Anesthesia for Orthopedic Surgery and Evoked Potentials Monitoring

1. Anesthesia for Orthopedic Surgery and Evoked Potentials Monitoring Jampierre Mato CRNA,MSN,ARNP Clinical Adjunct Professor Anesthesiology Nursing Program Florida International University

2. The Specialty • Orthopedics has grown immensely within the past 2 to 3 decades, mainly due to the development of arthroscopic equipment and hardware to replace joints • Total joint replacement (shoulder, elbow, wrist, hip, knee, and ankle)-may offer a vast improvement in quality of life • Inter-vertebral disc replacements are now being offered • Benefits of arthroscopy • Much less invasive than open techniques • Allows direct visualization and manipulation with specialized equipment • Reduced discomfort and length of stay (many procedures done as outpatient)

3. Tourniquets • Pneumatic Tourniquets • Provide virtually bloodless field • Cuff should overlap only 3 to 6 inches • Area underneath must be padded and wrinkle-free • Overlap of cuff should be opposite of neurovascular bundle (e.g. on the humerus, overlap is on the lateral aspect-opposite the brachial plexus) • Inflation pressure usually 100mmHg greater than systolic blood pressure

4. Tourniquets Must exsanguinate extremity prior to inflation (elevate or use Esmarch bandage) Elevation is preferred in infected extremities Inflation pressures • Should not exceed 300mmHg in upper extremities • Should not exceed 500 mmHg in lower extremities

5. Tourniquet Pain Compression of intra-neural blood vessels • Causes secondary nerve ischemia • Leads to stimulation of pain pathways • Onset 45-60 minutes after inflation • Similar to thrombotic vessel occlusion • Activation of C fibers – burning and aching • Activation of A delta fibers – pins and needles • Difficult to treat, once it begins: analgesics and anesthetics have little effect, may need to treat sympathetic activation (tachycardia and hypertension)-What is the only true treatment?

6. Effects of Tourniquets

7. Tourniquet Safety -Always place cuff where nerves are best protected in the musculature -Check proper function of machine -Never inflate for longer than 2 hours: 10 to 15 minute reperfusion interval required prior to re-inflation -Minimally effective pressure to occlude blood flow -Put display where you can see it • Report 60 minutes, then 15 min increments after that to the surgeon and be sure to chart that you did so • Always chart times on your record

8. Hip Fractures

9. Hip Surgery -ORIF – Open Reduction with Internal fixation • Done for fractures (usually frail/elderly) • Requires use of special fracture table (legs split with traction applied) • Frequent concomitant diseases (dementia, Parkinson’s, CAD, diabetes, etc.) • Frequently dehydrated • Occult blood loss can be significant • Intracapsular • Subcapital, transcervical – less blood loss • Extracapsular • Femoral neck, intertrochanteric, subtrochanteric – expect higher blood loss -Bipolar hip replacement (not a total hip arthroplasty): -done when fracture is not amenable to permanent fixation - femoral head and partial femoral neck are resected and replaced with a prosthesis -acetabular component is not fixed to the acetabulum -procedure usually takes less than an hour

10. Bipolar Hip Prosthesis • Cup is not attached to acetabulum • Utilized when patient will be non-ambulatory or will limit weight-bearing activities on hip for the rest of his life

11. Fat Embolism • High correlation with long bone, hip, and pelvic fractures • Occurs, to some degree, in all hip fracture patients • Patients typically have low oxygen saturation and low-grade fever • Fat Embolism Syndrome • Presents within 72 hours of injury • 3 hallmark signs: confusion, dyspnea, petechiae • Fat globules released into the blood through tears in medullary vessels • Theory that chylomicrons result from aggregation of circulating fatty acids • Thrombocytopenia and prolonged clotting times may occur

12. Fat Embolism Under GA • Diagnosing fat embolism syndrome under general Anesthesia • Decline in end tidal CO2 • Decline in arterial oxygen saturation • Rise in pulmonary artery pressures • Ischemic-appearing ST segment changes • Right sided heart strain • If severe, may lead to RVOT obstruction with resultant CV failure/arrest

13. Anesthetic Choice in Hip Fracture • General or Regional? • Extensively evaluated • Regional has lower mortality in the first 2 months post surgery • No significant difference in mortality after 2 months • General is associated with more thrombo-embolic events than regional • Morbidity post-general is higher immediately post operatively

14. Total Hip Arthroplasty -Usually done in lateral decubitis position • Higher degree of visibility and range of motion -Most common indication is Osteoarthritis (OA) AKA Degenerative Joint Disease (DJD) -Surgical Concerns (large incision, muscle trauma): • Acetabulum and femoral head/neck are very vascular • Resection of femoral head and neck • Reaming of femoral shaft to accept stem • Reaming of acetabulum to accept cup • Three life threatening complications • Bone cement implantation syndrome (cement rarely utilized in primary arthroplasty) • Peri-operative hemorrhage • Thrombo-embolism

15. Cement Implantation Syndrome Methylmethacrylate (MMA) • Mixing Powder and liquid causes exothermic reaction • Reaction causes expansion of cement and forces fat, blood, and air into the femoral venous channels • Residual monomer (liquid) is a potent systemic vasodilator and pulmonary vasoconstrictor • Release of tissue thromboplastin may trigger thrombo-embolism and cause hemodynamic instability

16. Total Hip Replacement *Minimally invasive/muscle sparing techniques are in widespread use

17. Closed Hip Reduction • May be necessary if prosthesis dislocates • Often done with heavy MAC or IV general with short-acting muscle relaxant, unless contraindicated • Extremes of flexion and internal rotation can dislocate a new prosthesis- abduction pillow is placed immediately post-operatively to avoid dislocation • Repeated dislocation of a hip prosthesis may require revision of the prosthesis-this is usually a failure of either surgical technique or the implant itself

18. Lateral Decubitus Position Used in thoracic, renal, and orthopedic procedures • Presents unique challenges to the anesthetist • Importance of body alignment (cervical/thoracic/lumbar) • Use of bean bag, axillary roll, pillows, sandbag • Cardiovascular Considerations • Respiratory Considerations • FRC decreased • Ventilation/Perfusion mismatch • Atelectasis • Use of PEEP (may worsen mismatch)

19. Lateral Decubitus

20. Total Knee Arthroplasty • Usually done for osteoarthritis or late-stage rheumatoid arthritis • Supine position • Regional vs. general anesthesia • Cement implantation syndrome (when is this a concern?) • Tourniquet concerns (ensure it is working) • Autologous blood donation • Bleeding is usually an issue post-op (once tourniquet is down)

21. Revision Joint Replacements • Previous joint replacements may need to be revised • Lifespan of current implants is postulated to be 10 to 15 years (may be shorter or longer, depending on recipient use) • Revision procedures tend to be lengthy and bloody • Intra-operative cell salvage is usually recommended • Infected joints need to be removed, with placement of antibiotic spacers until infection resolves-don’t use cell savage in suspected infection cases

22. Spinal Surgery -Done for a variety of diagnoses -herniated discs -spondylolisthesis/spondylosis -spinal canal stenosis -radiculopathy -myelopathy -osteophyte compression -scoliosis -kyphosis -post-traumatic stabilization

23. Spondylolisthesis

24. Common Diagnoses in Spine Surgery • Intervertebral disc herniation • Herniated disc may impinge on nerve roots and the cord itself • Spinal stenosis • Refers to narrowing of the spinal canal, for whatever reason (herniation, degenerative disc disease, spondylolisthesis, osteophyte formation, etc.)

25. Minimally Invasive Spine Surgery • Traditional spinal surgery (laminectomy, fusion, etc.) • Large incisions • Large amount of blood loss and prolonged wound healing • Great post-operative discomfort • Lengthy hospital stays • Commonly required anterior approach for the lumbar spine (laparotomy incision) • Mini-invasive spine surgery • Small incisions • Decreased blood less and faster wound healing • Decreased post-operative discomfort • Shorter hospital stay • Allows more complex procedures to be performed at once • Often allows access to lumbar spine that formerly required laparotomy

26. Mini-Invasive Spine Procedures • Lateral interbody fusion (LIF): • Allows complete lumbar discectomy and cage placement/fusion through a small flank incision • Trans-foraminal lumbar interbody fusion (TLIF): allows near-total discectomy with cage placement/fusion through a para-spinous incision • Axia Lumbar Interbody fusion (AxLIF): • Allows fusion of the L5-S1 interspace through a sub-sacral incision • Micro-discectomy: allows removal of a herniated portion of disc through an access port (may utilize microscope) • Laminectomy: allows for total or hemi-laminectomy through a port

27. Microdiscectomy

28. Positioning on Andrews Frame

29. Positioning on Wilson Frame

30. Scoliosis • Lateral curvature of the spine • 75-80% of cases are idiopathic • Untreated, can lead to complex deformity • SSEP and MEP monitoring • Preoperative evaluation (cor pulmonale, pulmonary physiology changes) • PFTs, ABGs, EKG • Increased incidence of MH if caused by muscular dystrophy (in pediatric patients)

31. Scoliosis

32. Scoliosis Surgery • Gold standard is multi-level fusion with instrumentation/rods • Potential for large blood loss (weighing of laps/sponges and tight I & O recording)- cell salvage usually utilized • “Wake up” test is uncommon, due to modern monitoring of evoked potentials • Severe respiratory disease may exist preoperatively, may be left intubated postoperatively • Major concerns with positioning (may have severe deformities) • Posterior, anterior, or thoraco-abdominal approaches may be necessary • May require double lumen tube if utilizing anterior thoracic approach

33. Monitoring of Evoked Potentials • Types: MEP, SSEP, EMG, VEP, BAEP • Indications: • Evaluation of pathology • Monitoring during any procedure which may compromise a nerve pathway

34. Cuneatus and Gracilis Tracts • Part of the dorsal-lemniscal sensory system • Responsible for touch, pressure, and vibration sensation • Located in the dorsal cord • Integrity of dorsal tract is assessed by SSEP monitoring (somato-sensory evoked potentials) • Sensations ascend on the ipsilateral side of the cord and cross into the contralateral side at the thalamus (considered a direct pathway to the cerebral cortex) • Procedures that may require SSEP monitoring: cerebral aneurysm clipping, spine surgery, CEA (questionable applicability), complex thoraco-abdominal aneurysm repairs (MEP’s are more useful since ischemia usually occurs in the ventral horn)

35. Reticular Activating System • Considered a secondary way by which sensory information arrives at the cerebral cortex • Deactivated during sleep • General anesthetics produce their effects through action on the RAS

36. Cortical Pathways • SSEP’s are recorded from the scalp • A peripheral nerve (ulnar/median or tibial) is stimulated, bilaterally, to procedure a potential that is recorded in the scalp • Stimulating electrodes are peripheral and detecting electrodes are central (the scalp)

37. Evoked Potential Waveforms • Amplitude: height of the waveform • Latency: can be thought of as the frequency • Decreased amplitude and/or increased latency indicate a compromise in nerve potential transmission • Factors that affect waveforms: temperature, PaO2, PaCO2, systemic blook pressure • VEP’s are most affected by our anesthetics, SSEP’s are moderately affected, and BAEP’s are marginally affected

38. Anesthesia During Evoked Potentials Monitoring • What can we do? • Maintain normothermia • Maintain blood pressure within 20% of baseline (critical in long-standing hypertension and/or small vessel disease)-consider invasive monitoring in select patients • Use anesthetics with minimal effects on waveform character (TIVA) • Maintain oxygenation (may be difficult during one-long ventilation) • Maintain normocapnea

39. The Ultimate Test of Nerve Pathway Integrity? • Wake up and move everything!

40. Foot and Ankle Surgery • Ankle fracture • Plate and screws • Bunionectomy • Hammer toe correction • Plantar fasciotomy • Achilles tendon repair

41. Ankle Block • Frequently used in podiatric cases • Insert needle lateral to the posterior tibial artery at the superior aspect of the medial malleolus (posterior tibial nerve) • Inject 5ml of local and 2ml as you withdraw the needle • Insert needle at the lateral border of the achilles tendon with the line between the malleoli, advance toward the lateral condyle, inject 5ml of local (sural nerve)

42. Posterior Tibial Nerve

43. Sural Nerve

44. Ankle Block Technique • Draw a line between the superior edge of the medial malleolus across the anterior portion of the ankle • Flex the foot and place the needle between the tendons medial to the big toe (deep peroneal nerve), inject 5ml of local • With the remaining local, fan inject across the same plane across the ankle (saphenous nerve)

45. Superficial Peroneal Nerve

46. Needle Directions in Ankle Block

47. Upper Extremity Procedures -Usually amenable to brachial plexus block (interscalene, supraclavicular, axillary) Shoulder arthroplasty or arthroscopy • Requires beach chair/sitting position • Venous air embolism precautions • Airway concerns • Cardiovascular considerations? • Elbow arthroplasty or arthroscopy • Prone position • Turn head away from field • Turn table 90 degrees

48. Shoulder Arthroplasty Painful!!

49. Hand Surgery • Hand surgery • General vs. regional • Bier block • Axillary block • Wrist block • Tourniquet concerns • Long cases • Often awake, often uncomfortable (consider general)