The Back of the Brain

three-sphinxes-of-bikini
The Three Sphinxes of Bikini – Dali

Notes from ch 18, Gupta/Gelb, Anesthesia for posterior fossa lesions:

Posterior Fossa –> master controller of CV and respiratory fx

Pathology

  • tumors most common, 60% of all kid tumors
  • adults: acoustic neuroma, mets (lung/breast), meningioma, hemangioblastoma
    • heamngioblastoma can be a/w occult pheochromocytoma
  • Acoutstic neuroma -> CN 8, small via retromastoid, large lesions via suboccipital, goal to preserve cocholear and facial nerve fx
  • Chiari
    • type 1 = cerebellar tonsils in cervical spine canal (teens)
    • type 2 = inferior vermis herniates through foramen magnum
    • lower cranial nerve dysfx => stridor, resp distress, dysphagia, aspiration
  • Trigeminal neuralgia (tic douloureux) – small vessles wraps nerve ->neuralgia

Pre-Op Eval

  • assess for raised ICP
  • more sensitive to sedatives and analgesic

Positioning

  • prone, semiprone, park bench, sitting

I/O

Monitors

  • a line for bp, cpp and paCO2
  • vae is increaed in spontaneous respiration, and hypercapnia, but some argue brainstem manipulation seen better with spontaneous ventilation

Induction and maintenance

  • dealer’s choice
  • adapt according to neuromonitoring needs

Arrythmias

  • bradycardia 2/2 brainstem stimulus
  • tx: glycopyrrolate, atropine, ephedrine
  • severe htn from cranial nerve manipulation

Emergence

  • neuro exam awakening
  • leak test if prone
  • avoid htn p/o as increases edema and p/o hemorrhage
  • incision local reduces need for p/o opiates

Venous Air Embolism

Pathophys: elevated pulmonary vascular pressure -> gas x impair, hypox, hypercap but decrease ETCO2, bronchoconstrict; hemodynamic instability–> MI/CHF/CV Collapse

PFO (25% in adults and tt echo is <50% sensitive, TCD similar

Monitor: precordial doppler 0.25ml air detection; TEE controversial/over the top/side effects from prolonged use, petco2 also decreases

Pre-Op: make sure CVC is 2cm below junction of svc and atrium, with single orifice catheter 3cm above (cxr, biphasic p wave), talk to surgeon in time out

  • Prevent
    • decrease head to heart to surgery gradient
    • normovolemia to hypervolemia
    • apply bone wax
    • avoid PEEP as it increases RA pressure and potentiates risk for PAE)
  • Treatment 
    • FLOOD SITE, LOWER SITE
    • stop N2O, give 100% O2
    • compress jugulars
    • aspirate through CVC
    • supportive measures (fluids, pressors, inotropes)
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One thought on “The Back of the Brain

  1. With advent of neuromonitoring and short-acting opioids, the relevance of monitoring respiration I/O is diminished as patient either paralyzed or on high dose opioids blunting ability to breathe spontaneously.

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