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You are in Home >> Exams >> Mitchell Anaesthetic Notes


Orthopaedic Anaesthesia

Created: 26/6/2006
Updated: 8/1/2007
 

Total hip replacement

  • Surgery
    • Ranges in complexity from simple cementless arthroplasty to re-do with bone grafting, revision of acetabular protrusion etc.
    • Moderate to high risk
  • Issues
    • Choice of anaesthetic technique
    • Positioning
    • Blood loss
    • Cement
    • Thromboprophylaxis
  • Preoperative
    • Assessment
      • Patient
        • Typically old patient, may have multi-system disease
        • Exercise tolerance difficult to assess if limited by hip pain
        • Discussion of anaesthetic technique
      • Surgery
        • Complexity and likelihood of blood loss
        • Suitability or desire for autologous predonation
        • Likely requirement for haemodilution, cell-saver
    • Monitoring
      • Simple surgery
        • Routine SpO2, ECG, NIBP, large IV
      • Complex surgery, GA, induced hypotension
        • Temperature, IDC, arterial line, CVC
  • Intraoperative
    • Spinal or CSE
      • Lumbar placement
      • Plain (hypobaric) bupivacaine if lateral position
        • 3-4 ml 0.5% spinal dose
    • GA
      • Relaxant technique if complex procedure
      • Consider use of induced hypotension
        • Reduces blood loss 30-50% (as does spinal)
    • Either
      • Intraoperative forced-air warming, avoid hypothermia
    • Position
      • Commonly lateral
        • V/Q mismatch in ventilated patients
        • Pressure on dependent brachial plexus, axillary artery
        • Lateral rest may press on femoral canal
      • Pressure necrosis more likely with hypotension
    • Reaming and cementing
      • Sudden profound hypotension, hypoxaemia or arrest may follow reaming or cemented prosthesis insertion
        • Associated with increased PA pressure
        • Possibly due to methyl methacrylate or fat, air and marrow emboli
        • May be delayed by femoral vein obstruction with leg position
  • Postoperative
    • Analgesia
      • Epidural not commonly used because of incidence of urinary retention
      • Systemic narcotic plus paracetamol and NSAID (if not contraindicated)
    • Level of care
      • Usually ward unless high-risk

Other orthopaedic surgery


Total knee replacement

  • Surgery
    • Unilateral or bilateral
      • Higher incidence of complications if bilateral and HDU care may be required
    • Commonly done below a tourniquet
  • Issues
    • Cement associated hypotension with femoral component
    • Blood loss
      • Tourniquet
      • Antifibrinolytics (e-aminocaproic acid)
    • Postoperative analgesia
      • Epidural catheter
      • Femoral catheter
      • Spinal morphine
      • Femoral, sciatic, obturator blocks

Spinal surgery

  • Surgery
    • Major surgery, commonly in prone position
  • Issues
    • Patient deformity and respiratory or neuromuscular disease
    • Positioning
    • Spinal cord monitoring: SSEP, wake-up test
    • Blood loss and conservation techniques
    • Duration, temperature conservation

Tourniquets 


Inflation

  • Local
    • Folds or lines under tourniquet may cause bruising or pressure necrosis of skin
  • Metabolic
    • By 8 min mitochondrial PO2 approaches 0
    • Anaerobic metabolism
      • Decreased ATP, NAD+, CP, decreased pH
      • Release of myoglobin, K+, intracellular enzymes, thromboxane
    • Tissue oedema develops after 60 min
    • Tissue temperature approaches room temperature
  • Haemodynamic
    • Exsanguination increased CVP, PAP
    • Inflation increased SVR, BP
    • 45-60 min hypertension “tourniquet pain” unresponsive to anaesthesia
      • Not prevented by axial blockade
      • May be prevented or delayed by plexus blockade
  • Neurological
    • Conduction ceases by 30 min
    • Neuropraxia may be due to ischaemia or shear forces
      • Prevented by periodic deflation

Release 

  • Metabolic
    • Rapid washout of metabolic products and equilibration of temperature
    • Decreased core temperature, SvO2 falls to 20%, increased PCO2
  • Haemodynamic
    • Direct: decreased SVR, decreased CVP
    • Metabolites: marked vasodilation, myocardial depression
    • Potential embolisation of distal venous clot or debris

Anaesthesia for a patient with unstable cervical spine fracture for fixation 

  • Halo traction
    • Emergency surgery in a trauma patient at high risk of catastrophic neurological injury
  • Issues
    • Cervical immobilization
    • Other injuries
    • Minimizing anaesthetic intervention
  • Preoperative
    • Assessment
      • Routine, plus
      • Trauma patient
        • ABC priorities
        • Conscious state, and fluctuation
        • Other injuries, particularly head and airway
        • Careful airway assessment
      • Neurological state
        • Documentation of any defect
    • Optimization
      • Urgency of surgery usually does not allow much time
      • Cervical spine immobilization
        • Hard collar, sand bags, spinal board
    • Premedication
      • None
      • Detailed explanation of procedure
    • Transport
      • Supine on spinal board
      • Transfers on board or lifting frame
      • Log-rolling for turning
  • Intraoperative
    • Preferred anaesthetic technique is local infiltration for bolts and no sedation
    • Monitoring and access
      • Large bore IV access, routine monitors
    • Induction
      • Drugs available for induction of general anaesthesia
      • Emergency drugs for CVS support
      • Difficult airway equipment available
      • GA only if unmanageable otherwise
        • Aim to minimize cervical spine movement
        • In-line immobilization for laryngoscopy or use of FOB or Fastrach or Bullard if appropriate
  • Postoperative
    • Traction frame bed or body-harness
    • Minimal analgesia required

Kindly provided by Dr James Mitchell from his pharmacodynamics series


ArticleDate:20060626
SiteSection: Article
 
   
    
                                            
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