional preoperative information and/or medical optimization.

2. Preoperative evaluation

Preoperative evaluation for RCR should follow standard anesthesia guidelines for elective surgery.

Shoulder surgery may be performed in a lateral or sitting (beach chair) position. The physiology of the sitting position presents a certain level of risk for patients with a history of cerebrovascular disease, carotid arterial disease, and hypertension, which could affect cerebral perfusion. Chronic hypertension shifts the limits of autoregulation toward higher blood pressure levels and, thus, the lower boundary of autoregulation is unknown.

Both lateral and sitting positions can present a challenge for unexpected intraoperative airway management. Airway evaluation is critical. Airway management should be directed by a thorough airway evaluation and pulmonary aspiration risk assessment. Duration of surgery should be considered when planning for airway management. In obese patients, in the sitting and lateral positions, the potential for difficult airway management and positional injury is heightened.

As with any anesthetic, pulmonary status is important. If ISB is a part of the anesthesia plan, patients should be able to tolerate a decrease in pulmonary function secondary to phrenic nerve block and resultant hemidiaphragmatic paresis.

In obese patients, due to restrictive pulmonary mechanics, the perception of reduced breathing associated with hemidiaphragmatic paresis may be more profound. This may be further exacerbated in obese patients undergoing general anesthesia with a volatile anesthetic in conjunction with ISB. Specific benefits of ISB including avoidance of volatile anesthetics, potential avoidance of airway manipulation, and reduced opioid consumption and opioid-related side effects must be weighed against the risks in the obese population.

In addition to restrictive pulmonary mechanics, difficult airway management, and difficult positioning, anesthetic considerations in obese patients presenting for shoulder surgery include increased pulmonary aspiration risk, difficult intravenous access, difficult ISB placement, and comorbidities such as gastroesophageal reflux disease (GERD), diabetes mellitus (DM), hypertension, and obstructive sleep apnea (OSA). Each must be carefully evaluated.

OSA presents many challenges for the anesthesiologist and, depending on severity, is associated with increased perioperative adverse events. In patients with moderate to severe OSA, the appropriateness of RCR in the outpatient setting, where it is most commonly performed, may be questioned due to the potential increased risk of postoperative respiratory adverse events at home. Regional anesthesia provides many benefits in patients with OSA over general anesthesia. The effects of ISB and resultant hemidiaphragmatic paresis on OSA are unknown. However, it is clear that opioid reduction achieved with regional anesthesia as part of a multimodal postoperative analgesic regimen is beneficial in patients with OSA.

While a surgeon would be reluctant to perform an RCR in the setting of an acute nerve injury (i.e., dislocation with rotator cuff tear and brachial plexopathy), a history and physical exam documenting neurologic assessment of the extremity is important. It is not uncommon for patients to present with some numbness and tingling in the extremity. The etiology of neurologic symptoms should be evaluated and discussed with the surgeon. Decisions to incorporate ISB as part of the anesthesia plan should be made with the patient and surgeon, after the etiology is understood. For some patients, the preoperative work-up will include an electromyelogram, while for others this will not be available or will not be necessary. In these cases, the anesthesia practitioner must choose when to rely on the history, exam, and opinion of the surgeon regarding the etiology, and whether to proceed with performing an ISB. If the patient and/or surgeon does not elect for an ISB, it should not be included in the anesthesia plan.

3. What are the implications of co-existing disease on perioperative care?

b. Cardiovascular system

Acute/unstable conditions: In the setting of acute/unstable cardiovascular conditions, surgery should be postponed in order to stabilize, characterize, and/or optimize these conditions.

Baseline coronary artery disease or cardiac dysfunction - Goals of management: In patients undergoing shoulder surgery with stable coronary artery disease or cardiac dysfunction, the American Heart Association (AHA) guidelines for elective noncardiac surgery should be followed. Patients receiving anticoagulation and regional anesthesia should be managed according to ASRA (American Society of Regional Anesthesia and Pain Medicine) and individual hospital guidelines. Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) do not have to be held in order to perform an ISB. In fact, in the setting of coronary artery disease with coronary stent intervention, aspirin should be continued perioperatively, if surgical bleeding risk allows. Consultation with the patient's cardiologist is appropriate in this situation.

c. Pulmonary

If ISB is a part of the anesthesia plan, patients should be able to tolerate an approximate 25% decrease in pulmonary function secondary to phrenic nerve block and resultant hemidiaphragmatic paresis. Patients without acute respiratory signs or symptoms do not require preoperative spirometry, unless history suggests moderate to severe pulmonary dysfunction.

In obese patients, due to restrictive pulmonary mechanics, the perception of reduced breathing associated with hemidiaphragmatic paresis may be more profound. This may be further exacerbated in obese patients undergoing general anesthesia with a volatile anesthetic in conjunction with ISB. Specific benefits of ISB including avoidance of volatile anesthetics, potential avoidance of airway manipulation, and reduced opioid consumption and opioid-related side effects must be weighed against the risks in the obese population.

OSA presents many challenges for the anesthesiologist and, depending on severity, is associated with increased perioperative adverse events. In patients with moderate to severe OSA, the appropriateness of RCR in the outpatient setting, where it is most commonly performed, may be questioned due to the potential increased risk of postoperative respiratory adverse events at home. Regional anesthesia provides many benefits in patients with OSA over general anesthesia. The effects of ISB and resultant hemidiaphragmatic paresis on OSA are unknown. However, it is clear that opioid reduction achieved with regional anesthesia as part of a multimodal postoperative analgesic regimen is beneficial in patients with OSA.

d. Renal-GI:

Patients should be questioned regarding a history of GERD, or symptoms of reflux as part of an aspiration risk assessment. While patients who are well controlled and asymptomatic can likely undergo heavy sedation for these procedures, a more secure airway should be implemented for those with poor control and active symptoms.

e. Neurologic:

Shoulder surgery may be performed in a lateral or sitting (beach chair) position. The physiology of the sitting position presents a certain level of potential risk for patients with a history of cerebrovascular disease, carotid arterial disease, and hypertension, which could affect cerebral perfusion. Chronic hypertension shifts the limits of autoregulation toward higher blood pressure levels and, thus, the lower boundary of autoregulation is unknown.

Additionally, the lateral and sitting positions require vigilant attention to patient positioning by both the surgeon and anesthesiologist in an effort to avoid positional injury.

While a surgeon would be reluctant to perform an RCR in the setting of an acute nerve injury (i.e., dislocation with rotator cuff tear and brachial plexopathy), a history and physical exam documenting neurologic assessment of the extremity is important. It is not uncommon for patients to present with some numbness and tingling in the extremity. The etiology of neurologic symptoms should be evaluated and discussed with the surgeon. Decisions to incorporate ISB as part of the anesthesia plan should be made with the patient and surgeon, after the etiology is understood. For some patients, the preoperative work-up will include an electromyelogram, while for others this will not be available or will not be necessary. In these cases, the anesthesia practitioner must choose when to rely on the history, exam, and opinion of the surgeon regarding the etiology, and whether to proceed with performing an ISB. If the patient and/or surgeon does not elect for an ISB, it should not be included in the anesthesia plan.

f. Endocrine:

Diabetic management should be optimized prior to an elective procedure such as RCR. Specific concerns related to RCR include increased risk of pulmonary aspiration secondary to delayed gastric emptying, increased susceptibility to soft tissue ischemia and nerve injury from positioning as a result of microvascular disease. For this same reason, there is theoretical concern for nerve injury as a result of epinephrine added to local anesthetics injected perineurally. However, even in diabetic patients, 1:200,000 and 1:400,000 epinephrine is commonly added to local anesthetic solutions for perineural injection, serving as a marker for intravascular uptake. One must evaluate the benefit of epinephrine as an intravascular marker versus the risk of nerve injury in diabetic patients.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

4. What are the patient's medications and how should they be managed in the perioperative period?

Anticoagulants, in the setting of ISB, should be managed consistent with ASRA and hospital guidelines. Aspirin and NSAIDs do not have to be held to perform an ISB. In fact, in the setting of coronary artery disease with coronary stent intervention, aspirin should be continued perioperatively, if surgical bleeding risk allows. It is recommended that herbal medications that may have an effect on bleeding such as Ginseng and Ginkgo biloba be held.

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may be associated with a more profound degree of anesthesia-induced hypotension. Consideration should be given to holding these medications the morning of surgery. For shoulder surgery, the beach chair position with decreased venous return to the heart may further exacerbate this hypotension.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

i. What should be recommended with regard to continuation of medications taken chronically?

Cardiac: Beta-blockers, calcium channel blockers, and antiarrhythmics should be continued. Consideration should be given to holding angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, as they are associated with a higher incidence and more profound degree of hypotension with induction. Holding these medications for patients undergoing surgery in the beach chair position may be even more prudent. Additionally, diuretics should be held.

Pulmonary: Should be continued, including postoperative CPAP for OSA

Antiplatelet: Anticoagulants, in the setting of ISB, should be managed consistent with ASRA guidelines. Aspirin and NSAIDs do not have to be held to perform ISB. In fact, in the setting of coronary artery disease with coronary stent intervention, aspirin should be continued perioperatively by the surgeon, if surgical bleeding risk allows perioperatively It is recommended that herbal medications that may have an effect on bleeding such as Ginseng and Ginkgo biloba be held.

j. How To modify care for patients with known allergies -

Cephalosporins are frequently administered for preoperative surgical prophylaxis. Clindamycin and/or vancomycin are alternatives in penicillin-allergic patients.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Avoid latex products and ensure that operating room team is aware.

l. Does the patient have any antibiotic allergies? [Tier 2- Common antibiotic allergies and alternative antibiotics]

Cefazolin or cefuroxime is administered for preoperative surgical prophylaxis. If beta-lactam allergy: vancomycin or clindamycin.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia (MH)

Documented: Avoid all trigger agents such as succinylcholine and inhalational agents:

  1. Proposed general anesthetic plan:

  2. Ensure MH cart available: [MH protocol]

  3. Family history or risk factors for MH:

Local anesthetics/muscle relaxants:

Allergic reactions to local anesthetics most commonly occur in the ester class of local anesthetics and are associated with the release of para-aminobenzoic acid (PABA) as a metabolic product. Allergies to the amide class of local anesthetics are exceedingly rare. Often, patients report allergies that, on questioning, are related to epinephrine absorption and palpitations.

5. What laboratory tests should be obtained and has everything been reviewed?

Hemoglobin levels: Blood loss with RCR is minimal. Hemoglobin levels should be evaluated on a case-by-case basis in the context of patient comorbidities and/or signs/symptoms of anemia.

Coagulation panel: Prior to regional anesthesia, in the setting of anticoagulation with Coumadin, a normal coagulation panel should be documented

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Most commonly, surgery for RCR is performed under a general anesthetic or heavy sedation in combination with an ISB. Airway, comorbidities, anticoagulation status, preexisting neuropathies, patient position, and case duration are critical factors in evaluating anesthetic management for shoulder surgery.

Shoulder surgery may be performed in a lateral or sitting (beach chair) position. The physiology of the sitting position presents a certain level of risk for patients with a history of cerebrovascular disease, carotid arterial disease, and hypertension, which could affect cerebral perfusion. Chronic hypertension shifts the limits of autoregulation toward higher blood pressure levels and, thus, the lower boundary of autoregulation is unknown.

Both lateral and sitting positions can present a challenge for unexpected intraoperative airway management. Airway evaluation is critical. Airway management should be directed by a thorough airway evaluation and aspiration risk assessment.

a. Regional anesthesia

The most common regional anesthetic technique for shoulder surgery is an ISB. This block is performed at the root/trunk level of the brachial plexus. It provides both brachial (C5-7) and cervical (C3-4) plexus blockade. Incomplete blockade of the inferior trunk (C8, T1) is not uncommon. It is performed as a single injection or as a continuous catheter technique under ultrasound or nerve stimulation guidance, or a combination of the two.

As with any anesthetic, pulmonary status is important. If an ISB is a part of the anesthesia plan, patients should be able to tolerate an approximate 25% decrease in pulmonary function secondary to phrenic nerve block and resultant hemidiaphragmatic paresis.

Additional side effects of an interscalene brachial plexus block include a transient Horner's syndrome and recurrent laryngeal nerve block resulting in hoarseness. The transient and expected nature of these side effects should be discussed with the patient prior to block performance.

ISB may be used in combination with heavy sedation, or general anesthesia using a total intravenous technique or volatile anesthetic. Airway evaluation is critical. Airway management should be directed by a thorough airway evaluation and aspiration risk assessment.

Alternative regional anesthesia options for postoperative pain include suprascapular nerve block alone or in combination with an axillary nerve block or subacromial/intra-articular local anesthetic injection by the surgeon. These techniques would not provide surgical anesthesia and thus would be used in combination with general anesthesia. Subacromial/intra-articular injections provide minimal postoperative analgesia for rotator cuff repairs. Additionally, the potential for local anesthetic-induced chondrolysis has raised concerns with this procedure. While suprascapular nerve block provides inferior analgesia to interscalene brachial plexus blockade, it does not cause phrenic nerve blockade or arm weakness. Thus, suprascapular nerve block used alone or in combination with axillary nerve blockade may provide alternative analgesia to ISB in patients with moderate to severe pulmonary dysfunction.

Peripheral nerve block

Benefits: Postoperative pain control, potential avoidance of volatile anesthetics

Drawbacks: Side effects, including diaphragmatic paresis. Potential complications including postoperative neurologic symptoms, bleeding, infection, intravascular injection, and local anesthetic toxicity

b. General Anesthesia

Benefits:Ability to secure airway with endotracheal tube, unconsciousness

Drawbacks: Airway manipulation, difficulty positioning, potential profound hypotension in sitting position, nausea and vomiting with volatile anesthetics

c. Monitored Anesthesia Care: N/A

6. What is the author's preferred method of anesthesia technique and why?

What prophylactic antibiotics should be administered?

Under the current Surgical Care Improvement Project (SCIP) recommendations, cefazolin or cefuroxime is administered for preoperative surgical prophylaxis. If beta-lactam allergy: vancomycin or clindamycin.

What do I need to know about the surgical technique to optimize my anesthetic care?

Potential positioning for shoulder surgery includes the lateral or sitting (beach chair) position. These positions can present a challenge for unexpected intraoperative airway management. Airway evaluation is critical. Airway management should be directed by a thorough airway evaluation and aspiration risk assessment. Case duration should be considered when planning for airway management. Frequent surgical procedures in combination with RCR include impingement surgery and arthroscopy. Impingement surgery includes acromioplasty or subacromial decompression performed to allow the rotator cuff tendons to move freely within the shoulder. Shoulder arthroscopy allows less invasive visualization of the shoulder but limited access.

While RCR usually entails an open procedure, some small repairs may be made through arthroscopy alone. Labral repairs and other shoulder procedures may be performed through arthroscopy alone. RCR most commonly involves an open skin incision, incision through the deltoid muscle, and drilling into the bone, requiring a heightened degree of postoperative analgesia. While single-injection ISB may provide adequate anesthesia for simple arthroscopic procedures, more involved surgical repairs including RCR benefit from continuous ISB for postoperative analgesia.

What can I do intraoperatively to assist the surgeon and optimize patient care?

As with other arthroscopic procedures, it is not uncommon for surgeons to request lowering of the patient's blood pressure in effort to reduce bleeding obscuring visualization of the joint through the arthroscopic camera and to reduce irrigation pressure. The anesthesiologist must assess the validity of poor visualization, and discuss with the surgeon the risks and benefits of decreasing the blood pressure in these situations. While a 20% decrease in blood pressure from baseline is usually considered reasonable, in the beach chair position, the anesthesiologist must consider whether blood pressure readings at the arm can be used to assess postural cerebral perfusion. In healthy patients, mean arterial pressure can be safely maintained within a conservative range of autoregulation, 70-100 mm Hg (CPP >50-80).

What are the most common intraoperative complications and how can they be avoided/treated?

Both lateral and sitting positions can present a challenge for unexpected intraoperative airway management. While minor airway obstruction in patients without endotracheal intubation are not infrequent, more serious airway obstruction can occur. Airway obstruction leading to tracheal compression from extra-articular extravasation of irrigation fluid, while rare, has been reported in cases of long duration. Airway evaluation is critical. Airway management should be directed by a thorough airway evaluation and aspiration risk assessment. Case duration should be considered when planning for airway management.

Complications

Cardiac:Sudden hypotensive bradycardic events (HBE) have been reported during shoulder surgery in the sitting position under ISB. The Bezold-Jarish reflex has been one proposed mechanism for the occurrence of HBE. The Bezold-Jarisch reflex originates in cardiac sensory receptors with vagal afferent pathways in the left ventricle. Stimulation of these inhibitory cardiac receptors by stretch, chemical substances, or drugs increases parasympathetic activity and inhibits sympathetic activity. These effects promote reflex bradycardia, vasodilation, and hypotension. Venous pooling in the sitting position with a resultant decreased preload stimulates endogenous catecholamine release and increased cardiac contractility, which may stimulate this reflex.

Additionally, exogenous catecholamine sources in this setting include epinephrine added to local anesthetic for ISB and irrigation solution. Proposed prophylactic interventions include increasing preload by intravenous fluid administration, beta-blockade, and adequate sedation, as a less-sedated patient may have more endogenous catecholamines and heightened vagal tone.

Pulmonary: Loss of airway and reduced ventilation due to phrenic paralysis, as discussed.

Neurologic: While a surgeon would be reluctant to perform an RCR in the setting of an acute nerve injury (i.e. dislocation with rotator cuff tear and brachial plexopathy), a history and physical exam documenting neurologic assessment of the extremity are important. It is not uncommon for patients to present with some numbness and tingling in the extremity. The etiology of neurologic symptoms should be evaluated and discussed with the surgeon. Decisions to incorporate ISB as part of the anesthesia plan should be made with the patient and surgeon, after the etiology is understood.

For some patients, the preoperative work-up will include an electromyelogram, while for others this will not be available or will not be necessary. In these cases, the anesthesia practitioner must choose when to rely on the history, exam, and opinion of the surgeon regarding the etiology, and whether to proceed with performing an ISB. If the patient and/or surgeon does not elect for an ISB, it should not be included in the anesthesia plan. Postoperative neurologic symptoms must be identified and addressed by the surgeon and anesthesiologist. New onset of postoperative neurologic symptoms (PONS) such as numbness and/or tingling in the surgical extremity may occur after surgery, with or without ISB. Causes of PONS such as positional injury and tight splint/cast must be addressed/excluded prior to more detailed work-up/evaluation.

Often, after speaking with the patient and obtaining a detailed history and report of signs/symptoms, serious etiologies can be excluded, and patient reassurance about the transient nature of such symptoms is the only necessary intervention. While transient numbness/tingling of the extremity is not uncommon, motor weakness after block resolution, if an ISB was performed, is more alarming and requires more immediate evaluation. While motor weakness of the surgical shoulder would be difficult for the patient to report, motor function of the hand can easily be recognized.

The physiology of the sitting position presents a certain level of potential risk for patients with a history of cerebrovascular disease, carotid arterial disease, and hypertension, which could affect cerebral perfusion. Chronic hypertension shifts the limits of autoregulation toward higher blood pressure levels and, thus, the lower boundary of autoregulation is unknown.

a. Neurologic:

While a surgeon would be reluctant to perform an RCR in the setting of an acute nerve injury (i.e., dislocation with rotator cuff tear and brachial plexopathy), a history and physical exam documenting neurologic assessment of the extremity is important. It is not uncommon for patients to present with some numbness and tingling in the extremity. The etiology of neurologic symptoms should be evaluated and discussed with the surgeon. Decisions to incorporate ISB as part of the anesthesia plan should be made with the patient and surgeon, after the etiology is understood.

For some patients, the preoperative work-up will include an electromyelogram, while for others this will not be available or will not be necessary. In these cases, the anesthesia practitioner must choose when to rely on the history, exam, and opinion of the surgeon regarding the etiology and whether to proceed with performing an ISB. If the patient and/or surgeon does not elect for an ISB, it should not be included in the anesthesia plan. Postoperative neurologic symptoms must be identified and addressed by the surgeon and anesthesiologist.

New onset of postoperative neurologic symptoms (PONS) such as numbness and/or tingling in the surgical extremity may occur after surgery, with or without ISB. Causes of PONS such as positional injury, tight splint/cast must be addressed/excluded prior to more detailed work-up/evaluation. Often, after speaking with the patient and obtaining a detailed history and report of signs/symptoms, serious etiologies can be excluded, and patient reassurance about the transient nature of such symptoms is the only necessary intervention. While transient numbness/tingling of the extremity is not uncommon, motor weakness after block resolution, if an ISB was performed, is more alarming and requires more immediate evaluation. While motor weakness of the surgical shoulder would be difficult for the patient to report, motor function of the hand can easily be recognized.

Shoulder surgery may be performed in a lateral or sitting (beach chair) position. The physiology of the sitting position presents a certain level of potential risk for patients with a history of cerebrovascular disease, carotid arterial disease, and hypertension, which could affect cerebral perfusion. Chronic hypertension shifts the limits of autoregulation toward higher blood pressure levels and, thus, the lower boundary of autoregulation is unknown.

b. If the patient is intubated, are there any special criteria for extubation?

No special criteria.

c. Postoperative management

What analgesic modalities can I implement?

Studies with ISB for shoulder surgery have demonstrated superior recovery profiles, improved analgesia, reduced opioid consumption, and reduced opioid-related side effects compared to suprascapular nerve block, subacromial/intra-articular local anesthetic infiltration, and general anesthesia without peripheral nerve blockade.

What level bed acuity is appropriate?

RCR can be performed on an outpatient basis.

What are common postoperative complications, and ways to prevent and treat them?

As previously discussed, if ISB is a part of the anesthesia plan, patients should be able to tolerate an approximate 25% decrease in pulmonary function secondary to the side effect of phrenic nerve block and resultant hemidiaphragmatic paresis. Additional side effects of an ISB include a transient Horner's syndrome and recurrent laryngeal nerve block resulting in hoarseness. The transient and expected nature of these side effects should be discussed with the patient prior to block performance.

In obese patients, the perception of reduced breathing associated with hemidiaphragmatic paresis may be more profound. This may be further exacerbated in obese patients undergoing general anesthesia with a volatile anesthetic in conjunction with ISB. Allowing adequate ventilatory excretion of volatile anesthetic prior to extubation or laryngeal mask airway removal and transport to the post anesthesia care unit is critical in these patients.

Additionally, in the PACU, optimizing patient positioning to improve ease of breathing and patient reassurance of adequate breathing is beneficial. Specific benefits of ISB including avoidance of volatile anesthetics, potential avoidance of airway manipulation, and reduced opioid consumption and opioid-related side effects must be weighed against the risks in the obese population.

What's the Evidence?

Urmey, WF, McDonald, M. "Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics". Anesth Analg. vol. 74. 1992. pp. 352-7.

(ISB associated with an approximate 25% decrease in pulmonary function. PUBMED:1539813)

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. vol. 72. 1991. pp. 498-503.

(ISB associated with 100% hemidiaphragmatic paresis. PUBMED:2006740)

Fredrickson, MJ, Krishnan, S, Chen, CY. "Postoperative analgesia for shoulder surgery: a critical appraisal and review of current techniques". Anaesthesia. vol. 65. 2010. pp. 608-24.

Hadzic, A, Williams, BA, Karaca, PE. "For outpatient rotator cuff surgery, nerve block anesthesia provides superior same-day recovery over general anesthesia". Anesthesiology. vol. 102. 2005. pp. 1001-7.

Klein, SM, Grant, SA, Greengrass, RA. "Interscalene brachial plexus block with a continuous catheter insertion system and a disposable infusion pump". Anesth Analg. vol. 91. 2000. pp. 1473-8.

Klein, S, Steele, S, Nielsen, K. "The difficulties of ambulatory interscalene and intra-articular infusions for rotator cuff surgery: a preliminary report". Can J Anesth. vol. 50. 2003. pp. 265-9.

Horlocker, TT, Wedel, DJ, Rowlingson, JC, Enneking, FK, Kopp, SL, Benzon, HT, Brown, DL, Heit, JA, Mulroy, MF, Rosenquist, RW, Tryba, M, Yuan, CS. "Regional anesthesia in the patient receiving antithrombotic or thrombolytic therapy: American Society of Regional Anesthesia and Pain Medicine Evidence-Based Guidelines (Third Edition)". Reg Anesth Pain Med.. vol. 35. 2010. pp. 64-101.

Liguori, GA, Kahn, RL, Gordon, J. "The use of metoprolol and glycopyrrolate to prevent hypotensive/bradycardic events during shoulder arthroscopy in the sitting position under interscalene block". Anesth Analg. vol. 87. 1998. pp. 1320-5.

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