Lesson 19

Orthopedic Surgery Overview

Methyl Methacrylate Effects

  • Increases intramedullary pressure (up to 500 mmHg), causing microemboli (fat, bone marrow, cement).
  • Leads to ventilation/perfusion (V/Q) mismatch and can potentiate right heart failure.
  • Residual methyl methacrylate can enter systemic circulation, causing:
    • Bradycardia, dysrhythmias, hypotension (↓ SVR),
    • Pulmonary hypertension (↑ PVR), hypoxia, cardiac arrest.
  • This constellation of complications is known as Bone Cement Implantation Syndrome (BCIS).
  • Hip arthroplasty has the highest risk of BCIS; also seen in knee arthroplasty, vertebroplasty, kyphoplasty.
  • First signs in awake patients: dyspnea, altered mental state; in anesthetized patients: decreased EtCO2.
  • First-line treatment: 100% FiO2, IV hydration, phenylephrine for hypotension.

Fat Embolism Syndrome (FES)

  • Recognized complication of long bone trauma, risk highest in first 72 hours.
  • Important for prompt stabilization of injury.
  • Risk factors: pelvic fracture, femoral fracture, instrumentation of femoral canal.
  • Triad of FES:
    • Respiratory insufficiency (hypoxemia, bilateral infiltrates, ARDS),
    • Neurologic involvement (confusion to coma),
    • Petechial rash (neck, axilla, mucosa, conjunctiva).
  • Treatment: supportive; corticosteroids may or may not improve outcomes.

Pneumatic Tourniquet Use

  • Reduces blood loss in extremity surgeries.
  • Maximum inflation time to reduce ischemic damage: 2 hours.
  • Inflation pressures:
    • Upper extremity: 70-90 mmHg above SBP.
    • Lower extremity: 2x SBP.
  • Bier block inflation:
    • Upper: 250 mmHg or 100 mmHg above SBP.
    • Lower: 350-400 mmHg.
  • Tourniquet must remain inflated 20 minutes post-local anesthetic injection. Premature release increases risk of seizures/cardiac arrest.

Effects of Tourniquet Release

  • Transient physiological changes:
    • Increased EtCO2, decreased core temperature, blood pressure, SvO2, metabolic acidosis.
  • Tourniquet pain develops 45-60 minutes after inflation, caused by tissue ischemia.
  • Pain characteristics: dull, aching, burning; may become agonizing and unresponsive to analgesics.
  • Under general anesthesia: may manifest as hypertension and tachycardia; consider esmolol for CAD patients.