Anesthesia for Shoulder Arthroscopy

Anesthesia for Shoulder Arthroscopy

• Intercostal blocks provide intraoperative and postoperative pain relief.
• Beach chair positioning reduces brachial plexus injuries compared to lateral decubitus.
• In the beach chair position, arterial blood pressure (BP) readings in the arm don't accurately reflect brain pressure (MAP). Low arm MAP readings during beach chair positioning may not indicate adequate cerebral or coronary perfusion, posing a stroke risk. Measurements or estimates of the MAP can be made once the patient is in the beach chair position. The critical variable is the vertical distance from the circle of Willis to the BP cuff.
• Arthroscopic shoulder surgery is less invasive, allowing for faster patient discharge (within 24 hours).
• Arthroscopic shoulder surgery utilizes fiber optics, smaller instrumentation, and improved techniques for increased popularity.
• A rotator cuff injury affects one or more of the four shoulder muscles (supraspinatus, infraspinatus, teres minor, subscapularis).
• Injuries can be acute (e.g., falls) or chronic.
• Acute injuries can cause hemorrhage and inflammation of the bursa.
• Inflammation reduces space under the acromion, leading to impingement during shoulder abduction, creating a cycle of inflammation and impingement.
• The shoulder joint is supported by the clavicle, scapula, and humerus, along with ligaments.
• The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) stabilize the humeral head against the scapula, enabling lifting and rotation.
• The rotator cuff forms a covering around the humerus.
• A rotator cuff tear within the supraspinatus muscle is a common cause of shoulder pain in adults.
• The type of surgery depends on tear size and location.
• Tendon tears may require repair with suture via arthroscopy or an open technique.
• Tendon tears away from bone may require direct tendon-to-bone repair.
• Acromion removal may be needed due to impingement.
• Traction on the operative arm is often used to improve surgical conditions.
• Patient head must be protected from pressure and secured with a strap.
• Anesthetist needs to visualize and ensure proper head and neck alignment due to surgical manipulations.
• Surgeons often prefer the beach chair position for rotator cuff repair, improving visualization and minimizing brachial plexus injury.
• Physiologic changes in the upright position include decreased MAP, stroke volume (SV), cardiac output (CO), and PaO2, along with increased alveolar-arterial oxygen gradient, pulmonary, and vascular resistance.
• Systemic vascular resistance (SVR) increases up to 50–80% in awake patients to compensate.
• General anesthetics inhibit this response, leading to vasodilation and decreased cardiac output further compromising cerebral perfusion.
• Cerebral perfusion pressure (CPP) decreases by about 15% in the sitting position, calculated as MAP minus intracranial pressure (ICP) or central venous pressure (CVP)
• General anesthetics cause vasodilation, myocardial depression, and impaired venous return, further impairing cerebral blood flow.
• Inspiratory subatmospheric pressure during spontaneous ventilation increases cerebral venous return; this effect is lost with positive pressure ventilation.
• Flexion of the head can obstruct internal jugular veins, causing cerebral venous engorgement. Head extension impairs cerebral blood flow (CBF), possibly leading to cerebral ischemia.
• Cerebral autoregulation maintains constant blood flow when MAP is between 60 and 160 mmHg.
• Outside this range, CBF becomes pressure-dependent.
• For poorly controlled hypertensive patients, autoregulation is shifted to the right, needing a higher MAP for adequate perfusion.
• Orthopedic surgeons sometimes request deliberate hypotension for shoulder arthroscopy, specifically rotator cuff repair.
• Hypocapnia significantly reduces internal carotid artery and CBF. This change will be exacerbated when the patient is placed in the sitting position. Significant hypocapnia should be avoided to decrease the potential for cerebral hypoperfusion.
• Maintaining normocarbia is important for patients in the beach chair position.

Surgical Procedure Details

• Traction on operative arm improves surgical conditions.
• Patient head protection, secured by Velcro or tape, with ear checks.
• Anesthetist needs to periodically check patient head and neck alignment.

Anesthetic Management and Considerations

Preoperative Period

• Interscalene block consent is discussed.
• Patient information includes risks, benefits, anesthetic procedure expectations.
• Thorough patient history and medication list are gathered.
• Rotator cuff innervation involves the cervical plexus, dividing into roots, trunks, divisions, cords, and branches.
• Supraspinatus and infraspinatus innervated by the suprascapular nerve.
• Teres minor innervated by the axillary nerve.
• Subscapularis innervated by the subscapular nerve.
• Emergency airway and resuscitation equipment are checked prior to regional anesthetic.
• Aseptic technique is essential.

Intraoperative Period

• Hypotension during beach chair arthroscopy should be aggressively treated. This includes vigilant monitoring, titration of anesthetic gases, gradual position changes, IV fluid administration, and vasopressors as needed.

Inter-Scalene Block Placement

• Patient positioned supine, head facing opposite the anesthetized shoulder.
• Patient slightly elevates head to see the sternocleidomastoid muscle's clavicular head.
• Palpating finger placed behind sternocleidomastoid muscle, patient relaxes head lift.
• Palpate the interscalene groove between anterior and middle scalene muscles.
• Injection site is at C6 (cricoid level), guided by ultrasound.
• Incremental local anesthetic injection; aspirate continually to avoid intravascular injection.
• This method minimizes local anesthetic systemic toxicity (LAST).
• LAST symptoms initially include lightheadedness, tinnitus or metal taste; progressing to seizures, loss of consciousness, and respiratory arrest.
• Cardiovascular LAST sign is bradycardia, then asystole.
• Prevention and intralipid infusion are treatments for LAST.

Postoperative Period

• Respiratory depression can occur due to increased opioids during surgery. The anesthetist must be aware of possible postoperative respiratory depression because analgesia from the interscalene block results in decreased postoperative pain.