MetroHealthAnesthesiaIntracranial Tumors


Presentation/Diagnosis
  • 40 to 60 years of age
  • signs and symptoms reflecting increasing ICP (intracranial pressure)
  • adult onset seizure disorder
  • CT or MRI

Management of Anesthesia

  • Prevent undesirable changes in CBF (cerebral blood flow) and ICP.
  • Position depends on tumor location
    • Supratentorial: supine
    • Infratentorial: prone or sitting (BEWARE: greatly increases risk of venous air embolism)

Cerebral Blood Flow

  • Normal: 50 ml/100 Gm/min (15% of cardiac output)
  • Depends on:
    • Cerebral metabolic rate for O2 (CMRO2)
    • PaCO2
    • Cerebral perfusion pressure
    • PaO2
    • anesthetic agents
    • temperature
    Cerebral Blood Flow Graph
  • CBF is proportional to CMRO2
    • relationship unaffected by intravenous agents, but
    • may be uncoupled by inhalation agents
  • PaCO2
    • 1 mmHg change in PaCO2 produces 1 ml/100 Gm/min change in CBF (in same direction) but
    • transient effect (wanes in 6-8 hours)
    • normal patients: for normal CBF maintain normal PaCO2 = 40 mmHg
    • CBF and thus ICP may be acutely lowered hyperventilating to lower PaCO2
  • Cerebral perfusion pressure (CPP) and autoregulation
    • CPP is proportional to mean arterial pressure (MAP)
    • if ICP > right atrial pressure (RAP), then
      CPP = MAP - ICP
    • if RAP > ICP, then
      CPP = MAP - RAP
    • normal: autoregulation keeps CBF relatively constant as long as CPP is between 50 and 150 mmHg
    • if CPP < 50 mmHg or CPP > 150 mmHg, then CBF is proportional to CPP
    • chronic hypertension shifts the CBF-CPP curve to the right so
      • higher CPP tolerated but
      • lower CPP (< 50 mmHg) may result in too-low CBF
    • autoregulatory response
      • impaired by intracranial tumors
      • not impaired by inhalation anesthetics
  • PaO2
    • PaO2 < 50 mmHg causes significant increases in CBF
  • Anesthetic agents
    • inhalation agents
      • decrease CMRO2, but
      • > 0.6 MAC (minimum alveolar concentration) leads to cerebral vasodilation and dose-dependent increases in CBF
      • vasodilation greatest with halothane >> isoflurane, desflurane, sevoflurane
    • ketamine
      • generally increases CMRO2 and CBF
      • if PaCO2 maintained normal in presence of elevated ICP or cerebral trauma, then ketamine does not adversely alter CBF or ICP *
    • thiopental
      • potent cerebral vasoconstrictor
      • decreases CMRO2, CBF, and ICP
    • propofol
      • decreases CMRO2, CBF, and ICP
      • decreased MAP leads to decreases CPP
    • etomidate
      • decreases CMRO2, CBF, and ICP
      • increases EEG activity
    • opoids
      • depress ventilation, increasing PaCO2 leading to increases in CBF and ICP
      • depress level of consciousness
      • cause miosis

Pressure-volume (elastance) curves

  • elastance = (change in pressure)/(change in volume)
  • when intracranial compensatory mechanisms are exhauted, small changes in volume lead to dramatic changes in ICP

Intracranial pressure (ICP)

  • normal: < 10 mmHg
  • to lower elevated ICP, consider:
    • elevate head (to encourage venous drainage)
    • hyperventilate (effect wanes in 6-8 hours)
      PaCO2 25-30 mmHg probably safest ( <20 mmHg: too much vasoconstriction with risk of cerebral ischemia)
    • drain CSF
    • drugs:
      • osmotic diuretics
      • steroids
      • barbiturates
  • inhaled anesthetic agents
    • dose-dependent increase in CBF and ICP (especially in patients with intracranial tumors)
    • hyperventilation to PaCO2 = 30 mitigates to some extent the elevation of ICP caused by inhaled agents

Preoperative evaluation

  • Evidence of intracranial hypertension
    • nausea and vomiting
    • hypertension
    • bradycardia
    • personality change
    • altered level of consciousness
    • altered pattern of breathing
    • papilledema
    • seizures
  • MRI or CT
    midline shift > 5 mm and/or encroachment on CSF cisterns suggest intracranial hypertension
  • avoid preop pharmacologic sedation and ventilatory depression

Induction of Anesthesia

  • thiopental, propofol, or etomidate -> prompt induction without ICP elevation
  • muscle relaxant to facilitate endotracheal intubation and mechanical hyperventilation (BEWARE: coughing causes marked increases in ICP)
  • succinylcholine does not significantly alter CBF or ICP in patients with neurological injury *
    succincylcholine vs ICP graph
  • more thiopental, opioids and/or lidocaine 1-2 minutes prior to direct larynogoscopy
  • ventilate to PaCO2 25-30
  • BEWARE: PEEP may decrease cerebral venous return leading to elevated ICP

Maintenance of anesthesia

  • N2O, opioids, benzodiazepines and/or barbiturates
  • inhaled agents - isoflurane, desflurane, sevoflurane - at < 0.6 MAC OK with PaCO2 25-30
  • in patients with elevated ICP, avoid vasodilators (nitroprusside, nitroglycerine, trimethophan) before the dura is opened
  • muscle relaxants (muscle activity may lead to elevated ICP)
  • may decide to treat cerebral swelling
    • mannitol 0.25-1 Gm/kg IV
    • furosemide 0.5-1 mg/kg IV
    • thiopental
    • head up position
  • IV fluids
    • minimal, 1-3 ml/kg/hr
    • glucose NOT recommended
      • may increase cerebral edema
      • hyperglycemia worsens cellular ischemic injury
    • isotonic crystalloids
    • hetastarch OK

Monitors

  • standard (including ETCO2) plus:
  • arterial line
  • maybe ICP monitor
  • probably bladder catheter
  • sitting position: CVP catheter

Awakening

  • avoid coughing, straining
  • thiopental or lidocaine
  • BEWARE: N2O may cause tension pneumocephalus
  • delayed return to consciousness or neurologic deterioration: CT or MRI

Venous Air Embolism (VAE)

  • consider whenever head > 5 cm above heart
  • transected veins in cut edge of bone or dura may not collapse
  • air -> RV -> pulmonary circulation
  • decreased pulmonary blood flow, pulmonary edema, bronchoconstriction, cardiovascular collapse, hypoxemia
  • paradoxical (air) embolism
    • coronary or cerebral circulations
    • via patent foramen ovale (PFO) (20-30% of adults have probe-patent foramen ovale)
  • detection
    • precordial Doppler ultrasound near right upper sternal border is most sensitive non-invasive monitor (detects 0.25 ml)
    • trans-esophageal echocardiography is more sensitive, but more invasive and cumbersome
    • sudden decrease in ETCO2, incease in ETN2
    • gasping, hypotension, dysrhythmias, cyanosis, "mill-wheel" murmur
  • treatment
    • irrigate operative site with fluid
    • apply occlusive material to bone edges
    • gently compress internal jugular veins
    • head down position
    • aspirate air through right atrial catheter (best if tip is at SVC-RA junction)
    • discontinue N2O
    • inotropes may be needed
    • BEWARE: PEEP, by reversing RA-LA pressure gradient, may lead to paradoxical air emboli via PFO



Send Comments to Greg Gordon MD, gjg@po.cwru.edu
Department of Anesthesiology
The MetroHealth System
2500 MetroHealth Drive
Cleveland, Ohio 44109-1998
Phone: (216) 778-4801
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