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


Vascular Anaesthesia

Created: 20/6/2006
Updated: 8/1/2007
 

Carotid endarterectomy

  • Indication
    • Symptomatic carotid disease >70% occlusion: proven benefit in long-term stroke rate
    • Asymptomatic disease >50-60% occlusion: reduces ipsilateral stroke rate
  • Perioperative morbidity
    • Stroke 3-5%, most postoperatively (>50% after 4 hours post-op)
      • Risk factors: previous stroke, poor BP control post-op
    • AMI 0-4%
  • Preparation
    • Cardiac investigation indicated only for unstable angina, recent MI or decompensated CCF
    • 70% of patients have silent IHD, diagnosis does not alter management
    • Relative priority of CAGS is undetermined
  • Anaesthetic management
    • Objectives
      • Cardiac and neurological protection from ischaemia
      • Cardiovascular stability
      • Early postoperative neurological examination
    • Monitoring
      • Routine plus ST segment monitoring, arterial line, large IV
      • Arterial line in arm with highest BP on examination
      • CVC generally avoided
    • GA
      • Fairly routine
      • Consider propofol “book-end” technique for rapid awakening
      • O2, N2O, isoflurane maintenance
      • Ready availability of pressors and nitrates for BP control
      • Continued BP control with emergence and post-op
      • Maintain normocapnia and normoglycaemia
      • Cerebral protection: high dose barbiturates for burst-suppression
    • Regional
      • Deep and superficial cervical plexus block
        • Exclude contraindications, monitor, IV access, assistant
        • Detail of technique
      • Advantages
        • Continuous functional neurological monitoring
        • High level of patient acceptance: 92% would have again
        • Possible lower risk of perioperative stroke
        • Possible lower risk of cardiopulmonary complications
        • Less BP lability intra- and postoperatively
        • No instability on “wake-up”
      • Disadvantages
        • High plasma levels of LA
        • Phrenic nerve block
        • Higher catecholamine levels, ? more tachycardia
    • Clamping
      • Order: ICA, CCA, ECA
      • Observe neurological findings for 2-3 minutes (regional) or BP, stump pressure, other monitors (GA)
    • Unclamping
      • Order: ICA (flush), clamp ICA, ECA, CCA, ICA
  • Postoperative complications
    • Neurological complications
      • Usually due to intraoperative embolization or hypoperfusion or endarterectomy site embolization or thrombosis  
      • Some due to intracerebral haemorrhage (0.4-2%) or hyperperfusion
      • Rate strongly correlates with surgical technique
    • Hypertension, hypotension
      • Usually due to carotid sinus baroreceptor dysfunction but hypoventilation, pain, bladder distension should be excluded
      • Treated agressively to minimize risk of cerebral or myocardial injury
    • Nerve injury
      • Commonly recurrent laryngeal, superior laryngeal, hypoglossal or marginal mandibular
    • Wound haematoma requires prompt drainage if airway compromised

Preoperative assessment of a patient for carotid endarterectomy


Surgery 

  • Elective, high risk
  • 1-2% mortality, 4-10% morbidity
  • Issues
    • Access to airway
    • Cerebral protection

Assessment

  • Identify myself and patient, confirm procedure, explain role
  • History
    • CVS
      • Symptoms of cerebrovascular disease
      • Hypertension, usual BP as basis for intraoperative aim
      • Coronary vascular disease
        • MI, angina, SOB, symptoms of failure
      • Peripheral vascular disease symptoms
      • NYHA functional classification
    • Respiratory disease
      • Commonly smokers, COAD
    • Other illnesses
      • Diabetes
      • Renal impairment
  • Examination
    • Focused on cardiac and respiratory complications
    • Document neurological status
  • Medications
    • Decision whether to continue or withhold
    • Commonly on multiple medications
      • Antiplatelet, β-blockers, diuretics, ACEI, others
  • Investigation
    • ECG: high incidence of IHD
    • U&E, FBE
    • If IHD, consider echo, thallium scan or angiography
      • Carotid disease is generally treated before CAGS
      • But other revascularization options may be considered
  • Overall
    • Diseases unstable or stable, optimized or not
    • Plan for risk minimization
  • Consult
    • Appropriate referral for optimization of function
  • Consent
    • Anaesthetic plan: GA or regional
      • Regional requires detailed explanation in advance
    • Risks
      • General: allergy, aspiration, blood transfusion, cardiac event, dental injury, death, awareness
      • Specific: stroke risk
    • Postoperative plan
      • Ward or HDU
      • Analgesia
  • Premedicate
    • Aiming for normotension, normocapnia, anxiolysis
    • Usual antihypertensives, antiplatelet drugs as per surgeon’s instructions
    • Anxiolytic: temazepam

Abdominal aortic aneuysm


Natural history

  • Progressive enlargement and rupture
    • 5 y rupture rate
      • 4-7 cm - 25%
      • 7-10 cm - 45%
      • >10 cm - 60%
  • Risk of rupture rises with diameter and rate of expansion
    • Greater than risk of surgery at ≥5 cm or increase ≥0.5 cm in 6 months

Preoperative

  • Assessment
    • Similar to endarterectomy

Intraoperative

  • Monitoring
    • Routine, plus arterial line, multiple large IVs, CVC or Swan sheath
    • Cell-saver for large anticipated blood loss
    • Consider nasopharyngeal airway placement prior to heparinization if extubation planned
  • Induction
    • GA with minimized BP rise, epidural catheter or
    • Spinal or CSE for endoluminal repair
  • Crossclamping
    • Effects depend on level of clamping, collateral circulation and physiological reserve
      • Little effect from infrarenal clamp, major changes with thoracic clamp
    • Haemodynamic
      • Increased SVR (direct): increased BP, decreased ejection fraction, decreased CO, increased LVEDV, increased contractility, increased coronary flow
      • Reflex increase in sympathetic tone: increased SVR, increased venous return, increased PAOP & CVP, increased LVEDV, increased CO (if good myocardial function)
      • If coronary stenosis: segmental wall motion abnormality, ischaemia or LV failure
        • Wall motion abnormalities in 40% of infrarenal and 90% of supracoeliac clamps
    • Metabolic
      • Distal ischaemia: decreased VO2, decreased CO2 excretion, increased SvO2, increased catecholamines
      • Metabolic acidosis, if ventilated: respiratory alkalosis
    • Intervention
      • Afterload reduction
        • SNP, volatiles, amrinone, epidural, remifentanil
      • Preload reduction
        • GTN, epidural, shunt or left heart bypass
      • Renal protection
        • Mannitol, dopamine, fluids
        • Suprarenal clamp --> 90% reduction in RBF
        • Infrarenal clamp --> 40% reduction in RBF
  • Unclamping
    • Haemodynamic
      • Decreased SVR, decreased CVP, decreased CO, decreased BP, decreased contractility
    • Metabolic
      • Increased VO2, decreased SvO2, increased lactate, PGs, activated complement, myocardial depressants
    • Intervention
      • Decreased vasodilators & volatiles, IV filling, pressors
      • Reapply crossclamp if unacceptable hypotension
  • Emergence
    • Extubate on table if stable: normothermia, normal ABG, no massive transfusion


 

Thoracic aortic aneurysms

  • Classification
    • DeBakey
      • I thoracoabdominal
      • II ascending and arch
      • III descending ± abdominal
    • Crawford I-IV
  • Risk with surgery
    • Mortality 5-15%
    • Paraplegia 5-40%
    • ARF 3-30%
      • All depending on extent of aneurysm
  • Issues
    • Planned technique
      • Extracorporeal circulation
      • One-lung ventilation
    • Monitoring
      • Spinal cord function
    • Protection
      • Spinal cord, renal, cerebral, myocardial
  • Preoperative
    • Assessment
      • As any vascular or thoracic patient, plus anatomical detail of aneurysm
      • Respiratory function if OLV planned
  • Intraoperative
    • Monitoring
      • Routine, plus
      • IV access: 8.5 Fr x 3 (PA catheter and 2 rapid infusers)
      • Arterial line in right radial ± femoral if femoral bypass
      • Temperature (core and periphery), TOE, SSEPs
    • Induction
      • Minimizing hypertension with cardiac-type induction
      • Left-sided DLT for left lung deflation (minimizes risk of occluding RUL)
    • Maintenance
      • Bypass
        • Full bypass with flow into ascending aorta
        • Partial bypass with flow LA --> femoral artery
        • Passive shunt around clamped aorta
        • No bypass “clamp and run”
          • Clamp duration
            • 30 min - 10% paraplegia
            • 60 min - 90% paraplegia
        • Deep hypothermic circulatory arrest (DHCA) for arch aneurysms ± cold oxygenated retrograde cerebral perfusion
      • Spinal protection
        • CSF drainage, hypothermia, intrathecal papaverine
      • Renal protection
        • Dopamine, mannitol, fluid loading, frusemide
      • Myocardial protection
        • Clamping and unclamping: compensate for haemodynamic changes with vasoactive drugs
    • Emergence
      • Change DLT for single-lumen tube with changing catheter
      • Transfer ventilated to ICU

Kindly provided by Dr James Mitchell from his pharmacodynamics series


ArticleDate:20060620
SiteSection: Article
 
   
    
                                            
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